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   344296篇
  免费   5895篇
  国内免费   748篇
电工技术   6428篇
综合类   586篇
化学工业   53152篇
金属工艺   10919篇
机械仪表   9475篇
建筑科学   8999篇
矿业工程   928篇
能源动力   9252篇
轻工业   35731篇
水利工程   2845篇
石油天然气   3819篇
武器工业   12篇
无线电   41724篇
一般工业技术   64449篇
冶金工业   65282篇
原子能技术   5631篇
自动化技术   31707篇
  2021年   3061篇
  2020年   2298篇
  2019年   2741篇
  2018年   4939篇
  2017年   4781篇
  2016年   4940篇
  2015年   3520篇
  2014年   5646篇
  2013年   16693篇
  2012年   9443篇
  2011年   12012篇
  2010年   9436篇
  2009年   10469篇
  2008年   11159篇
  2007年   10925篇
  2006年   9518篇
  2005年   8736篇
  2004年   8543篇
  2003年   8220篇
  2002年   7952篇
  2001年   7924篇
  2000年   7575篇
  1999年   8044篇
  1998年   20387篇
  1997年   14469篇
  1996年   11142篇
  1995年   8480篇
  1994年   7755篇
  1993年   7430篇
  1992年   5456篇
  1991年   5248篇
  1990年   5110篇
  1989年   4963篇
  1988年   4826篇
  1987年   4024篇
  1986年   4156篇
  1985年   4896篇
  1984年   4428篇
  1983年   4135篇
  1982年   3738篇
  1981年   3905篇
  1980年   3584篇
  1979年   3518篇
  1978年   3325篇
  1977年   3966篇
  1976年   5197篇
  1975年   2855篇
  1974年   2717篇
  1973年   2741篇
  1972年   2258篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
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   
103.
104.
105.
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   
106.
107.
108.
The Journal of Supercomputing - Deadlock-free dynamic network reconfiguration process is usually studied from the routing algorithm restrictions and resource reservation perspective. The dynamic...  相似文献   
109.
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   
110.
Linear friction welding of the Ti6Al4V alloy is studied. A new definition of the energy input rate is proposed, based on an integration over time of the in-plane force and velocity; a strong correlation with the upset rate is then found. The effective friction coefficient is estimated to be 0·5±0·1 for varying frequencies and amplitudes, with only a weak dependence on the processing conditions displayed. A model is proposed that accounts for both the conditioning and equilibrium stages of the process, which is shown to be in good agreement with the experimental data. The model is used to study the mechanism by which the flash is formed. A criterion is proposed by which the rippled nature of its morphology can be predicted.  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