全文获取类型
收费全文 | 1403篇 |
免费 | 69篇 |
国内免费 | 90篇 |
学科分类
工业技术 | 1562篇 |
出版年
2024年 | 4篇 |
2023年 | 65篇 |
2022年 | 71篇 |
2021年 | 104篇 |
2020年 | 80篇 |
2019年 | 81篇 |
2018年 | 78篇 |
2017年 | 83篇 |
2016年 | 62篇 |
2015年 | 38篇 |
2014年 | 71篇 |
2013年 | 62篇 |
2012年 | 69篇 |
2011年 | 101篇 |
2010年 | 67篇 |
2009年 | 80篇 |
2008年 | 84篇 |
2007年 | 69篇 |
2006年 | 60篇 |
2005年 | 35篇 |
2004年 | 30篇 |
2003年 | 31篇 |
2002年 | 18篇 |
2001年 | 24篇 |
2000年 | 21篇 |
1999年 | 15篇 |
1998年 | 14篇 |
1997年 | 11篇 |
1996年 | 12篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有1562条查询结果,搜索用时 15 毫秒
1.
A vacuum-annealed La0.6Ca0.4CoO3−x was consecutively oxygenated in air at temperatures decreasing from 800 to 100 °C, and its electrocatalytic activities for oxygen reduction and evolution were then measured as a function of the oxygenation temperature. The valence of Co cation, changing between +2 and +3, was found susceptible to annealing either in vacuum or air. The catalytic activities initially decrease monotonically as the oxygenation temperature was decreased from 800 to 300 °C, as a result of increasing oxygen content, and then rise abruptly with the oxygen reduction activity reaching a maximum at 200 °C and the oxidation activity at 150 °C. X-ray photoelectron spectroscopy analysis indicated that the enhancements by the low-temperature oxygenation involved increased OH coverage and less charged cations at surface. The results clearly reveal the importance of the post-calcination annealing process for optimizing the performance of La0.6Ca0.4CoO3−x in air electrode applications. 相似文献
2.
R. Wongmaneerung W. Chaisan O. Khamman R. Yimnirun S. Ananta 《Ceramics International》2008,34(4):813-817
The potential of the vibro-milling technique as a simple method to obtain usable quantities of single-phase electroceramic powders with nanosized particles was examined. A detailed study considering the role of both milling time and firing condition on phase formation and particle size of the final product was performed. The calcination temperature for the formation of the desired phase was lower when longer milling times have been applied. More importantly, by employing an appropriate choice of the milling time and calcination condition, high purity electroceramic nanopowders have been successfully prepared with a simple solid-state reaction method. 相似文献
3.
Francesco Donsì Stefano Cimino Almerinda Di Benedetto Raffaele Pirone Gennaro Russo 《Catalysis Today》2005,105(3-4):551-559
The oxidative dehydrogenation of ethane is carried out in short contact time reactors over Pt and LaMnO3 based catalysts supported on a large number of different ceramic substrates (45, 60 and 80 ppi foam monoliths and 200, 400, 600, 900 and 1200 cpsi honeycomb monoliths). Experimental results, obtained under the same conditions at varying the C2H6/O2 ratio, showed that the highest performance in terms of ethylene selectivity and yield is always attained on LaMnO3 catalysts. Furthermore, the results are significantly influenced by the morphology and cell density of the support, with 45 and 60 ppi foams and 400 and 600 cpsi honeycombs giving the best performance. The experimental results are explained by means of geometrical and fluid dynamic considerations on the support, and by means of a 2D mathematical model, which clearly indicates an optimal intermediate cell density for maximising ethylene selectivity and yield. 相似文献
4.
Microwave irradiation processing (MIP) was considered as a potential method to synthesize perovskite-type oxides rapidly, cleanly and energy-efficiently. In this paper, La0.7Sr0.3MnO3+λ, a kind of promising catalyst for automobile exhaust purification, was successfully prepared by MIP in not more than 5 min. The sol–gel method was also used for comparison. All the samples were evaluated by catalytic activity tests in the simulated exhaust and characterized by XRD, BET, TEM and XRF analyses. The results showed that the integrated perovskite-type phase and uniform particle size were obtained in the microwave-treated samples. And those ones exhibited a better oxidation activity under slightly oxygen-rich condition than that by sol–gel method, which may be related to more A-site cation vacancies and larger bulk oxygen content generated in MIP. Possible formation mechanism of perovskites in MIP was also discussed. 相似文献
5.
《中国稀土学报(英文版)》2022,40(10):1509-1518
Gd2O3:Eu3+@CsPbBr3 quantum dots (QDs) mesoporous hollow nanocomposites with good luminescent properties and high stability were built. Among which, the hollow Gd2O3:Eu3+ spheres and CsPbBr3 QDs were prepared by urea homogeneous precipitation and hot-injection method, respectively. Finally, the Gd2O3:Eu3+@CsPbBr3 QDs shell–core compounds were constructed through mechanical stirring. The structure, morphology, stability and luminescent properties were studied by Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry/thermogravity (DSC/TG), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence excitation/photoluminescence (PLE/PL) and life decay tools. Compared to the original CsPbBr3 QDs, Gd2O3:Eu3+@CsPbBr3 QDs display better photostability, thermal stability and current stability. The resulting Gd2O3:Eu3+@CsPbBr3 QDs composite exhibits good yellow emission. The Gd2O3:Eu3+@CsPbBr3 QDs mixed silicone resin was directly coated on the blue LED chip, then the w-LED device with the color coordinate of (0.31, 0.32) was successfully assembled. The Gd2O3:Eu3+@CsPbBr3 QDs compounds with excellent luminescent properties and stability are expected to be widely used in lighting and display areas. 相似文献
6.
