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   6292篇
  免费   207篇
  国内免费   26篇
化学   4435篇
晶体学   39篇
力学   176篇
数学   965篇
物理学   910篇
  2024年   6篇
  2023年   57篇
  2022年   187篇
  2021年   201篇
  2020年   161篇
  2019年   157篇
  2018年   114篇
  2017年   116篇
  2016年   253篇
  2015年   213篇
  2014年   223篇
  2013年   331篇
  2012年   398篇
  2011年   492篇
  2010年   282篇
  2009年   258篇
  2008年   388篇
  2007年   361篇
  2006年   364篇
  2005年   334篇
  2004年   306篇
  2003年   244篇
  2002年   207篇
  2001年   78篇
  2000年   69篇
  1999年   75篇
  1998年   48篇
  1997年   52篇
  1996年   77篇
  1995年   48篇
  1994年   46篇
  1993年   39篇
  1992年   48篇
  1991年   39篇
  1990年   23篇
  1989年   22篇
  1988年   13篇
  1987年   16篇
  1986年   19篇
  1985年   24篇
  1984年   21篇
  1983年   22篇
  1982年   16篇
  1981年   12篇
  1980年   14篇
  1979年   17篇
  1977年   8篇
  1976年   4篇
  1975年   3篇
  1906年   2篇
排序方式: 共有6525条查询结果,搜索用时 15 毫秒
141.

Background  

The aim of this study was to examine the relationship between chronic neuropathic pain after incomplete peripheral nerve lesion, chronic nociceptive pain due to osteoarthritis, and the excitability of the motor cortex assessed by transcranial magnetic stimulation (TMS). Hence in 26 patients with neuropathic pain resulting from an isolated incomplete lesion of the median or ulnar nerve (neuralgia), 20 patients with painful osteoarthritis of the hand, and 14 healthy control subjects, the excitability of the motor cortex was tested using paired-pulse TMS to assess intracortical inhibition and facilitation. These excitability parameters were compared between groups, and the relationship between excitability parameters and clinical parameters was examined.  相似文献   
142.
Let P be a bounded analytic polyhedron in ℂ2 whose boundary is smooth except for normal crossing singularities. We show that P is a holomorphic quotient of the bidisc, if its automorphism group is noncompact.  相似文献   
143.
Given an integer polyhedron , an integer point , and a point , the primal separation problem is the problem of finding a linear inequality which is valid for P I , violated by x *, and satisfied at equality by . The primal separation problem plays a key role in the primal approach to integer programming. In this paper we examine the complexity of primal separation for several well-known classes of inequalities for various important combinatorial optimization problems, including the knapsack, stable set and travelling salesman problems.Received: November 2002, Revised: March 2003,  相似文献   
144.
Breaking of ensemble equivalence between the microcanonical ensemble and the canonical ensemble may occur for random graphs whose size tends to infinity, and is signaled by a non-zero specific relative entropy between the two ensembles. In Garlaschelli et al. (2017) and Garlaschelli et al. (0000) it was shown that breaking occurs when the constraint is put on the degree sequence (configuration model). It is not known what is the effect on the relative entropy when the number of constraints is reduced, i.e., when only part of the nodes are constrained in their degree (and the remaining nodes are left unconstrained). Intuitively, the relative entropy is expected to decrease. However, this is not a trivial issue because when constraints are removed both the microcanonical ensemble and the canonical ensemble change. In this paper a formula for the relative entropy valid for generic discrete random structures, recently formulated by Squartini and Garlaschelli, is used to prove that the relative entropy is monotone in the number of constraints when the constraint is on the degrees of the nodes. It is further shown that the expression for the relative entropy corresponds, in the dense regime, to the degrees in the microcanonical ensemble being asymptotically multivariate Dirac and in the canonical ensemble being asymptotically Gaussian.  相似文献   
145.
We consider time-dependent Schrödinger equations with a double well potential and an external nonlinear, both local and non-local, perturbation. In the semiclassical limit, the finite dimensional eigenspace associated to the lowest eigenvalues of the linear operator is almost invariant for times of the order of the beating period and the dominant term of the wavefunction is given by means of the solutions of a finite dimensional dynamical system. In the case of local nonlinear perturbation, we assume the spatial dimension d=1 or d=2.  相似文献   
146.
We study the complexity of the problem of deciding the existence of a spanning subgraph of a given graph, and of that of finding a maximum (weight) such subgraph. We establish some general relations between these problems, and we use these relations to obtain new NP-completeness results for maximum (weight) spanning subgraph problems from analogous results for existence problems and from results in extremal graph theory. On the positive side, we provide a decomposition method for the maximum (weight) spanning chordal subgraph problem that can be used, e.g., to obtain a linear (or O(nlogn)) time algorithm for such problems in graphs with vertex degree bounded by 3.  相似文献   
147.
The authors consider the multidimensional aggregation equation tp-div(p K* ρ) = 0 in which the radially symmetric attractive interaction kernel has a mild singularity at the origin (Lipschitz or better), and review recent results on this problem concerning well-posedness of nonnegative solutions and finite time blowup in multiple space dimensions depending on the behavior of the kernel at the origin. The problem with bounded initial data, data in L^p ∩ L^1, and measure solutions are also considered.  相似文献   
148.
The complete equipartite graph $K_m * {\overline{K_n}}$ has mn vertices partitioned into m parts of size n, with two vertices adjacent if and only if they are in different parts. In this paper, we determine necessary and sufficient conditions for the existence of a decomposition of $K_m * {\overline{K_n}}$ into closed trails of length k. © 2009 Wiley Periodicals, Inc. J Combin Designs 17: 374–403, 2009  相似文献   
149.
Methyltransferases have proven useful to install functional groups site‐specifically in different classes of biomolecules when analogues of their cosubstrate S‐adenosyl‐l ‐methionine (AdoMet) are available. Methyltransferases have been used to address different classes of RNA molecules selectively and site‐specifically, which is indispensable for biophysical and mechanistic studies as well as labeling in the complex cellular environment. However, the AdoMet analogues are not cell‐permeable, thus preventing implementation of this strategy in cells. We present a two‐step enzymatic cascade for site‐specific mRNA modification starting from stable methionine analogues. Our approach combines the enzymatic synthesis of AdoMet with modification of the 5′ cap by a specific RNA methyltransferase in one pot. We demonstrate that a substrate panel including alkene, alkyne, and azido functionalities can be used and further derivatized in different types of click reactions.  相似文献   
150.
A semiempirical addition of dispersive forces to conventional density functionals (DFT-D) has been implemented into a pseudopotential plane-wave code. Test calculations on the benzene dimer reproduced the results obtained by using localized basis set, provided that the latter are corrected for the basis set superposition error. By applying the DFT-D/plane-wave approach a substantial agreement with experiments is found for the structure and energetics of polyethylene and graphite, two typical solids that are badly described by standard local and semilocal density functionals.  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