全文获取类型
收费全文 | 2440篇 |
免费 | 192篇 |
国内免费 | 128篇 |
专业分类
化学 | 1881篇 |
晶体学 | 93篇 |
力学 | 33篇 |
综合类 | 4篇 |
数学 | 14篇 |
物理学 | 735篇 |
出版年
2024年 | 2篇 |
2023年 | 26篇 |
2022年 | 24篇 |
2021年 | 40篇 |
2020年 | 71篇 |
2019年 | 59篇 |
2018年 | 64篇 |
2017年 | 49篇 |
2016年 | 104篇 |
2015年 | 87篇 |
2014年 | 109篇 |
2013年 | 174篇 |
2012年 | 96篇 |
2011年 | 169篇 |
2010年 | 122篇 |
2009年 | 138篇 |
2008年 | 110篇 |
2007年 | 116篇 |
2006年 | 113篇 |
2005年 | 100篇 |
2004年 | 100篇 |
2003年 | 80篇 |
2002年 | 68篇 |
2001年 | 54篇 |
2000年 | 64篇 |
1999年 | 56篇 |
1998年 | 44篇 |
1997年 | 54篇 |
1996年 | 39篇 |
1995年 | 46篇 |
1994年 | 28篇 |
1993年 | 36篇 |
1992年 | 30篇 |
1991年 | 22篇 |
1990年 | 27篇 |
1989年 | 24篇 |
1988年 | 24篇 |
1987年 | 26篇 |
1986年 | 27篇 |
1985年 | 25篇 |
1984年 | 19篇 |
1983年 | 12篇 |
1982年 | 23篇 |
1981年 | 17篇 |
1980年 | 18篇 |
1979年 | 18篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有2760条查询结果,搜索用时 15 毫秒
1.
2.
We have simultaneously used adsorption isotherm volumetry and Fourier transform infrared spectroscopy in order to take the investigations on amorphous ice structure a step further, especially concerning porosity and annealing-induced modifications. We have studied surface reorganization during annealing and found that the number of surface sites decreases before crystallization, their relative ratios being different for amorphous and crystalline ice. We also present results confirming that ice can have a large specific surface area and nevertheless be non-microporous. 相似文献
3.
V. Ballarini G. Barucca E. Bennici C. F. Pirri C. Ricciardi E. Tresso F. Giorgis 《Physica E: Low-dimensional Systems and Nanostructures》2003,16(3-4):591
All amorphous silicon-nitride planar optical microcavities operating in the visible range have been grown by plasma enhanced chemical vapor deposition. The luminescence intensity of the N-rich silicon-nitride layer from a microcavity with 6 period distributed Bragg reflectors (DBRs) is two order of magnitude higher than that of the luminescent layer without the cavity. Moreover, a strong directionality of the microcavities emission can be observed. Such results can be ascribed to the anisotropic optical density of states induced in the Fabry–Perot structure. The quality factors of the resonators are strictly correlated to the number of periods of the DBRs. 相似文献
4.
The yet unknown intermetallic phase La5Al3Ni2 was obtained by partially crystallizing amorphous La50Al25Ni25 at 550 K (further heating above 600 K leads to irreversible disappearance of this phase), and its crystal structure was determined from X‐ray powder diffraction data. The crystal structure of the La5Al3Ni2 phase constitutes a new structure type (Cmcm, a = 14.231Å, b = 6.914Å, c = 10.460Å, oC40) and is built from [Al3Ni2] chains surrounded by La atoms. In the ternary system La‐Al‐Ni La5Al3Ni2 is located on the section La50Al50−nNin (0 ≤ n ≤ 50) with the binary compounds LaAl and LaNi as end members. Strikingly, also the crystal structures of the end members can be conceived as chain structures with Al and Ni chains surrounded by La, respectively. 相似文献
5.
G. Gargaro F. Gasparrini D. Misiti G. Palmieri M. Pierini C. Villani 《Chromatographia》1987,24(1):505-509
Summary Enantiomers of several sulfoxides and some selenoxides can be easily separated by using a new chiral stationary phase (CSP-DACH-DNB)
containing the 3,5-dinitrobenzoyl derivative of R,R-(-)1,2-diamino-cyclohexane as selector, covalently bonded to the siliceous
matrix. The easy operative conditions and the high enantioselectivity values (α) allow a direct transfer of the analytical
separations to a semi-preparative and preparative scale. 相似文献
6.
H.L. Li H.T. Lin Y.H. Wu T. Liu Z.L. Zhao G.C. Han T.C. Chong 《Journal of magnetism and magnetic materials》2006
We report on the growth and characterization of delta-doped amorphous Ge:Mn diluted magnetic semiconductor thin films on GaAs (0 0 1) substrates. The fabricated samples exhibit different magnetic behaviors, depending on the Mn doping concentration. The Curie temperature was found to be dependent on both the Mn doping concentration and spacing between the doping layers. A sharp drop in magnetization and rise in resistivity are observed at low temperature in samples with high Mn doping concentrations, which is also accompanied by a negative thermal remanent magnetization (TRM) in the higher temperature range. The temperature at which the magnetization starts to drop and the negative TRM appears show a correlation with the Mn doping concentration. The experimental results are discussed based on the formation of ferromagnetic regions at high temperature and antiferromagnetic coupling between these regions at low temperature. 相似文献
7.
Combining layered positional order as smectic order and chirality can generate complex architectures since twist parallel
to the layers is not allowed. This paper will review some new experimental results on different phases resulting from the
competition between smectic positional order and twist orientational order. It concerns the TGBA and the NL*, that is the liquid line phase as well as the SmQ phase. Chiral effects in the isotropic phase will also be discussed. 相似文献
8.
9.
Pulsed laser deposition with a Nd:YAG laser was used to grow thin films from a pre-synthesized Ti3SiC2 MAX-phase formulated ablation target on oxidized Si(1 0 0) and MgO(1 0 0) substrates. The depositions were carried out in a substrate temperature range from 300 to 900 K, and the pressure in the deposition chamber ranged from vacuum (10−5 Pa) to 0.05 Pa Argon background pressure. The properties of the films have been investigated by Rutherford backscattering spectrometry for film thickness and stoichiometric composition and X-ray diffraction for the crystallinity of the films. The silicon content of the films varied with the energy density of the laser beam. To suppress especially the silicon re-sputtering from the substrate, the energy of the incoming particles must be below a threshold of 20 eV. Therefore, the energy density of the laser beam must not be too high. At constant deposition energy density the film thickness depends strongly on the background pressure. The X-ray diffraction measurements show patterns that are typical of amorphous films, i.e. no Ti3SiC2 related reflections were found. Only a very weak TiC(2 0 0) reflection was seen, indicating the presence of a small amount of crystalline TiC. 相似文献
10.
The electron-stimulated desorption (ESD) of D− and H− ions from condensed D2O and H2O films is investigated. Three low-energy peaks are observed in the ESD anion yield, which are identified as arising from excitation of 2B1, 2A1 and 2B2 dissociative electron attachment (DEA) resonances. Additional structure is observed between 18 and 32 eV, which may be due to ion pair formation or to DEA resonances involving the 2a1 orbital. The ion yield resulting from excitation of the 2B1 resonance increases as the film is heated. We attribute the increase in the ion yield to thermally induced hydrogen bond breaking near the surface, which enhances the lifetimes of the excited states that lead to desorption. 相似文献