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   274880篇
  免费   5015篇
  国内免费   1847篇
电工技术   5566篇
技术理论   5篇
综合类   1206篇
化学工业   45089篇
金属工艺   11297篇
机械仪表   8026篇
建筑科学   7235篇
矿业工程   1701篇
能源动力   6052篇
轻工业   26866篇
水利工程   2996篇
石油天然气   6047篇
武器工业   243篇
无线电   28800篇
一般工业技术   51846篇
冶金工业   49156篇
原子能技术   5725篇
自动化技术   23886篇
  2021年   3007篇
  2020年   2012篇
  2019年   2474篇
  2018年   3848篇
  2017年   3788篇
  2016年   4173篇
  2015年   3226篇
  2014年   5120篇
  2013年   12340篇
  2012年   8565篇
  2011年   11243篇
  2010年   8844篇
  2009年   9365篇
  2008年   10181篇
  2007年   10276篇
  2006年   8959篇
  2005年   7834篇
  2004年   6992篇
  2003年   6524篇
  2002年   6513篇
  2001年   6500篇
  2000年   6071篇
  1999年   6057篇
  1998年   13049篇
  1997年   9704篇
  1996年   7447篇
  1995年   5675篇
  1994年   5217篇
  1993年   5081篇
  1992年   4043篇
  1991年   3814篇
  1990年   3928篇
  1989年   3875篇
  1988年   3601篇
  1987年   3102篇
  1986年   3133篇
  1985年   3497篇
  1984年   3403篇
  1983年   3138篇
  1982年   2787篇
  1981年   2984篇
  1980年   2709篇
  1979年   2900篇
  1978年   2794篇
  1977年   2909篇
  1976年   3748篇
  1975年   2500篇
  1974年   2329篇
  1973年   2349篇
  1972年   2009篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The online version of the original article can be found at  相似文献   
992.
On The Measurement of Temperature in Material Removal Processes   总被引:5,自引:0,他引:5  
Because it is key to understanding the performance of material removal processes and resultant workpiece quality, the measurement of temperature during material removal is done extensively. We review several widely used temperature measurement methods and show how they can be applied to temperature monitoring during material removal. Since there is little documentation on measurement uncertainties as relates to material removal, this paper outlines the physics of each method, detailing the sources and evaluation of uncertainty. Finally, using criteria critical in measuring material removal, methods are compared, and the results presented in guide-format for participants in this field of work.  相似文献   
993.
994.
995.
996.
997.
An exact solution inside, outside, and within two arbitrary concentric spherical shells is presented for an impinging monochromatic linearly polarized electromagnetic wave. Specifically, the solution was found for a double-shell spherical acrylic plastic enclosure irradiated with 2450-MHz microwaves. The enclosure is used as an environmentally controlled exposure chamber for experimental animals during microwave irradiation. The analysis shows that an air foamed material, such as styrofoam, would be a better material than either Plexiglas or Teflon, provided it is sufficiently durable.  相似文献   
998.
MAN is but a part of the universe; his capabilities make him a significant link, in the cycle of life. To ensure this life, man must live in harmony with his environment. Recently, a disharmony has been discovered which could have grave effects upon the existence of man. It appears that man in his great thrust forward is destroying his own environment. The gravity of this threat to man's own existence carries some intrinsic problems of its own: man must allow his reason rather than his emotion to take command.  相似文献   
999.
Ruminant livestock systems are a significant source of greenhouse gases (GHGs). Thus far, mitigation options for GHG emissions mainly focused on a single gas, and are treated as isolated activities. The present paper proposes a framework for a farm level approach for the full accounting of GHG emissions. The methodology accounts for the relevant direct and indirect emissions of methane, nitrous oxide and carbon dioxide, including carbon sequestration. Furthermore, the potential trade-off with ammonia volatilisation and nitrate leaching are taken into account. A ruminant livestock farm is represented with a conceptual model consisting of five pools: animal, manure, soil, crop and feed. The carbon and nitrogen inputs, throughputs and outputs are described, and the direct emissions are related to the carbon and nitrogen flows. The indirect emissions included in the methodology are mainly carbon dioxide emissions from energy use and nitrous oxide emissions related to imported resources and nitrogen losses. The whole farm approach is illustrated with a case of two dairy farms with contrasting livestock density and grassland management. It is shown that the inclusion of carbon sequestration and all indirect emissions have a major impact on the GHG budget of the farm. For one farm, the effect of four mitigation options on the GHG emissions was quantified. It was concluded that a whole farm approach of full accounting contributes to a better insight in the interactions between the carbon and nitrogen flows and the resulting emissions, within and outside the farm boundaries. Consequently, the methodology can be used to develop efficient and effective mitigation strategies.  相似文献   
1000.
Current methods for determining the activity of long chain quaternary ammonium compounds (QACS) are based either on dye partition, titration, or colorimetric analysis. The two major disadvantages of these methods are the disparity of partition coefficients among differently constituted QACS and the difficulty in detecting visual end points. Some potentiometric titration methods for QACS have been reported in the literature. However, back titration techniques, as well as complicated electrode systems, are generally involved. A new potentiometric titration system is presented which uses aqueous sodium tetraphenylborate (TPB) solution as a titrant and a platinum-platinum electrode system to detect the end point. Standard potentiometric titration instruments may be used for this method. This new potentiometric method is superior in precision and accuracy to visual (colorimetric) methods. Original version presented at the 1986 Annual AOCS Meeting in Honolulu, HI.  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