全文获取类型
收费全文 | 3008篇 |
免费 | 133篇 |
国内免费 | 259篇 |
专业分类
电工技术 | 29篇 |
综合类 | 163篇 |
化学工业 | 135篇 |
金属工艺 | 1441篇 |
机械仪表 | 105篇 |
建筑科学 | 2篇 |
矿业工程 | 52篇 |
能源动力 | 101篇 |
轻工业 | 9篇 |
水利工程 | 1篇 |
石油天然气 | 7篇 |
武器工业 | 40篇 |
无线电 | 103篇 |
一般工业技术 | 642篇 |
冶金工业 | 552篇 |
原子能技术 | 15篇 |
自动化技术 | 3篇 |
出版年
2024年 | 2篇 |
2023年 | 34篇 |
2022年 | 59篇 |
2021年 | 70篇 |
2020年 | 77篇 |
2019年 | 66篇 |
2018年 | 76篇 |
2017年 | 85篇 |
2016年 | 64篇 |
2015年 | 84篇 |
2014年 | 136篇 |
2013年 | 130篇 |
2012年 | 157篇 |
2011年 | 221篇 |
2010年 | 131篇 |
2009年 | 181篇 |
2008年 | 125篇 |
2007年 | 208篇 |
2006年 | 195篇 |
2005年 | 153篇 |
2004年 | 167篇 |
2003年 | 135篇 |
2002年 | 127篇 |
2001年 | 106篇 |
2000年 | 112篇 |
1999年 | 93篇 |
1998年 | 69篇 |
1997年 | 72篇 |
1996年 | 41篇 |
1995年 | 57篇 |
1994年 | 50篇 |
1993年 | 41篇 |
1992年 | 27篇 |
1991年 | 11篇 |
1990年 | 19篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1984年 | 1篇 |
1979年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有3400条查询结果,搜索用时 15 毫秒
41.
The properties of high‐speed tool steels can be improved by modifying their chemical composition or the technology of production. Nitrogen alloying is an attractive technology to enhance the mechanical and physical properties of tool steels. In this work, modified super hard high‐speed tool steel was produced through nitrogen alloying and decreasing the level of cobalt content in investigated steels. This work aims to study the effect of nitrogen as alloying element on carbides and carbo‐nitrides precipitates type, shape, and size for investigated steels. From the results obtained from Thermo‐Calc, it was concluded that nitrogen alloying produced large amount of stable austenite, also eutectic carbides precipitates (M6C and M7C3) were stable at room temperature. Transmission electron microscope (TEM) images for traditional grade showed that the as cast structure contains beside the carbides network other single carbides precipitates. While on the other hand the selected area diffraction pattern (SADP) images of nitrogen alloyed grade shows fine carbides and carbo‐nitrides precipitates with more amount of retained austenite in the ferrite matrix, they showed also the presence of the eutectic precipitates as well as the dislocations. 相似文献
42.
G.F. de Lima Andreani M.M. Miglioli M.R.M. Triques V. Roche C.S. Kiminami W.J. Botta A.M. Jorge 《International Journal of Hydrogen Energy》2017,42(16):11493-11500
2Mg-Fe mixtures produced by high-energy ball milling were consolidated into bulk form by hot extrusion at different processing temperatures (573 K (300 °C), 623 K (350 °C) and 673 K (400 °C)), aiming to evaluate their influence on the structure and microstructure of bulk materials and their consequent influence on the hydrogen sorption properties. In spite being in the nanosize range, the highest the processing temperature, the larger the grain sizes. However, the nanometric grain size remained after any hot extrusion condition, as estimated by Rietveld refinement. The pinning effect of Fe on Mg grain boundaries explained this effect. In the first absorption (activation), powders showed a hydrogen storage capacity of ~4.53 wt%, while the extruded samples (bulk materials) reached almost the same capacity during the period of hydrogenation (~94% of the maximum hydrogen storage capacity for Mg2FeH6 - 5.5 wt%). The smallest crystallite sizes and highest surface area for hydrogenation explain the good performance of powders. However, when comparing only extruded samples, it was observed that the highest capacity and the lowest incubation times were mainly related to grain sizes and to the favorable texture along (002) plane of αMg. The desorption temperature of bulk materials was very similar to that of powders, which is good considering the lower surface area of bulk materials. 相似文献
43.
