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   1825篇
  免费   21篇
  国内免费   13篇
电工技术   29篇
综合类   5篇
化学工业   285篇
金属工艺   50篇
机械仪表   66篇
建筑科学   102篇
矿业工程   9篇
能源动力   41篇
轻工业   142篇
水利工程   25篇
石油天然气   15篇
无线电   190篇
一般工业技术   363篇
冶金工业   216篇
原子能技术   17篇
自动化技术   304篇
  2024年   26篇
  2023年   14篇
  2022年   42篇
  2021年   51篇
  2020年   59篇
  2019年   48篇
  2018年   41篇
  2017年   31篇
  2016年   40篇
  2015年   52篇
  2014年   58篇
  2013年   121篇
  2012年   88篇
  2011年   98篇
  2010年   83篇
  2009年   69篇
  2008年   92篇
  2007年   65篇
  2006年   82篇
  2005年   79篇
  2004年   45篇
  2003年   61篇
  2002年   32篇
  2001年   36篇
  2000年   22篇
  1999年   30篇
  1998年   44篇
  1997年   34篇
  1996年   23篇
  1995年   28篇
  1994年   14篇
  1993年   18篇
  1992年   9篇
  1991年   14篇
  1990年   17篇
  1989年   15篇
  1988年   14篇
  1987年   10篇
  1986年   12篇
  1985年   14篇
  1984年   8篇
  1983年   7篇
  1982年   12篇
  1981年   10篇
  1977年   9篇
  1976年   10篇
  1973年   9篇
  1970年   7篇
  1968年   5篇
  1967年   4篇
排序方式: 共有1859条查询结果,搜索用时 0 毫秒
41.
In this paper, we use an energy–economy–environment computable general equilibrium (CGE) model of the Scottish economy to examine the impacts of an exogenous increase in energy augmenting technological progress in the domestic commercial Transport sector on the supply and use of energy. We focus our analysis on Scottish refined oil, as the main type of energy input used in commercial transport activity. We find that a 5% increase in energy efficiency in the commercial Transport sector leads to rebound effects in the use of oil-based energy commodities in all time periods, in the target sector and at the economy-wide level. However, our results also suggest that such an efficiency improvement may cause a contraction in capacity in the Scottish refined oil supply sector. This ‘disinvestment effect’ acts as a constraint on the size of rebound effects. However, the magnitude of rebound effects and presence of the disinvestment effect in the simulations conducted here are sensitive to the specification of key elasticities of substitution in the nested production function for the target sector, particularly the substitutability of energy for non-energy intermediate inputs to production.  相似文献   
42.
This paper presents United States energy portfolios for the year 2030, developed from seven different Perspectives. The Perspectives are characterized by different weights placed on fourteen defining values (e.g., cost, social acceptance). The portfolios were constructed to achieve three primary goals, energy independence, energy security, and greenhouse gas reductions. The portfolios are also evaluated over a comprehensive set of secondary criteria (e.g., economic growth, technical feasibility). It is found that very different portfolios based on very different defining values can achieve the three primary goals. Commonalities among the portfolios include reliance upon cellulosic ethanol, nuclear power, and energy efficiency to meet year 2030 energy demands. It is concluded that the US energy portfolio must be diverse and to achieve national energy goals will require an explicit statement of goals, a strong role for government, and coordinated action across society.  相似文献   
43.
Critical strains causing environmental stress cracking of injection-molded poly(acrylonitrile-butadiene-styrene) (ABS) and poly(styrene-acrylonitrile) (SAN) plaques were determined upon exposure to methanol. Measurements were obtained for samples strained either parallel or perpendicular to the melt flow direction and for samples located at various distances from the mold gate. Critical strains were significantly higher in the direction parallel to the melt flow compared to the transverse direction. The degree of anisotropy increased with increasing rubber content. For ABS containing 46 percent rubber, the critical strain at one point was determined to be 2.99 percent in the direction of melt flow, but only 0.47 percent in the orthogonal direction. For this material, critical strains determined parallel to the melt flow decreased with distance from the gate; whereas, critical strains for SAN and ABS containing 30 percent rubber remained essentially constant. Orientation of the plaques was assessed using shrinkage determinations and a thermal conductivity technique. Though a straightforward correlation of orientation with critical strain is observed for ABS, a similar relationship is not observed for SAN. These results suggest that although stress cracking occurs in the glassy matrix of ABS, it is the dispersed rubbery phase which controls the magnitude of strain required to initiate cracking.  相似文献   
44.
Vapor and liquid equilibrium phase compositions have been determined at 310.9, 394.3, and 477.6 K for the mesitylene–methane binary system and at 310.9, 338.7, 394.3, and 477.6 K for the mesitylene–carbon dioxide system. At each temperature, the pressure ranged from the vapor pressure of mesitylene to about 15 MPa, although in the case of the mesitylene–carbon dioxide system, pressures were extended to the vicinity of the critical region at about 18 MPa. The data were used to calculate equilibrium ratios for each component in the binary system.  相似文献   
45.
46.
47.
    
  相似文献   
48.
49.
    
ABSTRACT

This paper proposes the multiple-hypotheses image segmentation and feed-forward neural network classifier for food recognition to improve the performance. Initially, the food or meal image is given as input. Then, the segmentation is applied to identify the regions, where a particular food item is located using salient region detection, multi-scale segmentation, and fast rejection. Then, the features of every food item are extracted by the global feature and local feature extraction. After the features are obtained, the classification is performed for each segmented region using a feed-forward neural network model. Finally, the calorie value is computed with the aid of (i) food volume and (ii) calorie and nutrition measure based on mass value. The experimental results and performance evaluation are validated. The outcome of the proposed method attains 0.947 for Macro Average Accuracy (MAA) and 0.959 for Standard Accuracy (SA), which provides better classification performance.  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