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   9823篇
  免费   234篇
  国内免费   61篇
化学   6839篇
晶体学   92篇
力学   218篇
数学   1239篇
物理学   1730篇
  2022年   78篇
  2021年   86篇
  2020年   132篇
  2019年   135篇
  2018年   90篇
  2017年   67篇
  2016年   172篇
  2015年   158篇
  2014年   165篇
  2013年   437篇
  2012年   530篇
  2011年   633篇
  2010年   318篇
  2009年   276篇
  2008年   540篇
  2007年   627篇
  2006年   609篇
  2005年   597篇
  2004年   556篇
  2003年   450篇
  2002年   399篇
  2001年   172篇
  2000年   163篇
  1999年   122篇
  1998年   139篇
  1997年   107篇
  1996年   143篇
  1995年   124篇
  1994年   107篇
  1993年   111篇
  1992年   84篇
  1991年   86篇
  1990年   84篇
  1989年   80篇
  1988年   73篇
  1987年   70篇
  1986年   71篇
  1985年   109篇
  1984年   98篇
  1983年   85篇
  1982年   80篇
  1981年   83篇
  1980年   80篇
  1979年   69篇
  1978年   79篇
  1977年   79篇
  1976年   81篇
  1975年   72篇
  1974年   64篇
  1973年   61篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Definitions, theorems and examples are established for a general model of Laurent polynomial spaces and ordered orthogonal Laurent polynomial sequences, ordered with respect to ordered bases and orthogonal with respect to inner products ·=L° decomposed into transition functional ⊙ and strong moment functional, or, more generally, sample functional L couplings. Under this formulation that is shown to subsume those in the existing literature, new fundamental results are produced, including necessary and sufficient conditions for ordered OLPS to be sequences of nth numerators of continued fractions, in contrast to the classical result concerning nth denominators which is shown to hold only in special cases.  相似文献   
32.
The intention of the research reported here was to seek explanations for low achievement in school mathematics, as conventionally assessed, that derive from broad understandings of mathematics as social. Such a broad social perspective can provide explanations for low achievement, which could lead to different understandings and hence to different teaching approaches. This study centered on 5- to 8-year-old children from a White working-class area in England. Data were collected during visits to the children in school, in their homes, and in the broader community over a 3-year period. Parents, teachers, and other professionals in the broad school context were interviewed, and data were also collected from school documents and policy statements. Interpretations of these data in terms of ways of understanding children's achievements in school mathematics are put forward. The potential effects of these factors on low schooled numeracy attainment are discussed, together with some possible strategic implications for practice and policy.  相似文献   
33.
A study has been carried out aimed at reducing perinatal mortality in the municipality of Rio de Janeiro through a better distribution of health care facilities. The algorithmic aspects are detailed elsewhere and here the emphasis is on practical issues and difficulties encountered. A 3-level hierarchical model was developed. Both uncapacitated and capacitated versions are briefly described together with some results based on actual data. The project brought to light many contradictions between OR theory and practice in developing countries and, unfortunately, the models developed were not implemented by the municipality health authorities. Possible reasons for this outcome are analysed.  相似文献   
34.
35.
36.
37.
38.
The thermolysis of dicarbonylcyclopentadienyliron dimer in a sealed tube at 300°C has been reported to produce ferrocene, carbon monoxide, carbon dioxide, cyclopentadiene and elemental iron. We observe in addition to these products the production of biferrocene and elemental carbon. Thermolysis of carbonylcyclopentadienyliron tetramer (produced from the dimer by thermolysis in refluxing xylene) produces ferrocene, iron and carbon monoxidre; no biferrocene, carbon dioxide or elemental carbon are produced. A scheme is proposed to account for these products.  相似文献   
39.
40.
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