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   17351篇
  免费   428篇
  国内免费   425篇
化学   2079篇
晶体学   115篇
力学   124篇
综合类   38篇
数学   13974篇
物理学   1874篇
  2023年   34篇
  2022年   62篇
  2021年   104篇
  2020年   89篇
  2019年   393篇
  2018年   428篇
  2017年   255篇
  2016年   166篇
  2015年   197篇
  2014年   431篇
  2013年   1016篇
  2012年   554篇
  2011年   938篇
  2010年   839篇
  2009年   1263篇
  2008年   1253篇
  2007年   1284篇
  2006年   1082篇
  2005年   794篇
  2004年   634篇
  2003年   491篇
  2002年   426篇
  2001年   399篇
  2000年   398篇
  1999年   437篇
  1998年   386篇
  1997年   302篇
  1996年   368篇
  1995年   351篇
  1994年   365篇
  1993年   280篇
  1992年   246篇
  1991年   164篇
  1990年   167篇
  1989年   193篇
  1988年   123篇
  1987年   126篇
  1986年   122篇
  1985年   171篇
  1984年   135篇
  1983年   77篇
  1982年   123篇
  1981年   89篇
  1980年   100篇
  1979年   73篇
  1978年   77篇
  1977年   51篇
  1976年   49篇
  1974年   27篇
  1973年   28篇
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
1.
2.
3.
We relate the distribution characters and the wave front sets of unitary representation for real reductive dual pairs of type I in the stable range.  相似文献   
4.
Two new divalent copper (C1) and zinc (C2) chelates having the formulae [M(PIMC)2] (where M = Cu(II), Zn(II) and PIMC = Ligand [(E)-3-(((3-hydroxypyridin-2-yl)imino)methyl)-4H-chromen-4-one] were obtained and characterized by several techniques. Structures and geometries of the synthesized complexes were judged based on the results of alternative analytical and spectral tools supporting the proposed formulae. IR spectral data confirmed the coordination of the ligands to the copper and zinc centers as monobasic tridentate in the enol form. Thermal analysis, UV-Vis spectra and magnetic moment confirmed the geometry around the copper center to be tetrahedral, square pyramidal and octahedral. Study of the binding ability of the synthesized compounds with Circulating tumor DNA (CT-DNA) bas been evaluated applying UV-Vis spectral titration and viscosity measurements. The copper and zinc oxides were achieved from the copper and zinc nano-particles structures Schiff base complexes as the raw material after calcination for 5 hr at 600°C. On the other hand, synthesized of C1 and C2 NPs were used as suitable precursors to the preparation of CuO and ZnO NPs. Finally, the synthesized of the two complexes exhibited enhanced activity against the tested bacterial (Staphylococcus aureus and Escherichia Coli) and fungal strains (Candida albicans and Aspergillus fumigatus) as compared to HPIMC. Among all these synthesized compounds, C1 exhibits good cleaving ability compared to other newly synthesized C2.  相似文献   
5.
A manifold that contains small perturbations will induce a perturbed partial differential equation. The partial differential equation that we select is the Poisson equation – in order to explore the interplay between the geometry of the manifold and the perturbations. Specifically, we show how the problem of symmetry determination, for higher-order perturbations, can be elegantly expressed via geometric conditions.  相似文献   
6.
We show the short-time existence and nonlinear stability of vortex sheets for the nonisentropic compressible Euler equations in two spatial dimensions, based on the weakly linear stability result of Morando and Trebeschi (2008) [20]. The missing normal derivatives are compensated through the equations of the linearized vorticity and entropy when deriving higher-order energy estimates. The proof of the resolution for this nonlinear problem follows from certain a priori tame estimates on the effective linear problem in the usual Sobolev spaces and a suitable Nash–Moser iteration scheme.  相似文献   
7.
8.
We investigate congruence classes and direct congruence classes of m-tuples in the complex projective space ℂP n . For direct congruence one allows only isometries which are induced by linear (instead of semilinear) mappings. We establish a canonical bijection between the set of direct congruence classes of m-tuples of points in ℂP n and the set of equivalence classes of positive semidefinite Hermitean m×m-matrices of rank at most n+1 with 1's on the diagonal. As a corollary we get that the direct congruence class of an m-tuple is uniquely determined by the direct congruence classes of all of its triangles, provided that no pair of points of the m-tuple has distance π/2. Examples show that the situation changes drastically if one replaces direct congruence classes by congruence classes or if distances π/2 are allowed. Finally we do the same kind of investigation also for the complex hyperbolic space ℂH n . Most of the results are completely analogous, however, there are also some interesting differences. Received: 15 January 1996  相似文献   
9.
10.
Summary. We generalise and apply a refinement indicator of the type originally designed by Mackenzie, Süli and Warnecke in [15] and [16] for linear Friedrichs systems to the Euler equations of inviscid, compressible fluid flow. The Euler equations are symmetrized by means of entropy variables and locally linearized about a constant state to obtain a symmetric hyperbolic system to which an a posteriori error analysis of the type introduced in [15] can be applied. We discuss the details of the implementation of the refinement indicator into the DLR--Code which is based on a finite volume method of box type on an unstructured grid and present numerical results. Received May 15, 1995 / Revised version received April 17, 1996  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