全文获取类型
收费全文 | 49906篇 |
免费 | 3975篇 |
国内免费 | 2023篇 |
专业分类
化学 | 7380篇 |
晶体学 | 287篇 |
力学 | 3697篇 |
综合类 | 367篇 |
数学 | 28274篇 |
物理学 | 15899篇 |
出版年
2023年 | 373篇 |
2022年 | 431篇 |
2021年 | 524篇 |
2020年 | 977篇 |
2019年 | 1288篇 |
2018年 | 1047篇 |
2017年 | 973篇 |
2016年 | 961篇 |
2015年 | 811篇 |
2014年 | 1417篇 |
2013年 | 3329篇 |
2012年 | 1747篇 |
2011年 | 2587篇 |
2010年 | 2090篇 |
2009年 | 2520篇 |
2008年 | 2746篇 |
2007年 | 2684篇 |
2006年 | 2395篇 |
2005年 | 2106篇 |
2004年 | 2232篇 |
2003年 | 2347篇 |
2002年 | 2773篇 |
2001年 | 2570篇 |
2000年 | 2381篇 |
1999年 | 2504篇 |
1998年 | 2214篇 |
1997年 | 1470篇 |
1996年 | 878篇 |
1995年 | 594篇 |
1994年 | 501篇 |
1993年 | 284篇 |
1992年 | 275篇 |
1991年 | 275篇 |
1990年 | 335篇 |
1989年 | 242篇 |
1988年 | 196篇 |
1987年 | 179篇 |
1986年 | 223篇 |
1985年 | 279篇 |
1984年 | 259篇 |
1983年 | 118篇 |
1982年 | 221篇 |
1981年 | 310篇 |
1980年 | 281篇 |
1979年 | 161篇 |
1978年 | 204篇 |
1977年 | 133篇 |
1976年 | 94篇 |
1975年 | 86篇 |
1974年 | 86篇 |
排序方式: 共有10000条查询结果,搜索用时 24 毫秒
91.
We consider immersions: and construct a subspace of which corresponds to a set of embedded manifolds which are either parallel to f, tubes around f or, in general, partial tubes around f. This space is invariant under the action of the normal holonomy group, We investigate the case where is non-trivial and obtain some results on the number of connected components of .
Received 24 March 2000. 相似文献
92.
J. Kalliongis 《Mathematische Zeitschrift》2002,241(4):801-828
For compact irreducible sufficiently large 3-manifolds containing 2-sided projective planes, we consider the following Realization
Problem: Given a finite subgroup of the outer automorphism group of the fundamental group, is there a finite group of homeomorphisms,
which induces this subgroup?
Received: 16 November 1999; in final form: 18 January 2001 / Published online: 8 November 2002 相似文献
93.
1.引 言 本文的目的是用求解偏微分方程(PDE)的方法来消除离散三角形曲面的噪声,所使用的方程是热传导方程到曲面的推广.热传导方程应用于图像处理已有二十余年的历史,有关参考文献相当丰富(见[1,11,12,19]).众所周知,对于给定的初始图像ρ0,热传导方程 在τ时刻的解与用Gauss滤波器Gσ(x)= (当标准差σ=2τ,时)和ρ0作卷积的结果相同.容易看出Gρ和ρ0的卷积运算相当于对ρ0做加权平均,当标准离差σ变大时,该加权平均在一个较大的范围实现,这解释了热传导方程的滤波作用.近来热传导方程已推广到空间曲面[4,5]以及高维空间中的二维流形(见[3]),对 相似文献
94.
Milan Medved? 《Journal of Mathematical Analysis and Applications》2002,267(2):643-650
A criterion for the nonexplosion of solutions to semilinear evolution equations on Banach spaces is proved. The result is obtained by applying a modification of the Bihari type inequality to the case of a weakly singular nonlinear integral inequality. 相似文献
95.
In this work we study nonnegativity and positivity of a discrete quadratic functional with separately varying endpoints. We introduce a notion of an interval coupled with 0, and hence, extend the notion of conjugate interval to 0 from the case of fixed to variable endpoint(s). We show that the nonnegativity of the discrete quadratic functional is equivalent to each of the following conditions: The nonexistence of intervals coupled with 0, the existence of a solution to Riccati matrix equation and its boundary conditions. Natural strengthening of each of these conditions yields a characterization of the positivity of the discrete quadratic functional. Since the quadratic functional under consideration could be a second variation of a discrete calculus of variations problem with varying endpoints, we apply our results to obtain necessary and sufficient optimality conditions for such problems. This paper generalizes our recent work in [R. Hilscher, V. Zeidan, Comput. Math. Appl., to appear], where the right endpoint is fixed. 相似文献
96.
Annegret K. Wagler 《Mathematical Methods of Operations Research》2002,56(1):127-149
An edge e of a perfect graph G is critical if G−e is imperfect. We would like to decide whether G−e is still “almost perfect” or already “very imperfect”. Via relaxations of the stable set polytope of a graph, we define two
superclasses of perfect graphs: rank-perfect and weakly rank-perfect graphs. Membership in those two classes indicates how
far an imperfect graph is away from being perfect. We study the cases, when a critical edge is removed from the line graph
of a bipartite graph or from the complement of such a graph. 相似文献
97.
In this paper we introduce a generalization of stable sets: stable multi-sets. A stable multi-set is an assignment of integers
to the vertices of a graph, such that specified bounds on vertices and edges are not exceeded. In case all vertex and edge
bounds equal one, stable multi-sets are equivalent to stable sets.
For the stable multi-set problem, we derive reduction rules and study the associated polytope. We state necessary and sufficient
conditions for the extreme points of the linear relaxation to be integer. These conditions generalize the conditions for the
stable set polytope. Moreover, the classes of odd cycle and clique inequalities for stable sets are generalized to stable
multi-sets and conditions for them to be facet defining are determined.
The study of stable multi-sets is initiated by optimization problems in the field of telecommunication networks. Stable multi-sets
emerge as an important substructure in the design of optical networks.
Received: February 14, 2001/Revised version: September 7, 2001 相似文献
98.
99.
方程w"-w+f(t,w)=O的Dirichlet边值问题的正解存在性与多解性 总被引:1,自引:0,他引:1
姚庆六 《应用泛函分析学报》2002,4(1):4-9
考察了下列常微分方程的Dirichlet边值问题的正解[w″(t)-w(t) f(t,w(t))=0,0≤t≤1 w(0)=w(1)=0建立了n正解的存在性,其中n是一个任意的自然数。 相似文献
100.
Alexander Krasnosel'skii Dmitrii Rachinskii 《NoDEA : Nonlinear Differential Equations and Applications》2002,9(1):93-115
We consider autonomous systems with a nonlinear part depending on a parameter and study Hopf bifurcations at infinity. The
nonlinear part consists of the nonlinear functional term and the Prandtl--Ishlinskii hysteresis term. The linear part of the
system has a special form such that the close-loop system can be considered as a hysteresis perturbation of a quasilinear
Hamiltonian system. The Hamiltonian system has a continuum of arbitrarily large cycles for each value of the parameter. We
present sufficient conditions for the existence of bifurcation points for the non-Hamiltonian system with hysteresis. These
bifurcation points are determined by simple characteristics of the hysteresis nonlinearity. 相似文献