全文获取类型
收费全文 | 1424篇 |
免费 | 23篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 108篇 |
综合类 | 25篇 |
化学工业 | 371篇 |
金属工艺 | 60篇 |
机械仪表 | 18篇 |
建筑科学 | 46篇 |
矿业工程 | 81篇 |
能源动力 | 155篇 |
轻工业 | 33篇 |
水利工程 | 9篇 |
石油天然气 | 4篇 |
武器工业 | 2篇 |
无线电 | 13篇 |
一般工业技术 | 136篇 |
冶金工业 | 372篇 |
原子能技术 | 6篇 |
自动化技术 | 25篇 |
出版年
2024年 | 2篇 |
2023年 | 16篇 |
2022年 | 11篇 |
2021年 | 21篇 |
2020年 | 39篇 |
2019年 | 23篇 |
2018年 | 22篇 |
2017年 | 26篇 |
2016年 | 18篇 |
2015年 | 32篇 |
2014年 | 51篇 |
2013年 | 54篇 |
2012年 | 49篇 |
2011年 | 120篇 |
2010年 | 91篇 |
2009年 | 96篇 |
2008年 | 64篇 |
2007年 | 97篇 |
2006年 | 59篇 |
2005年 | 44篇 |
2004年 | 37篇 |
2003年 | 25篇 |
2002年 | 30篇 |
2001年 | 21篇 |
2000年 | 54篇 |
1999年 | 45篇 |
1998年 | 38篇 |
1997年 | 29篇 |
1996年 | 34篇 |
1995年 | 42篇 |
1994年 | 51篇 |
1993年 | 43篇 |
1992年 | 39篇 |
1991年 | 21篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1981年 | 2篇 |
排序方式: 共有1464条查询结果,搜索用时 15 毫秒
51.
The synthesis of different phases in the manganese oxi-hidroxyde system has been achieved by using supercritical water from the manganese (II) acetate as precursor, using only two high pressure pumps. The synthesis conditions to obtain the Mn(OH)2 and Mn3O4 phases have been optimized concerning the temperature and the ratio between manganese solution and water flow rates as key parameters. All phases have been microstructurally characterized in features such as size, shape, size distribution and crystallinity. The magnetic response has been evaluated from magnetization experiments. 相似文献
52.
Dongwei Li Fanhui Meng Xiuling Yan Lishan Yang Hua Heng Ye Zhu 《Nanoscale research letters》2013,8(1):535
Mn3O4/Ni foam composites were synthesized by a one-step hydrothermal method in an aqueous solution containing only Mn(NO3)2 and C6H12N4. It was found that Mn3O4 nanorods with lengths of 2 to 3 μm and diameters of 100 nm distributed on Ni foam homogeneously. Detailed reaction time-dependent morphological and component evolution was studied to understand the growth process of Mn3O4 nanorods. As cathode material for supercapacitors, Mn3O4 nanorods/composite exhibited superior supercapacitor performances with high specific capacitance (263 F · g-1 at 1A · g-1), which was more than 10 times higher than that of the Mn3O4/Ni plate. The enhanced supercapacitor performance was due to the porous architecture of the Ni foam which provides fast ion and electron transfer, large reaction surface area, and good conductivity. 相似文献
53.
In this paper, the oxidation of calcium bisulfite in the presence of ferrous ions as a catalyst is studied in a laboratory scale apparatus at a fixed oxygen partial pressure (21.3 kPa) and at a temperature of 45 °C. The analysis of the experimental results, carried out by using the theory of mass transfer with chemical reaction, indicates that the slow reaction regime has been explored, and the transition from the kinetic to the diffusional subregime identified. A kinetic analysis allows to develop a reaction rate equation, assuming that the bisulfite oxidation in the presence of ferrous ions follows a parallel reaction mechanism; the resulting overall reaction rate has been found to be of first order with respect to ferrous ion concentration and of three halves with respect to bisulfite concentration. Moreover, the catalytic effect of ferrous ions has been compared with that of manganese ions previously studied, showing that ferrous is a catalyst more active than manganese. 相似文献
54.
Manganese is a commonly found substance in groundwater in Finland. As a powerful oxidant, ozone can be used for the oxidizing of manganese even without raising the pH. The SFS (Finnish Standards Association) standard has set the accepted limit for soluble manganese to 0.45 μm. However, some research papers have used the limit of 30 kD (kilodalton) for soluble manganese. This research concentrates on the size fractions of manganese in four samples of untreated groundwater and in four samples of ozonized groundwater when treated with 0.45 μm, 0.20 μm, 100 kD, 30 kD, and 10 kD filters. In all tests, nearly all manganese contained in raw water penetrated all filters. There were slight variations in the flocculation of manganese in ozonized groundwater; nevertheless, hardly any reduction in manganese levels took place beyond 100 kD. After ozonation, there were two water samples which surpassed the manganese limit of 50 μgl?1 set for domestic water when the filtration was 0.20 μm and another two samples when the filtration was 100 kD. 相似文献
55.
