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   1439334篇
  免费   26997篇
  国内免费   6873篇
电工技术   33915篇
综合类   6352篇
化学工业   265903篇
金属工艺   63328篇
机械仪表   40486篇
建筑科学   44958篇
矿业工程   11231篇
能源动力   50053篇
轻工业   105669篇
水利工程   14390篇
石油天然气   37240篇
武器工业   129篇
无线电   194244篇
一般工业技术   274281篇
冶金工业   130899篇
原子能技术   33690篇
自动化技术   166436篇
  2021年   15367篇
  2019年   14486篇
  2018年   13981篇
  2017年   13216篇
  2016年   20392篇
  2015年   17100篇
  2014年   28489篇
  2013年   87435篇
  2012年   33601篇
  2011年   44790篇
  2010年   40755篇
  2009年   49536篇
  2008年   42290篇
  2007年   39183篇
  2006年   43383篇
  2005年   37653篇
  2004年   40286篇
  2003年   40342篇
  2002年   39629篇
  2001年   36059篇
  2000年   34756篇
  1999年   33163篇
  1998年   33986篇
  1997年   32722篇
  1996年   31253篇
  1995年   28429篇
  1994年   26978篇
  1993年   26732篇
  1992年   25714篇
  1991年   22719篇
  1990年   23143篇
  1989年   22169篇
  1988年   20726篇
  1987年   19059篇
  1986年   18411篇
  1985年   21792篇
  1984年   22176篇
  1983年   20100篇
  1982年   19114篇
  1981年   19151篇
  1980年   17746篇
  1979年   18435篇
  1978年   17651篇
  1977年   17045篇
  1976年   17525篇
  1975年   15914篇
  1974年   15475篇
  1973年   15542篇
  1972年   13036篇
  1971年   11706篇
排序方式: 共有10000条查询结果,搜索用时 62 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