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   1636篇
  免费   37篇
  国内免费   8篇
电工技术   1篇
综合类   56篇
化学工业   816篇
金属工艺   31篇
机械仪表   39篇
建筑科学   6篇
矿业工程   83篇
能源动力   20篇
轻工业   327篇
水利工程   1篇
石油天然气   75篇
武器工业   9篇
无线电   5篇
一般工业技术   157篇
冶金工业   37篇
原子能技术   10篇
自动化技术   8篇
  2024年   1篇
  2023年   4篇
  2022年   49篇
  2021年   21篇
  2020年   26篇
  2019年   25篇
  2018年   26篇
  2017年   33篇
  2016年   31篇
  2015年   40篇
  2014年   52篇
  2013年   163篇
  2012年   87篇
  2011年   125篇
  2010年   73篇
  2009年   103篇
  2008年   77篇
  2007年   62篇
  2006年   68篇
  2005年   67篇
  2004年   57篇
  2003年   42篇
  2002年   61篇
  2001年   34篇
  2000年   47篇
  1999年   48篇
  1998年   35篇
  1997年   46篇
  1996年   40篇
  1995年   41篇
  1994年   40篇
  1993年   17篇
  1992年   13篇
  1991年   10篇
  1990年   2篇
  1989年   4篇
  1988年   4篇
  1987年   1篇
  1985年   2篇
  1980年   1篇
  1979年   2篇
  1974年   1篇
排序方式: 共有1681条查询结果,搜索用时 15 毫秒
61.
62.
Kyeongseok Oh  Milind D. Deo 《Fuel》2011,90(6):2113-2117
Paraffinic waxes precipitate from bulk oil when oil temperatures are lower than the oil wax appearance temperature. The oil can form a gel if the temperature goes below the pour point, especially under quiescent conditions. The strength of the gelled waxy oil increases as temperature decreases further. Application of a mechanical shear deforms and fractures the gel. It is shown that this strength reduction in the gel is irreversible under isothermal conditions. In subsequent cooling, the prior fractured gel even showed much less yield stress than the gel from the shear-free condition at measured temperature. This study explored the gel strength behavior in water-in-oil (w/o) emulsion state. Three different model oils, water-free oil, 10 wt.% w/o and 30 wt.% w/o, were used to determine the yield stress using vane method. Both emulsified oils showed less yield stress values at temperatures between the pour points and ice temperature. Compared to water-free oil at temperatures below ice formation, the higher yield stresses were observed in 10 wt.% w/o oil; however, the lower yield stresses in 30 wt.% w/o oil. Subsequent cooling option after prior gel breakage was also examined.  相似文献   
63.
以甲基丙烯酸甲酯(MMA)和丙烯酸丁酯(BA)为主要原料,过硫酸铵为引发剂,进行无皂乳液聚合.结果表明:在不添加乳化剂的情况下,当MMA/BA=1:1、引发剂用量为0.24%、反应温度为80℃、反应时间8.0h时,所得乳液最稳定,单体转化率为81.84%,此无皂乳液对牛皮纸的粘接性比常规乳液好.  相似文献   
64.
We report the validation of an expression to accurately describe the power draw of an in-line rotor–stator mixer over a range of flow rates and rotor speeds. The expression consists of a term which reflects the power required to rotate the shaft in response to the liquid resistance and a term to reflect the power convected away from the mixing chamber. A specially commissioned high speed (12,000 rpm), instrumented 150/250 MS Silverson mixer has been developed with power draw determined from both torque and calorimetric measurements. Experiments are carried out using water over a range of independently controlled flow rates and rotor speeds with losses for both techniques carefully accounted for. For the torque measurement the value of the constants for the two terms above are Poz=0.197 and k1=9.35, respectively. For the calorimetric technique the measured temperature rise was similar to some of the corrections and losses over a significant range of the experimental space but nevertheless with careful experimentation constants similar to those for the torque technique were obtained, Poz=0.229 and k1=7.46. Allowing the calibration of the temperature probes to be a fit parameter in the regression routine increased the value of k1=8.10 but did not affect the value of Poz. A simple graphical method is also proposed using a dimensionless form of the expression which yielded slightly higher value of Poz but a slightly lower value of k1. The accuracy of both measurement techniques improves with rotor speed and the differences between the constants is attributed to the better accuracy of the torque technique at higher flow rates whereas the calorimetric technique is more accurate at low flow rates where the temperature rise is larger. Several repeats of the calorimetric technique with a reduced set of experimental points show good reproducibility. Finally at low flow rates (<10% of the maximum) the power unexpectantly increases and a modification to the expression is proposed by considering the pumping efficiency.  相似文献   
65.
