全文获取类型
收费全文 | 6230篇 |
免费 | 164篇 |
国内免费 | 188篇 |
专业分类
电工技术 | 56篇 |
综合类 | 121篇 |
化学工业 | 229篇 |
金属工艺 | 469篇 |
机械仪表 | 851篇 |
建筑科学 | 245篇 |
矿业工程 | 29篇 |
能源动力 | 174篇 |
轻工业 | 29篇 |
水利工程 | 9篇 |
石油天然气 | 55篇 |
武器工业 | 16篇 |
无线电 | 267篇 |
一般工业技术 | 1895篇 |
冶金工业 | 211篇 |
原子能技术 | 53篇 |
自动化技术 | 1873篇 |
出版年
2024年 | 4篇 |
2023年 | 43篇 |
2022年 | 59篇 |
2021年 | 115篇 |
2020年 | 104篇 |
2019年 | 93篇 |
2018年 | 95篇 |
2017年 | 142篇 |
2016年 | 270篇 |
2015年 | 346篇 |
2014年 | 350篇 |
2013年 | 390篇 |
2012年 | 348篇 |
2011年 | 454篇 |
2010年 | 258篇 |
2009年 | 370篇 |
2008年 | 337篇 |
2007年 | 348篇 |
2006年 | 353篇 |
2005年 | 281篇 |
2004年 | 267篇 |
2003年 | 231篇 |
2002年 | 205篇 |
2001年 | 163篇 |
2000年 | 145篇 |
1999年 | 143篇 |
1998年 | 160篇 |
1997年 | 82篇 |
1996年 | 93篇 |
1995年 | 75篇 |
1994年 | 65篇 |
1993年 | 41篇 |
1992年 | 34篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1989年 | 13篇 |
1988年 | 16篇 |
1987年 | 7篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有6582条查询结果,搜索用时 250 毫秒
11.
Comparative fatigue tests were carried out on Friction Stir Welded specimens of a 2195-T8 aluminum–lithium alloy that differed significantly in width. The width of the larger specimens was over thirteen times greater than that of the small specimens. Fatigue results showed a clear “size effect”, i.e. fatigue life of large specimens was about 40% of the corresponding value of small specimens. The Equivalent Initial Flaw Size methodology was adopted to correlate the two sets of results. Fatigue crack initiation life was disregarded with respect to crack propagation life, and fatigue life was evaluated only as propagation of a small pre-existing defect. Following this methodology, test results of small specimens were used to evaluate the initial equivalent flaw contained in each specimen. It was assumed that this data followed a normal distribution. The equivalent initial flaw in larger specimens was evaluated by simple geometrical considerations. A very good assessment of mean fatigue life and scatter in the fatigue results of large specimens was obtained by simulating the propagation of these defects. Calculations were carried out by taking also welding residual stresses into account, but the results demonstrated that this effect was not significant. 相似文献
12.
The Friction Stir Welding process for producing corner and T-joints out of 6 mm Ti–6Al–4V was developed in this effort using previous work on butt weld joints as a starting point. A limited number of corner joints were also subjected to a bending fatigue test to preliminarily assess the applicability of the process in producing fatigue critical structures. These results were also compared to predictions made by applying stress concentration factors to previously generated uniaxial butt joint test data. While additional testing is still required to obtain a higher degree of confidence in the conclusions of this study, it was found that the performance of these corner joints in fatigue could be compared to butt joint data when a geometrically based stress concentration factor is applied. Furthermore, these welded joints possessed equivalent fatigue performance relative to identical test specimens machined from wrought product forms, both bar and extrusion. Thus, from the perspective of fatigue design, this study has shown that Friction Stir Welding is able to produce structures with the same performance as currently made from wrought materials. 相似文献
13.
Fatigue crack propagation of multiple coplanar cracks with the coupled extended finite element/fast marching method 总被引:1,自引:0,他引:1
A numerical technique for modeling fatigue crack propagation of multiple coplanar cracks is presented. The proposed method couples the extended finite element method (X-FEM) [Int. J. Numer. Meth. Engng. 48 (11) (2000) 1549] to the fast marching method (FMM) [Level Set Methods & Fast Marching Methods: Evolving Interfaces in Computational Geometry, Fluid Mechanics, Computer Vision, and Materials Science, Cambridge University Press, Cambridge, UK, 1999]. The entire crack geometry, including one or more cracks, is represented by a single signed distance (level set) function. Merging of distinct cracks is handled naturally by the FMM with no collision detection or mesh reconstruction required. The FMM in conjunction with the Paris crack growth law is used to advance the crack front. In the X-FEM, a discontinuous function and the two-dimensional asymptotic crack-tip displacement fields are added to the finite element approximation to account for the crack using the notion of partition of unity [Comput. Meth. Appl. Mech. Engng. 139 (1996) 289]. This enables the domain to be modeled by a single fixed finite element mesh with no explicit meshing of the crack surfaces. In an earlier study [Engng. Fract. Mech. 70 (1) (2003) 29], the methodology, algorithm, and implementation for three-dimensional crack propagation of single cracks was introduced. In this paper, simulations for multiple planar cracks are presented, with crack merging and fatigue growth carried out without any user-intervention or remeshing. 相似文献
14.
