全文获取类型
收费全文 | 25779篇 |
免费 | 1729篇 |
国内免费 | 1182篇 |
专业分类
电工技术 | 1628篇 |
综合类 | 1235篇 |
化学工业 | 5189篇 |
金属工艺 | 576篇 |
机械仪表 | 1075篇 |
建筑科学 | 460篇 |
矿业工程 | 282篇 |
能源动力 | 10642篇 |
轻工业 | 239篇 |
水利工程 | 55篇 |
石油天然气 | 2988篇 |
武器工业 | 322篇 |
无线电 | 293篇 |
一般工业技术 | 1090篇 |
冶金工业 | 602篇 |
原子能技术 | 1473篇 |
自动化技术 | 541篇 |
出版年
2024年 | 84篇 |
2023年 | 487篇 |
2022年 | 828篇 |
2021年 | 990篇 |
2020年 | 1026篇 |
2019年 | 960篇 |
2018年 | 817篇 |
2017年 | 884篇 |
2016年 | 807篇 |
2015年 | 668篇 |
2014年 | 1390篇 |
2013年 | 1811篇 |
2012年 | 1644篇 |
2011年 | 2458篇 |
2010年 | 1808篇 |
2009年 | 1616篇 |
2008年 | 1440篇 |
2007年 | 1664篇 |
2006年 | 1384篇 |
2005年 | 1070篇 |
2004年 | 969篇 |
2003年 | 775篇 |
2002年 | 658篇 |
2001年 | 573篇 |
2000年 | 448篇 |
1999年 | 288篇 |
1998年 | 258篇 |
1997年 | 187篇 |
1996年 | 164篇 |
1995年 | 114篇 |
1994年 | 68篇 |
1993年 | 56篇 |
1992年 | 63篇 |
1991年 | 42篇 |
1990年 | 32篇 |
1989年 | 39篇 |
1988年 | 19篇 |
1987年 | 13篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 14篇 |
1983年 | 3篇 |
1982年 | 13篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1959年 | 11篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Barry D. Solomon 《Energy Policy》1985,13(1):97-101
The prospects for rapid near-term development of a synfuel industry in the USA have decreased, due to depressed world oil prices, synfuel project cost overruns, and the lukewarm support of the Reagan administration. Nonetheless, socioeconomic and environmental impact analysis studies can provide valuable information for determining the regional welfare effects of proposed projects. The author discusses the results of a regional econometric analysis of the synfuel projects planned for Western Kentucky, which focuses on environmental impacts, and reveals the inevitable trade-offs that would accompany synfuel development. Some policy issues are briefly reviewed, especially that of efficient energy pricing. 相似文献
12.
The feasibility of a new alloy design concept utilizing the principle of ‘tungsten bronze effect’ is critically evaluated for the development of metallic bipolar plates for proton exchange membrane fuel cell (PEMFC). An austenitic stainless steel (ASS) is modified with W and La to improve the stability of the passive film in an acidic environment as well as to reduce the contact resistance by the tungsten bronze effect. The experimental ASS containing W and La was evaluated in a simulated PEMFC environment of H3PO4 and H2SO4 solutions at 80 °C, and the electrical property was evaluated by performing a contact resistance test. The test results show that the ASS modified with W and La has good passive film stability for corrosion resistance and low contact resistance. The X-ray photoelectron spectroscopy (XPS) analysis clearly suggests the possibility of the tungsten bronze effect from the change in valency state of W6+ to W5+ in the passive film formed on the modified ASS. The feasibility of a new alloy design concept utilizing the ‘tungsten bronze effect’ is well demonstrated; however, more study is highly required for the development of metallic bipolar plates of PEMFC. 相似文献
13.
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
14.
