全文获取类型
收费全文 | 462篇 |
免费 | 28篇 |
国内免费 | 4篇 |
专业分类
化学 | 244篇 |
晶体学 | 25篇 |
力学 | 3篇 |
数学 | 4篇 |
物理学 | 218篇 |
出版年
2023年 | 8篇 |
2022年 | 13篇 |
2021年 | 6篇 |
2020年 | 14篇 |
2019年 | 7篇 |
2018年 | 10篇 |
2017年 | 9篇 |
2016年 | 13篇 |
2015年 | 10篇 |
2014年 | 11篇 |
2013年 | 64篇 |
2012年 | 28篇 |
2011年 | 25篇 |
2010年 | 18篇 |
2009年 | 21篇 |
2008年 | 16篇 |
2007年 | 14篇 |
2006年 | 15篇 |
2005年 | 11篇 |
2004年 | 19篇 |
2003年 | 14篇 |
2002年 | 15篇 |
2001年 | 28篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 10篇 |
1997年 | 9篇 |
1996年 | 13篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有494条查询结果,搜索用时 156 毫秒
41.
V. M. Naumenko 《International Journal of Infrared and Millimeter Waves》1981,2(1):149-158
Interaction of host magnons with impurity magnetic excitations in antiferromagnetic crystals CoCO3 and CoF2 containing substitutional impurity amounting to 10–4 and (4±2)×10–3 (by weight) Mn2+ respectively, has been investigated in the wavelength range 0.35–0.8 mm in a magnetic field of up to 20 T. In the CoCO3+10–4 Mn2+ crystal the impurity line was observed to merge with the AFMR line, which is peculiar to incoherent spectrum rearrangement. In the CoF2+4×10–3 Mn2+ crystal the cross splitting of spectrum was revealed as the impurity lower lying Zeeman level approached the AFMR low frequency mode, peculiar to coherent spectrum rearrangement. In both cases the impurity line intensity increases very much as it approaches the spin-wave band of the crystal. The constant of resonance interaction of the impurity excitation with magnons is determined for CoF2+Mn2+ to be m=18 cm–1. 相似文献
42.
根据密度泛函理论,用自洽迭代的方法求解二维方形量子点中有杂质时电子(N=1~12)的薛定谔方程,对绝对零度情况下处于基态电子的总能量进行了数值计算,并讨论了杂质对量子点中电子基态能量的影响,得出了方形量子点中多电子系统基态的一些性质. 相似文献
43.
Sergiu Muncaci Carlos Mattea Siegfried Stapf Ioan Ardelean 《Magnetic resonance in chemistry : MRC》2013,51(2):123-128
Frequency‐dependent NMR relaxation studies have been carried out on water (polar) and cyclohexane (nonpolar) molecules confined inside porous ceramics containing variable amounts of iron oxide (III). The porous ceramics were prepared by compression of powders mixed with iron oxide followed by thermal treatment. The pore size distribution was estimated using a technique based on diffusion in internal fields that exposed a narrow distribution of macropore sizes with an average pore dimension independent of iron oxide content. The relaxation dispersion curves were obtained at room temperature using a fast field cycling NMR instrument. They display an increase of the relaxation rate proportional to the iron oxide concentration. This behavior is more prominent at low Larmor frequencies and is independent of the polar character of the confined molecules. The results reported here can be fitted well with a relaxation model considering exchange between molecules in the close vicinity of the paramagnetic centers located in the surface and bulk‐like molecules inside the pores. This model allows the extraction of the transverse diffusional correlation time that can be related to the polar character of the confined molecules. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
44.
首次采用光子能量小于硅中浅受主杂质电离能的可调谐远红外激光器作为激发源,获得了硅中浅受主杂质的光电导谱.可调谐半导体远红外激光器的调谐范围为380~500cm~(-1),光子流密度约10~(18)/cm~2·sec,用双光子跃迁对光电导谱进行了解释.对于Si:Al样品,光电导谱中的双峰分别相应于2P~1和2P~2中间态的双光子共振跃迁.也观察到了双光子透明的反共振现象. 相似文献
45.
