全文获取类型
收费全文 | 3056篇 |
免费 | 59篇 |
国内免费 | 62篇 |
专业分类
电工技术 | 82篇 |
综合类 | 56篇 |
化学工业 | 698篇 |
金属工艺 | 480篇 |
机械仪表 | 68篇 |
建筑科学 | 35篇 |
矿业工程 | 115篇 |
能源动力 | 823篇 |
轻工业 | 17篇 |
水利工程 | 1篇 |
石油天然气 | 20篇 |
无线电 | 98篇 |
一般工业技术 | 471篇 |
冶金工业 | 174篇 |
原子能技术 | 18篇 |
自动化技术 | 21篇 |
出版年
2024年 | 5篇 |
2023年 | 56篇 |
2022年 | 86篇 |
2021年 | 101篇 |
2020年 | 97篇 |
2019年 | 133篇 |
2018年 | 93篇 |
2017年 | 113篇 |
2016年 | 43篇 |
2015年 | 44篇 |
2014年 | 156篇 |
2013年 | 183篇 |
2012年 | 118篇 |
2011年 | 279篇 |
2010年 | 157篇 |
2009年 | 217篇 |
2008年 | 216篇 |
2007年 | 168篇 |
2006年 | 131篇 |
2005年 | 77篇 |
2004年 | 76篇 |
2003年 | 102篇 |
2002年 | 66篇 |
2001年 | 51篇 |
2000年 | 52篇 |
1999年 | 66篇 |
1998年 | 61篇 |
1997年 | 57篇 |
1996年 | 36篇 |
1995年 | 36篇 |
1994年 | 20篇 |
1993年 | 21篇 |
1992年 | 20篇 |
1991年 | 12篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1974年 | 2篇 |
排序方式: 共有3177条查询结果,搜索用时 15 毫秒
21.
《中国稀土学报(英文版)》2022,40(1):57-62
High surface area mixed oxide 8.7% NiO-CeO2 nanoparticles (122 m2/g; 6–7 nm) were prepared using a reversed microemulsion method, and were tested for dry methane reforming (DRM). The catalytic activity of these nanoparticles remains stable under the severe conditions of DRM (700 °C), and they show better carbon resistance than conventional NiO-CeO2 catalysts prepared without control of the size. The activity and selectivity of nanoparticles and reference catalyst are similar, but nanoparticles reduce the accumulation of carbon by 63% during the DRM tests, which is a key feature for this reaction. XPS and H2-TPR suggest that the improved carbon resistance of the nanoparticles is due to the better interaction and cooperation between NiO and CeO2 mixed phases. In nanoparticles, the participation of cerium cations in the redox processes taking place during DRM stabilizes cationic species of nickel. On the contrary, the catalyst prepared without control of the size suffers segregation of Ni during DRM reaction, and segregated Ni explains the higher catalytic formation of carbon. 相似文献
22.
对含铪铸造高温合金在TIG焊接凝固过程中物理冶金特性的研究结果表明,铪显著降低合金焊接裂纹的敏感性。铪增加合金r+r’共晶量并扩大凝固温度范围,使合金枝晶间微液池在很宽温度范围内相互连通。凝固后期富铪熔体具有良好的流动性和润湿性并具有趋肤效应,趋肤液是含铪量高于6%的多元共晶液,它具有自钎接性能,对裂纹起“自愈合”作用。这些结果证明,合金凝固范围宽窄不是影响焊接裂纹的唯一因素,最后凝固液体的物理化学性质具有重要作用。 相似文献
23.
Shape and size of the synthesized NiO nano-sheets were retained during transformation of sheet-like β-Ni(OH)2 to NiO at elevated temperatures via nano-sized zirconia coating on the surface of β-Ni(OH)2. The average grain size was 6.42 nm after 600 °C treatment and slightly increased to 10 nm after 1000 °C treatment, showing
effective sintering retardation between NiO nano-sheets. The excellent thermal stability revealed potential application at
elevated temperatures, especially for high temperature catalysts and solid-state electrochemical devices. 相似文献
24.
The first use of nickel foam (NF) as electrocatalytic negative electrode in a polysulfide/bromine battery (PSB) is described. The performance of a PSB employing NF and polyacrylonitrile (PAN)-based carbon felt (CF) as negative and positive electrode materials, respectively, was evaluated by constant current charge-discharge tests in a single cell. Charge/discharge curves of the cell, positive and negative electrodes show that the rapid fall in cell voltage is due to the drop of positive potential caused by depletion of Br2 dissolved in the catholyte at the end of discharge. Cell voltage efficiency was limited by the relatively high internal ohmic resistance drop (iR drop). Polarization curves indicated that both NF and CF have excellent catalytic activity for the positive and negative redox reactions of PSB. The average energy efficiency of the single cell designed in this work could be as high as 77.2% at 40 mA cm−2 during 48 charge-discharge cycles. 相似文献
25.
