全文获取类型
收费全文 | 730篇 |
免费 | 60篇 |
国内免费 | 23篇 |
专业分类
化学 | 317篇 |
晶体学 | 1篇 |
力学 | 50篇 |
综合类 | 4篇 |
数学 | 27篇 |
物理学 | 414篇 |
出版年
2023年 | 5篇 |
2022年 | 17篇 |
2021年 | 17篇 |
2020年 | 19篇 |
2019年 | 18篇 |
2018年 | 10篇 |
2017年 | 13篇 |
2016年 | 21篇 |
2015年 | 17篇 |
2014年 | 22篇 |
2013年 | 70篇 |
2012年 | 32篇 |
2011年 | 21篇 |
2010年 | 29篇 |
2009年 | 47篇 |
2008年 | 31篇 |
2007年 | 30篇 |
2006年 | 29篇 |
2005年 | 17篇 |
2004年 | 31篇 |
2003年 | 25篇 |
2002年 | 27篇 |
2001年 | 21篇 |
2000年 | 28篇 |
1999年 | 16篇 |
1998年 | 11篇 |
1997年 | 19篇 |
1996年 | 13篇 |
1995年 | 16篇 |
1994年 | 11篇 |
1993年 | 12篇 |
1992年 | 20篇 |
1991年 | 7篇 |
1990年 | 14篇 |
1989年 | 7篇 |
1988年 | 12篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 1篇 |
1974年 | 8篇 |
1973年 | 5篇 |
1969年 | 3篇 |
排序方式: 共有813条查询结果,搜索用时 15 毫秒
111.
112.
A novel in-needle sample preparation device has been developed for the determination of volatile aldehydes in gaseous samples.
The needle device is designed for the gas chromatographic (GC) analysis of aldehydes and ketones commonly found in typical
in-house environments. In order to prepare the extraction device, a bundle of polymer-coated filaments was longitudinally
packed into a specially designed needle. Derivatization reactions were prompted by 2,4-dinitrophenylhydrazine (NDPH) included
in the needle, and so the aldehydes and ketones were derivatized to the corresponding hydrazones and extracted with the extraction
needle. A reproducible extraction needle preparation process was established, along with a repeatable derivatization/extraction
process that ensures the successful determination of aldehydes. The storage performance of the extraction needle was also
evaluated at room temperature for three days. The results demonstrate the successful application of the fiber-packed extraction
device to the preparation of a gaseous sample of aldehydes, and the future possibility of applying the extraction device to
the analysis of in-house environments. 相似文献
113.
114.
Abstract Deuterium patterns of natural compounds and their synthetic analogues, preferably obtained by NMR-measurements, are routinely determined in context with authenticity checks and origin assignments. So far, the use of the data is nearly exclusively empirically, and systematic correlations between the patterns and isotope effects on or mechanisms of the reactions involved have not yet been established. 相似文献
115.
Um zu prūfen, ob und unter welchen Bedingungen es möglich ist, den Fūllstand in Flüssiggaspatronen mittels Isotopenstrahlenschranken zu messen, wurden Röntgenaufnahmen bei verschiedenen Kapseltemperaturen gemacht. 相似文献
116.
J. W. Leonhardt H.-J. Große P. Popp 《Isotopes in environmental and health studies》2013,49(12):388-392
Die Multiplikation von Ladungsträgern durch feldbeschleunigte Elektronen erfolgt im Bereich der unselbständigen Entladung. Sie wurde von Lovelock [1] erstmals für β-Argondetektoren zur Steigerung der Empfindlichkeit EN angewandt. Detektoren im Bereich der selbständigen Entladung [2] haben sich nicht bewährt. 相似文献
117.
The aim of this paper is to show that the procedure of maximum entropy principle for the closure of the moments equations for rarefied monatomic gases can be extended also to polyatomic gases. The main difference with respect to the usual procedure is the existence of two hierarchies of macroscopic equations for moments of suitable distribution function, in which the internal energy of a molecule is taken into account. The field equations for 14 moments of the distribution function, which include dynamic pressure, are derived. The entropy and the entropy flux are shown to be a generalization of the ones for classical Grad’s distribution. The results are in perfect agreement with the recent macroscopic approach of extended thermodynamics for real gases. 相似文献
118.
Alain Polian 《高压研究》2013,33(1-6):205-217
Abstract The scattering of light by elementar excitations in the matter is results in two phenomena, discriminated by the zero wavevector frequency of the excitation: if this frequency is zero, one deals with Brillouin scattering, and with Raman scattering in the other case. Brillouin scattering results from the interaction of light with thermal excitations (acoustic phonons in a crystal) of a material, or, from a classical point of view, with density waves. Contrary to Raman scattering, the selection rules allow always the observation of at least one mode. It is a powerful technic in the study of rare gases under pressure: at ambient temperature, rare gases crystallize in the face centered cubic structure (except helium which structure was recently found to be hexagonal) and are therefore Raman and infrared inactive. Experimental results will be reviewed on rare gases and rare gas mixtures in the fluid phase, like He-Ne and He-H2. These results will be discussed in relation with recent measurements of the frequency of global oscillations of Jupiter. 相似文献
119.
The promotion/prevention mechanism of dissolved gases on cavitation inception is essential for many high-tech industries and research. In the present study, large-scale molecular dynamics simulations are performed to investigate the effects of water cavitation caused by different gas types by using nitrogen and oxygen gases with TIP4P/2005 water. The cavitation inception behaviour is analyzed via Mean First Passage Time method. Water with dissolved gases has a higher nucleation rate and is easier to cavitate than pure water. At the same gas concentration, the cavitation of water with nitrogen is promoted to a greater extent than that with oxygen. The number and energy of hydrogen bond (HB) are further calculated by the Acceptor-Hydrogen-Donor method to explain this promotion mechanism. The number and energy of HB in water with gases decrease compared with those in pure water. The introduction of gases weakens the HB network and promotes cavitation inception because of weaker interactions between gas and water molecules. A model is developed to describe the relationship between nucleation rate and HB energy. Gas molecules assemble on the surface of bubbles during water cavitation, which may decrease the free energy of bubble surface, maintain the existing bubble, and contribute to the growth process. 相似文献
120.
Abstract Measurements of both secondary electron emission coefficient γ and SiL23 Auger yield ρA obtained from (111) Si target bombarded by high fluence of noble gas ions were performed. For Si irradiated at room temperature at doses more than 1017 ions per cm2, monotonous increasing variation of γ and ρA versus incidence angle i was observed. For Si irradiated at a temperature more than a critical value, γ(i) and ρA(i) curves exhibited, superimposed to monotonous variation, some minima when the ion beam penetrates the crystal along low index directions. In the range 20–650°C, the Auger yield temperature dependence showed a sharp variation around a critical value depending on the ion mass for a given incident energy. These results are linked to an amorphous-crystalline phase transition. 相似文献