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   1753260篇
  免费   43563篇
  国内免费   15155篇
电工技术   45853篇
技术理论   13篇
综合类   17995篇
化学工业   303104篇
金属工艺   74447篇
机械仪表   55843篇
建筑科学   61739篇
矿业工程   16961篇
能源动力   55262篇
轻工业   136790篇
水利工程   19397篇
石油天然气   47756篇
武器工业   1539篇
无线电   218122篇
一般工业技术   316872篇
冶金工业   207508篇
原子能技术   35950篇
自动化技术   196827篇
  2022年   16447篇
  2021年   23928篇
  2020年   18134篇
  2019年   19563篇
  2018年   21991篇
  2017年   22034篇
  2016年   27449篇
  2015年   24964篇
  2014年   38021篇
  2013年   99025篇
  2012年   49570篇
  2011年   63681篇
  2010年   54543篇
  2009年   61647篇
  2008年   57081篇
  2007年   53957篇
  2006年   55598篇
  2005年   49162篇
  2004年   48422篇
  2003年   47399篇
  2002年   45880篇
  2001年   42607篇
  2000年   40693篇
  1999年   40777篇
  1998年   58421篇
  1997年   48570篇
  1996年   42298篇
  1995年   35582篇
  1994年   32815篇
  1993年   31903篇
  1992年   27960篇
  1991年   24979篇
  1990年   24968篇
  1989年   24042篇
  1988年   22480篇
  1987年   20505篇
  1986年   19973篇
  1985年   23233篇
  1984年   23111篇
  1983年   20963篇
  1982年   19742篇
  1981年   19847篇
  1980年   18492篇
  1979年   18985篇
  1978年   18187篇
  1977年   18802篇
  1976年   21211篇
  1975年   16333篇
  1974年   15779篇
  1973年   15887篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Due to the demand of miniaturization and integration for ceramic capacitors in electronic components market, TiO2-based ceramics with colossal permittivity has become a research hotspot in recent years. In this work, we report that Ag+/Nb5+ co-doped (Ag1/4Nb3/4)xTi1−xO2 (ANTOx) ceramics with colossal permittivity over a wide frequency and temperature range were successfully prepared by a traditional solid–state method. Notably, compositions of ANTO0.005 and ANTO0.01 respectively exhibit both low dielectric loss (0.040 and 0.050 at 1 kHz), high dielectric permittivity (9.2 × 103 and 1.6 × 104 at 1 kHz), and good thermal stability, which satisfy the requirements for the temperature range of application of X9R and X8R ceramic capacitors, respectively. The origin of the dielectric behavior was attributed to five dielectric relaxation phenomena, i.e., localized carriers' hopping, electron–pinned defect–dipoles, interfacial polarization, and oxygen vacancies ionization and diffusion, as suggested by dielectric temperature spectra and valence state analysis via XPS; wherein, electron-pinned defect–dipoles and internal barrier layer capacitance are believed to be the main causes for the giant dielectric permittivity in ANTOx ceramics.  相似文献   
2.
Multimedia Tools and Applications - Remote Sensing categorical signature classification has gained significant implications on spatial resolution image analysis due to differences in the...  相似文献   
3.
4.
Journal of Materials Science -  相似文献   
5.
6.
Grachev  A. I. 《Semiconductors》2022,56(2):67-70
Semiconductors - In this work, we discuss for the first time the principle of rotation in the constant electric field of a conducting particle with participation of the Lorentz force, which ensures...  相似文献   
7.
Journal of Communications Technology and Electronics - A quantitative comparison of the spectral characteristics of the human visual system and matrix photodetectors is carried out. Criteria for a...  相似文献   
8.
Hepatic fibrosis occurs when liver tissue becomes scarred from repetitive liver injury and inflammatory responses; it can progress to cirrhosis and eventually to hepatocellular carcinoma. Previously, we reported that neoagarooligosaccharides (NAOs), produced by the hydrolysis of agar by β-agarases, have hepatoprotective effects against acetaminophen overdose-induced acute liver injury. However, the effect of NAOs on chronic liver injury, including hepatic fibrosis, has not yet been elucidated. Therefore, we examined whether NAOs protect against fibrogenesis in vitro and in vivo. NAOs ameliorated PAI-1, α-SMA, CTGF and fibronectin protein expression and decreased mRNA levels of fibrogenic genes in TGF-β-treated LX-2 cells. Furthermore, downstream of TGF-β, the Smad signaling pathway was inhibited by NAOs in LX-2 cells. Treatment with NAOs diminished the severity of hepatic injury, as evidenced by reduction in serum alanine aminotransferase and aspartate aminotransferase levels, in carbon tetrachloride (CCl4)-induced liver fibrosis mouse models. Moreover, NAOs markedly blocked histopathological changes and collagen accumulation, as shown by H&E and Sirius red staining, respectively. Finally, NAOs antagonized the CCl4-induced upregulation of the protein and mRNA levels of fibrogenic genes in the liver. In conclusion, our findings suggest that NAOs may be a promising candidate for the prevention and treatment of chronic liver injury via inhibition of the TGF-β/Smad signaling pathway.  相似文献   
9.
Koroteev  A. S. 《Atomic Energy》2021,130(4):202-208
Atomic Energy - The history and direction of further development of space nuclear energetics are examined. The functional diagram and principle of operation of a promising, powerful,...  相似文献   
10.
Wireless Personal Communications - Chronic kidney disease (CKD) is a gradual loss of kidney function over the period of time and it is irrevocable once functionality reaches the critical state....  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