首页 | 官方网站   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   53909篇
  免费   2483篇
  国内免费   69篇
工业技术   56461篇
  2024年   103篇
  2023年   455篇
  2022年   1034篇
  2021年   1513篇
  2020年   1081篇
  2019年   1278篇
  2018年   1829篇
  2017年   1817篇
  2016年   1913篇
  2015年   1528篇
  2014年   1939篇
  2013年   3847篇
  2012年   3006篇
  2011年   3338篇
  2010年   2546篇
  2009年   2485篇
  2008年   2249篇
  2007年   2015篇
  2006年   1585篇
  2005年   1364篇
  2004年   1226篇
  2003年   1122篇
  2002年   1040篇
  2001年   730篇
  2000年   725篇
  1999年   767篇
  1998年   3230篇
  1997年   2212篇
  1996年   1478篇
  1995年   875篇
  1994年   713篇
  1993年   785篇
  1992年   295篇
  1991年   303篇
  1990年   216篇
  1989年   245篇
  1988年   231篇
  1987年   210篇
  1986年   176篇
  1985年   229篇
  1984年   177篇
  1983年   139篇
  1982年   175篇
  1981年   184篇
  1980年   201篇
  1979年   107篇
  1978年   116篇
  1977年   353篇
  1976年   751篇
  1973年   89篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
BACKGROUND: There is no empirical data available on attitudes concerning AIDS and habits towards HIV infected patients of physicians in general or private practice. In this study results of a self-evaluation are presented. METHODS: 178 physicians working with out-patients in different medical fields were randomly selected for a cross sectional study and interviewed using a standardised questionnaire. RESULTS: 89% think that they are sufficiently informed about AIDS (in the USA 20%). They regarded the risk of infection to be lower than the Anglo-American physicians. They believed there is a lack of interchange of information between colleagues regarding the degree of infectiousness of referred patients. A third of the physicians fear that other patients will go elsewhere if they find out that their physician is treating AIDS patients. 54% would hold special clinic sessions for HIV-patients outside the normal schedule for practice times. 89% believed that HIV patients were partly to blame for their illness. CONCLUSIONS: Although the physicians recognise the problem of HIV-infection, they partly deny the real necessities and facts. A reason for this could be the emotions underlying the general attitude to everything pertaining to HIV-disease. Attitudes to HIV-disease and the dealing with it in daily practice must be considered on the basis of individual emotional motives.  相似文献   
72.
73.
74.
75.
76.
The plasma membrane (PM) H(+)-ATPase has been proposed to play important transport and regulatory roles in plant physiology, including its participation in auxin-induced acidification in coleoptile segments. This enzyme is encoded by a family of genes differing in tissue distribution, regulation, and expression level. A major expressed isoform of the maize PM H(+)-ATPase (MHA2) has been characterized. RNA gel blot analysis indicated that MHA2 is expressed in all maize organs, with highest levels being in the roots. In situ hybridization of sections from maize seedlings indicated enriched expression of MHA2 in stomatal guard cells, phloem cells, and root epidermal cells. MHA2 mRNA was induced threefold when nonvascular parts of the coleoptile segments were treated with auxin. This induction correlates with auxin-triggered proton extrusion by the same part of the segments. The PM H(+)-ATPase in the vascular bundies does not contribute significantly to auxin-induced acidification, is not regulated by auxin, and masks the auxin effect in extracts of whole coleoptile segments. We conclude that auxin-induced acidification in coleoptile segments most often occurs in the nonvascular tissue and is mediated, at least in part, by increased levels of MHA2.  相似文献   
77.
78.
A deletion mutant of the catalytic RNA component of Escherichia coli RNase P missing residues 87-241 retains the ability to interact with the protein component to form a functional catalyst. The deletion of this phylogenetically conserved region significantly increases the Km, indicating that the deleted structures may be important for binding to the precursor tRNA substrate but not for the cleavage reaction. Under some reaction conditions, this RNase P deletion mutant can become a relatively non-specific nuclease, indicating that this RNA's catalytic center may be more exposed. The catalytic core of the RNase P is formed by less than one third of the 377 residues of the RNase P RNA.  相似文献   
79.
Two hundred twenty-eight patients with successful coronary stent implantation were randomized either to protamine administration and femoral sheath removal (group I, n = 117) or no heparin neutralization and delayed sheath removal (group II, n = 111). The hospital stay after treatment was shorter in patients receiving protamine; therefore, protamine use for neutralizing circulating heparin may be safely administered immediately after stent implantation.  相似文献   
80.
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-23

京公网安备 11010802026262号