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   1960660篇
  免费   49428篇
  国内免费   19682篇
电工技术   53237篇
技术理论   56篇
综合类   26852篇
化学工业   332768篇
金属工艺   83803篇
机械仪表   67864篇
建筑科学   74831篇
矿业工程   22997篇
能源动力   59665篇
轻工业   145772篇
水利工程   22193篇
石油天然气   60028篇
武器工业   2844篇
无线电   234228篇
一般工业技术   339904篇
冶金工业   248334篇
原子能技术   37630篇
自动化技术   216764篇
  2022年   19225篇
  2021年   28165篇
  2020年   21696篇
  2019年   22495篇
  2018年   27988篇
  2017年   28837篇
  2016年   32016篇
  2015年   29846篇
  2014年   44587篇
  2013年   106671篇
  2012年   59046篇
  2011年   76075篇
  2010年   64849篇
  2009年   71350篇
  2008年   67205篇
  2007年   64503篇
  2006年   65112篇
  2005年   58507篇
  2004年   54033篇
  2003年   52841篇
  2002年   50702篇
  2001年   47484篇
  2000年   45653篇
  1999年   47476篇
  1998年   74113篇
  1997年   58433篇
  1996年   49510篇
  1995年   40596篇
  1994年   36750篇
  1993年   35336篇
  1992年   29519篇
  1991年   26291篇
  1990年   26138篇
  1989年   24952篇
  1988年   23339篇
  1987年   21199篇
  1986年   20471篇
  1985年   23518篇
  1984年   23057篇
  1983年   20949篇
  1982年   19830篇
  1981年   20003篇
  1980年   18616篇
  1979年   18880篇
  1978年   18116篇
  1977年   18842篇
  1976年   21373篇
  1975年   16247篇
  1974年   15680篇
  1973年   15833篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
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.
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   
7.
The proliferating need for sustainability intervention in food grain transportation planning is anchoring the attention of researchers in the interests of stakeholders and environment at large. Uncertainty associated with food grain supply further intensifies the problem steering the need for designing robust, cost-efficient and sustainable models. In line with this, this paper aims to develop a robust and sustainable intermodal transportation model to facilitate single type of food grain commodity shipments while considering procurement uncertainty, greenhouse gas emissions, and intentional hub disruption. The problem is designed as a mixed integer non-linear robust optimisation model on a hub and spoke network for evaluating near optimal shipment quantity, route selection and hub location decisions. The robust optimisation approach considers minimisation of total relative regret associated with total cost subject to several real-time constraints. A version of Particle Swarm Optimisation with Differential Evolution is proposed to tackle the resulting NP-hard problem. The model is tested with two other state-of the art meta-heuristics for small, medium, and large datasets subject to different procurement scenarios inspired from real time food grain operations in Indian context. Finally, the solution is evaluated with respect to total cost, model and solution robustness for all instances.  相似文献   
8.
9.
10.
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