首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1667篇
  免费   152篇
  国内免费   19篇
电工技术   73篇
综合类   39篇
化学工业   257篇
金属工艺   20篇
机械仪表   104篇
建筑科学   20篇
矿业工程   15篇
能源动力   980篇
轻工业   8篇
水利工程   1篇
石油天然气   11篇
武器工业   1篇
无线电   27篇
一般工业技术   206篇
冶金工业   10篇
原子能技术   10篇
自动化技术   56篇
  2024年   8篇
  2023年   46篇
  2022年   37篇
  2021年   69篇
  2020年   117篇
  2019年   90篇
  2018年   38篇
  2017年   48篇
  2016年   68篇
  2015年   55篇
  2014年   95篇
  2013年   133篇
  2012年   118篇
  2011年   91篇
  2010年   84篇
  2009年   97篇
  2008年   55篇
  2007年   91篇
  2006年   70篇
  2005年   54篇
  2004年   35篇
  2003年   34篇
  2002年   42篇
  2001年   30篇
  2000年   21篇
  1999年   24篇
  1998年   12篇
  1997年   9篇
  1996年   10篇
  1995年   7篇
  1994年   9篇
  1993年   6篇
  1992年   10篇
  1991年   7篇
  1990年   5篇
  1989年   7篇
  1988年   7篇
  1987年   24篇
  1986年   26篇
  1985年   10篇
  1984年   7篇
  1983年   2篇
  1981年   3篇
  1980年   2篇
  1978年   2篇
  1973年   3篇
  1972年   3篇
  1968年   5篇
  1967年   2篇
  1951年   4篇
排序方式: 共有1838条查询结果,搜索用时 11 毫秒
51.
喷嘴对涡流管能量分离效应影响   总被引:6,自引:2,他引:6       下载免费PDF全文
何曙  吴玉庭  姜曙  马重芳  葛满初 《化工学报》2005,56(11):2073-2076
涡流管,又称兰克-赫尔胥(Ranque-Hilsch)管.它是一种结构非常简单的能量分离装置,由一根两端开口的管子以及喷嘴、孔板和调节阀构成,工作时高压气体由进气管进入喷嘴,经喷嘴内膨胀加速后,以很高的速度沿切线方向进入涡流室,气流在涡流室内形成高速涡旋,由于热阀与冷端孔板之间的压力差,在涡流管内的中心区域形成回流气体,经过涡流变换后分离成总温不相等的两部分气流.其中,处于中心部位的回流气流温度较低,  相似文献   
52.
The influence of hydrothermal treatment of coal prior to carbonization, on the oxidation susceptibility of resultant coke/char, calcined at 1350, 1800 and 2200 °C has been investigated. The non-isothermal thermogravimetric analysis technique has been employed, and parameters such as onset, DTG peak temperatures, and cumulative oxidation loss (wt.%) at different temperatures have been utilized to compare proneness to oxidation with respective untreated samples apart from electrical resistivity. Data suggest that all the cokes/chars samples produced from hydrothermally treated coals are less reactive and more electrically conductive (less resistive) than their respective untreated counterparts. But the extent of improvement of oxidation resistance and electrical conductivity appears to be coal-specific. The kinetic parameters obtained by non-linear regression analysis on multi-curve reveal that the nth order reaction model (where ‘n’ was found to vary from 0.9 to 1.3) is the best-fitted model. The higher activation energy values observed for hydrothermally treated coke samples are in agreement with the observation of TG analysis data. Overall results indicate the importance of introducing a hydrothermal treatment step for the improvement of oxidation resistance as well as electrical conductivity of the coke samples.  相似文献   
53.
This paper presents the fluid flow and heat transfer characteristics of supercritical CO2 in a horizontal multi-port extruded aluminum test section consisting of 10 circular channels with an inner diameter of 1.31 mm. Both local and average pressure drop and heat transfer coefficients were measured as CO2 was cooled in the multi-port circular channels with pressures ranging from 7.4 to 8.5 MPa, inlet fluid temperatures ranging from 22 to , and mass velocity ranging from 113.7 to 418.6 kg/m2 s. The results indicate that the operating pressure, the mass velocity and the temperature of CO2 had significant effects on fluid flow and heat transfer characteristics. The pressure drop and the average heat transfer coefficient increased greatly with increasing the average temperatures of CO2 in the near-critical region; the average heat transfer coefficient attained a peak value near the corresponding pseudocritical temperature; and the maximum heat transfer coefficient decreased as the pressure increased. Both the pressure drop and the heat transfer coefficient increased with the mass velocity, but decreased with the operating pressure. The measured average heat transfer coefficients were compared with the experimental data reported in the literatures and a large discrepancy was observed. Based on the experimental data collected in the present work, a new correlation was developed for forced convection of supercritical CO2 in horizontal multi-port mini channels under cooling conditions.  相似文献   
54.