A model is developed to address the uniformity of displacement deposition of nickel inside porous silicon with an ultrahigh aspect ratio as high as 200. The nickel distribution is treated as a current distribution issue as in electrodeposition. It is shown that the deposition distribution along the pore depth exhibits a strong dependence on a polarization parameter ξ. High values of ξ correspond to mass transport limitations and lead to non-uniform distributions, whereas small ξ values, representing interfacial reaction control, produce uniform distributions. Non-uniform deposition primarily occurs at an initial stage in which the reaction is dominated by mass transfer. As the deposition process continues, the deposition rate drops to a low value, and the deposition uniformity shifts from Ni2+ mass transport limitations to its interfacial reaction control, leading to uniform Ni2+ concentration and deposition rate distributions. It is predicted that the non-uniformity at the initial stage could be remedied by increasing the bulk concentration of the nickel ions and decreasing the plating bath pH. In addition, the uniformity of the deposition distribution can be significantly improved by introducing inhibiting additive coumarin to the plating solution. 相似文献
26.
Hajime Arai Masayuki Tsuda Masahiko Hayashi Hideaki Ohtsuka Yoji Sakurai 《Electrochimica acta》2005,50(9):1821-1828
Several polymorphs of layered nickel dioxide were prepared by using the chemical insertion of alkaline ions into Li0.10NiO2. We used aqueous AOH (A = Li, Na, K) solutions as reducing agents. Sodium and potassium insertion resulted in hydrated layered compounds that can be classified as γ-NiOOH with high crystallinity, while lithium insertion occurred without hydration. We discuss the coordination environment around the A+ ions for these inserted compounds. The thermal behavior, analyzed using high temperature (HT) X-ray diffraction (XRD) and thermogravimetric (TG) measurements, indicated that heating the hydrate at 150 °C yielded its dehydrate. The electrode performance of the nickelate was studied in lithium cells. We discuss the effect of interlayer water on cell rechargeability and the similarity between these nickelate and hydrated manganese dioxide (birnessite). 相似文献
27.
Luis Carlos Ferreira Jr.Marcos A.S. Costa Pedro Ivo C. GuimarãesLuiz Claudio de Santa Maria 《Polymer》2002,43(14):3857-3862
Styrene polymerization was carried out with Ni(acac)2/MAO and Ni(acac)2/SiO2/MAO. The influence of reaction parameters (Al/Ni mole ratio, catalyst concentration, temperature and time polymerization) on styrene polymerization was evaluated. It was observed that both catalytic systems were affected by reaction parameters and that the heterogeneous catalyst presented higher activity than the homogeneous one. Polystyrenes with different molecular weight, stereoregularity and polydispersity were obtained. These results suggest that different active catalyst species could have been present. In addition, two types of methylaluminoxane (MAO) with different molecular weights were also evaluated as cocatalyst. As a result, the catalyst activity and stereospecificity were strongly affected by the MAO type. 相似文献
28.
New lithium nickel nitrides Li3−2xNixN (0.20 ≤ x ≤ 0.60) have been prepared and investigated as negative electrode in the 0.85/0.02 V potential window. These materials are prepared from a Ni/Li3N mixture at 700 °C under a nitrogen flow. Their structural characteristics as well as their electrochemical behaviour are investigated as a function of the nickel content. For the first time are reported here the electrochemical properties of a lithium intercalation compound based on a layered nitride structure. The Li3−2xNixN compounds can be reversibly reduced and oxidized around 0.5 V versus Li/Li+ leading to specific capacities in the range 120-160 mAh/g depending on the nickel content and the C rate. Due to a large number of lithium vacancies, the structural stability provides an excellent capacity retention of the specific capacity upon cycling. 相似文献
29.
Dry reforming of methane has been investigated on two series of catalysts either prepared by co-precipitation: n(NixMgy)/Al, NixMgy and NixAly or prepared by impregnation: Ni/MgO (mol% Ni = 5, 10). The catalysts, calcined at 600–900 °C, were characterized by different techniques: BET, H2-TPR, TPO, XRD, IR, and TEM-EDX analysis. The surface BET (30–182 m2 g−1) decreased with increasing the temperature of calcination, after reduction and in the presence of Mg element. The XRD analysis showed, for n(NixMgy)/Al catalysts, the presence of NiAl2O4 and NiO–MgO solid solutions. The catalyst reducibility decreased with increasing the temperature of pretreatment. The n(NixMgy)/Al catalysts were active for dry reforming of methane with a good resistance to coke formation. The bimetallic catalyst Ni0.05Mg0.95 (calcined at 750 °C and tested at 800 °C) presents a poor activity. In contrast, the 5% Ni/MgO catalyst, having the same composition but prepared by impregnation, presents a high activity for the same calcination and reaction conditions. For all the catalysts the activity decreased with increasing the temperature of calcination and a previous H2-reduction of the catalyst improves the performances. The TPO profiles and TEM-EDX analysis showed mainly four types of coke: CHx species, surface carbon, nickel carbide and carbon nanotubes. 相似文献
30.
本文报道Ni(naph)_2-n-C_4H_9Li-BF_3·OEt_2催化体系对丁二烯的聚合活性.发现.只有Ni(naph)_2与n-C_4H_9Li二元陈化方式有较好的聚合活性.聚合物的特性粘度[η]和5%苯乙烯的动力粘度(η_(c.p)均低.顺式-1,4结构含量约为94%.几乎不生成凝胶。 相似文献