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   214141篇
  免费   1755篇
  国内免费   636篇
化学   103055篇
晶体学   3344篇
力学   9295篇
综合类   5篇
数学   22604篇
物理学   69066篇
综合类   9163篇
  2021年   1686篇
  2020年   1819篇
  2019年   2008篇
  2018年   2714篇
  2017年   2629篇
  2016年   3783篇
  2015年   2316篇
  2014年   3636篇
  2013年   9105篇
  2012年   7433篇
  2011年   8989篇
  2010年   6114篇
  2009年   5935篇
  2008年   8103篇
  2007年   8358篇
  2006年   7993篇
  2005年   7154篇
  2004年   6674篇
  2003年   5879篇
  2002年   5722篇
  2001年   6972篇
  2000年   5439篇
  1999年   4034篇
  1998年   3073篇
  1997年   3075篇
  1996年   2811篇
  1995年   2631篇
  1994年   2472篇
  1993年   2355篇
  1992年   2906篇
  1991年   2873篇
  1990年   2840篇
  1989年   2611篇
  1988年   2646篇
  1987年   2647篇
  1986年   2457篇
  1985年   3141篇
  1984年   3369篇
  1983年   2760篇
  1982年   2894篇
  1981年   2858篇
  1980年   2721篇
  1979年   2924篇
  1978年   2978篇
  1977年   2971篇
  1976年   3006篇
  1975年   2824篇
  1974年   2920篇
  1973年   2898篇
  1972年   1862篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Crystalline materials that are transparent in the vacuum UV spectral region and currently used have been reviewed. Transmission of crystals of solid solutions with the fluorite structure Ca1?x R xF2+x (R = Sc, Y, La, Yb, Lu) in the UV and vacuum UV spectral regions has been investigated. It is shown that application of different methods of purification of fluorides from some impurities can significantly improve the optical quality of fluoride multicomponent crystals in the short-wavelength spectral region.  相似文献   
12.
Unsteady motion in single-line flow-injection systems consisting of n tubular elements with valve or hydrodynamic injection is studied theoretically. A formula for the duration of the initial period of unsteady flow is derived. This initial period is much shorter than the mean residence time of the analyte in practical systems. It can therefore be neglected in mathematical modelling of such systems. Experimental data obtained with single-line systems with valve and hydrodynamic injection confirmed the validity of the theoretical equations.  相似文献   
13.
分子间的范德华力是十分微弱的,但可以说普遍的存在着,在很多体系中起着巨大的作用,在物理学、化学、生物学等学科中得到了广泛的研究。但怎样计算范德华力?如何考虑各种条件对范德华力的影响?  相似文献   
14.
In this study, a novel stepwise extraction method has been examined. The guest molecules housed between the helices of the clathrate δ form of syndiotactic polystyrene can be removed completely with this method. A systematic study of the preparation of a solvent‐free mesophase (emptied clathrate) membrane, its helical and residual solvent contents, and its structural transformations has been performed. In this first attempt, an enhancement in the TTGG helical content has been observed in the extracted membrane, and a conceptual mechanism is proposed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 269–273, 2003  相似文献   
15.
16.
17.
18.
The growth of the isolated (100) face of a KDP crystal at exposure of the phase boundary to the initial ultrasound field and a standing acoustic wave has been investigated. A significant growth response of this face, exposed to sound normally along the acoustic axis in the near zone of a piston-like half-wave vibrator with f = 20 kHz and tangentially in the pulsed two-frequency (f = 600 and 900 kHz) standing-wave mode, has been revealed. It is shown that the mechanisms of mass exchange enhancement in these acoustic modes are different. The results obtained show a fundamental possibility of controlling crystal growth and dissolution by varying the parameters of inhomogeneous acoustic field.  相似文献   
19.
The features of doping of KDP crystals with cerium ions and organocerium complexes with alizarin complexon and arsenazo III have been investigated. It is established that “direct” doping by introducing cerium salts into the initial solution cannot be implemented. The effect of organometallic complexes of cerium on the crystal growth has been studied. Organocerium complexes predominantly enter the prismatic or pyramidal growth sectors. It is shown that the complex arsenazo III + Ce blocks the growth of the prismatic sector. Cerium-doped KDP crystals exhibit a photoluminescence band peaking at the wavelength λmax= 350 nm.  相似文献   
20.
A new method was developed for studying voids and channels in crystal structures based on the Voronoi-Dirichlet partition of crystal space, and 822 structurally characterized ternary compounds Li p X q O r were analyzed for the first time. For these compounds, the dimensionality was determined and the migration patterns of channel systems capable of providing lithium-ion transport were constructed. The calculated coordinates of lithium atoms in the centers of the voids are consistent (within 0.4 ?) with the known structural data. Among these compounds, 113 compounds have infinite channel systems, 60 compounds (18 structural types, STs) have been described earlier in the literature as solid electrolytes, and 53 compounds (23 STs) can be considered as potential one-, two-, or three-dimensional ionic conductors (13, 3, and 7 STs, respectively). Original Russian Text ? N.A. Anurova, V.A. Blatov, G.D. Ilyushin, O.A. Blatova, A.K. Ivanov-Shitz, L.N. Dem’yanets, 2008, published in Kristallografiya, 2008, Vol. 53, No. 6, pp. 987–993.  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