维普中文期刊产品整合服务
136篇 您的检索式:作者名="Evgeniy"
    题名 作者 年代 出处 被引量
1Antiangiogenic therapy for portal hypertension in liver cirrhosis: Current progress and perspectives显示文摘Developing medicines for hemodynamic disorders that are characteristic of cirrhosis of the liver is a relevant problem in modern hepatology. The increase in hepatic vascular resistance to portal blood flow and subsequent hyperdynamic circulation underlie portal hypertension(PH) and promote its progression, despite the formation of portosystemic collaterals. Angiogenesis and vascular bed restructurization play an important role in PH pathogenesis as well. In this regard, strategic directions in the therapy for PH in cirrhosis include selectively decreasing hepatic vascular resistance while preserving or increasing portal blood flow, and correcting hyperdynamic circulation and pathological angiogenesis. The aim of this review is to describe the mechanisms of angiogenesis in PH and the methods of antiangiogenic therapy. The Pub Med database, the Google Scholar retrieval system, and the reference lists from related articles were used to search for relevant publications. Articles corresponding to the aim of the review were selected for 2000-2017 using the keywords: 'liver cirrhosis', 'portal hypertension', 'pathogenesis', 'angiogenesis', and 'antiangiogenic therapy'. Antiangiogenic therapy for PH was the inclusion criterion. In this review, we have described angiogenesis inhibitors and their mechanism of action in relation to PH. Although most of them were studie donly in animal experiments, this selective therapy for abnormally growing newly formed vessels is pathogenetically reasonable to treat PH and associated complications.Dmitry Victorovich Garbuzenko Nikolay Olegovich Arefyev Evgeniy Leonidovich Kazachkov 2018World Journal of Gastroenterology2018,24,33:13
2水文地质学的新概念及其生态问题显示文摘水文地质学最初是由地质学及水文学相结合而形成的一门学科,它基本上采用地质学的研究方法。从本世纪70年代中期开始,研究地下水的水文地质学已逐渐变为研究地下水圈的学科。地下水圈是指地壳内部的统一的含水系统,它包含有相互作用的不同状态和形式的H2O。近年来,一些新理论的引入,拓宽了原有水文地质学的概念,使之从对现象的研究转向为对过程及其规律的研究。水文地质学传统的和新的问题应在适当的工程标准上予以解决,同时应重视其生态效应。水是地球内部具有高度流动性的物质,因此,人类活动对岩石圈的影响将首先导致水文地质条件的变化,并进而引起地下水圈的污染、水的枯竭及自然条件的恶化。文章主要论述生态水文地质学研究的目的、原则及生态水文地质系统的体系。生态水文地质学研究的目的是提出管理地下水圈体系及其质量状态的方法。Evgenii V.Pinneker(Institute of the Earth’S Crust,664033,Irkutsk, Russia) 1996地学前缘1996,3,1:7
3Chronic hepatitis C virus infection:Prevalence of extrahepatic manifestations and association with cryoglobulinemia in Bulgarian patients显示文摘AIM: To assess the prevalence of extrahepatic manifestations in Bulgarian patients with chronic hepatitis C virus (HCV) infection and identify the clinical and biological manifestations associated with cryoglobulinemia. METHODS: The medical records of 136 chronically infected HCV patients were reviewed to assess the prevalence of extrahepatic manifestations. Association between cryoglobulin-positivity and other manifestations were identified using χ2 and Fisher’s exact test. Risk factors for the presence of extrahepatic manifestations were assessed by logistic regression analysis. RESULTS: Seventy six percent (104/136) of the patients had at least one extrahepatic manifestation. Clinical manifestations included fatigue (59.6%), kidney impairment (25.0%), type 2 diabetes (22.8%), paresthesia (19.9%), arthralgia (18.4%), palpable purpura (17.6%), lymphadenopathy (16.2%), pulmonary fi brosis (15.4%), thyroid dysfunction (14.7%), Raynaud’s phenomenon (11.8%), B-cell lymphoma (8.8%), sicca syndrome (6.6%), and lichen planus (5.9%). The biological manifestations included cryoglobulinproduction (37.5%), thrombocytopenia (31.6%), and autoantibodies: anti-nuclear (18.4%), anti-smooth muscle (16.9%), anti-neutrophil cytoplasm (13.2%) and anti-cardiolipin (8.8%). All extrahepatic manifestations showed an association with cryoglobulin-positivity, with the exception of thyroid