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   183850篇
  免费   38100篇
  国内免费   31255篇
化学   123709篇
晶体学   2573篇
力学   11444篇
综合类   1194篇
数学   23537篇
物理学   90748篇
  2024年   721篇
  2023年   2710篇
  2022年   4659篇
  2021年   4750篇
  2020年   5212篇
  2019年   5439篇
  2018年   5151篇
  2017年   5543篇
  2016年   7136篇
  2015年   7446篇
  2014年   8530篇
  2013年   12037篇
  2012年   13688篇
  2011年   15336篇
  2010年   16041篇
  2009年   16078篇
  2008年   10580篇
  2007年   9371篇
  2006年   8742篇
  2005年   7942篇
  2004年   7550篇
  2003年   6021篇
  2002年   5601篇
  2001年   5627篇
  2000年   4645篇
  1999年   4731篇
  1998年   3817篇
  1997年   3449篇
  1996年   3758篇
  1995年   3991篇
  1994年   3947篇
  1993年   3762篇
  1992年   3327篇
  1991年   2827篇
  1990年   2385篇
  1989年   2355篇
  1988年   2201篇
  1987年   1479篇
  1986年   1535篇
  1985年   1111篇
  1984年   1177篇
  1983年   524篇
  1982年   1016篇
  1981年   822篇
  1980年   833篇
  1979年   567篇
  1978年   554篇
  1977年   653篇
  1976年   1065篇
  1972年   537篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
The relation of the isoelectric point (IEP) and the point of zero net charge (PZNC) of the hydrotalcite-like compounds was discussed. It was found that the IEP does not equal to the PZNC and the IEP is higher than the PZNC. The structural positive charges existing in the HTlc,which cause the difference between the IEP and the PZNC. The effects of the structural positive charges of the HTlc on its IEP and PZNC are the same as the specific adsorption of metal cations.  相似文献   
132.
The crystal structures of two potential tumor imaging agents and therapeutic agents -copper(Ⅱ) complexes with salicylidene-tyrosinato Schiff base and nitrogen-donor chelating Lewis base, [Cu(sal-tyr)(bipy)] 1 and [Cu(sal-tyr)(phen)]2CH3OH 2 are presented. Our work is helpful to get deep understanding of novel 64Cu tumor imaging agents and therapeutic agents.  相似文献   
133.
The notion of Kuratowski convergence is applied to describe a kind of convergence in the context of holomorphic functions. We associate it to a convenient topology, explore its relation with the compact-open topology, thus providing a new set theoretic point of view of this classic topology, and present it in the framework of set-valued mappings.  相似文献   
134.
We consider a spinning charge coupled to the Maxwell field. Through the appropriate symmetry in the initial conditions the charge remains at rest. We establish that any time-dependent finite energy solution converges to a sum of a soliton wave and an outgoing free wave. The convergence holds in global energy norm. Under a small constant external magnetic field the soliton manifold is stable in local energy seminorms and the evolution of the angular velocity is guided by an effective finite-dimensional dynamics. The proof uses a non-autonomous integral inequality method.  相似文献   
135.
136.
We give a Gray code and constant average time generating algorithm for derangements, i.e., permutations with no fixed points. In our Gray code, each derangement is transformed into its successor either via one or two transpositions or a rotation of three elements. We generalize these results to permutations with number of fixed points bounded between two constants.  相似文献   
137.
We prove here that the surface of the regular icosahedron can be triangulated with 8 non-obtuse and with 12 acute triangles. We also show these numbers to be smallest possible.  相似文献   
138.
The extensive study of metric spaces and their embeddings has so far focused on embeddings that preserve pairwise distances. A very intriguing concept introduced by Feige allows us to quantify the extent to which larger structures are preserved by a given embedding. We investigate this concept, focusing on several major graph families such as paths, trees, cubes, and expanders. We find some similarities to the regular (pairwise) distortion, as well as some striking differences.  相似文献   
139.
An overview of the use of non-protein amino acids in the design of conformationally well-defined peptides, based on work from the author’s laboratory, is discussed. The crystal structures of several designed oligopeptides illustrate the useα-aminoisobutyric acid (Aib) in the construction of helices, D-amino acids in the design of helix termination segments andDPro-Xxx segments for nucleating ofβ-hairpin structures.β- andγ-amino acid residues have been used to expand the range of designed polypeptide structures. Dedicated to Professor C N R Rao on his 70th birthday  相似文献   
140.
He  Qi-Ming  Li  Hui 《Queueing Systems》2003,44(2):137-160
In this paper, we study the stability conditions of the MMAP[K]/G[K]/1/LCFS preemptive repeat queue. We introduce an embedded Markov chain of matrix M/G/1 type with a tree structure and identify conditions for the Markov chain to be ergodic. First, we present three conventional methods for the stability problem of the queueing system of interest. These methods are either computationally demanding or do not provide accurate information for system stability. Then we introduce a novel approach that develops two linear programs whose solutions provide sufficient conditions for stability or instability of the queueing system. The new approach is numerically efficient. The advantages and disadvantages of the methods introduced in this paper are analyzed both theoretically and numerically.  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