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   312247篇
  免费   4214篇
  国内免费   715篇
电工技术   6227篇
综合类   560篇
化学工业   47259篇
金属工艺   10373篇
机械仪表   8866篇
建筑科学   8022篇
矿业工程   868篇
能源动力   8614篇
轻工业   31268篇
水利工程   2558篇
石油天然气   3677篇
武器工业   8篇
无线电   39951篇
一般工业技术   58824篇
冶金工业   57708篇
原子能技术   5471篇
自动化技术   26922篇
  2021年   2298篇
  2019年   2164篇
  2018年   3628篇
  2017年   3469篇
  2016年   3571篇
  2015年   2560篇
  2014年   4479篇
  2013年   14403篇
  2012年   7432篇
  2011年   10217篇
  2010年   7965篇
  2009年   9200篇
  2008年   9684篇
  2007年   9652篇
  2006年   8558篇
  2005年   7962篇
  2004年   7830篇
  2003年   7562篇
  2002年   7406篇
  2001年   7608篇
  2000年   7249篇
  1999年   7610篇
  1998年   17915篇
  1997年   13012篇
  1996年   10227篇
  1995年   7969篇
  1994年   7277篇
  1993年   7000篇
  1992年   5334篇
  1991年   5097篇
  1990年   4973篇
  1989年   4817篇
  1988年   4704篇
  1987年   3922篇
  1986年   4032篇
  1985年   4753篇
  1984年   4309篇
  1983年   4054篇
  1982年   3634篇
  1981年   3792篇
  1980年   3482篇
  1979年   3448篇
  1978年   3244篇
  1977年   3846篇
  1976年   4921篇
  1975年   2816篇
  1974年   2674篇
  1973年   2693篇
  1972年   2223篇
  1971年   1972篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Powder Metallurgy and Metal Ceramics - Multiphase La 2 MgNi 9 alloys are synthesized by induction melting. The crystalline structures of all phases in the alloys are determined with X-ray...  相似文献   
83.
84.
85.
86.
Anthropogenic influences, including climate change, are increasing river temperatures in northern and temperate regions and threatening the thermal habitats of native salmonids. When river temperatures exceed the tolerance levels of brook trout and Atlantic salmon, individuals exhibit behavioural thermoregulation by seeking out cold‐water refugia – often created by tributaries and groundwater discharge. Thermal infrared (TIR) imagery was used to map cold‐water anomalies along a 53 km reach of the Cains River, New Brunswick. Trout and salmon parr did not use all identified thermal anomalies as refugia during higher river temperature periods (>21°C). Most small‐bodied trout (8–30 cm) were observed in 80% of the thermal anomalies sampled. Large‐bodied trout (>35 cm) required a more specific set of physical habitat conditions for suitable refugia, that is, 100% of observed large trout used 30% of the anomalies sampled and required water depths >65 cm within or adjacent to the anomaly. Densities of trout were significantly higher within anomalies compared with areas of ambient river temperature. Salmon parr were less aligned with thermal anomalies at the observed temperatures, that is, 59% were found in 65% of the sampled anomalies; and densities were not significantly different within/ outside anomalies. Salmon parr appeared to aggregate at 27°C, and after several events over 27°C variability in aggregation behaviour was observed – some fish aggregated at 25°C, others did not. We stipulate this is due to variances of thermal fatigue. Habitat suitability curves were developed for velocity, temperature, depth, substrate, and deep water availability to characterize conditions preferred by fish during high‐temperature events. These findings are useful for managers as our climate warms, and can potentially be used as a tool to help conserve and enhance thermal refugia for brook trout and Atlantic salmon in similar systems.  相似文献   
87.
88.
89.
A renewable chemical, eugenol, is methacrylated to produce methacrylated eugenol (ME) employing the Steglich esterification reaction without any solvent. The resulting ME is used as a low‐viscosity co‐monomer to replace styrene in a commercial epoxy‐based vinyl ester resin (VE). The volatility and viscosity of ME and styrene are compared. The effect of ME loading and temperature on the viscosity of the VE–ME resin is investigated. Moreover, the thermomechanical properties, curing extent and thermal stability of the fully cured VE–ME thermosets are systematically examined. The results indicate that ME is a monomer with low volatility and low viscosity, and therefore the incorporation of ME monomer in VE resins allows significant reduction of viscosity. Moreover, the viscosity of the VE–ME resin can be tailored by adjusting the ME loadings and processing temperature to meet commercial liquid molding technology requirements. The glass transition temperatures of VE–ME thermosets range from 139 to 199 °C. In addition, more than 95% of the monomer is incorporated and fixed in the crosslinked network structure of VE–ME thermosets. Overall, the developed ME monomer exhibits promising potential for replacing styrene as an effective low‐viscosity co‐monomer. The VE–ME resins show great advantages for use in polymer matrices for high‐performance fiber‐reinforced composites. This work is of great significance to the vinyl ester industry by providing detailed experimental support. © 2018 Society of Chemical Industry  相似文献   
90.
Neural Computing and Applications - The goal of this paper is to introduce a novel hybrid model called multi-fuzzy N-soft set, and to design an adjustable decision-making methodology for solving...  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