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   3739篇
  免费   97篇
  国内免费   16篇
化学   2573篇
晶体学   17篇
力学   84篇
数学   660篇
物理学   518篇
  2021年   48篇
  2020年   39篇
  2019年   45篇
  2018年   44篇
  2017年   43篇
  2016年   54篇
  2015年   72篇
  2014年   78篇
  2013年   195篇
  2012年   202篇
  2011年   211篇
  2010年   124篇
  2009年   115篇
  2008年   218篇
  2007年   199篇
  2006年   204篇
  2005年   160篇
  2004年   157篇
  2003年   125篇
  2002年   120篇
  2001年   62篇
  2000年   38篇
  1999年   24篇
  1998年   25篇
  1997年   28篇
  1996年   54篇
  1995年   36篇
  1994年   39篇
  1993年   44篇
  1992年   34篇
  1991年   36篇
  1990年   33篇
  1989年   37篇
  1988年   43篇
  1987年   26篇
  1985年   57篇
  1984年   58篇
  1983年   36篇
  1982年   63篇
  1981年   55篇
  1980年   35篇
  1979年   50篇
  1978年   48篇
  1977年   45篇
  1976年   42篇
  1975年   29篇
  1974年   39篇
  1973年   48篇
  1972年   25篇
  1971年   24篇
排序方式: 共有3852条查询结果,搜索用时 62 毫秒
1.
2.
Optics and Spectroscopy - Scattering of light by disordered structures is normally detrimental to their applicability in many optoelectronic devices. However, some micro and nanostructures are...  相似文献   
3.
In this paper, we investigate the evolution of joint invariants under invariant geometric flows using the theory of equivariant moving frames and the induced invariant discrete variational complex. For certain arc length preserving planar curve flows invariant under the special Euclidean group , the special linear group , and the semidirect group , we find that the induced evolution of the discrete curvature satisfies the differential‐difference mKdV, KdV, and Burgers' equations, respectively. These three equations are completely integrable, and we show that a recursion operator can be constructed by precomposing the characteristic operator of the curvature by a certain invariant difference operator. Finally, we derive the constraint for the integrability of the discrete curvature evolution to lift to the evolution of the discrete curve itself.  相似文献   
4.
An abstract scheme using particular types of relations on filters leads to general unifying results on stability under supremum and product of local topological properties. We present applications for Fréchetness, strong Fréchetness, countable tightness and countable fan-tightness, some of which recover or refine classical results, some of which are new. The reader may find other applications as well.  相似文献   
5.
It is shown that, if t is an integer ≥3 and not equal to 7 or 8, then there is a unique maximal graph having the path Pt as a star complement for the eigenvalue ?2. The maximal graph is the line graph of Km,m if t = 2m?1, and of Km,m+1 if t = 2m. This result yields a characterization of L(G ) when G is a (t + 1)‐vertex bipartite graph with a Hamiltonian path. The graphs with star complement PrPs or PrCs for ?2 are also determined. © 2003 Wiley Periodicals, Inc. J Graph Theory 43: 137–149, 2003  相似文献   
6.
7.
Generalizations of the Nikodym boundedness and Vitali–Hahn–Saks theorems for scalar-valued measures on rings of sets that are in general not σ-rings are presented. As a consequence, the rings of subsets of N with density zero and uniform density zero are shown to have the Nikodym property. In addition, vector measure generalizations of the Vitali–Hahn–Saks theorem are given.  相似文献   
8.
Random copolymers of poly{(methacrylamide)-co-(vinyl trimethoxysilane)} and poly{(methacrylic acid)-co-(vinyl trimethoxysilane)} were synthesized via a free radical polymerization reaction. Acid catalyzed sol-gel process of tetraethylorthosilicate (TEOS) with aforementioned polymers in the presence of methyl xanthine class of alkaloid like caffeine resulted in the formation of highly transparent monoliths. Solvent extraction of the template leaves behind the recognition sites intact with high selectivity towards the print molecule. The ionic and non-specific adsorptions, which are considered to be the main disadvantages of the molecularly imprinted polymers (MIP), are prevented to a considerable extent by the end capping of surface silanol groups. The template binding efficiencies of MIP were determined by HPLC analysis.  相似文献   
9.
This study critically examines the similarities and differences between poly(ethylene oxide) (PEO) stabilized latices of polynorbornene and polybutadiene. Features such as the kinetics of copolymerization of norbornene and cyclooctadiene with a macromonomer of PEO, the particles' size and morphology, the type of copolymer formed, and the stability of these latices were investigated and the results obtained are considered. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2705–2716, 2004  相似文献   
10.
An equation for the kinetics of partial drop spreading is proposed. This equation was empirically derived from experimental data for the spreading kinetics of partially wetting liquids in terms of the wet area versus time. The equation has the form of an exponential power law (EPL), and transforms into the well-known power law for complete wetting, when the equilibrium contact angle approaches zero. The EPL fits very well available experimental data. To lend additional support to the validity of this generalized equation, it will be demonstrated that when it is transformed to present the dynamic contact angle (DCA), it fits very well DCA experimental data for other wetting processes, such as capillary flow and tape coating.  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