F. M. Xu S. J. Zhu J. Zhao M. Qi F. G. Wang S. X. Li Z. G. Wang 《Materials Science and Engineering: A》2003,360(1-2):191-196
The SiC/Al graded composite was fabricated by powder metallurgy processing and its fatigue crack growth behavior was studied. The volume percentage of SiC particulates was distributed from 5 to 30% layer by layer on the cross section. Since the aluminium was dissolved together, there was no evident interface between the two layers with different volume fraction of SiC particulates. Fatigue crack growth was in direction of from 5 to 30% SiC layers under sinusoidal wave-form. The retardation of fatigue crack growth was found when crack propagated from low volume fraction of SiC to high volume fraction of SiC. The crack deflection and branching between two layers were observed, which decreased crack growth rates. In view of crack tip driving force, the plasticity mismatch between the layers shielded crack tip driving force, i.e. decreased the effective J-integral at the tip of the crack as the plastic zone of the crack tip spread from the weaker material into the stronger material. 相似文献
15.
通过对广州市电视台综合信息平台网络系统的应用现状及安全风险进行分析,提出基于网络层、系统层、用户层和安全策略管理全方位的网络信息安全体系. 相似文献
16.
Y. N. Lenets 《Fatigue & Fracture of Engineering Materials & Structures》1997,20(2):249-256
Abstract— The behaviour of fatigue cracks in an Al-alloy under cyclic compression, either with or without overloads, was studied. For constant-amplitude compressive cycling, a non-catastrophic (saturation) character of the fatigue crack behaviour was confirmed, with the final depth of a crack depending on the applied load level. Single (tensile or compressive) intermittent overloads were shown to re-activate a previously arrested crack while reversed (tensile—compressive or compressive—tensile) ones were also shown to maintain continual fatigue crack extension under otherwise fully compressive cycling. 相似文献
17.
提出了一种用于检测在役车辆车轴产生疲劳裂纹的超声波方法,设计了中心孔探头与斜角探头一起,完成了对车辆车轴的关键区域探伤。 相似文献
18.
数据采集与监控软件Genie 总被引:2,自引:0,他引:2
Genie是具有国际先进水平的数据采集与监控软件,它提供了一个面向对象的图形化用户界面,因此简化了数据采集过程、控制应用程序开发和操作员界面。本文介绍了Genie的特点、功能、基本用途以及VISUALBA-SIC在设计这类监控软件中的作用。 相似文献
19.
Sung D. Kwon Sung J. Song Dong H. Bae Young Z. Lee 《Journal of Mechanical Science and Technology》2002,16(9):1084-1092
The frequency dependency of Rayleigh surface wave is investigated indirectly by measuring the angular dependency of the backward
radiation of the incident ultrasonic wave in two kinds of degraded specimens by scuffing or corrosion. Then, the frequency
dependency is compared with the residual stress distribution or the corrosion-fatigue characteristics for the scuffed or corroded
specimens, respectively. The width of the backward radiation profile increases with the increase of the variation in residual
stress distribution for the scuffed specimens. In the corroded specimens, the profile width decreases with the increase of
the effective aging layer thickness and is inversely proportional to the exponent, m, in the Paris’ law that can predict the
crack size increase due to fatigue. The result observed in this study demonstrates high potential of backward radiated ultrasound
as a tool for nondestructive evaluation of subsurface gradient of material degradation generated by scuffing or corrosion. 相似文献
20.
汽车稳定杆组织与疲劳性能研究 总被引:1,自引:0,他引:1
对28Mn6钢制造的汽车稳定杆,分别采用整体感应加热-整体淬火、连续感应加热淬火两种不同热处理工艺,并进行了台架疲劳寿命试验,采用光学显微镜和扫描电镜,分析了经两种不同热处理工艺处理的稳定杆的金相组织及其早期疲劳断裂的断口形貌,提出,获得细小的高韧性索氏体组织是保证良好疲劳寿命的关键,稳定杆喷丸表面质量,游离铁素体也是影响疲劳性能的重要因素。 相似文献