全文获取类型
收费全文 | 101666篇 |
免费 | 5952篇 |
国内免费 | 4101篇 |
专业分类
电工技术 | 6973篇 |
技术理论 | 19篇 |
综合类 | 9733篇 |
化学工业 | 10225篇 |
金属工艺 | 2885篇 |
机械仪表 | 4409篇 |
建筑科学 | 13855篇 |
矿业工程 | 3630篇 |
能源动力 | 2856篇 |
轻工业 | 4373篇 |
水利工程 | 4492篇 |
石油天然气 | 3854篇 |
武器工业 | 540篇 |
无线电 | 9513篇 |
一般工业技术 | 5633篇 |
冶金工业 | 6292篇 |
原子能技术 | 1130篇 |
自动化技术 | 21307篇 |
出版年
2024年 | 240篇 |
2023年 | 1019篇 |
2022年 | 2137篇 |
2021年 | 2609篇 |
2020年 | 2500篇 |
2019年 | 1783篇 |
2018年 | 1565篇 |
2017年 | 2165篇 |
2016年 | 2621篇 |
2015年 | 2874篇 |
2014年 | 7331篇 |
2013年 | 6300篇 |
2012年 | 7044篇 |
2011年 | 8049篇 |
2010年 | 6152篇 |
2009年 | 6732篇 |
2008年 | 6477篇 |
2007年 | 7613篇 |
2006年 | 6749篇 |
2005年 | 5519篇 |
2004年 | 4697篇 |
2003年 | 4178篇 |
2002年 | 3374篇 |
2001年 | 2564篇 |
2000年 | 2016篇 |
1999年 | 1584篇 |
1998年 | 1113篇 |
1997年 | 859篇 |
1996年 | 685篇 |
1995年 | 588篇 |
1994年 | 466篇 |
1993年 | 364篇 |
1992年 | 266篇 |
1991年 | 210篇 |
1990年 | 157篇 |
1989年 | 149篇 |
1988年 | 106篇 |
1987年 | 74篇 |
1986年 | 89篇 |
1985年 | 105篇 |
1984年 | 110篇 |
1983年 | 104篇 |
1982年 | 55篇 |
1981年 | 47篇 |
1980年 | 93篇 |
1979年 | 31篇 |
1978年 | 13篇 |
1977年 | 26篇 |
1975年 | 14篇 |
1959年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Svetlana A. Yashnik Zinfer R. Ismagilov Vladimir F. Anufrienko 《Catalysis Today》2005,110(3-4):310-322
The effect of ion exchange conditions, such as Si/Al ratio, precursor copper salt, pH and concentration of the solution, on the catalytic activity in SCR of NO by propane and on the electronic state of copper ions in Cu-ZSM-5 has been studied. The NO conversion in NO SCR by C3H8 has been found to reach a maximum value at Cu/Al ratio about 0.37–0.4 and remain constant at higher Cu/Al.
ESR and UV–vis DR spectroscopy have been used to elucidate stabilization conditions of copper ions in Cu-ZSM-5 zeolites as isolated Cu2+ ions, chain copper oxide structures and square-plain oxide clusters. The ability of copper ions for reduction and reoxidation in the chain structures may be responsible for the catalytic activity of Cu-ZSM-5. These transformations of copper ions are accompanied by the observation of intervalence transitions Cu2+–Cu+ and CTLM of the chain structures in the UV–vis spectra. 相似文献
12.
Amanda Alliband Daniel W. Lenz Laura E. Stevenson Travis Whitmer Rex Cash Dennis Burns Sarah Hall William T.K. Stevenson 《Progress in Organic Coatings》2008
A model has been proposed to explain the failure of the original BMS10-39 epoxy paint on upper vertical surfaces in B-52 fuel tanks. The model involves interaction of the paint with DIEGME, a fuel system ice inhibitor (FSII) in jet fuel, that is distilled from the liquid fuel. In this communication, distillation experiments used to support the model are refined to better match the mass transfer of vapor from fuel in a B-52 fuel tank at close to room temperature. The interaction of these lower temperature distillates with the paint affirms the earlier model. On the basis of these experiments it is proposed that paint failure may be controlled or eliminated by reducing the level of DIEGME in the fuel. Proposed changes in military jet fuel composition are detailed. 相似文献
13.
Penedo Frank J.; Dahn Jason R.; Gonzalez Jeffrey S.; Molton Ivan; Carver Charles S.; Antoni Michael H.; Roos Bernard A.; Schneiderman Neil 《Canadian Metallurgical Quarterly》2003,22(2):220
This study evaluated relations among optimism, perceived stress management skills (PSMS), and positive mood in 46 men who had surgical treatment for localized prostate cancer. The authors found that optimism, PSMS, and positive mood scores were positively correlated. Positive mood was unrelated to demographic and disease-related control variables. In a hierarchical regression model controlling for PSMS, the relationship between optimism and positive mood became nonsignificant, whereas PSMS remained a correlate of positive mood. Results suggest that the relationship between optimism and positive mood may be mediated by belief in being able to use stress management techniques effectively. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
14.
