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   260947篇
  免费   3437篇
  国内免费   822篇
电工技术   5146篇
综合类   330篇
化学工业   37403篇
金属工艺   10262篇
机械仪表   8493篇
建筑科学   6140篇
矿业工程   1077篇
能源动力   6406篇
轻工业   22931篇
水利工程   2568篇
石油天然气   3915篇
武器工业   68篇
无线电   34830篇
一般工业技术   50185篇
冶金工业   46960篇
原子能技术   5424篇
自动化技术   23068篇
  2021年   2046篇
  2019年   2040篇
  2018年   3481篇
  2017年   3548篇
  2016年   3739篇
  2015年   2324篇
  2014年   4055篇
  2013年   11327篇
  2012年   6579篇
  2011年   8897篇
  2010年   7011篇
  2009年   7873篇
  2008年   8710篇
  2007年   8643篇
  2006年   7832篇
  2005年   7163篇
  2004年   6912篇
  2003年   6759篇
  2002年   6397篇
  2001年   6493篇
  2000年   6185篇
  1999年   6281篇
  1998年   14368篇
  1997年   10325篇
  1996年   8164篇
  1995年   6451篇
  1994年   5743篇
  1993年   5613篇
  1992年   4566篇
  1991年   4229篇
  1990年   4071篇
  1989年   3789篇
  1988年   3630篇
  1987年   3182篇
  1986年   3071篇
  1985年   3621篇
  1984年   3390篇
  1983年   3036篇
  1982年   2857篇
  1981年   2960篇
  1980年   2777篇
  1979年   2653篇
  1978年   2508篇
  1977年   2964篇
  1976年   3586篇
  1975年   2332篇
  1974年   2322篇
  1973年   2326篇
  1972年   1854篇
  1971年   1750篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
In this paper, we report on the indoor concentrations from a suite of full-scale outdoor tracer-gas point releases conducted in the downtown area of Oklahoma City in 2003. A point release experiment consisted of releases of sulfur hexafluoride (SF6) in multiple buildings and from different outdoor locations. From the measurements, we are able to estimate the concentration variations indoors for a building operating under “typical” operating conditions. The mean indoor spatial coefficients of variation are 30% to 45% from a daytime outdoor release are around 80% during an outdoor evening release. Having estimates of the spatial coefficient of variation provides stakeholders, including first responders, with the likely range of concentrations in the building when little is known about the building characteristics and operating behavior, such as developing urban-scale hazard and consequence analyses. We show differences in indoor measurements at different distances to the release points, floors of the building, and heating, ventilation, and air conditioning system (HVAC) operation. We also show estimates at different time resolutions. The statistics show that in the studied medium to large commercial buildings, spatial differences would result in peak indoor concentrations in certain parts of the buildings that may be substantially higher than the building average. To our knowledge, very few tracer gas measurements have been conducted in buildings of this scope, particularly with measurements on multiple floors and within a floor. The resulting estimates of spatial variability provide a unique opportunity for hazard assessment, and comparison to multi-zone models.  相似文献   
43.
44.
Combined photochemical arylation, “nuisance effect” (SNAr) reaction sequences have been employed in the design of small arrays for immediate deployment in medium-throughput X-ray protein–ligand structure determination. Reactions were deliberately allowed to run “out of control” in terms of selectivity; for example the ortho-arylation of 2-phenylpyridine gave five products resulting from mono- and bisarylations combined with SNAr processes. As a result, a number of crystallographic hits against NUDT7, a key peroxisomal CoA ester hydrolase, have been identified.  相似文献   
45.
46.
47.
Lund  Brady D.  Maurya  Sanjay Kumar 《Scientometrics》2020,125(3):2491-2504
Scientometrics - This study investigates a potential relationship between highly-cited scholarly papers and the number of citations received by other papers with which they share a journal issue....  相似文献   
48.
Morozov  Yu. D.  Pemov  I. F.  Matrosov  M. Yu.  Zin’ko  B. F. 《Metallurgist》2020,63(9-10):933-950
Metallurgist - We consider domestic and foreign standards for rolled metals used in bridge building. Domestic standards contain elevated requirements to the reliability of rolled metals in terms of...  相似文献   
49.
Russian Journal of Non-Ferrous Metals - This article is devoted to the influence of sodium lignosulfonate (SL), anionic surfactants (sodium dodecylsulfate (SDS), sodium dodecylbenzene sulfonate...  相似文献   
50.
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