全文获取类型
收费全文 | 30297篇 |
免费 | 384篇 |
国内免费 | 424篇 |
专业分类
化学 | 11416篇 |
晶体学 | 284篇 |
力学 | 1516篇 |
综合类 | 24篇 |
数学 | 9081篇 |
物理学 | 8784篇 |
出版年
2023年 | 36篇 |
2022年 | 80篇 |
2021年 | 104篇 |
2020年 | 86篇 |
2019年 | 66篇 |
2018年 | 1256篇 |
2017年 | 1504篇 |
2016年 | 784篇 |
2015年 | 651篇 |
2014年 | 576篇 |
2013年 | 775篇 |
2012年 | 3270篇 |
2011年 | 2459篇 |
2010年 | 1888篇 |
2009年 | 1639篇 |
2008年 | 645篇 |
2007年 | 695篇 |
2006年 | 666篇 |
2005年 | 4478篇 |
2004年 | 3926篇 |
2003年 | 2310篇 |
2002年 | 499篇 |
2001年 | 309篇 |
2000年 | 121篇 |
1999年 | 197篇 |
1998年 | 130篇 |
1997年 | 89篇 |
1996年 | 73篇 |
1995年 | 54篇 |
1994年 | 59篇 |
1993年 | 32篇 |
1992年 | 174篇 |
1991年 | 167篇 |
1990年 | 157篇 |
1989年 | 122篇 |
1988年 | 109篇 |
1987年 | 67篇 |
1986年 | 48篇 |
1985年 | 38篇 |
1979年 | 30篇 |
1976年 | 81篇 |
1975年 | 37篇 |
1974年 | 40篇 |
1973年 | 48篇 |
1972年 | 39篇 |
1970年 | 34篇 |
1969年 | 37篇 |
1968年 | 35篇 |
1967年 | 30篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Let R be a ring with involution *. We consider R as a ring equipped with a new product r s = rs + sr*. The relationship between (ordinary) ideals of R and right ideals of R with respect to the product is studied.AMS Subject Classification (2000): 16W10, 16D25 相似文献
992.
Determinantal point processes have arisen in diverse settings in recent years and have been investigated intensively. We study basic combinatorial and probabilistic aspects in the discrete case. Our main results concern relationships with matroids, stochastic domination, negative association, completeness for infinite matroids, tail triviality, and a method for extension of results from orthogonal projections to positive contractions. We also present several new avenues for further investigation, involving Hilbert spaces, combinatorics, homology, and group representations, among other areas. 相似文献
993.
In this paper we introduce two tree-width-like graph
invariants. The first graph invariant, which we denote by
=(G), is defined in terms of positive
semi-definite matrices and is similar to the graph invariant
(G), introduced by Colin de Verdière in
[J. Comb. Theory, Ser. B., 74:121–146, 1998]. The second graph
invariant, which we denote by (G), is defined in terms of a certain
connected subgraph property and is similar to (G), introduced by van der Holst,
Laurent, and Schrijver in [J. Comb. Theory, Ser. B., 65:291–304,
1995]. We give some theorems on the behaviour of these
invariants under certain transformations. We show that
=(G)=(G)
for any graph G with
=(G)4, and we give minimal forbidden
minor characterizations for the graphs satisfying
=(G)k
for k=1,2,3,4.This paper is extracted from two chapters of [7].
This work was done while the author was at the Centrum voor
Wiskunde en Informatica, Kruislaan 413, 1098 SJ Amsterdam, The
Netherlands. 相似文献
994.
A four dimensional summability matrix is stronger than convergence in the Pringsheim sense if it sums a divergent double sequence. Presented in this paper are sufficient conditions on a four dimensional matrix transformation which ensure that the summability matrix is stronger than convergence in the Pringsheim sense. Also other sufficient conditions will be presented to ensure the failure of inclusion between two summability matrices.AMS Subject Classification (2000): Primary 40B05. 相似文献
995.
