全文获取类型
收费全文 | 16969篇 |
免费 | 1234篇 |
国内免费 | 551篇 |
专业分类
电工技术 | 216篇 |
综合类 | 1110篇 |
化学工业 | 2053篇 |
金属工艺 | 4386篇 |
机械仪表 | 4452篇 |
建筑科学 | 220篇 |
矿业工程 | 513篇 |
能源动力 | 292篇 |
轻工业 | 458篇 |
水利工程 | 82篇 |
石油天然气 | 549篇 |
武器工业 | 173篇 |
无线电 | 420篇 |
一般工业技术 | 2284篇 |
冶金工业 | 1044篇 |
原子能技术 | 40篇 |
自动化技术 | 462篇 |
出版年
2024年 | 148篇 |
2023年 | 461篇 |
2022年 | 529篇 |
2021年 | 611篇 |
2020年 | 604篇 |
2019年 | 534篇 |
2018年 | 558篇 |
2017年 | 695篇 |
2016年 | 680篇 |
2015年 | 600篇 |
2014年 | 715篇 |
2013年 | 799篇 |
2012年 | 830篇 |
2011年 | 945篇 |
2010年 | 746篇 |
2009年 | 824篇 |
2008年 | 690篇 |
2007年 | 1039篇 |
2006年 | 1066篇 |
2005年 | 791篇 |
2004年 | 776篇 |
2003年 | 613篇 |
2002年 | 538篇 |
2001年 | 480篇 |
2000年 | 375篇 |
1999年 | 302篇 |
1998年 | 293篇 |
1997年 | 278篇 |
1996年 | 247篇 |
1995年 | 219篇 |
1994年 | 155篇 |
1993年 | 93篇 |
1992年 | 97篇 |
1991年 | 81篇 |
1990年 | 60篇 |
1989年 | 62篇 |
1988年 | 50篇 |
1987年 | 35篇 |
1986年 | 23篇 |
1985年 | 17篇 |
1984年 | 26篇 |
1983年 | 16篇 |
1982年 | 24篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1975年 | 2篇 |
1965年 | 2篇 |
1964年 | 3篇 |
1955年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
61.
62.
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
63.
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
64.
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
65.
66.
The attack of nickel, cobalt, iron, and alloys of these metals containing chromium and aluminum, by gases containing sulfur-oxygen,
carbon-oxygen, and nitrogen-oxygen has been studied at temperatures of 600 and 900°C. The degradation of these metals and
alloys was characterized by using standard analytical techniques with emphasis on optical metallography. Three types of accelerated
degradation were identified for the attack of alloys by gases containing another oxidant in addition to oxygen. One type of
degradation occurred because of the formation of reaction products composed of mixtures of phases involving both of the oxidants.
Another type resulted from the reaction of second oxidant phases with oxygen. The third form of degradation involved the development
of less protective phases due to thermodynamic instabilities. Thermodynamic stability diagrams are used to help account for
the effects produced by different elements in the alloys. 相似文献
67.
Solid lubricants lead to substantial weight savings relative to the use of liquid lubricant, especially in the weight-conscious aerospace industry. A new PTFE-Al alloy composite(A) containing 60% area proportion of PTFE composite was developed. Another type of common metal-plastics multilayer composite, also called DU, was selected for a comparative investigation. Friction and wear tests were carried out in an oscillating sliding tribotester in air at an oscillating frequency of 0.13 Hz and contact mean pressures from 10 to 80 MPa. The composites slid against a 38CrMoAlA steel shaft. The results show that the composite A exhibits low coefficient of dry sliding friction less than 0.1 and long wear life of 2 000 m. This is because the composite A can provide a sufficient solid lubrication during the whole tests. SEM examination of the transfer films for the composite A confirms that uniform, thin and coherent transfer films are prerequisites for low friction and good wear resistance. 相似文献
68.
EPS模陶瓷型精密铸造失模工艺研究 总被引:1,自引:0,他引:1
针对EPS陶瓷壳型精铸失模时容易裂壳的现象,对EPS消失模精密铸造工艺进行了研究。利用自制的膨胀率检测设备对不同密度的EPS模试样在不同加热温度下的最大膨胀率进行了测试,研究了壳型膨胀与失模温度之间的关系;对陶瓷壳型中EPS模失模时的温度场分布进行测量,发现EPS模试样的密度大小对失模时温度场有着很重要的影响。在试验和分析的基础上,对EPS模失模机制进行了探讨,提出了高温失模机制。高温失模有利于降低失模时对壳型的膨胀作用力,为获得洁净而健全的陶瓷型壳提供了可靠保证。 相似文献
69.
通过GCr15钢碳氮共渗,在表层获得大量的残余奥氏体。磨损中,马氏体组织剥落,残余奥氏体则成小岛状,进而在表面迁移发生形变诱发马氏体相变,使耐磨性得以提高。同时,共渗在空心滚子内表面造成的压应力对改善弯曲疲劳性能有利。 相似文献
70.