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   1621344篇
  免费   152639篇
  国内免费   1725篇
  1775708篇
  2021年   18247篇
  2019年   16271篇
  2018年   19137篇
  2017年   17976篇
  2016年   29211篇
  2015年   43222篇
  2014年   51336篇
  2013年   77530篇
  2012年   46749篇
  2011年   37660篇
  2010年   46966篇
  2009年   47208篇
  2008年   34577篇
  2007年   33211篇
  2006年   36497篇
  2005年   37555篇
  2004年   36689篇
  2003年   33973篇
  2002年   31838篇
  2001年   51761篇
  2000年   49608篇
  1999年   44861篇
  1998年   27546篇
  1997年   27369篇
  1996年   26531篇
  1995年   24702篇
  1994年   24320篇
  1993年   23543篇
  1992年   37792篇
  1991年   35864篇
  1990年   34476篇
  1989年   34917篇
  1988年   32166篇
  1987年   30197篇
  1986年   28574篇
  1985年   29983篇
  1984年   28122篇
  1983年   24338篇
  1982年   23100篇
  1981年   21965篇
  1980年   20460篇
  1979年   23751篇
  1978年   21251篇
  1977年   20111篇
  1976年   18836篇
  1975年   18906篇
  1974年   19679篇
  1973年   19949篇
  1972年   17107篇
  1971年   15625篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
The capillaries of the cardiac muscle were investigated in the goat by means of light microscopy, transmission electron microscopy and scanning electron microscopy, and the following results were obtained. The capillaries of the working cardiac muscles were numerous, arranged mainly parallel to the long axis of muscle cells and formed dense elongated networks. On the contrary, those of the terminal Purkinje fibers were relatively few in number, oriented in various directions and formed loose and circularly meshed networks surrounding the fibers. Such findings were discussed in correlation with the physiology and functional morphology of various types of the cardiac muscle cells.  相似文献   
992.
Five cases of coincident salmonellosis and ulcerative colitis are described. In three the diagnostic combination was recognized late. If corticosteroid therapy is given for the colitis once the combination is recognized, then simultaneous systemic antibiotic cover is advisable. One of the five patients died during corticosteroid therapy alone with salmonella septicaemia due to a usually non-invasive organism.  相似文献   
993.
Seven patients with “coeliac axis compression syndrome” are reported. Five were treated surgically, but only two did well. A survey of 200 healthy adults showed epigastric bruits in 6·5%; only one of these had dyspepsia, though dyspepsia was present in 12·5% overall.Caution is urged in attributing a causal relationship between coeliac axis compression and pain and in proceeding to arteriography when compression is suspected on clinical grounds.  相似文献   
994.
From experience in the Northampton/Kettering area 9 to 10% of all patients in a general hospital requiring care in an intensive therapy unit were aged 12 years or under. Fifty-nine children were admitted to the intensive therapy unit of Northampton General Hospital between May 1967 and August 1969. Of these, 22 had been injured in road traffic accidents, five were surgical emergencies, five had meningitis, four status epilepticus, and four respiratory infections.All of the 30 families interviewed were in favour of their child being admitted to the unit, and none considered that the experience had had any lasting adverse psychological effect on the child. It is suggested that certain carefully selected child patients do benefit from the facilities of an intensive therapy unit, and for this reason such units must be designed, equipped, and staffed with this in mind.  相似文献   
995.
S ummary . This paper describes the development and use of a selective diagnostic medium for the detection and enumeration of Clostridium perfringens in foods. The medium gives higher counts of Cl. perfringens and fewer false positives than existing media.  相似文献   
996.
997.
998.
Morphogenesis and Homology in Arthropod Limbs   总被引:1,自引:0,他引:1  
Arthropods exhibit highly diverse limb morphologies rangingfrom unbranched walking legs to multibranched swimming paddles.Understanding morphogenesis in structurally diverse limbs canbe useful for ascertaining homologies between limbs. Structurallysimilar limbs have been produced by different evolutionary modificationsof morphogenesis in certain cases. Whereas it is easy to supportthe claim that whole arthropod limbs are homologous structures,I demonstrate that it is not always possible to draw well-foundedhomologies between parts of different limbs. This result isimportant with regard to general models of appendage developmentand evolution in arthropods because it clarifies contradictoryexplanations based exclusively on gene expression data.  相似文献   
999.
1000.
Genetic programming for development in Drosophila   总被引:2,自引:0,他引:2  
  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