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   203180篇
  免费   1473篇
  国内免费   431篇
化学   104971篇
晶体学   3394篇
力学   10275篇
综合类   10篇
数学   21876篇
物理学   64558篇
  2021年   1971篇
  2020年   2009篇
  2019年   2567篇
  2018年   3660篇
  2017年   3669篇
  2016年   4811篇
  2015年   2345篇
  2014年   4301篇
  2013年   8588篇
  2012年   6846篇
  2011年   8057篇
  2010年   6470篇
  2009年   6660篇
  2008年   7662篇
  2007年   7621篇
  2006年   6711篇
  2005年   5948篇
  2004年   5668篇
  2003年   5181篇
  2002年   5169篇
  2001年   5614篇
  2000年   4142篇
  1999年   3137篇
  1998年   2703篇
  1997年   2765篇
  1996年   2547篇
  1995年   2213篇
  1994年   2332篇
  1993年   2225篇
  1992年   2523篇
  1991年   2647篇
  1990年   2554篇
  1989年   2630篇
  1988年   2532篇
  1987年   2552篇
  1986年   2413篇
  1985年   3033篇
  1984年   3104篇
  1983年   2599篇
  1982年   2565篇
  1981年   2533篇
  1980年   2338篇
  1979年   2710篇
  1978年   2673篇
  1977年   2873篇
  1976年   2874篇
  1975年   2670篇
  1974年   2607篇
  1973年   2715篇
  1972年   2085篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
We investigate necessary and sufficient conditions under which one estimate of exponential type is valid for large deviation probabilities of sums of independent identically distributed random variables. Bibliography: 3 titles.  相似文献   
992.
Experimental data obtained by studying the effect of internal waves with known space-time parameters on the propagation of a 240-Hz tone signal and on the space-time interference structure of the sound field generated by a noiselike sound source are presented.  相似文献   
993.
The behavior of inorganic macrocomponents (Fe3 +, Fe2 +, Cu2 +, and Cl-) and organic additives (judged from the relative concentration of total carbon) in regeneration and reuse of spent etching solutions used in fabrication of copper type-plates was studied. The conditions of electrochemical and sorption stages of the regeneration process were discussed.  相似文献   
994.
995.
The influence of the sequence of Cu and Pd introduction into zeolite matrice when preparing Cu, Pd-zeolite catalysts on their acidity and degree of metal reduction was studied. The mutual influence of Cu and Pd on their reducibility was analyzed. The selectivity of Cu, Pd-zeolite catalysts in conversion of synthesis gas to different products was elucidated.  相似文献   
996.
N. Elgun  E. A. Davis 《Journal of Non》2003,330(1-3):226-233
Hydrogenated amorphous GaP films have been prepared by reactive rf sputtering. Infrared spectroscopy, optical transmission and reflection, photothermal deflection spectroscopy and dc conductivity have been studied to investigate the local bonding configurations, the optical absorption edges and the temperature dependence of the conductivity as a function of hydrogen content. The results are discussed and compared with the effects of hydrogenation on amorphous Si.  相似文献   
997.
The enthalpies and free energies of proton affinity (PA) were calculated by the PM3 method for 27 thiophenoxide anions. For thiophenols, linear correlation has been found between the PAs and the values of pK a measured by different authors in aqueous acetone, aqueous ethanol, and methanol media. The dependences found permit one to predict a priori the protolytic properties of thiophenols. The differential effects of aqueous ethanol media with different ethanol contents on thiophenol acidity were evaluated based on quantum-chemical data.Original Russian Text Copyright © 2004 by A. N. Pankratov and A. V. Shalabai__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 800–806, September–October, 2004.  相似文献   
998.
Liquid-vapor equilibria and azeotropy in isobutanol-n-butanol-butyl butenyl ether ternary system and in isobutanol-butyl butenyl ether and n-butanol-butyl butenyl ether binary systems were studied experimentally and calculated, as well as azeotropy in butyl alcohols-butyl butenyl ether-water systems under atmospheric and reduced pressure. Recovery of commercial butyl alcohols by distillation of alcohol-ether fractions was studied.  相似文献   
999.
Based on an analysis of experimental results and published data, the main elementary steps of the anionic coordination polymerization of butadiene rubber on a cobalt-containing catalyst in the presence of ethylene were found, and a mathematical model of the periodic process at an optimum water content was developed. The molecular-weight characteristics of the process depending on ethylene concentration were studied with the use of this model.  相似文献   
1000.
This is the report of neutrino and astroparticle physics working group at WHEPP-7. Discussions and work on CP violation in long baseline neutrino experiments, ultra high energy neutrinos, supernova neutrinos and water Cerenkov detectors are discussed.  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