全文获取类型
收费全文 | 45748篇 |
免费 | 3585篇 |
国内免费 | 1986篇 |
专业分类
电工技术 | 1242篇 |
综合类 | 1996篇 |
化学工业 | 14755篇 |
金属工艺 | 4396篇 |
机械仪表 | 907篇 |
建筑科学 | 1390篇 |
矿业工程 | 1445篇 |
能源动力 | 3863篇 |
轻工业 | 3444篇 |
水利工程 | 152篇 |
石油天然气 | 964篇 |
武器工业 | 307篇 |
无线电 | 2656篇 |
一般工业技术 | 8189篇 |
冶金工业 | 4725篇 |
原子能技术 | 404篇 |
自动化技术 | 484篇 |
出版年
2024年 | 179篇 |
2023年 | 939篇 |
2022年 | 1406篇 |
2021年 | 1772篇 |
2020年 | 1681篇 |
2019年 | 1545篇 |
2018年 | 1491篇 |
2017年 | 1627篇 |
2016年 | 1474篇 |
2015年 | 1470篇 |
2014年 | 2230篇 |
2013年 | 2429篇 |
2012年 | 2791篇 |
2011年 | 3456篇 |
2010年 | 2663篇 |
2009年 | 2524篇 |
2008年 | 2195篇 |
2007年 | 2745篇 |
2006年 | 2536篇 |
2005年 | 2163篇 |
2004年 | 1877篇 |
2003年 | 1664篇 |
2002年 | 1448篇 |
2001年 | 1187篇 |
2000年 | 1121篇 |
1999年 | 844篇 |
1998年 | 750篇 |
1997年 | 579篇 |
1996年 | 501篇 |
1995年 | 381篇 |
1994年 | 375篇 |
1993年 | 272篇 |
1992年 | 244篇 |
1991年 | 166篇 |
1990年 | 151篇 |
1989年 | 123篇 |
1988年 | 68篇 |
1987年 | 41篇 |
1986年 | 20篇 |
1985年 | 37篇 |
1984年 | 25篇 |
1983年 | 19篇 |
1982年 | 30篇 |
1981年 | 24篇 |
1980年 | 18篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1959年 | 5篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
超细粉碎技术现状及发展趋势 总被引:14,自引:2,他引:12
综述了国内外超细粉碎技术及设备的现状、进展,指出了其发展趋势,从工作原理、结构特点等方面详细介绍了超细粉碎典型设备,同时又指出了近年来国内外在此领域中的新进展,基于现存问题指出了今后超细粉碎研究的方向。 相似文献
43.
Study on Oxygen Isotope Fractionation in RE Oxide Minerals 总被引:2,自引:0,他引:2
StudyonOxygenIsotopeFractionationinREOxideMineralsFangTao(方涛),QiuYuzhuo(裘愉卓)(InstituteofGeochemistry,AcademiaSinica,Guiyang5... 相似文献
44.
W. Sjoerd Kijlstra Joop C.M.L. Daamen Jolinde M. van de Graaf Bart van der Linden Eduard K. Poels Alfred Bliek 《Applied catalysis. B, Environmental》1996,7(3-4):337-357
The effect of water on the selective catalytic reduction (SCR) of nitric oxide with ammonia over alumina supported with 2–15 wt.-% manganese oxide was investigated in the temperature range 385–600 K, with the emphasis on the low side of this temperature window. Studies on the effect of 1–5 vol.-% water vapour on the SCR reaction rate and selectivity were combined with TPD experiments to reveal the influence of water on the adsorption of the single SCR reactants. It turned out that the activity decrease due to water addition can be divided into a reversible inhibition and an irreversible deactivation. Inhibition is caused by molecular adsorption of water. TPD studies showed that water can adsorb competitively with both ammonia and nitric oxide. Additional kinetic experiments revealed that adsorbed ammonia is present in excess on the catalyst surface, even in the presence of water. Reduced nitric oxide adsorption is responsible for the observed reversible decrease in the reaction rate; the fractional reaction order changes from 0.79 in the absence of water to 1.07 in its presence. Deactivation is probably due to the dissociative adsorption of water, resulting in the formation of additional surface hydroxyls. As the amount of surface hydroxyls formed is limited to a saturation level, the deactivating effect on the catalyst is limited too. The additional hydroxyls condense and desorb in the temperature range 525–775 K, resulting in a lower degree of deactivation at higher temperature. A high temperature treatment at 775 K results in a complete regeneration. The amount of surface hydroxyls formed per unit surface area decreases at increasing MnOx-loading. The selectivity to the production of nitrogen is enhanced significantly by the presence of gas phase water. 相似文献
45.
