全文获取类型
| 收费全文 | 8504篇 |
| 免费 | 893篇 |
| 国内免费 | 445篇 |
专业分类
| 电工技术 | 446篇 |
| 综合类 | 668篇 |
| 化学工业 | 732篇 |
| 金属工艺 | 1165篇 |
| 机械仪表 | 1706篇 |
| 建筑科学 | 504篇 |
| 矿业工程 | 161篇 |
| 能源动力 | 216篇 |
| 轻工业 | 208篇 |
| 水利工程 | 318篇 |
| 石油天然气 | 97篇 |
| 武器工业 | 56篇 |
| 无线电 | 698篇 |
| 一般工业技术 | 1217篇 |
| 冶金工业 | 232篇 |
| 原子能技术 | 67篇 |
| 自动化技术 | 1351篇 |
出版年
| 2025年 | 84篇 |
| 2024年 | 194篇 |
| 2023年 | 246篇 |
| 2022年 | 283篇 |
| 2021年 | 274篇 |
| 2020年 | 339篇 |
| 2019年 | 336篇 |
| 2018年 | 298篇 |
| 2017年 | 374篇 |
| 2016年 | 390篇 |
| 2015年 | 362篇 |
| 2014年 | 432篇 |
| 2013年 | 525篇 |
| 2012年 | 652篇 |
| 2011年 | 546篇 |
| 2010年 | 384篇 |
| 2009年 | 452篇 |
| 2008年 | 487篇 |
| 2007年 | 563篇 |
| 2006年 | 447篇 |
| 2005年 | 358篇 |
| 2004年 | 313篇 |
| 2003年 | 230篇 |
| 2002年 | 239篇 |
| 2001年 | 182篇 |
| 2000年 | 158篇 |
| 1999年 | 120篇 |
| 1998年 | 98篇 |
| 1997年 | 78篇 |
| 1996年 | 90篇 |
| 1995年 | 51篇 |
| 1994年 | 31篇 |
| 1993年 | 48篇 |
| 1992年 | 34篇 |
| 1991年 | 27篇 |
| 1990年 | 20篇 |
| 1989年 | 19篇 |
| 1988年 | 19篇 |
| 1987年 | 9篇 |
| 1986年 | 8篇 |
| 1985年 | 7篇 |
| 1984年 | 14篇 |
| 1983年 | 7篇 |
| 1982年 | 6篇 |
| 1980年 | 3篇 |
| 1979年 | 2篇 |
| 1976年 | 1篇 |
| 1975年 | 2篇 |
排序方式： 共有9842条查询结果，搜索用时 15 毫秒
81.
Marcelo Krajnc Alves Rodrigo Rossi 《International journal for numerical methods in engineering》2003,57(11):1523-1552
In this work we propose a method which combines the element‐free Galerkin (EFG) with an extended partition of unity finite element method (PUFEM), that is able to enforce, in some limiting sense, the essential boundary conditions as done in the finite element method (FEM). The proposed extended PUFEM is based on the moving least square approximation (MLSA) and is capable of overcoming singularity problems, in the global shape functions, resulting from the consideration of linear and higher order base functions. With the objective of avoiding the presence of singular points, the extended PUFEM considers an extension of the support of the classical PUFE weight function. Since the extended PUFEM is closely related to the EFG method there is no need for special approximation functions with complex implementation procedures, and no use of the penalty and/or multiplier method is required in order to approximately impose the essential boundary condition. Thus, a relatively simple procedure is needed to combine both methods. In order to attest the performance of the method we consider the solution of an analytical elastic problem and also some coupled elastoplastic‐damage problems. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
82.
Peter Bettess Joseph Shirron Omar Laghrouche Bernard Peseux Rie Sugimoto Jon Trevelyan 《International journal for numerical methods in engineering》2003,56(4):531-552
The theory for integrating the element matrices for rectangular, triangular and quadrilateral finite elements for the solution of the Helmholtz equation for very short waves is presented. A numerical integration scheme is developed. Samples of Maple and Fortran code for the evaluation of integration abscissæ and weights are made available. The results are compared with those obtained using large numbers of Gauss–Legendre integration points for a range of testing wave problems. The results demonstrate that the method gives correct results, which gives confidence in the procedures, and show that large savings in computation time can be achieved. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
83.
84.
Jin Woo Lee Gang‐Won Jang 《International journal for numerical methods in engineering》2012,91(5):552-570
When seeking to enhance the acoustic attenuation performance of a reactive muffler, it is necessary to ensure that the flow resistance does not increase significantly. To date, there have been very few attempts to simultaneously optimize the transmission loss and pressure drop of a muffler. In this study, a multiobjective topology optimization problem is formulated to maximize the transmission loss at a target frequency and minimize the pressure drop simultaneously. The objective function in the formulation is given as the sum of weighted transmission loss and weighted pressure drop. The effect of the weighting factors on the optimal topologies of a muffler is investigated. Furthermore, the physical interpretation of partition layouts of optimized mufflers is discussed. The proposed muffler design method involving multiobjective topology optimization is compared with the previous muffler design method that involves single‐objective topology optimization to maximize only the transmission loss. The most important advantage of this study is shown by considering numerical results; the proposed muffler design method is applicable to nonconcentric expansion chamber mufflers, unlike the previous muffler design method. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
85.
