维普中文期刊产品整合服务
2655篇 您的检索式:作者名="Centers A"
    题名 作者 年代 出处 被引量
1Inhibiting effect of antisense oligonucleotides phosphorthioate on gene expression of TIMP-1 in rat liver fibrosis显示文摘AIM To observe the inhibition of antisenseoligonucleotides (asON) phosphorthioate to thetissue inhibitors metalloproteinase-1 (TIMP-1)gene and protein expression in the liver tissue ofimmunologically induced hepatic fibrosis rats.The possibility of reversing hepatic fibrosisthrough gene therapy was observed.METHODS Human serum albumin (HSA) wasused to attack rats, as hepatic fibrosis model, inwhich asONs were used to block the gene andprotein expressing TIMP-1. According to theanalysis of modulator, structure protein, codingseries of TIMP-1 genome, we designed fourdifferent asONs. These asONs were injected intothe hepatic fibrosis models through coccygealvein. The results was observed by RT-PCR formeasuring TIMP-1 mRNA expression,immunohistochemistry and in situ hybridizationfor collagen Ⅰ, Ⅲ, special staining of collagenfiber, and electron microscopic examination.RESULTS Hepatic fibrosis could last within 363days in our modified model. The expressinglevel of TIMP-1 was high during hepatic fibrosisprocess. It has been proved by theimmunohistochemical and the electronmicroscopic examination that the asONphosphorthioate of TIMP-1 could exactly expressin vivo. The effect of colchicine wasdemonstrated to inhibit the expressing level ofmRNA and the content of collagen Ⅰ, Ⅲ in theliver of experimental hepatic fibrosis rats.However, the electron microscopy research andthe pathologic grading of hepatic fibrosisshowed that there was no significant differencebetween the treatment group and the modelgroup (P>0.05).CONCLUSION The experimental rat model ofhepatic fibrosis is one of the preferable modelsto estimate the curative effect of anti-hepaticfibrosis drugs. The asON phosphorthioate ofTIMP-1 could block the gene and proteinexpression of TIMP-1 in the liver of experimentalhepatic fibrosis rats at the mRNA level. It ispossible to reverse hepatic fibrosis, and it isexpected to study a new drug of anti-hepaticfibrosis on the genetic level. Colchicine has verylimited therapeutic effect on hepatic fibrosis,furthermore, its toxicity and side effects areobvious.Qing He Nie Yong Qian Cheng Yu Mei Xie Yong Xing Zhou Yi Zhan Cao The Center of Infectious Disease Diagnosis and Treatment of PLA,Tangdu Hospital,Forth Military Medical University,Xi’an 710038,Shaanxi Province,ChinaDr,Qing He Nie graduated from Qinghai Medical College as a doctor in 1983,got master degree at Beijing 302 Army Hospital in 1993,got doctor degree at the Third Military Medical University in 1998,engaged in postdoctoral research at the Fourth Military Medical University from 1998 to 2000,now an associate professor,specialized in clinical and experimental research of infectious diseases,had more than 90 papers published,coauthor of ten books,first author of one book. 2001World Journal of Gastroenterology2001,7,3:73
2Alterations in metastatic properties of hepatocellular carcinoma cell following H-ras oncogene transfection显示文摘AIM To demonstrate the relationship betweenH-ras oncogene and hepatocellular carcinoma(HCC) metastasis.METHODS Activated H-ras oncogene wastransfected into SMMC 7721, a cell line derivedfrom human HCC, by calcium phosphatetransfection method. Some metastasis-relatedparameters were detected in vitro, includingadhesion assay, migration assay, expression ofcollagenase ⅣV (c ⅣV ase) and epidermal growthfactor receptor (EGFR).RESULTS The abilities of H-ras-transfected cellclones in adhesion to laminin (LN) or fibronectin(FN), migration, c Ⅳ ase secretion increasedmarkedly, and the expression of EGFR elevatedmoderately. More importantly, these alterationswere consistent positively with the expressionof p21, the protein product of H-ras oncogene.CONCLUSION H-ras oncogene could inducethe metastatic phenotype of HCC cell in vitro toraise its metastatic potential.Qing Wang~1 Zhi Ying Lin~2 Xiao Li Feng~3 ~1Department of Microbiology,Medical Center of Fudan University.the former Shanghai Medical University,Shanghai 200032,China ~2Liver Cancer Institute,Zhongshan Hospital,Shanghai 200032,China ~3Shanghai Institute of Biochemistry,Academy Sinica,Shanghai 200031,ChinaQing Wang earned master degree from Shanghai Medical University in 1996,now a senior lecturer of microbiology,specialized in the role of oncogcncs on tumor metastasis,having 8 papers published. 2001World Journal of Gastroenterology2001,7,3:48
