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   95503篇
  免费   9519篇
  国内免费   6086篇
电工技术   7721篇
技术理论   2篇
综合类   8186篇
化学工业   13494篇
金属工艺   5930篇
机械仪表   6530篇
建筑科学   8244篇
矿业工程   3047篇
能源动力   2772篇
轻工业   7686篇
水利工程   2343篇
石油天然气   4738篇
武器工业   1129篇
无线电   10941篇
一般工业技术   9585篇
冶金工业   3926篇
原子能技术   1141篇
自动化技术   13693篇
  2024年   461篇
  2023年   1453篇
  2022年   2924篇
  2021年   3872篇
  2020年   3012篇
  2019年   2366篇
  2018年   2678篇
  2017年   3015篇
  2016年   2709篇
  2015年   3944篇
  2014年   5140篇
  2013年   5643篇
  2012年   6664篇
  2011年   7057篇
  2010年   6536篇
  2009年   6399篇
  2008年   6396篇
  2007年   6020篇
  2006年   5843篇
  2005年   4746篇
  2004年   3672篇
  2003年   3452篇
  2002年   4159篇
  2001年   3493篇
  2000年   2273篇
  1999年   1727篇
  1998年   1042篇
  1997年   890篇
  1996年   761篇
  1995年   660篇
  1994年   562篇
  1993年   366篇
  1992年   290篇
  1991年   213篇
  1990年   151篇
  1989年   126篇
  1988年   98篇
  1987年   72篇
  1986年   54篇
  1985年   19篇
  1984年   24篇
  1983年   17篇
  1982年   23篇
  1981年   22篇
  1980年   13篇
  1979年   13篇
  1978年   2篇
  1966年   1篇
  1959年   19篇
  1951年   16篇
排序方式: 共有10000条查询结果,搜索用时 1 毫秒
1.
Many cables containing 1.3-/spl mu/m zero-dispersion single-mode (SM) optical fibers are installed in trunk and access networks. Recently, there have been a number of studies on wavelength-division-multiplexing (WDM) systems designed to increase transmission capacity and flexibility. If we can construct WDM systems using SM optical-fiber cable networks designed to transmit using wavelengths in the 1.3-/spl mu/m window (O-band), this will prove very effective in reducing construction costs. It is therefore important to examine the wavelength dependence of the transmission characteristics of SM optical-fiber cables and networks that have already been installed and in which several optical fibers are joined. In this paper, we describe the measured optical characteristics of SM optical-fiber cables and installed optical-fiber cable networks at various wavelengths. The optical characteristics were stable in the 1.46 to 1.625-/spl mu/m wavelength range and we confirmed that the installed SM optical-fiber cable networks could be used for WDM system applications.  相似文献   
2.
In this paper, we propose a new approach, appearance-guided particle filtering (AGPF), for high degree-of-freedom visual tracking from an image sequence. This method adopts some known attractors in the state space and integrates both appearance and motion-transition information for visual tracking. A probability propagation model based on these two types of information is derived from a Bayesian formulation, and a particle filtering framework is developed to realize it. Experimental results demonstrate that the proposed method is effective for high degree-of-freedom visual tracking problems, such as articulated hand tracking and lip-contour tracking.  相似文献   
3.
4.
5.
A novel reversible addition-fragmentation chain transfer (RAFT) reagent bearing triphenylamine (TPA) group, 4-diphenylamino-dithiobenzoic acid benzyl ester (DDABE), was designed and synthesized. It was used in the RAFT polymerizations of styrene (St) and methyl acrylate (MA) to prepare end-functionalized polymers. The results of the polymerization showed that the RAFT polymerizations could be well controlled using DDABE as the RAFT agent. Number-average molecular weight (Mn,GPC) increased linearly with monomer conversion, and molecular weight distributions were relatively narrow (PDI< 1.50). The results of chain-extension reaction, 1H NMR spectra and UV/Vis spectra confirmed that most of the polymers chains were end-capped by the functional triphenylamine (TPA) groups. The effect of feed molar ratios of St/DDABE/AIBN on polymerization was investigated.  相似文献   
6.
基于MoCA标准的家庭网络研究   总被引:1,自引:0,他引:1  
本文描述了一种基于MOCA标准的家庭网络,并对该网络及设备进行了基本性能的测试.本文首先介绍了家庭网络的发展现状,对目前的各种家庭网络标准进行了比较.在此基础上详细描述了基于MOCA标准的家庭网络,并对该网络的设计,实现、网络性能进行了详述.然后对该网络进行了测试并得出了相关的测试结论.最后指出该网络的不足及改进之处.  相似文献   
7.
8.
针对目前爆轰试验中使用的机械密封射频连接器存在的问题.设计了基于玻璃封接技术的新型密封射频连接器结构,并进行了射频反射补偿计算和强度分析.本项研究为爆轰条件下新型密封射频连接器的研制提供了设计依据.  相似文献   
9.
OBJECTIVE: To determine if a relationship exists between the extent of iron-catalyzed injury and the degree of tissue iron overload during reperfusion. METHODS: To selectively increase tissue iron only during early reperfusion, isolated, buffer perfused rabbit hearts were exposed to 20 microM Fe(2+)-100 microM ADP during the last 3 minutes of ischemia and the initial 4 minutes of reperfusion. Control groups were exposed to ADP and iron-ADP regimens that did not increase intracellular iron. All the hearts received 30 minutes of normothermic global ischemia and 30 minutes of reperfusion. Heart function was monitored continuously throughout each experiment. Tissue iron and biochemical markers were analyzed at the end of experiments. RESULTS: Hemodynamic recovery was decreased and tissue lipid peroxide levels were increased in the 20 microM Fe(2+)-100 microM ADP group compared to controls. The recoveries of developed pressure and positive/negative dP/dT at 30 minutes of reperfusion were negatively correlated with tissue iron levels, while cytosol and membrane lipid peroxide levels correlated positively with the iron levels during reperfusion. CONCLUSION: The extent of oxidative injury during reperfusion was directly related to the tissue iron burden present during reperfusion. Increased lipid peroxidation was the principal chemical marker of iron-catalyzed injury.  相似文献   
10.
This study focuses on the visualization of a series of large earthquake simulations collectively called TeraShake. The simulation series aims to assess the impact of San Andreas Fault earthquake scenarios in Southern California. We discuss the role of visualization in gaining scientific insight and aiding unexpected discoveries.  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