全文获取类型
收费全文 | 5469篇 |
免费 | 396篇 |
国内免费 | 187篇 |
专业分类
电工技术 | 15篇 |
综合类 | 197篇 |
化学工业 | 3503篇 |
金属工艺 | 155篇 |
机械仪表 | 63篇 |
建筑科学 | 11篇 |
矿业工程 | 30篇 |
能源动力 | 138篇 |
轻工业 | 152篇 |
水利工程 | 5篇 |
石油天然气 | 1410篇 |
武器工业 | 4篇 |
无线电 | 63篇 |
一般工业技术 | 193篇 |
冶金工业 | 60篇 |
原子能技术 | 9篇 |
自动化技术 | 44篇 |
出版年
2024年 | 7篇 |
2023年 | 75篇 |
2022年 | 146篇 |
2021年 | 192篇 |
2020年 | 143篇 |
2019年 | 157篇 |
2018年 | 133篇 |
2017年 | 141篇 |
2016年 | 185篇 |
2015年 | 186篇 |
2014年 | 281篇 |
2013年 | 264篇 |
2012年 | 333篇 |
2011年 | 309篇 |
2010年 | 249篇 |
2009年 | 271篇 |
2008年 | 254篇 |
2007年 | 299篇 |
2006年 | 276篇 |
2005年 | 307篇 |
2004年 | 252篇 |
2003年 | 230篇 |
2002年 | 207篇 |
2001年 | 153篇 |
2000年 | 160篇 |
1999年 | 130篇 |
1998年 | 120篇 |
1997年 | 86篇 |
1996年 | 69篇 |
1995年 | 74篇 |
1994年 | 83篇 |
1993年 | 55篇 |
1992年 | 50篇 |
1991年 | 42篇 |
1990年 | 24篇 |
1989年 | 9篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 19篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 28篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1951年 | 8篇 |
排序方式: 共有6052条查询结果,搜索用时 671 毫秒
61.
过渡金属碳化物具有类似贵金属的电子结构和加氢性能。采用等体积浸渍法制备了不同Ni/W比的NiW/γ-Al2O3催化剂,以程序升温碳化法转化为NiW碳化物后对芳烃模型化合物和低温煤焦油中分离所得芳烃组分进行加氢处理。催化剂的N2吸附、XRD、H2-TPR和SEM表征表明,Ni的添加促进了载体表面WO3物种的分散和还原,抑制了WO3晶体的团聚和大晶粒的生成。萘的加氢实验表明,Ni/W原子比为0.6时催化剂的活性最佳,而添加苯酚和吡啶后的模型油加氢过程中萘的转化率和十氢萘的产率均明显下降,Ni/W原子比为0.47和0.6的催化剂性能相近,煤焦油中芳烃组分加氢后Ni/W原子比为0.47的催化剂性能更优。结果表明,Ni和W均具有良好的加氢活性,但Ni耐杂原子性能较差,二者存在一个最佳的配比以使加氢性能更优。有杂原子化合物存在时,如煤基芳烃组分的加氢,Ni/W原子比为0.47的NiW碳化物催化剂具有更好的加氢性能。 相似文献
62.
63.
64.
对抚顺石油化工分公司石化三厂白油加氢装置进行技术改造,通过调整加氢工艺,采用一段加氢工艺生产高品级的加氢尾油,再经分馏系统生产出多种优级品的白油,满足了市场需求,并创造了可观的经济效益和社会效益。 相似文献
65.
Hydrotreatment of spent oil distillate was carried out on a commercial Ni-Mo-alumina catalyst in the temperature range 260–340 °C, with a liquid hourly space velocity (LHSV) of 0.7–2.0 h?1, pressure of 4.5 MPa and ratio of 300 NL L?1 (normal litre of H2 per litre of feedstock). U.v. spectra of hydrogenated and original spent oil distillates (measured in normal hexane) gave a band with a maximum at 230 nm. The change in absorbance at three selected wavelengths for original oil distillate and hydrotreated oil at different operating conditions was taken as a guide for the determination of hydrogenation reaction rates (including partial saturation of aromatics and sulphur compound hydrogenolysis). The rate constants of hydrogenation reactions (k) using a second-order equation and a model of two parallel first-order reactions (k1 and k2) were calculated. Finally, the apparent activation energy (Ea), enthalpy of activation () and entropy () were calculated based on the values of k, k1, and k2. The calculated values of Ea based on k, k1 and k2 were 81.479, 71.188 and 62.882 kJ mol?1, respectively. The values of based on the same rate constants were 76.670, 66.564 and 58.433 kJ mol?1, while the values of were ?117.150, ?133.779 and ?150.823 J mol?1 K?1, respectively. 相似文献
66.
67.
An anomalous rate enhancement with increasing conversion has been observed during the liquid phase hydrogenation of nitrobenzene and crotonaldehyde over Ge/Pd/C catalysts at ambient temperature and atmospheric pressure. Inductive coupled plasma atomic emission spectroscopy and electrochemical measurement of the oxidation state of catalysts during reaction revealed that the bimetallic particles were partially oxidized by the reactants, which resulted in Ge-dissolution and increased exposure of Pd on the surface. It is proposed that the surface and bulk composition of Ge/Pd catalysts are a function of their oxidation state. This behaviour is due to the unusually high mobility of Ge in the Pd lattice and to the good solubility of GeO2 in polar solvents. The influence of hydrogen transport on the corrosion process and the stability of other X/Pd type bimetallic catalysts during liquid phase hydrogenation are also discussed. 相似文献
68.
69.
P. Da Costa C. Potvin J.-M. Manoli M. Breysse G. Djega-Mariadassou 《Catalysis Letters》2003,86(1-3):133-138
Hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene on alumina-supported Mo2C has been studied. These catalysts are stable and active under deep HDS conditions (0-250 wt ppm S). However, although they are well known to have hydrogenation properties, they lead preferentially to a non-hydrogenated product of the HDS reaction: dimethylbiphenyl. For the same reaction, supported platinum and sulfided molybdenum oxide lead to the hydrogenated products dimethyldicyclohexyl and methylcyclohexyltoluene, respectively. The ranking of HDS activity is as follows: MoS2/Al2O3 < Mo2C/Al2O3 < Pt/SiO2. 相似文献
70.