全文获取类型
收费全文 | 10384篇 |
免费 | 771篇 |
国内免费 | 305篇 |
专业分类
化学 | 1294篇 |
晶体学 | 28篇 |
力学 | 1074篇 |
综合类 | 166篇 |
数学 | 7443篇 |
物理学 | 1455篇 |
出版年
2024年 | 17篇 |
2023年 | 98篇 |
2022年 | 271篇 |
2021年 | 347篇 |
2020年 | 206篇 |
2019年 | 225篇 |
2018年 | 247篇 |
2017年 | 339篇 |
2016年 | 322篇 |
2015年 | 233篇 |
2014年 | 483篇 |
2013年 | 589篇 |
2012年 | 638篇 |
2011年 | 502篇 |
2010年 | 479篇 |
2009年 | 595篇 |
2008年 | 603篇 |
2007年 | 644篇 |
2006年 | 522篇 |
2005年 | 466篇 |
2004年 | 352篇 |
2003年 | 346篇 |
2002年 | 316篇 |
2001年 | 288篇 |
2000年 | 280篇 |
1999年 | 211篇 |
1998年 | 231篇 |
1997年 | 209篇 |
1996年 | 148篇 |
1995年 | 170篇 |
1994年 | 144篇 |
1993年 | 116篇 |
1992年 | 106篇 |
1991年 | 87篇 |
1990年 | 83篇 |
1989年 | 67篇 |
1988年 | 55篇 |
1987年 | 41篇 |
1986年 | 45篇 |
1985年 | 83篇 |
1984年 | 54篇 |
1983年 | 17篇 |
1982年 | 23篇 |
1981年 | 23篇 |
1980年 | 17篇 |
1979年 | 31篇 |
1978年 | 21篇 |
1977年 | 30篇 |
1976年 | 19篇 |
1974年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
991.
In convex optimization the significance of constraint qualifications is evidenced by the simple duality theory, and the elegant subgradient optimality conditions which completely characterize a minimizer. However, the constraint qualifications do not always hold even for finite dimensional optimization problems and frequently fail for infinite dimensional problems. In the present work we take a broader view of the subgradient optimality conditions by allowing them to depend on a sequence of ε-subgradients at a minimizer and then by letting them to hold in the limit. Liberating the optimality conditions in this way permits us to obtain a complete characterization of optimality without a constraint qualification. As an easy consequence of these results we obtain optimality conditions for conic convex optimization problems without a constraint qualification. We derive these conditions by applying a powerful combination of conjugate analysis and ε-subdifferential calculus. Numerical examples are discussed to illustrate the significance of the sequential conditions. 相似文献
992.
We develop new algorithms for global optimization by combining well known branch and bound methods with multilevel subdivision
techniques for the computation of invariant sets of dynamical systems. The basic idea is to view iteration schemes for local
optimization problems – e.g. Newton’s method or conjugate gradient methods – as dynamical systems and to compute set coverings
of their fixed points. The combination with bounding techniques allow for the computation of coverings of the global optima
only. We show convergence of the new algorithms and present a particular implementation.
Michael Dellnitz - Research of the authors is partially supported by the Deutsche Forschungsgemeinschaft within the Sonderforschungsbereich
376 相似文献
993.
On Finite Element Approximations to a Shape Gradient Flow in Shape Optimization of Elliptic Problems
Chunxiao Liu & Shengfeng Zhu 《计算数学(英文版)》2023,41(5):957-980
Shape gradient flows are widely used in numerical shape optimization algorithms. We investigate the accuracy and effectiveness of approximate shape gradients flows for shape optimization of elliptic problems. We present convergence analysis with a priori error estimates for finite element approximations of shape gradient flows associated with a distributed or boundary expression of Eulerian derivative. Numerical examples are presented to verify theory and show that using the volume expression is effective for shape optimization with Dirichlet and Neumann boundary conditions. 相似文献
994.
