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   1561710篇
  免费   27692篇
  国内免费   7006篇
电工技术   35249篇
综合类   6449篇
化学工业   274991篇
金属工艺   66075篇
机械仪表   45810篇
建筑科学   47777篇
矿业工程   11884篇
能源动力   50600篇
轻工业   119075篇
水利工程   15848篇
石油天然气   38367篇
武器工业   147篇
无线电   199797篇
一般工业技术   296141篇
冶金工业   179707篇
原子能技术   34677篇
自动化技术   173814篇
  2021年   15643篇
  2020年   11942篇
  2019年   14769篇
  2018年   18687篇
  2017年   18482篇
  2016年   22844篇
  2015年   17644篇
  2014年   28839篇
  2013年   88385篇
  2012年   37676篇
  2011年   52538篇
  2010年   45758篇
  2009年   53703篇
  2008年   48361篇
  2007年   46159篇
  2006年   46269篇
  2005年   42055篇
  2004年   43307篇
  2003年   42974篇
  2002年   41749篇
  2001年   38106篇
  2000年   36433篇
  1999年   35552篇
  1998年   49293篇
  1997年   42052篇
  1996年   37116篇
  1995年   31853篇
  1994年   29665篇
  1993年   29493篇
  1992年   26529篇
  1991年   23656篇
  1990年   24017篇
  1989年   23099篇
  1988年   21610篇
  1987年   19869篇
  1986年   19207篇
  1985年   22590篇
  1984年   22577篇
  1983年   20550篇
  1982年   19452篇
  1981年   19516篇
  1980年   18151篇
  1979年   18679篇
  1978年   17890篇
  1977年   17844篇
  1976年   19008篇
  1975年   16133篇
  1974年   15605篇
  1973年   15721篇
  1972年   13179篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
791.
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   
792.
In this paper, the development of the models for the prediction of rock mass P wave velocity is presented. For model development, the database of 53 cases including widely used and recorded drilling parameters and P wave velocity was constructed from the field studies conducted in 13 open pit lignite mines. Both conventional linear, non-linear multiple regression and Adaptive Neuro Fuzzy Inference System (ANFIS) were used for model development. Prediction performance indicators showed that ANFIS model presented the best performance and it can successfully be used for the preliminary prediction of P wave velocities of rock masses.  相似文献   
793.
Removal by absorptive ceramic membranes can simultaneously absorb and separate metal ions from water. Alumina/yttria‐stabilized zirconia (Al2O3/YSZ) hollow‐fiber membranes, fabricated using phase inversion and sintering process, were deposited with iron oxide by an in‐situ hydrothermal process. The results showed that α‐Fe2O3 was produced and incorporated across the membranes. A reduction in flux was recorded with the deposition of α‐Fe2O3. However, it improved the adsorption capacity for heavy metal adsorption. The adsorption‐separation test demonstrated that the optimized membrane is able to completely remove Pb(II) ions after two hours.  相似文献   
794.
795.
Journal of Computer and Systems Sciences International - The height of a building is a basic characteristic needed for analytical services. It can be used to evaluate the population and functional...  相似文献   
796.
Multimedia Tools and Applications - Emotions are spontaneous feelings that are accompanied by fluctuations in facial muscles, which leads to facial expressions. Categorization of these facial...  相似文献   
797.
798.
An experimental methodology for inferring brine dissolution rate in monoethylene glycol (MEG) solutions at different temperatures using a webcam combined with a mathematical model is presented. The measurement system is designed to track the RGB (red, green, and blue) colour variations during the dissolution process. A dynamic model augmented with the population balance equation is applied to describe the dissolution process. Moreover, the dissolution rate is consistently related to the temperature and MEG concentration through the driving force based on the Gibbs energy and chemical affinity. The applied low-cost measurement apparatus proved to be a useful resource for tracking the dissolution dynamics in a wide range of undersaturation.  相似文献   
799.
800.
Bottom pour ladles with stopper rod systems are commonly used in the metal casting industry. However, stopper rod bottom-pouring systems have not yet been developed for the lower thermal masses of alloys typically used in the investment casting industry. Large thermal masses used with bottom pour systems are typically limited for ladles larger than 700 kg and to certain alloys with higher fluidity and longer solidification time like cast iron, aluminum alloys etc. In this study, bottom pour ladle designs and low thermal mass refractory systems have been developed and evaluated in production investment foundry trials with 300 kg pouring ladle. The ladles system and pouring practices used will be described along with the results from the pouring trials for SS304 that represents typical alloys used in Investment casting industries. Optimization of the variables used in an experimentation using Genetic algorithm is also explained.  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