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   1789812篇
  免费   169351篇
  国内免费   2047篇
  1961210篇
  2021年   18523篇
  2019年   16335篇
  2018年   20358篇
  2017年   19136篇
  2016年   29969篇
  2015年   43567篇
  2014年   51771篇
  2013年   77960篇
  2012年   53271篇
  2011年   46574篇
  2010年   49874篇
  2009年   49345篇
  2008年   42165篇
  2007年   41706篇
  2006年   43261篇
  2005年   44381篇
  2004年   43270篇
  2003年   40312篇
  2002年   38067篇
  2001年   56493篇
  2000年   54295篇
  1999年   48466篇
  1998年   28281篇
  1997年   28118篇
  1996年   27134篇
  1995年   25375篇
  1994年   24917篇
  1993年   24303篇
  1992年   41284篇
  1991年   39882篇
  1990年   38475篇
  1989年   38681篇
  1988年   35506篇
  1987年   33893篇
  1986年   32031篇
  1985年   33497篇
  1984年   30581篇
  1983年   26986篇
  1982年   24454篇
  1981年   23194篇
  1980年   21763篇
  1979年   27003篇
  1978年   23740篇
  1977年   22154篇
  1976年   21167篇
  1975年   21937篇
  1974年   23164篇
  1973年   23265篇
  1972年   20360篇
  1971年   18547篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
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   
993.
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   
994.
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   
995.
996.
The [3H]ketanserin binding characteristics in the apomorphine-induced aggressive and nonaggressive adult male Wistar rats were studied. Repeated apomorphine (0.5 mg/kg, once daily) treatment gradually induced aggressive behaviour in sixteen animals from twenty. Thereafter the animals were retrospectively divided into apomorphine-induced aggressive and nonaggressive group. The maximal number of the [3H]ketanserin binding sites was increased in the apomorphine-treated animals in the frontal (233.9+/-26.5, 364.6+/-31.7, and 367.0+/-34.8 fmol/mg protein for the vehicle, apomorphine-nonaggressive, and apomorphine-aggressive group, respectively) and cerebral cortex (164.2+/-6.7, 289.7+/-29.3, and 249.0+/-15.4 fmol/mg protein for the vehicle, apomorphine-nonaggressive, and apomorphine-aggressive group, respectively). In conclusion, our experiments demonstrate that repeated apomorphine treatment upregulates the maximal number of the 5-HT2A receptors in rat frontal and cerebral cortex as measured by [3H]ketanserin binding and this phenomenon is independent from the development of aggressive behaviour.  相似文献   
997.
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   
998.
999.
Genetic programming for development in Drosophila   总被引:2,自引:0,他引:2  
  相似文献   
1000.
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