全文获取类型
收费全文 | 145391篇 |
免费 | 13997篇 |
国内免费 | 9204篇 |
专业分类
电工技术 | 6064篇 |
技术理论 | 2篇 |
综合类 | 12812篇 |
化学工业 | 25914篇 |
金属工艺 | 11885篇 |
机械仪表 | 12293篇 |
建筑科学 | 11354篇 |
矿业工程 | 4093篇 |
能源动力 | 3905篇 |
轻工业 | 6661篇 |
水利工程 | 3392篇 |
石油天然气 | 4780篇 |
武器工业 | 1482篇 |
无线电 | 13848篇 |
一般工业技术 | 26172篇 |
冶金工业 | 5428篇 |
原子能技术 | 1736篇 |
自动化技术 | 16771篇 |
出版年
2024年 | 422篇 |
2023年 | 2250篇 |
2022年 | 3525篇 |
2021年 | 4715篇 |
2020年 | 4395篇 |
2019年 | 4064篇 |
2018年 | 3731篇 |
2017年 | 4604篇 |
2016年 | 5166篇 |
2015年 | 5572篇 |
2014年 | 7884篇 |
2013年 | 8381篇 |
2012年 | 9831篇 |
2011年 | 12055篇 |
2010年 | 9008篇 |
2009年 | 9967篇 |
2008年 | 8779篇 |
2007年 | 10153篇 |
2006年 | 8933篇 |
2005年 | 7691篇 |
2004年 | 6351篇 |
2003年 | 5609篇 |
2002年 | 4702篇 |
2001年 | 3371篇 |
2000年 | 3172篇 |
1999年 | 2604篇 |
1998年 | 2063篇 |
1997年 | 1750篇 |
1996年 | 1610篇 |
1995年 | 1272篇 |
1994年 | 1105篇 |
1993年 | 823篇 |
1992年 | 668篇 |
1991年 | 504篇 |
1990年 | 411篇 |
1989年 | 336篇 |
1988年 | 235篇 |
1987年 | 172篇 |
1986年 | 159篇 |
1985年 | 92篇 |
1984年 | 69篇 |
1983年 | 55篇 |
1982年 | 71篇 |
1981年 | 48篇 |
1980年 | 58篇 |
1979年 | 45篇 |
1978年 | 15篇 |
1977年 | 21篇 |
1976年 | 18篇 |
1974年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
W. F. J. Sampers A. P. G. G. Lamers A. A. van STEENHOVEN 《Chemical Engineering Communications》1993,125(1):187-196
In many applications swirling flow is used to enhance heat and mass transfer. One of the problems of modelling a turbulent swirling flow is the choice of the turbulent closure model which is acceptable for engineering purposes. To evaluate which model performs best, numerical results are compared with experimental data. Local velocity measurements are carried out on a swirling flow in a circular tube. The measurement method is hot-wire anemometry combined with visualization techniques. The numerical analysis is carried out using the k-ε model and the Algebraic Stress Model. In the experiment a symmetrical swirl was observed, Comparing the experimental data with the numerical results shows that the Algebraic Stress Model represents the experimental data quite well, whereas the k-ε model fails. 相似文献
993.
Stress concentration and fatigue of profiled reinforcing steels 总被引:1,自引:0,他引:1
Stress concentrations arise from profiles of ribbed reinforcing steel bars and in this study the results of calculated stress concentration factors (SCF), by using finite element method, are related to the fatigue test results. It is apparent that the degree of confinement of a ribbed bar embedded in concrete not only affects the magnitude of the ultimate bond stress but also the bond stress-slip relation. Thus the rib geometry or profile pattern is designed for optimum bond characteristics and not for fatigue considerations. However the rib geometry influences the fatigue performance through the SCFs arising from the root radius, width and flank angles of the profiles. It is shown that these latter factors have a significant influence on the fatigue behaviour of reinforcing steel bars. 相似文献
994.