Jiajie Li Shengfeng Zhu Xiaoqin Shen 《Numerical Methods for Partial Differential Equations》2023,39(2):1604-1634
For shape optimization of fluid flows governed by the Navier–Stokes equation, we investigate effectiveness of shape gradient algorithms by analyzing convergence and accuracy of mixed finite element approximations to both the distributed and boundary types of shape gradients. We present convergence analysis with a priori error estimates for the two approximate shape gradients. The theoretical analysis shows that the distributed formulation has superconvergence property. Numerical results with comparisons are presented to verify theory and show that the shape gradient algorithm based on the distributed formulation is highly effective and robust for shape optimization. 相似文献
995.
Stanislav Budzinskiy Nikolai Zamarashkin 《Numerical Linear Algebra with Applications》2023,30(6):e2520
In this work, we estimate the number of randomly selected elements of a tensor that with high probability guarantees local convergence of Riemannian gradient descent for tensor train completion. We derive a new bound for the orthogonal projections onto the tangent spaces based on the harmonic mean of the unfoldings' singular values and introduce a notion of core coherence for tensor trains. We also extend the results to tensor train completion with auxiliary subspace information and obtain the corresponding local convergence guarantees. 相似文献
996.
In this paper, we propose a method based on deep neural networks to solve obstacle problems. By introducing penalty terms, we reformulate the obstacle problem as a minimization optimization problem and utilize a deep neural network to approximate its solution. The convergence analysis is established by decomposing the error into three parts: approximation error, statistical error and optimization error. The approximate error is bounded by the depth and width of the network, the statistical error is estimated by the number of samples, and the optimization error is reflected in the empirical loss term. Due to its unsupervised and meshless advantages, the proposed method has wide applicability. Numerical experiments illustrate the effectiveness and robustness of the proposed method and verify the theoretical proof. 相似文献
997.
Reconfigurable intelligent surface (RIS), a planar metasurface consisting of a large number of low-cost reflecting elements, has received much attention due to its ability to improve both the spectrum and energy efficiency (EE) by reconfiguring the wireless propagation environment. In this paper, we propose a base station (BS) beamforming and RIS phase shift optimization technique that maximizes the EE of a RIS-aided multiple-input–single-output system. In particular, considering the system circuits’ energy consumption, an EE maximization problem is formulated by jointly optimizing the active beamforming at the BS and the passive beamforming at the RIS, under the constraints of each user’ rate requirement, the BS’s maximal transmit power budget and unit-modulus constraint of the RIS phase shifts. Due to the coupling of optimization variables, this problem is a complex non-convex optimization problem, and it is challenging to solve it directly. To overcome this obstacle, we divide the problem into active and passive beamforming optimization subproblems. For the first subproblem, the active beamforming is given by the maximum ratio transmission optimal strategy. For the second subproblem, the optimal phase shift matrix at the RIS is obtained by exploiting sine cosine algorithm (SCA). Moreover, for this case where each reflection element’s working state is controlled by a circuit switch, each reflection element’s switch value is optimized with the aid of particle swarm optimization algorithm. Finally, numerical results verify the effectiveness of our proposed algorithm compared to other algorithms. 相似文献
998.
999.
The topological optimization for truss structures with stress constraints based on the exist-null combined model 总被引:7,自引:0,他引:7
A new exist-null combined model is proposed for the structural topology optimization. The model is applied to the topology
optimization of the truss with stress constraints. Satisfactory computational result can be obtained with more rapid and more
stable convergence as compared with the cross-sectional optimization. This work also shows that the presence of independent
and continuous topological variable motivates the research of structural topology optimization.
The project supported by the State Key Laboratory for Structural Analysis of Industrial Equipment, Dalian University of Technology. 相似文献
1000.
回顾了实心弹性薄板优化研究的发展历程。给出了由无限密和无限细的肋骨加强的环板在常肋骨密度时的解析解;采用精确刚度阵的有限元法计算了具有有限根肋骨加强的板的柔顺性,它低于光滑优化解的柔顺性。这些结果进一步说明近期文献中出现的枕头形的光滑解并不是几何受约束实心弹性薄板优化问题的全局最优解。 相似文献