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   1539368篇
  免费   27670篇
  国内免费   7028篇
电工技术   34237篇
综合类   6443篇
化学工业   269900篇
金属工艺   64514篇
机械仪表   42962篇
建筑科学   47159篇
矿业工程   11377篇
能源动力   50248篇
轻工业   117602篇
水利工程   15782篇
石油天然气   37300篇
武器工业   133篇
无线电   196555篇
一般工业技术   287852篇
冶金工业   187650篇
原子能技术   33863篇
自动化技术   170489篇
  2021年   15514篇
  2020年   11900篇
  2019年   14671篇
  2018年   15156篇
  2017年   14296篇
  2016年   21190篇
  2015年   17367篇
  2014年   28780篇
  2013年   87923篇
  2012年   36154篇
  2011年   48481篇
  2010年   42337篇
  2009年   50490篇
  2008年   45370篇
  2007年   42579篇
  2006年   45629篇
  2005年   40029篇
  2004年   42282篇
  2003年   42113篇
  2002年   41148篇
  2001年   38496篇
  2000年   36555篇
  1999年   36224篇
  1998年   53452篇
  1997年   44063篇
  1996年   38449篇
  1995年   32557篇
  1994年   30311篇
  1993年   30129篇
  1992年   26519篇
  1991年   23824篇
  1990年   23960篇
  1989年   23017篇
  1988年   21656篇
  1987年   19804篇
  1986年   19221篇
  1985年   22568篇
  1984年   22566篇
  1983年   20551篇
  1982年   19465篇
  1981年   19574篇
  1980年   18203篇
  1979年   18718篇
  1978年   17947篇
  1977年   18124篇
  1976年   19868篇
  1975年   16166篇
  1974年   15649篇
  1973年   15741篇
  1972年   13188篇
排序方式: 共有10000条查询结果,搜索用时 718 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.
The aim of this exploratory study has been to investigate the fire properties and environmental aspects of different upholstery material combinations, mainly for domestic applications. An analysis of the sustainability and circularity of selected textiles, along with lifecycle assessment, is used to qualitatively evaluate materials from an environmental perspective. The cone calorimeter was the primary tool used to screen 20 different material combinations from a fire performance perspective. It was found that textile covers of conventional fibres such as wool, cotton and polyester, can be improved by blending them with fire resistant speciality fibres. A new three‐dimensional web structure has been examined as an alternative padding material, showing preliminary promising fire properties with regard to ignition time, heat release rates and smoke production.  相似文献   
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