3The precipitation strengthening behavior of Cu-rich phase in Nb contained advanced Fe-Cr-Ni type austenitic heat resistant steel for USC power plant applicationCheng-yu Chi a, Hong-yao Yu b, Jian-xin Dong b, Wen-qing Liu c, Shi-chang Cheng d, Zheng-dong Liu d, Xi-shan Xie b a School of Metallurgical and Ecological Engineering, University of Science & Technology Beijing, Beijing 100083, China b School of Materials Science and Engineering, University of Science & Technology Beijing, Beijing 100083, China c Instrumental Analysis & Research Center, Shanghai University, Shanghai 200444, China d Central Iron and Steel Research Institute, Beijing 100081, China 2012Progress in Natural Science:Materials International2012,22,3:20
4Research progress on electrical signals in higher plants显示文摘This review introduces the characteristics of electrical signals in higher plants and their corresponding physiological significance, and describes in detail the impact of environmental factors (e.g. light and temperature) on the electrical potential of the plants. Also, we evaluate the measurement techniques used for electrical signals in plants, including intracellular measurement, extracellular measurement, measurement of the ion channel based on the patch-clamp technique and on the non-invasive microelectrode vibrating probe technique. We also give a brief review of the applications of these methods for investigating electrical signals in plants. The ionic mechanism of electrical activity in plants is then discussed in terms of environmental response in higher plants, and this is used to provide a theoretical basis for quantitative description of the electrical signals in plants. A model for interpretation of the electrical signal mechanisms in higher plants is discussed, but further experiments are required for the verification of this model.Xiaofei Yana, Zhongyi Wang a, Lan Huang a, Cheng Wang b, Ruifeng Hou b, Zhilong Xu b, Xiaojun Qiao b a College of Information and Electrical Engineering, China Agricultural University, Beijing 100083, China b National Engineering Research Center for Information Technology in Agriculture, Beijing 100097, China 2009Progress in Natural Science:Materials International2009,19,5:13
5Mobile Ubiquitous Service Environment显示文摘The Mobile Ubiquitous Service Environment (MUSE),established through the coordination and integration of mobile telecommunications and ubiquitous network,in the pursuit of Always Best Experience (ABE),represents the major development trend for the next generation mobile wireless network. Research on MUSE will involve the integration of the computing model system,service platform system,operating system and terminal structure system,all of which involve exploration and innovation of a new networking structure,its control and management as well as way of measuring. The change in network resources triggers the change in network computing models. To let readers have a basic understanding of MUSE,this lecture introduces it in four sections. This section focuses on the development and demand analysis of the service platform.Zhang Ping,Ji Yang,Feng Zhiyong (Research Center for Wireless New Technology,Beijing University of Posts and Telecommunications,Beijing 100876,China) The Mobile Ubiquitous Service Environment (MUSE),established through the coordination and integration of mobile telecommunications and ubiquitous network,in the pursuit of Always Best Experience (ABE),represents the major development trend for the next generation mobile wireless network. Research on MUSE will involve the integration of the computing model system,service platform system,operating system and terminal structure system,all of which involve exploration and innovation of a new networking structure,its control and management as well as way of measuring. The change in network resources triggers the change in network computing models. To let readers have a basic understanding of MUSE,this lecture introduces it in four sections. This section focuses on the development and demand analysis of the service platform. 2007ZTE Communications2007,5,2:10
