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   222180篇
  免费   1835篇
  国内免费   657篇
化学   123066篇
晶体学   3293篇
力学   8513篇
综合类   6篇
数学   24024篇
物理学   65770篇
  2021年   1852篇
  2020年   2102篇
  2019年   2412篇
  2018年   3327篇
  2017年   3213篇
  2016年   4511篇
  2015年   2565篇
  2014年   4026篇
  2013年   9604篇
  2012年   7377篇
  2011年   9015篇
  2010年   6354篇
  2009年   6133篇
  2008年   8584篇
  2007年   8651篇
  2006年   8064篇
  2005年   7356篇
  2004年   6479篇
  2003年   5917篇
  2002年   5704篇
  2001年   6024篇
  2000年   4743篇
  1999年   3505篇
  1998年   3056篇
  1997年   3070篇
  1996年   2878篇
  1995年   2373篇
  1994年   2459篇
  1993年   2499篇
  1992年   2630篇
  1991年   2694篇
  1990年   2590篇
  1989年   2557篇
  1988年   2487篇
  1987年   2462篇
  1986年   2378篇
  1985年   3079篇
  1984年   3226篇
  1983年   2582篇
  1982年   2854篇
  1981年   2725篇
  1980年   2524篇
  1979年   2735篇
  1978年   2850篇
  1977年   2880篇
  1976年   2845篇
  1975年   2700篇
  1974年   2676篇
  1973年   2818篇
  1972年   1886篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
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   
52.
53.
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   
54.
55.
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   
56.
57.
58.
Fix integers m, n such that 1 ≤ mn ? 3. Let X ? Pn be an integral non-degenerate m-dimensional variety. Assume either char(K) = 0 or char(K) > deg(X). Here we prove that all general 0-dimensional sections of X containing a tangent vector to a smooth point of X are protectively equivalent if and only if n ? m + 1 ≤ deg(X) ≤ n ? m + 2.  相似文献   
59.
A semiclassical theory of electromagnetically induced transparency in a Bose-Einstein condensate is considered. A nonlinear Schrödinger equation that describes the interaction of the Bose-Einstein condensate with an electromagnetic field is derived. An analysis of the obtained solutions to this equation demonstrates a decrease in the group velocity of the light pulse.  相似文献   
60.
We construct commuting rank 2 formally self-adjoint ordinary differential operators corresponding to a curve of genus 2.  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