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   14582篇
  免费   976篇
  国内免费   409篇
化学   9886篇
晶体学   103篇
力学   517篇
综合类   36篇
数学   2214篇
物理学   3211篇
  2023年   125篇
  2022年   147篇
  2021年   237篇
  2020年   311篇
  2019年   299篇
  2018年   279篇
  2017年   214篇
  2016年   420篇
  2015年   434篇
  2014年   498篇
  2013年   854篇
  2012年   922篇
  2011年   985篇
  2010年   665篇
  2009年   619篇
  2008年   847篇
  2007年   800篇
  2006年   774篇
  2005年   677篇
  2004年   603篇
  2003年   550篇
  2002年   486篇
  2001年   283篇
  2000年   286篇
  1999年   248篇
  1998年   194篇
  1997年   153篇
  1996年   226篇
  1995年   162篇
  1994年   160篇
  1993年   154篇
  1992年   136篇
  1991年   106篇
  1990年   121篇
  1989年   91篇
  1988年   89篇
  1987年   94篇
  1985年   130篇
  1984年   125篇
  1983年   87篇
  1982年   109篇
  1981年   133篇
  1980年   130篇
  1979年   106篇
  1978年   113篇
  1977年   116篇
  1976年   96篇
  1975年   80篇
  1974年   82篇
  1973年   82篇
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
101.
With the emergence of new capital markets and liberalization of stock markets in recent years, there has been an increase in investors' interest in international diversification. This is so because international diversification allows investors to have a larger basket of foreign securities to choose from as part of their portfolio assets, so as to enhance the reward-to-volatility ratio. This benefit would be limited if national equity markets tend to move together in the long run. This paper thus studies the issue of co-movement between stock markets in major developed countries and those in Asian emerging markets using the concept of cointegration. We find that there is co-movement between some of the developed and emerging markets, but some emerging markets do differ from the developed markets with which they share a long-run equilibrium relationship. Furthermore, it has been observed that there has been increasing interdependence between most of the developed and emerging markets since the 1987 Stock Market Crash. This interdependence intensified after the 1997 Asian Financial Crisis. With this phenomenon of increasing co-movement between developed and emerging stock markets, the benefits of international diversification become limited.  相似文献   
102.
For the Queens_n 2 graph coloring problems no chromatic numbers are available for n > 9 except where n is not a multiple of 2 or 3. In this paper we propose an exact algorithm that takes advantage of the particular structure of these graphs. The algorithm works on the independent sets of the graph rather than on the vertices to be colored. It combines branch and bound, for independent set assignment, with a clique based filtering procedure. A first experimentation of this approach provided the coloring number values ranging for n = 10 to n = 14.  相似文献   
103.
Reported are fiber de-multiplexers based on side-polished fibers with a long interaction length and intra-core fiberBragg gratings. In conjunction with the silicon processing technologies, we demonstrate fiber filters and advantages ofour approaches are addressed.  相似文献   
104.
研究了电感耦合等离子体发射光谱法测定涂料中的重金属Pb,Cd,Cr和Hg,确定了测定涂料中的重金属Pb,Cd,Cr和Hg的最佳条件。加标回收试验和实际样品测定结果表明,方法的回收率和精密度分别在99.5%-110.0%和0.95%-1.98%范围,该方法快速、准确、可靠,各元素的检出限能满足涂料安全标准,适用于涂料的日常检验。  相似文献   
105.
In this paper we provide an error bound estimate and an implicit multifunction theorem in terms of smooth subdifferentials and abstract subdifferentials. Then, we derive a subdifferential calculus and Fritz–John type necessary optimality conditions for constrained minimization problems.  相似文献   
106.
We study the asymptotic behaviour of the solution of elliptic problems with periodic data when the size of the domain on which the problem is set becomes unbounded. To cite this article: M. Chipot, Y. Xie, C. R. Acad. Sci. Paris, Ser. I 339 (2004).  相似文献   
107.
When trains of impulse controls are present on the right-hand side of a system of ordinary differential equations, the solution is no longer smooth and contains jumps which can accumulate at several points in the time interval. In technological and physical systems the sum of the absolute value of all the impulses is finite and hence the total variation of the solution is finite. So the solution at best belongs to the space BV of vector functions with bounded variation. Unless variable node methods are used, the loss of smoothness of the solution would a priori make higher-order methods over a fixed mesh inactractive. Indeed in general the order of -convergence is and the nodal rate is . However in the linear case -convergence rate remains but the nodal rate can go up to by using one-step or multistep scheme with a nodal rate up to when the solution belongs to . Proofs are given of error estimates and several numerical experiments confirm the optimality of the estimates. Received March 15, 1996 / Revised version received January 3, 1997  相似文献   
108.
We study a processor-sharing model in which users choose between a high- and a low-priority service, based on their utility functions and prices charged by the service provider. The latter aims at revenue maximization. The model is motivated by file transmissions in data networks with distributed congestion control.  相似文献   
109.
We prove embedding results of weighted W1,p(RN) spaces of radially symmetric functions. The results then are used to obtain ground and bound state solutions of quasilinear equations with unbounded or decaying radial potentials.  相似文献   
110.
This paper outlines the results of a study undertaken to investigate the nature of Community Operational Research (COR). The objective was to contact the people involved in COR through a series of personal interviews and a questionnaire survey, in order to clarify many of the issues that have emerged within the profession relating to the practice of OR within the community and voluntary sector. A total of 20 individuals were successfully contacted, and they have been responsible for at least two-thirds of the projects in the COR area.  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