6Current progress in epigenetic research for hepato-carcinomagenesis显示文摘Hepatocellular carcinoma is the main type of primary liver cancer,and also one of the most malignant tumors.At present,the pathogenesis mechanisms of liver cancer are not entirely clear.It has been shown that inactivation of tumor suppressor genes and activation of oncogenes play a significant role in carcinogenesis,caused by the genetic and epigenetic aberrance.In the past,people generally thought that genetic mutation is a key event of tumor pathogenesis,and somatic mutation of tumor suppressor genes is in particular closely associated with oncogenesis.With deeper understanding of tumors in recent years,increasing evidence has shown that epigenetic silencing of those genes,as a result of aberrant hypermethylation of CpG islands in promoters and histone modification,is essential to carcinogenesis and metastasis.The term epigenetics refers to heritable changes in gene expression caused by regulation mechanisms,other than changes in the underlying DNA sequence.Specific epigenetic processes include DNA methylation,genome imprinting,chromotin remodeling,histone modification and microRNA regulations.This paper reviews recent epigenetics research progress in the hepatocellular carcinoma study,and tries to depict the relationships between hepatocellular carcinomagenesis and DNA methylation as well as microRNA regulation.HUANG Jian National Human Genome Research Center at Shanghai-Ministry of Science and Technology to build a healthy and disease Ge-nomics Laboratory,Shanghai 201203,China 2009Science China(Life Sciences)2009,52,1:9
7Inflammatory pseudotumor of the liver: 13 cases of MRI findings显示文摘INTRODUCTIONInflammatory pseudotumor of the liver ,a rare benign lesion ,is often confused with the malignant tumors .Until 1998,less than 80 cases had been reported in the world [1,2].The accuracy of the pre-surgical diagnosis was low p[3,4] ,and very few materials on the diagnosis using dynamic MRI were reported [5-7] .We collected thirteen cases of inflammatory pseudotumor of the liver were collected and roved by pathology with MRI studies .Our purpose is to describe and analyze the MRI findings of this lesion and find out the valuable signs suggesting the diagnosis so as to avoid unnecessary operations.Fu Hua Yan Kang Rong Zhou Ya Ping Jiang Wei Bin Shi Department of Radiology,Zhongshan Hospital,Medical Center of Fudan University (Former Shanghai Medical University),180 Fenglin Road,Shanghai 200032,ChinaDr.Fu Hua Yan graduated from Shanghai Medical University as a postgraduate in 1996,now an associated professor,a radiologist in chief specialized in the diagnosis of CT and MRI in hepatic diseases,having 22 papers published.She is the associated editor of the books Spiral CT and Body MRI. 2001World Journal of Gastroenterology2001,7,3:8
8Transretinoic acid inhibits rats gastric epithelial dysplasia induced by N-methyi-N-nitro-N-nitrosoguanidine:influences on cell apoptosis and expression of its regulatory genes显示文摘INTRODUCTIONGastric epithelial dysplasia (GED) hypothetically is a straight-forward concept: dysplastic epithelium replacing the normal gastric epithelium of the stomach [1].In the stomach ,like any other segment of the gut ,it is defined as an unequivocal non-invasive epithelial change[2,3].The observation of gastric dysplasia as a cancerous lesion was recognized over a century ago ,but it is only after the advent of gastroscopy that its clinical significance has been stressed[4-7].Ru Tao Cui~1 Gan Cai~2 Zhao Bao Yin~(2*) Yong Cheng~2 Qiu Hong Yang~1 Tao Tian~(3#) ~1Liver Center,Beijing Friendship Hospital Affiliated to CapitalUniversity of Medical Sciences~2Department of Gastroenterology,Shuguang Hospital Affiliated to Shanghai University of Traditional Chinese Medicine,Shanghai China and Department of Pathophysiology.Shanghai Medical University.Shanghai,China ~3Pathological Department,Shanghai Medical University (?)Now working at UCLA,USA ~#Now working at University of Michigan,USADr.Ru Tao Cui graduated and got the bachelor degree from Shandong University of Traditional Chinese Medicine in 1994,got doctor degree from Shanghai University of Traditional Chinese Medicine in 2000,now studying as a postdoc,majoring gastroenterology,having 29 papers published. 2001World Journal of Gastroenterology2001,7,3:8
