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   301757篇
  免费   1430篇
  国内免费   344篇
化学   139115篇
晶体学   4689篇
力学   16940篇
综合类   3篇
数学   42789篇
物理学   99995篇
  2021年   3188篇
  2020年   3491篇
  2019年   4261篇
  2018年   6321篇
  2017年   6520篇
  2016年   8053篇
  2015年   3609篇
  2014年   6969篇
  2013年   12337篇
  2012年   10303篇
  2011年   12033篇
  2010年   10131篇
  2009年   10299篇
  2008年   11605篇
  2007年   11393篇
  2006年   10157篇
  2005年   8776篇
  2004年   8504篇
  2003年   7885篇
  2002年   8150篇
  2001年   7729篇
  2000年   6103篇
  1999年   4521篇
  1998年   4297篇
  1997年   4150篇
  1996年   3757篇
  1995年   3315篇
  1994年   3382篇
  1993年   3405篇
  1992年   3393篇
  1991年   3817篇
  1990年   3804篇
  1989年   3807篇
  1988年   3553篇
  1987年   3641篇
  1986年   3339篇
  1985年   3872篇
  1984年   4113篇
  1983年   3508篇
  1982年   3704篇
  1981年   3398篇
  1980年   3153篇
  1979年   3645篇
  1978年   3710篇
  1977年   3882篇
  1976年   3940篇
  1975年   3690篇
  1974年   3541篇
  1973年   3698篇
  1972年   3184篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
The results of optical study and quantum-chemical simulation of a conjugated organic system, 2-cyclooctylamino-5-nitropyridine (COANP)-fullerene, performed to determine its potential for application as a limiter of visible and near-IR laser radiation and as a material for diffraction elements in systems for reversible recording of optical information, are presented. Complexation between a COANP molecule and fullerene is considered as one of the main mechanisms responsible for the corresponding properties of this system. For the first time, nonlinear optical characteristics of COANP-C60 and COANP-C70 systems are comparatively studied and the intermolecular interaction between a COANP molecule and fullerene is analyzed on the quantum-chemical level.  相似文献   
112.
    
  相似文献   
113.
114.
The kinetics of formation of an anomalous phase from a solution with a small 3He impurity was studied in the temperature range 0.2–0.7 K up to a supersaturation of ~30 mbar. The phase diagram was determined for normal and anomalous growths. It is found that, in the presence of impurities, the formation of a fast-growing state is retarded. This experimental fact indicates that the dissipative processes in fluids have an appreciable effect on the phase formation kinetics. The retardation is, possibly, caused by the direct interaction of an impurity with the crystal surface.  相似文献   
115.
We construct an integral Newton-type interpolation polynomial with a continual set of nodes. This interpolant is unique and preserves an operator polynomial of the corresponding degree.  相似文献   
116.
117.
118.
The kinetics of hydrogen peroxide decomposition in a guaiacol solution, catalyzed by potassium hexacyanoferrate(II), were studied. The reaction mainly follows the pathway of guaiacol hydroxylation. The reaction order is 1 with respect to H2O2, 0.5 with respect to hexacyanoferrate, and from 0.4 to 0 with respect to guaiacol (the latter parameter decreases with increasing guaiacol concentration). The apparent activation energy is 105 kJ mol- 1. A kinetic scheme of the process was proposed. An expression consistent with the experiment was obtained for the rate of hydrogen peroxide decomposition in the presence of guaiacol, catalyzed by hexacyanoferrate(II).  相似文献   
119.
Methods and schemes to inspect the EUV mirror shape are developed on the basis of a point diffraction interferometer with computer processing of interferograms. A measurement accuracy to within 0.001 of a wavelength in the visual range is achieved.  相似文献   
120.
The kinetics of the formation of poly(carbosiloxane), as well as of alkyl-substituted poly(siloxane), by Karstedt's catalyst catalyzed hydrosilylation were investigated. Linear poly(carbosiloxane), poly[(1,1,3,3-tetramethyldisiloxanyl)ethylene], (PTMDSE), was obtained by hydrosilylation of 1,3-divinyltetramethyldisiloxane (DVTMDS) and 1,1,3,3-tetramethyldisiloxane (TMDS), while alkyl-substituted poly(siloxane), poly(methyldecylsiloxane), (PMDS), was synthesized by hydrosilylation of poly(methylhydrosiloxane) (PMHS) and 1-decene. To investigate the kinetics of PTMDSE formation, two series of experiments were performed at reaction temperatures ranging from 25 to 56 °C and with catalyst concentrations ranging from 7.0 × 10−6 to 3.1 × 10−5 mol Pt/mol CHCH2. A series of experiments was performed at reaction temperatures ranging from 28 to 48 °C, with catalyst concentrations of 7.0 ×10−6 mol of Pt per mol of CHCH2, when kinetics of PMDS formation was investigated. All reactions were carried out in bulk, with equimolar amounts of the reacting Si H and CHCH2 groups. The course of the reactions was monitored by following the disappearance of the Si H bands using quantitative infrared spectroscopy. The results obtained showed typical first order kinetics for the PTMDSE formation, consistent with the proposed reaction mechanism. In the case of PMDS an induction period occurred at lower reaction temperatures, but disappeared at 44 °C and the rate of Si H conversion also started to follow the first-order kinetics. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2246–2258, 2007  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