全文获取类型
收费全文 | 42272篇 |
免费 | 597篇 |
国内免费 | 787篇 |
专业分类
电工技术 | 727篇 |
综合类 | 51篇 |
化学工业 | 6403篇 |
金属工艺 | 3095篇 |
机械仪表 | 1386篇 |
建筑科学 | 863篇 |
矿业工程 | 151篇 |
能源动力 | 1429篇 |
轻工业 | 2275篇 |
水利工程 | 356篇 |
石油天然气 | 1387篇 |
无线电 | 4011篇 |
一般工业技术 | 10686篇 |
冶金工业 | 7263篇 |
原子能技术 | 791篇 |
自动化技术 | 2782篇 |
出版年
2021年 | 342篇 |
2020年 | 276篇 |
2019年 | 375篇 |
2018年 | 666篇 |
2017年 | 657篇 |
2016年 | 745篇 |
2015年 | 539篇 |
2014年 | 811篇 |
2013年 | 2392篇 |
2012年 | 1413篇 |
2011年 | 1886篇 |
2010年 | 1491篇 |
2009年 | 1782篇 |
2008年 | 1626篇 |
2007年 | 1772篇 |
2006年 | 1401篇 |
2005年 | 1227篇 |
2004年 | 1181篇 |
2003年 | 1082篇 |
2002年 | 1069篇 |
2001年 | 1126篇 |
2000年 | 967篇 |
1999年 | 1008篇 |
1998年 | 2130篇 |
1997年 | 1667篇 |
1996年 | 1443篇 |
1995年 | 985篇 |
1994年 | 762篇 |
1993年 | 776篇 |
1992年 | 601篇 |
1991年 | 577篇 |
1990年 | 525篇 |
1989年 | 491篇 |
1988年 | 372篇 |
1987年 | 403篇 |
1986年 | 366篇 |
1985年 | 381篇 |
1984年 | 306篇 |
1983年 | 300篇 |
1982年 | 303篇 |
1981年 | 297篇 |
1980年 | 349篇 |
1979年 | 341篇 |
1978年 | 294篇 |
1977年 | 418篇 |
1976年 | 634篇 |
1975年 | 308篇 |
1974年 | 294篇 |
1973年 | 312篇 |
1972年 | 275篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
31.
Several kinds of waveguide components such as curved waveguide bends, arbitrary angle waveguide bends and T-junctions have been analyzed with boundary element method in this paper. A new discretization method for the boundary element method to solve the waveguide discontinuities has been given. The numerical results obtained agree well with the experimental results and numerical results in other literature. Especially, the scattering characteristics of Forded E-, H-plane T-junctions in 3mm band have been analyzed using boundary element method and the calculation results are presented. 相似文献
32.
33.
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
34.
35.
F. M. Xu S. J. Zhu J. Zhao M. Qi F. G. Wang S. X. Li Z. G. Wang 《Materials Science and Engineering: A》2003,360(1-2):191-196
The SiC/Al graded composite was fabricated by powder metallurgy processing and its fatigue crack growth behavior was studied. The volume percentage of SiC particulates was distributed from 5 to 30% layer by layer on the cross section. Since the aluminium was dissolved together, there was no evident interface between the two layers with different volume fraction of SiC particulates. Fatigue crack growth was in direction of from 5 to 30% SiC layers under sinusoidal wave-form. The retardation of fatigue crack growth was found when crack propagated from low volume fraction of SiC to high volume fraction of SiC. The crack deflection and branching between two layers were observed, which decreased crack growth rates. In view of crack tip driving force, the plasticity mismatch between the layers shielded crack tip driving force, i.e. decreased the effective J-integral at the tip of the crack as the plastic zone of the crack tip spread from the weaker material into the stronger material. 相似文献
36.
37.
New information systems and recent applications (grid computing, Web Services, and so on) are often distributed, large-scale, open, heterogeneous, and characterized by a dynamic environment. To model these complex systems, researchers have spent much effort during the last few years on multiagent systems. The aim is to model complex distributed systems as a set of (possibly organized) software agents that interact in a common environment. The decomposition of a system into a number of agents lets the system react and adapt better in a changing environment. Moreover, organized structures ("social" structures) can emerge from interactions between agents, which in turn constrain and coordinate the agents' behavior. A multiagent system takes its metaphors of interaction from social systems rather than using the metaphor of the isolated thinker that early artificial intelligence researchers preferred. An important issue when dealing with this increasing complexity is to build adaptive agents and multiagent systems. Agents and multiagent systems must be aware of their own capabilities and of changes to other agents and their environment. To remain effective, agents must be able to adapt their structures and knowledge while they execute. 相似文献
38.
A simple template‐free high‐temperature evaporation method was developed for the growth of crystalline Si microtubes for the first time. As‐grown Si microtubes were characterized using X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and room‐temperature photoluminescence. The lengths of the Si tubes can reach several hundreds of micrometers; some of them have lengths on the order of millimeters. Each tube has a uniform outer diameter along its entire length, and the typical outer diameter is ≈ 2–3 μm. Most of the tubes have a wall thickness of ≈ 400–500 nm, though a considerable number of them exhibit a very thin wall thickness of ≈ 50 nm. Room‐temperature photoluminescence measurement shows the as‐synthesized Si microtubes have two strong emission peaks centered at ≈ 589 nm and ≈ 617 nm and a weak emission peak centered at ≈ 455 nm. A possible mechanism for the formation of these Si tubes is proposed. We believe that the present discovery of the crystalline Si microtubes will promote further experimental studies on their physical properties and smart applications. 相似文献
39.
Effect of doping of carbon nanotubes by magnetic transition metal atoms has been considered in this paper. In the case of
semiconducting tubes, it was found that the system has zero magnetization, whereas in metallic tubes the valence electrons
of the tube screen the magnetization of the dopants: the coupling to the tube is usually antiferromagnetic (except for Cr). 相似文献
40.
Wavelet-based Rayleigh background removal in MRI 总被引:1,自引:0,他引:1
Rayleigh distribution governs noise in 'no signal' regions of magnetic resonance magnitude images. Large areas of background noise in MRI images will seriously affect their effective utilisation. A new wavelet-based algorithm is presented that can work efficiently either as a standalone procedure or couple with existing denoising algorithms to significantly improve their effectiveness. 相似文献