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   1476001篇
  免费   27233篇
  国内免费   6946篇
电工技术   34288篇
综合类   6507篇
化学工业   267856篇
金属工艺   63761篇
机械仪表   41974篇
建筑科学   45545篇
矿业工程   11414篇
能源动力   50172篇
轻工业   109954篇
水利工程   14769篇
石油天然气   37509篇
武器工业   186篇
无线电   195730篇
一般工业技术   280161篇
冶金工业   148284篇
原子能技术   33887篇
自动化技术   168183篇
  2021年   15432篇
  2020年   11785篇
  2019年   14543篇
  2018年   15344篇
  2017年   14677篇
  2016年   21020篇
  2015年   17265篇
  2014年   28607篇
  2013年   87603篇
  2012年   34682篇
  2011年   46761篇
  2010年   41889篇
  2009年   50368篇
  2008年   43802篇
  2007年   40799篇
  2006年   44168篇
  2005年   38729篇
  2004年   40968篇
  2003年   40965篇
  2002年   40068篇
  2001年   36839篇
  2000年   35350篇
  1999年   34121篇
  1998年   40097篇
  1997年   36286篇
  1996年   33456篇
  1995年   29696篇
  1994年   27986篇
  1993年   27833篇
  1992年   26068篇
  1991年   23098篇
  1990年   23408篇
  1989年   22419篇
  1988年   20967篇
  1987年   19305篇
  1986年   18685篇
  1985年   21993篇
  1984年   22283篇
  1983年   20253篇
  1982年   19201篇
  1981年   19271篇
  1980年   17854篇
  1979年   18484篇
  1978年   17702篇
  1977年   17198篇
  1976年   17756篇
  1975年   15967篇
  1974年   15539篇
  1973年   15592篇
  1972年   13041篇
排序方式: 共有10000条查询结果,搜索用时 31 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