全文获取类型
收费全文 | 277篇 |
免费 | 10篇 |
专业分类
化学 | 225篇 |
晶体学 | 1篇 |
力学 | 2篇 |
数学 | 12篇 |
物理学 | 47篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 10篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 11篇 |
2015年 | 4篇 |
2014年 | 6篇 |
2013年 | 8篇 |
2012年 | 14篇 |
2011年 | 14篇 |
2010年 | 14篇 |
2009年 | 8篇 |
2008年 | 10篇 |
2007年 | 24篇 |
2006年 | 19篇 |
2005年 | 12篇 |
2004年 | 14篇 |
2003年 | 10篇 |
2002年 | 9篇 |
2001年 | 10篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 7篇 |
1986年 | 1篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1971年 | 2篇 |
1968年 | 1篇 |
1957年 | 2篇 |
1932年 | 1篇 |
排序方式: 共有287条查询结果,搜索用时 547 毫秒
261.
262.
263.
264.
Fluorine bound in organic matter can be determined volumetrically, after decomposition with sodium peroxide, by precipitation by means of a calcium chloride solution, the excess of which is measured chelatometncally 相似文献
265.
266.
Resonant Raman scattering experiments on n-Ge/n-GaAs (100) heterostructures reveal transitions involving quasi-two-dimensional electron states in Ge-accumulation layers. The experiments were performed in the range of the E1-gap of Ge. The electronic scattering transforms into E1-luminescence as the laser energy is tuned above the resonance. Spectra obtained at higher excitation energies show luminescence bands associated with the E1 and E1 + Δ1-gap of Ge. The latter results are compared with recent data for bulk heavily-doped Ge. 相似文献
267.
R. Merlin R. Tsu G. Güntherodt G. Abstreiter M.W. Shafer 《Solid State Communications》1977,22(10):609-613
Anti-Stokes luminescence or up-conversion has been observed in the europium monochalcogenides. The emission occurs from localized regions in the crystals and may be assigned to transitions within the 4f6 configurations of Eu3+. In addition, we have studied the temperature and magnetic field dependence of the previously reported luminescence within the 4f7 configurations of Eu2+. The data show that its previous interpretation in terms of magnon sidebands is questionable. A mechanism requiring the presence of impurities or defects is proposed for the spin-flip transitions involved in both luminescence processes. 相似文献
268.
269.
We report the temperature dependence of the low frequency part (ω < 100 cm?1) of the Raman spectra of the Pb(Ti1-x, Zrx)O3 and , Lax)TiO3 systems. The spectra indicate a coupled mode behavior between the soft E(TO) phonon and a mode which produces an additional band in the spectra. We discuss the possibility that the additional band might be due to zone boundary tranverse acoustical phonons which couple to the q ~ 0 soft E(TO) mode because of the disorder existing in the systems. 相似文献
270.
Inorganic UV absorbers which are widely used today were originally designed neither as a UV blocker in coatings applications, nor for wood protection. In recent years however, there has been extensive interest in these compounds, especially with regard to their properties as a UV blocker in coating applications.In this work, we carried out a comparative study to look into some inorganic and organic UV absorbers used in wood coating applications. The aim of this study is to determine the photostabilisation performances of each type of UV absorbers, to seek possible synergies and the influences of different wood species. We have also searched to find eventual correlation between these performances and the influence of UV absorbers on the film properties. Our study has compared the performances of the following UV absorbers: hombitec RM 300, hombitec RM 400 from the Sachtleben Company; transparent yellow and red iron oxides from Sayerlack as inorganic UV absorbers; organic UV absorbers Tinuvin 1130 and Tinuvin 5151 from Ciba Company.The study was carried out on three wood species: Abies grandis, tauari and European oak.The environmental constraints (in particular the limitation of the emission of volatile organic compounds VOCs) directed our choice towards aqueous formulations marketed by the Sayerlack Arch Coatings Company.The results obtained after 800 h of dry ageing showed that the Tinuvins and the hombitecs present better wood photostabilisations.On the other hand in wet ageing, with the hombitec, there are appearances of some cracks and an increase in the roughness of the surface. This phenomenon is absent when the Tinuvins are used. With regard to these results, the thermomechanical analyses relating to the follow-up of the change of the glass transition temperature (Tg) of the various coating systems, show a different behaviour between the two types of absorbers. However, contrary to organic UV absorbers, inorganic ones tend to increase Tg during ageing, and, consequently decrease the flexibility of films. These phenomena can lead to the appearance of cracks found in the case of the wet weathering. 相似文献