全文获取类型
收费全文 | 1306篇 |
免费 | 209篇 |
国内免费 | 119篇 |
专业分类
电工技术 | 133篇 |
综合类 | 132篇 |
化学工业 | 270篇 |
金属工艺 | 306篇 |
机械仪表 | 86篇 |
建筑科学 | 12篇 |
矿业工程 | 29篇 |
能源动力 | 74篇 |
轻工业 | 6篇 |
水利工程 | 1篇 |
石油天然气 | 11篇 |
武器工业 | 25篇 |
无线电 | 60篇 |
一般工业技术 | 210篇 |
冶金工业 | 214篇 |
原子能技术 | 33篇 |
自动化技术 | 32篇 |
出版年
2024年 | 4篇 |
2023年 | 56篇 |
2022年 | 54篇 |
2021年 | 69篇 |
2020年 | 66篇 |
2019年 | 73篇 |
2018年 | 67篇 |
2017年 | 73篇 |
2016年 | 49篇 |
2015年 | 41篇 |
2014年 | 76篇 |
2013年 | 84篇 |
2012年 | 84篇 |
2011年 | 110篇 |
2010年 | 66篇 |
2009年 | 77篇 |
2008年 | 57篇 |
2007年 | 84篇 |
2006年 | 82篇 |
2005年 | 71篇 |
2004年 | 61篇 |
2003年 | 61篇 |
2002年 | 35篇 |
2001年 | 34篇 |
2000年 | 19篇 |
1999年 | 19篇 |
1998年 | 15篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有1634条查询结果,搜索用时 15 毫秒
1.
This study deals with the anodisation of titanium grade 2 in 0.5-M sulphuric acid using a pulsed signal in a unipolar regime. The electrical parameters investigated are voltage, frequency and duty cycle. The use of duty cycles with a high percentage of anodic polarisation (90%), combined with high frequencies (1000 Hz) and the higher voltage tested (220 V), favoured the establishment of a plasma regime involving strong dielectric discharges, allowing the growth of thicker oxides but with rough architecture. The corrosion resistance of the formed film has been characterised by potentiodynamic tests in 0.5-M NaBr for localised corrosion resistance and by immersion tests in 10% v/v sulphuric acid solution for a uniform corrosion assessment. Current–time curves, visual observations and electron microscope analysis (scanning electron microscopy, energy-dispersive X-ray spectroscopy) were the tools selected to provide a correlation between technological parameters and oxide growth mechanism. For localised and uniform corrosion, anodisation at 220 V with a high level of anodic polarisation (90%) and frequency (1000 Hz) was verified to be particularly advantageous. 相似文献
2.
Hajime Tomita 《Electrical Engineering in Japan》2015,190(3):1-8
In this investigation, the nature of the electrostatic discharge (ESD) that occurs when a charged object moves toward a stationary grounded object is experimentally clarified. The spark lengths, discharge currents, and induced voltages in a magnetic probe were measured when a charged metallic spherical electrode connected to a 422 pF capacitor approached a stationary grounded object, which was the current target, for different moving speeds of the charged metallic spherical electrode in a range of 1 mm/s to 100 mm/s. The charge voltages of the capacitor were +6.5 kV and +10 kV. Based on the results, the average gap length shortened with the speed of the spherical electrode. The average peak values of the discharge current and the induced voltage were likely to increase with the speed of the spherical electrode. The average rise times of the discharge current and the induced voltage were likely to drop with the speed of the spherical electrode. The relation between the spark length and the discharge current due to the ESD can be explained qualitatively by using an equation derived from the spark resistance formula proposed by Rompe and Weizel. 相似文献
3.
Atilla Bilgin 《国际能源研究杂志》2002,26(11):987-1000
Flame front surface area and enflamed volume (the volume enclosed with flame front) is theoretically analysed for a spark‐ignition engine, having cylindrical disc‐shaped combustion chamber with two spark plugs located axisymmetrically on cylinder head, between cylinder axis and cylinder wall. Spherical flame front assumption is used. A computer code is developed based on purely geometric consideration of the flame development process in combustion chamber, and is used to investigate the effects of variations of spark plugs' locations on geometric features of the flame front. A comparison has also been made with a spark‐ignition engine having one spark plug at the same location. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
4.