Christian Thaulow Øyvind Ranestad Mons Hauge Zhiliang Zhang Masao Toyoda Fumiyoshi Minami 《Engineering Fracture Mechanics》1997,57(6):637-651
This paper investigates the stress fields for a crack located at the fusion line of a weldment. The strength mis-matching and the size of the HAZ were varied, and the corresponding distribution of the maximum principal stress was examined. The weld metal strength was globally overmatched with respect to the base material, but locally over- and undermatched with respect to the heat affected zone. Three cases of mis-match were compared, and it was found that reducing the strength of the HAZ lowered the maximum principal stresses. 相似文献
995.
This paper presents a 3D noncontacting sensor system designed to measure the position and orientation of a robot end effector. This measurement system includes two parts: a tridimensional object including four spheres placed along the axes of a tetrahedron and a set of three orthogonally pointed cameras. The purpose is to design a measurement system characterized by easy relationships in order to satisfy real-time constraints. The system has been used in two experiments: first, to calibrate a parallel robot and validate the geometrical control performance, then as an exteroceptive sensor in an assembly task. The system computes position and orientation of the tetrahedron in 100 ms time. The position and orientation accuracy are, respectively, 0.6 mm and 0.2 deg in a workspace, being a cube with 0.3 m sides. 相似文献
996.
机械结构结合部精确建模是对含结合部的机械结构进行动态分析和优化设计的关键问题之一。文章主要研究块体结构和平板由螺栓联接后构成的固定结合部的动力学建模问题。将结合部区域的刚度特性用结合部的材料机械特性参数等效表达,提出了虚拟接触材料的结合部刚度表达模型。通过模态实验和模型修正识别出不同结合面工况下虚拟接触材料的弹性模量,建立了含结合部动力特性的有限元模型。该模型可方便用于含结合部结构的有限元计算,经试验验证满足实际工程应用要求。 相似文献
997.
基于ARToolkit Plus的增强现实系统实现及框架研究 总被引:1,自引:0,他引:1
文章首先对基于ARToolkit Plus和WPF的增强现实系统实现的关键技术问题进行了描述,具体讨论了在MVC框架下如何将数据采集层与呈现层进行分划,在保证可用性的同时提供较强的扩展能力,并基于上述框架实现了一个应用于住房装修的实例。 相似文献
998.
针对地震数据信息量大的特点,文中提出了一种针对三维地震数据体绘制系统的框架。解决的方法是将数据处理、用户交互、渲染绘制分离成三个模块,并且设计了层次结构来保持模块之间的独立性,便于各个模块的修改、更换和扩展,提高了可视化绘制系统快速开发的灵活性。基于三维可视化开发工具包VTK,设计并编程实现了一个地震数据体绘制系统界面。通过实验结果证明,此体绘制方案是可行的、有效的。 相似文献
999.
In the present paper,the concepts of deductive element and maximal contraction are introduced in Boolean algebras,and corresponding theories of consistency and maximal contractions are studied.An algorithm principle is proposed to compute all maximal contractions for a consistent set with respect to its refutation in Boolean algebras.It is pointed out that the quotient algebra of the first-order language with respect to its provable equivalence relation constitutes a Boolean algebra,and hence the computation of R-contractions for closed formulas in first-order languages can be converted into the one in Boolean algebras proposed in this paper.Furthermore,the concept of basic element is introduced in Boolean algebras,which contributes to the definitions of clause and Horn clause transplanted from logic to a special type of Boolean algebras generated by basic elements.It is also pointed out that the computation of R-contractions for clauses in the classical propositional logic can be converted into the one in Boolean algebras generated by basic elements proposed in this paper. 相似文献
1000.
LIAN Feng HAN ChongZhao LIU WeiFeng LIU Jing & YUAN XiangHui SKLMSE Lab MOE KLINNS Lab 《中国科学:信息科学(英文版)》2012,(3):501-511
An extended product multi-sensor cardinalized probability hypothesis density (PM-CPHD) filter for spatial registration and multi-target tracking (MTT) is proposed. The number and states of targets and the biases of sensors are jointly estimated by this method without the data association. Monte Carlo (MC) simulation results show that the proposed method (i) outperforms, although computationally more expensive than, the extended multi-sensor PHD filter which has been proposed for joint spatial registration and MTT; (ii) outperforms the multi-sensor joint probabilistic data association (MSJPDA) filter which is also extended in this study for joint spatial registration and MTT when the clutter is relatively dense. 相似文献