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   10609篇
  免费   721篇
  国内免费   303篇
电工技术   355篇
综合类   380篇
化学工业   1557篇
金属工艺   519篇
机械仪表   614篇
建筑科学   497篇
矿业工程   169篇
能源动力   313篇
轻工业   457篇
水利工程   147篇
石油天然气   295篇
武器工业   30篇
无线电   1424篇
一般工业技术   1561篇
冶金工业   1959篇
原子能技术   92篇
自动化技术   1264篇
  2024年   33篇
  2023年   126篇
  2022年   221篇
  2021年   326篇
  2020年   263篇
  2019年   270篇
  2018年   261篇
  2017年   254篇
  2016年   255篇
  2015年   340篇
  2014年   406篇
  2013年   590篇
  2012年   546篇
  2011年   593篇
  2010年   491篇
  2009年   515篇
  2008年   459篇
  2007年   456篇
  2006年   414篇
  2005年   397篇
  2004年   271篇
  2003年   269篇
  2002年   258篇
  2001年   249篇
  2000年   211篇
  1999年   285篇
  1998年   604篇
  1997年   411篇
  1996年   312篇
  1995年   210篇
  1994年   197篇
  1993年   171篇
  1992年   101篇
  1991年   101篇
  1990年   70篇
  1989年   86篇
  1988年   82篇
  1987年   54篇
  1986年   58篇
  1985年   51篇
  1984年   29篇
  1983年   21篇
  1982年   37篇
  1981年   32篇
  1980年   25篇
  1979年   14篇
  1977年   48篇
  1976年   71篇
  1974年   19篇
  1973年   14篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
The authors examined cultural and individual differences in the relation between daily events and daily satisfaction. In a preliminary study, they established cross-cultural equivalence of 50 daily events. In the main study, participants in the United States, Korea, and Japan completed daily surveys on the 50 events and daily satisfaction for 21 days. The multilevel random coefficient model analyses showed that (a) the within-person association between positive events and daily satisfaction was significantly stronger among Asian American, Korean, and Japanese participants than among European American participants and (b) the within-person association between positive events and daily satisfaction was significantly weaker among individuals high in global life satisfaction than among those low in global life satisfaction. The findings demonstrate a weaker effect of positive events on daily well-being among individuals and cultures high in global well-being. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
72.
73.
74.
Wet etch rates at 25°C for Zn0.9Mg0.1O grown on sapphire substrates by pulsed laser deposition (PLD) were in the range 300–1100 nm · min−1 with HCl/H2O (5×10−3−2×10−2 M) and 120–300 nm · min−1 with H3PO4/H2O (5×10−3−2×10−2 M). Both of these dilute mixtures exhibited diffusion-limited etching, with thermal activation energies of 2–3 kCal · mol−1. By sharp contrast, the etch rates for ZnO also grown on sapphire by PLD were much slower in similar solutions, with rates of 1.2–50 nm · min−1 in HCl/H2O (0.01–1.2 M) and 12–54 nm · min−1 in H3PO4/H2O (0.02–0.15 M). The etching was reaction limited over the temperature range 25–75°C, with activation energies close to 6 kCal · mol−1. The resulting selectivity of Zn0.9Mg0.1O over ZnO can be a high as ∼400 with HCl and ∼30 with H3PO4.  相似文献   
75.
In this letter, we report on the electrical characteristic and the comparison of the metal-insulator-metal (MIM) capacitors with PECVD silicon nitride (SiN) and silicon oxynitride (SiON). Both capacitors are found to exhibit low leakage and high breakdown field strength, as well as absence of dispersive behavior, good linearity, and comparable quality factor behaviors.  相似文献   
76.
在线近红外光谱分析仪可以实时测定汽油调合组分及成品油的多种物化性质指标如烯烃、芳烃、苯及氧化物含量、辛烷值(RON、MON)、馏程、蒸气压等。文章介绍了用于汽油自动调舍工艺中的在线近红外光谱分析仪的原理、系统组成和特点,以及在国内外的汽油调合优化控制中的实际应用情况。典型的应用实例表明,将该分析仪用于汽油自动调合工艺中,可为炼油厂带来可观的经济效益和社会效益。  相似文献   
77.
Process technology of high-speed implant-apertured index-guide lateral-current-injection top dielectric-mirror quantum-well 850-nm vertical cavity surface-emitting lasers (VCSELs) has been developed. Oxygen and helium implantation for aperture definition and extrinsic capacitance reduction, dielectric mirror formation, p- and n-ohmic contact formation, VCSEL resistance, and thermal analysis were investigated. Employing this technology, GaAs/AlGaAs-based 850-nm VCSELs with small signal modulation bandwidths up to 11.5 Gb/s and an eye diagram generated at 12 Gb/s by a pseudorandom bit sequence of 2/sup 31/-1 were achieved. The bit-error rates were below 10/sup -13/. The threshold current is as low as 0.8 mA for 7-/spl mu/m-diameter current apertures and typical slope efficiencies of 0.45-0.5 mA/mW were obtained.  相似文献   
78.
79.
80.
Access path deployment is a critical issue in physical database design. Access paths typically include a clustered index as the primary access path and a set of secondary indexes as auxiliary access paths. To deploy the right access paths requires an effective algorithm and accurate estimation of the parameters used by the algorithm. One parameter central to any index-selection algorithm is the block selectivity of a query. Existing methods for estimating block selectivities are limited by restrictive assumptions. Furthermore, most existing methods produce estimates useful for aiding the selection of secondary indexes only. Little research has been done in the area of estimating block selectivities for supporting the selection of the clustered index. The paper presents a set of methods that do not depend on any specific assumption, produce accurate estimates, and can be used to aid in selecting the clustered index as well as secondary indexes  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