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   701940篇
  免费   18382篇
  国内免费   7059篇
电工技术   18593篇
技术理论   9篇
综合类   9169篇
化学工业   112360篇
金属工艺   30984篇
机械仪表   26815篇
建筑科学   22009篇
矿业工程   7834篇
能源动力   17879篇
轻工业   54974篇
水利工程   9621篇
石油天然气   22236篇
武器工业   1084篇
无线电   75269篇
一般工业技术   134888篇
冶金工业   102836篇
原子能技术   17227篇
自动化技术   63594篇
  2022年   8041篇
  2021年   11201篇
  2020年   8297篇
  2019年   8775篇
  2018年   13269篇
  2017年   13875篇
  2016年   13797篇
  2015年   11136篇
  2014年   16636篇
  2013年   33748篇
  2012年   24222篇
  2011年   30073篇
  2010年   24625篇
  2009年   26251篇
  2008年   26429篇
  2007年   25628篇
  2006年   22877篇
  2005年   20363篇
  2004年   18151篇
  2003年   17817篇
  2002年   17456篇
  2001年   16651篇
  2000年   15507篇
  1999年   14942篇
  1998年   29901篇
  1997年   21864篇
  1996年   17278篇
  1995年   13500篇
  1994年   12057篇
  1993年   11551篇
  1992年   9194篇
  1991年   8805篇
  1990年   8609篇
  1989年   8333篇
  1988年   7967篇
  1987年   7181篇
  1986年   6890篇
  1985年   7706篇
  1984年   6995篇
  1983年   6698篇
  1982年   6068篇
  1981年   6189篇
  1980年   5902篇
  1979年   6045篇
  1978年   5993篇
  1977年   6479篇
  1976年   8016篇
  1975年   5426篇
  1974年   5202篇
  1973年   5293篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Dysprosium-doped bismuth sodium titanate ceramics were prepared using the conventional mixed-oxide method. The amount of dysprosium used was varied from 0 to 2 at.%. The mixed powders were calcined at 800 °C and checked for phase purity using X-ray diffraction technique. The calcined powders were then cold-pressed into pellets and sintered at 1050 °C for the time ranging from 2 to 48 h. The ceramics were checked for phases and microstructures using an X-ray diffractometer and a scanning electron microscope, respectively. The analysis showed that undoped BNT ceramics sintered at longer time exhibited a significant grain growth with non-uniform grain size distribution and shape. The Dy-doped BNT however showed a much more limited grain growth behavior, resulting in smaller grain size and more equiaxed grain shape. It was also found that all Dy-doped BNT ceramics sintered at 48 h possessed lower porosity than those sintered for shorter time.  相似文献   
972.
A Ni catalyst was added to a cis-selective Pd catalyst in an attempt to further improve the Pd catalyst's cis-selectivity and activity for canola oil hydrogenation. The system was tested under reaction conditions known to be suitable for cis-selective hydrogenation with the Pd catalyst (50 ppm Pd, 70 °C, and 5.2 MPa). Although inactive on its own under these conditions, the addition of 100 ppm Ni increased the hydrogenation activity (from 2.12 to 2.49 10−2 min−1). Further addition of Ni up to 1000 ppm resulted in no further improvements in activity. The trans isomer contents of the oils hydrogenated with Pd and the Pd/Ni systems were similar. The level of conjugated dienes decreased rapidly during hydrogenation with both Pd alone and with the Pd/Ni combination and no changes in conjugation were detected in the presence of the Ni catalyst alone. The increased activity of the Pd/Ni system over Pd alone was attributed to adsorption of catalyst poisons from the oil by Ni.  相似文献   
973.
月桂醇聚氧乙烯醚硝酸酯助燃降污性能的研究   总被引:1,自引:1,他引:0  
通过柴油发动机台架试验证明 ,月桂醇聚氧乙烯醚硝酸酯用作柴油添加剂 ,既可提高柴油的燃烧性能 ,又可降低排放尾气中的一氧化碳 (CO)、未燃碳氢化合物 (HC)、氮氧化物 (NOx)含量及烟度等多种功能 ,是一种良好的多功能柴油助燃消烟添加剂。  相似文献   
974.
