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   437651篇
  免费   40537篇
  国内免费   950篇
  2018年   14417篇
  2017年   13114篇
  2016年   11434篇
  2015年   6579篇
  2014年   7369篇
  2013年   10378篇
  2012年   15321篇
  2011年   23784篇
  2010年   19069篇
  2009年   14831篇
  2008年   19403篇
  2007年   21352篇
  2006年   10220篇
  2005年   10211篇
  2004年   10658篇
  2003年   10432篇
  2002年   10019篇
  2001年   14903篇
  2000年   14686篇
  1999年   11854篇
  1998年   4463篇
  1997年   4465篇
  1996年   4254篇
  1995年   4053篇
  1994年   4110篇
  1993年   3999篇
  1992年   10075篇
  1991年   9661篇
  1990年   9452篇
  1989年   9161篇
  1988年   8591篇
  1987年   8218篇
  1986年   7419篇
  1985年   7596篇
  1984年   6411篇
  1983年   5618篇
  1982年   4520篇
  1981年   4107篇
  1980年   3897篇
  1979年   6334篇
  1978年   4781篇
  1977年   4530篇
  1976年   4206篇
  1975年   4469篇
  1974年   4873篇
  1973年   4892篇
  1972年   4699篇
  1971年   4413篇
  1970年   3577篇
  1969年   3446篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
6.
In vivo EMG biofeedback was found to be an effective pedagogical tool for removing unwanted left-hand tension in nine violin and viola players. Improvement occurred rapidly and persisted throughout a 5-month follow-up period. Further studies will be necessary to assess the effect of biofeedback independent of placebo effects. The brevity of the method and the magnitude of improvement warrant further investigation.  相似文献   
7.
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   
8.

Background  

With the growing number of public repositories for high-throughput genomic data, it is of great interest to combine the results produced by independent research groups. Such a combination allows the identification of common genomic factors across multiple cancer types and provides new insights into the disease process. In the framework of the proportional hazards model, classical procedures, which consist of ranking genes according to the estimated hazard ratio or the p-value obtained from a test statistic of no association between survival and gene expression level, are not suitable for gene selection across multiple genomic datasets with different sample sizes. We propose a novel index for identifying genes with a common effect across heterogeneous genomic studies designed to remain stable whatever the sample size and which has a straightforward interpretation in terms of the percentage of separability between patients according to their survival times and gene expression measurements.  相似文献   
9.
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   
10.
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   
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