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   6389篇
  免费   167篇
  国内免费   25篇
化学   4306篇
晶体学   65篇
力学   180篇
数学   753篇
物理学   1277篇
  2021年   45篇
  2020年   64篇
  2019年   68篇
  2018年   43篇
  2017年   42篇
  2016年   122篇
  2015年   92篇
  2014年   117篇
  2013年   257篇
  2012年   343篇
  2011年   397篇
  2010年   212篇
  2009年   171篇
  2008年   334篇
  2007年   366篇
  2006年   370篇
  2005年   336篇
  2004年   280篇
  2003年   251篇
  2002年   232篇
  2001年   99篇
  2000年   93篇
  1999年   51篇
  1998年   76篇
  1997年   71篇
  1996年   103篇
  1995年   67篇
  1994年   84篇
  1993年   87篇
  1992年   61篇
  1991年   74篇
  1990年   65篇
  1989年   68篇
  1988年   66篇
  1987年   44篇
  1986年   48篇
  1985年   91篇
  1984年   81篇
  1983年   58篇
  1982年   82篇
  1981年   88篇
  1980年   78篇
  1979年   71篇
  1978年   78篇
  1977年   73篇
  1976年   63篇
  1975年   66篇
  1974年   65篇
  1973年   70篇
  1972年   38篇
排序方式: 共有6581条查询结果,搜索用时 296 毫秒
11.
Let G be a 2-connected graph with minimum degree at least 3. We prove that there exists an even circuit C in G with factorization F={F1,F2} such that GE(F1) is 2-connected.  相似文献   
12.
An investigation of BELENE Nuclear Power Plant (NPP) free field signal is presented in the current study. An SH wave propagation trough multilayer geological media in the region is considered. An original structural model of the geological column has been developed. The investigated layers are isotropic, with constant depth and skyline parallel. The SH rays are with an arbitrary angle as far as the layers are concerned. The seismic SH waves have been generated by a special detonation device. The main results of the study are graphically illustrated. A comparison between the original BELENE NPP experimental and the numerical surface (free field) signals (obtained by the formulated direct problem) for the investigated geological column has been carried out and its results are hereby shown.  相似文献   
13.
It is shown that data on the dissociation rate of deuterium obtained in an experiment at the Sudbury Neutrino Observatory provides evidence that the Continuous Spontaneous Localization wavefunction collapse model should have mass–proportional coupling to be viable.  相似文献   
14.
15.
A series of optically active main chain polyesters were synthesized by high temperature polycondensation from biphenolic azo chromophores with azobenzene-4,4'-dicarbonylchloride and 1,4:3,6-dianhydro-D-sorbitol ([!]D25=+42.5°). The second harmonic generation of the polyesters is studied in thin films. The polar order in films is determined from the UV-visible absorption spectra. The variation in SHG intensity with chiral monomer concentration is explained as a function of polar order. The polymers with chiral units showed good second harmonic efficiency. The intensity of second harmonic light (532 nm) increased with angle of incidence and indicated the polar order in the plane of the film. The SH signal also showed good temporal stability.  相似文献   
16.
Periodic line structures with a period of 167 nm and linewidths varying from 30 to 100 nm have been produced in polyimide by direct ablation with a KrF laser using an interferometric technique. The characteristics of this interferometer as it applies to the ablation of these line structures, including linewidth and alignment sensitivity, are analyzed. The ability to control the linewidth by varying the average incident fluence is described theoretically and demonstrated experimentally. This externally generated period of 167 nm also prevents the spontaneous growth of laser induced periodic surface structures (LIPSS).  相似文献   
17.
We describe a new family of discrete spaces suitable for use with mixed methods on certain quadrilateral and hexahedral meshes. The new spaces are natural in the sense of differential geometry, so all the usual mixed method theory, including the hybrid formulation, carries over to these new elements with proofs unchanged. Because transforming general quadrilaterals into squares introduces nonlinearity and because mixed methods involve the divergence operator, the new spaces are more complicated than either the corresponding Raviart-Thomas spaces for rectangles or corresponding finite element spaces for quadrilaterals. The new spaces are also limited to meshes obtained from a rectangular mesh through the application of a single global bilinear transformation. Despite this limitation, the new elements may be useful in certain topologically regular problems, where initially rectangular grids are deformed to match features of the physical region. They also illustrate the difficulties introduced into the theory of mixed methods by nonlinear transformations.  相似文献   
18.
Let g be a Lie algebra all of whose regular subalgebras of rank 2 are type A1×A1, A2, or C2, and let B be a crystal graph corresponding to a representation of g. We explicitly describe the local structure of B, confirming a conjecture of Stembridge.  相似文献   
19.
A new consistency measure, the harmonic consistency index, is obtained for any positive reciprocal matrix in the analytic hierarchy process. We show how this index varies with changes in any matrix element. A tight upper bound is provided for this new consistency measure when the entries of matrix are at most 9, as is often recommended. Using simulation, the harmonic consistency index is shown to give numerical values similar to the standard consistency index but it is easier to compute and interpret. In addition, new properties of the column sums of reciprocal matrices are obtained.  相似文献   
20.
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