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   4767篇
  免费   674篇
  国内免费   285篇
电工技术   467篇
综合类   251篇
化学工业   815篇
金属工艺   304篇
机械仪表   305篇
建筑科学   392篇
矿业工程   31篇
能源动力   342篇
轻工业   544篇
水利工程   49篇
石油天然气   37篇
武器工业   13篇
无线电   501篇
一般工业技术   683篇
冶金工业   68篇
原子能技术   26篇
自动化技术   898篇
  2025年   35篇
  2024年   175篇
  2023年   204篇
  2022年   270篇
  2021年   218篇
  2020年   270篇
  2019年   240篇
  2018年   143篇
  2017年   165篇
  2016年   145篇
  2015年   154篇
  2014年   227篇
  2013年   263篇
  2012年   400篇
  2011年   394篇
  2010年   328篇
  2009年   391篇
  2008年   216篇
  2007年   383篇
  2006年   302篇
  2005年   146篇
  2004年   64篇
  2003年   40篇
  2002年   62篇
  2001年   39篇
  2000年   89篇
  1999年   72篇
  1998年   72篇
  1997年   38篇
  1996年   30篇
  1995年   19篇
  1994年   13篇
  1993年   7篇
  1992年   5篇
  1991年   6篇
  1989年   5篇
  1988年   10篇
  1987年   18篇
  1986年   18篇
  1985年   4篇
  1980年   6篇
  1979年   3篇
  1974年   2篇
  1972年   3篇
  1971年   3篇
  1967年   2篇
  1963年   4篇
  1962年   3篇
  1961年   3篇
  1960年   2篇
排序方式: 共有5726条查询结果,搜索用时 0 毫秒
1.
2.
Intense near-infrared emission at 1 μm has been obtained in ZnO-SiO2:Yb3+ composites via a facile sol-gel method upon broadband ultraviolet light excitation. Systematic optical measurements including static and time-resolved photoluminescence have been performed to elucidate the energy transfer from ZnO quantum dots to Yb3+ ions. The dependence of energy transfer efficiency on Yb3+ concentration has been investigated in detail. Codoping with Li+ ions leads to about twice enhancement of the near-infrared luminescence intensity around 1 μm at room temperature. The enhancement in the luminescence intensity could be mostly attributed to the modification of the local symmetry around Yb3+ ions by codoping with Li+ ions.  相似文献   
3.
Preparation of ultra fine nickel-copper bimetallic powder for BME-MLCC   总被引:1,自引:0,他引:1  
The preparation of ultra fine nickel-copper bimetallic powder with two-stage chemical reduction method was investigated. Reductive sugar and hydrazine hydrate were employed as reducing agent in different reductive stage, respectively. Reaction of CuSO4·5H2O with reductive sugar at 70 °C gives cuprous oxide and copper particles, then as-prepared mixture and nickelous hydroxide were reduced by hydrazine hydrate, and nickel-copper powder having excellent dispersibility was prepared. Influences of nickel added on composition and dispersibility of powder were studied. TG/DTG/DTA of nickel-copper powder, which is stable in room temperature, were discussed with thermal analyzer. Relation of nickel content to oxidation temperature was investigated. Ni-Cu bimetallic powder particles have a fully coated structure when nickel content is up to 30%. As-prepared nickel-copper powder was applied in base metal electrode-multilayer ceramic capacitor (BME-MLCC). The end termination has high adhesion force, fairly good densification, low resistivity, excellent solderibility behavior and resistance behavior to soldering.  相似文献   
4.
(NixZn0.825—xCu0.170Co0.005)Fe1.90O3.85铁氧体的电磁性能   总被引:1,自引:0,他引:1  
采用配方式(NixZn0.825-xCu0.170Co0.005)Fe1.90O3.85(简称NiCuZn铁氧体)在较宽的组成范围内(x=0.295~0.750)研究了NiCuZn铁氧体的电磁性能,发现NiCuZn铁氧体的μ,Q以及温度特性随Ni含量x的变化与NiZn铁氧体有很大不同,并对产生这种现象的原因进行了初步探讨。  相似文献   
5.
网络教学在“微波技术与天线”课程的应用   总被引:4,自引:1,他引:4  
网络教学利用互联网上丰富的教学资源作为教学媒体和教学环境来组织教学活动,使学生成为学习的主体。本文针对“微波技术与天线”课程的特点,指出了传统课程教学方法面临的问题,提出了利用网络教学平台建立网络课程、应用现代信息技术开展“微波与天线”课程网络教学的措施,并讨论了实施网络教学应面对的一些问题。  相似文献   
6.