Filled fibrous sorbents modified with transition metal ferro- and ferricyanides capable to recover americium(III) and rare-earth metals(III) from nitric acid solutions were prepared. The most complete and rapid recovery is attained on complex-forming and cation-exchange sorbents (as filled fibrous materials) saturated with nickel ions. The sorbents are characterized by good kinetic properties and can be used for recovery of the above metals.  相似文献   
975.
At times, people keep their emotions from showing during social interactions. The authors' analysis suggests that such expressive suppression should disrupt communication and increase stress levels. To test this hypothesis, the authors conducted 2 studies in which unacquainted pairs of women discussed an upsetting topic. In Study 1, one member of each pair was randomly assigned to (a) suppress her emotional behavior, (b) respond naturally, or (c) cognitively reappraise in a way that reduced emotional responding. Suppression alone disrupted communication and magnified blood pressure responses in the suppressors' partners. In Study 2, suppression had a negative impact on the regulators' emotional experience and increased blood pressure in both regulators and their partners. Suppression also reduced rapport and inhibited relationship formation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
976.
This research reports age and gender differences in cardiac reactivity and subjective responses to the induction of autobiographical memories related to anger, fear, sadness, and happiness. Heart rate (HR) and subjective state were assessed at baseline and after the induction of each emotion in 113 individuals (61 men, 52 women; 66% European American, 34% African American) ranging in age from 15 to 88 years (M = 50.0; SD = 20.2). Cardiac reactivity was lower in older individuals; however, for anger and fear, these age effects were significantly more pronounced for the women than the men. There were no gender differences in subjective responses, however, suggesting that the lower cardiac reactivity found among older people is dependent on gender and the specific emotion assessed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
977.
This study evaluated relations among optimism, perceived stress management skills (PSMS), and positive mood in 46 men who had surgical treatment for localized prostate cancer. The authors found that optimism, PSMS, and positive mood scores were positively correlated. Positive mood was unrelated to demographic and disease-related control variables. In a hierarchical regression model controlling for PSMS, the relationship between optimism and positive mood became nonsignificant, whereas PSMS remained a correlate of positive mood. Results suggest that the relationship between optimism and positive mood may be mediated by belief in being able to use stress management techniques effectively. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
978.
A process of physical refining wheat germ oil using the technique of molecular distillation (MD) is presented in this work. Wheat germ oil was obtained from the germ by solvent extraction using hexane and also by cold pressing. The oil extracted with hexane was degummed and bleached before deacidification in order to modify the parameters of phosphorus and color. The goal in carrying out the stage of physical refining by MD was to preserve the maximum amount of original antioxidative potential obtained from extraction of the crude oil. The effect of evaporation temperature of one‐stage MD on the efficiency of free fatty acid elimination was studied. The antioxidant portion was followed by means of analytic determination of tocopherols by high‐performance liquid chromatography. Tocopherol retention up to 98% was achieved in the oil extracted by pressing, and yields of up to 96% were achieved in the oil extracted with hexane. Copyright © 2007 Society of Chemical Industry  相似文献   
979.
A range of refractories is presented for handling steel outside a furnace, which are produced by the Borovichi Refractories Corporation. The refractory characteristics and working features are given. Translated from Novye Ogneupory, No. 9, pp. 29–35, September, 2008.  相似文献   
980.
Production methods used to prepare graphite crucibles with high operating properties are considered: use as a filler of good graphitizing acicular coke, vibration molding of the original coke mix, use of production cycles for impregnation with medium temperature coal-tar pitch — firing, firing of compacted billets in metal containers, graphitization of fired billets in graphite cylinders. The last two production methods make it possible to reduce the temperature drop throughout the volume of a billet during heat treatment, and as a consequence to reduce crack development to a minimum as a result of reducing thermal stresses. All of the production methods recommended may be entirely accomplished in existing electrode plants and may be used to increase markedly the quality crucible graphite. It is possible to achieve a quality for these materials at the best world level. Translated from Novye Ogneupory, No. 8, pp. 28–33, August 2008.  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