全文获取类型
收费全文 | 233007篇 |
免费 | 1996篇 |
国内免费 | 800篇 |
专业分类
化学 | 116822篇 |
晶体学 | 3996篇 |
力学 | 10757篇 |
综合类 | 1篇 |
数学 | 25503篇 |
物理学 | 78724篇 |
出版年
2020年 | 1787篇 |
2019年 | 2043篇 |
2018年 | 2719篇 |
2017年 | 2651篇 |
2016年 | 3913篇 |
2015年 | 2389篇 |
2014年 | 3967篇 |
2013年 | 10072篇 |
2012年 | 7529篇 |
2011年 | 9392篇 |
2010年 | 6685篇 |
2009年 | 6628篇 |
2008年 | 8702篇 |
2007年 | 8733篇 |
2006年 | 8271篇 |
2005年 | 7491篇 |
2004年 | 6917篇 |
2003年 | 6112篇 |
2002年 | 6060篇 |
2001年 | 7090篇 |
2000年 | 5372篇 |
1999年 | 4235篇 |
1998年 | 3563篇 |
1997年 | 3472篇 |
1996年 | 3293篇 |
1995年 | 3008篇 |
1994年 | 2951篇 |
1993年 | 3042篇 |
1992年 | 3151篇 |
1991年 | 3332篇 |
1990年 | 3084篇 |
1989年 | 3027篇 |
1988年 | 3066篇 |
1987年 | 2955篇 |
1986年 | 2800篇 |
1985年 | 3808篇 |
1984年 | 4005篇 |
1983年 | 3198篇 |
1982年 | 3410篇 |
1981年 | 3336篇 |
1980年 | 3230篇 |
1979年 | 3335篇 |
1978年 | 3422篇 |
1977年 | 3350篇 |
1976年 | 3448篇 |
1975年 | 3141篇 |
1974年 | 3150篇 |
1973年 | 3194篇 |
1972年 | 2235篇 |
1971年 | 1849篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
942.
We use the topological tool of Nielsen fixed-point theory to study the controllability of perturbed linear control processes whose control space can be reduced to a finite-dimensional one. These methods produce a lower bound on the number of controls that achieve a given target. We concentrate particularly on the case where the perturbation has sublinear growth, and we exhibit examples of multiple controls of various types that are detected by the Nielsen theory method.This research was partly supported by the Research Grant Teoria del Controllo dei Sistemi Dinamici, Ministero della Pubblica Istruzione, Roma, Italy. 相似文献
943.
A necessary and sufficient condition for regularity of the
-Neumann operator on (0,q)-forms in a smooth bounded pseudoconvex domain in Cn is that the orthogonal projections onto
-closed forms of degrees (0,q−1), (0,q), and (0,q+1) all be regular.
The first author partially supported by NSF Grant DMS-8701038 相似文献
944.
V. P. Yakovets 《Ukrainian Mathematical Journal》1990,42(11):1403-1409
Asymptotic expansions with respect to a small parameter e are constructed for a fundamental system of solutions of a linear singularity perturbed system of equations of the form
相似文献
945.
When can a k-edge-coloring of a subgraph K of a graph G be extended to a k-edge-coloring of G? One necessary condition is that for all X ? E(G) - E(K), where μi(X) is the maximum cardinality of a subset of X whose union with the set of edges of K colored i is a matching. This condition is not sufficient in general, but is sufficient for graphs of very simple structure. We try to locate the border where sufficiency ends. 相似文献
946.
For an exactly soluble classical spin model with long-range inhomogeneous coupling it is proved that in the absence of external magnetic field the free energy is aC
function of the temperature at the critical point. 相似文献
947.
Summary Utilizing kernel structure properties a unified construction of Hankel matrix inversion algorithms is presented. Three types of algorithms are obtained: 1)O(n
2) complexity Levinson type, 2)O (n) parallel complexity Schur-type, and 3)O(n log2
n) complexity asymptotically fast ones. All algorithms work without additional assumption (like strong nonsingularity). 相似文献
948.
Ordinary differential equations with impulse action are considered at fixed moments of time when finite limits points are admitted to the set of moments of the shocks. The topological structure of this set is clarified: it must be resolvable, in particular nowhere dense in R.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 42, No. 3, pp. 378–383, March, 1990. 相似文献
949.
Summary We propose and analyse a method of estimating the poles near the unit circleT of a functionG whose values are given at a grid of points onT: we give an algorithm for performing this estimation and prove a convergence theorem. The method is to identify the phase for an estimate by considering the peaks of the absolute value ofG onT, and then to estimate the modulus by seeking a bestL
2 fit toG over a small arc by a first order rational function. These pole estimates lead to the construction of a basis ofL
2 which is well suited to the numerical representation of the Hankel operator with symbolG and thereby to the numerical solution of the Nehari problem (computing the bestH
, analytic, approximation toG relative to theL
norm), as analysed in [HY]. We present the results of numerical tests of these algorithms.Partially supported by grants from the AFOSR and NSF 相似文献
950.
David P. Dobkin Steven J. Friedman Kenneth J. Supowit 《Discrete and Computational Geometry》1990,5(1):399-407
LetS be any set ofN points in the plane and let DT(S) be the graph of the Delaunay triangulation ofS. For all pointsa andb ofS, letd(a, b) be the Euclidean distance froma tob and let DT(a, b) be the length of the shortest path in DT(S) froma tob. We show that there is a constantc (≤((1+√5)/2) π≈5.08) independent ofS andN such that $$\frac{{DT(a,b)}}{{d(a,b)}}< c.$$ 相似文献
|