Circular recesses have been fabricated on indium tin oxide (ITO) anodes to enhance light extraction of organic light-emitting diodes (OLEDs). The effects of recess depth and recess coverage ratio on the performance of a green OLED were systematically investigated. Results showed that the current efficiency could be enhanced from 40.7 cd/A of a planar device to 47.2 cd/A of the device with a recess depth of 100 nm and a recess coverage ratio of 14.1%. The enhanced light extraction by the recess wall effect was realized to be the major factor leading to the improved efficiency. The efficiency is however limited by the accompanying increase in electrical resistivity of the ITO films at deep recesses and high recess coverage ratios. Despite of the insignificant efficiency enhancement (up to 16%) in this study, this recessed ITO approach provides a simple architecture to enhance waveguide mode light extraction without adding an internal medium.  相似文献   
7.
Neighbourhood preserving based semi-supervised dimensionality reduction   总被引:1,自引:0,他引:1  
Wei  J. Peng  H. 《Electronics letters》2008,44(20):1190-1191
A semi-supervised linear dimensionality reduction method based on side information and neighbourhood preserving is proposed. In this problem, only must-link constraints (pairs of instances belong to the same class) and cannot-link constraints (pairs of instances belong to different classes) are given. The proposed neighbourhood preserving based semi-supervised dimensionality reduction algorithm can not only preserve the must-link and cannot-link constraints but can preserve the local structure of the input data in the low dimensional embedding subspace. Experimental results on several datasets demonstrate the effectiveness of the method.  相似文献   
8.
In this study we demonstrate an easy solution-processed highly efficient deep-blue polymer light-emitting diode (PLED) via a simple one-step coating of self-assembly hole injection/transport nanocomposites to achieve both a finer hole ohmic contact and an increased light outcoupling, which is the first time report about both the optical and electrical optimization without necessitating changes in the design or structure of the wide bandgap deep-blue PLEDs themselves. The contact angle and surface energy measurement results demonstrate that triazine-based hole injection molecules can vertically migrate towards the bottom PEDOT:PSS layer to obtain a stable minimum of free energy, resulting in an optimal top-to-bottom HOMO energy level arrangement and an improved hole mobility in deep-blue PLEDs. The random surface nanostructure was formed on top of the hole bilayer, leading to the enhancement of light outcoupling verified by transmittance, transmittance haze and light extraction efficiency. Furthermore, in order to explore the reasons of the hole light scattering formation process, a transient drying monitoring technique is applied to track the drying process of the nanostructure films, revealing this approach effectiveness by easily modifying mixing ratios for obtaining different light outcoupling abilities.  相似文献   
9.
为满足传输数据的高速低功耗的要求,文章设计了一种半速率时钟驱动的二级多路选择开关式的10:1并串转换器。第一级为两个5:1的并行串化器,共用一个多相发生器。多相发生器由五个动态D触发器构成。第二级为一个2:1的并行串化器。采用半速率时钟、多路选择开关结构降低了大部分电路的工作频率,降低了工艺要求,也降低了功耗。通过调整时钟与数据间的相位关系,提高相位裕度,降低了数据抖动。采用1.8V 0.18μm CMOS工艺进行设计。用Hspice仿真器在各种PVT情况下做了仿真,结果表明该转换器在输出4Gbps数据时平均功耗为395μW,抖动18s^-1.  相似文献   
10.
冷冻储存对鸡蛋理化性质及微观结构的影响   总被引:2,自引:0,他引:2  
本文通过测定pH、粘度、回弹高度和结构的变化,表征了置于-20 ℃下,储存不同的时间的新鲜鸡蛋的全蛋、蛋清、蛋黄、熟蛋及熟蛋黄的性质变化。实验结果表明:在-20 ℃下,新鲜鸡蛋随储存时间的增加,煮熟的全蛋回弹高度变小,熟蛋黄的回弹高度增大,从5 h到36 h,熟蛋黄的回弹高度从提高了2倍到4倍;蛋黄、蛋清和全蛋的pH值和粘度均发生了明显的变化,且pH的变化在储存10 h后更为显著;储存10 h的蛋清、蛋黄结构开始发生变化,蛋黄在冷冻24 h后质地变得较为平滑、紧密,可清楚表现为形成凝胶,到冷冻36 h后达到不可逆的变化。因此:在-20 ℃下,储存10 h,新鲜鸡蛋的品质已经由合格品下降为不合格的次品。  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