全文获取类型
收费全文 | 173395篇 |
免费 | 14176篇 |
国内免费 | 10070篇 |
专业分类
电工技术 | 6499篇 |
技术理论 | 2篇 |
综合类 | 12496篇 |
化学工业 | 50002篇 |
金属工艺 | 13907篇 |
机械仪表 | 5936篇 |
建筑科学 | 11771篇 |
矿业工程 | 4100篇 |
能源动力 | 6188篇 |
轻工业 | 10052篇 |
水利工程 | 1584篇 |
石油天然气 | 8313篇 |
武器工业 | 1065篇 |
无线电 | 15957篇 |
一般工业技术 | 21888篇 |
冶金工业 | 7507篇 |
原子能技术 | 2202篇 |
自动化技术 | 18172篇 |
出版年
2024年 | 527篇 |
2023年 | 2613篇 |
2022年 | 5229篇 |
2021年 | 5874篇 |
2020年 | 4763篇 |
2019年 | 4279篇 |
2018年 | 4071篇 |
2017年 | 5007篇 |
2016年 | 5567篇 |
2015年 | 5489篇 |
2014年 | 8826篇 |
2013年 | 9504篇 |
2012年 | 11151篇 |
2011年 | 12943篇 |
2010年 | 10097篇 |
2009年 | 11633篇 |
2008年 | 10385篇 |
2007年 | 12752篇 |
2006年 | 11989篇 |
2005年 | 9439篇 |
2004年 | 7215篇 |
2003年 | 6699篇 |
2002年 | 5327篇 |
2001年 | 4312篇 |
2000年 | 3904篇 |
1999年 | 3225篇 |
1998年 | 2522篇 |
1997年 | 2042篇 |
1996年 | 1711篇 |
1995年 | 1435篇 |
1994年 | 1251篇 |
1993年 | 939篇 |
1992年 | 804篇 |
1991年 | 647篇 |
1990年 | 546篇 |
1989年 | 441篇 |
1988年 | 326篇 |
1987年 | 254篇 |
1986年 | 243篇 |
1985年 | 227篇 |
1984年 | 196篇 |
1983年 | 136篇 |
1982年 | 148篇 |
1981年 | 147篇 |
1980年 | 160篇 |
1979年 | 114篇 |
1978年 | 99篇 |
1977年 | 100篇 |
1976年 | 104篇 |
1975年 | 102篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
In this paper we show that by the analysis of 2D images collected with a laboratory X-ray microdiffractometer it is possible to non-destructively evaluate the structure, the microstructure, and the preferred orientation of films. In particular, the structural analysis of Co/Au multilayers on Si(1 0 0) deposited at different Ar pressures are reported and discussed. 相似文献
22.
Hung‐Yee Shu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(3):273-280
Liquid–liquid two‐phase epoxidation from cyclohexene and cyclooctene in aqueous potassium peroxymonosulfate (commercially available as Oxone®) solution was studied as an application in pollution prevention. To avoid potential emissions of volatile organic compounds an aqueous solution was employed to replace the usual chlorinated solvents used in epoxide production. A droplet column reactor and stirred tank reactor were used to investigate two‐phase synthesis of epoxide. An aqueous Oxone® solution was used to oxidize a dispersion of alkene droplets and form epoxide. The study of aqueous epoxidation in both reactors showed that the epoxidation of alkenes can be represented as a first order reaction with respect to alkene. The salting out effect of Oxone® concentration was studied in both reactors and found to be very similar at optimal conditions. In comparing the two reactors, it was found that the droplet column reactor produces larger quantities of product per unit reactor volume for the same reaction time. The objective of this study is to provide an alternative reactor design and synthesis route that can meet pollution prevention goals. Copyright © 2004 Society of Chemical Industry 相似文献
23.
24.
VK Tzitzios V Georgakilas TN Angelidis 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(6):699-704
A study of nitrous oxide (N2O) reduction with methane (CH4) and propene (C3H6) in the presence of oxygen (5%) over Ag/Al2O3, Rh/Al2O3 and Ag–Rh/Al2O3 catalysts, with Ag and Rh loadings of 5 wt% and 0.05 wt% respectively, has been performed. From the results, it was observed that the Ag–Rh bimetallic catalyst was the most active for both nitrous oxide removal (more than 95%) and hydrocarbon oxidation. This high activity seems to be connected with a synergistic effect between Ag and Rh. The findings from X‐ray diffraction and X‐ray photoelectron spectroscopy studies showed also, that there were no strong interactions (eg alloying) between Ag and Rh. Copyright © 2005 Society of Chemical Industry 相似文献
25.
Exchange and oxidation of C16O were investigated at 450°C on 18O-predosed Rh and Pt catalysts supported on A12O3, CeO2 and CeO2-Al2O3. In all cases, a rapid exchange of C16O with the surface can be observed. CO oxidation leads to C16O2, C16O18O and C18O2. Significant formation of C16O2 is due to the relatively high 16O coverage in reaction resulting from the C16O exchange and from an exchange between O surface species and 16O internal atoms. Hydrogen is also formed via a water-gas shift reaction (CO + surface OH) in higher proportion on CeO2-containing catalysts than on A12O3. Chlorine inhibits all the reactions (exchange, oxidation and WGS) and particularly the internal exchange. 相似文献
26.
The authors highlight several possible ways in which the construction industry could lower present emissions of the greenhouse gas, carbon dioxide. It is an excellent discussion document and is recommended reading. 相似文献
27.
The nature of the interaction of monomer, and the early stages of growth of oligomers of ethylene on a rather more uniform surface of Cr/SiO2 catalyst than hitherto studied has been investigated by differenceFTIR spectroscopy using C2D4 and C2H4 as reactants both with and without subsequent treatment of the catalyst with CO andTHF. The active catalyst was prepared by reaction of vapour phase CrO2Cl2 with the vicinal hydroxyls of the silica surface. Three distinct kinds of methylene groups were detected. Arguments are given for assigning the peaks at 2935 and 2860 cm–1 to CH2 groups directly bound to the active site and those at 2920 and 2850 to CH2s in the growing chain well removed from the Cr. The peaks at 2160 and 2165 cm–1 are attributed to CD2 groups hydrogen bonded to surface hydroxyls. 相似文献
28.
29.
隧道小孔中超薄SiO2的生长是EEPROM电路制造的关键工艺之一。采用SUPREM-Ⅲ工艺模拟程序对超薄SiO2的热生长进行了工艺模拟,经过大量的工艺实验及优化,确定了超薄SiO2的最佳生长条件,生长出的SiO2性能良好,完全可满足EEPROM研制的要求。 相似文献
30.
Kwang Soo Lee In Soo Park & Dong Sun Lee 《International Journal of Food Science & Technology》1996,31(1):7-13
The aim of this study was to design a modified atmosphere package for a mixed vegetable salad consisting of 75 g of cut carrot, 55 g of cut cucumber, 20 g of sliced garlic and 50 g of whole green pepper. Respiration data of all the components were combined with film permeability data to predict package atmospheres and design optimal packages for experimental testing for improved shelf-life of the produce. The optimal package avoided minimum O2 and maximum CO2 tolerance limits, and chilling injury temperatures for any component. A pouch form package made of 27 mm low density polyethylene developed a modified atmosphere of 2.0–2.1% O2 and 5.5–5.7% CO2 , which was beneficial for all components and provided better quality retention than other test packages. 相似文献