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   399570篇
  免费   6058篇
  国内免费   1887篇
电工技术   7162篇
综合类   518篇
化学工业   58147篇
金属工艺   17001篇
机械仪表   11889篇
建筑科学   9284篇
矿业工程   2081篇
能源动力   9740篇
轻工业   34036篇
水利工程   3955篇
石油天然气   7778篇
武器工业   40篇
无线电   46706篇
一般工业技术   79371篇
冶金工业   79949篇
原子能技术   8825篇
自动化技术   31033篇
  2021年   3177篇
  2019年   2895篇
  2018年   5355篇
  2017年   5187篇
  2016年   5603篇
  2015年   3879篇
  2014年   6230篇
  2013年   17444篇
  2012年   10027篇
  2011年   13493篇
  2010年   11117篇
  2009年   12683篇
  2008年   13203篇
  2007年   13240篇
  2006年   11664篇
  2005年   10657篇
  2004年   9906篇
  2003年   9508篇
  2002年   9225篇
  2001年   9330篇
  2000年   8761篇
  1999年   9312篇
  1998年   25082篇
  1997年   17631篇
  1996年   13565篇
  1995年   9772篇
  1994年   8794篇
  1993年   8590篇
  1992年   6053篇
  1991年   5972篇
  1990年   5745篇
  1989年   5605篇
  1988年   5392篇
  1987年   4472篇
  1986年   4504篇
  1985年   5166篇
  1984年   4835篇
  1983年   4390篇
  1982年   4145篇
  1981年   4292篇
  1980年   4064篇
  1979年   3883篇
  1978年   3892篇
  1977年   4583篇
  1976年   6283篇
  1975年   3473篇
  1974年   3311篇
  1973年   3336篇
  1972年   2857篇
  1971年   2631篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Intended learning outcomes (ILOs) indicate what learners will be able to achieve after they are taught. Traditionally, ILOs are expressed as plain text or unstructured documents. What if all ILOs of a specific course of study can be conceptualized through a structured diagrammatic technique? It was hypothesized that learners can benefit from this conceptualization in learning, especially in self‐regulated learning. The aim of this study was to investigate whether the ILOs represented in unstructured or structured formats can facilitate learners to identify learning paths. The results revealed that the mean ratings of all learning paths were statistically significantly higher with structured ILOs.  相似文献   
102.
103.
104.
105.
106.
107.
Spinel LiSr0·1Cr0·1Mn1·8O4 was synthesised by high temperature solid state method in order to enhance the electrochemical performance. The LiSr0·1Cr0·1Mn1·8O4 (LSCMO) materials were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. The XRD and SEM studies confirm that LSCMO had spinel crystal structure with a space group of Fd3m, and the particle of LSCMO shows irregular shape. The cyclic voltammetry data illustrated that the heavy current charge–discharge performance of LMO was improved by Sr2+ and Cr3+ doping. The galvanostatic charge–discharge of LSCMO cathode materials was measured at 1, 5, 10 and 20 C. The results indicated that LSCMO improved the capacity retention.  相似文献   
108.
The authors have determined the causes of drop in performance of induced block caving using fans of blastholes 105 mm in diameter and single blastholes 250 mm in diameter, as well as the sources of increased drilling cost and expansion of start-up time of production blocks in Abakan underground mine. Alternatives of improvement in drilling efficiency under current conditions are discussed.  相似文献   
109.
Tian  J. Y.  Xu  G.  Hu  H. J.  Zhou  M. X. 《Strength of Materials》2019,51(3):439-449
Strength of Materials - A metallographic method, dilatometry, and X-ray diffraction were applied to investigate the effects of undercooling and holding time on bainitic transformation,...  相似文献   
110.
In this work, the sintering behaviour of fluorapatite (FAp)–silicate composites prepared by mixing variable amounts of natural quartz (2.5 wt% to 20 wt%) and FAp was studied. The composites were pressureless sintered in air at temperatures from 1000 °C to 1350 °C. The effects of temperatures on the densification, phase formation, chemical bonding and Vickers hardness of the composites were evaluated. All the samples exhibited mixed phase, comprising FAp and francolite as the major constituents along with some minor phases of cristobalite, wollastonite, dicalcium silicate and/or whitlockite dependent on the quartz content and sintering temperature. The composite containing 2.5 wt% quartz exhibited the best sintering properties. The highest bulk density of 3 g/cm3 and a Vickers hardness of >4.2 GPa were obtained for the 2.5 wt% quartz–FAp composite when sintered at 1100 °C. The addition of quartz was found to alter the microstructure of the composites, where it exhibited a rod-like morphology when sintered at 1000 °C and a regular rounded grain structure when sintered at 1350 °C. A wetted grain surface was observed for composites containing high quartz content and was believed to be associated with a transient liquid phase sintering.  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