全文获取类型
收费全文 | 33443篇 |
免费 | 2476篇 |
国内免费 | 1601篇 |
专业分类
电工技术 | 2795篇 |
综合类 | 2738篇 |
化学工业 | 4687篇 |
金属工艺 | 2444篇 |
机械仪表 | 3759篇 |
建筑科学 | 2596篇 |
矿业工程 | 1279篇 |
能源动力 | 1557篇 |
轻工业 | 1640篇 |
水利工程 | 799篇 |
石油天然气 | 1398篇 |
武器工业 | 460篇 |
无线电 | 2667篇 |
一般工业技术 | 4358篇 |
冶金工业 | 1046篇 |
原子能技术 | 484篇 |
自动化技术 | 2813篇 |
出版年
2024年 | 110篇 |
2023年 | 402篇 |
2022年 | 754篇 |
2021年 | 880篇 |
2020年 | 892篇 |
2019年 | 763篇 |
2018年 | 722篇 |
2017年 | 961篇 |
2016年 | 1039篇 |
2015年 | 1136篇 |
2014年 | 1674篇 |
2013年 | 2072篇 |
2012年 | 1991篇 |
2011年 | 2661篇 |
2010年 | 1883篇 |
2009年 | 2164篇 |
2008年 | 2079篇 |
2007年 | 2503篇 |
2006年 | 2174篇 |
2005年 | 1723篇 |
2004年 | 1502篇 |
2003年 | 1299篇 |
2002年 | 1067篇 |
2001年 | 851篇 |
2000年 | 730篇 |
1999年 | 615篇 |
1998年 | 515篇 |
1997年 | 485篇 |
1996年 | 374篇 |
1995年 | 339篇 |
1994年 | 254篇 |
1993年 | 206篇 |
1992年 | 166篇 |
1991年 | 135篇 |
1990年 | 83篇 |
1989年 | 89篇 |
1988年 | 68篇 |
1987年 | 37篇 |
1986年 | 31篇 |
1985年 | 24篇 |
1984年 | 18篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 2篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1959年 | 6篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The effects of boiling Aqua Regia (AQ), N2/Cl2 plasma followed by AQ and O2 plasma followed by AQ surface treatments prior to Ni/Au (20 nm/20 nm) metallization to p-GaN:Mg (∼ 3 × 1017 cm− 3) have been investigated. N2/Cl2 plasma was employed in a bid to lower the Ga/N and O/Ga ratios of the GaN surface to improve the contact properties to p-GaN, while O2 plasma was employed as an alternative to incorporate O into the Ni/Au system. Results show that a low Ga/N ratio does not necessarily correspond to a better contact. The positive effect of O2 over N2 anneal is observed only for the AQ-treated sample, although the mechanisms responsible for its positive effect: NiO formation and Ni/Au layer-reversal were observed for all O2-annealed contacts. We conclude that the effect of O2 anneal on the Ni/Au contact is dependant on the p-GaN surface prior to metallization. 相似文献
92.
David P. Cormode Jason J. Davis Paul D. Beer 《Journal of Inorganic and Organometallic Polymers and Materials》2008,18(1):32-40
Disulfide and dithiocarbamate functionalized porphyrins have been synthesized and used as protecting ligands for gold nanoparticle
formation either via ligand substitution reactions or by direct synthesis. These nanoparticles have been shown to recognize
anions via changes in the absorbance spectrum of the surface adsorbed porphyrin moieties. Association constants, derived from
quantitative titrations, indicate a remarkable surface enhancement effect where the surface bound porphyrins bind anions much
more strongly than the free receptor in solution. 相似文献
93.
94.
Mapping surface temperature in large lakes with MODIS data 总被引:1,自引:0,他引:1
Satellite sensor MODIS on two platforms can produce Sea Surface Temperature over certain regions about three to four times per day. Our objective was to test if the MODIS SST product can be applied for lakes whose surface areas are large enough to be observed at the MODIS spatial resolution and to compare the satellite-derived lake surface temperatures with in situ measurements. Surface temperatures for Lakes Vänern and Vättern in Sweden, two of the largest European lakes, are extracted from the MODIS/Terra images for period 2001-2003. The results are analyzed on different quality levels, as all MODIS L2 products are equipped with an additional quality flag. We present temperature development over 2001-2003, and show the capability of the MODIS SST product to couple the known thermodynamical features in the lakes under study, where temperature varies greatly with space and time. These results can complement lake monitoring programs anywhere. 相似文献
95.
