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   1601956篇
  免费   27652篇
  国内免费   8007篇
电工技术   36420篇
综合类   8046篇
化学工业   282535篇
金属工艺   67079篇
机械仪表   47200篇
建筑科学   49395篇
矿业工程   12303篇
能源动力   51126篇
轻工业   125731篇
水利工程   16592篇
石油天然气   39101篇
武器工业   289篇
无线电   201848篇
一般工业技术   300067篇
冶金工业   185852篇
原子能技术   34830篇
自动化技术   179201篇
  2021年   17031篇
  2020年   13146篇
  2019年   15803篇
  2018年   20266篇
  2017年   20111篇
  2016年   24364篇
  2015年   19221篇
  2014年   30704篇
  2013年   90943篇
  2012年   40421篇
  2011年   55233篇
  2010年   47923篇
  2009年   55640篇
  2008年   50309篇
  2007年   48025篇
  2006年   47505篇
  2005年   42986篇
  2004年   43892篇
  2003年   43428篇
  2002年   42118篇
  2001年   38395篇
  2000年   36672篇
  1999年   35805篇
  1998年   51265篇
  1997年   43360篇
  1996年   37881篇
  1995年   32254篇
  1994年   29981篇
  1993年   29833篇
  1992年   26553篇
  1991年   23742篇
  1990年   24064篇
  1989年   23151篇
  1988年   21661篇
  1987年   19877篇
  1986年   19242篇
  1985年   22580篇
  1984年   22544篇
  1983年   20519篇
  1982年   19442篇
  1981年   19554篇
  1980年   18194篇
  1979年   18639篇
  1978年   17893篇
  1977年   18031篇
  1976年   19478篇
  1975年   16123篇
  1974年   15589篇
  1973年   15717篇
  1972年   13157篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
为研究织物组织结构与复合纱线线密度对织物凉爽性能的影响,将线密度为7.4和9.8 tex涤纶分别与线密度为7.8 tex锦纶反向加捻、并线后作为纬纱,以8.3 tex涤纶/竹浆纤维50/50混纺纱作经纱,设计平纹、二上一下斜纹和透孔组织织物.测试织物的瞬间接触凉感、热湿舒适性能及织物干、湿态升温曲线,并采用凉爽温度指数对织物的综合凉爽性能进行评价.研究结果表明:6种设计织物的瞬间接触凉感均高于标准,且平纹织物最好,纬纱粗细对瞬间接触凉感影响不显著;透孔织物透气性最好,且在人体出汗的状态下具有较好的导湿散热性能.平纹织物凉爽温度指数最高,最大凉爽温度为2.8℃,综合凉爽性能最好.  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.
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   
6.
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   
7.
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