全文获取类型
收费全文 | 74869篇 |
免费 | 2975篇 |
国内免费 | 1961篇 |
专业分类
电工技术 | 2221篇 |
综合类 | 1974篇 |
化学工业 | 12203篇 |
金属工艺 | 4605篇 |
机械仪表 | 3273篇 |
建筑科学 | 3858篇 |
矿业工程 | 761篇 |
能源动力 | 2459篇 |
轻工业 | 4306篇 |
水利工程 | 833篇 |
石油天然气 | 3191篇 |
武器工业 | 210篇 |
无线电 | 7961篇 |
一般工业技术 | 14895篇 |
冶金工业 | 8909篇 |
原子能技术 | 1216篇 |
自动化技术 | 6930篇 |
出版年
2023年 | 511篇 |
2022年 | 925篇 |
2021年 | 1435篇 |
2020年 | 1115篇 |
2019年 | 1090篇 |
2018年 | 1449篇 |
2017年 | 1585篇 |
2016年 | 1590篇 |
2015年 | 1634篇 |
2014年 | 2238篇 |
2013年 | 4225篇 |
2012年 | 3340篇 |
2011年 | 3987篇 |
2010年 | 3258篇 |
2009年 | 3555篇 |
2008年 | 3346篇 |
2007年 | 3462篇 |
2006年 | 3147篇 |
2005年 | 2796篇 |
2004年 | 2267篇 |
2003年 | 2043篇 |
2002年 | 2027篇 |
2001年 | 1922篇 |
2000年 | 1857篇 |
1999年 | 1968篇 |
1998年 | 3051篇 |
1997年 | 2426篇 |
1996年 | 2195篇 |
1995年 | 1609篇 |
1994年 | 1246篇 |
1993年 | 1221篇 |
1992年 | 904篇 |
1991年 | 796篇 |
1990年 | 745篇 |
1989年 | 636篇 |
1988年 | 493篇 |
1987年 | 493篇 |
1986年 | 436篇 |
1985年 | 432篇 |
1984年 | 348篇 |
1983年 | 331篇 |
1982年 | 333篇 |
1981年 | 315篇 |
1980年 | 367篇 |
1979年 | 351篇 |
1978年 | 301篇 |
1977年 | 425篇 |
1976年 | 641篇 |
1975年 | 313篇 |
1973年 | 319篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
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
82.
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
83.
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
84.
85.
Shiao-Shien Chen Tung-Yang Chen Tien-Hao Tang Jin-Lian Su Tzer-Min Shen Jen-Kon Chen 《Electron Devices, IEEE Transactions on》2003,50(7):1683-1689
This paper proposes a novel low-leakage BiCMOS deep-trench (DT) diode in a 0.18-/spl mu/m silicon germanium (SiGe) BiCMOS process. By means of the DT and an n/sup +/ buried layer in the SiGe BiCMOS process, a parasitic vertical p-n-p bipolar transistor with an open-base configuration is formed in the BiCMOS DT diode. Based on the two-dimensional (2-D) simulation and measured results, the BiCMOS DT diode indeed has the lowest substrate leakage current as compared to the conventional p/sup +//n-well diode even at high temperature conditions, which mainly results from the existence of the parasitic open-base bipolar transistor. Considering the applications of the diode string in electrostatic discharge (ESD) protection circuit designs, the BiCMOS DT diode string also provides a good ESD performance. Owing to the characteristics of the low leakage current and high ESD robustness, it is very convenient for circuit designers to use the BiCMOS DT diode string in their IC designs. 相似文献
86.
87.
88.
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
89.
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
90.
以3D软件应用为中心的设计管理模式——PDS在配管设计中的应用 总被引:1,自引:0,他引:1
由PDS的特点入手,结合工程实践的应用情况,阐明了3D软件可以更广泛的应用于配管的设计中,强调了以3D模型为中心开展设计和管理的新模式. 相似文献