全文获取类型
收费全文 | 449篇 |
免费 | 18篇 |
国内免费 | 6篇 |
学科分类
工业技术 | 473篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 6篇 |
2020年 | 11篇 |
2019年 | 9篇 |
2018年 | 5篇 |
2017年 | 10篇 |
2016年 | 7篇 |
2015年 | 11篇 |
2014年 | 26篇 |
2013年 | 26篇 |
2012年 | 26篇 |
2011年 | 48篇 |
2010年 | 32篇 |
2009年 | 32篇 |
2008年 | 23篇 |
2007年 | 24篇 |
2006年 | 24篇 |
2005年 | 25篇 |
2004年 | 20篇 |
2003年 | 25篇 |
2002年 | 8篇 |
2001年 | 5篇 |
1999年 | 8篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 2篇 |
排序方式: 共有473条查询结果,搜索用时 31 毫秒
71.
The vapor-liquid-solid (V-L-S) flow boiling evaporator has the features of fouling preventing and heat-transfer enhancing. However, the mechanisms of flow and heat-transfer are still not well understood due to the system complex and the limitation of the measuring methods due to the characteristic of opaque of the system in practice. In this paper, a charge coupled device (CCD) measuring system is developed to investigate the hydrodynamic characteristics including the axial profiles of solid holdup and of solid velocity in a V-L-S three-phase natural circulating flow boiling system. The CCD measuring technique makes the three-phase qualitative observation and quantitative research possible. The heat-transfer characteristic of this system is also studied. The main results are as follows. The distributions of solid holdup and velocity are not uniform along the axial direction of the heating tube and both in liquid-solid two-phase region and in V-L-S three-phase region; however, the particle velocity in V-L-S three-phase region is much higher than that in liquid-solid two-phase region in heating tube. When increasing the heat flux, the solid holdup first increases and then decreases and the solid velocity gradually increases in heating tube. But in circulating tube, both the solid holdup and the solid velocity gradually increase. With the increase of the volume of added solid particles, the measured local solid holdup increases in both tubes; however, the variation of the solid velocity with the increase of the solid particles shows a characteristic of the wave and the general tendency is climbing for both tubes. The solid particles holdup in heating tube is always larger than that in circulating tube and the solid velocity in heating tube is lower than that in circulating tube. The presence of solid particles enhances the boiling evaporation process. The heat-transfer coefficient of the system increases with the increase of the heat flux and the volume of added solid particles. These research results provide some valuable references for the academic interest and for the industry application of this fouling preventing and heat-transfer enhancing installation. 相似文献
72.
Chandrashekar P. Kelkar Jale F. Akyurtlu Ates Akyurtlu Charles E. Hamrin Jr. 《Chemical Engineering Communications》1992,117(1):101-109
A novel annular catalytic three-phase reactor is theoretically investigated for a second order hydrogenation reaction. The results indicate that the ratio of the gaseous reactant to the liquid reactant within the reaction zone of the annular reactor can be adjusted by changing the reactor dimensions and the concentration of the gaseous reactant in the feed. As a consequence, the annular reactor may have a significant advantage over the trickle-bed reactor with respect to the selectivities that may be achieved in the reactor. 相似文献
73.
The effect of a solid presence on global hydrodynamic parameters and heat transfer in an external loop airlift reactor has been experimentally investigated. Results obtained in both two- and three-phase flow are presented in this study. Two different external loop airlift reactor sizes have been used and local hydrodynamic characteristics including local gas hold-up and bubble velocity have been obtained in two-phase flow. Optical and ultrasound probes have been used to obtain this information, respectively. It was found that an increase of solid hold-up leads to a decrease of liquid velocity and heat transfer coefficient. Measured in a two- and three-phase reactor using a horizontal-heating probe, a correlation of the average gas hold-up and heat transfer coefficient is proposed. Correlation parameters are identified in homogeneous and heterogeneous flow regimes, which have been derived from the gas slip velocity concept. The experimental liquid velocity and gas hold-up in the riser have been represented in a satisfactory way by a hydrodynamic model, either in the absence or in the presence of solid particles. 相似文献
74.
本文介绍了三相磁控电抗器的发展历史和研究现状,分析了不同种类的三相磁控电抗器的工作原理和电磁特性,结合其优缺点对未来的研究做出展望. 相似文献
75.
77.
This paper proposes an important improvement of the hysteresis band current control (HBCC) technique for three-phase shunt active power filter (APF) to eliminate harmonics and to compensate the reactive power generated by three-phase rectifier. In this technique, a simple and quick prediction of the hysteresis band is added to a phase-locked-loop (PLL) control to ensure constant switching frequency and synchronization of modulation pulses independently on system parameters. This allows the advantages of quick response, good current tracking accuracy and minimal ripple in three-phase systems. This technique is robust and it is characterized by the simplicity, this aspect is very significant for a practice realization because it constitutes the factors which determine the cost and the reliability of industrial assembly. The proposed technique determines the switching signals of the three-phase shunt APF and the algorithm which is based on the dc bus capacitors voltage regulation using proportional-integral (PI) controller is used to determine the suitable current reference signals. The behavior of the proposed technique has been fully verified by digital simulation, where the obtained results show that the proposed technique can improve shunt APF performances noticeably. 相似文献
78.
三相异步电动机的振动、噪声一直是电机设计中重点关注的问题之一,其中铸铝转子利用斜槽来削弱齿谐波对电磁转矩和电流的影响是较常用的方法,但斜槽度的确定以往大多数都是依靠经验和制作样机来完成的。使用Ansoft Maxwell等电磁场有限元分析软件的瞬态分析功能,计算出电机的电磁转矩和绕组电流波形而得出谐波频率,就能计算出所需的转子斜槽度。 相似文献
79.
高压高速三相异步电动机在试验时,有少许电机振动值超标,有些电机振动值还比较大,严重影响电机的质量,通过一系列的拆检分析电机振动的原因并提出处理意见。 相似文献
80.