首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6191篇
  免费   661篇
  国内免费   1篇
  2022年   30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6853条查询结果,搜索用时 125 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.
7.
8.
9.
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.
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   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号