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   357324篇
  免费   6690篇
  国内免费   4938篇
化学   172977篇
晶体学   5303篇
力学   20792篇
综合类   325篇
数学   50826篇
物理学   118729篇
  2021年   4675篇
  2020年   5143篇
  2019年   5923篇
  2018年   7912篇
  2017年   7955篇
  2016年   10043篇
  2015年   5379篇
  2014年   9265篇
  2013年   15456篇
  2012年   13759篇
  2011年   15502篇
  2010年   12763篇
  2009年   12873篇
  2008年   14349篇
  2007年   13881篇
  2006年   12525篇
  2005年   10813篇
  2004年   10267篇
  2003年   9417篇
  2002年   9743篇
  2001年   9220篇
  2000年   7293篇
  1999年   5601篇
  1998年   5281篇
  1997年   4964篇
  1996年   4573篇
  1995年   4006篇
  1994年   4100篇
  1993年   4082篇
  1992年   4005篇
  1991年   4404篇
  1990年   4386篇
  1989年   4314篇
  1988年   4031篇
  1987年   4082篇
  1986年   3747篇
  1985年   4309篇
  1984年   4516篇
  1983年   3892篇
  1982年   4058篇
  1981年   3701篇
  1980年   3456篇
  1979年   3997篇
  1978年   4075篇
  1977年   4203篇
  1976年   4362篇
  1975年   4059篇
  1974年   3963篇
  1973年   4085篇
  1972年   3544篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
1.
2.
3.
4.
The γcmc values of CTAB-SDS decrease from 63.67 mN/m at 10‡C to 36.38 mN/m at 90‡C, slightly lower than those of either CTAB or SDS. Correspondingly, the CMC of CTAB-SDS decreases almost by half. The increase of surface activity of CTAB-SDS can be attributed to the relatively weak electrostatic interaction at high temperature, which is supported by the increase of solubility of CTAB-SDS with rise in temperature. Catalytic effect on oxidation of toluene derivatives with potassium permanganate follows the order CTAB-SDS > SDS > CTAB. This is not caused by the dissociative effect of CTAB-SDS with low surface activity at low temperature, as seen from the fact that almost all oxidative products can be retrieved for different toluene derivatives and surfactants by mimicking the conditions of reaction. In the emulsifications of toluene derivatives at 90‡C, the time that turbid water layers of surfactant solutions take to become clear is the same as that of the catalytic effect on oxidation of toluene derivatives. Thus, it can be inferred that surfactants can improve the oxidation yields of toluene derivatives by increasing the contact between two reacting phases.  相似文献   
5.
The excitation of eigen surface waves by tubular electron beams in cylindrical discharge devices is studied. The influence of the wave‐field azimuthal structure on the excitation efficiency and nonlinear stage of the plasmabeam instability is investigated both numerically and analytically. Analytical expressions for the saturation amplitude and excitation efficiency of the wave under study are derived. They are found to agree well with results obtained by numerical modelling of the plasma‐beam interaction presented in this paper. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
6.
7.
The Langevin dynamics and fluctuational-dissipative relationships for the hydrodynamic fluctuations for systems which are described in the third Barnett order with respect to the gradients of the hydrodynamic variables are generalized on the basis of a kinetic approach.  相似文献   
8.
Numerical and analytical studies are performed for the free vibration analysis of non-cylindrical (conical, barrel and hyperboloidal types) helical springs. The stiffness matrix method is used in the numerical analysis. A total of 12 degrees of freedom (six displacements and six rotations) is described for an element. The exact element stiffness matrix and the exact concentrated element inertia matrix are used in the formulation. The rotary inertia, the shear and extensional deformation effects are considered in the analysis. Comparison of the numerical results with the reported results obtained numerically and experimentally gives satisfactory values. After verification of the numerical frequencies, the non-dimensional fundamental frequencies of fixed-fixed non-cylindrical helical springs with circular section are expressed in a simple formula with a maximum absolute relative error of 5% using those numerical values for the constant helix pitch angles (5°, 10°, and 15°). These expressions restricted to the fundamental frequencies are also verified with ANSYS results.  相似文献   
9.
The purpose of this paper is to investigate problems of the Navier-Stokes approximation to kinetic equations in terms of the so-called Chapman-Enskog projection. One considers properties of the Chapman-Enskog projection for the Cauchy problem for moment approximations of the kinetic equation and primarily the Chapman-Enskog projection for the Boltzmann-Peierls kinetic equation. The existence of the Chapman-Enskog projection for the Cauchy problem is proved for the phase space of conservative variables (phenomena of nonlinear diffusion) and for the phase space of physical variables (the second sound projection). __________ Translated from Trudy Seminara imeni I. G. Petrovskogo, No. 25, pp. 184–225, 2005.  相似文献   
10.
An infinite graph is 2‐indivisible if the deletion of any finite set of vertices from the graph results in exactly one infinite component. Let G be a 4‐connected, 2‐indivisible, infinite, plane graph. It is known that G contains a spanning 1‐way infinite path. In this paper, we prove a stronger result by showing that, for any vertex x and any edge e on a facial cycle of G, there is a spanning 1‐way infinite path in G from x and through e. Results will be used in two forthcoming papers to establish a conjecture of Nash‐Williams. © 2005 Wiley Periodicals, Inc. J Graph Theory  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