Tony Maillet Jacques Barbier Jr. Daniel Duprez 《Applied catalysis. B, Environmental》1996,9(1-4):251-266
A 1% Pd catalyst (38% dispersion) was prepared by impregnating a γ-alumina with palladium acetylacetonate dissolved in acetone. The behaviour of this catalyst in oxidation and steam reforming (SR) of propane was investigated. Temperature-programmed reactions of C3H8 with O2 or with O2 + H2O were carried out with different stoichiometric ratios S(S =[O2]/5[C3H8]). The conversion profiles of C3H8 for the reaction carried out in substoichiometry of O2 (S < 1) showed two discrete domains of conversion: oxidation at temperatures below 350°C and SR at temperatures above 350°C. The presence of steam in the inlet gases is not necessary for SR to occur: there is sufficient water produced in the oxidation to form H2 and carbon oxides by this reaction. Contrary to what was observed with Pt, an apparent deactivation between 310 and 385°C could be observed with Pd in oxidation. This is due to a reduction of PdOx into Pd0, which is much less active than the oxide in propane oxidation. Steam added to the reactants inhibits oxidation while it prevents the reduction of PdOx into Pd0. Compared to Pt and to Rh, Pd has a higher thermal resistance: no deactivation occurred after treatment up to 700°C and limited deactivation after treatment up to 900°C, provided that the catalyst is maintained in an oxygen-rich atmosphere during the cooling. 相似文献
46.
A. Andreev L. Prahov M. Gabrovska A. Eliyas V. Ivanova 《Applied catalysis. B, Environmental》1996,8(4):365-373
The catalytic activity of a wide range of transition metal oxides in oxidation of sulphide ions by air in aqueous medium was studied. Some specific features of the reaction mechanism on some of the studied oxides were considered. The transition metal oxides are promising catalysts for practical application. Some of these oxides will allow the preparation of catalysts possessing activity comparable to that of the cobalt phthalocyanine based catalysts, popular in industrial practice. 相似文献
47.
介绍了新型浅色补强填充剂LEE白滑粉的组成、物化性质、加工特性、硫化胶性能及应用前景。 相似文献
48.
高性能各向异性Sm2Fe17Nx磁粉的制备 总被引:5,自引:0,他引:5
本文研究了高性能各向异性Sm2Fe17Nx磁粉的制备工艺路线与工艺参数。优化了制备与工艺参数。已制备出磁性能达到:Br=1.39T,Hci=850KA/m和(BH)m=236KJ/m^3的各向异性Sm2Fe17N2.88磁粉,该磁粉的各向异性场HA达到20T。 相似文献
49.
氯化铁催化合成富马酸二甲酯 总被引:9,自引:0,他引:9
氯化铁可代替硫酸催化酯化反应,探讨了氯化铁催化合成富马酸二甲酯的条件,操作简便,反应温和,无腐蚀,减少了污染与产品纯化。 相似文献
50.
添加剂对尖晶石型锰酸锂性质表征的影响 总被引:1,自引:0,他引:1
以LiOH·H_20和MnO_2为原料,分别掺入H_2BO_3、Al_2O_3、SiO_2和P_2O_5等添加剂,用固相分段法制备尖晶石型锰酸锂。结果表明,SiO_2和P_2O_5可以有效地改善LiMn_2O_4的电化学性能,H_3BO_3对锰酸锂的电化学性能影响不大,而Al_2O_3破坏了LiMn_2O_4的电化学性能。面扫描结果显示,Si或P元素各自都均匀地分散于LiMn_2O_4的物相中。从元素电负性和原子半径的角度分析了B、Si、P和Al元素对尖晶石型LiMn_2O_4结构和性能的影响。 相似文献