dysfunction, sicca syndrome, and lichen planus. Risks factors for the presence of extrahepatic manifestations (univariate analysis) were: age ≥ 60 years, female gender, virus transmission by blood transfusions, longstanding infection (≥ 20 years), and extensive liver fi brosis. The most signifi cant risks factors (multivariate analysis) were longstanding infection and extensive liver fi brosis. CONCLUSION: We observed a high prevalence of extrahepatic manifestations in patients with chronic HCV infection. Most of these manifestations were associated with impaired lymphoproliferation and cryoglobulin production. Longstanding infection and extensive liver fi brosis were signifi cant risk factors for the presence of extrahepatic manifestations in HCV patients.Diana V Stefanova-Petrova Anelia H Tzvetanska Elisaveta J Naumova Anastasia P Mihailova Evgenii A Hadjiev Rumiana P Dikova Mircho I Vukov Konstantin G Tchernev 2007World Journal of Gastroenterology2007,13,48:5
4Genes associated with testicular germ cell tumors and testicular dysgenesis in patients with testicular microlithiasis显示文摘阴囊的 microlithiasis (TM ) 是阴囊的 dysgenesis 症候群(TDS ) 的症状之一。TM 作为阴囊的细菌房间肿瘤(TGCT ) 的一个增进知识的标记特别地有趣。工具包 ligand 基因( KITLG ), BCL2 对手/杀手 1 ( BAK1 ),并且表明对手 4 的 sprouty RTK ( SPRY4 ),基因与 TGCT 的高风险被联系骨头形态基因的蛋白质 7 基因( BMP7 ),转变生长因素贝它受体 3 基因( TGFBR3 ),并且 homeobox D 簇基因( HOXD )与 TDS 有关。使用的聚合酶链反应限制碎片长度多型性( PCR-RFLP )分析,我们为 KITLG 调查了等位基因和遗传型频率( rs995030 , rs1508595 ), SPRY4 ( rs4624820 , rs6897876 ), BAK1 ( rs210138 ), BMP7 ( rs388286 ), TGFBR3 ( rs12082710 ),并且在 142 个 TGCT 病人, 137 个 TM 病人,和 153 个肥沃的人(控制组)的 HOXD ( rs17198432 )。我们在 TM 在 KITLG GG_rs995030 遗传型发现了重要差别(P = 0.01 ) 并且 TGCT 病人(P = 0.0005 ) 与控制相比。我们也揭示了在 KITLG_rs1508595 和 TM 之间的强壮的协会(G 等位基因, P = 0.003;GG 遗传型, P = 0.01 ) 并且在 KITLG_rs1508595 和 TGCT 之间(G 等位基因, P = 0.0001;GG 遗传型, P = 0.0007 ) 。而且,在在 TGCT 组和控制之间的 BMP7_rs388286 有重要差别(T 等位基因, P = 0.00004;TT 遗传型, P = 0.00006 ) 并且在 TM 组和控制之间(T 等位基因, P = 0.04 ) 。HOXD 也与 TGCT 表明了一个强壮的协会(rs17198432 A 等位基因, P = 0.0001;AA 遗传型, P = 0.001 ) 。而且,重要差别在 BAK1_rs210138 G 等位基因在 TGCT 组和控制之间被发现(P = 0.03 ) 并且 GG 遗传型(P = 0.01 ) 。KITLG 和 BMP7 基因,与 TGCT 的发展联系了,可能也与 TM 有关。在摘要, KITLG GG_rs995030, GG_rs1508595, BMP7 TT_rs388286, HOXD AA_rs17198432,和 BAK1 GG_rs210138,遗传型与 TGCT 开发的高风险被联系。Ilya S Dantsev Evgeniy V Ivkin Aleksey A Tryakin Dmitriy N Godlevski Oleg Yu Latyshev Victoriya V Rudenko Dmitry S Mikhaylenko Vyacheslav B Chernykh Elena A Volodko Aleksey B Okulov Oleg B Loran Marina V Nemtsova 2018Asian Journal of Andrology2018,20,6:4
5Resolution limit of label-free far-field microscopy显示文摘The Abbe diffraction limit,which relates the maximum optical resolution to the numerical aperture of the lenses involved and the optical wavelength,is generally considered a practical limit that cannot be overcome with conventional imaging systems.However,it does not represent a fundamental limit to optical resolution,as demonstrated by several new imaging techniques that prove the possibility of finding the subwavelength information from the far field of an optical image.These include super-resolution fluorescence microscopy,imaging systems that use new data processing algorithms to obtain dramatically improved resolution,and the use of super-oscillating metamaterial lenses.This raises the key question of whether there is in fact a fundamental limit to the optical resolution,as opposed to practical limitations due to noise and imperfections,and if so then what it is.We derive the fundamental limit to the resolution of optical imaging and demonstrate that while a limit to the resolution of a fundamental nature does exist,contrary to the conventional wisdom it is neither exactly equal to nor necessarily close to Abbe’s estimate.Furthermore,our approach to imaging resolution,which combines the tools from the physics of wave phenomena and the methods of information theory,is general and can be extended beyond optical microscopy,e.g.,to geophysical and ultrasound imaging.Evgenii Narimanov 2019Advanced Photonics2019,1,5:3
