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   21662篇
  免费   661篇
  国内免费   734篇
化学   4241篇
晶体学   865篇
力学   463篇
综合类   74篇
数学   14760篇
物理学   2654篇
  2023年   74篇
  2022年   144篇
  2021年   174篇
  2020年   170篇
  2019年   504篇
  2018年   518篇
  2017年   356篇
  2016年   365篇
  2015年   334篇
  2014年   686篇
  2013年   1143篇
  2012年   702篇
  2011年   1419篇
  2010年   1449篇
  2009年   1647篇
  2008年   1672篇
  2007年   1652篇
  2006年   1320篇
  2005年   994篇
  2004年   942篇
  2003年   738篇
  2002年   626篇
  2001年   469篇
  2000年   433篇
  1999年   434篇
  1998年   373篇
  1997年   318篇
  1996年   441篇
  1995年   381篇
  1994年   372篇
  1993年   317篇
  1992年   267篇
  1991年   163篇
  1990年   141篇
  1989年   148篇
  1988年   107篇
  1987年   115篇
  1986年   113篇
  1985年   168篇
  1984年   98篇
  1983年   68篇
  1982年   99篇
  1981年   90篇
  1980年   58篇
  1979年   44篇
  1978年   49篇
  1977年   55篇
  1976年   47篇
  1975年   15篇
  1974年   21篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
This paper deals with the Cauchy–Dirichlet problem for the fractional Cahn–Hilliard equation. The main results consist of global (in time) existence of weak solutions, characterization of parabolic smoothing effects (implying under proper condition eventual boundedness of trajectories), and convergence of each solution to a (single) equilibrium. In particular, to prove the convergence result, a variant of the so-called ?ojasiewicz–Simon inequality is provided for the fractional Dirichlet Laplacian and (possibly) non-analytic (but C1) nonlinearities.  相似文献   
4.
It is believed that there are more fundamental gauge symmetries beyond those described by the Standard Model of particle physics. The scales of these new gauge symmetries are usually too high to be reachable by particle colliders. Considering that the phase transition (PT) relating to the spontaneous breaking of new gauge symmetries to the electroweak symmetry might be strongly first order, we propose considering the stochastic gravitational waves (GW) arising from this phase transition as an indirect way of detecting these new fundamental gauge symmetries. As an illustration, we explore the possibility of detecting the stochastic GW generated from the PT of \begin{document}$ {\bf{B}}-{\bf{L}}$\end{document} in the space-based interferometer detectors. Our study demonstrates that the GW energy spectrum is reachable by the LISA, Tianqin, Taiji, BBO, and DECIGO experiments only for the case where the spontaneous breaking of \begin{document}$ {\bf{B}}-{\bf{L}}$\end{document} is triggered by at least two electroweak singlet scalars.  相似文献   
5.
All 3-dimensional convex polytopes are known to be rigid. Still their Minkowski differences (virtual polytopes) can be flexible with any finite freedom degree. We derive some sufficient rigidity conditions for virtual polytopes and present some examples of flexible ones. For example, Bricard's first and second flexible octahedra can be supplied by the structure of a virtual polytope.  相似文献   
6.
We prove that to most of the known hypercyclic operators A on separable Banach spaces there exist compact (compact convex, compact connected) subsets K of E such that each compact (compact convex, compact connected) subset of E can be approximated with respect to Hausdorff's distance by for suitable . Received July 8, 1997, in final form October 17, 1997  相似文献   
7.
8.
In this note we show that the chain space belonging to a quadric can be embedded into the chain geometry over a Clifford algebra via a generalized stereographic projection.  相似文献   
9.
The strength of basic sites has been measured by pyrrole-IR on alkali metal cation exchanged β and X zeolites, as well as NaOH loaded Naβ. The influence of cation type and the structure of zeolites on their basicity has been studied. The acidic and basic properties of the samples were investigated by NH3-TPD and isopropanol reaction. It was shown that the strength of basic sites on samples could be characterized by the shift of vNH band in the pyrrole-IR spectra. The framework oxygen charges were calculated from the Sanderson electronegativity. The changes in basic properties with various alkali metal cation are consistent with the changes of local oxygen charges of the zeolite framework.  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