《中国稀土学报(英文版)》2022,40(6):888-896
The LaCo0.94Pt0.06O3 catalyst is reduced under 5% H2/Ar at different temperatures to get Pt/LaCoO3 with high catalytic activity for soot oxidation. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller method (BET), X-ray photoelectron spectroscopy (XPS), H2-temperature programmed reduction (H2-TPR), O2-temperature programmed desorption (O2-TPD) and thermogravimetric analysis (TGA) were used to study the physicochemical properties of the catalyst. SEM and TEM results indicate that Pt nanoparticles (<10 nm) are grown homogeneously on the surface of the LaCoO3 matrix after in-situ reduction. XRD shows that the reduced catalyst has a high symmetrical structure. TGA results indicate that all reduced catalysts exhibit an excellent activity, especially the catalyst reduced at 350 °C (T10 = 338 °C, T50 = 393 °C, T90 = 427 °C). And perovskite is the primary active component. According to XPS study, the high symmetrical structure benefits the mobility of oxygen vacancy, and Pt nanoparticles induce the oxygen vacancy to move to its adjacent situation, resulting in more adsorbed oxygen on the surface of the reduced catalyst and increasing the activity. The possible reaction principle is also proposed. 相似文献
7.
8.
以天然高岭土为原料,经精细化处理煅烧制备莫来石.用常压、开放水热技术制备出莫来石复相纳米晶体材料.实验表明:常压、开放水热条件下制备莫来石复相纳米晶粉体的水热反应中,采用质量比为m(Na2O)/m(SiO2)=2.8,m(H2O)/m(Na2O)=35~30,0~80℃控温升温1 h,在80℃保温2 h,可制备出尺寸为80~100 nm莫来石复相纳米晶体.所制备的莫来石纳米晶体的水热溶液相变驱动力△μ为(3.609~4.672)×10-20 J/mol;水热体系溶解度控制在3.891×10-6 mol/L;熔解热△E为18.846 kJ/mol;晶体生长速率常数选择0.85~0.92,有利于快速成核和晶体生长,并且可以很好地控制晶体尺寸和分散度. 相似文献
9.
Direct nitric oxide decomposition over perovskites is fairly slow and complex, its mechanism changing dramatically with temperature. Previous kinetic study for three representative compositions (La0.87Sr0.13Mn0.2Ni0.8O3−δ, La0.66Sr0.34Ni0.3Co0.7O3−δ and La0.8Sr0.2Cu0.15Fe0.85O3−δ) has shown that depending on the temperature range, the inhibition effect of oxygen either increases or decreases with temperature. This paper deals with the effect of CO2, H2O and CH4 on the nitric oxide decomposition over the same perovskites studied at a steady-state in a plug-flow reactor with 1 g catalyst and total flowrates of 50 or 100 ml/min of 2 or 5% NO. The effect of carbon dioxide (0.5–10%) was evaluated between 873 and 923 K, whereas that of H2O vapor (1.6 or 2.5%) from 723 to 923 K. Both CO2 and H2O inhibit the NO decomposition, but inhibition by CO2 is considerably stronger. For all three catalysts, these effects increase with temperature. Kinetic parameters for the inhibiting effects of CO2 and H2O over the three perovskites were determined. Addition of methane to the feed (NO/CH4=4) increases conversion of NO to N2 about two to four times, depending on the initial NO concentration and on temperature. This, however, is still much too low for practical applications. Furthermore, the rates of methane oxidation by nitric oxide over perovskites are substantially slower than those of methane oxidation by oxygen. Thus, perovskites do not seem to be suitable for catalytic selective NO reduction with methane. 相似文献
10.
J.-M. Giraudon A. Elhachimi F. Wyrwalski S. Siffert A. Aboukaïs J.-F. Lamonier G. Leclercq 《Applied catalysis. B, Environmental》2007,75(3-4):157-166
Calcined and reduced catalysts Pd/LaBO3 (B = Co, Fe, Mn, Ni) were used for the total oxidation of toluene. Easiness of toluene destruction was found to follow the sequence based on the T50 values (temperature at which 50% of toluene is converted): Pd/LaFeO3 > Pd/LaMnO3+δ > Pd/LaCoO3 > Pd/LaNiO3. In order to investigate the activation process (calcination and reduction) in detail, the reducibility of the samples was evaluated by H2-TPR on the calcined catalysts. Additionally, characterization of the Pd/LaBO3 (B = Co, Fe) surface was carried out by X-ray photoelectron spectroscopy (XPS) at each stage of the global process, namely after calcination, reduction and under catalytic reaction at either 150 or 200 °C for Pd/LaFeO3 and either 200 or 250 °C for LaCoO3. The different results showed that palladium oxidized entities were totally reduced after pre-reduction at 200 °C for 2 h (2 L/h, 1 °C/min). As LaFeO3 was unaffected by such a treatment, for the other perovskites, the cations B are partially reduced as B3+ (B = Mn) or B2+ even to B0 (B = Co, Ni). In the reactive stream (0.1% toluene in air), Pd0 reoxidized partially, more rapidly over Co than Fe based catalysts, to give a Pd2+/Pd4+ and Pd0/Pd2+/Pd4+ surface redox states, respectively. Noticeably, reduced cobalt species are progressively oxidized on stream into Co3+ in a distorted environment. By contrast, only the lines characteristic of the initial perovskite lattice were detected by XRD studies on the used catalysts. The higher activity performance of Pd/LaFeO3 for the total oxidation of toluene was attributed here to a low temperature of calcination and to a remarkable high stability of the perovskite lattice whatever the nature of the stream which allowed to keep a same palladium dispersion at the different stages of the process and to resist to the oxidizing experimental conditions. On the contrary, phase transformations for the other perovskite lattices along the process were believed to increase the palladium particle size responsible of a lower activity. 相似文献