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   1478013篇
  免费   27247篇
  国内免费   6949篇
电工技术   34296篇
综合类   6508篇
化学工业   269116篇
金属工艺   63770篇
机械仪表   41985篇
建筑科学   45580篇
矿业工程   11419篇
能源动力   50178篇
轻工业   110061篇
水利工程   14770篇
石油天然气   37512篇
武器工业   186篇
无线电   195807篇
一般工业技术   280321篇
冶金工业   148512篇
原子能技术   33889篇
自动化技术   168299篇
  2021年   15448篇
  2020年   11796篇
  2019年   14552篇
  2018年   15358篇
  2017年   14689篇
  2016年   21037篇
  2015年   17276篇
  2014年   28617篇
  2013年   87631篇
  2012年   34717篇
  2011年   46797篇
  2010年   41919篇
  2009年   50381篇
  2008年   43838篇
  2007年   40838篇
  2006年   44211篇
  2005年   38758篇
  2004年   40998篇
  2003年   40995篇
  2002年   40090篇
  2001年   36854篇
  2000年   35366篇
  1999年   34136篇
  1998年   40168篇
  1997年   36341篇
  1996年   33486篇
  1995年   29703篇
  1994年   28007篇
  1993年   27846篇
  1992年   26072篇
  1991年   23108篇
  1990年   23415篇
  1989年   22428篇
  1988年   20972篇
  1987年   19309篇
  1986年   18694篇
  1985年   21999篇
  1984年   22287篇
  1983年   20252篇
  1982年   19202篇
  1981年   19278篇
  1980年   17855篇
  1979年   18484篇
  1978年   17700篇
  1977年   17203篇
  1976年   17775篇
  1975年   15970篇
  1974年   15541篇
  1973年   15593篇
  1972年   13042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