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   1479083篇
  免费   27259篇
  国内免费   6999篇
电工技术   34326篇
综合类   6514篇
化学工业   270126篇
金属工艺   63798篇
机械仪表   41996篇
建筑科学   45699篇
矿业工程   11420篇
能源动力   50215篇
轻工业   110053篇
水利工程   14804篇
石油天然气   37514篇
武器工业   190篇
无线电   195903篇
一般工业技术   280370篇
冶金工业   148108篇
原子能技术   33906篇
自动化技术   168399篇
  2021年   15533篇
  2020年   11824篇
  2019年   14570篇
  2018年   15366篇
  2017年   14693篇
  2016年   21069篇
  2015年   17300篇
  2014年   28637篇
  2013年   87646篇
  2012年   34735篇
  2011年   46836篇
  2010年   41946篇
  2009年   50426篇
  2008年   43856篇
  2007年   40858篇
  2006年   44227篇
  2005年   38781篇
  2004年   41019篇
  2003年   40986篇
  2002年   40101篇
  2001年   36861篇
  2000年   35386篇
  1999年   34158篇
  1998年   40061篇
  1997年   36280篇
  1996年   33455篇
  1995年   29714篇
  1994年   28006篇
  1993年   27840篇
  1992年   26086篇
  1991年   23128篇
  1990年   23421篇
  1989年   22442篇
  1988年   20973篇
  1987年   19322篇
  1986年   18706篇
  1985年   22007篇
  1984年   22303篇
  1983年   20268篇
  1982年   19212篇
  1981年   19298篇
  1980年   17867篇
  1979年   18494篇
  1978年   17712篇
  1977年   17207篇
  1976年   17748篇
  1975年   15980篇
  1974年   15556篇
  1973年   15601篇
  1972年   13046篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
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   
142.
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