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   29239篇
  免费   927篇
  国内免费   65篇
电工技术   427篇
综合类   74篇
化学工业   6326篇
金属工艺   605篇
机械仪表   501篇
建筑科学   1259篇
矿业工程   361篇
能源动力   742篇
轻工业   2489篇
水利工程   259篇
石油天然气   280篇
武器工业   4篇
无线电   1812篇
一般工业技术   4440篇
冶金工业   6262篇
原子能技术   292篇
自动化技术   4098篇
  2022年   236篇
  2021年   480篇
  2020年   315篇
  2019年   391篇
  2018年   500篇
  2017年   445篇
  2016年   582篇
  2015年   459篇
  2014年   718篇
  2013年   1797篇
  2012年   1031篇
  2011年   1282篇
  2010年   1015篇
  2009年   1076篇
  2008年   1231篇
  2007年   1153篇
  2006年   1025篇
  2005年   918篇
  2004年   790篇
  2003年   763篇
  2002年   803篇
  2001年   583篇
  2000年   432篇
  1999年   487篇
  1998年   494篇
  1997年   460篇
  1996年   492篇
  1995年   465篇
  1994年   478篇
  1993年   454篇
  1992年   449篇
  1991年   291篇
  1990年   423篇
  1989年   399篇
  1988年   348篇
  1987年   416篇
  1986年   356篇
  1985年   452篇
  1984年   473篇
  1983年   404篇
  1982年   383篇
  1981年   305篇
  1980年   307篇
  1979年   362篇
  1978年   306篇
  1977年   245篇
  1976年   232篇
  1975年   255篇
  1974年   227篇
  1973年   236篇
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
1.
2.
Ca3Co4O9 is a promising p-type thermoelectric oxide material having intrinsically low thermal conductivity. With low cost and opportunities for automatic large scale production, thick film technologies offer considerable potential for a new generation of micro-sized thermoelectric coolers or generators. Here, based on the chemical composition optimized by traditional solid state reaction for bulk samples, we present a viable approach to modulating the electrical transport properties of screen-printed calcium cobaltite thick films through control of the microstructural evolution by optimized heat-treatment. XRD and TEM analysis confirmed the formation of high-quality calcium cobaltite grains. By creating 2.0 at% cobalt deficiency in Ca2.7Bi0.3Co4O9+δ, the pressureless sintered ceramics reached the highest power factor of 98.0 μWm?1 K-2 at 823 K, through enhancement of electrical conductivity by reduction of poorly conducting secondary phases. Subsequently, textured thick films of Ca2.7Bi0.3Co3.92O9+δ were efficiently tailored by controlling the sintering temperature and holding time. Optimized Ca2.7Bi0.3Co3.92O9+δ thick films sintered at 1203 K for 8 h exhibited the maximum power factor of 55.5 μWm?1 K-2 at 673 K through microstructure control.  相似文献   
3.
Journal of Low Temperature Physics - This study modeled and investigated the magnetocaloric effect in Ni2MnGa Heusler alloy characterized by its magnetic entropy change (ΔSm) and its...  相似文献   
4.
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   
5.
A hybrid sorbent material for removal of hydrogen sulfide from air was developed. The material is based on activated carbon and iron compounds obtained from waste iron(II) sulfate(VI) heptahydrate. The iron salt is deposited on the carbonaceous support and subjected to oxidation (Fe2+ to Fe3+) using atmospheric oxygen under alkaline conditions. An effect of H2O2 addition to the process on the composition of the resultant material was also examined. X-ray diffraction (XRD) analyses confirmed easy conversion of waste FeSO4·7H2O to iron oxides Fe3O4 and FeOOH. The activated carbon supporting iron oxides revealed a higher efficiency in H2S elimination from air compared to the commercial activated carbon, without any modification.  相似文献   
6.
This paper presents the results of ongoing research carried out by the author exploring methods to provide a more robust estimate of rock mass properties specifically for use in tunnel design. Data from various large-scale rock mass failures are introduced, including coal pillars. The damage-initiation,spalling-limit approach is compared to the coal pillar database. New comparisons of estimating the geological strength index(GSI) and relationships to estimate the Hoeke Brown failure criterion parameters, mb, s and a, are presented.  相似文献   
7.
8.
9.
A contact layer element for large deformations   总被引:1,自引:0,他引:1  
  相似文献   
10.
Bile acids have been reported as important cofactors promoting human and murine norovirus (NoV) infections in cell culture. The underlying mechanisms are not resolved. Through the use of chemical shift perturbation (CSP) NMR experiments, we identified a low-affinity bile acid binding site of a human GII.4 NoV strain. Long-timescale MD simulations reveal the formation of a ligand-accessible binding pocket of flexible shape, allowing the formation of stable viral coat protein–bile acid complexes in agreement with experimental CSP data. CSP NMR experiments also show that this mode of bile acid binding has a minor influence on the binding of histo-blood group antigens and vice versa. STD NMR experiments probing the binding of bile acids to virus-like particles of seven different strains suggest that low-affinity bile acid binding is a common feature of human NoV and should therefore be important for understanding the role of bile acids as cofactors in NoV infection.  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