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   468170篇
  免费   5756篇
  国内免费   1489篇
化学   255694篇
晶体学   6870篇
力学   19416篇
综合类   14篇
数学   55834篇
物理学   137587篇
  2021年   4152篇
  2020年   4696篇
  2019年   5045篇
  2018年   6217篇
  2017年   6098篇
  2016年   9687篇
  2015年   6254篇
  2014年   9407篇
  2013年   21699篇
  2012年   17523篇
  2011年   21394篇
  2010年   14688篇
  2009年   14403篇
  2008年   19585篇
  2007年   19360篇
  2006年   18060篇
  2005年   16279篇
  2004年   14989篇
  2003年   13109篇
  2002年   12874篇
  2001年   13885篇
  2000年   10543篇
  1999年   8306篇
  1998年   6926篇
  1997年   6706篇
  1996年   6509篇
  1995年   5771篇
  1994年   5759篇
  1993年   5530篇
  1992年   6131篇
  1991年   6203篇
  1990年   5900篇
  1989年   5691篇
  1988年   5696篇
  1987年   5605篇
  1986年   5284篇
  1985年   6918篇
  1984年   7013篇
  1983年   5586篇
  1982年   5713篇
  1981年   5635篇
  1980年   5246篇
  1979年   5592篇
  1978年   5727篇
  1977年   5602篇
  1976年   5537篇
  1975年   5110篇
  1974年   5051篇
  1973年   5001篇
  1972年   3546篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
The main transitions of cellulose fatty esters with different degrees of substitution (DSs) were investigated with dynamic mechanical thermal analysis. Two distinct main relaxations were observed in partially substituted cellulose esters (PSCEs). They were attributed to the glass‐transition temperature and to the chain local motion of the aliphatic substituents. The temperatures of both transitions decreased when DS or the number of carbon atoms (n) of the acyl substituent increased. Conversely, all the transitions of fully substituted cellulose esters occurred within a narrow temperature range, and they did not vary significantly with n. This phenomenon was explained by the formation of a crystalline phase of the fatty substituents. The presence of few residual OH groups in PSCEs was responsible for a large increase in the storage bending modulus, and it eliminated the effect of n on damping. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 281–288, 2003  相似文献   
112.
In this paper, we find the approximate solution of a second order nonlinear partial differential equation on a simple connected region inR 2. We transfer this problem to a new problem of second order nonlinear partial differential equation on a rectangle. Then, we transformed the later one to an equivalent optimization problem. Then we consider the optimization problem as a distributed parameter system with artificial controls. Finally, by using the theory of measure, we obtain the approximate solution of the original problem. In this paper also the global error inL 1 is controlled.  相似文献   
113.
An arbitrary operator-valued function from the generalized Shur class is realized as the transfer function of a minimal optimal and minimal *-optimal dissipative scattering system with the Pontryagin state space. These results generalize Arov's results for the case of the Hilbert state space. Bibliography: 11 titles.  相似文献   
114.
115.
116.
The projection approach is applied to construct and investigate an operator-difference scheme for fluid dynamics in Lagrangean variables which has first-order local approximation in the axisymmetric case near the symmetry axis. The scheme also has operator properties that make it suitable for rederiving and substantiating previous results, methods, and algorithms.  相似文献   
117.
Journal of Nanoparticle Research - It was shown that the thermoelastic martensite transformation B2 ? B19 inside nanoparticles surrounded by amorphous matrix in Ni–Ti–Cu alloys as...  相似文献   
118.
119.
120.
We report on the effect of commercially important polysaccharides (maltodextrins with variable dextrose equivalent (Paselli SA-2, MD-6 and MD-10) on the surface activity at the air–water interface of small-molecule surfactants (sms), possessing different hydrophobic–lipophilic balance ((SSL (Na+), the main component is a sodium salt of stearol–lactoyl lactic acid, and PGE (080), polyglycerol ester of C18 fatty acid), and widely used in food products. A marked change of the surface activity of sms was found in the presence of maltodextrins by tensiometry. The combined data of laser multiangle light scattering and mixing calorimetry have suggested that this result is governed by specific complex formation between maltodextrins and sms in aqueous medium. Measurements have been made of the molar mass, the second virial coefficient and the enthalpy of intermolecular interactions in aqueous solutions. The implication of a degree of polymerization of maltodextrins in this phenomenon was shown. The interrelation between the molecular parameters of the formed complexes and their surface activity at the air–water interface has been revealed and 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