Denote by
the class of all triangle-free
graphs on n vertices and
m edges. Our main result is
the following sharp threshold, which answers the question for
which densities a typical triangle-free graph is bipartite. Fix
> 0 and let
. If
n/2 m (1 – ) t
3, then almost
all graphs in
are not bipartite, whereas if
m (1 + )t
3, then almost
all of them are bipartite. For m (1 + )t
3, this allows
us to determine asymptotically the number of graphs in
. We also obtain corresponding
results for C
-free graphs, for any
cycle C
of fixed odd length.
Forschergruppe Algorithmen, Struktur, Zufall
supported by Deutsche Forschungsgemeinschaft grant FOR
413/1-1 相似文献
996.
Let
be a compact set with interior G. Let L
1
(G,dx), >0 dx-a.e. on G, and m:=dx. Let A=(a
ij
) be symmetric, and globally uniformly strictly elliptic on G. Let be such that
; f,
, is closable in L
2
(G,m) with closure (
r
,D(
r
)). The latter is fulfilled if satisfies the Hamza type condition, or
i
L
1
loc
(G,dx), 1id. Conservative, non-symmetric diffusion processes X
t
related to the extension of a generalized Dirichlet form
where
satisfies
are constructed and analyzed. If G is a bounded Lipschitz domain, H
1,1
(G), and a
ij
D(
r
), a Skorokhod decomposition for X
t
is given. This happens through a local time that is uniquely associated to the smooth measure 1{
Tr
()>0}
d, where Tr denotes the trace and the surface measure on G.This research has been financially supported by TMR grant HPMF-CT-2000-00942 of the European Union.
Mathematics Subject Classification (2000): 60J60, 60J55, 31C15, 31C25, 35J25 相似文献
997.
Difference Fourier transforms for nonreduced root systems 总被引:1,自引:0,他引:1
In the first part of the paper kernels are constructed which
meromorphically extend the Macdonald-Koornwinder polynomials in their degrees.
In the second part the kernels associated with
rank one root systems are used to define nonsymmetric variants of the
spherical Fourier transform on the quantum SU(1,1) group.
Related Plancherel and inversion formulas are derived using double
affine Hecke algebra techniques. 相似文献
998.
Adam?N.?LetchfordEmail author Andrea?Lodi 《4OR: A Quarterly Journal of Operations Research》2003,1(3):209-224
Given an integer polyhedron
, an integer point
, and a point
, the primal separation problem is the problem of finding a linear inequality which is valid for P
I
, violated by x
*, and satisfied at equality by
. The primal separation problem plays a key role in the primal approach to integer programming. In this paper we examine the complexity of primal separation for several well-known classes of inequalities for various important combinatorial optimization problems, including the knapsack, stable set and travelling salesman problems.Received: November 2002, Revised: March 2003, 相似文献
999.
M.J.H.?AnthonissenEmail author R.M.M.?Mattheij J.H.M. ten Thije?Boonkkamp 《Numerische Mathematik》2003,95(3):401-425
Summary. This paper is concerned with the convergence analysis of the local defect correction (LDC) method for diffusion equations. We derive a general expression for the iteration matrix of the method. We consider the model problem of Poisson's equation on the unit square and use standard five-point finite difference discretizations on uniform grids. It is shown via both an upper bound for the norm of the iteration matrix and numerical experiments, that the rate of convergence of the LDC method is proportional to H
2
with H the grid size of the global coarse grid.
Mathematics Subject Classification (2000):65N22, 65N50 相似文献
1000.
A directed balanced incomplete block design (or D
B(k,;v)) (X,) is called self-converse if there is an isomorphic mapping f from (X,) to (X,–1), where –1={B
–1:B} and B
–1=(x
k
,x
k
–1,,x
2,x
1) for B=(x
1,x
2,,x
k
–1,x
k
). In this paper, we give the existence spectrum for self-converse D
B(4,1;v).
AMS Classification:05BResearch supported in part by NSFC Grant 10071002 and SRFDP under No. 20010004001 相似文献