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   258385篇
  免费   1470篇
  国内免费   650篇
化学   106246篇
晶体学   3279篇
力学   15932篇
综合类   2篇
数学   62544篇
物理学   72502篇
  2021年   1039篇
  2020年   1171篇
  2019年   1383篇
  2018年   18399篇
  2017年   18977篇
  2016年   11156篇
  2015年   2833篇
  2014年   2550篇
  2013年   4978篇
  2012年   11016篇
  2011年   24667篇
  2010年   14525篇
  2009年   14867篇
  2008年   19645篇
  2007年   24684篇
  2006年   4528篇
  2005年   11443篇
  2004年   8036篇
  2003年   8161篇
  2002年   5414篇
  2001年   2980篇
  2000年   2502篇
  1999年   1674篇
  1998年   1632篇
  1997年   1494篇
  1996年   1578篇
  1995年   1309篇
  1994年   1226篇
  1993年   1247篇
  1992年   1238篇
  1991年   1287篇
  1990年   1206篇
  1989年   1258篇
  1988年   1212篇
  1987年   1142篇
  1986年   1096篇
  1985年   1371篇
  1984年   1529篇
  1983年   1270篇
  1982年   1383篇
  1981年   1266篇
  1980年   1168篇
  1979年   1233篇
  1978年   1372篇
  1977年   1291篇
  1976年   1157篇
  1975年   1104篇
  1974年   1105篇
  1973年   1101篇
  1972年   756篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
111.
Nonperturbative nolocal structure of QCD vacuum is well described by instanton model. Specific helicity and flavor structure of zero modes of quarks, in instanton field allows simultaneously to explain some important features of low-and high-energy hadron phenomemology. The basic characteristics of hadron spectrum, partonic sum rules, heavyquark potential etc within the instanton liquid model are briefly discussed.  相似文献   
112.
The microhardness and content of carbon in electroplated gold coatings were studied as influenced by the operation time of citrate and citrate-phosphate gold-plating electrolytes. Such physicomechanical properties as porosity, microhardness, internal stress, plasticity, and microstructure of electroless-plated and electroplated nickel coatings were studied and analyzed.  相似文献   
113.
We consider the inverse problem for the identification of the coefficient in a parabolic equation. The model is applied to describe the functioning of a hierarchical structure [1]; it is also relevant for heat-conduction theory [2]. Unique solvability of the inverse problem is proved.  相似文献   
114.
A forecasting model is developed for the number of daily applications for loans at a financial services telephone call centre. The purpose of the forecasts and the associated prediction intervals is to provide effective staffing policies within the call centre. The model building process is constrained by the availability of only 2 years and 7 months of data. The distinctive feature of the data is that demand is driven in the main by advertising. The analysis given focuses on applications stimulated by press advertising. Unlike previous analyses of broadly similar data, where ARIMA models were used, a model with a dynamic level, multiplicative calendar effects and a multiplicative advertising response is developed and shown to be effective.  相似文献   
115.
A mixed boundary-value problem for the nonlinear Schrödinger equation and its generalization is studied by the method used for the inverse scattering problem. A connection is established between conservation laws and boundary conditions in integrable boundary-value problems for higher nonlinear Schrödinger equations. It is shown that the generalized boundary-value problem requires a joint consideration of regular and singular solutions for the nonlinear Schrödinger equation with repulsion.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 169, pp. 151–165, 1988.  相似文献   
116.
This paper describes three case studies which investigated issues relating to the implementation and management of advanced information technology. The benefits derived from information technology were found to vary from one organization to another. These studies provide further evidence to support earlier research findings that senior management has an important role to play in the effective exploitation of information technology, and that the investment approach taken by an organization has a significant effect on the development of computer-based information systems. The effectiveness of a system depends not only on applying the appropriate technology, but also on how successfully technical and behavioural issues are resolved.  相似文献   
117.
Preface     
  相似文献   
118.
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   
119.
120.
Summary The main purpose of this paper is to introduce the concepts of η-sets, ηζ-sets,η-continuity and ηζ-continuity and to obtain a decomposition of continuity.  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