全文获取类型
收费全文 | 115135篇 |
免费 | 13391篇 |
国内免费 | 8037篇 |
专业分类
电工技术 | 10624篇 |
技术理论 | 6篇 |
综合类 | 9668篇 |
化学工业 | 15860篇 |
金属工艺 | 6667篇 |
机械仪表 | 8052篇 |
建筑科学 | 9614篇 |
矿业工程 | 4084篇 |
能源动力 | 3392篇 |
轻工业 | 8480篇 |
水利工程 | 3040篇 |
石油天然气 | 5617篇 |
武器工业 | 1741篇 |
无线电 | 14472篇 |
一般工业技术 | 10935篇 |
冶金工业 | 4381篇 |
原子能技术 | 1658篇 |
自动化技术 | 18272篇 |
出版年
2024年 | 582篇 |
2023年 | 1928篇 |
2022年 | 4192篇 |
2021年 | 6000篇 |
2020年 | 4202篇 |
2019年 | 3263篇 |
2018年 | 3608篇 |
2017年 | 4032篇 |
2016年 | 3692篇 |
2015年 | 5569篇 |
2014年 | 6853篇 |
2013年 | 8051篇 |
2012年 | 9743篇 |
2011年 | 9947篇 |
2010年 | 9056篇 |
2009年 | 8619篇 |
2008年 | 8291篇 |
2007年 | 7623篇 |
2006年 | 7003篇 |
2005年 | 5695篇 |
2004年 | 3881篇 |
2003年 | 2662篇 |
2002年 | 2542篇 |
2001年 | 2083篇 |
2000年 | 1747篇 |
1999年 | 1334篇 |
1998年 | 794篇 |
1997年 | 682篇 |
1996年 | 627篇 |
1995年 | 560篇 |
1994年 | 374篇 |
1993年 | 271篇 |
1992年 | 256篇 |
1991年 | 154篇 |
1990年 | 135篇 |
1989年 | 91篇 |
1988年 | 73篇 |
1987年 | 47篇 |
1986年 | 47篇 |
1985年 | 23篇 |
1984年 | 24篇 |
1983年 | 11篇 |
1982年 | 20篇 |
1981年 | 23篇 |
1980年 | 29篇 |
1979年 | 16篇 |
1978年 | 11篇 |
1976年 | 21篇 |
1959年 | 17篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
61.
文章简要介绍了煤矿工业场地的特点和低压配电系统接地方式分类,从安全性、经济性的角度分析了TN接地系统和TT接地系统在道路照明回路中的优缺点。通过对比TN-S系统与TT系统的接地故障电流差异、TN-S接地系统用于道路照明的等电位联结困难程度,总结出煤矿工业场地的道路照明配电系统适宜采用TT接地方式。并且详细阐述了TT接地系统剩余电流动作保护器保护整定方法和灵敏度校验方法,列举了煤矿工业场地道路照明选用TT系统时需要注意的中性线不可重复接地的问题。 相似文献
62.
Although Mg alloy attracts great attention for engineering applications because of high specific strength and low density, low corrosion resistance limits its extensive use. In this study, Mg–Al–Zn–Mn alloy was treated via a laser cladding process to generate a dense and compact laser cladding layer with solid metallurgical bonding on the substrate for improving corrosion resistance, effectively hindering the corrosion pervasion into Mg alloy. The corrosion current density declined from 103 μA/cm2 for Mg alloy to 13 μA/cm2 for the laser cladding layer in NaCl aqueous solution. Moreover, the laser cladding layer was slightly corroded in comparison with Mg alloy in NaCl aqueous solution. Besides, the microhardness of the cladding layer reached a mean value of 170.5 HV, 3.1 times of Mg alloy (56.8 HV) due to the in situ formation of hardening intermetallic phases. Wear resistance of laser cladding layer was also obviously improved. These results demonstrated that the laser cladding layer obviously enhanced anticorrosion property of Mg alloy for engineering applications. 相似文献
63.
Although Mg alloy possesses high specific strength, low density, and good biocompatibility, poor corrosion resistance hinders its further applications. In the present study, an innovative protective layer against corrosion was prepared on the AZ31 Mg alloy via alkali pretreatment followed by vanillic acid treatment. The alkali pretreatment supplied –OH for the AZ31 Mg alloy surface to react with vanillic acid. The vanillic acid treatment played a crucial role in enhancing the corrosion resistance due to the excellent ability to act as a barrier and retard aqueous solution penetration, which effectively isolated the underlying Mg alloy from the corrosive environment. The corrosion current density of alkali and vanillic acid-treated Mg alloy (AZ31V) almost showed two orders of magnitude lower values in comparison with that of the AZ31 Mg alloy, and the corrosion potential of AZ31V Mg alloy increased from −1.41 to −1.25 V. The immersion tests proved that there was no occurrence of severe corrosion. Hence, the alkali pretreatment and vanillic acid treatment may represent a promising method to improve the corrosion resistance of Mg alloy. 相似文献
64.
65.
66.
68.
69.
This study addresses the problem of choosing the most suitable probabilistic model selection criterion for unsupervised learning
of visual context of a dynamic scene using mixture models. A rectified Bayesian Information Criterion (BICr) and a Completed
Likelihood Akaike’s Information Criterion (CL-AIC) are formulated to estimate the optimal model order (complexity) for a given
visual scene. Both criteria are designed to overcome poor model selection by existing popular criteria when the data sample
size varies from small to large and the true mixture distribution kernel functions differ from the assumed ones. Extensive
experiments on learning visual context for dynamic scene modelling are carried out to demonstrate the effectiveness of BICr
and CL-AIC, compared to that of existing popular model selection criteria including BIC, AIC and Integrated Completed Likelihood
(ICL). Our study suggests that for learning visual context using a mixture model, BICr is the most appropriate criterion given
sparse data, while CL-AIC should be chosen given moderate or large data sample sizes. 相似文献
70.