The dehydroalkylation of toluene with ethane to the isomeric ethyltoluenes was studied on 0.4Pt/H-ZSM-5 at varying contact
times (1/WHSV). At a high contact time of 1.0 h, toluene disproportionation and hydrogenolysis reactions dominate, resulting
in low selectivity to the desired ethyltoluenes via the alkylation reaction. However, at a low contact time of 0.12 h side
reactions are eliminated, resulting in maximum selectivities to the kinetically favored ethyltoluenes and hydrogen. Results
at high selectivities to ethyltoluenes provide significant insight into reaction pathways. 相似文献
15.
16.
Hydroprocessing catalysts based on Ni, Co, Mo and W are used in various refinery processing applications where several deactivation mechanisms become of importance (coke formation, active phase sintering, metals deposition, poisoning) in the catalyst's life cycle. The life cycle of commercial hydroprocessing catalysts is very complex and includes the catalyst production, sulfidation, use, oxidative regeneration followed by re-sulfidation and reuse or, if reuse is not possible, recycling or disposal. To understand the changes in catalyst properties taking place during a life cycle, the catalyst quality in the different stages can be best monitored by using advanced analytical techniques. The catalyst's life cycle is further complicated by numerous technical, environmental and organizational issues involved. In principle, different companies can be involved in each of the life cycle steps. Leading catalyst manufacturers, together with specialized firms, offer refineries a total catalyst management concept, starting with the purchase of the fresh catalyst and ending with its final recycling or disposal. Total catalyst management includes a broad range of services, ensuring optimal timing during the change-out process, reliable, smooth and safe operations, minimal downtime and maximum catalyst and unit performance. 相似文献
17.
结合工程概况及工程特点,从机械设备配置、劳动力组织、现场管理等方面介绍了大窝山隧道进口Ⅱ级,Ⅲ级围岩段的快速掘进施工组织与管理措施,为类似隧道的快速掘进施工组织与管理提拱了相关经验. 相似文献
18.
Chris Harty 《Building Research & Information》2005,33(6):512-522
An alternative approach to understanding innovation is made using two intersecting ideas. The first is that successful innovation requires consideration of the social and organizational contexts in which it is located. The complex context of construction work is characterized by inter-organizational collaboration, a project-based approach and power distributed amongst collaborating organizations. The second is that innovations can be divided into two modes: 'bounded', where the implications of innovation are restricted within a single, coherent sphere of influence, and 'unbounded', where the effects of implementation spill over beyond this. Bounded innovations are adequately explained within the construction literature. However, less discussed are unbounded innovations, where many firms' collaboration is required for successful implementation, even though many innovations can be considered unbounded within construction's inter-organizational context. It is argued that unbounded innovations require an approach to understand and facilitate the interactions both within a range of actors and between the actors and technological artefacts. The insights from a sociology of technology approach can be applied to the multiplicity of negotiations and alignments that constitute the implementation of unbounded innovation. The utility of concepts from the sociology of technology, including 'system building' and 'heterogeneous engineering', is demonstrated by applying them to an empirical study of an unbounded innovation on a major construction project (the new terminal at Heathrow Airport, London, UK). This study suggests that 'system building' contains outcomes that are not only transformations of practices, processes and systems, but also the potential transformation of technologies themselves. 相似文献
19.
Heidi Bernas Arie J. Plomp Johannes H. Bitter Dmitry Yu. Murzin 《Catalysis Letters》2008,120(1-2):8-13
The density functional theory (DFT/B3LYP) calculations were applied to investigate the interaction of a Pt6 particle with the ZSM-5 zeolite framework. The electronic structure of the metal particle is strongly affected by the interaction with basic framework oxygens and acid sites of the zeolite support. Adsorption on basic sites (Eads = 6 kcal/mol) favors the formation of the electron enriched metal cluster. Interaction of the platinum cluster with the acid site characterized by stabilization energy of 47 kcal/mol results in oxidation of the metal particle and suppression of Brønsted acidity of the support. The hypothesis is put forward that the oxidized platinum particle can function as an active site for the alkane isomerisation on platinum supported high silica zeolites. 相似文献
20.
M. Jayasankar 《Materials Letters》2007,61(3):790-793
Formation of aluminium titanate (AT) has been achieved at low temperature through sol-gel process using boehmite and titanium hydroxide as precursors by controlling the particle size at nanoscale followed by in-situ peptisation. The formations of AT phase, particle size distributions, sintering and thermal expansion characteristics, and microstructural features have been reported. DTA and XRD analysis have been performed to confirm the formation of AT. A 94% relative density was obtained for aluminium titanate sintered at 1550 °C with controlled grain size in the range of 2-3 μm. 相似文献