全文获取类型
收费全文 | 5570篇 |
免费 | 739篇 |
国内免费 | 227篇 |
专业分类
电工技术 | 217篇 |
综合类 | 225篇 |
化学工业 | 2085篇 |
金属工艺 | 255篇 |
机械仪表 | 144篇 |
建筑科学 | 103篇 |
矿业工程 | 370篇 |
能源动力 | 259篇 |
轻工业 | 296篇 |
水利工程 | 11篇 |
石油天然气 | 1218篇 |
武器工业 | 2篇 |
无线电 | 233篇 |
一般工业技术 | 465篇 |
冶金工业 | 571篇 |
原子能技术 | 36篇 |
自动化技术 | 46篇 |
出版年
2024年 | 30篇 |
2023年 | 122篇 |
2022年 | 178篇 |
2021年 | 173篇 |
2020年 | 274篇 |
2019年 | 236篇 |
2018年 | 197篇 |
2017年 | 211篇 |
2016年 | 249篇 |
2015年 | 228篇 |
2014年 | 383篇 |
2013年 | 376篇 |
2012年 | 393篇 |
2011年 | 397篇 |
2010年 | 274篇 |
2009年 | 226篇 |
2008年 | 214篇 |
2007年 | 269篇 |
2006年 | 288篇 |
2005年 | 253篇 |
2004年 | 203篇 |
2003年 | 234篇 |
2002年 | 189篇 |
2001年 | 168篇 |
2000年 | 141篇 |
1999年 | 123篇 |
1998年 | 89篇 |
1997年 | 67篇 |
1996年 | 74篇 |
1995年 | 44篇 |
1994年 | 33篇 |
1993年 | 33篇 |
1992年 | 24篇 |
1991年 | 30篇 |
1990年 | 24篇 |
1989年 | 15篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1975年 | 1篇 |
1961年 | 1篇 |
1956年 | 1篇 |
1951年 | 4篇 |
排序方式: 共有6536条查询结果,搜索用时 31 毫秒
41.
Quinkal Isabelle; Davasse Valerie; Gaillard Jacques; Moulis Jean-Marc 《Protein engineering, design & selection : PEDS》1994,7(5):681-687
The widespread occurrence of Pro residues adjacent to Cys ligandsin the sequences of [4Fe-4S] electron transfer proteins hasnot yet found a functional basis. The two such Pro of Clostridiumpasteurianum 2[4Fe-4S] ferredoxin have been probed by site-directedmutagenesis. Any one of them, but not both simultaneously, canbe substituted without impairing the proper folding of the protein.The reduction potentials of the ferredoxin variants fall ina narrow range of <20 mV above the potential of the nativeprotein. The biological activities with C.pasteurianum hydrogenaseand pyruvate-ferredoxin oxidoreductase do not change significantly,except when Lys replaces Pro. In these cases, the data suggestthat the two clusters of 2[4Fe-4S] ferredoxin may not alwaysbe equivalent in the interaction with the redox partners. Destabilizationof the structure has been observed as the consequence of theProl9 or Pro48 substitutions. Using 2-D NMR, this effect hasbeen associated with perturbations of both the hydrogen bondnetwork and one amino acid side chain around the [4Fe-4S] clusters.Thus, the conserved Pro found in the binding motif of [4Fe-4S]clusters in proteins strongly stabilizes the active site butdoes not play an essential role in the mechanism of electrontransfer. 相似文献
42.
43.
44.
Stakheev A. Yu. Gabrielsson P. Gekas I. Teleguina N. S. Bragina G. O. Tolkachev N. N. Baeva G. N. 《Topics in Catalysis》2007,42(1-4):143-147
Pt/Al2O3 and Pt/BaO/Al2O3 catalysts (1 wt% Pt, 10 wt%BaO) were sulfated under conditions simulating a real NSR catalyst operation. Comparative TPR
and XPS studies of sulfur removal from Pt/Al2O3 and Pt/BaO/Al2O3 catalysts indicate that the sulfur removal from Al2O3 surface precedes reductive decomposition of BaSO4 (250–400 °C). Barium sulfate decomposition started with further increase in desulfation temperature at the point of surface
atomic ratio Ba:S = 1 (~450o). Simultaneously, an intensive formation of sulfide species on the catalyst surface was observed. Thermodynamic analysis
of the desulfation process allows us to hypothesize that barium sulfide formation may hinder sulfur removal under reducing
conditions. 相似文献
45.