6Thermal state calculation of chamber in small thrust liquid rocket engine for steady state pulsed mode显示文摘This paper presents a method of thermal state calculation of combustion chamber in small thrust liquid rocket engine. The goal is to predict the thermal state of chamber wall by using basic parameters of engine: thrust level, propellants, chamber pressure, injection pattern, film cooling parameters, material of wall and their coating, etc. The difficulties in modeling the startup and shutdown processes of thrusters lie in the fact that there are the conjugated physical processes occurring at various parameters for non-design conditions. A mathematical model to predict the thermal state of the combustion chamber for different engine operation modes is developed. To simulate the startup and shutdown processes, a quasi-steady approach is applied by replacing the transient process with time-variant operating parameters of steady-state processes. The mathematical model is based on several principles and data commonly used for heat transfer modeling: geometry of flow part, gas dynamics of flow, thermodynamics of propellants and combustion spices, convective and radiation heat flows, conjugated heat transfer between hot gas and wall, and transient approach for calculation of thermal state of construction. Calculations of the thermal state of the combustion chamber in single-turn-on mode show good convergence with the experimental results. The results of pulsed modes indicate a large temperature gradient on the internal wall surface of the chamber between pulses and the thermal state of the wall strongly depends on the pulse duration and the interval.Alexey Gennadievich VOROBYEV Svatlana Sergeevna VOROBYEVA Lihui ZHANG Evgeniy Nikolaevich BELIAEV 2019Chinese Journal of Aeronautics2019,32,2:2
7Origins of high ductility exhibited by an extruded magnesium alloy Mg-1.8Zn-0.2Ca:Experiments and crystal plasticity modeling显示文摘Low ductility and strength are major bottlenecks against Mg alloys’wide applications.In this work,we systematically design the composition and fabrication process for a low-alloyed Mg-Zn-Ca alloy,showing that it can be extruded at low temperatures(~250℃)and high speeds(~2 mm/s).After the extrusion,this alloy exhibits a substantially weakened basal texture,relatively small grain size,very high tensile elongation(~30%),and good strength.The origin of the considerably improved ductility was studied using a combination of three-dimensional atom probe tomography(3D-APT),transmission electron microscopy(TEM),electron backscattered diffraction(EBSD)in conjunction with surface slip trace analysis,in-situ synchrotron X-ray diffraction,and elasto-plastic self-consistent(EPSC)modeling.Co-segregation of Zn and Ca atoms at a grain boundary is observed and associated with texture weakening and grain boundary mediated plasticity,both improving the ductility.While basal slip and prismatic slip are identified as the dominant deformation systems in the alloy,the ratio between their slip resistances is substantially reduced relative to pure Mg and most other Mg alloys,significantly contributing to the improved ductility of the alloy.This Mg-Zn-Ca alloy exhibiting excellent mechanical properties and low fabrication cost is a promising candidate for industrial productions.Jie Wang Gaoming Zhu Leyun Wang Evgenii Vasilev Jun-Sang Park Gang Sha Xiaoqin Zeng Marko Knezevic 2021Journal of Materials Science & Technology2021,,25:2
