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   53110篇
  免费   2983篇
  国内免费   2276篇
化学   30930篇
晶体学   836篇
力学   2519篇
综合类   189篇
数学   5281篇
物理学   18614篇
  2022年   572篇
  2021年   828篇
  2020年   915篇
  2019年   922篇
  2018年   976篇
  2017年   923篇
  2016年   1473篇
  2015年   1146篇
  2014年   1607篇
  2013年   2818篇
  2012年   2983篇
  2011年   3404篇
  2010年   2469篇
  2009年   2308篇
  2008年   2650篇
  2007年   2458篇
  2006年   2330篇
  2005年   2098篇
  2004年   1848篇
  2003年   1620篇
  2002年   1646篇
  2001年   1814篇
  2000年   1393篇
  1999年   1171篇
  1998年   878篇
  1997年   834篇
  1996年   758篇
  1995年   704篇
  1994年   609篇
  1993年   550篇
  1992年   608篇
  1991年   593篇
  1990年   566篇
  1989年   507篇
  1988年   516篇
  1987年   475篇
  1986年   427篇
  1985年   493篇
  1984年   493篇
  1983年   365篇
  1982年   401篇
  1981年   390篇
  1980年   320篇
  1979年   401篇
  1978年   376篇
  1977年   392篇
  1976年   390篇
  1975年   340篇
  1974年   319篇
  1973年   334篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
程愿应  王又青  胡进  李家熔 《物理学报》2004,53(8):2576-2582
根据有限元法单元划分的思想,提出了一种新颖的模拟光腔模式及光束传输的特征向量法. 该方法的关键之处在于基于衍射积分理论构造了一种新的光束传输矩阵,通过求解特征矩阵方程可一次性得到谐振腔的一系列特征向量,每一列特征向量即代表了腔镜上光场的一个确定模式的振幅及相位分布. 并可采用该方法模拟光场传输到腔内或腔外任意地方的场分布. 该方法将传统方法中大量的迭代过程转化成为本征积分方程特征向量的求解过程,并与初值取值无关,且可一次性求得多个模式分布,从而可方便地分析谐振腔的模式鉴别能力. 特征向量法对圆形镜共焦 关键词: 谐振腔 特征向量法 模式分布  相似文献   
122.
The adsorption of polar organic substances (methanol, pyridine, and acetonitrile) and water was studied from the vapor phase on microporous adsorbent prepared by the substitution of polyhydroxyaluminum ions for the sodium ions of natural montmorillonite clay. The differential isosteric heats of adsorption of these substances were calculated and analyzed in a wide range of fillings.  相似文献   
123.
Baker‘s yeast mediated reduction of optically active diketone is described. The two keto groups are efficiently differentiated and the ee value of the recovered material is considerably raised. It affords highly optically active key intermediates efficiently for the synthesis of natural polyhydroxylated agarofuran products.  相似文献   
124.
A Glaser coupling reaction of terminal alkynes in the presence of nickel chloride withoutany organics and bases in hot water has been developed, which produces the correspondinghomo-coupling products in good yields.  相似文献   
125.
In this paper, a model of a linear multilevel programming problem with dominated objective functions (LMPPD(l)) is proposed, where multiple reactions of the lower levels do not lead to any uncertainty in the upper-level decision making. Under the assumption that the constrained set is nonempty and bounded, a necessary optimality condition is obtained. Two types of geometric properties of the solution sets are studied. It is demonstrated that the feasible set of LMPPD(l) is neither necessarily composed of faces of the constrained set nor necessarily connected. These properties are different from the existing theoretical results for linear multilevel programming problems.  相似文献   
126.
127.
In this paper, we prove convergence rates for spherical spline Hermite interpolation on the sphere Sd−1 via an error estimate given in a technical report by Luo and Levesley. The functionals in the Hermite interpolation are either point evaluations of pseudodifferential operators or rotational differential operators, the desirable feature of these operators being that they map polynomials to polynomials. Convergence rates for certain derivatives are given in terms of maximum point separation.  相似文献   
128.
Let X be a (real or complex) Banach space with dimension greater than 2 and let B0(X) be the subspace of B(X) spanned by all nilpotent operators on X. We get a complete classification of surjective additive maps Ф on B0(X) which preserve nilpotent operators in both directions. In particular, if X is infinite-dimensional, we prove that Ф has the form either Ф(T) = cATA^-1 or Ф(T) = cAT'A^-1, where A is an invertible bounded linear or conjugate linear operator, c is a scalar, T' denotes the adjoint of T. As an application of these results, we show that every additive surjective map on B(X) preserving spectral radius has a similar form to the above with |c| = 1.  相似文献   
129.
130.
We study condensation of ethanol-hexanol vapour by numerical solution of kinetic equations. The number of droplets formed in unit volume is computed within self-consistent classical model. It is shown that formation of ethanol-rich droplets prevails at the initial stage of nucleation process, but in the stationary state formation of droplets near the saddle point (on cluster formation energy surface) plays the dominant role. Presented at the 6th Joint Seminar “Development of Materials Science in Research and Education”, Karlštejn, Czech Republic, 17–19 September 1996. This work was supported by Grant No. A1010615 of the Grant Agency of the Academy of Sciences of the Czech Republic.  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