全文获取类型
收费全文 | 14311篇 |
免费 | 1027篇 |
国内免费 | 472篇 |
专业分类
电工技术 | 162篇 |
综合类 | 1001篇 |
化学工业 | 1227篇 |
金属工艺 | 4150篇 |
机械仪表 | 4045篇 |
建筑科学 | 298篇 |
矿业工程 | 500篇 |
能源动力 | 179篇 |
轻工业 | 277篇 |
水利工程 | 140篇 |
石油天然气 | 459篇 |
武器工业 | 164篇 |
无线电 | 259篇 |
一般工业技术 | 1805篇 |
冶金工业 | 778篇 |
原子能技术 | 31篇 |
自动化技术 | 335篇 |
出版年
2024年 | 112篇 |
2023年 | 321篇 |
2022年 | 413篇 |
2021年 | 467篇 |
2020年 | 499篇 |
2019年 | 433篇 |
2018年 | 479篇 |
2017年 | 622篇 |
2016年 | 568篇 |
2015年 | 505篇 |
2014年 | 597篇 |
2013年 | 625篇 |
2012年 | 742篇 |
2011年 | 807篇 |
2010年 | 641篇 |
2009年 | 725篇 |
2008年 | 616篇 |
2007年 | 908篇 |
2006年 | 946篇 |
2005年 | 692篇 |
2004年 | 666篇 |
2003年 | 521篇 |
2002年 | 457篇 |
2001年 | 398篇 |
2000年 | 327篇 |
1999年 | 271篇 |
1998年 | 242篇 |
1997年 | 263篇 |
1996年 | 212篇 |
1995年 | 186篇 |
1994年 | 120篇 |
1993年 | 79篇 |
1992年 | 79篇 |
1991年 | 55篇 |
1990年 | 47篇 |
1989年 | 45篇 |
1988年 | 40篇 |
1987年 | 24篇 |
1986年 | 6篇 |
1985年 | 15篇 |
1984年 | 14篇 |
1983年 | 8篇 |
1982年 | 13篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1963年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
By use of X-ray diffractometry and scanning electron microscope(SEM),the friction and wear results obtained from MM-1000 dynamometer tests of CVI pitch/resin C/C composites were analyzed.By investigating the factors that affected the friction and wear properties,such as matrix carbon,applcation environment,graphitization degree and brake pressure,etc,friction and wear mechanism of carbon materials were probed.The results indicate that pitch densified CVI initially treated composite is more graphitizable with its graphitization degree up 59 62%,and which results in uniform small debris easier to generate,more smooth friction curves with the coefficient of 0.3-0.4 and relatively higher wear and mass loss,compared with CVI/resin C/C composites.It was further proved by SEM observation that tribological behavior of C/C composite was system dependent.Factors determining the friction and wear properties such as the size of debris and its influence on friction and wear,brake pressure,graphization degree and debris bilm formation interacted and affected each other.The friction and wear mechanism of C/C composites under different high temperature treatments needs further research. 相似文献
82.
It is well known that the mechanical properties such as strength and hardness of structural steel are usually enhanced by the martensite-phase transformation method. In many industrial applications, hardness has always been used as an index to reflect the wear-resistance performance. As a result, steel is quenched to a large extent in order to increase the hardness and wear-resistance performance. In general, from the wear mechanism, no exact relationship between the hardness and wear resistance of materials can be formulated. Also there are few conclusive studies on the effects of running procedures on wear-resistance performance. Therefore, the friction behavior of S45C carbon steel with and without a quenching process was evaluated by a rotating tribometer under various test conditions. The experimental results show that the running conditions cause a great influence on the wear-resistance performance of the materials. Under low speed and light apparent pressure conditions, the quenched specimens have high wear-resistance performance. Contrarily, at high speed and heavy loading, the wear-resistance performance of hardened specimens decreases due to tempering effects at the rubbing surface when the contact temperature becomes increased. Therefore, this causes more severe wear to the hardened specimens than to the unhardened specimens. 相似文献
83.