8A historical literature review of coronary microvascular obstruction and intra-myocardial hemorrhage as functional/structural phenomena显示文摘The analysis of experimental data demonstrates that platelets and neutrophils are involved in the no-reflow phenomenon,also known as microvascular obstruction(MVO).However,studies performed in the isolated perfused hearts subjected to ischemia/reperfusion(I/R)do not suggest the involvement of microembolization and microthrombi in this phenomenon.The intracoronary administration of alteplase has been found to have no effect on the occurrence of MVO in patients with acute myocardial infarction.Consequently,the major events preceding the appearance of MVO in coronary arteries are independent of microthrombi,platelets,and neutrophils.Endothelial cells appear to be the target where ischemia can disrupt the endothelium-dependent vasodilation of coronary arteries.However,reperfusion triggers more pronounced damage,possibly mediated by pyroptosis.MVO and intra-myocardial hemorrhage contribute to the adverse post-infarction myocardial remodeling.Therefore,pharmacological agents used to treat MVO should prevent endothelial injury and induce relaxation of smooth muscles.Ischemic conditioning protocols have been shown to prevent MVO,with L-type Ca2+channel blockers appearing the most effective in treating MVO.Leonid N.Maslov Natalia V.Naryzhnaya Sergey V.Popov Alexandr V.Mukhomedzyanov Ivan A.Derkachev Boris K.Kurbatov Andrey V.Krylatov Feng Fu Jianming Pei Vyacheslav V.Ryabov Evgenii V.Vyshlov Svetlana V.Gusakova Alla A.Boshchenko Akpay Sarybaev 2023The Journal of Biomedical Research2023,37,4:2
9Zener-Hollomon参数对含铁锻造铝合金热变形处理过程中亚结构和织构演变的影响(英文)显示文摘研究Zener-Hollomon参数对含铁锻造铝合金(AA8011)亚结构和织构演变的影响。采用X射线织构分析、电子背散射衍射(EBSD)和光学显微镜等技术进行表征。结果表明,Zener-Hollomon参数对含铁铝合金热变形处理过程中立方织构的演变具有显著影响。增大Zener-Hollomon参数会减少热变形过程中立方织构的数量,且能加强退火过程中的颗粒诱发形核(PSN)的能力。然而,低温热变形处理会导致活性沉淀,这些细而分散的颗粒会阻碍除了产生立方大晶粒的晶核外的所有晶核。综上,在含铁锻造铝合金中,Zener-Hollomon参数与亚晶粒尺寸之间的相关性与在3xxx系列合金中观察到的类似,可以用系列推导方程描述。Evgenii ARYSHENSKII Jürgen HIRSCH Vladimir BAZHIN Rudolf KAWALLA Ulrich PRAL 2019Transactions of Nonferrous Metals Society of China2019,29,5:2
10Binuclear and Hexanuclear Ti(Ⅳ) Complexes Supported by [OOOO]^(4–)-type Ligand for Preparing Disentangled UHMWPE显示文摘Binuclear and hexanuclear titanium complexes stabilized by tetradentate [OOOO]^(4–)-type ligand were active in ethylene polymerization in the presence of Et2 AlCl/Bu2 Mg binary co-catalyst, giving high molecular weight polyethylene. The binuclear complex showed significantly higher catalytic activity and thermal stability in comparison to mononuclear analogue. Ultra high molecular weight polyethylene(UHMWPE) samples were processed by a solid-state uniaxial deformation into high-strength(up to 2.5 GPa) and highmodulus(over 100 GPa) oriented film tapes, which indirectly indicates a low degree of entanglements between the macromolecular chains.Vladislav A.Tuskaev Svetlana Ch.Gagieva Dmitry A.Kurmaev Viktor G.Vasil'ev Nikolay A.Kolosov Sergey V.Zubkevich Elena S.Mikhaylik Evgenii K.Golubev Galina G.Nikiforova Pavel A.Zhizhko Olga A.Serenko Boris M.Bulychev 2019Chinese Journal of Polymer Science2019,37,5:2
11Empagliflozin alleviates podocytopathy and enhances glomerular nephrin expression in db/db diabetic mice显示文摘BACKGROUND Modern guidelines recommend sodium-glucose cotransporter-2(SGLT2)inhibitors as the preferred antihyperglycemic agents for patients with type 2 diabetes and chronic kidney disease.However,the mechanisms underlying the renal protective effect of SGLT2 inhibitors are not fully understood.structure of podocytes and nephrin expression in glomeruli in db/db diabetic mice.METHODS We treated 8-wk-old male db/db mice with EMPA(10 mg/kg/d)or vehicle for 8 wk.Age-matched male db/+mice were included as non-diabetic controls.Parameters of body composition,glycemic and lipid control,and plasma concentrations of leptin,insulin and glucagon were assessed.We evaluated renal hypertrophy as kidney weight adjusted to lean mass,renal function as plasma