A Ml (NiCoMnA1)5 hydrogen storage alloys was prepared by double-roller rapid quenching.Its microstructure, electrochemically and kinetic characteristic were studied.A uniform crystal phase with CaCu5 structure could be detected by XRD analyses, whose average grain size is 30 ~ 50 nm and the ratio of c/a of nano-crystal hydrogen storage alloy is larger.The hydrogen absorption/desertion p - C isotherms of alloy show that its fiat-performance is perfect and the magnetic stagnant effect is very little.An simulate cell is used for electrochemical measurement.Electrode is 10C, the capacity decreasing rate via the 450 cycles at 7C is less than 20%. 相似文献
96.
利用Love波特性计算地基动力响应 总被引:5,自引:2,他引:3
本文利用Love波弥散特性在频域上对地基出平面振动及扭振问题进行了研究。在计算区域内结构将采用有限单元划分,而在边界上则根据Love 面波特性使用传递边界有限单元。本文同时讨论了不同模态波对结构动力响应的贡献。本文方法也适合于静力分析。 相似文献
97.
多孔硅发光的物理机制——纳米量子限制效应及表面态在发光中的作用 总被引:4,自引:1,他引:3
采用阳极氧化腐蚀的方法制备了多孔硅(PS),这种PS的微结构为纳米量级的,并具有光致发光特性,这无疑将对全硅光电子学的发展具有很大意义。根据大量实验与理论分析,提出了这种PS发光的物理机制:纳米量子限制效应和表面态及其物质在发光中的作用,从量子力学的薛定锷方程出发,用沟道势阱的近似模型,推导得到进入量子线的电子和空穴的能量势垒,PS的有效带宽E=E_0+ΔE,对于Si(E_0=1.12ev)。完美地解释了目前在PS研究中的PL谱的篮移现象。 相似文献
98.
采用表面效应集总模型综合考虑表面费米能级钉扎和表面复合效应,对AlGaAs/GaAsHBT表面效应的影响进行了二维数值模拟。结果表明,表面态的存在对集电极电流几乎不产生影响,但显著增加基极电流,使得电流增益明显下降。同时还发现在台面结构AIGaAs/GaAsHBT中外基区表面复合的集边效应,即外基区表面复合主要发生在发射极台面与外基区的交界处附近,与外基区长度基本无关。模拟还表明基区缓变结构可以减少表面复合,提高电流增益。 相似文献
99.
提高大口径金属主镜面形精度的方法 总被引:1,自引:1,他引:0
分析了影响Ritchey-Chreitien光学系统中金属主反射镜面形精度因素,采用有限元法对立交易的加工过程及其安装进行了模拟,指出提高主镜的面形镜度,既要合理主镜材料的热处理工艺,也要对加工参数进行控制。良好的稳定化处理可以有效地消除材料内部的残余应力,保证主镜尺寸的稳定性。提高加工基准的精度,并采用组合加工镜面,可以大大提高主镜的面形精度,最后,给出了主镜的干涉仪检测结果。 相似文献
100.
The condition of the surfaces is of crucial importance for the deuterium permeation through materials. In this work a study of the surface constants for the adsorption (σk1) and release (σk2) of deuterium under different surface conditions on the martensitic steel DIN 1.4914 (MANET) has been carried out. The growth of an oxide surface layer (Cr2O3) of about 25–30 nm in a MANET sample, heat treated in an oxidizing environment, compared to the bare MANET that have a ‘natural' oxide of about 5 nm has provoked a reduction of both the permeation rate and the recombination coefficient (about 3 orders of magnitude). In addition, the permeation governing process has changed from diffusion-limited to surface-limited. The measurements of the permeation rate of deuterium were performed by a gas-phase permeation technique over the temperature range 574–746 K and for deuterium driving pressures in the range from 3 to 105 Pa. 相似文献