Seong-Cheol Jang Byung Yong Lee Suk Woo Nam Hyung Chul Ham Jonghee Han Sung Pil Yoon Seong-Geun Oh 《International Journal of Hydrogen Energy》2014
Lump-free Ni-5 wt% Al alloy powder was successfully prepared using an AlCl3 activator at 400 °C under vacuum. The AlCl3 activator served as the catalyst, lowering the fabrication temperature by 1000 °C compared with the temperature required for the conventional process. The Ni–Al alloy was formed by the following steps: the formation of NiAl by the reaction of the Ni surface with AlCl2 or AlCl produced by the reaction between Al and AlCl3, the formation of Ni3Al by Al diffusion and reaction, and the formation of a Ni–Al solid solution by Al diffusion into the Ni matrix until the solubility limitation was reached. Although lowering the alloying temperature lengthens the reaction time, the time could be reduced by controlling the amount of AlCl3. A single cell test and a creep test were also conducted using a green sheet of as-prepared Ni–Al alloy powder as an anode of a molten carbonate fuel cell (MCFC). 相似文献
44.
A range of alloys based on the Al-4Mg-0·4Mn system were produced with selected quaternary microalloying additions. In Part 1 of this study, the electrochemical and corrosion response was studied. To characterise the sensitisation behaviour of these alloys, where sensitisation is the major mode of degradation of 5xxx alloys, heat treatment at 150°C was carried out and followed by the Nitric Acid Mass Loss Test (NAMLT) according to ASTM G67-04. Herein the alloying elements studied include silicon, zinc, titanium, zirconium and strontium. The results indicate that strontium (Sr), silicon (Si) and titanium (Ti) have a significant influence in reducing intergranular corrosion (IGC) susceptibility. 相似文献
45.
A Mg-Y-Ca-Ce magnesium alloy was optimized for high ignition-proof property, which did not burn in air at 1233 K up to 30 min. Oxidation behavior of the alloy was investigated by X-ray diffraction (XRD... 相似文献
46.
《粉末冶金学》2013,56(4):273-279
AbstractThis work concerns the mechanical alloying processing of Fe–C powders likely to be utilised for sintering of tool steel. The influence of synthesis conditions, such as milling time, gas nature in the vial (shown here as reactive) and carbon concentration in the different powder mixtures of iron and graphite, is characterised. In the second stage, the role of thermal treatment, at moderate temperature, on the highly metastable as milled products is studied. It appears that the structure is heterogeneous and shows α-ferrite, α′′′-like cubic disordered phase, hexagonal ?-carbonitride and θ-cementite. The presence of N2 gas phase appears to favour a precipitation phenomenon of the Fe3C cementite on the one hand and of epsilon carbonitride on the other hand. 相似文献
47.
Copper Tin Selenide (CuSnSe) powder was mechanically alloyed by high energy planetary ball milling, starting from elemental powders. Synthesis time and velocity have been optimized to produce Cu2SnSe3 materials. Thin films were prepared by thermal evaporation on Corning glass substrate at Ts = 300 °C. The structural, compositional, morphological and optical properties of the synthesized semiconductor have been analyzed by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), scanning electron microscopy (SEM) and transmission electron microscopy. The analyzed powder exhibited a cubic crystal structure, with the presence of Cu2Se as a secondary phase. On the other hand, the deposited films showed a cubic Cu2SnSe3 ternary phase and extra peaks belonging to some binary compounds. Furthermore, optical measurements showed that the deposited layers have a relatively high absorption coefficient of 105 cm−1 and present a band gap of 0.94 eV. 相似文献
48.
利用高能卧式搅拌球磨机,研究了利用机械合金化法制备Finemet非晶粉体的工艺,研究结果表明,通过高速球磨可以得到部分非晶粉体。非晶化机制是局域熔体的快速冷却,粉体结块和粘壁,是机械合金化法制备高纯度Finemet非晶粉体的主要阻碍因素。 相似文献
49.
50.
AbstractOrdered B2-NiAl intermetallic compound powder was successfully synthesised by mechanical alloying after 20 h in an attritor mill, starting from elemental Ni and Al powders and without subsequent heat treatment. NiAl powder obtained was homogenous and had a nanocrystalline microstructure. It was consolidated by field assisted hot pressing (FAHP), in a novel configuration with a Gleeble 3800 thermomechanical simulator. The powder was also processed by hot isostatic pressing (HIP) in order to compare both methods. The consolidation was successful by both methods obtaining above 98% of NiAl theoretical density (5·86 g cm?3). The results showed that the consolidation process by FAHP technique is effective and uniform throughout the sample as indicated by homogenous hardness values, obtaining microstructure and properties similar to those obtained with HIP technique, with certain advantages over it. The achieved room temperature yield strength of 850 MPa and fracture strain 26–28% corresponds to the bulk values of NiAl intermetallic. 相似文献