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   394799篇
  免费   38825篇
  国内免费   180篇
  2018年   3808篇
  2017年   3962篇
  2016年   6408篇
  2015年   10656篇
  2014年   11126篇
  2013年   13530篇
  2012年   13934篇
  2011年   11556篇
  2010年   8388篇
  2009年   7712篇
  2008年   8968篇
  2007年   9353篇
  2006年   8808篇
  2005年   15450篇
  2004年   14325篇
  2003年   12062篇
  2002年   8787篇
  2001年   15110篇
  2000年   14558篇
  1999年   12581篇
  1998年   4273篇
  1997年   4262篇
  1996年   4011篇
  1995年   3913篇
  1994年   3921篇
  1993年   3773篇
  1992年   11270篇
  1991年   10942篇
  1990年   10855篇
  1989年   10465篇
  1988年   9914篇
  1987年   9436篇
  1986年   8477篇
  1985年   8660篇
  1984年   6928篇
  1983年   5969篇
  1982年   4553篇
  1981年   4035篇
  1980年   3798篇
  1979年   6942篇
  1978年   5170篇
  1977年   4774篇
  1976年   4483篇
  1975年   5026篇
  1974年   5471篇
  1973年   5560篇
  1972年   5141篇
  1971年   4848篇
  1970年   4133篇
  1969年   4042篇
排序方式: 共有10000条查询结果,搜索用时 609 毫秒
951.
952.
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   
953.
954.
955.
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   
956.
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   
957.
958.
959.
960.
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