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   537523篇
  免费   5257篇
  国内免费   1279篇
化学   275946篇
晶体学   7698篇
力学   26166篇
综合类   17篇
数学   69312篇
物理学   164920篇
  2021年   5106篇
  2020年   5625篇
  2019年   6387篇
  2018年   8515篇
  2017年   8663篇
  2016年   11980篇
  2015年   6542篇
  2014年   10824篇
  2013年   24236篇
  2012年   19114篇
  2011年   22459篇
  2010年   16845篇
  2009年   16612篇
  2008年   21305篇
  2007年   21096篇
  2006年   19239篇
  2005年   17162篇
  2004年   15912篇
  2003年   14336篇
  2002年   14175篇
  2001年   14858篇
  2000年   11475篇
  1999年   8831篇
  1998年   7662篇
  1997年   7533篇
  1996年   7019篇
  1995年   6324篇
  1994年   6315篇
  1993年   6090篇
  1992年   6438篇
  1991年   6909篇
  1990年   6619篇
  1989年   6522篇
  1988年   6360篇
  1987年   6166篇
  1986年   5926篇
  1985年   7487篇
  1984年   7829篇
  1983年   6559篇
  1982年   6869篇
  1981年   6378篇
  1980年   6061篇
  1979年   6551篇
  1978年   6789篇
  1977年   6667篇
  1976年   6631篇
  1975年   6327篇
  1974年   6157篇
  1973年   6450篇
  1972年   4716篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
We study initial boundary value problems for linear scalar evolutionpartial differential equations, with spatial derivatives ofarbitrary order, posed on the domain {t > 0, 0 < x <L}. We show that the solution can be expressed as an integralin the complex k-plane. This integral is defined in terms ofan x-transform of the initial condition and a t-transform ofthe boundary conditions. The derivation of this integral representationrelies on the analysis of the global relation, which is an algebraicrelation defined in the complex k-plane coupling all boundaryvalues of the solution. For particular cases, such as the case of periodic boundaryconditions, or the case of boundary value problems for even-orderPDEs, it is possible to obtain directly from the global relationan alternative representation for the solution, in the formof an infinite series. We stress, however, that there existinitial boundary value problems for which the only representationis an integral which cannot be written as an infinite series.An example of such a problem is provided by the linearized versionof the KdV equation. Similarly, in general the solution of odd-orderlinear initial boundary value problems on a finite intervalcannot be expressed in terms of an infinite series.  相似文献   
992.
We obtain exponential upper bounds for tails of distributions of generalized L-statistics based on a sample from an exponential distribution. We prove the asymptotic normality of generalized L-statistics based on a sample from the uniform distribution on [0,1] and of L-statistics with decomposed kernels (without any restrictions on the sample distribution type).  相似文献   
993.
994.
Ohanian  M.  Caraballo  R.  Dalchiele  E. A.  Quagliata  E. 《Hyperfine Interactions》2003,148(1-4):193-198
Hyperfine Interactions - Corrosion products formed on low alloy steel under two marine environments are characterised. Both environments are classified as C4 according to the ISO 9223 Standard. The...  相似文献   
995.
In this article the main theorem establishes the necessity and sufficiency of the Poincaré-Hopf inequalities in order for the Morse inequalities to hold. The convex hull of the collection of all Betti number vectors which satisfy the Morse inequalities for a pre-assigned index data determines a Morse polytope defined on the nonnegative orthant. Using results from network flow theory, a scheme is provided for constructing all possible Betti number vectors which satisfy the Morse inequalities for a pre-assigned index data. Geometrical properties of this polytope are described.

  相似文献   

996.
997.
The first stage in a multi-attribute value analysis is the development of a hierarchical structure of the attributes of the problem. This paper reports the process of developing such a structure for the problem of choosing a suitable mode of transport for radioactive waste. The initial hierarchy of attributes went through several stages of development as new insights emerged about the nature of the problem. Some of the reasons behind this restructuring are discussed, and several important questions about the structuring process are formulated.  相似文献   
998.
Methods for obtaining alkylindoles, excluding the Fischer synthesis and direct alkylation, developed during the last 15 years are correlated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1155–1172, September, 1987.  相似文献   
999.
We develop a theory of the magnetic-zenith effect (MZE) observed upon the ionosphere modification by powerful radio waves. The dependences of MZE on main parameters, such as the magnetic-field inclination angle, pump-wave frequency and power, and angular width of HF beam are obtained. The optimal elevation angle of pump-wave beam is predicted. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 9, pp. 772–787, September 2005.  相似文献   
1000.
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