全文获取类型
收费全文 | 13776篇 |
免费 | 726篇 |
国内免费 | 1108篇 |
专业分类
电工技术 | 228篇 |
综合类 | 623篇 |
化学工业 | 1322篇 |
金属工艺 | 5995篇 |
机械仪表 | 439篇 |
建筑科学 | 47篇 |
矿业工程 | 145篇 |
能源动力 | 481篇 |
轻工业 | 46篇 |
水利工程 | 3篇 |
石油天然气 | 61篇 |
武器工业 | 114篇 |
无线电 | 690篇 |
一般工业技术 | 4101篇 |
冶金工业 | 977篇 |
原子能技术 | 121篇 |
自动化技术 | 217篇 |
出版年
2024年 | 33篇 |
2023年 | 277篇 |
2022年 | 236篇 |
2021年 | 433篇 |
2020年 | 417篇 |
2019年 | 401篇 |
2018年 | 364篇 |
2017年 | 416篇 |
2016年 | 321篇 |
2015年 | 380篇 |
2014年 | 554篇 |
2013年 | 878篇 |
2012年 | 658篇 |
2011年 | 1151篇 |
2010年 | 689篇 |
2009年 | 825篇 |
2008年 | 744篇 |
2007年 | 821篇 |
2006年 | 842篇 |
2005年 | 663篇 |
2004年 | 671篇 |
2003年 | 613篇 |
2002年 | 442篇 |
2001年 | 347篇 |
2000年 | 338篇 |
1999年 | 301篇 |
1998年 | 227篇 |
1997年 | 272篇 |
1996年 | 194篇 |
1995年 | 175篇 |
1994年 | 163篇 |
1993年 | 120篇 |
1992年 | 115篇 |
1991年 | 83篇 |
1990年 | 75篇 |
1989年 | 76篇 |
1988年 | 31篇 |
1987年 | 31篇 |
1986年 | 31篇 |
1985年 | 24篇 |
1984年 | 38篇 |
1983年 | 20篇 |
1982年 | 28篇 |
1981年 | 19篇 |
1980年 | 16篇 |
1979年 | 18篇 |
1978年 | 15篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
41.
Ferdinando Auricchio Lorenza Petrini 《International journal for numerical methods in engineering》2004,61(6):807-836
An always increasing knowledge on material properties as well as a progressively more sophisticated production technology make shape memory alloys (SMA) extremely interesting for the industrial world. At the same time, SMA devices are typically characterized by complex multi‐axial stress states as well as non‐homogeneous and non‐isothermal conditions both in space and time. This aspect suggests the finite element method as a useful tool to help and improve application design and realization. With this aim, we focus on a three‐dimensional macroscopic thermo‐mechanical model able to reproduce the most significant SMA features (Int. J. Numer. Methods Eng. 2002; 55 : 1255–1264), proposing a simple modification of such a model. However, the suggested modification allows the development of a time‐discrete solution algorithm, which is more effective and robust than the one previously discussed in the literature. We verify the computational tool ability to simulate realistic mechanical boundary value problems with prescribed temperature dependence, studying three SMA applications: a spring actuator, a self‐expanding stent, a coupling device for vacuum tightness. The effectiveness of the model to solve thermo‐mechanical coupled problems will be discussed in a forthcoming work. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
42.
本文研究了具有典型分解特征的Al-Zn-Ce非晶合金的形成和晶化过程,探讨了各种相的生成顺序。XRD和DSC测试结果表明强烈的化合物短程序有利于Al-Zn-Ce非晶合金的形成。在Al-Zn-Ce非晶合金的晶化过程中存在复杂的相选择行为,多种相的竞争形核和有限生长使其具有复杂的结构特点。同时,结果也表明冷速对该体系非晶的形成有很大影响。 相似文献
43.
