全文获取类型
收费全文 | 3423篇 |
免费 | 428篇 |
国内免费 | 504篇 |
专业分类
化学 | 1712篇 |
晶体学 | 36篇 |
力学 | 443篇 |
综合类 | 63篇 |
数学 | 1541篇 |
物理学 | 560篇 |
出版年
2024年 | 7篇 |
2023年 | 29篇 |
2022年 | 45篇 |
2021年 | 68篇 |
2020年 | 91篇 |
2019年 | 85篇 |
2018年 | 86篇 |
2017年 | 130篇 |
2016年 | 112篇 |
2015年 | 118篇 |
2014年 | 193篇 |
2013年 | 296篇 |
2012年 | 196篇 |
2011年 | 207篇 |
2010年 | 156篇 |
2009年 | 191篇 |
2008年 | 180篇 |
2007年 | 206篇 |
2006年 | 172篇 |
2005年 | 180篇 |
2004年 | 189篇 |
2003年 | 168篇 |
2002年 | 151篇 |
2001年 | 109篇 |
2000年 | 122篇 |
1999年 | 131篇 |
1998年 | 104篇 |
1997年 | 110篇 |
1996年 | 66篇 |
1995年 | 64篇 |
1994年 | 61篇 |
1993年 | 40篇 |
1992年 | 40篇 |
1991年 | 37篇 |
1990年 | 30篇 |
1989年 | 16篇 |
1988年 | 21篇 |
1987年 | 20篇 |
1986年 | 23篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 9篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1972年 | 4篇 |
排序方式: 共有4355条查询结果,搜索用时 15 毫秒
941.
Solutions to nonlinear partial differential equations of fourth order are studied. Boundary regularity is proved for solutions
that satisfy mixed boundary conditions. Various geometric situations including so called triple points are considered. Regularity is measured in Sobolev-Slobodeckii spaces and the results are sharp in this scale. The approach
is based on the use of a first order difference quotient method. 相似文献
942.
Multi-Item, Multi-Facility Supply Chain Planning: Models, Complexities, and Algorithms 总被引:2,自引:0,他引:2
We propose a planning model for products manufactured across multiple manufacturing facilities sharing similar production capabilities. The need for cross-facility capacity management is most evident in high-tech industries that have capital-intensive equipment and a short technology life cycle. We propose a multicommodity flow network model where each commodity represents a product and the network structure represents manufacturing facilities in the supply chain capable of producing the products. We analyze in depth the product-level (single-commodity, multi-facility) subproblem when the capacity constraints are relaxed. We prove that even the general-cost version of this uncapacitated subproblem is NP-complete. We show that there exists an optimization algorithm that is polynomial in the number of facilities, but exponential in the number of periods. We further show that under special cost structures the shortest-path algorithm could achieve optimality. We analyze cases when the optimal solution does not correspond to a source-to-sink path, thus the shortest path algorithm would fail. To solve the overall (multicommodity) planning problem we develop a Lagrangean decomposition scheme, which separates the planning decisions into a resource subproblem, and a number of product-level subproblems. The Lagrangean multipliers are updated iteratively using a subgradient search algorithm. Through extensive computational testing, we show that the shortest path algorithm serves as an effective heuristic for the product-level subproblem (a mixed integer program), yielding high quality solutions with only a fraction (roughly 2%) of the computer time. 相似文献
943.
944.
945.
Adriana Buic? Veronica Ana Ilea 《Journal of Mathematical Analysis and Applications》2007,330(1):576-583
In this paper we study the existence of ω-periodic solutions for some functional-differential equations of mixed type. Among the main results are the averaging principle and existence theorems for some equations with homogeneous nonlinearities. We use here the coincidence degree theory of Mawhin. 相似文献
946.
Let Ω ⊆ ℝn be a bounded convex domain with C
2 boundary. For 0 < p, q ⩽ ∞ and a normal weight φ, the mixed norm space H
k
p,q,φ
(Ω) consists of all polyharmonic functions f of order k for which the mixed norm ∥ · ∥p,q,φ < ∞. In this paper, we prove that the Gleason’s problem (Ω, a, H
k
p,q,φ
) is always solvable for any reference point a ∈ Ω. Also, the Gleason’s problem for the polyharmonic φ-Bloch (little φ-Bloch) space is solvable. The parallel results for the hyperbolic harmonic mixed norm space are obtained. 相似文献
947.
钴铈复合氧化物在催化氧化中吸附氧的EPR研究 总被引:3,自引:0,他引:3
以溶胶-凝胶法制备了钴、铈及其复合氧化物,考察了其对对甲酚催化氧化的性能,复合氧化物表现出优良的活性和选择性.用EPR方法对3个催化剂样品表面吸附氧及其在可控气氛下与对甲酚的作用进行了研究,实验表明,O2-可能为活性氧物种,其吸附量及配位环境可与催化活性和选择性相关联。 相似文献
948.
O. Chkadua 《Mathematische Nachrichten》1998,189(1):61-105
The Dirichlet, Neumann and mixed problems of statics of the theory of elasticity for anisotropic homogeneous media are studied in n-dimensional (n ≧ 2) domains with boundaries containing closed cuspidal edges. Theorems of the existence and uniqueness of solutions of these problems in the Besov and Bessel potential spaces are obtained. Smoothness of solutions in a closed domain occupied by elastic medium is investigated. 相似文献
949.
在多连通区域上研究带有可测系数的二阶非线性抛物型方程组的初-混合边值问题,首先我们将其化为复形式的方程组,并给出在一定条件下的上述初-这值问题解的先验估计,然后利用解的估计和列紧性原理,证明了这种初-边值问题解的存在性。在论证过程中,我们始终用复分析方法讨论文中所提出的问题,没有看到国外有人使用这种方法处理此类问题。 相似文献
950.
We present in this paper various iterative methods for the solution of large linear and non‐linear systems resulting from the discretization of the generalized Stokes problem. A second‐order (O(h2)) P2‐P1 mixed finite element is used for the approximation of the velocity and the pressure. Solution strategies based on conjugate gradient‐like methods, the Uzawa's and Arrow–Hurwicz's methods are presented. Schur complement methods are also explored in the context of a hierarchical decomposition of the velocity field. The ever present preconditioning problem is also addressed. The performance of these iterative methods will be discussed on complex flows of industrial interest. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献