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   38276篇
  免费   959篇
  国内免费   70篇
电工技术   423篇
综合类   37篇
化学工业   7417篇
金属工艺   912篇
机械仪表   763篇
建筑科学   2028篇
矿业工程   255篇
能源动力   1133篇
轻工业   3112篇
水利工程   371篇
石油天然气   232篇
武器工业   2篇
无线电   2677篇
一般工业技术   5981篇
冶金工业   8450篇
原子能技术   397篇
自动化技术   5115篇
  2022年   217篇
  2021年   442篇
  2020年   372篇
  2019年   450篇
  2018年   535篇
  2017年   564篇
  2016年   569篇
  2015年   501篇
  2014年   809篇
  2013年   2329篇
  2012年   1323篇
  2011年   1752篇
  2010年   1295篇
  2009年   1371篇
  2008年   1598篇
  2007年   1613篇
  2006年   1388篇
  2005年   1295篇
  2004年   1160篇
  2003年   1130篇
  2002年   1173篇
  2001年   745篇
  2000年   722篇
  1999年   733篇
  1998年   1117篇
  1997年   851篇
  1996年   843篇
  1995年   679篇
  1994年   655篇
  1993年   668篇
  1992年   546篇
  1991年   395篇
  1990年   488篇
  1989年   487篇
  1988年   459篇
  1987年   469篇
  1986年   431篇
  1985年   570篇
  1984年   565篇
  1983年   495篇
  1982年   514篇
  1981年   498篇
  1980年   406篇
  1979年   421篇
  1978年   380篇
  1977年   394篇
  1976年   414篇
  1975年   345篇
  1974年   290篇
  1973年   320篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Many organisations suspect that their internal security threat is more pressing than their external security threat. The internal threat is predominantly the result of poor user security behaviour. Yet, despite that, security awareness programmes often seem more likely to put users to sleep than to improve their behaviour. This article discusses the influences that affect a user's security behaviour and outlines how a well structured approach focused on improving behaviour could be an excellent way to take security slack out of an organisation and to achieve a high return for a modest, low-risk investment.  相似文献   
82.
A meta-analytic review of group comparison design studies evaluating peer-assisted learning (PAL) interventions with elementary school students produced positive effect sizes (ESs) indicating increases in achievement (unweighted mean ES = 0.59, SD = 0.90; weighted ES, d = 0.33, p  相似文献   
83.
A combination of dynamic shear rheology, thermomechanical analysis (TMA), scanning electron microscopy (SEM), Near-Edge X-ray Absorption Fine Structure (NEXAFS), and fracture toughness testing was utilized to characterize the thermal, mechanical, chemical, and fracture properties of alumina (α-Al2O3)-filled epoxy resins as a function of average filler size, size distribution, particle shape, loading, and epoxy crosslink density. In general the cured properties of the filled composites were robust. Small changes in particle size, shape, and size distribution had little impact on the final properties. Resin crosslink density and filler loading were the most critical variables, causing changes in all properties. However, most applications could likely tolerate small changes in these variables also. SEM and NEXAFS characterization of the fracture surfaces revealed that the fracture occurs at the filler interface and the interfacial epoxy composition is similar to the bulk resin, indicating a weak epoxy-alumina interaction. These results are critical for implementation of particulate-filled polymer composites in practical applications because relaxed material specifications and handling procedures can be incorporated in production environments to improve efficiency.  相似文献   
84.
85.
Rogue Servers     
Rogue servers are a constant threat and pose a variety of problems for the IT security team. This article summarises the threats that come from not managing rogue servers and gives prevention and detection tips.  相似文献   
86.
The ears of lizards are highly directional. The directionality is generated by strong acoustical coupling of the eardrums. A simple lumped-parameter model of the ear followed by binaural comparisons has been shown to perform successful phonotaxis in robot implementations. However, such a model will produce localization errors in the form of response bias if the ears are asymmetrical. We have evaluated how large errors are generated by asymmetry using simulations of the ear model in Mathematica 5.2. The study shows that the effect of asymmetry is minimal around the most directional frequency of the ear, but that biases reduce the useful bandwidth of localization. This work was presented in part at the First European Workshop on Artificial Life and Robotics, Vienna, Austria, July 12–13, 2007  相似文献   
87.
88.
D-ribose, a naturally occurring pentose carbohydrate, has been shown to replenish high- energy phosphates following myocardial ischemia and high intensity, repetitive exercise. Human studies have mainly involved short-term assessment, including potential toxicity. Reports describing adverse effects of D-ribose with prolonged ingestion have been lacking. Therefore, this study assessed the toxicity of extended consumption of D-ribose in healthy adults. Nineteen subjects ingested 20 grams/Day (10 grams, twice a Day) of ribose with serial measurements of biochemical and hematological parameters at Days 0, 7, and 14. No significant toxic changes over the 14-day assessment period occurred in complete blood count, albumin, alkaline phosphatase, gamma glutamyltransferase, alanine amiotransferase, and aspartate aminotransferase. However, D-ribose did produce an asymptomatic, mild hypoglycemia of short duration. Uric acid levels increased at Day 7, but decreased to baseline values by Day 14. D-ribose consumption for 14 days appears not to produce significant toxic changes in both hematological and biochemical parameters in healthy human volunteers.  相似文献   
89.
Argues that children's failure on one of Piaget's best known tasks, conservation of solid quantity, reflects ignorance of physical properties rather than inadequate reasoning ability. The evidence for conservation itself, seen from the child's position, is analyzed. It is emphasized that children can learn and enjoy the concepts and methods of physics at much earlier ages than current orthodoxies would indicate. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
90.
In this paper a fuller and clear derivation of the weight vector theory of Coriolis mass flowmeters is given indicating its potential for the prediction of velocity profile effects in both the traditional kind of meter (vibrating tube) and the compact kind (vibrating element inside a duct).  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