全文获取类型
收费全文 | 40580篇 |
免费 | 3889篇 |
国内免费 | 2816篇 |
专业分类
电工技术 | 1172篇 |
技术理论 | 1篇 |
综合类 | 3381篇 |
化学工业 | 6028篇 |
金属工艺 | 3814篇 |
机械仪表 | 2214篇 |
建筑科学 | 6636篇 |
矿业工程 | 834篇 |
能源动力 | 1140篇 |
轻工业 | 1462篇 |
水利工程 | 534篇 |
石油天然气 | 715篇 |
武器工业 | 202篇 |
无线电 | 6432篇 |
一般工业技术 | 8151篇 |
冶金工业 | 1443篇 |
原子能技术 | 2159篇 |
自动化技术 | 967篇 |
出版年
2024年 | 148篇 |
2023年 | 519篇 |
2022年 | 867篇 |
2021年 | 1085篇 |
2020年 | 1261篇 |
2019年 | 1224篇 |
2018年 | 1188篇 |
2017年 | 1416篇 |
2016年 | 1360篇 |
2015年 | 1383篇 |
2014年 | 2110篇 |
2013年 | 2249篇 |
2012年 | 2862篇 |
2011年 | 3186篇 |
2010年 | 2340篇 |
2009年 | 2536篇 |
2008年 | 2338篇 |
2007年 | 2792篇 |
2006年 | 2523篇 |
2005年 | 2084篇 |
2004年 | 1746篇 |
2003年 | 1566篇 |
2002年 | 1361篇 |
2001年 | 1175篇 |
2000年 | 1013篇 |
1999年 | 819篇 |
1998年 | 691篇 |
1997年 | 570篇 |
1996年 | 522篇 |
1995年 | 417篇 |
1994年 | 412篇 |
1993年 | 275篇 |
1992年 | 249篇 |
1991年 | 206篇 |
1990年 | 170篇 |
1989年 | 125篇 |
1988年 | 123篇 |
1987年 | 92篇 |
1986年 | 81篇 |
1985年 | 41篇 |
1984年 | 46篇 |
1983年 | 21篇 |
1982年 | 25篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1974年 | 4篇 |
1959年 | 15篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Spinel LiSr0·1Cr0·1Mn1·8O4 was synthesised by high temperature solid state method in order to enhance the electrochemical performance. The LiSr0·1Cr0·1Mn1·8O4 (LSCMO) materials were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. The XRD and SEM studies confirm that LSCMO had spinel crystal structure with a space group of Fd3m, and the particle of LSCMO shows irregular shape. The cyclic voltammetry data illustrated that the heavy current charge–discharge performance of LMO was improved by Sr2+ and Cr3+ doping. The galvanostatic charge–discharge of LSCMO cathode materials was measured at 1, 5, 10 and 20 C. The results indicated that LSCMO improved the capacity retention. 相似文献
3.
Cyclic tension and bend tests were performed on heat-resistant 12Cr1MoV steel specimens in as-supplied condition as well as after Zr+ ion beam surface irradiation. Distinct differences in strain induced relief, as well in cracking pattern of modified surface layer were observed by optical microscopy and interference profilometry. Changes in subsurface layer are characterized by means of nano- and microindentation and fractography of fracture surfaces (with the help of scanning electron microscopy). It is shown that the main influence on mechanical properties is mostly induced by thermal treatment during irradiation rather than formation of a 2 μm thick layer doped with Zr. The differences in deformation behavior may be explained by physical mesomechanics concepts. 相似文献
4.
The limited research on the geopolymer concrete mix design for targeting a specific strength is identified an obstacle for their effective design and wide use. In this paper, a mix design procedure has been proposed for fly-ash based geopolymer concrete and its use as infill hybrid composite beam is investigated. Then, the structural performance of geopolymer concrete filled hybrid composite beam is investigated to determine their possible application in civil infrastructure. Firstly, a detailed procedure of mix design for fly-ash based geopolymer concrete is presented. Secondly, three hybrid beams filled with geopolymer concrete were prepared and tested in a four-point bending setup to evaluate their flexural modulus and modulus of rupture. Numerical and analytical evaluation of the behaviour of hybrid beam were performed and results showed a good agreement with the experimental investigation. Thirdly, the suitability of the beam for a composite railway sleeper is evaluated and compared with existing timber and composite sleepers. Finally, the beams’ performance in a ballast railway track is analysed using Strand7 finite element simulation software and the results showed that the new concept of using geopolymer concrete as infill to pultruded composite section satisfied the stiffness and strength requirements for a railway sleeper. 相似文献
5.
6.
7.
H. L. Du S. R. Rose Z. D. Xiang P. K. Datta X. Y. Li 《Materialwissenschaft und Werkstofftechnik》2003,34(4):421-426
The oxidation/sulphidation behaviour of a Ti‐46.7Al‐1.9W‐0.5Si alloy with a TiAl3 diffusion coating was studied in an environment of H2/H2S/H2O at 850oC. The kinetic results demonstrate that the TiAl3 coating significantly increased the high temperature corrosion resistance of Ti‐46.7Al‐1.9W‐0.5Si. The SEM, EDX, XRD and TEM analysis reveals that the formation of an Al2O3 scale on the surface of the TiAl3‐coated sample was responsible for the enhancement of the corroison resistance. The Ti‐46.7Al‐1.9W‐0.5Si alloy was also modified by Nb ion implantation. The Nb ion implanted and as received sampels were subjected to cyclic oxidation in an open air at 800oC. The Nb ion implantation not only increased the oxidation resistance but also substantially improved the adhesion of scale to the substrate. 相似文献
8.
由于干态聚合物电解质目前还不能满足聚合物锂离子电池的应用要求,人们致力于开发含液体增塑剂的聚合物电解质,包括凝胶型和微孔型两类体系。本文综述了含液聚合物电解质的最新进展,重点论述了各种新体系和新方法。 相似文献
9.
10.
Electro-organic synthesis without supporting electrolyte: Possibilities of solid polymer electrolyte technology 总被引:1,自引:0,他引:1
J. Jörissen 《Journal of Applied Electrochemistry》2003,33(10):969-977
The application of ion exchange membranes as solid polymer electrolytes (SPE) in fuel cells is state-of-the-art. This technology needs no supporting electrolyte; consequently it can be applied for electro-organic syntheses in order to save process steps. In this case the process is not predetermined to a maximized energy efficiency so that the selection of the cell design, of the electrode materials and of the operating conditions can be focused on a high selectivity of the electrode reactions. The electro-osmotic stream, which is caused by the solvation shells of the ions during their migration through the membrane, and hence is a typical property of SPE technology, has a significant effect on the electrode reactions. It generates enhanced mass transfer at the electrodes, which is beneficial for reaction selectivity. It can be influenced by the choice of, and possibly by the preparation of, the membrane. An additional remarkable advantage of SPE technology is the exceptional long durability of oxide coated electrodes. By combination of several process engineering methods stable operation of SPE cells has been realized, even for examples of non-aqueous reaction systems. Experiments up to 6000 h duration and in cells of up to 250 cm2 membrane area show the potential for industrial application. 相似文献