全文获取类型
收费全文 | 10124篇 |
免费 | 1224篇 |
国内免费 | 335篇 |
专业分类
电工技术 | 108篇 |
综合类 | 937篇 |
化学工业 | 4697篇 |
金属工艺 | 316篇 |
机械仪表 | 196篇 |
建筑科学 | 180篇 |
矿业工程 | 164篇 |
能源动力 | 880篇 |
轻工业 | 1212篇 |
水利工程 | 92篇 |
石油天然气 | 528篇 |
武器工业 | 121篇 |
无线电 | 102篇 |
一般工业技术 | 842篇 |
冶金工业 | 988篇 |
原子能技术 | 137篇 |
自动化技术 | 183篇 |
出版年
2024年 | 19篇 |
2023年 | 139篇 |
2022年 | 204篇 |
2021年 | 222篇 |
2020年 | 328篇 |
2019年 | 314篇 |
2018年 | 304篇 |
2017年 | 299篇 |
2016年 | 325篇 |
2015年 | 310篇 |
2014年 | 498篇 |
2013年 | 597篇 |
2012年 | 614篇 |
2011年 | 722篇 |
2010年 | 531篇 |
2009年 | 601篇 |
2008年 | 528篇 |
2007年 | 639篇 |
2006年 | 550篇 |
2005年 | 536篇 |
2004年 | 427篇 |
2003年 | 449篇 |
2002年 | 399篇 |
2001年 | 333篇 |
2000年 | 317篇 |
1999年 | 264篇 |
1998年 | 225篇 |
1997年 | 189篇 |
1996年 | 138篇 |
1995年 | 135篇 |
1994年 | 104篇 |
1993年 | 98篇 |
1992年 | 75篇 |
1991年 | 52篇 |
1990年 | 43篇 |
1989年 | 40篇 |
1988年 | 24篇 |
1987年 | 17篇 |
1986年 | 20篇 |
1985年 | 14篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 1篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
41.
催化技术在降低汽油机排放方面的应用 总被引:3,自引:2,他引:1
本文介绍了当前催化技术在改善和降低汽油机排放方面的应用情况,指出:催化技术是改善汽油机排放的一种有效措施和重要手段。 相似文献
42.
以自制的磷铝杂原子固体酸催化剂催化合成了马来酸二丁酯,考察了反应时间、醇酸摩尔比、带水剂用量、催化剂用量等对酯化率的影响;同时考察了催化剂的重复使用性。对酯化产物物理性能进行了测试,其实测值与文献值相符。 相似文献
43.
The aim of this research is to investigate how ammonia treatment of the surface can influence the activity of a viscose-based activated carbon cloth (ACC) for the oxidative retention of H2S and SO2 in humid air at 25 °C. Surface basic nitrogen groups were introduced either by treatment with ammonia/air at 300 °C or with ammonia/steam at 800 °C. The pore structure of the samples so prepared was examined by adsorption measurements. Changes in the surface chemistry were assessed by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and temperature programmed desorption (TPD). The change of ACC activity could not be merely attributed to surface nitrogen groups but to other changes in the support. Ammonia/steam treatment improved ACC performance the most, not only by introducing nitrogen surface groups, but also by extending the microporosity and by modifying the distribution of surface oxygen groups. Successive adsorption-regeneration cycles showed important differences between oxidative retention of H2S and SO2 and the subsequent catalyst/support regeneration process. 相似文献
44.
As an alternative to previously developed catalytic FeCrAlloy fibre mat burners based on perovskite catalysts, new catalytic burners have been developed based on Pd catalyst on lantana-stabilised Al2O3 and different fibre structures (NIT100A, NIT100S and NIT200S by ACOTECH NV). All development steps are considered, shifting from catalyst preparation (based on combustion synthesis of γ-Al2O3) to the optimisation of lantana and Pd loadings, from the definitions of the best catalyst-deposition conditions (washcoating) to the catalytic burners performances, determined in an ad hoc developed combustion chamber. The results show almost half pollutants emissions and better performance compared to various non-catalytic counterparts, especially as far as CO and NOx emissions are concerned. Some flame instability problems were though registered, especially for one of the catalytic burner mattresses employed, at low specific power inputs and excesses of air (<375 kW/m2 and <12%, respectively). Further, PdO/Pd transition is shown to influence the dynamic behaviour of the catalytic burners. 相似文献
45.
