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   53958篇
  免费   4533篇
  国内免费   2744篇
化学   23382篇
晶体学   300篇
力学   4535篇
综合类   624篇
数学   9279篇
物理学   10876篇
无线电   12239篇
  2024年   118篇
  2023年   529篇
  2022年   1294篇
  2021年   1427篇
  2020年   1460篇
  2019年   1270篇
  2018年   1152篇
  2017年   1620篇
  2016年   2151篇
  2015年   1768篇
  2014年   2684篇
  2013年   3833篇
  2012年   3383篇
  2011年   3171篇
  2010年   2566篇
  2009年   3040篇
  2008年   3147篇
  2007年   3476篇
  2006年   2891篇
  2005年   2548篇
  2004年   2459篇
  2003年   2064篇
  2002年   1630篇
  2001年   1324篇
  2000年   1264篇
  1999年   1117篇
  1998年   1058篇
  1997年   909篇
  1996年   829篇
  1995年   792篇
  1994年   699篇
  1993年   554篇
  1992年   512篇
  1991年   437篇
  1990年   389篇
  1989年   265篇
  1988年   257篇
  1987年   158篇
  1986年   131篇
  1985年   169篇
  1984年   134篇
  1983年   73篇
  1982年   112篇
  1981年   69篇
  1980年   59篇
  1979年   87篇
  1978年   40篇
  1977年   23篇
  1976年   30篇
  1957年   10篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The reactions of ethylene glycol mononitrate and glycerol 1,3-dinitrate with methylphosphonic dichloride afforded new nitroxyalkyl methylphosphonates.  相似文献   
92.
运用中学生男性性别角色期望调查表和因子分析方法对贵阳市中学生进行男性性别角色期望调查和定性与定量分析,为中学生树立适宜的性别角色观,促进其心理健康发展提供量化依据.分析显示:传统的男性角色并不被现代中学生完全接受,无论是男中学生还是女中学生都在力图探求一种新的男性性别角色模式,且两性中学生对这一新的男性性别角色模式的期望和把握是有一定差异的.  相似文献   
93.
Numerical solutions to three systems of integrable evolutionary equations from the Toda lattice hierarchy are analyzed. These are the classical Toda lattice, the second local dispersive flow, and the second extended dispersive flow. Special attention is given to the properties of soliton solutions. For the equations of the second local flow, two types of solitons interacting in a special manner are found. Solutions corresponding to various initial data are qualitatively outlined.  相似文献   
94.
The general problem of finding a distribution in hyperfine interaction parameters from experimental Mössbauer spectra is outlined. Existing methods may lack flexibility to be easily applicable to simple problems. A line shape for hyperfine parameter distributions is given, which is based on linear segments in the probability function. This method is applied in the analysis of samples containing iron in a silicate glass.  相似文献   
95.
The prepared amorphous γ-ZrP\SiO2 composite had a complicated composition, since a part of γ-ZrP is converted to α-form during the exfoliation of it. The γ-ZrP\SiO2 composite have specific surface area of 421 m2g–1. The acidic P–OH groups of the lamellae species placed on the surface (it is ≈1.0 meq g–1), do not destroy until the temperature of 1030 K. During the thermal treatment the total mass loss of 7.79% was found. This value corresponds to 0.42 mole of H2O per molecule unit. The water loss process was found very slow, because of the placing of bilamellar species in the composite.  相似文献   
96.
Many Ligularia species have long been used as traditional folk medicine for theirantibiotic, antiphlogistic and antitussive activities1, and were found to be an importantsource of eremophilane. In the course of our search for bioactive sesquiterpenoids, w…  相似文献   
97.
98.
In this paper we study Clifford and harmonic analysis on some examples of conformal flat manifolds that have a spinor structure, or more generally, at least a pin structure. The examples treated here are manifolds that can be parametrized by U/Γ where U is a subdomain of either Sn or Rn and Γ is a Kleinian group acting discontinuously on U. The examples studied here include RPn and the Hopf manifolds S1×Sn−1. Also some hyperbolic manifolds will be treated. Special kinds of Clifford-analytic automorphic forms associated to the different choices of Γ are used to construct explicit Cauchy kernels, Cauchy integral formulas, Green's kernels and formulas together with Hardy spaces and Plemelj projection operators for Lp spaces of hypersurfaces lying in these manifolds.  相似文献   
99.
In this paper, the possibility of using the gradients of the temperature and of the internal parameters as additional state variables in Continuum Thermodynamics is considered. The expressions of the two principles are discussed and Clausius–Duhem inequality is derived under an appropriate statement of the internal entropy production. Several formulations are proposed and compared to existing results in the literature. To cite this article: P. Ireman, Q.S. Nguyen, C. R. Mecanique 332 (2004).  相似文献   
100.
Dimitris  Georgios   《Ad hoc Networks》2008,6(3):474-482
The paper evaluates the performance effects of exposed terminals in IEEE 802.11 ad hoc networks in finite load conditions. It derives analytical models for the estimation of channel utilization and media access delay for IEEE 802.11 ad hoc networks in finite load conditions with and without exposed terminals. The simulation results show that the analytical estimated channel utilization and media access delay metrics are fairly accurate.  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