全文获取类型
收费全文 | 151323篇 |
免费 | 5202篇 |
国内免费 | 907篇 |
专业分类
157432篇 |
出版年
2022年 | 414篇 |
2021年 | 855篇 |
2020年 | 529篇 |
2019年 | 641篇 |
2018年 | 12460篇 |
2017年 | 11267篇 |
2016年 | 8642篇 |
2015年 | 2970篇 |
2014年 | 2789篇 |
2013年 | 3614篇 |
2012年 | 8358篇 |
2011年 | 16765篇 |
2010年 | 14450篇 |
2009年 | 10496篇 |
2008年 | 13063篇 |
2007年 | 14616篇 |
2006年 | 3624篇 |
2005年 | 3904篇 |
2004年 | 4296篇 |
2003年 | 4136篇 |
2002年 | 3860篇 |
2001年 | 966篇 |
2000年 | 691篇 |
1999年 | 754篇 |
1998年 | 875篇 |
1997年 | 617篇 |
1996年 | 611篇 |
1995年 | 591篇 |
1994年 | 579篇 |
1993年 | 626篇 |
1992年 | 554篇 |
1991年 | 504篇 |
1990年 | 398篇 |
1989年 | 414篇 |
1988年 | 419篇 |
1987年 | 351篇 |
1986年 | 341篇 |
1985年 | 396篇 |
1984年 | 452篇 |
1983年 | 391篇 |
1982年 | 461篇 |
1981年 | 409篇 |
1980年 | 364篇 |
1979年 | 240篇 |
1978年 | 293篇 |
1977年 | 284篇 |
1976年 | 231篇 |
1974年 | 236篇 |
1972年 | 372篇 |
1971年 | 397篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Giovanni Murtas 《Systems and synthetic biology》2010,4(2):85-93
One of the major properties of the semi-synthetic minimal cell, as a model for early living cells, is the ability to self-reproduce
itself, and the reproduction of the boundary layer or vesicle compartment is part of this process. A minimal bio-molecular
mechanism based on the activity of one single enzyme, the FAS-B (Fatty Acid Synthase) Type I enzyme from Brevibacterium ammoniagenes, is encapsulated in 1-palmitoyl-2oleoyl-sn-glycero-3-phosphatidylcholine (POPC) liposomes to control lipid synthesis. Consequently molecules of palmitic acid released
from the FAS catalysis, within the internal lumen, move toward the membrane compartment and become incorporated into the phospholipid
bilayer. As a result the vesicle membranes change in lipid composition and liposome growth can be monitored. Here we report
the first experiments showing vesicles growth by catalysis of one enzyme only that produces cell boundary from within. This
is the prototype of the simplest autopoietic minimal cell. 相似文献
72.
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73.
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74.
75.
76.
Immunoprecipitation of NP-40 lysates of 125I-labeled lymph-node cells with different anti-H-2 sera and with anti-Qa-2 serum has shown that the BALB/cByA strain (H-2d, Qa-2-negative) expresses, besides H-2Ld, another molecule that is not detectable in the BALB/c-H-2dm2 strain. Electrophoresis in SDS polyacrylamide gels indicated that this molecule, provisionally designated Lq, has an apparent molecular weight of 41000 daltons, in contrast to approximately 49000 daltons for H-2Kd and H-2Ld, and 47000 daltons for H-2Dd molecules. The anti-Qa-2 serum precipitated from the Qa-2-positive strains BALB/cHeA but not from the Qa-2-negative strains BALB/cByA and BALB/c-H-2dm2 a protein that gave a very strong band corresponding to the molecular weight 41000 daltons in the gel electrophoresis. The biochemical characteristics of the Lq molecule are thus more similar to those of Qa-2 than of H-2 antigens. 相似文献
77.
78.
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
79.
80.
Does maternal condition or predation risk influence small mammal population dynamics? 总被引:2,自引:0,他引:2
There is strong debate over whether the intrinsic traits of individuals or the extrinsic environment exert the greater influence on small mammal population dynamics. We test the roles of maternal effects (an intrinsic factor) and predation risk (an extrinsic factor) in the population dynamics of wild strain house mice using a 2-factor enclosure experiment. Pre-release supplemental feeding with a high-fat diet created female treatment founders that were 6–10% heavier than controls, a condition that we predicted would be passed on as a maternal effect. Predation risk was enhanced using regular application of predator (red fox Vulpes vulpes ) scats. Founder populations of six females and six males released into eight, 15×15 m enclosures showed near exponential population growth over 17 weeks (maximum 3 generations). But there were no responses to either treatment in terms of survival, inherited body weights, fecundity or population size. We suggest that elevated maternal condition may have only minor and transient intergenerational effects with little long-term consequence. We also suggest that the general significance of predator scats as a cue to predation risk to alter prey behaviour may have been overestimated. Hence our results question the role of either factor in causing long-term responses that influence condition to affect population processes. 相似文献