全文获取类型
收费全文 | 4630篇 |
免费 | 418篇 |
国内免费 | 150篇 |
专业分类
电工技术 | 76篇 |
综合类 | 139篇 |
化学工业 | 1856篇 |
金属工艺 | 310篇 |
机械仪表 | 53篇 |
建筑科学 | 68篇 |
矿业工程 | 35篇 |
能源动力 | 436篇 |
轻工业 | 68篇 |
水利工程 | 11篇 |
石油天然气 | 93篇 |
武器工业 | 5篇 |
无线电 | 466篇 |
一般工业技术 | 1118篇 |
冶金工业 | 296篇 |
原子能技术 | 134篇 |
自动化技术 | 34篇 |
出版年
2024年 | 16篇 |
2023年 | 187篇 |
2022年 | 146篇 |
2021年 | 164篇 |
2020年 | 211篇 |
2019年 | 185篇 |
2018年 | 152篇 |
2017年 | 188篇 |
2016年 | 151篇 |
2015年 | 128篇 |
2014年 | 227篇 |
2013年 | 304篇 |
2012年 | 203篇 |
2011年 | 285篇 |
2010年 | 217篇 |
2009年 | 259篇 |
2008年 | 253篇 |
2007年 | 284篇 |
2006年 | 234篇 |
2005年 | 178篇 |
2004年 | 154篇 |
2003年 | 138篇 |
2002年 | 137篇 |
2001年 | 108篇 |
2000年 | 119篇 |
1999年 | 91篇 |
1998年 | 73篇 |
1997年 | 46篇 |
1996年 | 62篇 |
1995年 | 42篇 |
1994年 | 46篇 |
1993年 | 30篇 |
1992年 | 45篇 |
1991年 | 28篇 |
1990年 | 30篇 |
1989年 | 16篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有5198条查询结果,搜索用时 15 毫秒
11.
《Journal of the European Ceramic Society》2020,40(4):1644-1650
Possibility of formation of quinary and senary equimolar high entropy oxides from the Co-Cr-Fe-Mg-Mn-Ni-O system is presented. Different proposed compositions are synthesized using the solid-state reaction route at high temperatures (900−1100 °C) and quenched to room temperature. Phase composition of the samples is studied, showing tendency toward formation of two main phases: rock salt-structured Fm-3 m and spinel-structured Fd-3 m. It is documented that the annealing temperature has a profound effect on stability of both structures, and at 1100 °C usually the highest content of Fm-3 m phase is usually observed. Three different oxides, namely, (Co,Cr,Fe,Mn,Ni)3O4, (Co,Cr,Fe,Mg,Mn)3O4 and (Cr,Fe,Mg,Mn,Ni)3O4 are obtained as single-phase materials, which structure can be described as the high entropy Fd-3 m spinel one. The latter two compounds have not been previously reported in the literature. Activated character of the electrical conductivity dependence on temperature is observed, with relatively high total conductivity at high temperatures and corresponding high absolute values of Seebeck coefficient. 相似文献
12.
《International Journal of Hydrogen Energy》2020,45(49):26238-26253
The demands for high-purity hydrogen required in fuel-cell applications impose new goals and challenges for design of well performing water-gas shift (WGS) catalysts. Gold-based catalysts have exhibited high activity in the WGS reaction at low temperature. Preparation of appropriate and economically viable supports with complex composition by various synthesis procedures is an attractive approach to WGS performance improvement. The effect of two different preparation methods (wet impregnation or mechanical mixing) and ceria content (10, 20 or 30 wt%) on textural, structural, surface and reductive properties and WGS activity of gold catalysts was studied. Additionally, the role of Y2O3 as a promoter of ceria was examined. Long-term stability test was carried out at 260 °C over the most active catalyst. The composition of the best performing sample (composed of about 70 wt% alumina), prepared by mechanical mixing, was considered promising in case of practical applications because of its cost efficiency. The combination of gold nanoparticles and alumina supported Y-doped ceria proved an advantageous approach for developing new catalytic formulations with high effectiveness in clean hydrogen production. 相似文献
13.
《International Journal of Hydrogen Energy》2020,45(15):8605-8617
Single phase, crystalline NaFeTiO4 with tunnel structure is prepared by a solid state method and explored as a novel photocatalyst for the first time. Structural, optical and morphological properties of NaFeTiO4 are investigated by various characterization techniques such as X-ray diffraction (XRD), scanning & transmission electron microscopy (SEM & TEM), Energy dispersive X-ray spectroscopy (EDS), N2 adsorption-desorption study (BET), UV-vis, X-ray photoelectron, X-ray absorption (UV-vis DRS, XPS and XANES) and photoluminescence (PL) spectroscopy. The interfacial charge transfer ability of the prepared n-type NaFeTiO4 was also investigated by transient photocurrent response and electrochemical impedence spectroscopy which proved to be an efficient tool for better understanding of electronic properties of NaFeTiO4. The photocatalytic efficiency of NaFeTiO4 is evaluated for decomposition of methylene blue (MB) and Rhodamine B (RhB) dyes as well as for H2 evolution through water splitting reaction under visible light. NaFeTiO4 exhibits efficient charge separation properties, excellent photocatalytic activities and reusability. 相似文献
14.
15.
16.
17.
Marcia Cristina Kaezer Fran a Rosane Aguiar da Silva San Gil Jean-Guillaume Eon 《Catalysis Today》2003,78(1-4):105-115
γ-Al2O3 supported vanadium oxides were modified by tungsten and molybdenum oxides in order to improve dispersion and selectivity towards olefins in propane oxidative dehydrogenation (ODH). Both vanadium–tungsten and vanadium–molybdenum catalysts were obtained by adsorption of mixed isopolyanions (VW5O195−, V2W4O194−, VMo5O195− and V2Mo4O194−) from aqueous solutions. The isopolyanion solutions were characterized by UV-Vis and 51V NMR spectroscopy. Vanadium, vanadium–tungsten and vanadium–molybdenum precursors and catalysts were also characterized by UV-Vis (diffuse reflectance) and solid state 51V NMR spectroscopy. An improved selectivity to propene in the presence of tungsten and molybdenum in VOx/γ-Al2O3 was observed and attributed to dilution of vanadium by tungsten or molybdenum oxides on the γ-Al2O3 surface. 相似文献
18.
This review article is devoted to the materials containing niobium, which have been discovered or developed in the past few years and exhibit the potential application in heterogeneous catalysis. Niobium oxides and mixed oxides as well as sulfides, nitrides (oxynitrides), carbides (oxycarbides), and phosphates are considered. Among the catalytic processes in which Nb-containing materials were tested, liquid and gas phase oxidation is described in details, and the role of niobium in the prevention of the catalyst from SO2 poisoning is mentioned. 相似文献
19.
20.
The thermal decomposition products of pyridinium sulfate differ from those of pyridinium sulfate supported on zirconia which in turn differs from that of pyridine adsorbed on a sulfated zirconia. Unsupported pyridinium sulfate decomposes to produce pyridine and sulfuric acid, and these subsequently react to produce oxides of carbon and sulfur. Zirconia that is sulfated and then exposed to pyridine does not release detectable amount of pyridine during heating in an inert gas; rather the pyridine undergoes oxidation reduction reactions simultaneously to release CO2 and sulfur compounds. Pyridinium sulfate supported on zirconia decomposes upon heating to release pyridine and sulfuric acid, which reacts with the zirconia. The desorption of pyridine in one case and only CO2/SOx in the other case suggests that sulfated zirconia does not contain Brønsted acidity that can form pyridinium sulfate. 相似文献