全文获取类型
收费全文 | 1909篇 |
免费 | 174篇 |
国内免费 | 28篇 |
专业分类
电工技术 | 16篇 |
综合类 | 51篇 |
化学工业 | 1441篇 |
金属工艺 | 34篇 |
机械仪表 | 48篇 |
建筑科学 | 21篇 |
矿业工程 | 7篇 |
能源动力 | 8篇 |
轻工业 | 57篇 |
石油天然气 | 25篇 |
武器工业 | 21篇 |
无线电 | 38篇 |
一般工业技术 | 316篇 |
冶金工业 | 17篇 |
原子能技术 | 2篇 |
自动化技术 | 9篇 |
出版年
2024年 | 22篇 |
2023年 | 29篇 |
2022年 | 45篇 |
2021年 | 53篇 |
2020年 | 55篇 |
2019年 | 62篇 |
2018年 | 47篇 |
2017年 | 66篇 |
2016年 | 67篇 |
2015年 | 57篇 |
2014年 | 62篇 |
2013年 | 113篇 |
2012年 | 89篇 |
2011年 | 115篇 |
2010年 | 75篇 |
2009年 | 53篇 |
2008年 | 81篇 |
2007年 | 88篇 |
2006年 | 120篇 |
2005年 | 109篇 |
2004年 | 90篇 |
2003年 | 98篇 |
2002年 | 71篇 |
2001年 | 61篇 |
2000年 | 72篇 |
1999年 | 64篇 |
1998年 | 50篇 |
1997年 | 42篇 |
1996年 | 25篇 |
1995年 | 18篇 |
1994年 | 22篇 |
1993年 | 17篇 |
1992年 | 16篇 |
1991年 | 15篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有2111条查询结果,搜索用时 10 毫秒
1.
ABSTRACT The thermoplastic and low dielectric constants polyimides were introduced. The polyimides were prepared by pyromellitic dianhydride (PMDA) or 4,4?-(4,4?-Isopropylidenediphenoxy)diphthalic anhydride (BPADA) as anhydride monomer and 4,4?-oxydianiline (ODA) or 2,2-bis(4-(4-aminephenoxy)phenyl)propane (BAPP) as amine monomer. The polyimides were well characterized by FT-IR, thermogravimetric analysis, dynamic thermomechanical analysis, dielectric measurement, and tensile test. The dielectric constants were 2.32–2.95 compared with 3.10 of ODA-PMDA polyimide, while partly polyimides were thermoplastic. The results indicated anhydride monomers, containing lateral methyl groups, made polyimides become thermoplastic. The results of molecular simulations via Materials Studio also proved this conclusion. 相似文献
2.
3.
A series of novel thermoplastic elastomers, based on poly(dimethylsiloxane) (PDMS) as the soft segment and poly(butylene terephthalate) (PBT) as the hard segment, were synthesized by catalyzed two‐step, melt transesterification reactions of dimethyl terephthalate and methyl esters of carboxypropyl‐terminated poly(dimethylsiloxane)s (M?n = 550–2170 g mol?1) with 1,4‐butanediol. The lengths of both the hard and soft segments were varied while the weight ratio of the hard to soft segments in the reaction mixture was maintained constant (57/43). The molecular structure, composition and molecular weights of the poly(ester–siloxane)s were examined by 1H NMR spectroscopy. The effectiveness of the incorporation of the methyl‐ester‐terminated poly(dimethylsiloxane)s into the copolymer chains was verified by chloroform extraction. The effect of the segment length on the transition temperatures (Tm and Tg) and the thermal and thermo‐oxidative degradation stability, as well as the degree of crystallinity and hardness properties of the synthesized TPESs, were studied. Copyright © 2003 Society of Chemical Industry 相似文献
4.
利用废旧塑料生产阻燃建筑装饰材料探讨 总被引:4,自引:0,他引:4
本文介绍了一种综合利用废旧热塑性塑料和锯末粉通过加入阻燃剂改性 ,生产防火阻燃型建筑装饰材料的方法。所生产的产品 ,其阻燃性能均达到国家标准 (GB5464 - 85)中规定的不燃性材料的要求。 相似文献
5.
NBR/PP热塑性弹性体研究进展 总被引:12,自引:0,他引:12
阐述了NBR/PP共混热塑性弹性体动态硫化胶的国内外研究进展、微观相态结构、性能、应用及展望。 相似文献
6.
This paper evaluates the behavior and performance of laminated circular elastomeric bearings and compares them to those of square and rectangular bearings. The study included an experimental evaluation and a nationwide survey of state Department of Transportations on the use and performance of circular bearings and bearings in general in their states. The experimental investigation studied the bearings' behavior in compression, compression and rotation, and compression and shear. Results from this limited study showed that the three bearings have similar stress-strain behavior in compression and they are in agreement with the AASHTO LRFD guide stress–strain curves. In compression and rotation, the AASHTO LRFD substructure moments are slightly less than the measured values for circular bearings and rectangular bearings rotated about their strong axis for a compressive stress of 10.3?MPa (1.5?ksi) and slightly higher than those of rectangular bearings rotated about their weak axis. In compression and shear, the shear stiffness of circular and square bearings is in agreement with theoretical values within the range of design displacements. Results from the survey showed that many states are using circular bearings and more states would consider using them, however no maintenance or monitoring data were available on their short-term and long-term performance. 相似文献
7.
橡塑共混热塑性弹性体的形态结构与性能 总被引:2,自引:0,他引:2
综述了影响共混热塑性弹性体的形态结构与性能的主要因素。 相似文献
8.
9.
EPDM/PP热塑性弹性体相态研究 总被引:3,自引:1,他引:2
采用透射电镜(TEM)研究动态硫化EPDM/PP热塑性弹性体制备工艺及增容改性对形态结构的影响,研究发现通过添加增容剂可使EPDM相呈颗粒分布于连续相中。 相似文献
10.
Two thermoplastic and two thermosetting fibrereinforced plastic composites were subjected to dynamic tests over a wide range of temperature, covering both cryogenic and hot environments. The thermal behaviour of each composite, as indicated by its dynamic mechanical properties, was assessed individually, and was compared collectively with that of the other composites. 相似文献