收费全文 | 671篇 |
免费 | 19篇 |
国内免费 | 1篇 |
电工技术 | 76篇 |
化学工业 | 230篇 |
金属工艺 | 24篇 |
机械仪表 | 17篇 |
建筑科学 | 13篇 |
能源动力 | 22篇 |
轻工业 | 46篇 |
无线电 | 35篇 |
一般工业技术 | 88篇 |
冶金工业 | 92篇 |
原子能技术 | 10篇 |
自动化技术 | 38篇 |
2023年 | 3篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 8篇 |
2017年 | 7篇 |
2016年 | 12篇 |
2015年 | 8篇 |
2014年 | 12篇 |
2013年 | 19篇 |
2012年 | 11篇 |
2011年 | 23篇 |
2010年 | 23篇 |
2009年 | 27篇 |
2008年 | 27篇 |
2007年 | 14篇 |
2006年 | 27篇 |
2005年 | 21篇 |
2004年 | 11篇 |
2003年 | 17篇 |
2002年 | 15篇 |
2001年 | 15篇 |
2000年 | 12篇 |
1999年 | 9篇 |
1998年 | 44篇 |
1997年 | 23篇 |
1996年 | 20篇 |
1995年 | 22篇 |
1994年 | 11篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 13篇 |
1986年 | 15篇 |
1985年 | 16篇 |
1984年 | 13篇 |
1983年 | 18篇 |
1982年 | 8篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1977年 | 14篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1973年 | 4篇 |
1972年 | 5篇 |
This review paper summarizes early Mössbauer and DTA studies of different oxide glasses containing small amounts of iron (III) or tin (IV) as the probe. A lot of valuable information of the atomic level has been obtained about the role of nonbridging oxygen (NBO), network former (NWF), network modifier (NWM), local network structure, glass transition, structural relaxation, crystallization, etc. Introduction of alkali oxide into iron (III)-containing oxide glass causes a marked decrease in glass transition temperature (Tg) amounting to 100 °C and a concordant decrease in quadrupole splitting (Δ) of FeIII, which reflects decreased distortion of NWF–oxygen polyhedra and formation of NBO. By contrast, introduction of non-alkali oxide into oxide glass causes an increase in Tg amounting to more than 100 °C and a concordant increase in Δ, reflecting increased distortion of NWF–oxygen polyhedra in highly cross-linked network. These experimental results led to a discovery of “Tg-Δ rule”, which was consistent with the “conformer model” proposed for polymers by Matsuoka and Quan. Debye temperatures (θD) obtained by low-temperature Mössbauer measurements proved to be useful to determine short- and long-range structures of glass and glass ceramics. Isothermal annealing of vanadate glasses at temperatures higher than Tg or crystallization temperature (Tc) causes a “tunable” decrease in DC-resistivity from the order of MΩ cm to Ω cm. Introduction of metal oxide with a narrow bandgap (Eg) is highly effective to increase the conductivity after the annealing. It was proved that “structural relaxation” of NWF–oxygen polyhedra and resultant decrease in the activation energy (Ea) for conduction are responsible for the improved conductivity. Heat treatment of IR-transmitting aluminate, gallate, and tellurite glasses at temperatures higher than Tg or Tc revealed that crystallization was triggered by the cleavage of NWF–oxygen bonds. These findings will contribute to the development of functional glass and glass ceramics such as smart glass and eco-friendly glass.
相似文献