全文获取类型
收费全文 | 674篇 |
免费 | 58篇 |
国内免费 | 17篇 |
专业分类
749篇 |
出版年
2023年 | 5篇 |
2022年 | 7篇 |
2021年 | 14篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 8篇 |
2017年 | 10篇 |
2016年 | 22篇 |
2015年 | 33篇 |
2014年 | 33篇 |
2013年 | 30篇 |
2012年 | 38篇 |
2011年 | 39篇 |
2010年 | 31篇 |
2009年 | 26篇 |
2008年 | 30篇 |
2007年 | 35篇 |
2006年 | 33篇 |
2005年 | 35篇 |
2004年 | 33篇 |
2003年 | 23篇 |
2002年 | 27篇 |
2001年 | 16篇 |
2000年 | 12篇 |
1999年 | 14篇 |
1998年 | 17篇 |
1997年 | 15篇 |
1996年 | 11篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1985年 | 4篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 6篇 |
1973年 | 2篇 |
1971年 | 4篇 |
1969年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有749条查询结果,搜索用时 0 毫秒
41.
42.
43.
Beaver are well known to influence the geomorphology and geochemistry of boreal waters, in addition to being prominent vectors in the selective import of deciduous coarse woody debris (CWD). Because the stable carbon isotope ratios of deciduous trees are lower than those of coniferous trees, the possibility exists that the 13C values of particulate organic matter near beaver lodges may differ from those characteristic for littoral regions without beaver activity. In agreement with this supposition, 13C was found to significantly increase in progressively smaller size fractions of CWD collected from near lodges, probably due to the more rapid breakdown, decomposition and disappearance of deciduous material. 相似文献
44.
Characterization of Stg fimbriae from an avian pathogenic Escherichia coli O78:K80 strain and assessment of their contribution to colonization of the chicken respiratory tract 下载免费PDF全文
Lymberopoulos MH Houle S Daigle F Léveillé S Brée A Moulin-Schouleur M Johnson JR Dozois CM 《Journal of bacteriology》2006,188(18):6449-6459
45.
46.
YRKL sequence of influenza virus M1 functions as the L domain motif and interacts with VPS28 and Cdc42 下载免费PDF全文
Earlier studies have shown that the C-terminal half of helix 6 (H6) of the influenza A virus matrix protein (M1) containing the YRKL sequence is involved in virus budding (E. K.-W. Hui, S. Barman, T. Y. Yang, and D. P. Nayak, J. Virol. 77:7078-7092, 2003). In this report, we show that the YRKL sequence is the L domain motif of influenza virus. Like other L domains, YRKL can be inserted at different locations on the mutant M1 protein and can restore virus budding in a position-independent manner. Although YRKL is a part of the nuclear localization signal (NLS), the function of YRKL was independent of the NLS activity and the NLS function of M1 was not required for influenza virus replication. Some mutations in YRKL and the adjacent region caused a reduction in the virus titer by blocking virus release, and some affected virus morphology, producing elongated particles. Coimmunoprecipitation and Western blotting analyses showed that VPS28, a component of the ESCRT-I complex, and Cdc42, a member of the Rho family GTP-binding proteins, interacted with the M1 protein via the YRKL motif. In addition, depletion of VPS28 and Cdc42 by small interfering RNA resulted in reduction of influenza virus production. Moreover, overexpression of dominant-negative Cdc42 inhibited influenza virus replication, whereas a constitutively active Cdc42 mutant enhanced virus production in infected cells. These results indicated that VPS28, a component of ESCRT-I, and Cdc42, a small G protein, are associated with the M1 protein and involved in the influenza virus life cycle. 相似文献
47.
J France J H Thornley S Lopez R C Siddons M S Dhanoa P J Van Soest M Gill 《Journal of theoretical biology》1990,146(2):269-287
An analysis of the compartmental scheme used to determine the rate and extent of ruminal degradation of feeds is presented. Attention is given to the kinetic representation of the degradation of the potentially degradable fraction. Changing the kinetic order of the rate, and introducing indigestible substrate inhibition and microbial activity into its representation, are investigated. This leads to response functions such as the Gompertz and logistic for describing the cumulative disappearance of potentially degradable substrate during in-sacco and in-vitro incubation. 相似文献
48.
By shedding light on variation in time as well as in space, long-term biogeographic studies can help us define organisms’ distribution patterns and understand their underlying drivers. Here we examine distributions of Pseudomonas in and around 15 human homes, focusing on the P. putida and P. fluorescens species groups. We describe recovery from 10,941 samples collected during up to 8 visits per home, occurring on average 2.6 times per year. We collected a mean of 141 samples per visit, from sites in most rooms of the house, from the surrounding yards, and from human and pet occupants. We recovered Pseudomonas in 9.7% of samples, with the majority of isolates being from the P. putida and P. fluorescens species groups (approximately 62% and 23% of Pseudomonas samples recovered respectively). Although representatives of both groups were recovered from every season, every house, and every type of environment sampled, recovery was highly variable across houses and samplings. Whereas recovery of P. putida group was higher in summer and fall than in winter and spring, P. fluorescens group isolates were most often recovered in spring. P. putida group recovery from soils was substantially higher than its recovery from all other environment types, while higher P. fluorescens group recovery from soils than from other sites was much less pronounced. Both species groups were recovered from skin and upper respiratory tract samples from healthy humans and pets, although this occurred infrequently. This study indicates that even species that are able to survive under a broad range of conditions can be rare and variable in their distributions in space and in time. For such groups, determining patterns and causes of stochastic and seasonal variability may be more important for understanding the processes driving their biogeography than the identity of the types of environments in which they can be found. 相似文献
49.
At the leading edge of migrating cells, protrusive forces are developed by the assembly of actin filaments organised in a lamellipodial dendritic array at the front and a more distal lamellar linear array. Whether these two arrays are distinct or functionally linked and how they contribute to cell migration is an open issue. Tropomyosin severely inhibits lamellipodium formation and facilitates the lamellar array while enhancing migration, by a mechanism that is not understood. Here we show that the complex in vivo effects of tropomyosin are recapitulated in the reconstituted propulsion of neural Wiskott–Aldrich syndrome protein (N‐WASP)‐functionalised beads, which is based on the sole formation of a dendritic array of actin‐related protein (Arp)2/3‐branched filaments. Actin‐depolymerising factor (ADF) and tropomyosin control the length of the actin tail. By competing with Arp2/3 during filament branching, tropomyosin displays opposite effects on propulsion depending on the surface density of N‐WASP. Tropomyosin binding to the dendritic array is facilitated following filament debranching, causing its enrichment at the rear of the actin tail, like in vivo. These results unveil the mechanism by which tropomyosin generates two morphologically and dynamically segregated actin networks from a single one. 相似文献
50.