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   582027篇
  免费   6354篇
  国内免费   1634篇
化学   314735篇
晶体学   9035篇
力学   25093篇
综合类   22篇
数学   66327篇
物理学   174803篇
  2021年   4772篇
  2020年   5404篇
  2019年   5873篇
  2018年   7355篇
  2017年   7340篇
  2016年   11278篇
  2015年   7079篇
  2014年   11075篇
  2013年   26983篇
  2012年   20274篇
  2011年   24955篇
  2010年   17551篇
  2009年   17332篇
  2008年   22664篇
  2007年   22442篇
  2006年   20878篇
  2005年   18728篇
  2004年   17293篇
  2003年   15403篇
  2002年   15121篇
  2001年   17247篇
  2000年   13094篇
  1999年   10297篇
  1998年   8453篇
  1997年   8235篇
  1996年   7931篇
  1995年   7187篇
  1994年   7054篇
  1993年   6709篇
  1992年   7778篇
  1991年   7810篇
  1990年   7473篇
  1989年   7322篇
  1988年   7424篇
  1987年   7273篇
  1986年   6873篇
  1985年   8983篇
  1984年   9114篇
  1983年   7285篇
  1982年   7434篇
  1981年   7447篇
  1980年   6869篇
  1979年   7508篇
  1978年   7680篇
  1977年   7658篇
  1976年   7453篇
  1975年   6850篇
  1974年   6797篇
  1973年   6766篇
  1972年   4775篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Dielectric properties of polymer-liquid crystal mixture, having constituent polymer, poly-butyl methacrylate (PBMA) and liquid crystal, cholesteryl nonanoate, are reported as a function of frequency and temperature. The measurement has been done in a temperature range of 300-375 K and frequency range of 100 Hz-10 MHz. The dielectric permittivity and dielectric loss shows significant changes with the addition of polymer molecules in liquid crystal. The significant feature of composite formation is that the pure liquid crystal and polymer do not show dielectric relaxation in the frequency range covered, while the composite shows relaxation peak at a particular frequency. The optical transmittance of pure liquid crystal and composite has also been measured and compared.  相似文献   
63.
Space-time directional Lyapunov exponents are introduced. They describe the maximal velocity of propagation to the right or to the left of fronts of perturbations in a frame moving with a given velocity. The continuity of these exponents as function of the velocity and an inequality relating them to the directional entropy is proved.  相似文献   
64.
The paper mentioned above is a contribution of the authors to Volume 18 (2002) of this journal, see . Recently, J. Domsta pointed out to us that the proof of Theorem 4.2 in that paper contains an error. The purpose of this addendum is to present a correct argument for it.  相似文献   
65.
A test for a function to be a solution of an elliptic PDE is given in terms of extensions, as solutions, from the boundaries inside the domains belonging to an isotopic family. It generalizes a result of Ehrenpreis for spheres moved along a straight line.

  相似文献   

66.
We give sufficient conditions for Sobolev and Lipschitz functions in terms of their lower scaled-oscillation. The sharpness of these conditions is shown by examples. Our examples also show that a Stepanov-type differentiability theorem does not hold under the boundedness assumption of the lower scaled-oscillation.

  相似文献   

67.
68.
The feasibility of an 84 GHz, 500 kW, CW gyrotron for ECRH on an experimental tokamak will be presented in this paper. Mode competition and mode selection procedures are carefully investigated by considering various candidate modes and the TE10,4 mode is chosen as the operating mode. A conventional cylindrical cavity resonator with weak input and output tapers and parabolic roundings is considered for interaction studies. Self-consistent, both single mode and time-dependent, calculations are carried out and power and efficiencies are computed for a typical set of beam parameters. The results show that an output power of well over 500 kW, CW and efficiency around 40% can be reached without a depressed collector.  相似文献   
69.
A new solvent-free sample preparation method using silver trifluoroacetate (AgTFA) was developed for the analysis of low molecular weight paraffins and microcrystalline waxes by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOFMS). Experiments show that spectral quality can be enhanced by dispersing AgTFA directly in liquid paraffins without the use of additional solvents. This preparation mixture is applied directly to the MALDI probe. Solid waxes could be examined by melting prior to analysis. The method also provides sufficiently reproducible spectra that peak area ratios between mono- and bicyclic alkane peaks indicated variations in the cycloalkane content of paraffin samples. Dehydrogenation of hydrocarbons observed during the desorption/ionization process was studied by analysis of alkane standards.  相似文献   
70.
In this paper a new state called odd-excited binomial state (OEBS) is introduced. It interpolates between the odd number state and the odd-excited coherent state. We discuss some statistical properties, such as the Glauber second-order correlation function and squeezing phenomenon (normal and amplitude-squared squeezing) for this state. The quasiprobability distribution functions (Husimi Q-function and Wigner W-function) are also examined.  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