全文获取类型
收费全文 | 14539篇 |
免费 | 504篇 |
国内免费 | 440篇 |
专业分类
电工技术 | 381篇 |
综合类 | 581篇 |
化学工业 | 1123篇 |
金属工艺 | 1365篇 |
机械仪表 | 2642篇 |
建筑科学 | 1394篇 |
矿业工程 | 201篇 |
能源动力 | 617篇 |
轻工业 | 116篇 |
水利工程 | 114篇 |
石油天然气 | 185篇 |
武器工业 | 80篇 |
无线电 | 713篇 |
一般工业技术 | 2917篇 |
冶金工业 | 840篇 |
原子能技术 | 110篇 |
自动化技术 | 2104篇 |
出版年
2024年 | 11篇 |
2023年 | 116篇 |
2022年 | 183篇 |
2021年 | 259篇 |
2020年 | 206篇 |
2019年 | 237篇 |
2018年 | 253篇 |
2017年 | 263篇 |
2016年 | 328篇 |
2015年 | 559篇 |
2014年 | 690篇 |
2013年 | 787篇 |
2012年 | 868篇 |
2011年 | 1311篇 |
2010年 | 926篇 |
2009年 | 995篇 |
2008年 | 925篇 |
2007年 | 1053篇 |
2006年 | 888篇 |
2005年 | 795篇 |
2004年 | 699篇 |
2003年 | 598篇 |
2002年 | 468篇 |
2001年 | 319篇 |
2000年 | 294篇 |
1999年 | 228篇 |
1998年 | 217篇 |
1997年 | 181篇 |
1996年 | 164篇 |
1995年 | 130篇 |
1994年 | 112篇 |
1993年 | 71篇 |
1992年 | 79篇 |
1991年 | 71篇 |
1990年 | 48篇 |
1989年 | 34篇 |
1988年 | 32篇 |
1987年 | 12篇 |
1986年 | 13篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 3篇 |
1981年 | 9篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1964年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
A method and an algorithm for numerical estimation of effective mechanical properties of porous materials are presented. The effective properties are sought in the form of the nonlinear relation between the second Piola–Kirchhoff stress tensor and the Green strain tensor for anisotropic materials with second-order nonlinearities accounted for. The effective characteristics of test models are computed by means of a CAE Fidesys program module based on the proposed algorithm. The effective material properties as functions of porosity are examined. The finite element mesh that contained more than a million of elements was used while performing stress analysis of a specimen. To reduce computing time, assembly and solution of the global equation system was done in parallel using CUDA technology. The computations were carried out on NVIDIA Tesla C2050 graphics processors. Our results show that accounting for nonlinear effects is essential for correct estimation of effective properties of porous materials. 相似文献
172.
The present paper introduces an investigation into simultaneous optimization of the PbLaZrTi-based actuator configuration and corresponding applied light intensity for morphing beam structural shapes. A finite element formulation for multiphysics analysis of coupled opto-electro-thermo-mechanical fields in PbLaZrTi ceramics is derived and verified with the theoretical solution and the commercial software ANSYS. This element is then used to simulate beam bending shape control using the orthotropic PbLaZrTi actuators and the simultaneous optimization. In this procedure, the controlling and geometrical variables are simultaneously optimized via a hierarchical genetic algorithm. A bi-coded chromosome is proposed in a hierarchical mode, which consists of some control genes (i.e. actuator location and number) and parametric genes (i.e. applied light intensity). Whether the parametric gene is activated or not is managed by the value of the first-grade control genes. The numerical results demonstrate that the achieved beam bending shapes correlate remarkably well with the expected ones and the simultaneous optimization of photostrictive actuator locations, numbers and light intensities can result in optimal actuator layout with less PbLaZrTi actuators and irradiated light energy. The simulation results also show that the hierarchical genetic algorithm has more superior performance over the conventional real-coded genetic algorithm. 相似文献
173.
To join a medium or thick plate weldment with a full penetration, a groove is usually prepared in the space between two sections of metal. Because weld metal needs to be deposited within the groove to form the joint, it is expected that different groove type will require different heat input, which may consequently have influence on welding residual stress and deformation. Generally, different groove corresponds to different bead layout, so it can be foreseen that the groove type has a significant effect on temperature history, shape and size of heat affected zone, and region of sensitization in certain alloys such as austenitic stainless steel. The influences of groove type on residual stress, angular distortion and width of sensitization region in a SUS304 butt-welded joint were investigated by means of numerical simulation and experiment. Based on ABAQUS code, a computational approach with considering thermo-mechanical coupling behaviors, moving heat source, strain hardening and annealing effect was developed to simulate temperature profile, stress field and deformation in multi-pass joint. Welding temperature cycles, residual stress distributions and deformations in V, K and X groove joints were calculated through using the proposed computational procedure. Meanwhile, experiments were carried out to obtain residual stress distributions and angular distortions. Through comparing the numerical results and the measured data, the effectiveness and accuracy of the developed computational approach were verified. The simulation results show that groove type has a significant influence on welding residual stress distribution, angular distortion and width of sensitization region. 相似文献
174.
