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   757217篇
  免费   6157篇
  国内免费   1941篇
化学   383996篇
晶体学   11033篇
力学   38718篇
综合类   32篇
数学   102874篇
物理学   228662篇
  2020年   7043篇
  2019年   7930篇
  2018年   10624篇
  2017年   10780篇
  2016年   15106篇
  2015年   8401篇
  2014年   13874篇
  2013年   32790篇
  2012年   25089篇
  2011年   29966篇
  2010年   22183篇
  2009年   22044篇
  2008年   28295篇
  2007年   28155篇
  2006年   25924篇
  2005年   23091篇
  2004年   21498篇
  2003年   19416篇
  2002年   19413篇
  2001年   20713篇
  2000年   16162篇
  1999年   12557篇
  1998年   10902篇
  1997年   10795篇
  1996年   10119篇
  1995年   9205篇
  1994年   9258篇
  1993年   8898篇
  1992年   9486篇
  1991年   10031篇
  1990年   9599篇
  1989年   9381篇
  1988年   9259篇
  1987年   9098篇
  1986年   8688篇
  1985年   11308篇
  1984年   11806篇
  1983年   9992篇
  1982年   10301篇
  1981年   9820篇
  1980年   9423篇
  1979年   9951篇
  1978年   10506篇
  1977年   10364篇
  1976年   10410篇
  1975年   9874篇
  1974年   9753篇
  1973年   10131篇
  1972年   7423篇
  1971年   6421篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
The dependence of the energy characteristics on an adiabatically slowly increasing external force is determined analytically for an anharmonic oscillator. The analytical results are confirmed by a numerical calculation. The nature of the force dependences of the energy characteristics are determined and discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 153–157 (January 1997)  相似文献   
93.
Mass distributions of fragments in the low-energy fission of nuclei from 187Ir to 213At have been analysed. This analysis has shown that shell effects in symmetric-mode fragment mass yields from the fission of pre-actinide nuclei could be described if one assumes the existence of two strongly deformed neutron shells in the arising fragments with neutron numbers N1 ≈ 52 and N2 ≈ 68. A new method has been proposed for quantitatively describing the mass distributions of the symmetric fission mode for pre-actinides with A ≈ 180–220.  相似文献   
94.
We show that an electron confined to a single finite parabolic quantum well in crossed electric and magnetic fields can behave as a double quantum well system. The magnetic field is parallel to the heterostructure layers and the electric field is perpendicular to those. For a suitable choice of both fields and quantum well width, the electron can be confined to a double quantum well effective potential that is very similar to the electronic potential model for diatomic molecules. The double quantum well spectrum is calculated using a numerical algorithm based on semiclassical methods. A physical interpretation of this quantum system is given based on the analogy to the electrons bound to diatomic molecules.  相似文献   
95.
It is shown that the nonstable character of nonlinear interaction of a system of waves similar to that resulting from double stimulated Brillouin scattering is retained upon the oblique incidence of a powerful electromagnetic wave on a layer of supercritical plasma. In this case we have nonlinear back reflection from a layer of supercritical plasma. The threshold intensity of the pump wave is greater than that in the case of subcritical plasma for TE polarization waves but can markedly decrease for waves polarized in the incidence plane. Instability is possible only for a layer of finite thickness.Radiophysical Research Institute, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, Nos. 3–4, pp. 298–303, March–April, 1995.  相似文献   
96.
Flowing and static gas-phase samples of HNO3 in O2 and N2 were analyzed by long-path ultraviolet/visible (UV/VIS) spectroscopy to reveal the presence of both NO2 and NO3, the concentrations of which were calculated using differential absorption cross sections. NO2 is produced predominantly by the heterogeneous decomposition of HNO3, whereas NO3 is generated in the gas phase by the thermal decomposition of N2O5, a product of the self-disproportionation of liquid HNO3. © 1993 John Wiley & Sons, Inc.  相似文献   
97.
98.
It is shown that the exact solution of the problem of convective heat exchange in a low-Prandtl-number fluid flow (Pr ? 1) can be obtained for a two-dimensional body of arbitrary shape provided that the conformal mapping relating the body contour with a circle is known. By way of example, the Joukowsky airfoil is considered.  相似文献   
99.
A model kinetic equation is constructed for the transport of a massless Bose gas. This equation is applied to solve the boundary value problem for the transport of radiation in the half-space occupied by a dispersive medium that is in local thermal equilibrium with the radiation. It is shown that the difference in temperature between the dispersive medium and the incident radiation substantially depends on the character of the scattering properties of the particles in the medium. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 111, No. 3, pp. 462–472, June, 1997.  相似文献   
100.
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