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   273975篇
  免费   3909篇
  国内免费   871篇
化学   148673篇
晶体学   3818篇
力学   10581篇
综合类   2篇
数学   32705篇
物理学   82976篇
  2020年   2203篇
  2019年   2339篇
  2018年   2851篇
  2017年   2772篇
  2016年   4694篇
  2015年   3337篇
  2014年   4719篇
  2013年   12941篇
  2012年   9477篇
  2011年   11682篇
  2010年   7430篇
  2009年   7176篇
  2008年   10545篇
  2007年   10670篇
  2006年   9734篇
  2005年   9050篇
  2004年   7940篇
  2003年   7010篇
  2002年   6881篇
  2001年   7772篇
  2000年   5919篇
  1999年   4602篇
  1998年   3894篇
  1997年   3890篇
  1996年   3718篇
  1995年   3490篇
  1994年   3368篇
  1993年   3488篇
  1992年   3706篇
  1991年   3631篇
  1990年   3450篇
  1989年   3373篇
  1988年   3431篇
  1987年   3288篇
  1986年   3163篇
  1985年   4362篇
  1984年   4514篇
  1983年   3732篇
  1982年   4079篇
  1981年   3992篇
  1980年   3836篇
  1979年   3839篇
  1978年   4092篇
  1977年   3903篇
  1976年   4070篇
  1975年   3640篇
  1974年   3764篇
  1973年   4081篇
  1972年   2443篇
  1971年   1899篇
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
251.
The pure state space of Quantum Mechanics is investigated as Hermitian Symmetric Kähler manifold. The classical principles of quantum mechanics (Quantum Superposition Principle, Heisenberg Uncertainty Principle, Quantum Probability Principle) and Spectral Theory of observables are discussed in this non-linear geometrical context.  相似文献   
252.
For more than 25 years production has helped to sharpen our understanding of QCD. In proton induced reaction some observations are rather well understood while others are still unclear. The current status of the theory of production will be sketched, paying special attention to the issues of formation time and re-interaction in a nuclear medium.  相似文献   
253.
254.
Mutual–temporal coherence of the supercontinuum (SC) generation has been experimentally investigated using a diffraction grating based interferometer. A broadband SC generation was produced in a pyrex glass plate with a 1.6-μm coherence length at 550-nm center wavelength. The degree of mutual coherence of 0.34 was measured for a wavefront shift for zero and first diffraction orders of half of the beam diameter. A design of SC source with the capability of manipulating the amplitudes and phases of optical frequency components within the SC pulse is presented for coherence applications.  相似文献   
255.
256.
We have analyzed the methyl fluoride RQ(J,0)Q branch lines located near 1475 cm−1 using a simultaneous multi-spectrum fitting technique. In this analysis we have used previously recorded diode-laser data in which we collected many data points covering only one or two Q branch lines in a particular run. The analysis consists of simultaneously fitting 57 spectra collected with numerous pressure and path length conditions for all absorption lines. The data are concatenated to create one continuous spectrum of the Q branch. We have determined the intensity and self-broadened widths at 296 K for 23 RQ(J,0) lines.  相似文献   
257.
Thin films of Ti1−xCoxO2 (x=0 and 0.03) have been prepared on sapphire substrates by spin-on technique starting from metalorganic precursors. When heat treated in air at 550 and 700 °C, respectively, these films present pure anatase and rutile structures as shown both by X-ray diffraction and Raman spectroscopy. Optical absorption indicate a high degree of transparency in the visible region. Such films show a very small magnetic moment at 300 K. However, when the anatase and the rutile films are annealed in a vacuum of 1×10−5 Torr at 500 and 600 °C, respectively, the magnetic moment, at 300 K, is strongly enhanced reaching 0.36μB/Co for the anatase sample and 0.68μB/Co for the rutile one. The ferromagnetic Curie temperature of these samples is above 350 K.  相似文献   
258.
The results of experimental investigations on thermal nonequilibrium ionization in CO2: N2: He mixtures are presented. Measurements of electron density, ne, in vibrationally excited nitrogen were made in a supersonic flow with different CO2 contents as well as in a CO2: N2: He = 1 : 5 : 4 mixture laser gas. The mixtures were heated in a shock tube and expanded through a supersonic nozzle. Furthermore, supersonic mixing of N2 and CO2 + He was used in some experiments. The measured values of ne in the plenum chamber and in the supersonic nozzle are reported, and the processes responsible for nonequilibrium ionization in a laser-active medium are discussed.  相似文献   
259.
    
3-[4-(Azidocarbonyl)]phenylsydnone (2) obtained from 3-(4-hydrazinocarbonyl) phenylsydnone (1) on Curtius rearrangement with alcohols, water and amines afforded the corresponding carbamates (3a-h), 4,4′-(sydnone-3-yl) diphenyl urea (4) and 4-(heterocyclyl)phenyl ureas (5a-l). Compounds (5a-l) on one-pot ring conversion yielded the 1,3,4-oxadiazolin-2-one derivatives (6a-l), which on reaction with N2H4 gave the 4-amino-1,2,4-triazolin-3-ones (7a-l). All these compounds exhibited moderate antimicrobial activity against the few microbes tested. The carbamates have been found to be more toxic against fourth instar larvae ofAedes aegypti, in particular, then-butyl derivative (3e).  相似文献   
260.
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