全文获取类型
收费全文 | 1837篇 |
免费 | 104篇 |
国内免费 | 40篇 |
专业分类
化学 | 140篇 |
晶体学 | 1篇 |
力学 | 386篇 |
综合类 | 7篇 |
数学 | 989篇 |
物理学 | 458篇 |
出版年
2024年 | 6篇 |
2023年 | 42篇 |
2022年 | 17篇 |
2021年 | 16篇 |
2020年 | 23篇 |
2019年 | 39篇 |
2018年 | 26篇 |
2017年 | 32篇 |
2016年 | 51篇 |
2015年 | 46篇 |
2014年 | 62篇 |
2013年 | 137篇 |
2012年 | 98篇 |
2011年 | 85篇 |
2010年 | 74篇 |
2009年 | 110篇 |
2008年 | 111篇 |
2007年 | 121篇 |
2006年 | 93篇 |
2005年 | 96篇 |
2004年 | 62篇 |
2003年 | 62篇 |
2002年 | 69篇 |
2001年 | 65篇 |
2000年 | 57篇 |
1999年 | 41篇 |
1998年 | 40篇 |
1997年 | 32篇 |
1996年 | 30篇 |
1995年 | 16篇 |
1994年 | 15篇 |
1993年 | 19篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 20篇 |
1984年 | 18篇 |
1983年 | 16篇 |
1982年 | 15篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 16篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有1981条查询结果,搜索用时 11 毫秒
41.
Stelios Kotsios 《Journal of Difference Equations and Applications》2013,19(6):551-571
In this paper a method for discovering solutions of nonlinear polynomial difference equations is presented. It is based on the concepts of i -operator and star-product. These notions create a proper algebraic background by means of which we can find linear equations "included" into the original nonlinear one and to seek for solutions among them. A corresponding algorithm and some examples are also provided. 相似文献
42.
AbstractWe provide a modified augmented Lagrange method coupled with a Tikhonov regularization for solving ill-posed state constrained elliptic optimal control problems with sparse controls. We consider a linear quadratic optimal control problem without any additional L2 regularization terms. The sparsity is guaranteed by an additional L1 term. Here, the modification of the classical augmented Lagrange method guarantees us uniform boundedness of the multiplier that corresponds to the state constraints. We present a coupling between the regularization parameter introduced by the Tikhonov regularization and the penalty parameter from the augmented Lagrange method, which allows us to prove strong convergence of the controls and their corresponding states. Moreover, convergence results proving the weak convergence of the adjoint state and weak*-convergence of the multiplier are provided. Finally, we demonstrate our method in several numerical examples. 相似文献
43.
44.
The nonlinear rescaling principle (NRP) consists of transforming the objective function and/or the constraints of a given
constrained optimization problem into another problem which is equivalent to the original one in the sense that their optimal
set of solutions coincides. A nonlinear transformation parameterized by a positive scalar parameter and based on a smooth
sealing function is used to transform the constraints. The methods based on NRP consist of sequential unconstrained minimization
of the classical Lagrangian for the equivalent problem, followed by an explicit formula updating the Lagrange multipliers.
We first show that the NRP leads naturally to proximal methods with an entropy-like kernel, which is defined by the conjugate
of the scaling function, and establish that the two methods are dually equivalent for convex constrained minimization problems.
We then study the convergence properties of the nonlinear rescaling algorithm and the corresponding entropy-like proximal
methods for convex constrained optimization problems. Special cases of the nonlinear rescaling algorithm are presented. In
particular a new class of exponential penalty-modified barrier functions methods is introduced.
Partially supported by the National Science Foundation, under Grants DMS-9201297, and DMS-9401871.
Partially supported by NASA Grant NAG3-1397 and NSF Grant DMS-9403218. 相似文献
45.
46.