董宜放  于樱迎  胡学功  裴刚 《化工学报》2022,73(7):2952-2961
竖直微槽群毛细结构广泛应用在重力热管、蒸发器等散热设备内,但受重力等因素影响易达到毛细极限。引入电场的主动强化方式来提高竖直微槽的毛细极限,并通过实验和建立数学模型研究电场对竖直微槽内液体润湿及毛细流动特性的影响。结果表明,电场可以提高竖直微槽内液体润湿高度,当电场为5.0 kV时与无电场时相比,润湿高度强化比可达到30.0%。同时,电场作用下流体在微槽道内的毛细润湿流动呈分段效应:润湿流动初期,润湿高度与时间的1/2次方呈线性关系,即h-t1/2,润湿速率与润湿高度的倒数呈线性关系,即v-1/h;润湿流动中后期,润湿高度与时间的1/3次方呈线性关系,即h-t1/3,润湿速率与润湿高度平方的倒数呈线性关系,即v-1/h2,且润湿速率随时间呈下降趋势。  相似文献   
55.
Radiative cooling can achieve cooling effect without consuming any energy by delivering energy into outer space(3K) through"atmospheric window"(8–13 μm). Conventional radiative cooling coating with multi-layer structure was severely restricted during application due to its complex preparation process and high cost. In this study, a single-layer radiative cooling coating with mixture of TiO_2 particles and SiO_2 particles was proposed. The algorithm for calculating the radiative properties of the multi-particle system was developed. Monte Carlo ray-tracing method combined with that algorithm was used to solve the radiative transfer equation(RTE) of the single-layer radiative cooling coating with mixture of TiO_2 particles and SiO_2 particles.The effects of particle diameter, volume fraction and coating thickness on radiative cooling performance were analyzed to obtain the best radiative cooling performance. The numerical results indicated that the average reflectivity of the single-layer radiative cooling coating with mixture of TiO_2 particles and SiO_2 particles in the solar spectrum can reach 95.6%, while and the average emissivity in the "atmospheric window" spectrum can reach 94.9% without additional silver-reflectance layer. The average reflectivity in the solar spectrum and average emissivity in the "atmospheric window" spectrum of the single-layer radiative cooling coating with mixture of TiO_2 particles and SiO_2 particles can increase 4.6% and 4.8% compared to the double-layer radiative cooling coating. This numerical research results can provide a theoretical guidance for design and optimization of single-layer radiative cooling coatings containing mixed nanoparticles.  相似文献   
56.
An experimental study was conducted to investigate the structural stability of ethylene glycol-based titanium dioxide nanoparticle suspensions (nanofluids) prepared by two-step method. The effects of particle concentration, fluid temperature, shear rate and shear duration were examined. Particle size and thermal conductivity measurements in quiescent state indicated the existence of aggregates and that they were stable in temperatures up to 60°C. Shear stability tests suggested that the structure of nanoparticle aggregates was stable in a shear interval of 500-3000 s-1 measured over a temperature range of 20-60°C. These findings show directions to resolve controversies surrounding the underlying mechanisms of thermal conduction and convective heat transfer of nanofluids.  相似文献   
57.
介绍了国内外生物油的发展现状。根据生物油制备原料不同,将其分为植物油、热裂解油和生物柴油等。概括了生物油制备的方法和原理,分析3种生物油的物理化学性质。综述了生物油的主要应用方式,包括食品加工、化工应用和燃烧应用等。最后总结了生物油领域存在的主要问题,并对生物油应用方面的发展方向进行了展望。  相似文献   
58.
在小型循环流化床中对铁矿石粉在氮气气氛下用大同煤粉直接还原进行了实验研究,在800~950℃考察了反应温度对铁矿石粉的还原程度及还原产物微观结构的影响. 结果表明,随反应温度提高,铁矿石粉还原产物的金属化率及还原度均增加,800~850℃时增幅较大,850~900℃时增幅平缓,900~950℃时又出现较大增幅,950℃时达到63%的金属化率和87%的还原度;与还原前的铁矿石粉相比,还原产物的比表面积和总孔体积在800℃时均增加,而在其他温度时均减小,对应的平均孔径变化规律则相反.  相似文献   
59.
利用TG/DTA 6300型热分析仪研究了宁夏石沟驿煤的气化残炭的燃烧特性,从着火特性、燃尽特性和稳燃特性三个方面分析了升温速率、粒径和氧气浓度对气化残炭燃烧特性的影响,并采用正交实验分析了升温速率、粒径和氧气浓度三个因素对气化残炭燃烧特性影响的耦合作用.实验结果表明,提高升温速率可以改善气化残炭的燃尽特性;粒径的减小有助于气化残炭的着火;氧气浓度的增加对改善气化残炭燃烧特性有明显的作用,但这种改善效果随氧气浓度的增加而减弱;升温速率对气化残炭的着火特性影响最大,而氧气浓度对气化残炭的燃尽特性和稳燃特性影响最大.  相似文献   
60.
文爽  齐宏  刘少斌  任亚涛  阮立明 《化工学报》2020,71(4):1432-1439
将无迹卡尔曼滤波技术(unscented Kalman filter, UKF)用于求解一维介质热物性参数反演问题;也对利用扩展卡尔曼滤波技术(extended Kalman filter, EKF)反演一维介质中热导率问题进行了研究。首先给出了正问题模型,然后详细介绍了EKF算法和UKF算法的基本原理。最后为了验证当前算法的可行性,采用UKF算法重建了介质内部随位置变化的热导率,并采用EKF算法重建了介质内部随时间变化的热导率。计算结果表明,UKF算法和EKF算法均能较为准确地反演介质的热导率。为了减小重建结果的时间滞后,建议使用较小的测量误差协方差R。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号