Young Hee Lee Mayavan Viji Eunhwa Lee Hyeju Jo Kyung Yoo Jaeuk Sim Sunhwan Lee Kiho Lee Heesoon Lee Jae-Kyung Jung 《Tetrahedron letters》2017,58(26):2614-2617
During the process development for multistep synthesis of Rosuvastatin calcium several impurities were obtained along with the final Rosuvastatin calcium. Out of this; synthesis of impurity A (acetone adduct) a minor impurity of Rosuvastatin calcium (3R,5S,6E)-7-[4-(4-fluorophenyl)-2-[[(2-hydroxy-2-methylpropyl)sulfonyl(methyl)amino]-6-(1-methylethyl)-pyrimidin-5-yl]-3,5-dihydroxyheptenoicacid hemicalcium salt, is described. The synthesis of impurity A has been accomplished in 6 steps; starting from formation of β-hydroxy sulfonamide as the key intermediate and followed by using convenient routes with overall yield of 13.5%. The target compound can be used as the reference substance of impurity of the Rosuvastatin calcium. 相似文献
46.
Rebeca D. Gonçalves Sérgio Azevedo Fernando Moraes M. Machado 《International journal of quantum chemistry》2010,110(9):1778-1783
We have investigated, using first‐principles calculations, the role of a substitutional carbon atom on the geometric stability of boron nitride monolayers, nanotubes, and nanocones. It is shown that the formation of energy depends on the number of atoms for the monolayers and on the diameter for the tubes. It is also found, for the carbon‐doped boron nitride nanotubes, that the value for the strain energy approaches the one obtained for nondoped tubes with increasing diameter. For the structural stability, we have verified that the doping, which introduces an excess of nitrogen or boron, makes each structure more favorable in its reverse atmosphere, i.e., excess of nitrogen is more stable in a boron‐rich growth environment, whereas excess of boron is preferred in a nitrogen‐rich condition. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
47.
X‐ray standing wave (XSW) field generated under Bragg reflection condition in a periodic Mo/Si multilayer structure has been used to determine the concentration and location of various trace element contaminants embedded in different layers of that multilayer structure. We have used intense synchrotron X rays for XSW analysis. It is observed that various trace element impurities such as Cr, Fe, Ni and W get embedded unintentionally in the multilayer structure during the deposition process. Consequences of such impurity incorporation on the optical properties of the multilayer structure are discussed in hard and soft X‐ray regions. Present measurements are important in order to optimize the deposition methods on one hand and to better correlate the measured optical properties of a multilayer structure with theoretical models on the other. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
48.
A microscopic theory of resonant states for the Zn-doped CuO2 plane in the superconducting phase is formulated in the effective t–J model. In the model derived from the original p–d model, Zn impurities are considered as vacancies for the d states at Cu sites. In the superconducting phase, in addition to the local static perturbation induced by the vacancy, a dynamical perturbation appears that results in a frequency-dependent perturbation matrix. Using the T-matrix formalism for the Green's functions in terms of the Hubbard operators, we calculate the local density of electronic states with d, p, and s symmetries. 相似文献
49.
E. S. Voropai A. P. Zazhogin K. I. Chervyakovskii 《Journal of Applied Spectroscopy》2003,70(2):195-200
The process of formation of a radiating discharge cloud in the case of a diffusion mechanism of impurity exit to the surface of a molten small-weight sample is considered. An analytical expression describing the behavior of the relative rate of impurity entry into a discharge is obtained. 相似文献
50.
The effect of heat treatment on the Fe2+/Fe3+ ratio in some alkali phosphate glasses containing antimony and iron oxides has been investigated. Differential thermal analysis, Mossbauer spectroscopy, magnetic susceptibility and density measurements as well as the molar volume calculations were used in this study. The obtained data indicate that all glasses show approximately unchangeable stability. It is found, from the area under the Mossbauer absorption spectra that ferrous transformed gradually to ferric ions and the transformation rate constant was found to be 48 min−1. The elapsed time was found to be 160 min. This transformation represents a first-order solid state reaction. The molar magnetic susceptibility measurements confirm the above results. 相似文献