9Global cancer statistics显示文摘Jemal A Bray F Center MM CA:A Cancer Journal for Clinicians0,,:8
10Engineering of drug nanoparticles by HGCP for pharmaceutical applications显示文摘This paper reviews our work on the fundamental principles of high gravity controlled precipitation (HGCP) technology, and its applications in the production of drug nanoparticles, which was carried out in a rotating packed bed (RPB). Several kinds of drug nanoparticles with narrow particle size distributions (PSDs) were successfully prepared via HGCP, including the 300-nm Cefuroxime Axetil (CFA) particles, 200–400-nm cephradine particles, 500-nm salbutamol sulfate (SS) particles (100 nm in width), and 850-nm beclomethasone dipropionate (BDP) particles, etc. Compared to drugs available in the current market, all the drug nanoparticles produced by HGCP exhibited advantages in both formulation and drug delivery, thus improving the bioavailability of drugs. HGCP is essentially a platform technology for the preparation of poorly water-soluble drug nanoparticles for oral and injection delivery, and of inhalable drugs for pulmonary delivery. Consequently, HGCP offers potential applications in the pharmaceutical industry due to its cost-effectiveness, efficient processing and the ease of scaling-up.Ting-Ting Hua, Jie-Xin Wanga, Zhi-Gang Shena, Jian-Feng Chena,b, a Key Lab for Nanomaterials, Ministry of Education, Beijing University of Chemical Technology, Beijing 100029, China b Research Center of Ministry of Education for High Gravity Engineering and Technology, Beijing University of Chemical Technology, Beijing 100029, China 2008Particuology2008,6,4:7
11Corrosion behavior of Mg-Y alloy in NaCl aqueous solutionXin Zhang a,b,c,Kui Zhang a,Xia Deng a,Hongwei Li b,c,Yongjun Li a,Minglong Ma a,Ning Li b,c,Yanlong Wang b,c a State Key Laboratory for Fabrication and Processing of Nonferrous Metals,Beijing General Research Institute for Nonferrous Metals,Beijing 100088,China b Beijing Engineering Research Center for Advanced Manufacturing and Evaluation of Special Vehicle Parts,Beijing 100072,China c Center of Technology,Beijing North Vehicle Group Corporation,Beijing 100072,China 2012Progress in Natural Science:Materials International2012,22,2:7
12Effects of disinhibition on spatiotemporal pattern of neuronal first recruitment in neuronal networks显示文摘The propagation of neuronal activities is a key feature to understanding information processing in networks. The analysis based on first-spikes of bursts in turn plays an important role in the research of neuronal activity propagation. Our focus here is to investigate how spatiotemporal patterns of neuronal first-spikes are affected by disinhibition. Multi-electrode arrays were used to record stimulation-evoked bursts of multiple neurons in randomly cultured neuronal networks. Both the precise timing of and the rank relationships between first-spikes were analyzed. Compared with evoked bursts in the network's native state, the precise first-spike latencies in its dis-inhibited state are more consistent and the propagation of its bursting activities is much faster. Additional points of interest are that disinhibited neuronal networks can be evoked to generate stable and distinguishable neuronal first recruitment spatiotemporal patterns specific to the stimulation site, and that the disinhibition may cause the original spatiotemporal patterns to change in a heterogeneous manner with regards to different propagation pathways.Liangbin Pana,b,c,1, Xindong Songa,b,c,1, Guangxin Xiang a,b,c, Jing Zhua,b,c, Jing Cheng a,b,c,d,a Medical Systems Biology Research Center, Tsinghua University School of Medicine, Beijing 100084, China b Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing 100084, China c National Engineering Research Center for Beijing Biochip Technology, 18 Life Science Parkway, Beijing 102206, China d State Key Laboratory of Biomembrane and Membrane Biotechnology, Tsinghua University, Beijing 100084, China 2009Progress in Natural Science:Materials International2009,19,5:6
