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   4527篇
  免费   416篇
  国内免费   405篇
化学   512篇
晶体学   12篇
力学   656篇
综合类   107篇
数学   3363篇
物理学   698篇
  2024年   7篇
  2023年   55篇
  2022年   62篇
  2021年   64篇
  2020年   101篇
  2019年   124篇
  2018年   142篇
  2017年   147篇
  2016年   165篇
  2015年   148篇
  2014年   223篇
  2013年   370篇
  2012年   208篇
  2011年   266篇
  2010年   199篇
  2009年   275篇
  2008年   308篇
  2007年   294篇
  2006年   259篇
  2005年   245篇
  2004年   222篇
  2003年   213篇
  2002年   189篇
  2001年   141篇
  2000年   151篇
  1999年   133篇
  1998年   112篇
  1997年   85篇
  1996年   82篇
  1995年   50篇
  1994年   62篇
  1993年   33篇
  1992年   38篇
  1991年   28篇
  1990年   23篇
  1989年   20篇
  1988年   13篇
  1987年   13篇
  1986年   10篇
  1985年   10篇
  1984年   16篇
  1983年   4篇
  1982年   12篇
  1981年   6篇
  1980年   5篇
  1979年   3篇
  1978年   7篇
  1977年   3篇
  1976年   1篇
  1957年   1篇
排序方式: 共有5348条查询结果,搜索用时 328 毫秒
101.
李念英  王维克 《应用数学》2006,19(2):348-355
本文研究一维空间中带松弛项的单个守恒律方程解的大时间状态估计.在松弛项满足耗散条件下通过对线性化方程Green函数的逐点估计得到方程解在时间充分大时的衰减估计,并由此反映出“弱”惠更斯原理.  相似文献   
102.
We continue investigations of forcing notions with strong ccc properties introducing new methods of building sweet forcing notions. We also show that quotients of topologically sweet forcing notions over Cohen reals are topologically sweet while the quotients over random reals do not have to be such. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
103.
We study notions of nondegeneracy and several levels of increasing degeneracy from the perspective of the local behavior of a local solution of a nonlinear program when problem parameters are slightly perturbed. Ideal nondegeneracy at a local minimizer is taken to mean satisfaction of second order sufficient conditions, linear independence and strict complimentary slackness. Following a brief exploration of the relationship of these conditions with the classical definition of nondegeneracy in linear programming, we recall a number of optimality and regularity conditions used to attempt to resolve degeneracy and survey results of Fiacco, McCormick, Robinson, Kojima, Gauvin and Janin, Shapiro, Kyparisis and Liu. This overview may be viewed as a structured survey of sensitivity and stability results: the focus is on progressive levels of degeneracy. We note connections of nondegeneracy with the convergence of algorithms and observe the striking parallel between the effects of nondegeneracy and degeneracy on optimality conditions, stability analysis and algorithmic convergence behavior. Although our orientation here is primarily interpretive and noncritical, we conclude that more effort is needed to unify optimality, stability and convergence theory and more results are needed in all three areas for radically degenerate problems.Research supported by National Science Foundation Grant ECS 90-00560 and Grant N00014-89-J-1537 Office of Naval Research  相似文献   
104.
The Hamiltonian formulation of the usual complex quantum mechanics in the theory of generalized quantum dynamics is discussed. After the total trace Lagrangian, total trace Hamiltonian and two kinds of Poisson brackets are introduced, both the equations of motion of some total trace functionals which are expressed by total trace Poisson brackets and the equations of motion of some operators which are expressed by the without-total-trace Poisson brackets are obtained. Then a set of basic equations of motion of the usual complex quantum mechanics are obtained, which are also expressed by the Poisson brackets and total trace Hamiltonian in the generalized quantum dynamics. The set of equations of motion are consistent with the corresponding Heisenberg equations. Project supported by Prof. T.D. Lee’s NNSC Grant, the National Natural Science Foundation of China, the Foundation of Ph. D. Directing Programme of Chinese University, and the Chinese Academy of Sciences.  相似文献   
105.
We use the topological tool of Nielsen fixed-point theory to study the controllability of perturbed linear control processes whose control space can be reduced to a finite-dimensional one. These methods produce a lower bound on the number of controls that achieve a given target. We concentrate particularly on the case where the perturbation has sublinear growth, and we exhibit examples of multiple controls of various types that are detected by the Nielsen theory method.This research was partly supported by the Research Grant Teoria del Controllo dei Sistemi Dinamici, Ministero della Pubblica Istruzione, Roma, Italy.  相似文献   
106.
A fixed-point equation on an infinite-dimensional space is proposed as an alternative to the usual definition of the infinite-volume limit in discrete lattice spin systems in the high-temperature phase. It is argued heuristically that the free energy and correlation functions one obtains by solving this equation agree with the usual definitions of these quantities. A theorem is then proved that says that if a certain finite-volume condition is satisfied, then this fixed-point equation has a solution and the resulting free energy is analytic in the parameters in the Hamiltonian. For particular values of the temperature this finite-volume condition may be checked with the help of a computer. The two-dimensional Ising model is considered as a test case, and it is shown that the finite-volume condition is satisfied for0.77 critical.  相似文献   
107.
We formulate the super-KMS condition suggested by Connes and Kastler, in the context of entire cyclic cohomology of quantum algebras. We show that the Chern character of Jaffe, Lesniewski, and Osterwalder — associated by Kastler to a super-KMS functional — satisfies the entire growth condition. Hence, a super-KMS functional defines a cocycle for the entire cyclic cohomology of quantum algebras.Supported in part by the National Science Foundation.  相似文献   
108.
比较了DB-1和HP-5石英毛细管柱在不同柱流速、柱温下对氯氰菊酯异构体的分离效果,表明采用DB-1石英毛细管柱(30m×0.25mmi.d.,0.25μm)较好,柱温为240℃,柱流速为12cm/s,分析时间40min。该分析方法重现性好,分析结果准确、可靠。  相似文献   
109.
采用WAXD、SAXS和X-射线平板照相法研究了不同聚合条件和拉伸倍数下的晶性3,4-聚异戊二烯的结构.结果发现,降低催化体系反应速度有利于产物结晶;不同的含氮类给电子试剂对聚合物的结晶结构影响较大.取向样品随着拉伸倍数的增加结晶度和长周期增大,微晶尺寸变小.SAXS的散射强度计算表明,该聚合物属多分散非均一粒子体系,微孔半径在3.5-16.4nm间.  相似文献   
110.
The oscillating conditions for a series piezoelectric quartz crystal (SPQC) are proposed and verified experimentally. The influence of the cell constant and oscillator phase on the oscillational ability of the SPQC was investigated. It is shown that the SPQC possesses excellent oscillational ability in low or high conductivity solutions, but in solution of intermediate conductivity, the oscillational ability decreases with increasing oscillator phase or decreasing cell constant, sometimes resulting in a cease-to-oscillate zone. The SPQC was applied to determine the urease activity in plant seeds with a detection limit of 0.004 U ml−1, based on the change in conductivity.  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