levels of creatinine,and albuminuria as the urinary albumin-to-creatinine ratio(UACR).Renal structures were studied by light and transmission electron microscopy with a focus on mesangial volume and podocyte structure,respectively.Glomerular nephrin and transforming growth factor beta(TGF-β)were assessed by immunohistochemistry.RESULTS Severe obesity and hyperglycemia developed in db/db mice prior to the start of the experiment;increased plasma concentrations of fructosamine,glycated albumin,cholesterol,leptin,and insulin,and elevated UACR were detected.Mesangial expansion,glomerular basement membrane thickening,and increased area of TGF-βstaining in glomeruli were revealed in vehicle-treated mice.Podocytopathy was manifested by effacement of foot processes;nephrin-positive areas in glomeruli were reduced.EMPA decreased the levels of glucose,fructosamine and glycated albumin,UACR,kidney hypertrophy,mesangial expansion,glomerular basement membrane thickening,and glomerular TGF-βstaining,alleviated podocytopathy and restored glomerular staining of nephrin.CONCLUSION These data indicate that EMPA attenuates podocytopathy in experimental diabetic kidney disease.The anti-albuminuric effect of EMPA could be attributed to mitigation of podocyte injury and enhancement of nephrin expression.Vadim V Klimontov Anton I Korbut Iuliia S Taskaeva Nataliya P Bgatova Maksim V Dashkin Nikolai BOrlov Anna S Khotskina Evgenii L Zavyalov Thomas Klein 2020World Journal of Diabetes2020,11,12:2
12A new karst-dwelling bent-toed gecko (Squamata: Gekkonidae Cyrtodactylus) from Xiangkhoang Province, northeastern Laos显示文摘We describe a new karst-dwelling Cyrtodactylus from Ban Thathom, Xiangkhoang Province, northeastern Laos. The new species can be distinguished from other congeners by having four dark dorsal bands between limb insertions, a discontinuous nuchal loop,10 precloacal pores in males or 10–12 precloacal pits(females) separated by a diastema from a series of enlarged femoral scales bearing 18 or 19 pores(male)or 8–10 pits(females) along each femur, 14–18 dorsal tubercle rows at midbody, no precloacal groove, 30–36 midbody scale rows across belly between ventrolateral skin folds, transversely enlarged subcaudal plates, and a maximal known snout-vent length of 75.5 mm. Our description brings to 22 the number of Cyrtodactylus species recorded from Laos.Roman A. Nazarov Olivier S.G. Pauwels Evgeniy L. Konstantinov Anatoliy S. Chulisov Nikolai L. Orlov Nikolay A. Poyarkov, Jr. 2018Zoological Research2018,39,3:2
13Sarcopenia in cirrhosis: Prospects for therapy targeted to gut microbiota显示文摘Decreased muscle mass and function,also known as sarcopenia,is common in patients with cirrhosis and is associated with a poor prognosis.Although the pathogenesis of this disorder has not been fully elucidated,a disordered gutmuscle axis probably plays an important role.Decreased barrier function of the gut and liver,gut dysbiosis,and small intestinal bacterial overgrowth(SIBO)can lead to increased blood levels of ammonia,lipopolysaccharides,pro-inflammatory mediators,and myostatin.These factors have complex negative effects on muscle mass and function.Drug interventions that target the gut microbiota(long-term use of rifaximin,lactulose,lactitol,or probiotics)positively affect most links of the compromised gut-muscle axis in patients with cirrhosis by decreasing the levels of hyperammonemia,bacterial translocation,and systemic inflammation and correcting gut dysbiosis and SIBO.However,although these drugs are promising,they have not yet been investigated in randomized controlled trials specifically for the treatment and prevention of sarcopenia in patients with cirrhosis.No data exist on the effects of fecal transplantation on most links of gut-muscle axis in cirrhosis;however,the results of animal experimental studies are promising.Roman Maslennikov Aliya Alieva Elena Poluektova Yury Zharikov Andrey Suslov Yana Letyagina Ekaterina Vasileva Anna Levshina Evgenii Kozlov Vladimir Ivashkin 2023World Journal of Gastroenterology2023,29,27:2
