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   1495159篇
  免费   27587篇
  国内免费   7077篇
电工技术   34593篇
综合类   6394篇
化学工业   266424篇
金属工艺   64927篇
机械仪表   42910篇
建筑科学   45529篇
矿业工程   11557篇
能源动力   50299篇
轻工业   109779篇
水利工程   15143篇
石油天然气   37965篇
武器工业   143篇
无线电   197029篇
一般工业技术   283592篇
冶金工业   160543篇
原子能技术   34146篇
自动化技术   168850篇
  2021年   15495篇
  2020年   11886篇
  2019年   14648篇
  2018年   16537篇
  2017年   15988篇
  2016年   21646篇
  2015年   17396篇
  2014年   28671篇
  2013年   87825篇
  2012年   35350篇
  2011年   48228篇
  2010年   43097篇
  2009年   51589篇
  2008年   44876篇
  2007年   42305篇
  2006年   44264篇
  2005年   39609篇
  2004年   41387篇
  2003年   41190篇
  2002年   40221篇
  2001年   36814篇
  2000年   35367篇
  1999年   34481篇
  1998年   44258篇
  1997年   38613篇
  1996年   34937篇
  1995年   30466篇
  1994年   28529篇
  1993年   28461篇
  1992年   25977篇
  1991年   23112篇
  1990年   23468篇
  1989年   22538篇
  1988年   21036篇
  1987年   19386篇
  1986年   18660篇
  1985年   22014篇
  1984年   22255篇
  1983年   20204篇
  1982年   18904篇
  1981年   18986篇
  1980年   17661篇
  1979年   18203篇
  1978年   17476篇
  1977年   17210篇
  1976年   17968篇
  1975年   15792篇
  1974年   15319篇
  1973年   15408篇
  1972年   12969篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Journal of Materials Science - For transformers and inductors to meet the world’s growing demand for electrical power, more efficient soft magnetic materials with high saturation magnetic...  相似文献   
142.
Mobile Networks and Applications - 5G/6G communication are first generation high speed wireless communication network which integrates the aerial data, terrestrial data and maritime data via...  相似文献   
143.
144.
Theoretical Foundations of Chemical Engineering - The effect of the electrolyte composition, mass-transfer conditions, pore diameter, interpore distance, and electric parameters on the formation of...  相似文献   
145.
Fluoro-substituted and heteroaromatic compounds are valuable intermediates for a variety of applications in pharma- and agrochemistry and synthetic chemistry. This study investigates the chemoenzymatic preparation of chiral alcohols bearing a heteroaromatic ring with an increasing degree of fluorination in α-position. Starting from readily available picoline derivatives prochiral α-halogenated acyl moieties were introduced with excellent selectivity and 64–95 % yield. The formed carbonyl group was subsequently reduced to the corresponding alcohols using the alcohol dehydrogenase from Lactobacillus kefir, yielding an enantiomeric excess of 95–>99 % and up to 98 % yield.  相似文献   
146.
Journal of Inorganic and Organometallic Polymers and Materials - This paper reports the performance of alizarin based SnO2 dye-sensitized solar cells. A novel template assisted method has been...  相似文献   
147.
Applied Composite Materials - Determining the impact behavior of adhesive joints allows the designing of high-strength joints. Therefore, the dynamic behavior of adhesive joints has recently become...  相似文献   
148.
149.
In flash sintering experiments, the thermal history of the sample is key to understanding the mechanisms underlying densification rate and final properties. By combining robust temperature measurements with current-ramp-rate control, this study examined the effects of the thermal profile on the flash sintering of yttria-stabilized zirconia, with experiments ranging from a few seconds to several hours. The final density was maximized at slower heating rates, although processes slower than a certain threshold led to grain growth. The amount of grain growth observed was comparable to a similar conventional thermal process. The bulk electrical conductivity correlated with the maximum temperature and cooling rate. The only property that exhibited behavior that could not be attributed to solely the thermal profile was the grain boundary conductivity, which was consistently higher than conventional in flash sintered samples. These results suggest that, during flash sintering, athermal electric field effects are relegated to the grain boundary.  相似文献   
150.
The main drawback of bioglasses is their restricted use in load bearing applications and the consequent need to develop stronger glassy materials. This has led to the consideration of oxynitride glasses for numerous biomedical applications. This paper investigated two different types of glasses at a constant cationic ratio, with and without nitrogen (a N containing and a N-free glass composition) to better understand the effect of N on the biological properties of glasses. The results revealed that the addition of N increased the glass transition temperature, isoelectric point (IEP) and slightly increased wettability. Moreover, compared to N including glass, N-free glass exhibited better anti-bacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), two key bacteria that infect implants. In summary, these in vitro results indicated that amine functional groups existing in N containing glasses which are missing in N-free glasses, caused a slight difference in wetting behavior and a more obvious change in isoelectric point and in bacterial response. N-free glasses exhibited better inhibitory results both against E. coli and S. aureus compared to N including glass suggesting that oxygen rich glasses should be further studied for their novel antibacterial properties.  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