全文获取类型
收费全文 | 19110篇 |
免费 | 605篇 |
国内免费 | 712篇 |
专业分类
化学 | 4061篇 |
晶体学 | 859篇 |
力学 | 467篇 |
综合类 | 69篇 |
数学 | 12382篇 |
物理学 | 2589篇 |
出版年
2023年 | 73篇 |
2022年 | 162篇 |
2021年 | 166篇 |
2020年 | 166篇 |
2019年 | 451篇 |
2018年 | 481篇 |
2017年 | 328篇 |
2016年 | 330篇 |
2015年 | 310篇 |
2014年 | 650篇 |
2013年 | 1004篇 |
2012年 | 624篇 |
2011年 | 1309篇 |
2010年 | 1337篇 |
2009年 | 1435篇 |
2008年 | 1452篇 |
2007年 | 1431篇 |
2006年 | 1181篇 |
2005年 | 870篇 |
2004年 | 839篇 |
2003年 | 667篇 |
2002年 | 555篇 |
2001年 | 427篇 |
2000年 | 353篇 |
1999年 | 334篇 |
1998年 | 317篇 |
1997年 | 266篇 |
1996年 | 380篇 |
1995年 | 318篇 |
1994年 | 340篇 |
1993年 | 289篇 |
1992年 | 229篇 |
1991年 | 133篇 |
1990年 | 134篇 |
1989年 | 123篇 |
1988年 | 84篇 |
1987年 | 101篇 |
1986年 | 100篇 |
1985年 | 141篇 |
1984年 | 83篇 |
1983年 | 59篇 |
1982年 | 84篇 |
1981年 | 70篇 |
1980年 | 45篇 |
1979年 | 22篇 |
1978年 | 37篇 |
1977年 | 54篇 |
1976年 | 43篇 |
1975年 | 9篇 |
1974年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
1.
2.
3.
4.
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 ) nonlinearities. 相似文献
5.
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
6.
G. Panina 《Central European Journal of Mathematics》2003,1(2):157-168
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
7.
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
8.
Andrea Blunck 《Monatshefte für Mathematik》1997,123(2):93-107
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.
XU Jun YAN Ai-Zhen XU Qin-Hua Department of Chemistry Nanjing University Nanjing Jiangsu China 《中国化学》1995,(2)
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.
For z1,z2,z3∈Zn, the tristance d3(z1,z2,z3) is a generalization of the L1-distance on Zn to a quantity that reflects the relative dispersion of three points rather than two. A tristance anticodeAd of diameter d is a subset of Zn with the property that d3(z1,z2,z3)?d for all z1,z2,z3∈Ad. An anticode is optimal if it has the largest possible cardinality for its diameter d. We determine the cardinality and completely classify the optimal tristance anticodes in Z2 for all diameters d?1. We then generalize this result to two related distance models: a different distance structure on Z2 where d(z1,z2)=1 if z1,z2 are adjacent either horizontally, vertically, or diagonally, and the distance structure obtained when Z2 is replaced by the hexagonal lattice A2. We also investigate optimal tristance anticodes in Z3 and optimal quadristance anticodes in Z2, and provide bounds on their cardinality. We conclude with a brief discussion of the applications of our results to multi-dimensional interleaving schemes and to connectivity loci in the game of Go. 相似文献