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   91898篇
  免费   2717篇
  国内免费   2373篇
化学   35231篇
晶体学   957篇
力学   7310篇
综合类   185篇
数学   33355篇
物理学   19950篇
  2023年   193篇
  2022年   408篇
  2021年   399篇
  2020年   467篇
  2019年   536篇
  2018年   10752篇
  2017年   10566篇
  2016年   6705篇
  2015年   1572篇
  2014年   1081篇
  2013年   1400篇
  2012年   5005篇
  2011年   11689篇
  2010年   6558篇
  2009年   6941篇
  2008年   7641篇
  2007年   9625篇
  2006年   1089篇
  2005年   2065篇
  2004年   2183篇
  2003年   2526篇
  2002年   1660篇
  2001年   783篇
  2000年   658篇
  1999年   444篇
  1998年   410篇
  1997年   349篇
  1996年   356篇
  1995年   256篇
  1994年   193篇
  1993年   223篇
  1992年   151篇
  1991年   179篇
  1990年   126篇
  1989年   114篇
  1988年   95篇
  1987年   90篇
  1986年   98篇
  1985年   84篇
  1984年   68篇
  1983年   57篇
  1982年   58篇
  1981年   46篇
  1980年   52篇
  1979年   53篇
  1914年   45篇
  1913年   40篇
  1912年   40篇
  1909年   41篇
  1908年   40篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The dielectric constant for rain medium is investigated by utilizing the system identification method. The rain rate model and frequency model of permittivity in millimeter waves band for rain medium are presented. The results obtained with models are in very good agreement with references in calculating the attenuation of electromagnetic waves induced by rain, which Shows that the obtained models are valid and practicable. The cross-polar discrimination gotten with rain rate model is in agreement with references.  相似文献   
92.
For ϕ a δ-subharmonic function, sharp results are obtained that connectA(r, ϕ), B(r, ϕ) andT(r, ϕ), whereA(r, ϕ)=inf|z|=r ϕ(z),B(r, ϕ)=sup|z|=r ϕ(z), andT(r, ϕ) is the Nevanlinna characteristics.  相似文献   
93.
The purpose of this paper is to investigate the asymptotic properties of the least squares estimates (L 2-estimates) and the least absolute deviation estimates (L 1-estimates) of the parameters of a nonlinear regression model subject to a set of equality and inequality restrictions, which has a long-range dependent stationary process as its stochastic errors. Then we will compare the asymptotic relative efficiencies of the above estimators.  相似文献   
94.
95.
96.
97.
In Shack–Hartmann wavefront sensor (SHWS), the behavior of the irradiance pattern produced by the micro-lens array is important for an accurate centroid estimation. In this paper, the behavior of a micro-lens array in SHWS is analyzed using Fourier optics, and reveals that in addition to the main, expected spots, secondary spots with smaller intensities also appeared as a result of diffraction by the small dimensions of the micro-lens and interference from the different micro-lenses. This result is confirmed by comparing with a irradiance pattern taken from an actual SHWS. The additional error in centroid estimation caused by these secondary spots is discussed and relationship to the parameters of the micro-lens of SHWS is analyzed.  相似文献   
98.
The vibrational dynamics of protein folding is analyzed in the framework of Tsallis statistics. We employ exact expressions for classical harmonic oscillators by considering the unnormalized constraints. As q→1, we show that these approximations agree with the result of Gaussian network model.  相似文献   
99.
The fusion evaporation reaction 122Sn(14N, 4n)132La was used to populate the high-spin states of 132La at the beam energy of 60 MeV. A new band consisting of mostly E2 transitions has been discovered. This band has the interesting links to the ground state 2- and the isomeric state 6-. A new transition of energy 351 keV connecting the low-spin states of the positive-parity band based on the πh 11/2 ⊗ νh 11/2 particle configuration, has been found. This has played a very important role in resolving the existing ambiguities and inconsistencies in the spin assignment of the band head. Received: 12 August 2002 / Accepted: 18 March 2003 / Published online: 7 May 2003  相似文献   
100.
The results of a numerical study are described in which the interactions of a primary shock wave with a secondary diaphragm in expansion tubes are taken into account. The developing wave pattern in the interacting process of the shock with a secondary diaphragm are visualized by many kinds of figures (e.g., the time-distance diagrams of the wave phenomena on the axis, the acoustic impedance contours, and the time histories of the pitot pressure on the axis), and the influences of the shape and rupture process of the diaphragm on the quality of the test gas are explored.  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