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   616721篇
  免费   7403篇
  国内免费   1715篇
电工技术   10961篇
综合类   1026篇
化学工业   92330篇
金属工艺   27715篇
机械仪表   20854篇
建筑科学   12536篇
矿业工程   5352篇
能源动力   14725篇
轻工业   37549篇
水利工程   7776篇
石油天然气   16977篇
武器工业   40篇
无线电   64300篇
一般工业技术   130345篇
冶金工业   114873篇
原子能技术   16594篇
自动化技术   51886篇
  2021年   5706篇
  2020年   4335篇
  2019年   5527篇
  2018年   10394篇
  2017年   10744篇
  2016年   11739篇
  2015年   7070篇
  2014年   11029篇
  2013年   27359篇
  2012年   18183篇
  2011年   23625篇
  2010年   17760篇
  2009年   19978篇
  2008年   20289篇
  2007年   19884篇
  2006年   17298篇
  2005年   18719篇
  2004年   17176篇
  2003年   16330篇
  2002年   14246篇
  2001年   13948篇
  2000年   12881篇
  1999年   13077篇
  1998年   34252篇
  1997年   23874篇
  1996年   18086篇
  1995年   13373篇
  1994年   11730篇
  1993年   11889篇
  1992年   8566篇
  1991年   8280篇
  1990年   8362篇
  1989年   7911篇
  1988年   7598篇
  1987年   6925篇
  1986年   6672篇
  1985年   7360篇
  1984年   6837篇
  1983年   6321篇
  1982年   5906篇
  1981年   6063篇
  1980年   5815篇
  1979年   5826篇
  1978年   5965篇
  1977年   6882篇
  1976年   8963篇
  1975年   5294篇
  1974年   5147篇
  1973年   5250篇
  1972年   4584篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
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   
2.
3.
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.
7.
8.
9.
10.

Stability constants and formation enthalpies of supramolecular complexes of crown ethers and their cyclic and acyclic analogues are determined on the basis of experimental data obtained by different physicochemical methods in the terms of a general approach developed and implemented in the ChemEqui software package. The established regularities of variation of stability of complexes are discussed as dependent on the ligand structure, nature of the cation, solvent, and anion. The applicability of the suggested method of determining complexation selectivity is shown for multicomponent equilibria in solutions.

  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