本文对发电机同轴励磁机电刷火花过大的原因进行了分析.并针对这些原因提出了相应的处理办法。对规范励磁机的运行维护有很大的帮助。 相似文献
5.
本文着重探讨直流电动机换向火花的形成、征状以及使用的一些对其进行判别、调整的简单方法,并阐述其原理及效果。 相似文献
6.
Zewen Chen Zhenhua Wang Boxiang Wang Juntang Yuan Lei Huang Zengbin Yin 《International Journal of Applied Ceramic Technology》2021,18(6):2010-2019
In this study, WC-8Co cemented carbides were prepared by spark plasma sintering. When the samples sintered at 1300℃ were cooled to room temperature, the samples were sintered multiple times at 1250℃. The changes in microstructure and mechanical properties of WC-8Co cemented carbides prepared by multiple spark plasma sintering were studied. The hardness of cemented carbides increased in the first two sintering, reaching 16.5 GPa. However, the hardness decreased seriously in the last two sintering. The attenuation rates of hardness were 6.2% and 2.5% due to the abnormal coarse grains. Furthermore, the crack path along the grain boundary was almost straight, causing a decrease in the indentation fracture toughness of cemented carbides. Additionally, the grains of cemented carbides were abnormally coarsened, and the morphologies of grains became unstable due to multiple sintering. 相似文献
7.
Ti3SiC2 materials have been fabricated by spark plasma sintering of the elemental powders with the addition of Al.At the heating rate of 80℃/min and under the pressure of 30MPa,the ideal synthesis temperature of Ti3SiC2 is in the range of 1150-1250℃.The addition of Al is in favor of the formation of Ti3SiC2.The synthesized compound has the molecular of Ti3Si0.8Al0.2C2 and lattice parameters of α=0.3069nm,c=1.7670nm.Its grain is plane-shape with a size of about 50μm in the elongated dimension.The prepared material has Vickers hardness of 3.5-5.5GPa(at 1N and 15s) and is as readily machinable as graphite‘s. 相似文献
8.
Electric and mechanical performances of Bi0.5Sb1.5Te3 prepared by spark plasma sintering 总被引:1,自引:0,他引:1
Thermoelectric (TE) materials are a kind of functional materials which can be used to convert directly heat energy to electricity or reversely.The thermoelectric effects hold great potential for application in power generation and refrigeration.Bi2Te3 and its alloys are well known as best TE materials currently available near room temperature.This paper studies respectively the effects of spark plasma sintering (SPS) on electric performance of Bi0.5Sb1.5Te3 thermoelectric materials that are prepared through vacuum melting and ball milling.Through X-ray Diffraction and cold field emission scanning electric microscope s4800, the phase constituent and microstructure of the TE materials samples were analyzed.Electric conductivity and power factor can be improved with the rise of Spark Plasma Sintering temperature (from 300 to 500 ℃) and pressure(from 30 to 60 MPa), and the density and mechanical strength of Bi0.5Sb1.5Te3 thermoelectric material increase, too. 相似文献
9.
用普通反应热压方法(RHP)和反应放电等离子体方法(R-SPS)原位反应制备了ZrB2-SiC,ZrB2-SiC—ZrC,ZrB2-SiC-ZrN,以及ZrB2-SiC-AIN4种复合材料。从密度,物相以及显微结构等方面比较了两种烧结方式之间的差别,对于升温速度较慢的普通热压方法,反应分步进行,显微结构不均匀;对于升温速度快的放电等离子体烧结,原料间的自蔓延反应被点着,反应速度快,显微结构均匀。同时以红外灯的热量为点火源,引发了Zr,Si及B4C间在空气气氛下的自蔓延反应,制备了较纯及粒径约为1μm的活性粉体。 相似文献
10.