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   1538485篇
  免费   26127篇
  国内免费   7060篇
电工技术   34440篇
综合类   6452篇
化学工业   271616篇
金属工艺   64886篇
机械仪表   43057篇
建筑科学   46712篇
矿业工程   11393篇
能源动力   50364篇
轻工业   115336篇
水利工程   15654篇
石油天然气   37461篇
武器工业   135篇
无线电   197208篇
一般工业技术   288161篇
冶金工业   184525篇
原子能技术   33993篇
自动化技术   170279篇
  2021年   15638篇
  2020年   11919篇
  2019年   14663篇
  2018年   15878篇
  2017年   15112篇
  2016年   21441篇
  2015年   17419篇
  2014年   28786篇
  2013年   88135篇
  2012年   35939篇
  2011年   48505篇
  2010年   42759篇
  2009年   50915篇
  2008年   45388篇
  2007年   42469篇
  2006年   45083篇
  2005年   39706篇
  2004年   41968篇
  2003年   41849篇
  2002年   40816篇
  2001年   38059篇
  2000年   36321篇
  1999年   35910篇
  1998年   51575篇
  1997年   42986篇
  1996年   37949篇
  1995年   32290篇
  1994年   30191篇
  1993年   29968篇
  1992年   26493篇
  1991年   23830篇
  1990年   23957篇
  1989年   23081篇
  1988年   21648篇
  1987年   19838篇
  1986年   19256篇
  1985年   22512篇
  1984年   22499篇
  1983年   20493篇
  1982年   19439篇
  1981年   19559篇
  1980年   18195篇
  1979年   18675篇
  1978年   17904篇
  1977年   18155篇
  1976年   20223篇
  1975年   16159篇
  1974年   15619篇
  1973年   15693篇
  1972年   13153篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
This paper presents part of the work ComEd and Quanta Technology have performed to quantify the locational and temporal value of DER to avoid distribution grid upgrade investments. It focuses on the formulation of a robust and efficient algorithm for DER optimal dispatch on a distribution feeder to mitigate the violation of current and voltage limits using the allocated cost of capacity and locational marginal value of real and reactive DER injection/withdrawal.  相似文献   
2.
3.
In this paper, we present a novel memory access reduction scheme (MARS) for two-dimension fast cosine transform (2-D FCT). It targets programmable DSPs with high memory-access latency. It reduces the number of memory accesses by: 1) reducing the number of weighting factors and 2) combining butterflies in vector-radix 2-D FCT pruning diagram from two stages to one stage with an efficient structure. Hardware platform based on general purpose processor is used to verify the effectiveness of the proposed method for vector-radix 2-D FCT pruning implementation. Experimental results validate the benefits of the proposed method with reduced memory access, less clock cycle and fewer memory space compared with the conventional implementation.  相似文献   
4.
5.
6.
One specific class of non-linear evolution equations, known as the Tzitzéica-type equations, has received great attention from a group of researchers involved in non-linear science. In this article, new exact solutions of the Tzitzéica-type equations arising in non-linear optics, including the Tzitzéica, Dodd–Bullough–Mikhailov and Tzitzéica–Dodd–Bullough equations, are obtained using the expa function method. The integration technique actually suggests a useful and reliable method to extract new exact solutions of a wide range of non-linear evolution equations.  相似文献   
7.
Clean Technologies and Environmental Policy - Food production and consumption is one of the major causes of global environmental degradation. One way to address environmental impacts in the food...  相似文献   
8.
ABSTRACT

Bacteriocin is a proteinaceous biomolecule produced by bacteria (both Gram-positive and Gram-negative) that exhibits antimicrobial activity against closely related species, and food-borne pathogens. It has recently gained importance and attracted the attention of several researchers looking to produce it from various substrates and bacterial strains. This ushers in a new era of food preservation where the use of bacteriocin in food products will be an alternative to chemical preservatives, and heat treatment which are understood to cause unwanted side effects, and reduce sensory and nutritional quality. However, this new market depends on the success of novel downstream separation schemes from various types of crude feedstocks which are both effective and economic. This review focuses on the downstream separation of bacteriocin from various sources using both conventional and novel techniques. Finally, recommendations for future interesting areas of research that need to be pursued are highlighted.  相似文献   
9.
10.
Abstract

Lung deposited surface area (LDSA) is a relatively new metric that has been argued to be more accurate at predicting health effects from aerosol exposure. For typical atmospheric aerosol, the LDSA concentration depends mainly on the concentration of ultrafine particles (e.g. vehicular exhaust emissions and residential wood combustion) and therefore optical methods cannot be used to measure and quantify it. The objective of this study was to investigate and describe typical characteristics of LDSA under different urban environments and evaluate how a diffusion charging-based Pegasor AQ Urban sensor (Pegasor Ltd., Finland) can be used as an alternative to optical sensors when assessing local combustion emissions and respective LDSA concentrations. Long-term (12?months) sensor measurements of LDSA were carried out at three distinctly different measurement sites (four sensor nodes) in the Helsinki metropolitan area, Finland. The sites were affected mainly by vehicular exhaust emission (street canyon and urban background stations) and by residential wood combustion (two detached housing area stations). The results showed that the accuracy of the AQ Urban was good (R2 = 0.90) for the measurement of LDSA when compared to differential mobility particle sizer. The mean concentrations of LDSA were more than twice as high at the street canyon (mean 22 µm2 cm?3) site when compared to the urban background site (mean 9.4 µm2 cm?3). In the detached housing area, the mean concentrations were 12 µm2 cm?3, and wood combustion typically caused high LDSA peaks in the evenings. High correlations and similar diurnal cycles were observed for the LDSA and black carbon at street canyon and urban background stations. The utilization of a small-scale sensor network (four nodes) showed that the cross-station variability in hourly LDSA concentrations was significant in every site, even within the same detached housing area (distance between the two sites ~670?m).  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