全文获取类型
收费全文 | 12586篇 |
免费 | 1233篇 |
国内免费 | 1200篇 |
专业分类
电工技术 | 3716篇 |
综合类 | 956篇 |
化学工业 | 1577篇 |
金属工艺 | 769篇 |
机械仪表 | 780篇 |
建筑科学 | 435篇 |
矿业工程 | 344篇 |
能源动力 | 551篇 |
轻工业 | 547篇 |
水利工程 | 1361篇 |
石油天然气 | 264篇 |
武器工业 | 106篇 |
无线电 | 978篇 |
一般工业技术 | 1094篇 |
冶金工业 | 512篇 |
原子能技术 | 632篇 |
自动化技术 | 397篇 |
出版年
2024年 | 41篇 |
2023年 | 164篇 |
2022年 | 333篇 |
2021年 | 386篇 |
2020年 | 413篇 |
2019年 | 352篇 |
2018年 | 355篇 |
2017年 | 487篇 |
2016年 | 480篇 |
2015年 | 547篇 |
2014年 | 847篇 |
2013年 | 726篇 |
2012年 | 943篇 |
2011年 | 986篇 |
2010年 | 694篇 |
2009年 | 724篇 |
2008年 | 799篇 |
2007年 | 872篇 |
2006年 | 824篇 |
2005年 | 693篇 |
2004年 | 579篇 |
2003年 | 497篇 |
2002年 | 388篇 |
2001年 | 336篇 |
2000年 | 291篇 |
1999年 | 253篇 |
1998年 | 197篇 |
1997年 | 177篇 |
1996年 | 118篇 |
1995年 | 130篇 |
1994年 | 76篇 |
1993年 | 64篇 |
1992年 | 58篇 |
1991年 | 50篇 |
1990年 | 30篇 |
1989年 | 25篇 |
1988年 | 17篇 |
1987年 | 17篇 |
1986年 | 9篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1964年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
71.
Material removal and surface damage of Ti3SiC2 ceramic during electrical discharge machining (EDM) were investigated. Melting and decomposition were found to be the main material removal mechanisms during the machining process. Material removal rate was enhanced acceleratively with increasing discharge current, ie, working voltage, ui, but increased deceleratively with pulse duration, te. Microcracks in the surface and loose grains in the subsurface resulted from thermal shock were confirmed, and the surface damage in Ti3SiC2 ceramic led to a degradation of both strength and reliability. 相似文献
72.
I.Z. Ismagilov R.P. Ekatpure L.T. Tsykoza E.V. Matus E.V. Rebrov M.H.J.M. de Croon M.A. Kerzhentsev J.C. Schouten 《Catalysis Today》2005,105(3-4):516-2
This paper describes the optimization of three processes applied in fabrication of a microstructured reactor for complete oxidation of volatile organic compounds. The first process involves the optimization of the electro discharge machining (EDM) method to produce a set of microchannels with a high length to diameter ratio of 100, with a standard deviation from the average diameter below 0.2%, and with a surface roughness not higher than 2.0 μm. To satisfy these criteria, fabrication of microchannels must be carried out with two machining passes in the Al51st alloy. Then, the effect of several parameters on the anodization current efficiency with respect to oxide formation was studied. The best process conditions to get a 30 μm porous alumina layer in a 0.4 M oxalic acid electrolyte, were found to be a temperature of 1 °C, an anodic current density of 5 mA/cm2, and 23 h oxidation time. At last, the resulting coatings were impregnated with an aqueous solution of copper dichromate followed by drying and calcination at 450 °C to produce active catalysts. The effect of a copper dichromate concentration, number of impregnation cycles (1 or 2), and different after-treatments on catalytic activity and stability in complete oxidation of n-butane were studied. The catalytic activity of the obtained coatings is superior to that of alumina supported pelletized catalysts even at much lower loadings of active metals. 相似文献
73.
74.
汽轮机凝汽器的除垢问题通常采用化学方法或物理方法,这些除垢措施有一定的局限性。介绍了一种利用高压静电除垢技术。 相似文献
75.
76.
The hydrogen fuel cell is a promising option as a future energy resource; however, the nature of the gas is such that the conversion process of other fuels to hydrogen on board is necessary. Among the raw fuel resources, methane could be the best candidate as it is plentiful. In this experiment, the possibility of producing hydrogen with less carbon formation from methane by a dielectric barrier discharge (DBD) was investigated. Without the addition of a catalyst, the formation of hydrogen reached between 30% and 35% at methane residence time of 0.22 min and supplied powers in the range of 60-130 W. The hydrogen selectivity increased at higher supplied power, but the process efficiency, defined as a ratio of the produced hydrogen to the supplied power, decreased slightly. In order to boost the hydrogen production with less carbon formation, a mixed oxide catalyst of zinc and chromium was added to the reactor. It was shown that the production of hydrogen was ca. 40% higher than the non-catalytic plasma process. 相似文献
77.
健康黄河的内涵及其指标 总被引:18,自引:4,他引:14
本文从河流的自然和社会属性角度,基于健康河流的概念阐述了河流生命、河流健康的科学内涵,认为河流健康是人们对河流生命存在状态的描述,健康的河流是河流的社会功能与自然功能能够取得平衡的河流。河流的健康应包括连续的河川径流、通畅安全的水沙通道、良好的水质、良性运行的河流生态系统和一定的供水能力。利用黄河1956~2004年实测资料,论证了表征健康黄河标志的低限流量、河道最大排洪能力、平滩流量、滩地横比降、水质类别、湿地规模、水生生物、供水能力等指示因子的阈值范围。 相似文献
78.
79.
介绍了电熨斗底板真空静电喷涂的工作原理。说明了电晕放电在底板真空静电喷涂中的作用。分析了氟涂料微粒的带电过程及影响因素。这个工艺对产品质量提高的作用进行了分析。 相似文献
80.