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   1781667篇
  免费   173575篇
  国内免费   1866篇
  2021年   18080篇
  2018年   19688篇
  2017年   18563篇
  2016年   29712篇
  2015年   43723篇
  2014年   51997篇
  2013年   78193篇
  2012年   51356篇
  2011年   43300篇
  2010年   48526篇
  2009年   48322篇
  2008年   39404篇
  2007年   38648篇
  2006年   41076篇
  2005年   42036篇
  2004年   41164篇
  2003年   38383篇
  2002年   36317篇
  2001年   60071篇
  2000年   58457篇
  1999年   51385篇
  1998年   28635篇
  1997年   28453篇
  1996年   25998篇
  1995年   25602篇
  1994年   25194篇
  1993年   24513篇
  1992年   43282篇
  1991年   41305篇
  1990年   39834篇
  1989年   40056篇
  1988年   37164篇
  1987年   34938篇
  1986年   33130篇
  1985年   34512篇
  1984年   31461篇
  1983年   27195篇
  1982年   25006篇
  1981年   23587篇
  1980年   21975篇
  1979年   27664篇
  1978年   24152篇
  1977年   22690篇
  1976年   21288篇
  1975年   21990篇
  1974年   23335篇
  1973年   23438篇
  1972年   20486篇
  1971年   18739篇
  1970年   16396篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
The alga Analipus japonicus (Harv.) Wynne displays a distinct seasonal pattern in its development in Peter the Great Bay (Sea of Japan). In winter and spring, it occurs only in the form of basal crusts, and vertical axes develop in the summer–autumn period. It reproduces mostly asexually from July to November. Algae with unilocular sporangia occur very seldom, only in June and July.  相似文献   
13.
14.
15.
16.
17.
The discovery that the single p53 gene encodes several different p53 protein isoforms has initiated a flurry of research into the function and regulation of these novel p53 proteins. Full-length p53 protein level is primarily regulated by the E3-ligase Mdm2, which promotes p53 ubiquitination and degradation. Here, we report that all of the novel p53 isoforms are ubiquitinated and degraded to varying degrees in an Mdm2-dependent and -independent manner, and that high-risk human papillomavirus can degrade some but not all of the novel isoforms, demonstrating that full-length p53 and the p53 isoforms are differentially regulated. In addition, we provide the first evidence that Mdm2 promotes the NEDDylation of p53β. Altogether, our data indicates that Mdm2 can distinguish between the p53 isoforms and modify them differently.  相似文献   
18.
Comparison of bone marrow extracellular matrices.   总被引:1,自引:0,他引:1  
We have compared the structure and composition of adult and fetal bovine bone marrow extracellular matrices. In contrast to fetal bone marrow, adult bone marrow has more oval fenestration and accumulation of adipocytes as well as lower protein content. These differences could be due to remodeling of bone marrow tissue as it develops. Zymogram analysis of matrix metalloproteinase (MMP) and tissue inhibitor of MMP (TIMP) activities showed that fetal, but not adult bone marrow extract contained a 96-kDa MMP and TIMP-1 and -2. These activities may contribute to the structural differences between adult and fetal bone marrow tissues.  相似文献   
19.
Random amplified polymorphic DNA (RAPD) analysis was used tostudy variation among and within selectedIxora (Rubiaceae) populationsand mutants. Six populations of I. congesta yielded identicalbanding patterns suggesting genetic uniformity of this species.However, six populations of I. coccinea varieties (three red-flowered,two yellow-flowered and one red-flowered wild-type) exhibitedinfraspecific differences in RAPD profiles. Small and largeleaves of an atavistic mutant cultivar of I. coccinea were alsosubjected to RAPD analysis. An extra band was amplified in thelarge leaves that was absent in small leaves, suggesting thatthe phenotypic alteration in this taxon is due to genetic mutationrather than epigenetic changes. Similarly, an extra band wasdetected in the white sectors of I. Variegated compared to thegreen sectors, suggesting that the shoot apical meristems ofthis cultivar exist as a genetic chimera. DNA gel blot hybridizationwas performed to confirm the specificities of selected bands.Our study indicates that differences among individuals of variouspopulations and mutants may be detected using RAPD markers.Copyright 1999 Annals of Botany Company Ixora L., variegated variety, RAPD fingerprinting, DNA gel blot, intraspecific genetic similarity, atavistic mutant.  相似文献   
20.
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