全文获取类型
收费全文 | 3624篇 |
免费 | 728篇 |
国内免费 | 170篇 |
专业分类
电工技术 | 164篇 |
综合类 | 195篇 |
化学工业 | 212篇 |
金属工艺 | 1775篇 |
机械仪表 | 393篇 |
建筑科学 | 250篇 |
矿业工程 | 75篇 |
能源动力 | 58篇 |
轻工业 | 14篇 |
水利工程 | 16篇 |
石油天然气 | 469篇 |
武器工业 | 27篇 |
无线电 | 91篇 |
一般工业技术 | 455篇 |
冶金工业 | 204篇 |
原子能技术 | 36篇 |
自动化技术 | 88篇 |
出版年
2024年 | 19篇 |
2023年 | 52篇 |
2022年 | 84篇 |
2021年 | 91篇 |
2020年 | 114篇 |
2019年 | 97篇 |
2018年 | 111篇 |
2017年 | 182篇 |
2016年 | 179篇 |
2015年 | 156篇 |
2014年 | 242篇 |
2013年 | 282篇 |
2012年 | 248篇 |
2011年 | 247篇 |
2010年 | 210篇 |
2009年 | 236篇 |
2008年 | 197篇 |
2007年 | 247篇 |
2006年 | 248篇 |
2005年 | 180篇 |
2004年 | 183篇 |
2003年 | 167篇 |
2002年 | 124篇 |
2001年 | 142篇 |
2000年 | 95篇 |
1999年 | 85篇 |
1998年 | 56篇 |
1997年 | 51篇 |
1996年 | 47篇 |
1995年 | 40篇 |
1994年 | 29篇 |
1993年 | 14篇 |
1992年 | 27篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有4522条查询结果,搜索用时 31 毫秒
91.
WU Junfeng CHEN Shanben ZHANG Mingjun 《机械工程学报(英文版)》2007,20(5):32-36
The robust control law for gas tungsten arc welding dynamic process, which is a typical sampled-data system and full of uncertainties, is presented. By using the Lyapunov second method, the robust control and robust optimal control for a class of sampled-data systems whose underlying continuous-time systems are subjected to structured uncertainties are discussed in time-domain. As a result, some sufficient conditions of robust stability and the corresponding robust control laws are derived. All these results are designed by solving a class of linear matrix inequalities (LMIs) and a class of dynamic optimization problem with LMIs constraints respectively. An example adapted under some experimental conditions in the dynamic process of gas tungsten arc welding system in which the controlled variable is the backside width of weld pool and controlling variable pulse duty ratio, is worked out to illustrate the proposed results, it is shown that the sampling period is the crucial design parameter. 相似文献
92.
热壁加氢反应器深厚焊缝的TOFD检测技术 总被引:5,自引:3,他引:5
热壁加氢反应器是一种具有复杂结构的设备,本文对热壁加氢反应器深厚焊缝的TOFD检测技术进行分析和探讨,具有一定的指导意义。 相似文献
93.
后热温度对1000MPa级高强钢焊缝组织与性能的影响 总被引:3,自引:0,他引:3
采用GHS90高强焊丝为填充材料对1 000 MPa级工程机械用高强钢进行熔化极活性气体保护(Metal active gas,MAG)焊,并对接头进行250℃、480℃、600℃保温2 h的焊后热处理。通过拉伸试验、显微硬度测试、光学显微镜(Optical microscope,OM)、扫面电镜(Scanning electron microscope,SEM)、透射电镜(Transmission electron microscopy,TEM)及电子背散射衍射(Electron back-scattered diffraction,EBSD)观察不同热处理温度后的焊缝微观组织及力学性能进行对比研究。结果表明,随后热温度从250℃升高到600℃,接头抗拉强度从1 014.5 MPa降低到934.5 MPa;焊缝平均冲击吸收能量从66 J降低到24 J;随后热温度升高,焊缝板条组织粗化,碳化物析出长大且连续分布是导致焊缝韧性降低的原因之一;同时焊缝有效晶粒尺寸变大和大角度晶界密度降低也是导致其韧性降低的原因。 相似文献
94.
