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   593410篇
  免费   4436篇
  国内免费   1599篇
化学   289821篇
晶体学   8331篇
力学   31546篇
综合类   34篇
数学   86625篇
物理学   183088篇
  2021年   5138篇
  2020年   5622篇
  2019年   6409篇
  2018年   13142篇
  2017年   13517篇
  2016年   14108篇
  2015年   6749篇
  2014年   10744篇
  2013年   23835篇
  2012年   21124篇
  2011年   29342篇
  2010年   20814篇
  2009年   20788篇
  2008年   26982篇
  2007年   29073篇
  2006年   18955篇
  2005年   20181篇
  2004年   17331篇
  2003年   16279篇
  2002年   15057篇
  2001年   15073篇
  2000年   11747篇
  1999年   8913篇
  1998年   7744篇
  1997年   7595篇
  1996年   7193篇
  1995年   6455篇
  1994年   6435篇
  1993年   6200篇
  1992年   6553篇
  1991年   7040篇
  1990年   6754篇
  1989年   6657篇
  1988年   6501篇
  1987年   6307篇
  1986年   6035篇
  1985年   7603篇
  1984年   7999篇
  1983年   6728篇
  1982年   7027篇
  1981年   6506篇
  1980年   6214篇
  1979年   6735篇
  1978年   6990篇
  1977年   6799篇
  1976年   6828篇
  1975年   6523篇
  1974年   6359篇
  1973年   6685篇
  1972年   4932篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
71.
This paper reports on the first experimental observation of quantum-well states and sp-type resonances in thin single-crystal gold, silver, and copper layers formed on single-crystal W(110) surfaces, which result from spatial localization of Bloch-type electronic wave functions in a quantum well with potential barriers at the vacuum/metal and metal/W(110) interfaces. The quantization of the valence-band electronic structure in Au/W(110), Ag/W(110), and Cu/W(110) systems was studied experimentally using angle-resolved photoelectron spectroscopy.  相似文献   
72.
The Al2O3−CdSe interface of a thin-film transistor is investigated in the frequency range 30 Hz-30 kHz under weak depletion and accumulation. The surface states are, most likely, located in the insulator Al2O3 with a concentration varying from 4·1018 to 1019 cm−3 eV−1. The surface states have a negligible influence on the thin-film transistor operation.  相似文献   
73.
The problem of the vector and axial-vector dominance of weak interactions within the framework of the quark model of superconductivity type is discussed.  相似文献   
74.
The theory of tree-growing (RECPAM approach) is developed for outcome variables which are distributed as the canonical exponential family. The general RECPAM approach (consisting of three steps: recursive partition, pruning and amalgamation), is reviewed. This is seen as constructing a partition with maximal information content about a parameter to be predicted, followed by simplification by the elimination of ‘negligible’ information. The measure of information is defined for an exponential family outcome as a deviance difference, and appropriate modifications of pruning and amalgamation rules are discussed. It is further shown how the proposed approach makes it possible to develop tree-growing for situations usually treated by generalized linear models (GLIM). In particular, Poisson and logistic regression can be tree-structured. Moreover, censored survival data can be treated, as in GLIM, by observing a formal equivalence of the likelihood under random censoring and an appropriate Poisson model. Three examples are given of application to Poisson, binary and censored survival data.  相似文献   
75.
76.
Preface     
  相似文献   
77.
This paper presents an alternative to the beta continuous probability distribution for risk analysis. Particular attention has been given to two major applications of distributions, namely project management risk and critical path analysis (PERT). In conjunction with the beta, the triangular and normal distributions are frequently employed in order to give sufficient robustness to risk analysis. The beta distribution, as used in PERT, has a major theoretical implementation flaw. The new distribution was developed to give a possible alternative method of assessing risk. It is shown that the requirement to estimate the most pessimistic variate may be replaced by the probability to exceed the mode. Proposals for other simplifications in risk analysis are discussed. Practical means to validate the most appropriate distributions for risk analysis are outlined, and a cost-data case study is included.  相似文献   
78.
79.
80.
The article surveys the main results of the statistical approach to the solution of ill-posed problems of mathematical physics, in application to specific ill-posed inverse problems in geophysics.Invited paper presented at the International Seminar on Mathematical Foundations of the Interpretation of Geophysical Fields, Moscow, May–June 1972.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 79, pp. 67–81, 1978.  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