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   1356203篇
  免费   25836篇
  国内免费   7722篇
化学   677385篇
晶体学   20434篇
力学   74860篇
综合类   107篇
数学   242580篇
物理学   374395篇
  2021年   13548篇
  2020年   15986篇
  2019年   16112篇
  2018年   12889篇
  2016年   28131篇
  2015年   20866篇
  2014年   30556篇
  2013年   74544篇
  2012年   38540篇
  2011年   35634篇
  2010年   37431篇
  2009年   39724篇
  2008年   35036篇
  2007年   30532篇
  2006年   36465篇
  2005年   29011篇
  2004年   30164篇
  2003年   28574篇
  2002年   29459篇
  2001年   29439篇
  2000年   25320篇
  1999年   22710篇
  1998年   21118篇
  1997年   21061篇
  1996年   21220篇
  1995年   19247篇
  1994年   18734篇
  1993年   18248篇
  1992年   18444篇
  1991年   18681篇
  1990年   17943篇
  1989年   17930篇
  1988年   17534篇
  1987年   17504篇
  1986年   16401篇
  1985年   22787篇
  1984年   24000篇
  1983年   20143篇
  1982年   21741篇
  1981年   20966篇
  1980年   20300篇
  1979年   20607篇
  1978年   21848篇
  1977年   21499篇
  1976年   21153篇
  1975年   19877篇
  1974年   19501篇
  1973年   19947篇
  1972年   14435篇
  1967年   12675篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The influence of an electrical field on the charge transfer in crystals with orbital degeneration is investigated. An expression is obtained for the current density in crystals with narrow d-conduction bands in transition metal compounds. As the electrical field intensity increases, a current density maximum is observed with a subsequent section of negative differential conductivity. The results of the investigation agree qualitatively with experimental data.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 14–18, February, 1989.  相似文献   
992.
Summary We have estimated and measured the daily thermal expansion of an oceanographic platform. This has been found negligible as far as the calibration of a satellite altimeter is concerned.  相似文献   
993.
Conclusions Complex compounds of bisacyl derivatives of diaminodibenzo-18-crown-6 ether are active catalysts of the two stages of the synthesis of poly(ethylene terephthalate).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2544–2547, November. 1987.  相似文献   
994.
995.
In this paper, by extending Kucera's idea to the function field case, we obtain several determinant formulas involving the real class number and the relative class number of any subfield of cyclotomic function fields. We also provide several examples using these determinant formulas.

  相似文献   

996.
A brief review of the potential functions used in the molecular dynamics modeling of liquid benzene is presented. The structural characteristics of liquid benzene obtained from the correlation distribution functions are discussed. It is demonstrated that, within the framework of this approach, the predicted structure of liquid benzene is virtually independent of the form of the potential used.  相似文献   
997.
Settling of a large solid particle in bioconvection flow caused by gyrotactic microorganisms is investigated. The particle is released from the top of the bioconvection chamber; its settling pattern depends on whether it is released in the centre of the bioconvection plume or at its periphery. The Chimera method is utilized; a subgrid is generated around a moving particle. The method suggested by Liu and Wang (Comput. Fluid 2004; 33 :223–255) is further developed to account for the presence of a moving boundary in the streamfunction‐vorticity formulation using the finite‐difference method. A number of cases for different release positions of the particle are computed. It is demonstrated that bioconvection can either accelerate or decelerate settling of the particle depending on the initial position of the particle relative to the plume centre. It is also shown that the particle impacts bioconvection plume by changing its shape and location in the chamber. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
998.
The structural relaxation time for series of various liquids (alkanes, aliphatic alcohols, and diols) are calculated from published data on the shear viscosity and the heat of evaporation per unit volume. Liquids having a 3D H-bond network (diols) are characterized by relaxation times one to two orders of magnitudes longer than those typical of liquids without such a network (alkanes and aliphatic alcohols).  相似文献   
999.
1000.
The reactions of 2,3,6,11-tetrahydroanthra[2,1-d]isothiazole-3,6,11-trione with dimethyl sulfate, benzyl chloride, and allyl bromide afforded the corresponding 2-alkyl-2,3,6,11-tetrahydroanthra[2,1-d]isothiazole-3,6,11-triones and 3-(alkoxy)-6,11-dihydroanthra[2,1-d]isothiazole-6,11-diones. The reactions of 2,3,6,11-tetrahydroanthra[2,1-d]isothiazole-3,6,11-trione and its S-oxide with a formaldehyde—secondary amine system yielded 2-[(alkylamino)methyl]-2,3,6,11-tetrahydroanthra[2,1-d]isothiazole-3,6,11-triones and 2-[(alkylamino)methyl]-3,6,11-trioxo-2,3,6,11-tetrahydroanthra[2,1-d]isothiazole 1-oxides, respectively.  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