全文获取类型
收费全文 | 135891篇 |
免费 | 5309篇 |
国内免费 | 2399篇 |
专业分类
电工技术 | 3546篇 |
技术理论 | 5篇 |
综合类 | 5194篇 |
化学工业 | 20521篇 |
金属工艺 | 7932篇 |
机械仪表 | 6182篇 |
建筑科学 | 5940篇 |
矿业工程 | 2298篇 |
能源动力 | 2764篇 |
轻工业 | 7291篇 |
水利工程 | 2128篇 |
石油天然气 | 4106篇 |
武器工业 | 396篇 |
无线电 | 14907篇 |
一般工业技术 | 22452篇 |
冶金工业 | 5620篇 |
原子能技术 | 907篇 |
自动化技术 | 31410篇 |
出版年
2024年 | 243篇 |
2023年 | 891篇 |
2022年 | 1623篇 |
2021年 | 2308篇 |
2020年 | 1686篇 |
2019年 | 1463篇 |
2018年 | 15814篇 |
2017年 | 14923篇 |
2016年 | 11388篇 |
2015年 | 2684篇 |
2014年 | 2915篇 |
2013年 | 3296篇 |
2012年 | 6389篇 |
2011年 | 12874篇 |
2010年 | 11351篇 |
2009年 | 8321篇 |
2008年 | 9494篇 |
2007年 | 10447篇 |
2006年 | 2999篇 |
2005年 | 3664篇 |
2004年 | 2664篇 |
2003年 | 2515篇 |
2002年 | 1804篇 |
2001年 | 1097篇 |
2000年 | 1376篇 |
1999年 | 1537篇 |
1998年 | 1234篇 |
1997年 | 1038篇 |
1996年 | 1055篇 |
1995年 | 899篇 |
1994年 | 716篇 |
1993年 | 475篇 |
1992年 | 382篇 |
1991年 | 320篇 |
1990年 | 241篇 |
1989年 | 197篇 |
1988年 | 185篇 |
1987年 | 111篇 |
1986年 | 95篇 |
1985年 | 63篇 |
1984年 | 56篇 |
1983年 | 39篇 |
1968年 | 43篇 |
1966年 | 43篇 |
1965年 | 45篇 |
1959年 | 35篇 |
1958年 | 37篇 |
1957年 | 37篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
E. I. Basaldella J.C. Tara G. Aguilar Armenta M. E. Patiño Iglesias 《Journal of Porous Materials》2007,14(3):273-278
Samples of mesoporous silica SBA-15 were prepared under hydrothermal conditions where Cu cations were incorporated to the
structure by impregnation in order to compare the adsorption behavior in the presence and absence of this element. The adsorption/desorption
equilibrium isotherms of propylene, propane, and N2 were measured to evaluate their usefulness in the propane/propylene separation.
All the adsorption isotherms of SBA-15 measured in the absence of Cu cations were described by the Freundlich equation, while
the adsorption isotherms of propane on Cu/SBA-15 were better represented by the Henry equation and those of propylene were
satisfactorily described by the Langmuir model in the range P < 100 Torr. The adsorption uptake of propylene increased and that of propane decreased in Cu/SBA-15 as compared to the amounts
observed in the SBA-15 sample. The presence of Cu atoms in the adsorbent lattice increased the selectivity towards propylene.
Under some working conditions the adsorbed amount of propylene in Cu/SBA-15 sample was totally reversible and the propane
uptake, negligible. 相似文献
992.
993.
994.
995.
David W. L. Ma Catherine J. Field M. T. Clandinin 《Journal of the American Oil Chemists' Society》2002,79(8):755-758
CLA refers to a group of geometrical and positional isomers of linoleic acid. CLA has been shown to have potentially beneficial
effects on cancer, atherosclerosis, and body metabolism in animals. Mixtures containing equal amounts of these isomers are
commonly used in many research studies because of their greater availability and lower cost relative to pure isomers. This
has hindered progress in elucidating the biological properties of specific isomers and their relevance in animal and human
biology. A method was developed that offers a compromise between cost and utility to make available enriched mixtures of either
the Δ9c,11t- or Δ10t,12c-18:2 isomers for use in a wide range of experimental applications. A countercurrent approach was developed to separate the
Δ9c,11t- and Δ10t,12c-18:2 isomers from an equal mixture of these two isomers by urea complexation. After three successive rounds of complexation
using an equal amount of CLA and urea, a fraction enriched in Δ9c,11t-18:2 containing 42.5 and 17.4% of Δ9c,11t-and Δ10t,12c-18:2, respectively, was recovered. After a single round of complexation using 2.5 g urea/g CLA, a fraction enriched in Δ10t,12c-18:2 was recovered containing 29.7 and 69.1% of Δ9c,11t- and Δ10t,12c-18:2, respectively. 相似文献
996.
997.
Andreas Krell Paul Blank Hongwei Ma Thomas Hutzler Manfred Nebelung 《Journal of the American Ceramic Society》2003,86(4):546-53
Sintered corundum components with submicrometer grain sizes exhibit properties which enable numerous new applications. Wet powder processing is developed to associate minimum grain sizes at highest densities with the lowest population of macrodefects. A closest ratio of powder particle size and sintered grain size is important for obtaining most fine-grained microstructures. This target was approached best by using powders with particle sizes in the range of 100–200 nm rather than with smaller nanoparticles. 相似文献
998.
999.
浅谈国产化CO2汽提装置的相关问题 总被引:1,自引:0,他引:1
我国自20世纪70年代以来共引进了17套年产500~600kt的CO2汽提法大型尿素装置,1975年国内完成了年产240kt CO2汽提法尿素装置设计,并在上海吴泾化工厂建成投产,1991年又完成了日产140t CO2汽提法尿素装置设计,并在山东潍纺化肥厂、河北元氏化肥厂投产,标志着我国CO2汽提尿素工艺装置已基本实现了国产化。目前除液氨喷射器外, 相似文献
1000.
Boon-Seang Chu Sosaku Ichikawa Sumiyo Kanafusa Mitsutoshi Nakajima 《Journal of the American Oil Chemists' Society》2007,84(11):1053-1062
This work was initiated to prepare protein-stabilized β-carotene nanodispersions using emulsification–evaporation. A pre-mix
of the aqueous phase composed of a protein and hexane containing β-carotene was subjected to high-pressure homogenization
using a microfluidizer. Hexane in the resulting emulsion was evaporated under reduced pressures, causing crystallization and
precipitation of β-carotene inside the droplets and formation of β-carotene nanoparticles. Sodium caseinate (SC) was the most
effective emulsifier among selected proteins in preparing the nanodispersion, with a monomodal β-carotene particle-size distribution
and a 17-nm mean particle size. The results were confirmed by transmission-electron microscopy analysis. SC-stabilized nanodispersion
also had considerably high ζ-potential (−27 mV at pH 7), suggesting that the nanodispersion was stable against particle aggregation.
Increasing the SC concentration decreased the mean particle size and improved the polydispersity of the nanodispersions. Nanodispersions
prepared with higher β-carotene concentrations and higher organic-phase ratios resulted in larger β-carotene particles. Although
increased microfluidization pressure did not decrease particle size, it did improve the polydispersity of the nanodispersions.
Repeating the microfluidization process at 140 MPa caused the nanodispersions to become polydisperse, indicating the loss
of emulsifying capacity of SC due to protein denaturation. 相似文献