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   290290篇
  免费   6462篇
  国内免费   2889篇
电工技术   6860篇
技术理论   7篇
综合类   2864篇
化学工业   47123篇
金属工艺   12784篇
机械仪表   9707篇
建筑科学   8934篇
矿业工程   2658篇
能源动力   6362篇
轻工业   27472篇
水利工程   3414篇
石油天然气   8049篇
武器工业   456篇
无线电   30925篇
一般工业技术   52711篇
冶金工业   48741篇
原子能技术   5956篇
自动化技术   24618篇
  2022年   2356篇
  2021年   3708篇
  2020年   2687篇
  2019年   2891篇
  2018年   4325篇
  2017年   4306篇
  2016年   4588篇
  2015年   3917篇
  2014年   5995篇
  2013年   13087篇
  2012年   9518篇
  2011年   12055篇
  2010年   9795篇
  2009年   10314篇
  2008年   10997篇
  2007年   11101篇
  2006年   10053篇
  2005年   8723篇
  2004年   7513篇
  2003年   7015篇
  2002年   6933篇
  2001年   6922篇
  2000年   6562篇
  1999年   6665篇
  1998年   13513篇
  1997年   10136篇
  1996年   7821篇
  1995年   5967篇
  1994年   5428篇
  1993年   5201篇
  1992年   4137篇
  1991年   3905篇
  1990年   3938篇
  1989年   3869篇
  1988年   3608篇
  1987年   3070篇
  1986年   3097篇
  1985年   3432篇
  1984年   3344篇
  1983年   3090篇
  1982年   2715篇
  1981年   2913篇
  1980年   2650篇
  1979年   2840篇
  1978年   2736篇
  1977年   2841篇
  1976年   3693篇
  1975年   2457篇
  1974年   2290篇
  1973年   2320篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
Tested the ability of 4 adult male Sprague-Dawley rats to use odors in discrimination among littermates living as a group. Ss were trained in a Y-maze to discriminate the presence of a littermate from its absence. Results from transfer of training in 3 subsequent testing periods indicated that the animals were capable of distinguishing among individuals when relatedness and familiarity were held constant, that this ability was not due to training, and that performance was based solely on odor cues. Results suggest that laboratory rats exhibit odor sensitivities conmensurate with very complex social processes. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
152.
The composition of the Co-Cr-Mo alloy has been modified by additions of nickel and some trace elements aluminium, titanium and boron. In this paper, the first part of the present study, the effects of alloy additions on the microstructures and tensile properties of the as-cast Co-Cr-Mo alloy are discussed. The effects of alloy additions on the fatigue behaviour of the alloy will be discussed in the second part of the present study. It is found that alloy additions do not seem to result in changes in the nature of the casting structure. A directional, coarse dendritic cast structure is produced in the modified alloys as in the base alloY. However, the alloy additions affect the carbide precipitations and the formation of some fine details of the microstructure such as dislocations, stacking faults and twins produced during the solidification. A considerable improvement in the transient mechanical properties, especially in the tensile ductility, is achieved by modifying the base alloy with alloy additions.  相似文献   
153.
154.
155.
156.
The effect on mechanical behavior of ZrO2 additions to a dental porcelain was investigated. The ZrO2 was introduced into the glassy matrix phase of the porcelain by refritting the all-glass porcelain constituent. X-ray diffraction indicated that a sizeable fraction of the ZrO2 was retained in the tetragonal form after the porcelain was fired. Zirconia additions to the porcelain produced substantial improvements in fracture toughness, strength, and thermal shock resistance.  相似文献   
157.
Indoor body-area channel model for narrowband communications   总被引:1,自引:0,他引:1  
Using wireless sensors placed on a person to continuously monitor health information is a promising new application. At the same time, new low-power wireless standards such as Bluetooth and Zigbee have been proposed for short range, low data-rate communication matching the requirements of these bio-medical applications. However, there are currently few measurements or models describing propagation around the body. To address this problem, electromagnetic waves near the torso are measured and a statistical model is derived for communication in the 915 MHz and 2.45 GHz industrial, scientific and medical bands associated with Zigbee and Bluetooth. Measurement setup and statistical analysis are described.  相似文献   
158.
The structure of the recently introduced Brazilian government programme for monitoring pesticide residues in six major agricultural products is described. Residues found from the analysis of samples of tomatoes and strawberries are discussed in detail. The much greater frequency of detection of pesticide residues, many of which are not approved for use in Brazil, in produce being sold on the domestic market, as opposed to that produced for export, is of major concern. It is perceived that this new monitoring programme will become permanent and be used to underpin enforcement actions that will need to be taken to reduce the numbers of incidents of illegal residues occurring, particularly in fresh fruits and vegetables.  相似文献   
159.
160.
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