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   1459679篇
  免费   26993篇
  国内免费   6904篇
电工技术   34806篇
综合类   6332篇
化学工业   270866篇
金属工艺   65272篇
机械仪表   42932篇
建筑科学   44825篇
矿业工程   11641篇
能源动力   50173篇
轻工业   104225篇
水利工程   14611篇
石油天然气   38190篇
武器工业   138篇
无线电   196952篇
一般工业技术   279603篇
冶金工业   130661篇
原子能技术   34307篇
自动化技术   168042篇
  2021年   15467篇
  2020年   11749篇
  2019年   14509篇
  2018年   17441篇
  2017年   17087篇
  2016年   21889篇
  2015年   17381篇
  2014年   28571篇
  2013年   87811篇
  2012年   34470篇
  2011年   47767篇
  2010年   43696篇
  2009年   52482篇
  2008年   44357篇
  2007年   41858篇
  2006年   43039篇
  2005年   38905篇
  2004年   40625篇
  2003年   40349篇
  2002年   39421篇
  2001年   35572篇
  2000年   34365篇
  1999年   32853篇
  1998年   33753篇
  1997年   32616篇
  1996年   30940篇
  1995年   28069篇
  1994年   26734篇
  1993年   26620篇
  1992年   25563篇
  1991年   22529篇
  1990年   22976篇
  1989年   22075篇
  1988年   20490篇
  1987年   18897篇
  1986年   18207篇
  1985年   21539篇
  1984年   22006篇
  1983年   19946篇
  1982年   19023篇
  1981年   19103篇
  1980年   17673篇
  1979年   18267篇
  1978年   17523篇
  1977年   16845篇
  1976年   16942篇
  1975年   15850篇
  1974年   15393篇
  1973年   15457篇
  1972年   12940篇
排序方式: 共有10000条查询结果,搜索用时 109 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