全文获取类型
收费全文 | 1406篇 |
免费 | 131篇 |
国内免费 | 138篇 |
专业分类
化学 | 58篇 |
晶体学 | 2篇 |
力学 | 110篇 |
综合类 | 37篇 |
数学 | 1177篇 |
物理学 | 291篇 |
出版年
2024年 | 3篇 |
2023年 | 13篇 |
2022年 | 16篇 |
2021年 | 19篇 |
2020年 | 17篇 |
2019年 | 22篇 |
2018年 | 29篇 |
2017年 | 33篇 |
2016年 | 24篇 |
2015年 | 20篇 |
2014年 | 39篇 |
2013年 | 94篇 |
2012年 | 46篇 |
2011年 | 65篇 |
2010年 | 56篇 |
2009年 | 69篇 |
2008年 | 88篇 |
2007年 | 102篇 |
2006年 | 102篇 |
2005年 | 101篇 |
2004年 | 65篇 |
2003年 | 99篇 |
2002年 | 81篇 |
2001年 | 80篇 |
2000年 | 69篇 |
1999年 | 69篇 |
1998年 | 69篇 |
1997年 | 54篇 |
1996年 | 24篇 |
1995年 | 27篇 |
1994年 | 14篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有1675条查询结果,搜索用时 10 毫秒
101.
A theorem of Birkhoff‐Frink asserts that every algebraic closure operator on an ordinary set arises, from some algebraic structure on the set, as the corresponding generated subalgebra operator. However, for many‐sorted sets, i.e., indexed families of sets, such a theorem is not longer true without qualification. We characterize the corresponding many‐sorted closure operators as precisely the uniform algebraic operators. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
102.
In this paper we describe vanishing and non-vanishing of cohomology of “most” line bundles over Schubert subvarieties of flag
varieties for rank 2 semisimple algebraic groups. 相似文献
103.
Gabriela Jeronimo Teresa Krick Juan Sabia Martín Sombra 《Foundations of Computational Mathematics》2004,4(1):41-117
We present a bounded probability algorithm for the computation of the
Chowforms of the equidimensional components of an algebraic variety. In particular,
this gives an alternative procedure for the effective equidimensional decomposition
of the variety, since each equidimensional component is characterized by its Chow
form.
The expected complexity of the algorithm is polynomial in the size and the geometric
degree of the input equation system defining the variety. Hence it improves (or
meets in some special cases) the complexity of all previous algorithms for computing Chow forms. In addition to this, we clarify the probability and uniformity aspects,
which constitutes a further contribution of the paper.
The algorithm is based on elimination theory techniques, in line with the geometric
resolution algorithm due to M. Giusti, J. Heintz, L. M. Pardo, and their collaborators.
In fact, ours can be considered as an extension of their algorithm for zero-dimensional
systems to the case of positive-dimensional varieties. The key element for dealing
with positive-dimensional varieties is a new Poisson-type product formula. This
formula allows us to compute the Chow form of an equidimensional variety from a
suitable zero-dimensional fiber.
As an application, we obtain an algorithm to compute a subclass of sparse resultants,
whose complexity is polynomial in the dimension and the volume of the input
set of exponents. As another application, we derive an algorithm for the computation
of the (unique) solution of a generic overdetermined polynomial equation system. 相似文献
104.
Olof J. Staffans 《Transactions of the American Mathematical Society》1997,349(9):3679-3715
We consider the infinite horizon quadratic cost minimization problem for a stable time-invariant well-posed linear system in the sense of Salamon and Weiss, and show that it can be reduced to a spectral factorization problem in the control space. More precisely, we show that the optimal solution of the quadratic cost minimization problem is of static state feedback type if and only if a certain spectral factorization problem has a solution. If both the system and the spectral factor are regular, then the feedback operator can be expressed in terms of the Riccati operator, and the Riccati operator is a positive self-adjoint solution of an algebraic Riccati equation. This Riccati equation is similar to the usual algebraic Riccati equation, but one of its coefficients varies depending on the subspace in which the equation is posed. Similar results are true for unstable systems, as we have proved elsewhere.
105.
E. Getzler 《Journal of the American Mathematical Society》1997,10(4):973-998
We find a new relation among codimension algebraic cycles in the moduli space , and use this to calculate the elliptic Gromov-Witten invariants of projective spaces and .
106.
ALAIN HÉNAUT 《Geometriae Dedicata》1997,65(1):89-101
A d-web in (
,0) is given by d complex analytic foliations of codimension one in (
,0) which are in general position. A d-web
in (
,0) is linear if all the leaves are (pieces of) hyperplanes in
and
is algebraic if it is associated, by duality, to a nondegenerate algebraic curve in
of degree d. We characterize linear webs in (
,0). We give explicit conditions under which a linear d-web in (
,0) is algebraic and we obtain equations for
in this case. Some related problems are discussed and some questions are posed. 相似文献
107.
In this work we obtain an asymptotic estimate for the expected number of maxima of the random algebraic polynomial
, where a
j (j=0, 1,...,n–1) are independent, normally distributed random variables with mean and variance one. It is shown that for nonzero , the expected number of maxima is asymptotic to
log n, when n is large. 相似文献
108.
Jrg Winkelmann 《Mathematische Nachrichten》1997,186(1):285-302
We investigate under which conditions an algebraic group G defined over a locally compact field k admitr a subgroup Γ? G(k) which is dense in the Zariski topology, but discerte in the topology induced by the locally compact topology on k. For non—solvable groups we provide a complete answer. 相似文献
109.
I. E. Kaporin 《Computational Mathematics and Mathematical Physics》2008,48(11):1917-1926
Let A and B be real square positive definite matrices close to each other. A domain S on the complex plane that contains all the eigenvalues λ of the problem Az = λBz is constructed analytically. The boundary ?S of S is a curve known as the limacon of Pascal. Using the standard conformal mapping of the exterior of this curve (or of the exterior of an enveloping circular lune) onto the exterior of the unit disc, new analytical bounds are obtained for the convergence rate of the minimal residual method (GMRES) as applied to solving the linear system Ax = b with the preconditioner B. 相似文献
110.
We obtain spectral properties of the Pascal graphs by exploring its spectral graph invariants such as the algebraic connectivity, the first three largest Laplacian eigenvalues and the nullity. Some open problems pertaining to the Pascal graphs are given. 相似文献