Trygve Burchardt Pascal GouérecEmilio Sanchez-Cortezon Zia KarichevJames H Miners 《Fuel》2002,81(17):2151-2155
ZeTek Power recently introduced mass manufacturable and cost effective alkaline fuel cells on the market. Today's research is focused on further improvement both in terms of performance increase and cost reduction. This research is classically performed using small (4 cm2) experimental electrodes in the half-cell configuration. This allows the primary electrochemical losses in an anode or cathode to be determined independently. Additional performance losses occur when one integrates large electrodes into a module of 24 cells and in a stack comprised of many modules. By comparing the performance of half-cell experiments to that of modules, these losses can be distinguished and addressed. The information thus obtained, both for the small electrodes and in up-scaling is vital if one is to identify the key areas in which improvement is possible and where to focus future research. Furthermore, the identification of the losses in a module and system allows us to predict the final performance from half-cell measurements of a new laboratory scale experimental electrode. 相似文献
15.
The hydrodynamic and gas mixing characteristics have been determined in a FCC regenerator (0.48 m I.D.x3.4 m high) with FCC
particles. Solids holdup in the dense bed decreases with increasing gas velocity, but it increases in the freeboard region.
The bubble/void fraction increases with an increase along the bed height at a given gas velocity and increases with increasing
gas velocity at a constant bed height. Backmixed tracer gas at the wall region is higher than that at the center region of
the bed. The gas backmixing coefficient decreases with increasing gas velocity. 相似文献
16.
Utilising a pseudo-reference electrode in polymer electrolyte fuel cells allows for the separation of anodic and cathodic contributions to the entire cell impedance. Modelling the impedance responses by using equivalent circuits inhibits the investigation of kinetic parameters of the basic electrochemical reactions, which take place at single electrode-electrolyte interfaces. Therefore, we evaluate single electrode impedance measurements by a kinetic model, which is based on specific reaction pathways, either for the oxygen reduction reaction (ORR) or the hydrogen oxidation reaction (HOR). As a consequence, it is possible to obtain kinetic parameters for the specific reaction of interest. Furthermore, the information gained from the single electrode impedance measurements and the kinetic model can give insight into single reactions steps. In particular, the ORR has to include a chemical step in the reaction pathway. 相似文献
17.
18.
The factors affecting the adsorption and desorption kinetics in a TEOM are reviewed in detail with particular attention given to the assumptions required to obtain physical transport parameters from the data. Two models are presented to simulate TEOM adsorption data in the case that concentration differences down the catalyst bed can be neglected, as is appropriate when the amount of catalyst used is small, the carrier gas flowrate is large, and/or the adsorbate partial pressure is low. In the first model, the effective diffusion coefficient, De, is taken to be constant. In the second model, the effective diffusion coefficient is assumed to obey the Darken equation, De=D0/(1−θ). The TEOM results obtained on n-hexane, n heptane, n-octane, toluene and p-xylene on a commercial FCC catalyst and on pure rare-earth exchanged zeolite Y under non-reacting conditions (373-) are analysed in detail. It is found that intracrystalline diffusion is not the limiting factor affecting the overall rates of adsorption and desorption for the systems studied. Instead, it is the transport of molecules between the adsorbed and vapour phases at the edge of zeolite crystallites that is the limiting transport step affecting the overall kinetics. For the FCC catalyst, the limiting step is the transport of molecules at the zeolite-matrix interface rather than, say, the matrix-vapour interface. Local rate constants for the desorption of the hydrocarbons at the rate-controlling interface have been obtained. 相似文献
19.
20.
柴油机各个气缸的进气量、喷油量、燃烧等存在差异,导致气缸间存在做功差异,直接影响柴油机转速的平稳性以及排放性能等。针对位置式电控柴油机,采用PI闭环控制,通过瞬时转速信号识别并计算各缸的工作差异,利用分缸均衡控制算法对油量进行补偿修正。试验结果显示低转速稳态工况转速波动由7 r/min降至3 r/min,各缸工作不均匀度由±5 r/min降至±2 r/min,在瞬态过程和高转速3 400 r/min时该算法仍然适用有效。 相似文献