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   623286篇
  免费   172386篇
  国内免费   29744篇
  2018年   6584篇
  2016年   8288篇
  2015年   10971篇
  2014年   12554篇
  2013年   16875篇
  2012年   18909篇
  2011年   19441篇
  2010年   15410篇
  2009年   18988篇
  2008年   18271篇
  2007年   18741篇
  2006年   16737篇
  2005年   16489篇
  2004年   16333篇
  2003年   15710篇
  2002年   16118篇
  2001年   26752篇
  2000年   24897篇
  1999年   24517篇
  1998年   14364篇
  1997年   14162篇
  1996年   13358篇
  1995年   13307篇
  1994年   12803篇
  1993年   12384篇
  1992年   22178篇
  1991年   21664篇
  1990年   22053篇
  1989年   21106篇
  1988年   19651篇
  1987年   18501篇
  1986年   17051篇
  1985年   16850篇
  1984年   13883篇
  1983年   12114篇
  1982年   10353篇
  1981年   9511篇
  1980年   8964篇
  1979年   13572篇
  1978年   10789篇
  1977年   10300篇
  1976年   9681篇
  1975年   10056篇
  1974年   11063篇
  1973年   10941篇
  1972年   10497篇
  1971年   9645篇
  1970年   8443篇
  1969年   8362篇
  1968年   7314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.
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   
6.
Plant Molecular Biology -  相似文献   
7.
Conventional therapies for prostate cancer, especially in its androgen-independent form, may result in the survival of small populations of resistant cells with tumor-initiating potential. These “cancer stem cells” are believed to be responsible for cancer relapse, and therapeutic strategies targeting these cells are of great importance. Telomerase is a ribonucleoprotein enzyme responsible for telomere elongation and is activated in the majority of malignancies, including prostate cancer, but is absent in most normal cells. Putative tumor-initiating cells have significant levels of telomerase, indicating that they are an excellent target for telomerase inhibition therapy. In this review, we present some evidence for the hypothesis that conventional therapies (standard chemotherapy and/or radiation therapy) in combination with telomerase inhibitors may result in effective and more durable responses.  相似文献   
8.
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.
Essential genes were identified in the 1.5-map unit dpy-5 unc-13 region of chromosome I in the Caenorhabditis elegans genome by rescuing lethal mutations using the duplication sDp2. In this paper, we report the mapping and complementation testing of lethal mutations, 45 of which identify 18 new, essential genes. This analysis brings the number of essential genes defined by the sDp2 rescue of lethal mutants to 97; 64 of these map between dpy-5 and unc-13. 61% of these essential genes are identified by more than one allele. Positioning of the mutations was done using the breakpoints of six duplications. The mutant phenotypes of 14 loci essential for fertility were characterized by Nomarski microscopy and DAPI staining. None of the mutants were rescued by wild-type male sperm. The cytological data showed that four genes produced mutants with defects in gonadogenesis, let-395, let-603, let-605 and let-610. Mutations in seven genes, let-355, let-367, let-384, let-513, let-544, let-545 and let-606, affected germ cell proliferation or gametogenesis. Mutants for the remaining three genes, let-370, let-599 and let-604, produced eggs that failed to develop or hatch, thereby acting as maternal effect lethals. We observed a nonrandom distribution of arrest phenotypes with regard to map position. Received: 8 May 1996 / Accepted : 27 January 1997  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