Excimer laser crystallization is a well‐known industrially used technique to produce high‐performance polycrystalline silicon thin films on the commercially available inexpensive glass substrates for the development of high‐performance low temperature polycrystalline silicon thin‐film transistors in active matrix flat panel displays. A rapid optical measurement system for rapid surface roughness measurement of polycrystalline silicon thin films was developed in this study. Two kinds of thicknesses of polycrystalline silicon thin films were used to study rapid surface roughness measurements. Six different incident angles were employed for measuring surface roughness of polycrystalline silicon thin films. The results reveal that the incident angle of 20° was found to be a good candidate for measuring surface roughness of polycrystalline silicon thin films. Surface roughness (y) of polycrystalline silicon thin films can be determined rapidly from the average value of reflected direct current voltage (x) measured by the optical system developed using the trend equation of y = –8.9854x + 91.496. The maximum measurement error rate of the optical measurement system developed was less than 5.72%. The savings in measurement time was up to 83%. 相似文献
86.
Stéphane Bordas Phu Vinh Nguyen Cyrille Dunant Amor Guidoum Hung Nguyen‐Dang 《International journal for numerical methods in engineering》2007,71(6):703-732
This paper presents and exercises a general structure for an object‐oriented‐enriched finite element code. The programming environment provides a robust tool for extended finite element (XFEM) computations and a modular and extensible system. The programme structure has been designed to meet all natural requirements for modularity, extensibility, and robustness. To facilitate mesh–geometry interactions with hundreds of enrichment items, a mesh generator and mesh database are included. The salient features of the programme are: flexibility in the integration schemes (subtriangles, subquadrilaterals, independent near‐tip, and discontinuous quadrature rules); domain integral methods for homogeneous and bi‐material interface cracks arbitrarily oriented with respect to the mesh; geometry is described and updated by level sets, vector level sets or a standard method; standard and enriched approximations are independent; enrichment detection schemes: topological, geometrical, narrow‐band, etc.; multi‐material problem with an arbitrary number of interfaces and slip‐interfaces; non‐linear material models such as J2 plasticity with linear, isotropic and kinematic hardening. To illustrate the possible applications of our paradigm, we present 2D linear elastic fracture mechanics for hundreds of cracks with local near‐tip refinement, and crack propagation in two dimensions as well as complex 3D industrial problems. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
87.
S. Rajendran B. R. Zhang K. M. Liew 《International journal for numerical methods in engineering》2010,82(12):1574-1608
The recently published ‘FE–Meshfree’ QUAD4 element is extended to geometrical non‐linear analysis. The shape functions for this element are obtained by combining meshfree and finite element shape functions. The concept of partition of unity (PU) is employed for the purpose. The new shape functions inherit their higher order completeness properties from the meshfree shape functions and the mesh‐distortion tolerant compatibility properties from the finite element (FE) shape functions. Updated Lagrangian formulation is adopted for the non‐linear solution. Several numerical example problems are solved and the performance of the element is compared with that of the well‐known Q4, QM6 and Q8 elements. The results show that, for regular meshes, the performance of the element is comparable to that of QM6 and Q8 elements, and superior to that of Q4 element. For distorted meshes, the present element has better mesh‐distortion tolerance than Q4, QM6 and Q8 elements. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
88.
Thomas‐Peter Fries Ted Belytschko 《International journal for numerical methods in engineering》2010,84(3):253-304
An overview of the extended/generalized finite element method (GEFM/XFEM) with emphasis on methodological issues is presented. This method enables the accurate approximation of solutions that involve jumps, kinks, singularities, and other locally non‐smooth features within elements. This is achieved by enriching the polynomial approximation space of the classical finite element method. The GEFM/XFEM has shown its potential in a variety of applications that involve non‐smooth solutions near interfaces: Among them are the simulation of cracks, shear bands, dislocations, solidification, and multi‐field problems. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
89.
Bordat概念格构造算法的改进 总被引：1，自引：1，他引：1
陈庆燕 《计算机工程与应用》2010,46(35):33-35
作为一种重要的概念格构造算法,Bordat算法简洁、直观且易于并行化,但该算法本身的效率并不高。在深入研究格结构特性的基础上,给出了它的改进算法。首先对形式背景的属性集进行等价类划分,以减少参与计算的属性个数,并消除了在产生子节点集的过程中,对属性之间的多余比较,从而大大提高算法的效率,并通过实例和实验说明该算法的正确性和有效性。 相似文献
90.
研究了长期演进技术(LTE)系统下行链路中的 PSS定时同步。针对传统 PSS定时同步算法将接收信号与本地 PSS 信号在时域进行匹配滤波,计算复杂度较高的问题,提出了一种分段频域相关算法。该算法将接收时域数据分段做 FFT,转换到频域进行相关检测。多径信道下仿真结果表明,选择分段间隔为512时,所提算法与传统算法相比,在保证同步性能相当的情况下,可大大降低计算复杂度(约94%)。 相似文献