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   1489983篇
  免费   28406篇
  国内免费   7786篇
电工技术   35425篇
技术理论   5篇
综合类   7377篇
化学工业   270916篇
金属工艺   64589篇
机械仪表   42172篇
建筑科学   46890篇
矿业工程   11797篇
能源动力   50485篇
轻工业   113183篇
水利工程   14954篇
石油天然气   38296篇
武器工业   368篇
无线电   197034篇
一般工业技术   281416篇
冶金工业   147192篇
原子能技术   33962篇
自动化技术   170114篇
  2021年   16008篇
  2020年   12106篇
  2019年   14849篇
  2018年   15377篇
  2017年   14693篇
  2016年   21350篇
  2015年   17869篇
  2014年   29239篇
  2013年   88755篇
  2012年   36151篇
  2011年   48474篇
  2010年   43272篇
  2009年   51584篇
  2008年   45445篇
  2007年   42768篇
  2006年   45684篇
  2005年   39937篇
  2004年   41495篇
  2003年   41323篇
  2002年   40569篇
  2001年   36957篇
  2000年   35563篇
  1999年   34137篇
  1998年   39262篇
  1997年   35946篇
  1996年   33165篇
  1995年   29426篇
  1994年   27797篇
  1993年   27658篇
  1992年   26050篇
  1991年   22975篇
  1990年   23363篇
  1989年   22441篇
  1988年   20962篇
  1987年   19231篇
  1986年   18568篇
  1985年   21924篇
  1984年   22308篇
  1983年   20226篇
  1982年   19212篇
  1981年   19315篇
  1980年   17861篇
  1979年   18510篇
  1978年   17720篇
  1977年   17147篇
  1976年   17768篇
  1975年   15992篇
  1974年   15540篇
  1973年   15568篇
  1972年   13060篇
排序方式: 共有10000条查询结果,搜索用时 593 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.
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   
144.
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   
145.
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   
146.
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   
147.
148.
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   
149.
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   
150.
The influence of the microstructure on the corrosion rate of three monolithic SiC samples in FLiNaK salt at 900 °C for 250 h was studied. The SiC samples, labeled as SiC-1, SiC-2, and SiC-3, had corrosion rates of 0.137, 0.020, and 0.043 mg/cm2h, respectively. Compared with grain size and the presence of special grain boundaries (i.e., Σ3), the content of high-angle grain boundaries (HAGBs) appeared to have the strongest influence on the corrosion rate of SiC in FLiNaK salt, since the corrosion rate increased six times as the concentration of high-angle grain boundaries increased from 19 to 32% for SiC-2 and SiC-1, respectively. These results stress the importance of controlling the content of HAGBs during the production process of SiC.  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