全文获取类型
收费全文 | 11653篇 |
免费 | 1082篇 |
国内免费 | 1篇 |
出版年
2021年 | 138篇 |
2020年 | 99篇 |
2019年 | 129篇 |
2018年 | 118篇 |
2017年 | 107篇 |
2016年 | 172篇 |
2015年 | 314篇 |
2014年 | 350篇 |
2013年 | 433篇 |
2012年 | 524篇 |
2011年 | 563篇 |
2010年 | 335篇 |
2009年 | 330篇 |
2008年 | 475篇 |
2007年 | 422篇 |
2006年 | 429篇 |
2005年 | 436篇 |
2004年 | 411篇 |
2003年 | 384篇 |
2002年 | 377篇 |
2001年 | 260篇 |
2000年 | 237篇 |
1999年 | 233篇 |
1998年 | 146篇 |
1997年 | 148篇 |
1996年 | 150篇 |
1995年 | 95篇 |
1994年 | 100篇 |
1993年 | 118篇 |
1992年 | 202篇 |
1991年 | 201篇 |
1990年 | 203篇 |
1989年 | 175篇 |
1988年 | 162篇 |
1987年 | 151篇 |
1986年 | 153篇 |
1985年 | 198篇 |
1984年 | 179篇 |
1983年 | 167篇 |
1982年 | 148篇 |
1981年 | 130篇 |
1980年 | 139篇 |
1979年 | 125篇 |
1978年 | 132篇 |
1977年 | 130篇 |
1976年 | 98篇 |
1975年 | 96篇 |
1974年 | 133篇 |
1973年 | 91篇 |
1972年 | 113篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
1.
2.
3.
4.
5.
Yongbo Hu Erin Webb Jasbir Singh Barry A Morgan James A Gainor Thomas D Gordon Teruna J Siahaan 《The Journal of biological chemistry》2002,277(10):8366-8371
The molecular basis of the substrate specificity of Clostridium histolyticum beta-collagenase was investigated using a combinatorial method. An immobilized positional peptide library, which contains 24,000 sequences, was constructed with a 7-hydroxycoumarin-4-propanoyl (Cop) fluorescent group attached at the N terminus of each sequence. This immobilized peptide library was incubated with C. histolyticum beta-collagenase, releasing fluorogenic fragments in the solution phase. The relative substrate specificity (k(cat)/K(m)) for each member of the library was determined by measuring fluorescence intensity in the solution phase. Edman sequencing was used to assign structure to subsites of active substrate mixtures. Collectively, the substrate preference for subsites (P(3)-P(4)') of C. histolyticum beta-collagenase was determined. The last position on the C-terminal side in which the identity of the amino acids affects the activity of the enzyme is P(4)', and an aromatic side chain is preferred in this position. The optimal P(1)'-P(3)' extended substrate sequence is P(1)'-Gly/Ala, P(2)'-Pro/Xaa, and P(3)'-Lys/Arg/Pro/Thr/Ser. The Cop group in either the P(2) or P(3) position is required for a high substrate activity with C. histolyticum beta-collagenase. S(2) and S(3) sites of the protease play a dominant role in fixing the substrate specificity. The immobilized peptide library proved to be a powerful approach for assessing the substrate specificity of C. histolyticum beta-collagenase, so it may be applied to the study of other proteases of interest. 相似文献
6.
Free amino acids in the photoreceptor cells of the frog retina 总被引:6,自引:5,他引:1
7.
Virginia Edgcomb William Orsi John Bunge Sunok Jeon Richard Christen Chesley Leslin Mark Holder Gordon T Taylor Paula Suarez Ramon Varela Slava Epstein 《The ISME journal》2011,5(8):1344-1356
Microbial diversity and distribution are topics of intensive research. In two companion papers in this issue, we describe the results of the Cariaco Microbial Observatory (Caribbean Sea, Venezuela). The Basin contains the largest body of marine anoxic water, and presents an opportunity to study protistan communities across biogeochemical gradients. In the first paper, we survey 18S ribosomal RNA (rRNA) gene sequence diversity using both Sanger- and pyrosequencing-based approaches, employing multiple PCR primers, and state-of-the-art statistical analyses to estimate microbial richness missed by the survey. Sampling the Basin at three stations, in two seasons, and at four depths with distinct biogeochemical regimes, we obtained the largest, and arguably the least biased collection of over 6000 nearly full-length protistan rRNA gene sequences from a given oceanographic regime to date, and over 80 000 pyrosequencing tags. These represent all major and many minor protistan taxa, at frequencies globally similar between the two sequence collections. This large data set provided, via the recently developed parametric modeling, the first statistically sound prediction of the total size of protistan richness in a large and varied environment, such as the Cariaco Basin: over 36 000 species, defined as almost full-length 18S rRNA gene sequence clusters sharing over 99% sequence homology. This richness is a small fraction of the grand total of known protists (over 100 000–500 000 species), suggesting a degree of protistan endemism. 相似文献
8.
9.
10.
A Monte Carlo simulation of clone growth is discussed from the point of view of clonal volume. It is shown that clone volume is a good representation of the number of cells per clone for a wide range of single cell growth equations. However, the rate at which the coefficient of variation in clonal volume approaches that of cell number per clone is strongly dependent upon the particular growth equation. 相似文献