Propylene molecule owns two active sites, the direct epoxidation of propylene by dioxygen is still a challenge due to the limitation of selectivity. In this work, the direct liquid-phase propylene aerobic epoxidation protocol by chloride manganese meso-tetraphenylporphyrin (MnTPPCl) was developed. The conversion of propylene was 12.7%, and the selectivity towards PO (propylene oxide) reached up to 80.5%. The formation of PO was attributed to the mechanism via high-valent Mn species, which was confirmed by means of in situ UV–vis spectrum. 相似文献
56.
《Ceramics International》2022,48(13):18374-18383
In this study, freestanding carbon nanofibers embedded with bimetallic manganese-iron oxide are fabricated for flexible supercapacitor applications via electrospinning. A polyacrylonitrile solution is used as the carbon source, and poly(methyl methacrylate) functions as a sacrificial template to produce microporous carbon nanofibers. The concentrations of manganese acetate and iron acetylacetonate are varied to determine the fabrication conditions for maximal electrochemical performance. The optimized supercapacitor cell exhibits a capacitance of 467 F g?1 at a current density of 1 A g?1 and a capacitance retention of 94% at the end of N = 10,000 cycles. The higher mechanical durability of the electrode is confirmed by the absence of electrochemical deterioration at the end of performing 500 bending cycles. Overall, the sample comprising carbon nanofibers, in which the optimal amount of manganese-iron oxide is embedded, has the required pseudocapacitive characteristics and is an interesting choice for high-energy-storage supercapacitor electrodes. 相似文献
57.
58.
Joan Papavasiliou George Avgouropoulos Theophilos Ioannides 《Applied catalysis. B, Environmental》2009,88(3-4):490-496
Mechanistic aspects of steam reforming of methanol were studied via steady-state isotopic transient kinetic analysis over three copper-based catalysts, namely combustion-synthesized Cu-Ce-O and Cu-Mn-O, and commercial Cu-ZnO-Al2O3. The “C-path” and “O-path” for the production of CO2 via steam reforming of methanol was analysed with the following step changes in the feed: 12CH3OH/H2O/Ar/He → 13CH3OH/H2O/He and CH3OH/H216O/Ar/He → CH3OH/H216O/H218O/He. The presence of CH318OH in the products after the switch to 18O-labeled water indicates that a major path of the reaction is the one involving a methyl formate intermediate. This appears to be the main path over the Cu-Mn-O catalyst, while parallel paths via dioxomethylene and methyl formate intermediates appear to be operative over Cu-Ce-O and Cu-ZnO-Al2O3 catalysts. 相似文献
59.
碳化镧锰合金在室温常压下进行水解氧化反应,洗涤并在50~80℃烘干得到La(OH)3和Mn3O4纳米粉。探讨了反应温度、反应时间、悬浮液浓度和碳化镧锰颗粒大小对晶粒尺寸的影响。优化工艺条件为:反应温度35℃,反应时间18 h,悬浮液浓度0.1 g/ml,碳化镧锰颗粒小于0.15 mm,得到比表面积为122.6 m2/g的La(OH)3和Mn3O4纳米粉。将该纳米粉分别在400、600、800℃和1 000℃煅烧2 h,最终得到晶化程度较好的La0.978Mn0.946O3氧化物。 相似文献
60.
Manganese-molybdenum (Mn-Mo), manganese-molybdenum-vanadium (Mn-Mo-V), manganese-molybdenum-iron (Mn-Mo-Fe) and manganese-iron-vanadium (Mn-Fe-V) anodes were prepared by anodic electrodeposition on iridium oxide-coated titanium substrates for oxygen evolution in seawater electrolysis. XRD, FESEM, EDX and oxygen evolution efficient analysis revealed that the prepared anodes had a γ-MnO2 structure and show a unique mesh-like nanostructure. Oxygen evolution efficiencies were all measured to be more than 99%. The durability tests were performed at 1000 A·m− 2 in 3.5 wt% NaCl solution at pH 12 and 90 °C. The Mn-Fe-V anode was the most stable electrode during the sea water electrolysis, and maintained an oxygen evolution efficiency of 87.96% even after 500 h. It has been found that the main reason for the eventual decrease in oxygen evolution efficiency was partly because of the peeling and electrochemical dissolution of the oxide layer after electrolysis. Also, it was found that the addition of iron and vanadium would maintain a high level of oxygen evolution efficiency during electrolysis. 相似文献