全文获取类型
收费全文 | 8857篇 |
免费 | 1051篇 |
国内免费 | 711篇 |
专业分类
电工技术 | 1259篇 |
综合类 | 542篇 |
化学工业 | 2894篇 |
金属工艺 | 274篇 |
机械仪表 | 190篇 |
建筑科学 | 94篇 |
矿业工程 | 49篇 |
能源动力 | 73篇 |
轻工业 | 240篇 |
水利工程 | 26篇 |
石油天然气 | 82篇 |
武器工业 | 36篇 |
无线电 | 2216篇 |
一般工业技术 | 1706篇 |
冶金工业 | 101篇 |
原子能技术 | 227篇 |
自动化技术 | 610篇 |
出版年
2025年 | 6篇 |
2024年 | 249篇 |
2023年 | 280篇 |
2022年 | 288篇 |
2021年 | 379篇 |
2020年 | 400篇 |
2019年 | 439篇 |
2018年 | 363篇 |
2017年 | 420篇 |
2016年 | 365篇 |
2015年 | 360篇 |
2014年 | 380篇 |
2013年 | 508篇 |
2012年 | 599篇 |
2011年 | 539篇 |
2010年 | 400篇 |
2009年 | 447篇 |
2008年 | 447篇 |
2007年 | 550篇 |
2006年 | 505篇 |
2005年 | 411篇 |
2004年 | 411篇 |
2003年 | 349篇 |
2002年 | 252篇 |
2001年 | 219篇 |
2000年 | 183篇 |
1999年 | 145篇 |
1998年 | 128篇 |
1997年 | 94篇 |
1996年 | 89篇 |
1995年 | 68篇 |
1994年 | 48篇 |
1993年 | 46篇 |
1992年 | 42篇 |
1991年 | 52篇 |
1990年 | 26篇 |
1989年 | 38篇 |
1988年 | 16篇 |
1987年 | 7篇 |
1986年 | 9篇 |
1985年 | 17篇 |
1984年 | 13篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1981年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Low dielectric poly[methylsilsesquioxane‐ran‐trifluoropropylsilsesquioxane‐ran‐(2,4,6,8‐tetramethyl‐2,4,6,8‐tetraethylenecyclotetrasiloxane)silsesquioxane]s {P[M‐ran‐TFP‐ran‐(TCS)]SSQs} having various compositions were synthesized using trifluoropropyl trimethoxysilane, methyl trimethoxysilane and 2,4,6,8‐tetramethyl‐2,4,6,8‐tetra(trimethoxysilylethyl)cyclotetrasiloxane. The chemical composition of the polymers and the content of SiOH end‐groups were controlled by adjusting the reaction conditions, and they were characterized by 1H‐NMR. The thermally decomposable trifluoropropyl groups on the P[M‐ran‐TFP‐ran‐(TCS)]SSQ backbone and heptakis(2,3,6‐tri‐O‐methyl)‐β‐cyclodextrin (CD) were employed as pore generators. The dielectric constants of the porous CD/P[M‐ran‐TFP‐ran‐(TCS)]SSQ films were in the range 2.0–2.7 (at 100 kHz) depending on the concentration of the porogens, and showed no change over 4 days under aqueous conditions. The pore size of the films showed a bimodal distribution, with diameters of ca 0.5–1.0 nm for those originating from the trifluoropropyl groups and 1.7 nm from the CD. The elastic modulus and hardness of the 30 vol% CD‐blended film with a dielectric constant of 2.26 were 2.40 and 0.38 GPa, respectively, as determined by a nanoindenter. Copyright © 2005 Society of Chemical Industry 相似文献
2.
为改善复合泡沫塑料的介电性能,采用金属氧化物粒子填充改性双马来酰亚胺空芯玻璃微球复合泡沫塑料得到了高介电常数、低介质损耗因数、低密度、力学性能良好的电介质材料。 相似文献
3.
A polyester (PE) based on the glycolyzed products of PET was prepared and added in different concentrations to a series of SBR/PVC blends. The addition of the polyester showed that all properties of SBR/PVC blends were improved by incorporation of PE. Highest mechanical strength values were obtained at a polyester concentration of 7.5 phr. Thermal analysis as well as dynamic mechanical properties of SBR/PVC blends after the addition of 7.5 and 10 phr polyester indicated one single glass transition temperature. The dielectric losses (?") were analyzed in the frequency domains in the two terms of Fröhlich related to the Maxwell Wagner effect and the orientation of the aggregates caused by the movement of the main chain. The permittivity (?') values were found to increase by increasing the polyester content. This increase was followed by a decrease in the ?" up to a 7.5 phr polyester content after which no pronounced change was noticed. 相似文献
4.
5.
采用介质阻挡放电(DBD)降解常压下流动态的邻二甲苯模拟废气,系统地考察了放电极值电压,气体的初始质量浓度、停留时间以及相对湿度等工艺参数对邻二甲苯降解的影响,并初步探讨了邻二甲苯的降解产物.实验研究结果表明:在7.0kV的放电极间电压下,邻二甲苯的初始质量浓度为1 500mg/m3,停留时间为9s,其去除率可达到80%以上.降解产物主要为CO2、H2O以及苯甲酸、苯乙酸、苯乙醛等有机物,并且经降解后产物的生物可生化性得到提高,因而为后续的等离子-生物法联合处理VOCs提供了依据. 相似文献
6.
在电火花加工的工作液中添加络合剂,使之与被蚀除的金属颗粒产生络合化学反应,生成可溶于工作液中的络合物。利用这种原理,可提高电火花加工性能,在小孔、深槽等加工应用中起到促进排屑的作用。 相似文献
7.
8.
Marco Paluszny 《Computer aided design》2008,40(1):56-61
We consider patches that contain any given 3D polynomial curve as a pregeodesic (i.e. geodesic up to reparametrization). A curve is a pregeodesic if and only if its rectifying plane coincides with the tangent plane to the surface, we use this fact to construct ruled cubic patches through pregeodesics and bicubic patches through pairs of pregeodesics. We also discuss the G1 connection of (1,k) patches with abutting pregeodesics. 相似文献
9.
CHEN KenLe & ZHANG JinWen National Key Laboratory of Micro/Nano Fabrication Technology 《中国科学:信息科学(英文版)》2011,(2)
10.
Ivan Bozovic 《Journal of Superconductivity》1991,4(2):193-197
A novel optical method for accurate monitoring of the carrier densityN in layered conductors is introduced. It is applied to several cuprate superconductors, and it is found thatT
c
doesnot scale withN. However, if the closely spaced pairs or triplets of CuO2 planes were coupled together to act as distinct metallic slabs, the relevant variable could ben, theslab carrier density. Indeed, we found thatT
c
does scale nicely withn. This suggests that high-T
c
superconductivity is effectively a two-dimensional phenomenon; it can occur in a cuprate slab which is only one unit cell thick. Finally, estimates are obtained for the length scales of localization of charge carriers:d 8 Å andd
2 Å in all the cuprates under study. 相似文献