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   774916篇
  免费   82971篇
  国内免费   322篇
  2018年   8304篇
  2017年   7951篇
  2016年   10745篇
  2015年   14301篇
  2014年   16217篇
  2013年   23492篇
  2012年   27557篇
  2011年   27822篇
  2010年   17998篇
  2009年   15842篇
  2008年   24486篇
  2007年   24862篇
  2006年   23742篇
  2005年   22365篇
  2004年   21806篇
  2003年   21003篇
  2002年   20275篇
  2001年   35090篇
  2000年   35441篇
  1999年   27947篇
  1998年   9507篇
  1997年   9887篇
  1996年   9345篇
  1995年   8602篇
  1994年   8660篇
  1993年   8555篇
  1992年   22581篇
  1991年   21887篇
  1990年   21274篇
  1989年   21033篇
  1988年   19384篇
  1987年   18227篇
  1986年   16874篇
  1985年   16962篇
  1984年   13686篇
  1983年   11943篇
  1982年   9012篇
  1981年   8039篇
  1980年   7633篇
  1979年   12987篇
  1978年   10126篇
  1977年   9165篇
  1976年   8498篇
  1975年   9423篇
  1974年   9839篇
  1973年   9722篇
  1972年   8617篇
  1971年   7819篇
  1970年   6953篇
  1969年   6587篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
A patient with chronic anemia is presented who radiologically showed prominent rugae of the stomach. Angiography demonstrated an arteriovenous malformation with a large feeding artery and prominent draining veins.  相似文献   
3.
4.
5.
6.
7.
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   
8.
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   
9.
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   
10.
Recent studies have shown that Salmonella shedding status affects sows’ microbiota during gestation and that these modifications are reflected in the faecal microbiota of their piglets at weaning. The aims of this study were: (a) to evaluate the persistence, up to the fattening period, of the previously measured link between the microbiota of piglets and their mothers’ Salmonella shedding status; and (b) measure the impact of the measured microbiota variations on their Salmonella excretion at this stage. To achieve this, 76 piglets born from 19 sows for which the faecal microbiota was previously documented, were selected in a multisite production system. The faecal matter of these swine was sampled after 4 weeks, at the fattening stage. The Salmonella shedding status and faecal microbiota of these animals were described using bacteriological and 16S rRNA gene amplicon sequencing respectively. The piglet digestive microbiota association with the Salmonella shedding status of their sows did not persist after weaning and did not affect the risk of Salmonella excretion during fattening, while the birth mother still affected the microbiota of the swine at fattening. This supports the interest in sows as a target for potentially transferrable microbiota modifications.  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