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   2226篇
  免费   141篇
  2367篇
  2021年   16篇
  2020年   17篇
  2019年   16篇
  2018年   27篇
  2017年   29篇
  2016年   33篇
  2015年   43篇
  2014年   53篇
  2013年   87篇
  2012年   96篇
  2011年   97篇
  2010年   63篇
  2009年   54篇
  2008年   87篇
  2007年   86篇
  2006年   90篇
  2005年   116篇
  2004年   78篇
  2003年   95篇
  2002年   96篇
  2001年   73篇
  2000年   85篇
  1999年   83篇
  1998年   40篇
  1997年   27篇
  1996年   29篇
  1995年   25篇
  1994年   29篇
  1993年   29篇
  1992年   63篇
  1991年   42篇
  1990年   58篇
  1989年   47篇
  1988年   45篇
  1987年   33篇
  1986年   30篇
  1985年   29篇
  1984年   34篇
  1983年   14篇
  1981年   15篇
  1980年   15篇
  1979年   18篇
  1978年   27篇
  1977年   16篇
  1976年   18篇
  1975年   16篇
  1974年   19篇
  1973年   20篇
  1972年   20篇
  1970年   22篇
排序方式: 共有2367条查询结果,搜索用时 15 毫秒
21.
22.
23.
24.
Genetic data suggesting the absence of crossover in Saccharomycodes ludwigii have been described. Tetrad data obtained from 888 asci from 60 pairs of genes with 22 genetic markers showed the absence of tetratype asci, except for 5 asci in which a single pair of alleles showed tetratype segregation to the other genetic markers in each ascus. Spore arrays in the linear asci showed that the + - + - and + - - + (or - + + -) asci occurred at almost equal frequencies. The two coherent spores at each end of an ascus were always marked with different alleles of a gene.  相似文献   
25.
We report the discovery of securiosides A (1) and B (2), novel acylated triterpene bisdesmosides, isolated from the roots of Securidaca inappendiculata. Securiosides A and B showed potent selective cytotoxic activity against M-CSF-stimulated macrophages and were suggested to have potential as new agents for the treatment of inflammatory diseases such as RA and atherosclerosis.  相似文献   
26.
27.
The specification of anterior neuroectoderm is controlled by a highly conserved molecular mechanism in bilaterians. A forkhead family gene, foxQ2, is known to be one of the pivotal regulators, which is zygotically expressed in this region during embryogenesis of a broad range of bilaterians. However, what controls the expression of this essential factor has remained unclear to date. To reveal the regulatory mechanism of foxQ2, we performed cis‐regulatory analysis of two foxQ2 genes, foxQ2a and foxQ2b, in a sea urchin Hemicentrotus pulcherrimus. In sea urchin embryos, foxQ2 is initially expressed in the entire animal hemisphere and subsequently shows narrower expression restricted to the anterior pole region. In this study, as a first step to understand the foxQ2 regulation, we focused on the later restricted expression and analyzed the upstream cis‐regulatory sequences of foxQ2a and foxQ2b by using the constructs fused to short half‐life green fluorescent protein. Based on deletion and mutation analyses of both foxQ2, we identified each of the five regulatory sequences, which were 4–9 bp long. Neither of the regulatory sequences contains any motifs for ectopic activation or spatial repression, suggesting that later mRNA localization is regulated in situ. We also suggest that the three amino acid loop extension‐class homeobox gene Meis is involved in the maintenance of foxQ2b, the expression of which is dominant during embryogenesis.  相似文献   
28.
Release of cytotoxin by macrophages on treatment with human placenta lectin   总被引:1,自引:0,他引:1  
Human lectin purified from placenta induced release of cytotoxin from a murine macrophage cell line and human peritoneal monocytes. This activity was not due to contamination of the lectin preparation with lipopolysaccharide.  相似文献   
29.
Specific and sensitive assays for immunoglobulin G in pork, chicken, and beef were developed using polyester cloths coated with respective anti-immunoglobulin G antibodies. The captured immunoglobulin G proteins were detected by their reactions with the respective IgG antibody horseradish peroxidase conjugates and a chromogenic peroxidase substrate. This sensitive assay takes only 30 minutes and can detect the adulteration of ground meats.  相似文献   
30.
To elucidate the topochemical requirements for bioactivities of morphiceptin (Tyr-Pro-Phe-Pro-NH2) and dermorphin (Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2), we have designed and synthesized two diastereomers Tyr-(L and D)-(NMe)Ala-Phe-D-Pro-NH2. Both the analogs display high activities in the guinea pig ileum assay. The only difference in the composition of these two diastereomers arises from the chirality at residue 2. The high mu-receptor activities are attributed to structures where the Tyr1-L-(NMe)Ala2 amide bond assumes a cis configuration while the Tyr1-D-(NMe)Ala2 amide bond assumes a trans configuration. Accessible space studied for the second residues of these molecules confirms the fact that the L-(NMe)Ala2 analog belongs to the morphiceptin family of opioids while the D-(NMe)Ala2 analog belongs to the dermorphin class of opioids. The similarity in the spacial array of the analogs explains their high mu-receptor activities and indicates that they are likely recognized at the same opioid receptor.  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