全文获取类型
收费全文 | 59683篇 |
免费 | 1832篇 |
国内免费 | 801篇 |
专业分类
电工技术 | 828篇 |
综合类 | 63篇 |
化学工业 | 9790篇 |
金属工艺 | 3390篇 |
机械仪表 | 1714篇 |
建筑科学 | 1371篇 |
矿业工程 | 191篇 |
能源动力 | 1710篇 |
轻工业 | 5648篇 |
水利工程 | 569篇 |
石油天然气 | 1453篇 |
武器工业 | 2篇 |
无线电 | 4738篇 |
一般工业技术 | 13507篇 |
冶金工业 | 11435篇 |
原子能技术 | 850篇 |
自动化技术 | 5057篇 |
出版年
2022年 | 381篇 |
2021年 | 738篇 |
2020年 | 666篇 |
2019年 | 799篇 |
2018年 | 1435篇 |
2017年 | 1382篇 |
2016年 | 1480篇 |
2015年 | 1120篇 |
2014年 | 1533篇 |
2013年 | 3793篇 |
2012年 | 2514篇 |
2011年 | 2812篇 |
2010年 | 2283篇 |
2009年 | 2502篇 |
2008年 | 2363篇 |
2007年 | 2471篇 |
2006年 | 1845篇 |
2005年 | 1571篇 |
2004年 | 1546篇 |
2003年 | 1398篇 |
2002年 | 1362篇 |
2001年 | 1328篇 |
2000年 | 1150篇 |
1999年 | 1260篇 |
1998年 | 3515篇 |
1997年 | 2552篇 |
1996年 | 2005篇 |
1995年 | 1271篇 |
1994年 | 993篇 |
1993年 | 1043篇 |
1992年 | 682篇 |
1991年 | 650篇 |
1990年 | 598篇 |
1989年 | 560篇 |
1988年 | 446篇 |
1987年 | 464篇 |
1986年 | 429篇 |
1985年 | 461篇 |
1984年 | 352篇 |
1983年 | 337篇 |
1982年 | 348篇 |
1981年 | 357篇 |
1980年 | 394篇 |
1979年 | 364篇 |
1978年 | 316篇 |
1977年 | 510篇 |
1976年 | 803篇 |
1975年 | 321篇 |
1974年 | 307篇 |
1973年 | 323篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
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
82.
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
83.
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
84.
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
85.
86.
An Imhoff tank was reconstructed into a 250 m3 UASB reactor in order to treat a malting plant wastewater. The UASB was inoculated with sludge from an anaerobic lagoon used for slaughterhouse wastewater treatment. After two months of operation the reactor achieved full load with an HRT of 17 h, a COD removal higher than 80% and a biogas production of 300 m3/day (77% average methane content), with an organic loading rate of 3.6 kgCOD/m3.d (0.24 kgCOD/kgVSS.d). A yield coefficient of 0.09 gVSS/gCODrem was found from a mass balance. The fat present in the inoculated sludge (48 mg/gSSV) did not affect the start up performance. Sludge from the inoculum with high content of fat (270 mg/gSSV), was separated by flotation in the first week of operation. The COD removal efficiency was scarcely influenced by the reactor operation temperature (17-25 degrees C). 相似文献
87.
88.
89.
J. Gutirrez J. M. Barandiarn Z. Kaczkowski 《Materials Science and Engineering: A》2004,370(1-2):392-395
The change of magnetoelastic properties after thermal treatments has been investigated for two groups of metallic glasses. (Fe79Co21)75+xSi15−1.4xB10+0.4x (x (at.%)=0, 2, 4, 6, 8, 10) has been studied both in the as-prepared state and after thermal annealing in an applied magnetic field, to achieve a particular domain structure, at temperatures well below the crystallization temperatures. Changes in the ΔE effect, magnetomechanical coupling (k) and internal friction coefficient (Q−1) are reported, reaching values of about 60% of the saturation value ES. Fe64Ni10Nb3Cu1Si13B9 alloys annealed in vacuum for 1 h in the temperature range 350–550 °C showed maximum values of the ΔE effect and k of 61% and 0.85, respectively, accompanied by a minimum value of Q of around 2 for the sample annealed at 460 °C. These variations are related to the progress of nanocrystalization. The properties achieved are among the best reported for magnetomechanical applications. 相似文献
90.
A.L. Pan H.G. ZhengZ.P. Yang F.X. Liu Z.J. Ding Y.T. Qian 《Materials Research Bulletin》2003,38(5):789-796
Small Ag particles or clusters dispersed mesoporous SiO2 composite films were prepared by a new method: First the matrix SiO2 films were prepared by sol-gel process combined with the dip-coating technique, then they were soaked in AgNO3 solutions followed by irradiation of γ-ray at room temperature and in ambient pressure. The structures of these films were examined by X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), and optical absorption spectroscopy. It has been shown that the Ag particles grown within the porous SiO2 films are very small, and they are isolated and dispersed from each other with very narrow size distributions. With increasing the soaking concentration and an additional annealing, an opposite peakshift effect of the surface plasmon resonance (SPR) was observed in the optical absorption measurements. 相似文献