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   12208篇
  免费   275篇
  国内免费   345篇
化学   1890篇
晶体学   39篇
力学   90篇
综合类   20篇
数学   9892篇
物理学   897篇
  2023年   71篇
  2022年   72篇
  2021年   49篇
  2020年   104篇
  2019年   280篇
  2018年   301篇
  2017年   185篇
  2016年   116篇
  2015年   134篇
  2014年   314篇
  2013年   794篇
  2012年   400篇
  2011年   724篇
  2010年   633篇
  2009年   924篇
  2008年   924篇
  2007年   901篇
  2006年   686篇
  2005年   453篇
  2004年   404篇
  2003年   316篇
  2002年   243篇
  2001年   221篇
  2000年   234篇
  1999年   259篇
  1998年   257篇
  1997年   182篇
  1996年   246篇
  1995年   255篇
  1994年   252篇
  1993年   198篇
  1992年   175篇
  1991年   126篇
  1990年   144篇
  1989年   143篇
  1988年   93篇
  1987年   95篇
  1986年   105篇
  1985年   140篇
  1984年   111篇
  1983年   58篇
  1982年   96篇
  1981年   67篇
  1980年   78篇
  1979年   60篇
  1978年   61篇
  1977年   39篇
  1976年   33篇
  1975年   24篇
  1973年   17篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
Recently, the potential use of organic π-radicals and related spin systems has been expanded to modern technological applications. The unique excited-state dynamics of organic π-radicals can be useful to improve the stability of photochemically unstable organic compounds, make the polarization transfer applicable to information technology, and achieve effective up-conversion of interest for luminescence bioimaging, among others. Furthermore, highly luminescent stable π-radicals have been recently reported, which are especially interesting for application in organic light-emitting devices owing to their potential to provide an internal quantum efficiency of 100 %. Thus, the excited-state nature of stable π-radicals as well as the control of their excited-state spin dynamics are emerging topics both in terms of fundamental science and related technological applications. In this minireview, we focus on the excited-state dynamics of both photostable non(weakly)-luminescent and luminescent π-radicals, which are opposites of each other. In particular, we cover the following topics: 1) effective generation of high-spin photoexcited states and control of the excited-state dynamics by using non-luminescent π-radicals, 2) unique excited-state dynamics of luminescent π-radicals and radical excimers, and 3) applications utilizing excited-state dynamics of π-radicals.  相似文献   
3.
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   
4.
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   
5.
6.
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   
7.
8.
We consider normal ≡ Gaussian seemingly unrelated regressions (SUR) with incomplete data (ID). Imposing a natural minimal set of conditional independence constraints, we find a restricted SUR/ID model whose likelihood function and parameter space factor into the product of the likelihood functions and the parameter spaces of standard complete data multivariate analysis of variance models. Hence, the restricted model has a unimodal likelihood and permits explicit likelihood inference. In the development of our methodology, we review and extend existing results for complete data SUR models and the multivariate ID problem.  相似文献   
9.
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   
10.
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