95.
《Journal of Materials Processing Technology》2014,214(6):1236-1244
One of the main parameters in magnetic pulse welding (MPW) is the requirement of certain distance/spacing called “air gap” between the two sheets or tubes to be welded. This work presents means to alleviate this constraint through stamped humps in one of the sheets. The sheets remain in contact all over except at humps where a local air gap is sufficient to generate impact velocity required to produce spot welds using electromagnetic energy. The developed approach has been validated on the heterogeneous assembly of AA1199 aluminum to EN 355 steel. The microstructural analysis revealed that the weld interface is wavy and the waves are in two opposite directions from the center. Quasi-static tension–shear tests validated the joint efficiency of spot welds. 相似文献
96.
An attractive, alternative approach for the reduction of harmful residual stresses in weld zones is reviewed, which utilises low temperature, solid-state, displacive phase transformations in steel. The theory, latest concepts and practice for the design of such low transformation temperature (LTT) filler alloys are considered. By engineering the phase transformation temperature of the weld metal so as to take advantage of transformation expansion, the residual stress state within the weld zone can be significantly altered, most particularly where the weld thermally contracts with any movement of base parts constrained. To date, the technique has been shown to increase fatigue strength for some common weld geometries, which may enable engineering design codes to be favourably re-drafted where such LTT filler alloys are used. 相似文献
97.
S. A. Solovev V. I. Denisov B. A. Matyushkin A. A. Tolkachev 《Welding International》2017,31(12):959-963
The special features of pulsed arc welding of titanium are described. 相似文献
98.
V. Srinivas Ch. Kodanda Rama Rao N. Mohan Rao 《Tribology - Materials, Surfaces & Interfaces》2018,12(2):107-114
This paper studies the effect of surface modification of multiwall carbon nanotubes (MWCNTs) prior to dispersion in engine oil to improve the tribological properties. The MWCNTs are stabilised in the lubricant with two different surfactants cetrimonium bromide (CTAB) and sorbitan monooleate (SPAN 80) and the effect of surfactants on the tribological properties has been studied. Pristine and surface modified MWCNTs in weight per cent range of 0·5% are dispersed in CI4 plus diesel engine oil. The foaming tendency and other physico-chemical properties of test lubricant have been studied to investigate the effect of nano materials and surfactants. The anti-wear and anti-friction properties are tested on a four ball wear tester and the comparison is made to assess the relative performance of pristine MWCNTs over surface modified MWCNTs. A strong influence of the surface modification technique is found on lubricating and physico-chemical properties. Both CTAB and SPAN 80 could keep the MWCNTs stable in the lubricant without compromising the foaming tendency of lubricant and other physico-chemical properties. The friction and wear characteristics of lubricants have improved with the dispersion of surface modified MWCNTs while there is no improvement in the properties of lubricant dispersed with pristine MWCNTs. 相似文献
99.
为了减少焊缝识别中传感器安装位置带来的前置误差,提高识别精度,设计了一款多线激光传感器,对多线激光在V型焊缝上的图像进行处理得到焊缝轨迹。提出一种基于动态不规则感兴趣区域的图像分割方法,将多条激光分割后并行处理。单条激光线图像预处理后以像素行灰度值之和的极大值确定激光条纹所在行,对激光条纹分段拟合后求交点,得到坡口边缘与焊缝位置的特征点,并将焊缝位置特征点拟合得到焊缝轨迹。根据所提出的算法编写了焊缝轨迹识别程序,并进行实验,结果表明,所提出的算法识别焊缝走向误差在0.5°之内,符合焊缝跟踪的要求。 相似文献
100.
通过分析影响型钢柱焊接的主要因素,制定了一系列质量控制措施,然后在明确焊接质量标准和检验要求的基础上提出了质量管理措施,最后从安全、文明、环保方面总结了注意要点,以确保型钢柱焊接质量。 相似文献