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   1902910篇
  免费   189967篇
  国内免费   1694篇
  2021年   18659篇
  2018年   20106篇
  2017年   18848篇
  2016年   30153篇
  2015年   44476篇
  2014年   52696篇
  2013年   79290篇
  2012年   55407篇
  2011年   47793篇
  2010年   50277篇
  2009年   49769篇
  2008年   43879篇
  2007年   43645篇
  2006年   45420篇
  2005年   45864篇
  2004年   45291篇
  2003年   42476篇
  2002年   40514篇
  2001年   61932篇
  2000年   60315篇
  1999年   52643篇
  1998年   29269篇
  1997年   29162篇
  1996年   28206篇
  1995年   26400篇
  1994年   25987篇
  1993年   25508篇
  1992年   45518篇
  1991年   43858篇
  1990年   42773篇
  1989年   42816篇
  1988年   39479篇
  1987年   38067篇
  1986年   35820篇
  1985年   37409篇
  1984年   33893篇
  1983年   29706篇
  1982年   26646篇
  1981年   24966篇
  1980年   23473篇
  1979年   31094篇
  1978年   26543篇
  1977年   24872篇
  1976年   23671篇
  1975年   24514篇
  1974年   26133篇
  1973年   26319篇
  1972年   23217篇
  1971年   21421篇
  1970年   18610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.
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   
17.
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   
18.
N Bains  J Hoey 《CMAJ》1998,159(2):163
  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