This study introduces a welding process design tool to determine optimal arc welding process parameters based on Finite Element Method (FEM), Response Surface Method (RSM) and Genetic Algorithms (GA). Here, a sequentially integrated FEM–RSM–GA framework has been developed and implemented to reduce the weld induced distortion in the final welded structure. It efficiently incorporates finite element based numerical welding simulations to investigate the desired responses and the effect of design variables without expensive trial experiments. To demonstrate the effectiveness of the proposed methodology, a lap joint fillet weld specimen has been used in this paper. Four process parameters namely arc voltage, input current, welding speed and welding direction have been optimized to minimize the distortion of the structure. The optimization results revealed the effectiveness of the methodology for welding process design with reduced cost and time. 相似文献
175.
社会选择理论是研究如何表达和聚合个体选择的一门学问.而社会选择理论与计算机科学的融合产生了称为计算社会选择的交叉学科,该学科成为社会计算的重要研究内容之一,在人工智能、经济和计算性理论领域引起了轰动.其一方面引入了复杂性分析和算法设计等计算机学科中常用的技术来对社会选择机制进行研究;另一方面也通过引入社会选择理论中的概念来推动计算机技术的发展,特别是在多智能体系统研究中有着成功的应用.投票理论是计算社会选择中最重要的研究主题之一.首先介绍常见的投票方法以及投票理论的形式化框架;再对投票理论中所关心的操纵问题做分析;然后介绍在组合域上的投票;最后对其他相关问题作简要介绍,并对该领域未来的发展与应用做出展望. 相似文献
176.
基于英特尔集成众核(Many Integrated Core,MIC)架构,将有限元网格积分算法在至强融核(Xeon Phi)协处理器做了移植和性能分析。该应用全面测试了有限元分析的核心计算过程在MIC上的加速效果,实现了卸载模式(offload)[1]下利用OpenMP在MIC上的线程并行化。计算性能测试结果显示集成众核平台可以有效地加速有限元网格积分算法:1)一块被充分利用的MIC设备卡(3115A)的计算能力超过两路16核Intel XeonTM E5-2670 CPU;2)MIC并发的物理线程可能由于公共缓存访问存在竞争而降低程序的扩展性。测试结果还显示了在多CPU多MIC平台上进一步移植完整的MPI并行有限元模拟软件的可行性。这项工作有助于推动与有限元网格相关的科学和工程高性能计算的研究。 相似文献
177.
对含Karnopp摩擦的柔性滑移铰系统进行动力学建模和仿真.将滑移铰中的滑块视为柔性体,滑道视为刚性接触面,考虑滑道与滑块之间的间隙.由于柔性滑块与滑道的接触状态和摩擦情况比较复杂,采用有限元方法建立了柔性滑块的力学模型,基于罚函数方法建立含Karnopp摩擦柔性滑移铰接触力模型,通过试算迭代法判断柔性滑块各节点的接触状态,基于KED方法和Newmark方法给出了含该滑移铰机械系统动力学方程的数值算法.最后,以含Karnopp摩擦的柔性滑移铰和驱动摆杆构成的机械系统为例进行动力学仿真,分析了其动力学特性,验证了本文给出的方法的有效性. 相似文献
178.
Straight‐Line Tracking Control of an Agricultural Vehicle with Finite‐Time Control Technique
下载免费PDF全文
![点击此处可从《Asian journal of control》网站下载免费的PDF全文](/ch/ext_images/free.gif)
For the agricultural vehicle straight‐line tracking system, three control algorithms based upon the finite‐time control technique have been proposed to force the vehicle to track a straight line. Without considering the lumped disturbance, a backstepping‐like finite‐time state‐feedback controller is first developed. On this basis, an adaptive state‐feedback controller in conjunction with integral sliding mode is further developed in the presence of the lumped disturbance. Finally, a sliding mode disturbance observer is given to estimate the lumped disturbance, and the composite control scheme is presented. Under the composite controller, the lumped disturbance can be compensated and thus the disturbance rejection property has been significantly improved. Simulation results verify the proposed control algorithms. 相似文献
179.
SHAO Jun-peng DAI Chun-xi ZHANG Yan-qin YU Xiao-dong XU Xiao-qiu WANG Yun-fei College of Mechanical Power Engineering Harbin University of Science Technology Harbin China 《水动力学研究与进展(B辑)》2011,23(5):676-680
For a heavy hydrostatic bearing with a high linear velocity,the results of numerical calculations often differ from practical conditions if the viscosity is considered as constant.In this article,the influence of the oil cavity depth on the temperature field in the heavy hydrostatic bearing is discussed in the context of variable viscosity.The viscosity-temperature relations for the gap oil film are first established by fitting B-Spline curves,then,numerical calculations for the temperature field in the heavy hydrostatic bearing of different oil cavity depths are carried out based on Finite Volume Method (FVM) under the same rotating speed,and the influence of the oil cavity depth on the temperature distribution in the gap oil film of the hydrostatic bearing is discussed.The results of numerical calculations provide the temperature distribution state inside the hydrostatic bearing,which would help the selection and the design of hydrostatic bearings in engineering practice. 相似文献
180.