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   431941篇
  免费   3267篇
  国内免费   1458篇
化学   213864篇
晶体学   6407篇
力学   21195篇
综合类   9篇
数学   71936篇
物理学   123255篇
  2020年   3118篇
  2019年   3534篇
  2018年   14775篇
  2017年   14599篇
  2016年   12614篇
  2015年   4763篇
  2014年   6689篇
  2013年   16106篇
  2012年   15277篇
  2011年   24047篇
  2010年   15565篇
  2009年   15780篇
  2008年   19703篇
  2007年   21757篇
  2006年   12784篇
  2005年   12563篇
  2004年   11744篇
  2003年   11235篇
  2002年   10053篇
  2001年   10343篇
  2000年   8078篇
  1999年   6071篇
  1998年   5239篇
  1997年   5152篇
  1996年   4889篇
  1995年   4264篇
  1994年   4277篇
  1993年   4215篇
  1992年   4549篇
  1991年   4591篇
  1990年   4460篇
  1989年   4390篇
  1988年   4307篇
  1987年   4306篇
  1986年   4076篇
  1985年   5311篇
  1984年   5524篇
  1983年   4652篇
  1982年   5001篇
  1981年   4730篇
  1980年   4530篇
  1979年   4846篇
  1978年   5007篇
  1977年   4915篇
  1976年   4972篇
  1975年   4739篇
  1974年   4666篇
  1973年   5003篇
  1972年   3310篇
  1971年   2824篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
The class of previously found stationary axisymmetric perfect fluid solutions of Einstein's equations is written inh-orthogonal coordinates,h being a space-like coordinate. Matching of a big number of solutions of the class with each other seems to be possible for a proper choice of some parameters. The exterior solutions of the class are matched explicitly with interior solutions. Also, interior solutions are matched explicitly with each other.  相似文献   
103.
In this paper, we study the consistency of a variant of fractionalstep Runge–Kutta methods. These methods are designed tointegrate efficiently semi-linear multidimensional parabolicproblems by means of linearly implicit time integration processes.Such time discretization procedures are also related to a splittingof the space differential operator (or the spatial discretizationof it) as a sum of ‘simpler’ linear differentialoperators and a nonlinear term.  相似文献   
104.
105.
106.
The known plant growth regulator, Al'den [1-(3,7-dimethyloctyl)-1-allylpiperidinium bromide], and also 1-(3,7-dimethyloctyl)-1-methylpiperidinium iodide were synthesized by treatment with allyl bromide and methyl iodide, respectively, of exhaustively hydrogenated 1-nerylpiperidine which was obtained by anionic telomerization of isoprene with piperidine. Various quaternary ammonium salts having a terpene sub- stituent with unnatural dimethyloctane skeleton, which effectively stimulate florification of Aster Chinensis L., were prepared by the action of alkyl halides on telomerization products derived from isoprene and piperidine or morpholine in the presence of palladium complexes.  相似文献   
107.
The sub-millisecond protonation dynamics of the chromophore in S65T mutant form of the green fluorescent protein (GFP) was tracked after a rapid pH jump following laser-induced proton release from the caged photolabile compoundo-nitrobenzaldehyde. Following a jump in pH from 8 to 5 (which is achieved within 2 μs), the fluorescence of S65T GFP decreased as a single exponential with a time constant of ∼90 μs. This decay is interpreted as the conversion of the deprotonated fluorescent GFP chromophore to a protonated non-fluorescent species. The protonation kinetics showed dependence on the bulk viscosity of the solvent, and therefore implicates bulk solvent-controlled protein dynamics in the protonation process. The protonation is proposed to be a sequential process involving two steps: (a) proton transfer from solvent to the chromophore, and (b) internal structural rearrangements to stabilize a protonated chromophore. The possible implications of these observations to protein dynamics in general is discussed  相似文献   
108.
109.
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   
110.
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