全文获取类型
收费全文 | 7130篇 |
免费 | 597篇 |
国内免费 | 313篇 |
专业分类
电工技术 | 810篇 |
综合类 | 484篇 |
化学工业 | 2452篇 |
金属工艺 | 314篇 |
机械仪表 | 219篇 |
建筑科学 | 459篇 |
矿业工程 | 175篇 |
能源动力 | 224篇 |
轻工业 | 524篇 |
水利工程 | 107篇 |
石油天然气 | 404篇 |
武器工业 | 53篇 |
无线电 | 365篇 |
一般工业技术 | 612篇 |
冶金工业 | 396篇 |
原子能技术 | 114篇 |
自动化技术 | 328篇 |
出版年
2024年 | 39篇 |
2023年 | 127篇 |
2022年 | 230篇 |
2021年 | 258篇 |
2020年 | 245篇 |
2019年 | 192篇 |
2018年 | 151篇 |
2017年 | 231篇 |
2016年 | 234篇 |
2015年 | 238篇 |
2014年 | 424篇 |
2013年 | 420篇 |
2012年 | 554篇 |
2011年 | 568篇 |
2010年 | 381篇 |
2009年 | 440篇 |
2008年 | 314篇 |
2007年 | 447篇 |
2006年 | 397篇 |
2005年 | 376篇 |
2004年 | 285篇 |
2003年 | 248篇 |
2002年 | 206篇 |
2001年 | 204篇 |
2000年 | 162篇 |
1999年 | 108篇 |
1998年 | 113篇 |
1997年 | 83篇 |
1996年 | 60篇 |
1995年 | 51篇 |
1994年 | 48篇 |
1993年 | 33篇 |
1992年 | 26篇 |
1991年 | 29篇 |
1990年 | 26篇 |
1989年 | 17篇 |
1988年 | 15篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1976年 | 3篇 |
1966年 | 3篇 |
1961年 | 1篇 |
1959年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有8040条查询结果,搜索用时 0 毫秒
41.
Many high Miller index metals surfaces are naturally chiral, offering opportunities for performing enantiospecific chemistry. Previous theoretical treatments of adsorption on these surfaces have used surfaces truncated from bulk crystals. This paper examines the effect of surface relaxation on enantiospecific adsorption on chiral Pt surfaces by using relaxed surface structures determined using density functional theory. 相似文献
42.
43.
YAG掺铷——钇铝石榴石激光晶体胶粘剂以丁腈改性环氧树脂,酚醛变性胺为固化剂,用于掺铷——钇铝石榴石激光晶体与钢套粘接,安装在陕西省人民医院YAG激光医用治疗机,临床应用3年,效果很好。后中国电子科技集团第二十七研究所从1990年开始用YAG激光胶粘剂粘接各类激光产品至今,经高低温试验、振动试验、冲击试验等各项性能测试及15年来工程应用证明,在各类激光产品中从未出现开裂、脱胶现象,性能稳定可靠,其粘接强度、耐冲击、耐振动、耐高低温变化、耐水、耐化学介质、耐光、耐老化性能均好,能满足生产要求,用途广泛,符合激光及各种工程应用。文中详述了酚醛变性胺固化剂的选择及该胶粘剂的性能。 相似文献
44.
Cinchonidine and cinchonine have been grafted onto pure silica MCM-41. It has been shown that both supported alkaloids are active catalysts for the Michael addition of ethyl 2-oxocyclopentanecarboxylate and methyl vinyl ketone, anchored cinchonidine being more active and enantioselective than anchored cinchonine. The study of the influence of the polarity of the solvent and reaction temperature on the optical induction shows that there is not a direct correlation between solvent polarity and enantioselectivity, and the maximum optical yield was obtained between 278 and 273 K. 相似文献
45.
46.
X.Y.?Wang J.M.?WangEmail author H.B.?Shao J.Q.?Zhang C.N.?Cao 《Journal of Applied Electrochemistry》2005,35(2):213-216
The corrosion behavior of pure aluminum in inhibited and uninhibited 4 MKOH was investigated by means of hydrogen collection, polarization curve measurement and electrochemical impedance spectroscopy (EIS). The results showed that the corrosion of pure aluminum was greatly inhibited by the addition of ZnO and dimethyl amine epoxy propane (designated as DE). EIS and EDAX analyses revealed that ZnO produces its effect by depositing on the aluminum surface, which increases the overpotential of hydrogen evolution. It was also found that the addition of DE could greatly improve the deposition of zinc layers. 相似文献
47.
N,O,O′─三(对甲苯磺酰基)双(2─羟乙基)胺的合成 总被引:1,自引:0,他引:1
二乙醇胺和对甲苯磺酰氯在三乙胺存在下,反应生成N,0,O′-三(对甲苯磺酰基)双(2-羟乙基)胺,产率93%。从反应混合物中分离得副产物N,O-二(对甲苯磺酰基)双(2-羟乙基)胺。 相似文献
48.
Immobilization of new Mn(salen) complex over MCM-41 and its activity in asymmetric epoxidation of styrene 总被引:3,自引:0,他引:3
New tetradentate chelates of bis-Schiff bases were synthesized and then these chiral salen ligands were immobilized over mesoporous
MCM-41 by using the ion-exchange method. The efficiency of the chiral catalyst was examined in the asymmetric epoxidation
of styrene. Chiral Mn(salen) complexes immobilized onto mesoporous MCM-41 were stable during the reaction without any leaching
and exhibited relatively high enantioselectivity for epoxidation as compared with homogeneous complexes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
49.
50.
J. H. Bordon J. R. Handley J. A. McLean R. M. Silverstein L. Chong K. N. Slessor B. D. Johnston H. R. Schuler 《Journal of chemical ecology》1980,6(2):445-456
The aggregation pheromone ofGnathotrichus retusus was isolated and identified as (S)-(+)-sulcatol (6-methyl-5-hepten-2-ol). In laboratory and field experiments,G. retusus responded to (S)-(+)-sulcatol, but not to (±)-sulcatol, which was attractive to the sympatric species,G. sulcatus. G. sulcatus did not respond to optically pure (S)-(+)-sulcatol, but began to respond when 1% (R)-(–)-sulcatol was present in an enantiomeric mixture.Research supported by the National Science Foundation, U.S.A. (Grant BMS-74-13643), and the Natural Sciences and Engineering Research Council of Canada (Co-op grant A0243 and Operating Grant A3881 and A3785). 相似文献