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   453645篇
  免费   43946篇
  国内免费   212篇
  2018年   4426篇
  2017年   4439篇
  2016年   7546篇
  2015年   12723篇
  2014年   13336篇
  2013年   16677篇
  2012年   17916篇
  2011年   15687篇
  2010年   11130篇
  2009年   10127篇
  2008年   12594篇
  2007年   13042篇
  2006年   12324篇
  2005年   17588篇
  2004年   16409篇
  2003年   14362篇
  2002年   11965篇
  2001年   15880篇
  2000年   15128篇
  1999年   13363篇
  1998年   5220篇
  1997年   4941篇
  1996年   4696篇
  1995年   4590篇
  1994年   4563篇
  1993年   4449篇
  1992年   11855篇
  1991年   11474篇
  1990年   11303篇
  1989年   10926篇
  1988年   10385篇
  1987年   9858篇
  1986年   8872篇
  1985年   9131篇
  1984年   7498篇
  1983年   6437篇
  1982年   5093篇
  1981年   4548篇
  1980年   4243篇
  1979年   7250篇
  1978年   5551篇
  1977年   5127篇
  1976年   4770篇
  1975年   5319篇
  1974年   5754篇
  1973年   5820篇
  1972年   5306篇
  1971年   4992篇
  1970年   4307篇
  1969年   4191篇
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
991.
992.
Medical skills should be developed by the staffs of smaller hospitals for the differential study of patients with symptoms resembling those of poliomyelitis in order to provide the rudiments of care for the occasional patient with mild poliomyelitis, to recognize the indications which point to the necessity of superior technical assistance, and to decide when it is appropriate to move patients to better equipped centers. The impetuous acquisition of mechanical aids for the treatment of special problems will be effective in small communities only to the extent that this equipment is kept serviceable and is operated by persons of sufficient skill. Epidemic situations in a small community can be met only by mobilization of facilities under adequate direction and by integration of care with that provided by larger treatment centers.  相似文献   
993.
994.
995.
A simple dispenser using a 2-ml disposable syringe is described. The range of operation is 0.02–1.5 ml and an unusual accuracy is obtained by employing a new principle for dispensers: the dispensed volume is only a fraction of total tidal flow of fluid in the dispenser.  相似文献   
996.
Transfer RNAs, isolated from Escherichia coli F cells infected with T5 bacteriophage, were charged with radioactive amino acids and used in RNA-DNA hybridization studies to detect and locate T5 tRNA cistrons in the T5 DNA chromosome. Hybridization of 14 3H-aminoacyl-tRNA species, including purified T5 [35S]Met-tRNAm and [35S]Met-tRNAf, to the separated strands of T5+ DNA indicates that most, if not all, of the T5 tRNAs are transcribed from the continuous heavy strand of T5 DNA. Heteroduplex mapping of eight mutant T5 DNA deletions has enabled us to locate and determine the size of these deleted segments. By correlating this information with the presence and absence of specific tDNA sequences in these mutants, as determined by tRNA-DNA hybridization, we were able to define the physical limits of four tDNA-containing loci along the T5 DNA molecule. A physical map for 15 tRNA species examined indicates that the structural genes for these tRNAs are clustered within a segment length of T5 DNA that represents approximately 11.2% of the total wild type T5 DNA. The existence of the deletion mutants indicates that T5 tRNAs are dispensable for T5 replication under the growth conditions and for the host employed.  相似文献   
997.
998.
999.
1000.
Identical twins with goiter but without intellectual retardation and with slightly delayed bone age were found to have defective iodide organification as demonstrated by incomplete perchlorate discharge tests. They are grandnieces of a normal member of a sibship which included four children with severe retardation and complete thyroid iodide organification defect. The parents and grandparents are not consanguine. Possible explanations are considered for the problem of why the disorder is manifest completely in one sibship and only partially in the other.  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