14Effects of low temperatures on strength and power input into rock failure显示文摘Study results of low temperature effects on the strength index and specific power input into rock failure are presented.It has been experimentally determined that within the range of-5 °С to-15 °С,there is a local minimum at which the compression strength and specific power input into failure of some rocks are 10%–50% lower than those at positive temperatures.Evgenii V.Zakharov Alexander S.Kurilko 2014Research in Cold and Arid Regions2014,6,5:1
15Porous structure and sorption properties of nitrogen-containing activated carbon显示文摘Aryuna D Budaeva A D Evgeniy V 2010Fuel2010,89,9:1
16Feature Generation for Text Categorization Using World Knowledge显示文摘Evgeniy Gabrilovich Shaul Markovitch 2005IJCAI2005,,:1
17Placing Search in Context: the Concept Revisited 显示文摘F Lev G Evgeniy M Yossi 2002ACM Transactions on Information System2002,20,1:1
18Aberrant PGE 2 metabolism in bladder tumor microenvironment promotes immunosuppressive phenotype of tumor-infiltrating myeloid cells显示文摘Evgeniy Eruslanov Irina Daurkin Johannes Vieweg Yehia Daaka Sergei Kusmartsev 2011International Immunopharmacology2011,,7:1
19Sample entropy analysis of laser speckle fluctuations to suppress motion artifact on blood flow monitoring显示文摘Laser speckle imaging is a common technique to monitor blood flow.The fluctuations in speckle intensity can be related to the blood flow by calculating the speckle contrast,the ratio between the standard deviation of speckle fluctuations and the average intensity.However,this simple statistic calculation is easily affected by motion artifacts.In this study,we applied sample entropy analysis instead of calculating standard deviations of the speckle fluctuations.Similar to the traditional method,sample entropy-based speckle contrast increases linearly with flow rate but was shown to be more immune to sudden movements during an upper arm occlusion test.金星徹 Evgenii Kim Eloise Anguluan 金載官 2022Chinese Optics Letters2022,20,1:1
20Thermoelectric and electrical characteristics of SmS ceramic samples after exposure to a pulsed magnetic field显示文摘Samarium monosulfide(SmS)is a promising material for creating thermoelectric generators(TEG),gas sensors and strain gauges.Despite the high values of the generated thermo electromotive force(TEMF)(α≈170-350μV/K),methods for increasing the efficiency of TEGs based on SmS are of considerable interest.One of these methods can be short-term effects of magnetic fields,including pulsed ones,on these materials.The action of a pulsed magnetic field(PMF)leading to an increase in TEMF(U)of SmS ceramic samples is found.Samples that are not subjected to high frequency currents(HFC)annealing show an increase in UT of 44.54%-62.18%(from 11.9 to 17.2-19.3 mV).The conductivity(σ)of the samples is~22 Q/cm and is insensitive to short-term exposure to a PMF.Samples that undergo HFC annealing show an increase in Uof 23.47%-41.31%(from 21.3 to 26.3-30.1 mV)after exposure to a PMF.The conductivity of the samples is~15Ω^(-1)/cm and after a short exposure to the PMF is changing nonmo notonically,with an increase in the overall instability.The difference in the values of Uand a can be explained by presence of an ordered grain structure and a significant amount of the Sm_(2)O_(2)S phase in the samples subjected to HFC annealing.Possible mechanisms of the observed changes are discussed.Ivan Volchkov Evgeniy Baskakov Vladimir Strelov Vladimir Kanevskii 2022Journal of Rare Earths2022,40,11:1
返回顶部 每页显示:
共7页 首页 上一页 第1页 下一页 末页 /7 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