全文获取类型
收费全文 | 8967篇 |
免费 | 349篇 |
国内免费 | 589篇 |
专业分类
电工技术 | 105篇 |
综合类 | 302篇 |
化学工业 | 1032篇 |
金属工艺 | 1259篇 |
机械仪表 | 1193篇 |
建筑科学 | 91篇 |
矿业工程 | 52篇 |
能源动力 | 269篇 |
轻工业 | 68篇 |
水利工程 | 24篇 |
石油天然气 | 49篇 |
武器工业 | 78篇 |
无线电 | 2392篇 |
一般工业技术 | 2118篇 |
冶金工业 | 171篇 |
原子能技术 | 197篇 |
自动化技术 | 505篇 |
出版年
2024年 | 28篇 |
2023年 | 127篇 |
2022年 | 175篇 |
2021年 | 239篇 |
2020年 | 219篇 |
2019年 | 169篇 |
2018年 | 191篇 |
2017年 | 224篇 |
2016年 | 238篇 |
2015年 | 244篇 |
2014年 | 419篇 |
2013年 | 480篇 |
2012年 | 467篇 |
2011年 | 625篇 |
2010年 | 434篇 |
2009年 | 481篇 |
2008年 | 501篇 |
2007年 | 529篇 |
2006年 | 520篇 |
2005年 | 461篇 |
2004年 | 385篇 |
2003年 | 326篇 |
2002年 | 348篇 |
2001年 | 247篇 |
2000年 | 233篇 |
1999年 | 228篇 |
1998年 | 245篇 |
1997年 | 219篇 |
1996年 | 167篇 |
1995年 | 124篇 |
1994年 | 134篇 |
1993年 | 114篇 |
1992年 | 76篇 |
1991年 | 63篇 |
1990年 | 65篇 |
1989年 | 43篇 |
1988年 | 43篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1978年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有9905条查询结果,搜索用时 15 毫秒
91.
92.
XU Xiang-yang HAN Jian-min ZHONG Min-lin LIU Wen-jin . Institute of Materials Science Engineering Beijing Jiaotong University Beijing China . Department of Mechanical Engineering Tsinghua University Beijing China 《材料热处理学报》2004,25(5)
NiAl intermetallic alloys are potential high temperaturestructural materials in aeronautical and astronauticalindustries[1].However,the poor ductility andtoughness at room temperature severely restrict theirengineering applications[2,3].It is important todevelop new technology to product intermetallicmaterials for the improvement of the comprehensiveproperties and the workability.Laser powder depositionhas been used to synthesize many new materials.Furthermore,if incorporated with rapid proto… 相似文献
93.
94.
95.
The objective of this study is to experimentally investigate the cutting mechanisms of polycrystalline diamond compacts (PDC) using two different lasers: (a) a near infrared Nd:YAG laser (Neodymium-doped Yttrium Aluminum Garnet) of 1064 nm wavelength and 100 μs pulse width; and (b) a green light KTP (Potassium Titanyl Phosphate)/Nd:YAG laser of 532 nm wavelength and 120 ns pulse width. To realize the objective, the study applies polishing, lapping and etching processes to the cut-surfaces of the PDC samples. It further observes and analyzes the processed cut-surfaces with scanning electron microscopy (SEM) and Raman spectroscopy. A discussion is provided to reveal the underlying physics of the laser cutting mechanisms, and a conclusion is drawn based on the outcomes from the experimental investigation and the discussion. 相似文献
96.
介绍了激光切割工艺的优点及数控激光切割机的基本构成。在此基础上,重点论述了数控激光切割机主机的构成部件及设计要点。 相似文献
97.
The significance of deposition point standoff variations in multiple-layer coaxial laser cladding (coaxial cladding standoff effects) 总被引:3,自引:0,他引:3
Andrew J. Pinkerton Lin Li 《International Journal of Machine Tools and Manufacture》2004,44(6):573-584
Direct laser deposition (DLD) is an additive manufacturing process that builds up a part layer-by-layer by fusing metal powder to a solid substrate. A coaxial laser and powder delivery head is commonly used, and here a critical process variable is the standoff distance between the nozzle and the material deposition point. This contribution investigates the role of this variable and the effect that it has on the final part geometry. The experimental results show that good layer consistency can, in fact, be obtained with no movement of the substrate between layers for more than 20 layers, or 10 mm under tested conditions, and that poorer results are obtained by regular movement of the substrate by a badly chosen constant amount. A theoretical analysis of the situation establishes a method to estimate melt pool size using an analytically calculated temperature near the heat source. Based on this, simple heat and mass flow models are established to allow some of the results to be explained. 相似文献
98.
Wear resistant Cr–Cu–Si metal silicide alloys with different Cu contents were fabricated by the laser melting process. The Cr–Cu–Si alloys have a similar microstructure consisting of the Cr5Si3/CrSi dual-phase primary dendrites and the interdendritic Cu-based solid solution (Cuss). The Cu content has no effect on the phase constitutions of the alloys. The Cr5Si3/CrSi dendrite volume fraction and hardness of the Cr–Cu–Si alloys decrease with the increasing Cu content. Wear test results indicate that all the Cuss-toughened metal silicide alloys have excellent wear resistance and low coefficient of friction. Wear resistance increases and friction coefficient decreases with the decreasing Cu content. 相似文献
99.
This paper deals with a method for the dynamic calibration of the kinematic accuracy of lathes and thread grinding machines in screw-cutting mode but free of load. It utilizes a precision polygon mounted on the spindle, in conjunction with a trigger device to generate angular pulses. A laser interferometer system assesses the longitudinal position of the saddle with respect to a cube-corner affixed on the chuck. As the spindle rotates, a string of pulses is generated by the angular trigger device. These pulses are used for triggering the laser interferometer. A software package has been elaborated to enable on-the-fly data acquisition and to display the kinematic errors in graphical form. The components of the kinematic error considered are the progressive pitch error, the cyclic error and spindle-free float. Application of this kinematic error calibrator on a universal and a CNC lathe has been carried out. Test results are presented and commented. 相似文献
100.
Mar-M 247, a nickel-base cast alloy, is used widely in aeroengines for parts such as blades, vanes and airfoil. Hastelloy X is one of the most oxidation- and corrosion-resistant nickel-base wrought alloys. In order to join such alloys in aeroengine manufacturing, laser beam welding has been carried out with lap and butt joints using a 1.2 and a 6.0 kW CO2 laser. Cracks in the fusion zone can be eliminated by deliberate misalignments in the ranging of the laser beam by 0.2−0.3 mm onto Hastelloy X. Correlations between cracking behavior, hardness of the beads and misalignments have been investigated. Metallurgical analysis using electron microscopes has revealed the redistribution of alloy elements, the microstructures of the fusion zone and microfissures in the heat-affected zone (HAZ). 相似文献