A new model with comprehensive kinetics for propylene homopolymerization in fluidized bed reactors was developed to investigate the effect of mixing, operating conditions, kinetic and hydrodynamic parameters on the reactor performance as well as polymer properties. Presence of the particles in the bubbles and the excess gas in the emulsion phase was considered to improve the two-phase model, thus, considering the polymerization reaction to take place in both the bubble and emulsion phases. It was shown that in the practical range of superficial gas velocity and catalyst feed rate, the ratio of produced polymer in the bubble phase to the total production rate is roughly between 10% and 13%, which is a substantial amount and cannot be ignored. Simulation studies were carried out to compare the results of the improved two-phase, conventional well-mixed and constant bubble size models. The improved two-phase and well mixed models predicted a narrower and safer window at the same running conditions compared with the constant bubble size model. The improved two-phase model showed close dynamic behavior to the conventional models at the beginning of polymerization, but starts to diverge with the evolution of time.  相似文献   
66.
The transitional behaviours of emulsion polymerisation for styrene and butyl acrylate (BA) monomers from zero-one to pseudo-bulk regime were mechanistically investigated. A dynamic mathematical model, which incorporates cross-over mechanism from zero-one to pseudo-bulk kinetics was developed for emulsion polymerisation and compared with experimental data for conversion, particle size and molar mass. Particles smaller than cross-over size follow zero-one kinetics and particles greater than cross-over size, they follow pseudo-bulk kinetics. In our mechanistic approach, particles nucleated from micelles, grow until the cross-over size is attained, based on zero-one kinetics, and subsequently continue to grow based on pseudo-bulk kinetics. Key findings from our work are that the developed transitional model predictions agree reasonably with experimental data on process and product attributes such as conversion, average molecular weight, molecular weight distribution (MWD), average particle size and particle size distribution (PSD). Optimal strategies for semibatch operation was developed using reaction temperature and monomer feed rate as process variables with specified initial conditions.  相似文献   
67.
Pomegranate seeds are by‐products of pomegranate juice industry. Since the seeds contain valuable oil that has nutritional and medicinal properties, they can be useful for food applications (especially in juice and beverage industries) as a functional agent. In this study, the possibility of producing a stable pomegranate‐seed‐oil‐in‐water emulsion to be used as a base formula for a new functional beverage was investigated. The influence of gum Arabic (GA) concentration (10.0, 12.5, and 15.0%, w/w) with a constant oil phase content (6.0% w/w) on the turbidity loss rate, emulsion stability index, and droplet size distribution was investigated. Turbidity loss rate was inversely proportional to the GA concentration for all the formulations studied here. Compared to other emulsions, emulsion with 15.0% w/w GA did not show a discernible cream layer during 42 days of storage. Emulsion with 15.0% w/w GA indicated the smallest polydispersity index during this period. The results of this study showed that it was possible to produce a relatively stable pomegranate‐seed‐oil‐in‐water emulsion for use as a functional agent in beverages.  相似文献   
68.
Poly(vinyl acetate-co-butyl acrylate) latexes were prepared by using semi-continuous emulsion polymerization method in presence of two different protective colloids which were oligomeric N-methylol acrylamide and conventional poly(vinyl alcohol). The effects of these protective colloids on colloidal, surface and film properties of latexes were examined. Poly(vinyl acetate-co-butyl acrylate) synthesized with oligomeric N-methylol acrylamide, which was characterized by FT-IR, NMR and MALDI-TOF MS, was found to have lower viscosity, finer particle size, better latex stability, lower polydispersity, higher Tg and better film forming behavior compared to those synthesized from the poly(vinyl alcohol).  相似文献   
69.
通过白油/甘油/十六烷基磷酸酯精氨酸/水系统,对表面活性剂液晶的相行为,结构图象及溶液油性质进行了研究,利用最佳强度的液晶制备乳状液,得到的乳状液细小而均匀,解决了乳状液的聚结问题。  相似文献   
70.
对合适HLB值的乳化剂进行了筛选和评价,优选了具有较强稳定性能的乳状液。静态测试结果显示乳状液具有较好的耐温和耐盐性能,随着矿化度的提高,其稳定性能略有降低,但是幅度不大。该乳状液体系具有很高的黏度,渗流阻力能够提高140倍左右,说明乳状液体系能够在高温高盐条件下取得很好的驱替效果。驱替实验还表明乳状液滴与孔喉的匹配性决定了乳状液在多孔介质中的运移能力。  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