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   318983篇
  免费   37353篇
  国内免费   137篇
  356473篇
  2018年   2751篇
  2016年   3742篇
  2015年   5074篇
  2014年   6000篇
  2013年   8643篇
  2012年   9593篇
  2011年   9755篇
  2010年   6604篇
  2009年   5897篇
  2008年   8544篇
  2007年   8976篇
  2006年   8382篇
  2005年   8091篇
  2004年   8170篇
  2003年   7910篇
  2002年   7812篇
  2001年   14299篇
  2000年   14331篇
  1999年   11486篇
  1998年   4025篇
  1997年   4131篇
  1996年   3931篇
  1995年   3804篇
  1994年   3801篇
  1993年   3695篇
  1992年   9815篇
  1991年   9390篇
  1990年   9220篇
  1989年   8945篇
  1988年   8358篇
  1987年   7992篇
  1986年   7213篇
  1985年   7324篇
  1984年   6045篇
  1983年   5305篇
  1982年   4176篇
  1981年   3695篇
  1980年   3517篇
  1979年   6098篇
  1978年   4555篇
  1977年   4279篇
  1976年   3974篇
  1975年   4306篇
  1974年   4657篇
  1973年   4721篇
  1972年   4361篇
  1971年   4070篇
  1970年   3444篇
  1969年   3339篇
  1968年   2964篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
911.
Chromosome numbers were determined for 86 Anthurium species. Fifty-one of these were newly determined with counts ranging from 2n = 24 to 66 and 30 being the most common. All known Anthurium chromosome numbers were summarized, and 43 taxonomic changes were made in the previous reports to reflect current taxonomy. In terms of somatic chromosome numbers, the numbers form four polyploid series of 20–40–60, 24–30–48–84, 28–56 and 30–60–90–ca. 124. Paleoaneuploidy, polyploidy and B-chromosomes are basic features of the genus, but subsequent recent aneuploidy is not. The exact nature of chromosome evolution in Anthurium remains to be elucidated.  相似文献   
912.
913.
914.
915.
916.
917.
The simple technique for isolation of high-molecular eucaryotic DNA has been proposed. It includes cell or nuclei lysates by sodium dodecylsulfate in the presence of pronase, proteins precipitation by potassium acetate, DNA precipitation by ethanol. The DNA isolated by this technique is easily cleaved by restriction endonucleases and can be used for analysis of the unique genes by blot-hybridization. The yield of DNA is similar or somewhat higher than that in case of using the standard methods including phenol extraction or phenol-chloroform extraction.  相似文献   
918.
A Farmer-based approach to conserving crop germplasm   总被引:1,自引:0,他引:1  
In situ conservation of crop genetic resources from centers of agricultural diversity is considered. This strategy has been rejected for several reasons, but other factors make it an important potential contributor to the overall conservation effort. Case studies of potato agriculture in Peru, maize agriculture in Mexico, and rice agriculture in Thailand indicate that farmers frequently engage in de facto conservation of landraces. Five principles should guide planning of in situ conservation: complementarity with off-site conservation, minimal institutional development, continuity with existing programs, meeting the development goals of increasing income and food, and accepting germplasm as an international public good. Four means to implement on-site conservation are presented: the institutional framework; the information base; the policy framework; and the role of grassroots organizations.  相似文献   
919.
920.
Restriction fragments' length polymorphism in the region of apolipoprotein A-I (apo A-I) gene was investigated in Novosibirsk (Siberia, USSR) population. Correlation between PstI apo A-I alleles (2,2 kb-P1; 3,3 kb-P2) and total cholesterol, triglycerides, high density polyproteins cholesterol, and apolipoprotein A-I level was analysed. A tendency to increase in cholesterol index of atherogenicity and to decrease in high density lipoproteins cholesterol as well as apolipoprotein A-I level was shown to occur for P1P2 genotype patients.  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