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   1597311篇
  免费   28390篇
  国内免费   7151篇
电工技术   35124篇
综合类   6494篇
化学工业   274835篇
金属工艺   66431篇
机械仪表   46263篇
建筑科学   47777篇
矿业工程   11817篇
能源动力   50656篇
轻工业   121650篇
水利工程   16436篇
石油天然气   38336篇
武器工业   151篇
无线电   200415篇
一般工业技术   300140篇
冶金工业   207686篇
原子能技术   34486篇
自动化技术   174155篇
  2021年   15808篇
  2020年   12115篇
  2019年   14890篇
  2018年   18816篇
  2017年   18542篇
  2016年   22988篇
  2015年   17793篇
  2014年   29019篇
  2013年   88526篇
  2012年   38211篇
  2011年   52940篇
  2010年   45697篇
  2009年   53581篇
  2008年   48412篇
  2007年   46419篇
  2006年   46261篇
  2005年   42162篇
  2004年   43417篇
  2003年   43183篇
  2002年   41687篇
  2001年   38925篇
  2000年   37085篇
  1999年   37122篇
  1998年   59613篇
  1997年   47586篇
  1996年   40824篇
  1995年   33872篇
  1994年   31306篇
  1993年   31247篇
  1992年   26844篇
  1991年   24054篇
  1990年   24349篇
  1989年   23413篇
  1988年   22012篇
  1987年   20205篇
  1986年   19609篇
  1985年   22878篇
  1984年   22688篇
  1983年   20611篇
  1982年   19465篇
  1981年   19699篇
  1980年   18317篇
  1979年   18721篇
  1978年   17963篇
  1977年   18332篇
  1976年   20232篇
  1975年   16221篇
  1974年   15643篇
  1973年   15775篇
  1972年   13191篇
排序方式: 共有10000条查询结果,搜索用时 15 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