13Effect of Sr on microstructure and aging behavior of Mg-14Li alloysBin Jiang a,b,c,Ying Zeng b,Hengmei Yin a,b,Ruihong Li a,b,Fusheng Pan a,b a National Engineering Research Center for Magnesium Alloys,Chongqing University,Chongqing 400030,China b College of Materials Science and Engineering,Chongqing University,Chongqing 400030,China c New Materials Center,Chongqing Academy of Science and Technology,Chongqing 401123,China 2012Progress in Natural Science:Materials International2012,22,2:3
14^(99m)Tc-AMD3100:A novel potential receptor-targeting radiopharmaceutical for tumor imaging显示文摘The chemokine CXCR4 receptor is over-expressed in a wide variety of tumors.In this study,AMD3100,which was a prototype non-peptide antagonist of CXCR4 receptor,was labeled with ^(99m)Tc.^(99m)Tc-AMD3100 was verified by thin layer radio chromatography(TLRC).The tumor-localizing properties of ^(99m)Tc-AMD3100 were evaluated and proved in mice bearing Hep-G2 tumor xenograft.^(99m)Tc-AMD3100 was a promising,novel receptor-specific radiopharmaceutical with potential application in the imaging of human tumors.Jin Ming Zhang~(a,),Jia He Tian~a,Tian Ran Li~a, Hai Yu Guo~a,Li Shen~b a Department of Nuclear Medicine,The PLA General Hospital,Beijing,100853,China b Peking University Health Science Center,Beijing,100191,China 2010Chinese Chemical Letters2010,21,4:3
15Synthesis, Crystal Structure and Calculated β Value of a Tetrahedral Zinc (II) Complex——Zn(2-NH_2py)_2Br_2显示文摘A new zinc(II) complex, Zn(2-NH2py)2Br2 (py=pyridine), has been synthesized, and its molecular structure has been confirmed by IR, elemental analysis and -ray crystal structure analysis. Its space group is P21/n with Mr=413.43 (C10H12Br2N4Zn), a=7.435(2), b=12.865(3), c=14.186(4)? b=94.08(2)? V=1353.5(5) 3, Z=4, Dc=2.029 g/cm3, F(000)=328, ?2.378mm-1, R=0.0283, wR=0.0501. The total observed reflections with I≥2?I) were 5314, of which the independent reflections were 3106. The complex structure contains a distorted tetrahedron formed by four atoms coordinated to zinc atom, namely two bromide atoms and two nitrogen atoms. The two ZnBr bond lengths within one molecule, 2.3763(6) and 2.4002(5)? respectively, are not equal; and so are the two ZnN bond lengths, which are 2.031(2) and 2.044(2)?respectively. The calculation results using PM3 method through MOPAC software package in Chem 3D show that its first molecular hyperpolarizability b value is 5.210-30esu, which is comparable with that of p-nitroaniline. No bulk SHG effect has been detected due to the centrosymmetric space group.REN Peng a SU Nan-Bing a QIN Jin-Gui a Michael W. Day b CHEN Chuang-Tianc ( aDepartment of Chemistry, Wuhan University, Wuhan 43007, China) ( bBeckman Institute, California Institute of Technology, Pasadena, CA91125, USAQ ) ( cBeijing R & D Center 2002Chinese Journal of Structural Chemistry2002,21,1:3
16Immobilized enzyme reactors in HPLC and its application in inhibitor screening:A review显示文摘This paper sets out to summarize the literatures based on immobilized enzyme bio-chromatography and its application in inhibitors screening in the last decade.In order to screen enzyme inhibitors from a mass of compounds in preliminary screening,multi-pore materials with good biocompatibility are used for the supports of immobilizing enzymes,and then the immobilized enzyme reactor applied as the immobilized enzyme stationary phase in HPLC.Therefore,a technology platform of high throughput screening is gradually established to screen the enzyme inhibitors as new anti-tumor drugs.Here,we briefly summarize the selective methods of supports,immobilization techniques,co-immobilized enzymes system and the screening model.Si-Meng Fang a,Hai-Na Wang a,Zhong-Xi Zhao b,Wei-Hong Wang a,n a School of Pharmaceutical Sciences,Shandong University,Ji’nan,China b School of Pharmaceutical Sciences and Center for Pharmaceutical Research & Drug Delivery Systems,Shandong University,Ji’nan,China 2012Journal of Pharmaceutical Analysis2012,2,2:3
