全文获取类型
收费全文 | 3477篇 |
免费 | 314篇 |
国内免费 | 150篇 |
专业分类
电工技术 | 221篇 |
综合类 | 191篇 |
化学工业 | 585篇 |
金属工艺 | 200篇 |
机械仪表 | 212篇 |
建筑科学 | 282篇 |
矿业工程 | 97篇 |
能源动力 | 100篇 |
轻工业 | 220篇 |
水利工程 | 59篇 |
石油天然气 | 279篇 |
武器工业 | 24篇 |
无线电 | 407篇 |
一般工业技术 | 441篇 |
冶金工业 | 180篇 |
原子能技术 | 24篇 |
自动化技术 | 419篇 |
出版年
2024年 | 24篇 |
2023年 | 64篇 |
2022年 | 114篇 |
2021年 | 158篇 |
2020年 | 131篇 |
2019年 | 102篇 |
2018年 | 112篇 |
2017年 | 85篇 |
2016年 | 116篇 |
2015年 | 146篇 |
2014年 | 189篇 |
2013年 | 216篇 |
2012年 | 203篇 |
2011年 | 220篇 |
2010年 | 192篇 |
2009年 | 186篇 |
2008年 | 165篇 |
2007年 | 160篇 |
2006年 | 177篇 |
2005年 | 190篇 |
2004年 | 114篇 |
2003年 | 105篇 |
2002年 | 90篇 |
2001年 | 88篇 |
2000年 | 100篇 |
1999年 | 80篇 |
1998年 | 75篇 |
1997年 | 67篇 |
1996年 | 50篇 |
1995年 | 39篇 |
1994年 | 46篇 |
1993年 | 28篇 |
1992年 | 19篇 |
1991年 | 11篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1985年 | 4篇 |
1984年 | 8篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 1篇 |
排序方式: 共有3941条查询结果,搜索用时 15 毫秒
101.
基于SFS方法的三维表面重建算法研究 总被引:4,自引:0,他引:4
SFS(由明暗恢复形状)方法研究是计算机三维视觉研究领域中的一个重要分支.以朗伯体光照漫反射模型为基础,对物体表面图像明暗恢复其表面高度和梯度的抽象模型进行分析,研究基于朗伯体定律求解受光点梯度的算法及SFS方法的实现原理. 相似文献
102.
DInSAR technology was used to monitor subsidence caused by underground coal mining activities in mountainous area, with multi source SAR data, including 8 EnviSAT C-band and 4 ALOS L-band, and 4 programmed TerraSAR-X dataset. The results revealed that 2-pass DInSAR technique sometimes failed to retrieve the mining-caused subsidence due to spatial and/or temporal de-correlation. We also noticed that there existed residual topographic phase after the compensation with SRTM DEM, which could almost overwhelm the subsidence information when the perpendicular baseline was relatively large. Based on the mining materials, analysis was made on the shape of subsidence area. For the well geo-coded results from TerraSAR-X, confirmed by GPS surveying results of corner reflectors, we tried to extract the advance distance of influence besides the subsidence area. Due to the big deformation gradient over stopingfaces, the X-band SAR data could not capture the maximum value subsidence revealed by GPS survey in our preliminary results, the same as C-band EnviSAT data. This will turn to be our research subject in the next few months. 相似文献
103.
采用密度泛函理论的B3LYP方法,在6-311+G(d,p)基组水平上研究了CH3SCH3与H2O2的微观反应机理,全参数优化了反应势能面上各驻点的几何构型,振动分析和内禀反应坐标(IRC)分析结果证实了中间体和过渡态的真实性,计算所得的键鞍点电荷密度的变化情况也确认了反应过程.结果表明,反应共分2步进行,主要经历了O对S的进攻、H转移以及O-O键断裂的历程.并分别考察了其在水中和甲苯的溶剂效应.结果表明,溶剂效应降低了反应的活化能,并使过渡态红外光谱蓝移. 相似文献
104.
Kejian Bian 《Polymer》2006,47(16):5744-5753
2-(Dimethylamino)ethyl acrylate (DMAEA) was grafted from the surface of alkoxyamine-functionalized crosslinked poly(styrene-co-chloromethylstyrene) microspheres by nitroxide-mediated radical polymerization (NMRP). Latex particles (∼60 nm diameter) bearing chloromethyl groups were synthesized by emulsion polymerization. N-tert-butyl-N-(1-diethyl phosphono-2,2-dimethylpropyl)nitroxide (SG1) was then immobilized on the particle surface. Microspheres grafted with the homopolymer pDMAEA, as well as block copolymers poly(styrene-b-DMAEA) and poly(butyl acrylate-b-DMAEA) were prepared by surface-initiated NMRP in N,N-dimethylformamide at 112 °C, with the addition of free SG1 to ensure that control is maintained. Particle size increases with number average molecular weight (Mn) of untethered polymers. The polymerizations exhibit linear first order kinetic plots and slight curvature of evolution of Mn with conversion. The functional microspheres were analyzed by infrared spectroscopy, transmission electron microscopy and thermal analysis, as well as their dispersibility in water; the results support the formation of surface-grafted pDMAEA on the microspheres. 相似文献
105.
D. G. Zhao X. F. Liu Y. C. Pan Y. X. Liu X. F. Bian 《Journal of Materials Science》2006,41(13):4227-4232
AlSiCuMgNi piston composites reinforced with in-situ TiB2 particles were fabricated by mixing salts reaction process successfully. Microstructures of the composites were observed
by mean of scanning electron microscope (SEM) and transmission electron microscope (TEM). X-ray diffraction (XRD) was used
to identify the phases in the composites. TiB2 reinforcement grows in equiaxed or near equiaxed shape and the interfaces between reinforcements and matrix are clear. Compared
with the matrix alloys, the composites show an obvious aging peak and an incubation time in the hardness. The aging is accelerated
in the composites reinforced with TiB2. At room temperature, the ultimate tensile strength (UTS) of the composites increases as the percentage of TiB2 reinforcement increases. When the temperature is beyond 250°C, the ultimate tensile strength of the piston composites decreases
sharply. The fracture surfaces of the piston composites are analyzed. 相似文献
106.
ZnO thin films have been deposited by pulsed laser deposition (PLD) and ultrasonic spray pyrolysis (USP) method, respectively. X-ray diffraction and transmission electron microscopy characterizations indicate that ZnO film grown by PLD exhibits better crystallinity than that grown by USP. Photoluminescence spectra show that the near-band edge ultraviolet emission of film grown by PLD is narrower and shifts to higher energy, compared with that of film grown by USP. In the visible range, ZnO film grown by PLD exhibits four local level emission centered at 470 nm, 486 nm, 544 nm, and 613 nm, respectively, while the film grown by USP only presents a weak broad band emission centered at 502 nm. Hall measurement shows higher carrier density and lower hall mobility in ZnO film grown by PLD than that in film grown by USP. The higher density of intrinsic defects as well as higher crystallintiy is considered to account for the difference of photoluminescence in ZnO film grown by PLD with that in film grown by USP. 相似文献
107.
108.
文中对空间数学模型的建立方法以及不同方法的优缺点进行了分析比较,指出基于人工神经网络的建模方法是目前GIS应用领域中行之有效的方法之一,最后通过实例对该方法的有效性进行了验证。 相似文献
109.
110.