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   332165篇
  免费   38483篇
  国内免费   146篇
  2018年   3038篇
  2016年   4131篇
  2015年   5668篇
  2014年   6657篇
  2013年   9445篇
  2012年   10664篇
  2011年   10876篇
  2010年   7300篇
  2009年   6513篇
  2008年   9432篇
  2007年   9842篇
  2006年   9230篇
  2005年   8869篇
  2004年   8921篇
  2003年   8620篇
  2002年   8427篇
  2001年   14541篇
  2000年   14484篇
  1999年   11691篇
  1998年   4198篇
  1997年   4242篇
  1996年   3896篇
  1995年   3870篇
  1994年   3886篇
  1993年   3781篇
  1992年   9887篇
  1991年   9476篇
  1990年   9292篇
  1989年   9045篇
  1988年   8416篇
  1987年   8059篇
  1986年   7276篇
  1985年   7395篇
  1984年   6121篇
  1983年   5351篇
  1982年   4211篇
  1981年   3740篇
  1980年   3556篇
  1979年   6143篇
  1978年   4569篇
  1977年   4301篇
  1976年   3994篇
  1975年   4315篇
  1974年   4677篇
  1973年   4728篇
  1972年   4365篇
  1971年   4082篇
  1970年   3449篇
  1969年   3348篇
  1968年   2972篇
排序方式: 共有10000条查询结果,搜索用时 554 毫秒
1.
2.
3.
4.
5.
6.
The effect of waveguiding property (i.e., the intensity distribution) of the photoreceptor on the number of photons absorbed in a photoreceptor has been studied. It has been found that the effect is significant only for large values of the exposure and the maximum effect is less than 11% in the case of human rod photoreceptor. In the analysis, the funnelling effect, which follows from the coupling between the interior and exterior fields, has not been considered.Work partially supported by the Department of Science and Technology (India)B. D. Gupta is associated with the School of Bioscience Studies  相似文献   
7.
Female BALB/c mice were immunized with human melanoma (Mewo) cells containing ganglioside GD3 as a surface antigen. Immune splenocytes were fused with syngeneic P3-X63.Ag 8 myeloma cells. Antibodies produced by hybrid clones were analyzed by solid phase immunoassay. B, C, D and Q clones producing antibodies against Raja clavata brain gangliosides were obtained. Monoclonal B and C antibodies bound monosialogangliosides. Monoclonal D antibody bound a number of gangliosides but reacted predominantly with GD1a. Monoclonal Q antibody reacted selectively with GQ1c. It is assumed that ganglioside GQ1c is expressed on the melanoma cell surface and may be found only in the early stage of ontogenesis of high vertebrates.  相似文献   
8.
The degree of serotiny (i.e. the proportion of follicles remaining closed in each year's crop of cones since the last fire) was measured in Bank-sia attenuata, B. menziesii and B. prionotes at five sites along a climatic gradient extending 500 km north of Perth, Western Australia. The decrease in annual rainfall and increase in average temperature along the gradient paralleled a decrease in plant height and an increase in the degree of serotiny of all species. Extreme serotiny was recorded in the scrub-heath at the xeric end of the gradient whereas two species were essentially non-serotinous in the low woodland at the most mesic site. It is concluded that degree of serotiny is related to the fire characteristics of the site which depend on plant height. In xeric scrub-heath, the entire canopies of the Banksia spp. are consumed by fire which promotes massive release of seed. This facilitates recruitment in an otherwise unpredictable and unreliable seedbed. In mesic woodland, where cones rarely come into contact With flames, seeds are released spontaneously and site conditions are more conducive to recruitment in the inter-fire period.  相似文献   
9.
10.
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