全文获取类型
收费全文 | 1514263篇 |
免费 | 142289篇 |
国内免费 | 1557篇 |
出版年
2021年 | 17942篇 |
2019年 | 16190篇 |
2018年 | 18132篇 |
2017年 | 16873篇 |
2016年 | 28346篇 |
2015年 | 42710篇 |
2014年 | 50931篇 |
2013年 | 77121篇 |
2012年 | 40034篇 |
2011年 | 29215篇 |
2010年 | 44524篇 |
2009年 | 45649篇 |
2008年 | 27418篇 |
2007年 | 25816篇 |
2006年 | 30615篇 |
2005年 | 31586篇 |
2004年 | 30735篇 |
2003年 | 28363篇 |
2002年 | 26644篇 |
2001年 | 45818篇 |
2000年 | 43696篇 |
1999年 | 40421篇 |
1998年 | 26684篇 |
1997年 | 26560篇 |
1996年 | 25840篇 |
1995年 | 24016篇 |
1994年 | 23815篇 |
1993年 | 23023篇 |
1992年 | 34312篇 |
1991年 | 32599篇 |
1990年 | 30955篇 |
1989年 | 31518篇 |
1988年 | 29170篇 |
1987年 | 27496篇 |
1986年 | 26129篇 |
1985年 | 27827篇 |
1984年 | 26292篇 |
1983年 | 23097篇 |
1982年 | 22498篇 |
1981年 | 21505篇 |
1980年 | 19994篇 |
1979年 | 22597篇 |
1978年 | 20548篇 |
1977年 | 19498篇 |
1976年 | 18411篇 |
1975年 | 18485篇 |
1974年 | 19364篇 |
1973年 | 19638篇 |
1972年 | 16892篇 |
1971年 | 15516篇 |
排序方式: 共有10000条查询结果,搜索用时 72 毫秒
101.
Protein Kinase PKR Mediates the Apoptosis Induction and Growth Restriction Phenotypes of C Protein-Deficient Measles Virus 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ann M. Toth Patricia Devaux Roberto Cattaneo Charles E. Samuel 《Journal of virology》2009,83(2):961-968
The measles virus (MV) accessory proteins V and C play important roles in MV replication and pathogenesis. Infection with recombinant MV lacking either V or C causes more cell death than infection with the parental vaccine-equivalent virus (MVvac), and C-deficient virus grows poorly relative to the parental virus. Here, we show that a major effector of the C phenotype is the RNA-dependent protein kinase PKR. Using human HeLa cells stably deficient in PKR as a result of RNA interference-mediated knockdown (PKRkd cells), we demonstrated that a reduction in PKR partially rescued the growth defect of C knockout (Cko) virus but had no effect on the growth of either wild-type (WT) or V knockout (Vko) virus. Increased growth of the Cko virus in PKRkd cells correlated with increased viral protein expression, while defective growth and decreased protein expression in PKR-sufficient cells correlated with increased phosphorylation of PKR and the α subunit of eukaryotic initiation factor 2. Furthermore, infection with WT, Vko, or especially Cko virus caused significantly less apoptosis in PKRkd cells than in PKR-sufficient cells. Although apoptosis induced by Cko virus infection in PKR-sufficient cells was blocked by a caspase antagonist, the growth of Cko virus was not restored to the WT level by treatment with this pharmacologic inhibitor. Taken together, these results indicate that PKR plays an important antiviral role during MV infection but that the virus growth restriction by PKR is not dependent upon the induction of apoptosis. Furthermore, the results establish that a principal function of the MV C protein is to antagonize the proapoptotic and antiviral activities of PKR. 相似文献
102.
Summary The results of a recent quantitative analysis of the Teorell membrane oscillator are utilized to explore its role as an excitability analogue. Special attention is paid to its role as a mechano-electric transducer. A membrane of exceptionally well-defined pore structure has been used in this study. The analogue properties arise from nonlinear coupling between water and salt fluxes. When the membrane is simultaneously subjected to controlled gradients of hydrostatic pressure, electrical potential and concentration, bi-stable stationary states can be produced. These arise from the opposing effects of pressure and electro-osmosis on the volume flow. Transitions between these states show hysteresis. The factors governing such transitions are analogous to certain types of stimuli encountered in the natural excitation process. The membrane system also shows oscillatory behavior when the hydrostatic pressure gradient is allowed to vary under constant current conditions. This property is related to the bi-stable stationary state phenomena and is compared to the regenerative behavior found in biologically excitable tissues. Particular emphasis is placed upon analogies between the membrane oscillator and certain natural tissues. The importance of the nonlinear nature of the force-flux coupling in the analogue is stressed, and its possible relevance to biological excitability indicated. Some consideration is also given to the role of electro-osmotic flux coupling in biological tissues. 相似文献
103.
104.
J.G. Roddick 《Phytochemistry》1974,13(1):9-25
The literature relating to chemical, biochemical and biological aspects of the steroidal glycoalkaloid, α-tomatine, is reviewed. The alkaloid, which can be used as a starting compound for the synthesis of steroidal hormones, is toxic to a wide range of living organisms. The significance of tomatine to plants which elaborate it is discussed and some possible uses of the compound are mentioned. 相似文献
105.
106.
107.
108.
109.
110.
A. R. E. SINCLAIR 《African Journal of Ecology》1973,11(1):93-107
Censuses of buffalo and wildebeest in the Serengeti-Mara region have been carried out by various workers at intervals since 1958. The methods of these censuses, which normally employ a total count, are described and the errors inherent in such techniques are analysed in detail. After the appropriate corrections had been made the results showed that both populations have increased considerably over the years 1961–1971. 相似文献