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   1007202篇
  免费   105409篇
  国内免费   681篇
  2016年   11794篇
  2015年   18208篇
  2014年   20358篇
  2013年   27599篇
  2012年   29392篇
  2011年   27724篇
  2010年   19279篇
  2009年   18057篇
  2008年   23848篇
  2007年   24965篇
  2006年   23711篇
  2005年   28266篇
  2004年   26933篇
  2003年   24943篇
  2002年   22416篇
  2001年   38976篇
  2000年   39124篇
  1999年   32216篇
  1998年   11607篇
  1997年   12104篇
  1996年   11531篇
  1995年   10848篇
  1994年   10718篇
  1993年   10755篇
  1992年   28083篇
  1991年   27516篇
  1990年   27293篇
  1989年   26670篇
  1988年   25210篇
  1987年   24103篇
  1986年   22594篇
  1985年   23208篇
  1984年   19265篇
  1983年   16682篇
  1982年   13006篇
  1981年   12040篇
  1980年   11138篇
  1979年   18898篇
  1978年   14959篇
  1977年   13921篇
  1976年   13353篇
  1975年   14733篇
  1974年   16228篇
  1973年   15960篇
  1972年   14779篇
  1971年   13553篇
  1970年   11809篇
  1969年   11817篇
  1968年   10797篇
  1967年   9430篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
3.
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   
4.
5.
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   
6.
7.
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.
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