全文获取类型
收费全文 | 4447篇 |
免费 | 585篇 |
国内免费 | 392篇 |
专业分类
电工技术 | 138篇 |
综合类 | 418篇 |
化学工业 | 232篇 |
金属工艺 | 148篇 |
机械仪表 | 446篇 |
建筑科学 | 328篇 |
矿业工程 | 233篇 |
能源动力 | 128篇 |
轻工业 | 94篇 |
水利工程 | 138篇 |
石油天然气 | 58篇 |
武器工业 | 79篇 |
无线电 | 463篇 |
一般工业技术 | 703篇 |
冶金工业 | 42篇 |
原子能技术 | 57篇 |
自动化技术 | 1719篇 |
出版年
2024年 | 8篇 |
2023年 | 37篇 |
2022年 | 79篇 |
2021年 | 102篇 |
2020年 | 110篇 |
2019年 | 110篇 |
2018年 | 125篇 |
2017年 | 138篇 |
2016年 | 166篇 |
2015年 | 221篇 |
2014年 | 257篇 |
2013年 | 279篇 |
2012年 | 395篇 |
2011年 | 385篇 |
2010年 | 296篇 |
2009年 | 337篇 |
2008年 | 314篇 |
2007年 | 377篇 |
2006年 | 288篇 |
2005年 | 247篇 |
2004年 | 223篇 |
2003年 | 183篇 |
2002年 | 149篇 |
2001年 | 116篇 |
2000年 | 90篇 |
1999年 | 77篇 |
1998年 | 65篇 |
1997年 | 56篇 |
1996年 | 52篇 |
1995年 | 43篇 |
1994年 | 21篇 |
1993年 | 17篇 |
1992年 | 18篇 |
1991年 | 11篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 10篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有5424条查询结果,搜索用时 750 毫秒
941.
《Journal of Nuclear Science and Technology》2013,50(12):1176-1185
The exact solution of nuclide chain equations within arbitrary figures is obtained for a linear chain by employing the Bateman method in the multiple-precision arithmetic. The exact error estimation of major calculation methods for a nuclide chain equation is done by using this exact solution as a standard. The Bateman, finite difference, Runge-Kutta and matrix exponential methods are investigated. The present study confirms the following. The original Bateman method has very low accuracy in some cases, because of large-scale cancellations. The revised Bateman method by Siewers reduces the occurrence of cancellations and thereby shows high accuracy. In the time difference method as the finite difference and Runge-Kutta methods, the solutions are mainly affected by the truncation errors in the early decay time, and afterward by the round-off errors. Even though the variable time mesh is employed to suppress the accumulation of round-off errors, it appears to be nonpractical. Judging from these estimations, the matrix exponential method is the best among all the methods except the Bateman method whose calculation process for a linear chain is not identical with that for a general one. 相似文献
942.
943.
Jibum Kim Thap Panitanarak Suzanne M. Shontz 《International journal for numerical methods in engineering》2013,94(1):20-42
We propose a multiobjective mesh optimization framework for mesh quality improvement and mesh untangling. Our framework combines two or more competing objective functions into a single objective function to be solved using one of various multiobjective optimization methods. Methods within our framework are able to optimize various aspects of the mesh such as the element shape, element size, associated PDE interpolation error, and number of inverted elements, but the improvement is not limited to these categories. The strength of our multiobjective mesh optimization framework lies in its ability to be extended to simultaneously optimize any aspects of the mesh and to optimize meshes with different element types. We propose the exponential sum, objective product, and equal sum multiobjective mesh optimization methods within our framework; these methods do not require articulation of preferences. However, the solutions obtained satisfy a sufficient condition of weak Pareto optimality. Experimental results show that our multiobjective mesh optimization methods are able to simultaneously optimize two or more aspects of the mesh and also are able to improve mesh qualities while eliminating inverted elements. We successfully apply our methods to real‐world applications such as hydrocephalus treatment and shape optimization. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
944.
