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   456423篇
  免费   10523篇
  国内免费   3961篇
电工技术   11017篇
技术理论   8篇
综合类   3931篇
化学工业   68969篇
金属工艺   19287篇
机械仪表   16706篇
建筑科学   12239篇
矿业工程   3638篇
能源动力   13219篇
轻工业   31816篇
水利工程   5340篇
石油天然气   10681篇
武器工业   663篇
无线电   55776篇
一般工业技术   89344篇
冶金工业   77670篇
原子能技术   9847篇
自动化技术   40756篇
  2022年   4267篇
  2021年   6280篇
  2020年   4688篇
  2019年   5257篇
  2018年   8124篇
  2017年   8222篇
  2016年   8472篇
  2015年   6539篇
  2014年   9781篇
  2013年   23347篇
  2012年   14940篇
  2011年   18987篇
  2010年   15414篇
  2009年   16861篇
  2008年   17072篇
  2007年   16666篇
  2006年   15320篇
  2005年   13516篇
  2004年   12297篇
  2003年   11989篇
  2002年   11450篇
  2001年   11220篇
  2000年   10413篇
  1999年   10820篇
  1998年   25432篇
  1997年   17629篇
  1996年   13566篇
  1995年   10147篇
  1994年   8829篇
  1993年   8781篇
  1992年   6361篇
  1991年   5949篇
  1990年   5854篇
  1989年   5488篇
  1988年   5171篇
  1987年   4492篇
  1986年   4376篇
  1985年   4873篇
  1984年   4450篇
  1983年   4014篇
  1982年   3688篇
  1981年   3758篇
  1980年   3448篇
  1979年   3345篇
  1978年   3340篇
  1977年   3763篇
  1976年   4866篇
  1975年   2861篇
  1974年   2673篇
  1973年   2743篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Incorporating high level of potato flour into wheat flour enhances nutritional values of bread but induces a series of problems that lead to the decline of the bread quality. To overcome the barrier, wheat gluten and carboxymethylcellulose (CMC) were added into potato–wheat composite flour to improve dough machinability and bread quality. The rheological properties, thermo-mechanical properties and microstructures of dough were investigated. The results showed that the interaction between gluten and CMC mitigated the discontinuity of gluten matrix and gluten protein aggregation caused by the addition of potato flour, which yielded a more branched and compact gluten network. The compact three-dimensional viscoelastic structure induced improvements of gas retention capacity and dough stability, making it mimic the machinability properties of wheat flour dough. Bread qualities were apparently improved with the combined use of 4% gluten and 6% CMC, of which specific volume increased by 42.86%, and simultaneously, hardness reduced by 75.93%.  相似文献   
102.
Endotoxin exacerbates asthma. We designed the Louisa Environmental Intervention Project (LEIP) and assessed its effectiveness in reducing household endotoxin and improving asthma symptoms in rural Iowa children. Asthmatic school children (N = 104 from 89 homes) of Louisa and Keokuk counties in Iowa (aged 5-14 years) were recruited and block-randomized to receive extensive (education + professional cleaning) or educational interventions. Environmental sampling collection and respiratory survey administration were done at baseline and during three follow-up visits. Mixed-model analyses were used to assess the effect of the intervention on endotoxin levels and asthma symptoms in the main analysis and of endotoxin reduction on asthma symptoms in exploratory analysis. In the extensive intervention group, dust endotoxin load was significantly reduced in post-intervention visits. The extensive compared with the educational intervention was associated with significantly decreased dust endotoxin load in farm homes and less frequent nighttime asthma symptoms. In exploratory analysis, dust endotoxin load reduction from baseline was associated with lower total asthma symptoms score (Odds ratio: 0.52, 95% confidence interval: 0.29-0.92). In conclusion, the LEIP intervention reduced household dust endotoxin and improved asthma symptoms. However, endotoxin reductions were not sustained post-intervention by residents.  相似文献   
103.
Rapid synthesis of silver nanowires(Ag NWs) with high quality and a broad processing window is challenging because of the low selectivity of the formation of multiply twinned particles at the nucleation stage for subsequent Ag NWs growth.Herein we report a systematic study of the water-involved heterogeneous nucleation of Ag NWs with high rate(less than 20 min) in a simple and scalable preparation method.Using glycerol as a reducing agent and a solvent with a high boiling point,the reaction is rapidly heated to 210 ℃ in air to synthesize Ag NWs with a very high yield in gram level.It is noted that the addition of a small dose of water plays a key role for obtaining highly pure Ag NWs in high yield,and the optimal water/glycerol ratio is0.25%.After investigating a series of forming factors including reaction temperature and dose of catalysts,the formation kinetics and mechanism of the Ag NWs are proposed.Compared to other preparation methods,our strategy is simple and reproducible.These Ag NWs show a strong Raman enhancement effect for organic molecules on their surface.  相似文献   
104.
105.
106.
107.
108.
109.
110.
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