A. MONSALVE M. PÁEZ M. TOLEDANO A. ARTIGAS Y. SEPÚLVEDA y N. VALENCIA 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(8):748-758
The S-N-P (stress, number of cycles, failure probability) curves for 2024 T3 and 7075 T7351 aluminium alloys were obtained. Previously, surface treatments of degreasing and different types of anodizing were applied to samples, evaluating the influence of these treatments on the fatigue life of the alloys. The determination of the S-N-P curves was done using Maennig's method. Rotary fatigue was used because this technique produces greater stress on the sample surfaces, the zone in which it is important to evaluate fatigue resistance. Both the transition range and the finite life range were evaluated, calculating the 1, 50 and 99% fracture probability. SEM was performed in order to characterize the fracture micromechanism. The conclusions were that Maennig's method is useful to evaluate fatigue life of these materials in a fast and efficient manner. Moreover, surface treatments produce a decrease in the fatigue life of both alloys, associating this effect with the surface damage produced on each sample during the treatment. 相似文献
44.
Al-Li alloys being developed as lighter, substitutes for conventional high strength Al alloys are to be processed by routine
methods. During extrusion of a 8090 Al-Li alloy, the extrusion die container failed causing some alarm. This failed die container
was analysed to examine if the failure was caused by interaction of Li diffusing out of Al-Li alloy with the carbides of die
steel. The evidence, although not conclusive, is sufficient to exercise caution during such processing. 相似文献
45.
Flávio A. Pavan Sidinei A. Gobbi Celso C. Moro Tania M.H. Costa Edilson V. Benvenutti 《Journal of Porous Materials》2002,9(4):307-311
Anilinepropylsilica hybrid powder was synthesized by a sol-gel route in basic medium using HF as catalyst. The effect of the amount of HF catalyst on the morphologies and on organic content was studied. The xerogels were characterized using FTIR, SEM and N2 adsorption-desorption isotherms. The increase in the HF quantity results in an slight increase in organic content and changes in the particle size, surface area and pore structure. 相似文献
46.
机械合金化Fe50Ti50非晶的形成及球磨强度对它的影响 总被引:3,自引:0,他引:3
本文通过电子扫描和X衍射对机械合金人Fe50Ti50非晶粉末形成做了研究。研究发现:机械合金非晶形成可以大致地分为二个阶段-粉末的破碎阶段和非晶的形成阶段。另外,对球磨强度对非晶形成的影响进行了研究。结果表明:强度低时粉末需要较长的时间才能形成非晶,强度高时粉末形成非晶的时间大大缩短,但在随后的球磨中,粉末会重新晶化形成新相。 相似文献
47.
A general numerical model is described for the dissolution kinetics of spherical particles in binary systems for any combination of first order reactions at the particle-matrix interface and long distance diffusion within the matrix. The model is applicable to both finite and infinite media and handles both complete and partial particle dissolution. It is shown that interfacial reactions can have a strong effect on the dissolution kinetics, the solute concentration at the particle-matrix interface and the solute concentration profile in the matrix. 相似文献
48.
Investigations have been carried out on an erosion-corrosion apparatus to investigate the behaviour of corrosion-resistant highalloy iron-base materials containing hard phases. These materials had been optimized for increased wear resistance under complex stress conditions. As expected, in dry erosion tests, very low mass losses were established; there was little difference between the materials. Also, in corrosive environments (NaCl, H2SO4), the materials showed good stability; however, the duplex structures were superior to the martensitic ones. The combination of erosion and corrosion produced large differences and, in some cases, markedly reduced resistance to damage. These results confirmed observations that it is impossible to deduce the environmentally influenced mechanical behaviour of an alloy from its behaviour in separate corrosion and erosion experiments. The basic mechanisms underlying these processes have been investigated only tentatively. 相似文献
49.
50.
本文对激光结晶a-Si∶H SOI结构砷注入和快速退火行为作了研究.a-Si∶H激光结晶有Lp-LCR,OD,FCR-2,FCR-1四个结晶区.用剖面电镜观察了结晶区的结构.扩展电阻测量表明Lp-LCR区中有两种扩散机制,即杂质在晶粒体内扩散和沿缺陷扩散.OD区中有三种扩散形式,除有上述两种以外,还有沿缺陷的扩散.首次比较了沿晶界和缺陷的扩散速度. 相似文献