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   1316781篇
  免费   25720篇
  国内免费   7720篇
化学   654505篇
晶体学   19993篇
力学   74016篇
综合类   104篇
数学   238807篇
物理学   362796篇
  2021年   13470篇
  2020年   15884篇
  2019年   16026篇
  2016年   27234篇
  2015年   20529篇
  2014年   30338篇
  2013年   74149篇
  2012年   36773篇
  2011年   32334篇
  2010年   35665篇
  2009年   38255篇
  2008年   32164篇
  2007年   27280篇
  2006年   35190篇
  2005年   26611篇
  2004年   28648篇
  2003年   27236篇
  2002年   28603篇
  2001年   27794篇
  2000年   24420篇
  1999年   22305篇
  1998年   20911篇
  1997年   20913篇
  1996年   21017篇
  1995年   19111篇
  1994年   18531篇
  1993年   18075篇
  1992年   17957篇
  1991年   18257篇
  1990年   17442篇
  1989年   17541篇
  1988年   17054篇
  1987年   17070篇
  1986年   16010篇
  1985年   22405篇
  1984年   23688篇
  1983年   19900篇
  1982年   21594篇
  1981年   20839篇
  1980年   20162篇
  1979年   20281篇
  1978年   21651篇
  1977年   21227篇
  1976年   20935篇
  1975年   19646篇
  1974年   19271篇
  1973年   19783篇
  1972年   14275篇
  1968年   12093篇
  1967年   12479篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
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   
982.
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   
983.
984.
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   

985.
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   
986.
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   
987.
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   
988.
989.
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   
990.
N-Bromoamides catalyze effectively the aziridination of electron-deficient as well as electron-rich olefins using chloramine-T (N-chloro-N-sodio-p-toluenesulfonamide) as a nitrogen source under ambient conditions to afford the corresponding aziridines in good to excellent yields.  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