High-speed milling of titanium alloys using binderless CBN tools 总被引:4,自引:0,他引:4
Z. G. Wang Y. S. Wong M. Rahman 《International Journal of Machine Tools and Manufacture》2005,45(1):105-114
The performance of conventional tools is poor when used to machine titanium alloys. In this paper, a new tool material, which is binderless cubic boron nitride (BCBN), is used for high-speed milling of a widely used titanium alloy Ti–6Al–4V. The performance and the wear mechanism of the BCBN tool have been investigated when slot milling the titanium alloy in terms of cutting forces, tool life and wear mechanism. This type of tool manifests longer tool life at high cutting speeds. Observations based on the SEM and EDX suggest that adhesion of workpiece and attrition are the main wear mechanisms of the BCBN tool when used in high-speed milling of Ti–6Al–4V. 相似文献
84.
Cr3Si/Crl3Ni5Si2金属间化合物合金组织与高温滑动磨损性能的研究 总被引:2,自引:0,他引:2
利用水冷铜模激光熔炼炉制得了由初生枝晶Cr3Si和枝晶间Cr3Si/Crl3Ni5Si2共晶组成的金属间化合物合金。利用OM,SEM,TEM,EDS和XRD分析了该金属间化合物的显微组织,在400℃,500℃和600℃条件下测试了其耐磨性能。结果表明,由于Cr3Si和Crl3NisSi2硬度高、原子键合力强、组织细小、均匀,在高温滑动磨损条件下具有优良的耐磨性能。 相似文献
85.
86.
87.
Characterization and wear behavior of modified silicon nitride 总被引:3,自引:0,他引:3
E. Carrasquero A. Bellosi M.H. Staia 《International Journal of Refractory Metals and Hard Materials》2005,23(4-6):391-397
Silicon nitride-based materials are applied to many tribological components because of their superior thermal and mechanical properties and corrosion resistance. The purpose of this study is to investigate the wear performance of modified silicon nitride which contained 3 wt.% La2O3 and 3 wt.% Y2O3. The relationships between microstructure and mechanical properties have been also addressed. Vickers microhardness and toughness were measured, the later being determined by means of the direct crack measurement method (DCM). Scanning electron microscopy technique (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) was used for the morphological characterization of the samples as well as for the characterization of the wear scars. Wear properties were studied under a load of 10 N by using the ball-on-disk tribometer. AISI 52100 steel balls and balls of WC + 6% Co (6 mm diameter) were used as static counterparts, respectively. Steady state friction coefficients of 0.66 and 0.62 were measured for the tribological pairs WC + 6 % Co/Si3N4 and AISI 52100/Si3N4, respectively. The wear mechanism was determined in each case, and comparison between the wear performance of the traditional and modified silicon nitride is also presented. 相似文献
88.
THERMAL SPRAYING provides a large range ofcoatings,which increase the wear resistance ofsubstrates[1].One of the major coating families is thecermet,composed of hard ceramic particles with ametallic binder.The most commonly used cermetcoatings in industrial applications are based on eitherthe WC-Co or the Cr3C2-Ni(Cr)systems with WC-17wt%Co and Cr3C2-25wt%Ni(Cr)being typicalcompositions[2,3].Although WC-Co deposits are hardand wear resistant at ambient temperatures their rangeof ap… 相似文献
89.
The ceramic coating formed on AZ91 magnesium alloy by micro-arc oxidation (MAO) was characterized. The results show that the ceramic coating (3.4-23 μm in thickness)on the surface ofAZ91 alloy was attained under different micro-arc oxidation treatment conditions, which consist mainly of MgO, Mg2SiO4 and MgSiO3 phases. Nano-hardness in a cross-sectional specimen was determined by nano-indentation experiment. The MAO coatings exhibit higher hardness than the substrate. Dry sliding wear tests for the MAO coatings and AZ91 alloy were also carded out using an oscillating friction and wear tester in a ball-on-disc contact configuration. The wear resistance of the MAO coatings is improved respectively under different treatment time as a result of different structures of ceramic coatings formed on AZ91 alloy. 相似文献
90.