S. Walton O. Hassan K. Morgan 《International journal for numerical methods in engineering》2013,93(5):527-550
A new mesh optimisation scheme, reduced order mesh optimisation, is introduced. The technique uses proper orthogonal decomposition to reduce the number of dimensions in a mesh optimisation problem. This reduction in dimensionality allows the expression of the optimisation problem globally rather than the more traditional local mesh optimisation or smoothing algorithms. To perform the optimisation, the recently developed gradient‐free technique modified cuckoo search is applied. The effectiveness of the algorithm is shown by considering the problem of optimising meshes for use in co‐volume techniques. Co‐volume techniques require the existence of two mutually orthogonal meshes; this is achieved by utilising the Delaunay–Voronoi dual. A combination of considering the problem globally and the use of a gradient‐free technique results in a scheme that significantly outperforms previous methods in solving this particular problem. Although the examples presented in this paper are specific to optimising dual meshes, the technique is general and can be simply modified to any mesh optimisation problem. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
945.
D. Akçay Perdahcıoğlu M. Doreille A. de Boer T. Ludwig 《International journal for numerical methods in engineering》2013,96(6):390-404
A common mesh refinement‐based coupling technique is embedded into a component mode synthesis method, Craig–Bampton. More specifically, a common mesh is generated between the non‐conforming interfaces of the coupled structures, and the compatibility constraints are enforced on that mesh via L2‐minimization. This new integrated method is suitable for structural dynamic analysis problems where the substructures may have non‐conforming curvilinear and/or surface interface meshes. That is, coupled substructures may have different element types such as shell, solid, and/or beam elements. The proposed method is implemented into a commercial finite element software, B2000++, and its demonstration is carried out using an academic and industry oriented test problems. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
946.
Pramote Dechaumphai 《中国工程学刊》2013,36(3):375-380
Abstract A finite element method is combined with an adaptive meshing technique to improve the accuracy of the finite element solution. The effectiveness of the combined method is evaluated by a plane stress problem that has an exact solution. The problem is that of a panel with a circular cutout subjected to an applied load. The result demonstrates that the adaptive meshing technique can reduce the numbers of the finite elements, the analysis computational time, and improve the accuracy of the analysis solution. 相似文献
947.
Combining Shape Optimization (SO) with Adaptive Mesh Refinement (AMR) potentially offers a higher accuracy and higher computational efficiency, especially if the applied target error for AMR is reduced in the course of the optimization process. The disadvantage of that approach is that the rate of convergence of the corresponding optimization processes can be significantly lower as compared to processes which apply a fixed target error for AMR. In the present paper the so-called Multipoint Approximation Method (MAM) is used as a basis for SO in conjunction with AMR. Several techniques for improvement of the rates of convergence are presented and investigated. Firstly, alternative algorithms for determining the approximation functions using a weighted least squares method are investigated. The focus is on weights which depend on the discretization errors. Secondly, different strategies for moving and resizing the search sub-regions in the space of design variables are presented. The proposed methods are illustrated by means of several optimization problems in which the effect of AMR with changing discretization errors is modelled by artificially introduced numerical noise. 相似文献
948.
新型的压电致动网孔式雾化器基于微机械加工技术,具有雾滴直径小,功率小,效率高等优点.介绍了一种压电致动网孔式雾化器的原理,对主要部件换能器进行了符合设计要求的纵向振动有限元分析,并阐述了各个因数对换能器振动的影响,获得的结果为换能器的优化设计提供了参考. 相似文献
949.
将无网格Galerkin法(element-free Galerkin method,EFGM)和改进的Matlab遗传算法工具箱(matlab genetic toolbox,MGT)相结合,提出了一种新的连续体结构形状优化设计方法。针对形状优化设计的特点,建立了一种规则网格与有限元网格混合的EFG积分背景网格法。详细介绍了M函数文件的修改方法,解决了现有Matlab遗传算法工具箱不能直接施加的非线性与隐性约束条件的难题。最后,完成了一个工程实例的结构形状优化,优化结果表明该方法是有效可行的。 相似文献
950.
高强钢绞线网片-聚合物砂浆复合面层加固钢筋混凝土柱的数值模拟分析 总被引:1,自引:1,他引:0
对采用高强钢绞线网片-聚合物砂浆复合面层加固后的钢筋混凝土柱进行ANSYS有限元模拟分析,研究了几种参数对试件的影响。通过与实际试验结果进行比较,发现理论分析结果与试验结果吻合较好,为该加固方法提供了有效的理论依据。 相似文献