全文获取类型
收费全文 | 39839篇 |
免费 | 3180篇 |
国内免费 | 3187篇 |
出版年
2024年 | 81篇 |
2023年 | 490篇 |
2022年 | 1173篇 |
2021年 | 2124篇 |
2020年 | 1388篇 |
2019年 | 1775篇 |
2018年 | 1644篇 |
2017年 | 1235篇 |
2016年 | 1687篇 |
2015年 | 2446篇 |
2014年 | 2859篇 |
2013年 | 3024篇 |
2012年 | 3582篇 |
2011年 | 3194篇 |
2010年 | 2043篇 |
2009年 | 1773篇 |
2008年 | 2028篇 |
2007年 | 1781篇 |
2006年 | 1591篇 |
2005年 | 1353篇 |
2004年 | 1226篇 |
2003年 | 1082篇 |
2002年 | 961篇 |
2001年 | 806篇 |
2000年 | 718篇 |
1999年 | 637篇 |
1998年 | 408篇 |
1997年 | 402篇 |
1996年 | 372篇 |
1995年 | 300篇 |
1994年 | 261篇 |
1993年 | 208篇 |
1992年 | 278篇 |
1991年 | 218篇 |
1990年 | 181篇 |
1989年 | 139篇 |
1988年 | 114篇 |
1987年 | 127篇 |
1986年 | 89篇 |
1985年 | 80篇 |
1984年 | 66篇 |
1983年 | 62篇 |
1982年 | 33篇 |
1981年 | 14篇 |
1980年 | 20篇 |
1979年 | 20篇 |
1977年 | 15篇 |
1976年 | 11篇 |
1973年 | 10篇 |
1972年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
1.
Nonstructural protein 5A (NS5A) of hepatitis C virus (HCV) is an indispensable component of the HCV replication and assembly machineries. Although its precise mechanism of action is not yet clear, current evidence indicates that its structure and function are regulated by the cellular peptidylprolyl isomerase cyclophilin A (CyPA). CyPA binds to proline residues in the C-terminal half of NS5A, in a distributed fashion, and modulates the structure of the disordered domains II and III. Cyclophilin inhibitors (CPIs), including cyclosporine (CsA) and its nonimmunosuppressive derivatives, inhibit HCV infection of diverse genotypes, both in vitro and in vivo. Here we report a mechanism by which CPIs inhibit HCV infection and demonstrate that CPIs can suppress HCV assembly in addition to their well-documented inhibitory effect on RNA replication. Although the interaction between NS5A and other viral proteins is not affected by CPIs, RNA binding by NS5A in cell culture-based HCV (HCVcc)-infected cells is significantly inhibited by CPI treatment, and sensitivity of RNA binding is correlated with previously characterized CyPA dependence or CsA sensitivity of HCV mutants. Furthermore, the difference in CyPA dependence between a subgenomic and a full-length replicon of JFH-1 was due, at least in part, to an additional role that CyPA plays in HCV assembly, a conclusion that is supported by experiments with the clinical CPI alisporivir. The host-directed nature and the ability to interfere with more than one step in the HCV life cycle may result in a higher genetic barrier to resistance for this class of HCV inhibitors. 相似文献
2.
The functioning of the vertebrate eye depends on its absolute size, which is presumably adapted to specific needs. Eye size variation in lidless and spectacled colubrid snakes was investigated, including 839 specimens belonging to 49 genera, 66 species and subspecies. Variations of adult eye diameters (EDs) in both absolute and relative terms between species were correlated with parameters reflecting behavioral ecology. In absolute terms, eye of arboreal species was larger than in terrestrial and semiaquatic species. For diurnal species, EDs of terrestrial species do not differ from semiaquatic species; for nocturnal species the ED of terrestrial species is larger than fossorial species but not different from semiaquatic species. In relative terms, ED did not differ significantly by habitat for diurnal species. Although the ED of terrestrial species is larger than fossorial species there were no differences for nocturnal species between semiaquatic and fossorial snakes. In contrast to other vertebrates studied to date, colubrid EDs in absolute and relative terms are larger in diurnal than in nocturnal species. These observations suggest that among colubrid snakes, eye size variation reflects adaptation to specific habitats, foraging strategies and daily activities, independently of phylogeny. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc. 相似文献
3.
4.
5.
Plant and Soil - To investigate the effects of polystyrene microplastics (PS-beads) on the soil properties, photosynthesis of Flowering Chinese cabbage, the rhizosphere microbial community and... 相似文献
6.
Yunfan Sun Liang Wu Yu Zhong Kaiqian Zhou Yong Hou Zifei Wang Zefan Zhang Jiarui Xie Chunqing Wang Dandan Chen Yaling Huang Xiaochan Wei Yinghong Shi Zhikun Zhao Yuehua Li Ziwei Guo Qichao Yu Liqin Xu Jia Fan 《Cell》2021,184(2):404-421.e16
- Download : Download high-res image (233KB)
- Download : Download full-size image
7.
Plant and Soil - Seeds are involved in the transmission of microorganisms from one plant generation to the next, acting as initial inoculum for the plant microbiome, therefore provide a key source... 相似文献
8.
9.
Semiparametric Regression in Size-Biased Sampling 总被引:1,自引:0,他引:1
Ying Qing Chen 《Biometrics》2010,66(1):149-158
Summary . Size-biased sampling arises when a positive-valued outcome variable is sampled with selection probability proportional to its size. In this article, we propose a semiparametric linear regression model to analyze size-biased outcomes. In our proposed model, the regression parameters of covariates are of major interest, while the distribution of random errors is unspecified. Under the proposed model, we discover that regression parameters are invariant regardless of size-biased sampling. Following this invariance property, we develop a simple estimation procedure for inferences. Our proposed methods are evaluated in simulation studies and applied to two real data analyses. 相似文献