The catalytic activity of fresh Pd and Pt catalysts supported on γ-alumina in the complete oxidation of CH4 traces under lean-burn conditions was studied in the presence or the absence of water or H2S. Steam-aged catalysts were also studied in order to simulate long-term ageing in real lean-burn natural gas fuelled vehicles (NGVs) exhaust conditions. Without water or H2S added to the feed, Pd catalysts exhibit a superior catalytic activity in methane oxidation compared to Pt ones, whatever the catalysts were fresh or aged. The addition of 10 vol.% water vapour to the feed strongly affects the activity of the fresh Pd catalyst, thus being only slightly more efficient than the fresh Pt one. H2S has a strong poisoning effect on the catalytic activity of Pd catalysts, while Pt catalysts are more resistant. The fresh H2S-poisoned Pd/Al2O3 catalyst was studied by TPD in O2/He. Poisoning species decompose above 873 K as SO2 and O2 in relative concentrations consistent with the decomposition of surface sulphate species. However, a treatment in O2/He at temperatures as high as 923 K does not allow the complete regeneration of the catalytic activity of H2S-poisoned Pd/Al2O3. A mechanism involving the poisoning of PdO by sulphate species is proposed. Different diffusion processes by which these sulphate species can migrate back and forth between PdO and the support, depending on the experimental conditions, are suggested. 相似文献
46.
Chia‐Yin Chen Yu‐Chi Cheng Shau‐Wei Tsai 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2002,77(6):699-705
A lipase‐catalyzed enantioselective hydrolysis process under in situ racemization of the remaining (R)‐thioetser substrate with trioctylamine as the catalyst was developed for the production of (S)‐fenoprofen from (R,S)‐fenoprofen 2,2,2‐trifluoroethyl thioester in isooctane. Detailed investigations of trioctylamine concentration on the enzyme activation and the kinetic behavior of the thioester in racemization and enzymatic reactions were conducted, in which good agreement between the experimental data and theoretical results was observed. © 2002 Society of Chemical Industry 相似文献
47.
树脂悬浮光度法测定微量银 总被引:1,自引:0,他引:1
在pH6.9的缓冲溶液中,银与硫代米Chi酮(TMK)形成的螯合物在树脂甘油相中悬浮富集,用光度法测定银在波长461nm处有最大吸收,银在0~6μg/10mL范围内遵守比尔定律,可用于样品中微量银的测定。 相似文献
48.
49.
V. A. Roginsky T. K. Barsukova A. A. Remorova W. Bors 《Journal of the American Oil Chemists' Society》1996,73(6):777-786
The relative reactivities as well as the stoichiometric coefficients for a number of flavonoids, catechols, and—for comparison—standard
phenolic antioxidants were determined by analyzing the kinetics of oxygen consumption in organic and micellar systems, with
peroxidation initiated by lipid- and water-soluble azo initiators. The results demonstrated that the flavonoids did not behave
as classic phenolic antioxidants such as α-tocopherol, but showed only moderate chain-breaking activities. The results were
in line with other structure-activity relationship studies on the importance of the B-ring catechol structure, the 2,3-double
bond, and the 3,5-hydroxy groups. The data are discussed in view of possible explanations of the deviations flavonoids reveal
in their behavior compared with regular phenolic antioxidants. 相似文献
50.
本文在气相色谱仪联用微反应器装置上,研究了LaBO_3型催化剂中的B位元素对催化氧化活性的影响规律,并进行了程序升温脱附实验。另外,还对LaBO_3型载体催化剂进行了活性筛选,并在柴油机台架上与贵金属Pt/Al_2O_3进行了有害气体净化效果的对比实验。实验结果表明,LaBO_3氧化物中LaMnO_3对CO、CH_4的催化氧化活性最高,且CO、CH_4活性中心并不一致。LaMnO_3/γ-Al_2O_3浸渍微量助化剂后,能使CO在130℃完全氧化,CH_4的氧化温度在300~500℃范围内,LaMnO_3载体催化剂对柴油机有害排放物的净化率很低,浸渍微量助化剂后,净化率提高一倍以上,特别是LaMnO_3/堇青石蜂窝陶瓷,浸渍后的净化效果同贵金属Pt/Al_2O_3接近。 相似文献