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   1019127篇
  免费   108123篇
  国内免费   436篇
  2018年   9676篇
  2017年   9113篇
  2016年   13126篇
  2015年   17357篇
  2014年   20503篇
  2013年   29299篇
  2012年   32965篇
  2011年   33648篇
  2010年   23002篇
  2009年   21264篇
  2008年   29998篇
  2007年   31055篇
  2006年   29028篇
  2005年   28035篇
  2004年   27627篇
  2003年   26738篇
  2002年   26048篇
  2001年   41867篇
  2000年   41387篇
  1999年   33494篇
  1998年   12746篇
  1997年   12888篇
  1996年   12374篇
  1995年   11417篇
  1994年   11135篇
  1993年   11201篇
  1992年   27720篇
  1991年   27247篇
  1990年   26573篇
  1989年   26103篇
  1988年   24090篇
  1987年   23312篇
  1986年   21629篇
  1985年   21791篇
  1984年   17966篇
  1983年   15846篇
  1982年   12197篇
  1981年   11237篇
  1980年   10421篇
  1979年   17296篇
  1978年   13649篇
  1977年   12545篇
  1976年   12024篇
  1975年   13282篇
  1974年   14352篇
  1973年   14136篇
  1972年   12941篇
  1971年   11657篇
  1970年   10267篇
  1969年   10126篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
1.
2.
3.
4.
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   
5.
6.
7.
Polymorphisms at the Waxy locus of Amaranthus caudatus L. collected from a wide range of regions were used to investigate genetic diversity and mutation sites. A comparison of the Waxy locus revealed a very high level of sequence conservation. This result clearly showed low environmental and evolutionary variability in the Waxy gene. We also performed screening to confirm the mutation sites in the coding sequences of all accessions. The results indicate that one insertion in the coding region of Waxy genes was responsible for the change in perisperm starch leading to the waxy phenotype in all accessions of this species, and thus that a single mutation event altered the regulation of the Waxy gene during the domestication of this crop. In addition, phylogenetic analysis showed that waxy phenotypes within each of three species, A. caudatus, A. cruentus and A. hypochondriacus, originated separately or differentiated from nonwaxy phenotypes of each species through a single mutational event (i.e., a frame shift or base substitution). We also compared obvious structural features of the coding sequence of waxy and nonwaxy phenotypes with those of low-amylose phenotypes in A. caudatus. The Waxy coding sequences of low-amylose phenotypes do not show polymorphisms and are identical with those of waxy phenotypes. This could mean that there is another gene that encodes a key enzyme responsible for amylose synthesis as the elementary quantity in tissues other than perisperm in A. caudatus.  相似文献   
8.
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   
9.
10.
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   
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