17直接评估吗啡刺激糖尿病人隐静脉内皮一氧化氮释放减少显示文摘to directly measure in real time basal and stimulated levels of NO released from human saphenous vein endothelium and to quantify the expression of the μopiate receptor, which has been linked with NO release. METHODS: Saphenous vein segments from patients with type 2 diabetes ( n = 12) and patients without diabetes (n =8) were obtained. The release of NO was measured directly from the endothelium using a NO-specific amperometric probe. NΩ-nitro-L-arginine methyl ester (L-NAME, 0.1 mmol/L), a NO synthase (NOS) inhibitor, or morphine (1 μmol/L), a stimulant, was administered and the measurements were repeated. Values were reported relative to the mean initial measurement of NO release from diabetic endothelium, which was defined as the relative zero level of NO release. A RT-PCR was then performed on the endothelium to measureμ opiate receptor expression. RESULTS: Diabetic patients (n = 12) showed a relative and significantly diminished basal level of released NO, (0.049± 0.012) nmol/L, comparedThomas V BILHNGER, James A VOSSWINKEL, Patrick CADET, Christos M RIALAS, Harold I MAGAZINE, George B STEFANO(Division of Cardiothoracic Surgery, Department of Surgery, University Hospital and Medical Center, HSC, T19-080, Stony Brook, New York 11794-8191 Neuroscience Research Institute, State University of New York College at Old Westbury, Old Westbury, New York , USA) 2002Acta Pharmacologica Sinica2002,23,2:3
18Modeling contaminant transport in homogeneous porous media with fractional advection-dispersion equation显示文摘The newly developed Fractional Advection-Dispersion Equation (FADE), which is FADE was extended and used in this paper for modelling adsorbing contaminant transport by adding an adsorbing term. A parameter estimation method and its corresponding FORTRAN based program named FADEMain were developed on the basis of Nonlinear Least Square Algorithm and the analytical solution for one-dimensional FADE under the conditions of step input and steady state flow. Data sets of adsorbing contaminants Cd and NH4+-N transport in short homogeneous soil columns and conservative solute NaCI transport in a long homogeneous soil column, respectively were used to estimate the transport parameters both by FADEMain and the advection-dispersion equation (ADE) based program CXTFIT2.1. Results indicated that the concentration simulated by FADE agreed well with the measured data. Compared to the ADE model, FADE can provide better simulation for the concentration in the initial lower concentration part and the late higher concentration part of the breakthrough curves for both adsorbing contaminants. The dispersion coefficients for ADE were from 0.13 to 7.06 cm2/min, while the dispersion coefficients for FADE ranged from 0.119 to 3.05 cm1.856/min for NaCI transport in the long homogeneous soil column. We found that the dispersion coefficient of FADE increased with the transport distance, and the relationship between them can be quantified with an exponential function. Less scale-dependent was also found for the dispersion coefficient of FADE with respect to ADE.HUANG Guanhua, HUANG Quanzhong, ZHAN Hongbin , CHEN Jing, XIONG Yunwu & FENG Shaoyuan College of Hydraulic and Civil Engineering, China Agricultural University, Beijing 100083, China Chinese-Israeli International Center for Research and Training in Agriculture, Beijing 100083, China Department of Geology and Geophysics, Texas A& M University, TZ77843-3115, USA 2005Science China Earth Sciences2005,48,z2:3
19Synthesis of dental resins using diatomite and nano-sized SiO_2 and TiO_2Xiaoli Miao a,Meifang Zhu a,Yaogang Li b,Qinghong Zhang b,Hongzhi Wang a a State Key Laboratory for Modification of Chemical Fibers and Polymer Materials,Donghua University,Shanghai 201620,China b Engineering Research Center of Advanced Glasses Manufacturing Technology,MOE,Donghua University,Shanghai 201620,China 2012Progress in Natural Science:Materials International2012,22,2:3
20PHOTOELECTROCHEMICAL STUDY OF PASSIVE LAYERS ON COPPER ELECTRODES IN SOME ALKALINE MEDIA显示文摘PHOTOELECTROCHEMICALSTUDYOFPASSIVELAYERSONCOPPERELECTRODESINSOMEALKALINEMEDIA①A.Kamkina,1,ZhouGuodinga,XuQunjiebandB.H.cLooaE... A. Kamkina,1, Zhou Guodinga, Xu Qunjieb and B. H.c Loo a Electrochemical Research Group, Shanghai Institute of Electric Power, Shanghai 200090, P. R. China b Corrosion Prevention Center, East China University of 1998中国有色金属学会会刊:英文版1998,8,2:2
返回顶部 每页显示:
共133页 首页 上一页 第1页 下一页 末页 /133 跳转

网站首页 | 关于我们 | 联系我们 | 产品服务 | 客服中心 | 广告服务 | 版权声明 | 网站联盟 | 友情链接 | 售卡网点

版权所有© 渝B2-20050021-1 渝公网安备 50019002500403号 违法和不良信息举报中心

互联网出版许可证 新出网证(渝)字10号 全国400电话 - 免长途话费