Fei Guo 《Journal of Mathematical Analysis and Applications》2009,353(1):88-98
In this paper, the multiplicity of Lagrangian orbits on C2 smooth compact symmetric star-shaped hypersurfaces with respect to the origin in R2n is studied. These Lagrangian orbits begin from one Lagrangian subspace and end on another. An infinitely many existence result is proved via Z2-index theory. This is a multiplicity result about the Arnold Chord Conjecture in some sense, and is a generalization of the problem about the multiplicity of Lagrangian orbits beginning from and ending on the same Lagrangian subspace which was considered in the authors' previous paper [F. Guo, C. Liu, Multiplicity of Lagrangian orbits on symmetric star-shaped hypersurfaces, Nonlinear Anal. 69 (4) (2008) 1425-1436]. 相似文献
47.
M. C. Nucci 《Theoretical and Mathematical Physics》2009,160(1):1014-1021
It is well known that for any second-order ordinary differential equation (ODE), a Lagrangian always exists, and the key to its construction is the Jacobi last multiplier. Is it possible to find Lagrangians for first-order systems of ODEs or for higher-order ODEs? We show that the Jacobi last multiplier can also play a major role in this case. 相似文献
48.
Alexandre Salles da Cunha Nelson Maculan Mauricio G.C. Resende 《Discrete Applied Mathematics》2009,157(6):1198-1217
Given an undirected graph G with penalties associated with its vertices and costs associated with its edges, a Prize Collecting Steiner (PCS) tree is either an isolated vertex of G or else any tree of G, be it spanning or not. The weight of a PCS tree equals the sum of the costs for its edges plus the sum of the penalties for the vertices of G not spanned by the PCS tree. Accordingly, the Prize Collecting Steiner Problem in Graphs (PCSPG) is to find a PCS tree with the lowest weight. In this paper, after reformulating and re-interpreting a given PCSPG formulation, we use a Lagrangian Non Delayed Relax and Cut (NDRC) algorithm to generate primal and dual bounds to the problem. The algorithm is capable of adequately dealing with the exponentially many candidate inequalities to dualize. It incorporates ingredients such as a new PCSPG reduction test, an effective Lagrangian heuristic and a modification in the NDRC framework that allows duality gaps to be further reduced. The Lagrangian heuristic suggested here dominates their PCSPG counterparts in the literature. The NDRC PCSPG lower bounds, most of the time, nearly matched the corresponding Linear Programming relaxation bounds. 相似文献
49.
Nonexistence of invariant graphs in all supercritical energy levels of mechanical Lagrangians in T
2
Rafael O. Ruggiero 《Bulletin of the Brazilian Mathematical Society》2006,37(3):419-449
Let (T2, g) be a smooth Riemannian structure in the torus T2. We show that given ε > 0 and any C∞ function U : T2 → ℝ there exists a C1 function Uε with Lipschitz derivatives that is ε-C0 close to U for which there are no continuous invariant graphs in any supercritical energy level of the mechanical Lagrangian Lε : TT2 → ℝ given by
. We also show that given n ∈ ℕ, the set of C∞ potentials U : T2 → ℝ for which there are no continuous invariant graphs in any supercritical energy level E ≤ n of
is C0 dense in the set of C∞ functions.
Partially supported by CNPq, FAPERJ-Cientistas do nosso estado. 相似文献
50.
We consider in this paper the Lagrangian dual method for solving general integer programming. New properties of Lagrangian
duality are derived by a means of perturbation analysis. In particular, a necessary and sufficient condition for a primal
optimal solution to be generated by the Lagrangian relaxation is obtained. The solution properties of Lagrangian relaxation
problem are studied systematically. To overcome the difficulties caused by duality gap between the primal problem and the
dual problem, we introduce an equivalent reformulation for the primal problem via applying a pth power to the constraints. We prove that this reformulation possesses an asymptotic strong duality property. Primal feasibility
and primal optimality of the Lagrangian relaxation problems can be achieved in this reformulation when the parameter p is larger than a threshold value, thus ensuring the existence of an optimal primal-dual pair. We further show that duality
gap for this partial pth power reformulation is a strictly decreasing function of p in the case of a single constraint.
Dedicated to Professor Alex Rubinov on the occasion of his 65th birthday. Research supported by the Research Grants Council
of Hong Kong under Grant CUHK 4214/01E, and the National Natural Science Foundation of China under Grants 79970107 and 10571116. 相似文献