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   30653篇
  免费   1039篇
  国内免费   16篇
化学   21108篇
晶体学   230篇
力学   561篇
数学   4168篇
物理学   5641篇
  2023年   253篇
  2022年   182篇
  2021年   356篇
  2020年   514篇
  2019年   467篇
  2018年   674篇
  2017年   619篇
  2016年   1197篇
  2015年   960篇
  2014年   955篇
  2013年   2001篇
  2012年   2218篇
  2011年   2388篇
  2010年   1351篇
  2009年   1084篇
  2008年   1995篇
  2007年   1951篇
  2006年   1707篇
  2005年   1531篇
  2004年   1243篇
  2003年   960篇
  2002年   845篇
  2001年   648篇
  2000年   550篇
  1999年   409篇
  1998年   293篇
  1997年   213篇
  1996年   334篇
  1995年   219篇
  1994年   213篇
  1993年   264篇
  1992年   232篇
  1991年   158篇
  1990年   140篇
  1989年   119篇
  1988年   121篇
  1987年   120篇
  1986年   116篇
  1985年   178篇
  1984年   145篇
  1983年   120篇
  1982年   105篇
  1981年   98篇
  1980年   76篇
  1979年   93篇
  1978年   80篇
  1977年   73篇
  1976年   76篇
  1975年   70篇
  1973年   81篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
In some situations estimates of unknown parameters must be corrected by additional measurements. It is in principle no problem to calculate the corrected estimates, however, it is of more interest to find formulae for correction itself. The formulae enable us to design an additional experiment and to judge its usefulness. The aim of the paper is to find such formulae for several situations. Supported by the grant of the Council of Czech Government MSM 6 198 959 214.  相似文献   
52.
We investigate traces of functions, belonging to a class of functions with dominating mixed smoothness in ℝ3, with respect to planes in oblique position. In comparison with the classical theory for isotropic spaces a few new phenomenona occur. We shall present two different approaches. One is based on the use of the Fourier transform and restricted to p = 2. The other one is applicable in the general case of Besov-Lizorkin-Triebel spaces and based on atomic decompositions.  相似文献   
53.
The stoichiometric reactions of trimethylaluminum with 2,6‐(MeOCH2)2C6H3OH (LH) revealed compounds L3Al ( 1 ) and L2AlMe ( 2 ). On the other hand reaction of 1 equiv. of LH with trimethylaluminum did not lead to the formation of complex LAlMe2 ( 3 ), rather 2 together with Me3Al were observed as a result of a disproportionation of 3 . Compounds 1 and 2 were characterized by elemental analysis, 1H and 13C NMR spectroscopy and in the case of 1 by X‐ray diffraction. Derivative 2 underwent transmetalation with Ph3SnOH, giving LSnPh3 ( 4 ) as the result of a migration of ligand L from the aluminum to the tin atom. The identity of 4 was established by elemental analysis, 1H, 13C and 119Sn NMR spectroscopy and 1H, 119Sn HMBC experiments. The system 2 and B(C6F5)3 in a 1:1 molar ratio was shown to be active in the polymerization of propylene oxide and ε‐caprolactone. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
54.
This paper presents the results of plasma temperature and pressure calculations in the parallel plate accelerator during the accelerating process. The plasma pressure is calculated by means in Dalton's law.  相似文献   
55.
56.
Continuous solutions of the functional equation ?(x?(x)) = (?(x))2 for x ∈ [0,∞) have been characterized by Dhombres. They form a simple, two-parametric family and the result can be easily extended to solutions on the whole real line. However, the class of all solutions is much larger. We show that there is a solution ? whose graph has, among others, the full outer two-dimensional Lebesgue measure. It turns out that partial restrictions, like boundedness, monotonicity and/or continuity on a subinterval do not imply the continuity of solutions. In particular, the class of monotonic solutions has interesting properties. We provide some techniques of constructing such solutions and show that, among others, there is a strictly increasing solution ? whose points of discontinuity form a dense set in R.  相似文献   
57.
It is proved that if the intrinsic zero-index of the Sasaki metric of a tangent bundleTM n isk, thenk is even andM n is the metric product of a Riemannian manifoldM nk/2 by a Euclidean spaceE k/2, whileTM n is the metric product ofTM nk/2 byE k . An expression is obtained for the second fundamental forms of the imbeddingTF l TM n in terms of the second fundamental forms of the imbeddingF l M n and the curvature tensor ofM n . It is proved thatTF l is totally geodesic inTM n if and only ifF l is totally geodesic inM n .Translated from Ukrainskií Geometricheskií Sbornik, Issue 28, 1985, pp. 12–32.  相似文献   
58.
The kinetic equation of the classical homogeneous nucleation theory is rewritten in dimensionless form and it is shown that the numerical computation of the dimensionless kinetic equation is approximately 20 times faster in comparison with the original kinetic equation. The results are compared with known analytical results and with previous numerical results in the case of the constant and variable temperature for the model Li2O.2 SiO2 melt. It is shown, e.g., that under non-isothermal conditions the nucleation rate is greater than the quasistationary nucleation rate and the cluster distribution function is greater than the corresponding quasiequilibrium cluster distribution function.  相似文献   
59.
60.
The paper deals with the regime of advanced Bénard instabilities (described usually by the Lorenz system) in a more general system formulated firstly by Obukhov. It has been shown that triplet co-operation leads to characteristic courses where some new regularities occur.  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