全文获取类型
收费全文 | 112912篇 |
免费 | 2204篇 |
国内免费 | 830篇 |
专业分类
115946篇 |
出版年
2023年 | 102篇 |
2022年 | 219篇 |
2021年 | 465篇 |
2020年 | 209篇 |
2019年 | 314篇 |
2018年 | 12124篇 |
2017年 | 10900篇 |
2016年 | 7958篇 |
2015年 | 1563篇 |
2014年 | 1350篇 |
2013年 | 1554篇 |
2012年 | 5883篇 |
2011年 | 14357篇 |
2010年 | 12997篇 |
2009年 | 9052篇 |
2008年 | 11056篇 |
2007年 | 12585篇 |
2006年 | 1462篇 |
2005年 | 1682篇 |
2004年 | 2103篇 |
2003年 | 2084篇 |
2002年 | 1788篇 |
2001年 | 422篇 |
2000年 | 255篇 |
1999年 | 225篇 |
1998年 | 262篇 |
1997年 | 179篇 |
1996年 | 145篇 |
1995年 | 123篇 |
1994年 | 120篇 |
1993年 | 141篇 |
1992年 | 112篇 |
1991年 | 129篇 |
1990年 | 88篇 |
1989年 | 72篇 |
1988年 | 70篇 |
1987年 | 72篇 |
1986年 | 47篇 |
1985年 | 65篇 |
1984年 | 72篇 |
1983年 | 86篇 |
1982年 | 79篇 |
1981年 | 74篇 |
1980年 | 75篇 |
1978年 | 65篇 |
1977年 | 43篇 |
1975年 | 42篇 |
1972年 | 258篇 |
1971年 | 280篇 |
1962年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Background
Identifying essential genes in bacteria supports to identify potential drug targets and an understanding of minimal requirements for a synthetic cell. However, experimentally assaying the essentiality of their coding genes is resource intensive and not feasible for all bacterial organisms, in particular if they are infective. 相似文献62.
Following arteriolar occlusion, tissue oxygen concentration decreases and anoxic tissue eventually develops. Although anoxia
first appears in the region most distal to the capillary at the venous end, it eventually spreads throughout the entire region
of supply. In this paper the changing oxygen concentration, from the time of occlusion until the tissue is entirely anoxic,
is examined mathematically. The equations governing oxygen transport to tissue are solved by iterating a nonlinear integral
equation. This solution is valid until anoxia first appears. After anoxia develops it is necessary to solve a moving boundary
problem. This is done using the method of matched asymptotic expansions, and accurate solutions are obtained for a wide range
of physiological conditions. 相似文献
63.
Background
Phylogenies capture the evolutionary ancestry linking extant species. Correlations and similarities among a set of species are mediated by and need to be understood in terms of the phylogenic tree. In a similar way it has been argued that biological networks also induce correlations among sets of interacting genes or their protein products. 相似文献64.
65.
66.
67.
68.
69.
Dongliang Liu Jun Liu Weilan Wang Lijie Xia Jianhua Yang Surong Sun Fuchun Zhang 《Food biophysics》2016,11(4):319-331
Cecropin XJ, as a heat stable antimicrobial peptide (AMP), displayed broad bacteriostatic activities, effectively inhibited proliferation of cancer cells and induced cell apoptosis in vitro. However, it exhibited little hemolytic activity and very low cytotoxicity to erythrocytes and normal cells. Although exerts multiple remarkable bioactivities, the refined molecular conformation of native Cecropin XJ remains unsolved. The aim of the present study is to comprehensively investigate the physicochemical characteristics and structure-function relationship of this antimicrobial peptide by using a series of bioinformatics and experimental approaches. In this study, we revealed that the mature Cecropin XJ consists of 41 amino acids, containing two α-helical structures from Lys7 to Lys25 and from Ala29 to Ile39. The phylogenetic tree indicated that Cecropin XJ belongs to the Class I AMPs of cecropin family. Hydrophobic analysis showed Cecropin XJ is a typical amphiphilic molecule. The surface of Cecropin XJ was found to have a much wide range of electrostatic potential from ?83.243 to +83.243. The amphipathicity and surface potential of Cecropin XJ partially supported the AMP pore-forming hypothesis. Scanning electron microscopy experimentally confirmed the damages of Cecropin XJ to microbial membrane. Four predicted docking sites respectively for magnesium ion (Mg2+), adenosine diphosphate (ADP), bacteriopheophytin (BPH), and guanosine triphosphate (GTP) were found on the surface of Cecropin XJ. Thereinto, Mg2+ was experimentally proved to suppress the antibacterial activity of Cecropin XJ; both GTP and ADP enhanced the bactericidal activities to varying degrees. The present study provides a foundation for further investigation of molecular evolution, structural modification, and functional mechanisms of Cecropin XJ. 相似文献
70.
Roberta L. Millstein 《Journal of the history of biology》2008,41(2):339-367
Biologists and philosophers have been extremely pessimistic about the possibility of demonstrating random drift in nature,
particularly when it comes to distinguishing random drift from natural selection. However, examination of a historical case
– Maxime Lamotte’s study of natural populations of the land snail, Cepaea nemoralis in the 1950s – shows that while some pessimism is warranted, it has been overstated. Indeed, by describing a unique signature
for drift and showing that this signature obtained in the populations under study, Lamotte was able to make a good case for
a significant role for␣drift. It may be difficult to disentangle the causes of drift and selection acting in a population,
but it is not (always) impossible. 相似文献