全文获取类型
收费全文 | 6198篇 |
免费 | 661篇 |
国内免费 | 1篇 |
专业分类
6860篇 |
出版年
2022年 | 35篇 |
2021年 | 71篇 |
2020年 | 37篇 |
2019年 | 52篇 |
2018年 | 55篇 |
2017年 | 53篇 |
2016年 | 118篇 |
2015年 | 204篇 |
2014年 | 203篇 |
2013年 | 290篇 |
2012年 | 364篇 |
2011年 | 398篇 |
2010年 | 252篇 |
2009年 | 236篇 |
2008年 | 323篇 |
2007年 | 395篇 |
2006年 | 337篇 |
2005年 | 358篇 |
2004年 | 365篇 |
2003年 | 334篇 |
2002年 | 360篇 |
2001年 | 93篇 |
2000年 | 91篇 |
1999年 | 118篇 |
1998年 | 101篇 |
1997年 | 90篇 |
1996年 | 76篇 |
1995年 | 58篇 |
1994年 | 70篇 |
1993年 | 70篇 |
1992年 | 74篇 |
1991年 | 72篇 |
1990年 | 66篇 |
1989年 | 74篇 |
1988年 | 60篇 |
1987年 | 62篇 |
1986年 | 63篇 |
1985年 | 56篇 |
1984年 | 64篇 |
1983年 | 53篇 |
1982年 | 66篇 |
1981年 | 60篇 |
1980年 | 43篇 |
1979年 | 46篇 |
1978年 | 41篇 |
1977年 | 41篇 |
1976年 | 42篇 |
1975年 | 32篇 |
1973年 | 44篇 |
1972年 | 31篇 |
排序方式: 共有6860条查询结果,搜索用时 0 毫秒
1.
2.
3.
Dominant males of nonseasonally breeding species should have more opportunity than seasonal breeders to monopolize access to estrous females and thus enhance their reproductive success. They may also use other strategies for maximizing reproductive success such as producing offspring by relatively high ranking females. To test these hypotheses, the paternity of 35 (80%) of 44 Macaca fascicularis offspring, born over a 28-month period, was established using electrophoretically and serologically defined genetic markers. The social ranks of each of the seven potential fathers and 26 potential mothers were determined by recording outcomes of dyadio agonistic interactions. No evidence could be found to support either hypothesis. Further, in view of previously reported significant, positive correlations between male social rank and sexual activity rates in this study group, sexual activity rates do not appear to predict the number of offspring a male sires in this species. 相似文献
4.
There is an urgent need for effective prophylactic measures against Mycobacterium tuberculosis (Mtb) infection, particularly given the highly variable efficacy of Bacille Calmette-Guerin (BCG), the only licensed vaccine against tuberculosis (TB). Most studies indicate that cell-mediated immune responses involving both CD4+ and CD8+ T cells are necessary for effective immunity against Mtb. Genetic vaccination induces humoral and cellular immune responses, including CD4+ and CD8+ T-cell responses, against a variety of bacterial, viral, parasitic and tumor antigens, and this strategy may therefore hold promise for the development of more effective TB vaccines. Novel formulations and delivery strategies to improve the immunogenicity of DNA-based vaccines have recently been evaluated, and have shown varying degrees of success. In the present study, we evaluated DNA-launched Venezuelan equine encephalitis replicons (Vrep) encoding a novel fusion of the mycobacterial antigens α-crystallin (Acr) and antigen 85B (Ag85B), termed Vrep-Acr/Ag85B, for their immunogenicity and protective efficacy in a murine model of pulmonary TB. Vrep-Acr/Ag85B generated antigen-specific CD4+ and CD8+ T cell responses that persisted for at least 10 wk post-immunization. Interestingly, parenterally administered Vrep-Acr/Ag85B also induced T cell responses in the lung tissues, the primary site of infection, and inhibited bacterial growth in both the lungs and spleens following aerosol challenge with Mtb. DNA-launched Vrep may, therefore, represent an effective approach to the development of gene-based vaccines against TB, particularly as components of heterologous prime-boost strategies or as BCG boosters. 相似文献
5.
6.
Household‐level correlates of children's physical activity levels in and across 12 countries 下载免费PDF全文
Deirdre M. Harrington Fiona Gillison Stephanie T. Broyles Jean‐Philippe Chaput Mikael Fogelholm Gang Hu Rebecca Kuriyan Anura Kurpad Allana G. LeBlanc Carol Maher Jose Maia Victor Matsudo Timothy Olds Vincent Onywera Olga L. Sarmiento Martyn Standage Mark S. Tremblay Catrine Tudor‐Locke Pei Zhao Peter T. Katzmarzyk for the ISCOLE Research Group 《Obesity (Silver Spring, Md.)》2016,24(10):2150-2157
7.
8.
9.
The influence of contact guidance on the orientation of colonies of subcultured vascular smooth muscle cells 总被引:1,自引:0,他引:1
Robert C. Buck 《In vitro cellular & developmental biology. Plant》1982,18(9):783-788
Summary Subcultures of smooth muscle cells derived from rat thoracic aorta were grown on plane plastic substrata and on plastic substrata
having ridges molded in them by a heated, ruled template. The cells were found to have a very high degree of contact guidance
when distributed sparsely on the ridged substrata. When the cell density increased multilayered, elongated colonies formed.
On plane substrata these were irregular, curved, and disposed in all directions. On the ridged substrata, however, the colonies
were straight, evenly spaced, and positioned at right angles to the ridges.
Supported by Grant MT1011 from the Medical Research Council of Canada. 相似文献
10.
An Ecteola-cellulose chromatography assay for 3′-phosphoadenosine 5′-phosphosulfate: Phenol sulfotransferase 总被引:1,自引:0,他引:1
Ronald T. Borchardt Anna Baranczyk-Kuzma Carol L. Pinnick 《Analytical biochemistry》1983,130(2):334-338
A new assay procedure for phenol sulfotransferase which employs [35S]-3'-phosphoadenosine-5'-phosphosulfate as a sulfate donor and a variety of phenols as sulfate acceptors was developed. The appearance of the 35S-sulfated products or the disappearance of the [35S]-3'-phosphoadenosine-5'-phosphosulfate are determined simultaneously by chromatography of the assay incubation mixtures on Ecteola-cellulose columns, eluting with an NH4HCO3 step gradient. Various acidic, neutral, and basic phenols can be employed as substrates for phenol sulfotransferase using this procedure. 相似文献