The main disadvantage of the Claus process is that by introducing air as oxidant a large volume of tail gas is produced. This must be treated to reduce atmospheric emissions of sulfur-containing gases. The costs of the tail-gas unit are a significant fraction of the total capital and operating costs for sulfur recovery. A new process uses thermal decomposition of hydrogen sulfide in the presence of carbon dioxide instead of air oxidation. The products of this reaction are hydrogen, carbon monoxide, elemental sulfur, water vapor and carbonyl sulfide. Carbonyl sulfide is easily converted to H2S and C02 by liquid- or vapor-phase hydrolysis. Unreacted H2S and C02 are recovered by absorption and recycled to the reactor. Since no air is introduced, there is no tail gas and the tail-gas unit is eliminated, giving a substantial reduction in capital investment. The concentrations of sulfur-containing gases in the product streams depend only on the operation of the absorber and stripper units and can be controlled to very low levels by increasing stripper boil-up. Process operating costs depend on the level of sulfur recovery required and can also be much lower than those of the modified Claus Process.
The process chemistry depends on a shift in the equilibrium of H2S decomposition caused by reaction of hydrogen with C02 by the reverse of the water-gas-shift reaction. Catalysts for this chemistry have been identified. Reactor conversion is further improved by rapid cooling of the reactor effluent gas. Other aspects of process design and operation confer further advantages with respect to the Claus process; however, the process equipment used is similar to that used in a Claus plant. Retrofit of existing plant to the new technology can therefore be considered. 相似文献
The process chemistry depends on a shift in the equilibrium of H2S decomposition caused by reaction of hydrogen with C02 by the reverse of the water-gas-shift reaction. Catalysts for this chemistry have been identified. Reactor conversion is further improved by rapid cooling of the reactor effluent gas. Other aspects of process design and operation confer further advantages with respect to the Claus process; however, the process equipment used is similar to that used in a Claus plant. Retrofit of existing plant to the new technology can therefore be considered. 相似文献
46.
47.
硫黄硫化聚氨酯橡胶的性能研究 总被引:2,自引:0,他引:2
研究了不饱和聚醚型聚氨酯橡胶(PUR)的硫黄硫化体系,以及硫化剂硫黄和促进剂DM对胶料硫化特性、硫化胶的物理机械性能和耐热空气老化性能的影响。结果表明,硫黄对PUR性能影响明显,焦烧时间长,正硫化时间短,胶料有很好的操作安全性;硫化胶物理机械性能高,拉伸强度达到30MPa,耐热空气老化性能优异,100℃×72h后其拉仲强度保持率高达90%,硫黄用量以2~2.5份为佳;促进剂DM对PUR性能影响显著,有效提高其硫化反应速度,缩短正硫化时间,其用量以2~3份为宜。 相似文献
48.
Tjokorde W. Samadhi Linda E. Jones Alexis G. Clare 《Journal of the American Ceramic Society》2003,86(12):2044-2049
Carbon reacts with Na2 SO4 in glass batches, influencing SO x emissions. To study the role of carbon active surface area (ASA) in the decomposition phenomena, Na2 SO4 is reacted with three carbons with a wide ASA range. The decomposition behavior was evaluated by thermogravimetric analysis (TGA) and evolved gas analysis via mass spectrometry and Fourier transform infrared spectrometry. Higher carbon ASA yields lower decomposition temperatures. SO x emissions are realized at temperatures as low as 773 K. Isothermal Na2 SO4 –C decomposition initiates via the nucleation of Na2 S. The rate constants for the nucleation regime are normalized against ASA, yielding an activation energy of 275 kJ/mol for nucleation. 相似文献
49.
50.
采用稀释SO3磺化甲苯工艺,研究了磺化温度.SO3配气比,原料中水含量和二甲苯砜抑制剂等工艺因素对反应转化率,产物中甲苯磺酸异构体含量及副产物二甲苯砜含量的影响。在10℃.SO3浓度为6%(volume)的操作条件下,二甲苯砜为抑制剂,甲苯转化率达到35%(mass).反应产物中没有新增二甲苯砜,对甲苯磺酸含量达到88.24%.间甲苯磺酸含量降低到0.97%。 相似文献