全文获取类型
收费全文 | 1508篇 |
免费 | 36篇 |
国内免费 | 22篇 |
专业分类
电工技术 | 35篇 |
综合类 | 49篇 |
化学工业 | 298篇 |
金属工艺 | 253篇 |
机械仪表 | 179篇 |
建筑科学 | 91篇 |
矿业工程 | 21篇 |
能源动力 | 81篇 |
轻工业 | 17篇 |
水利工程 | 6篇 |
石油天然气 | 41篇 |
武器工业 | 6篇 |
无线电 | 65篇 |
一般工业技术 | 289篇 |
冶金工业 | 80篇 |
原子能技术 | 31篇 |
自动化技术 | 24篇 |
出版年
2023年 | 9篇 |
2022年 | 14篇 |
2021年 | 16篇 |
2020年 | 17篇 |
2019年 | 13篇 |
2018年 | 15篇 |
2017年 | 21篇 |
2016年 | 11篇 |
2015年 | 39篇 |
2014年 | 81篇 |
2013年 | 63篇 |
2012年 | 52篇 |
2011年 | 89篇 |
2010年 | 68篇 |
2009年 | 83篇 |
2008年 | 67篇 |
2007年 | 111篇 |
2006年 | 104篇 |
2005年 | 86篇 |
2004年 | 79篇 |
2003年 | 100篇 |
2002年 | 61篇 |
2001年 | 62篇 |
2000年 | 52篇 |
1999年 | 65篇 |
1998年 | 38篇 |
1997年 | 31篇 |
1996年 | 24篇 |
1995年 | 31篇 |
1994年 | 25篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 9篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有1566条查询结果,搜索用时 15 毫秒
1.
The heat transfer and flow characteristics of MWCNT-R141b nanorefrigerant with different mass fractions have been studied through experiments. Experimental results were compared with existing correlations. A two-step method was used to prepare the nanorefrigerants. Span-80 was used as surfactant with an average particle diameter of 20 nm. Transmittance method was used to evaluate the stability of nanorefrigerants. Results showed that the stability of MWCNT-R141b nanorefrigerant, which is the added dispersant, was good during the experiments. The 0.3 wt% MWCNT-R141b nanorefrigerants had optimal heat transfer enhancement effects compared with pure refrigerants. The maximum Nusselt number increased by 40%. The specific pressure drop of nanorefrigerant increased as the Reynolds number (Re) increased, and the specific pressure drop of the pure refrigerant was minimum, which is similar to R141b. 相似文献
2.
Bulge is a defect that causes geometrical inaccuracy and premature failure in the innovative incremental sheet forming (ISF) process. This study has two-fold objectives: (1) knowing the bulging behavior of a Cu clad tri-layered steel sheet as a function of forming conditions, and (2) analyzing the bending effect on bulging in an attempt to identify the associated mechanism. A series of ISF tests and bending analysis are performed to realize these objectives. From the cause-effect analysis, it is found that bulge formation in the layered sheet is sensitive to forming conditions in a way that bulging can be minimized utilizing annealed material and performing ISF with larger tool diameter and step size. The bending under tension analysis reveals that the formation of bulge is an outgrowth of bending moment that the forming tool applies on the sheet during ISF. Furthermore, the magnitude of bending moment depending upon the forming conditions varies from 0.046 to 10.24 N·m/m and causes a corresponding change in the mean bulge height from 0.07 to 0.91 mm. The bending moment governs bulging in layered sheet through a linear law. These findings lead to a conclusion that the bulge defect can be overcome by controlling the bending moment and the formula proposed can be helpful in this regards. 相似文献
3.
Hiroshi Takamatsu Hikaru Yamashiro Nobuo Takata Hiroshi Honda 《International Journal of Refrigeration》2003,26(6):79
Heat and mass transfer in a falling film vertical in-tube absorber was studied experimentally with LiBr aqueous solution. The presented results include the effect of solution flow rate, solution subcooling and cooling water temperature on the absorption in a smooth copper tube 16.05 mm I.D. and 400 mm long. The experimental data in the previous report for a 1200-mm-long tube was also re-examined and compared. It was demonstrated by the observation of the flow in the tube that the break down of the liquid film into rivulets leads to deterioration of heat and mass transfer at lower film Reynolds number or in longer tubes. An attempt to evaluate physically acceptable heat and mass transfer coefficients that are defined with estimated temperature and concentration at the vapor–liquid interface was also presented. 相似文献
4.
This paper presents a comparative study of the condensation heat transfer coefficients in a smooth tube when operating with pure refrigerant R134a and its mixture with lubricant Castrol “icematic sw”. The lubricant is synthetic polyol ester based oil commonly used in lubricating the compressors. Two concentrations of R134a-oil mixtures of 2% and 5% oil (by mass) were analysed for a range of saturation temperatures of refrigerant R134a between 35 °C and 45 °C. The mass flow rate of the refrigerant and the mixtures was carefully maintained at 1 g/s, with a vapour quality varying between 1.0 and 0. The effects of vapour quality, flow rate, saturation temperature and temperature difference between saturation and tube wall on the heat transfer coefficient are investigated by analysing the experimental data. The experimental results were then compared with predictions from earlier models [Int J Heat Mass Transfer (1979), 185; 6th Int Heat Transfer Congress 3 (1974) 309; Int J Refrig 18 (1995) 524; Trans ASME 120 (1998) 193]. Finally two new empirical models were developed to predict the two-phase condensation heat transfer coefficient for pure refrigerant R134a and a mixture of refrigerant R134a with Castrol “icematic sw”. 相似文献
5.
本文针对一往复式氢气压缩机管道振动十分强烈的情况,分析了管系的结构自振频率、气柱固有频率和气流脉动,采取了改变管系结构频率和气柱固有频率的减振措施,经实践证明获得了较为理想的减振效果。 相似文献
6.
论述了φ114mm无缝钢管车间采用改进型狄塞尔轧管机的车间设计,这是继烟台鲁宝钢管厂和成都无缝钢管厂φ177mm车间之后重庆院设计的这种类型的无缝钢管厂。 相似文献
7.
选用水面舰艇用945钢和潜艇用921A钢,研究了不同焊缝外形尺寸对爆炸试验中三缺口试样的中央缺口开裂行为的影响。通过大量的试验数据,确定了开裂判据e≤e_m,为试验前预示中央缺口开裂与否提供了可靠的依据。 相似文献
8.
9.
10.
本文介绍了一种用于成品钢管生产线上的悬臂式钢管喷印装置,它是一台结构和功能都较复杂的大型机电一体化设备。文中简介了它的性能、特点和工作原理,对其各部分机械装置的构成及动作以及喷印控制系统的组成和功能进行了较为深入的描述。 相似文献