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51.
TiO2 nanoparticles are prepared by a sol–gel method and annealed both in air and vacuum at different temperatures to obtain anatase, anatase–rutile mixed phase and rutile TiO2 nanoparticles. The phase conversion from anatase to anatase–rutile mixed phase and to rutile phase takes place via interface nucleation between adjoint anatase nanocrystallites and annealing temperature and defects take the initiate in this phase transformation. The samples are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis and photoluminescence spectroscopy (PL). Anatase TiO2 exhibits a defect related absorption hump in the visible region, which is otherwise absent in the air annealed samples. The Urbach energy is very high in the vacuum annealed and in the anatase–rutile mixed phase TiO2. Vacuum annealed anatase TiO2 has the lowest emission intensity, whereas an intense emission is seen in its air annealed counterpart. The oxygen vacancies in the vacuum annealed samples act as non-radiative recombination centers and quench the emission intensity. Oxygen deficient anatase TiO2 has the longest carrier lifetime. Time resolved spectroscopy measurement shows that the oxygen vacancies act as efficient trap centers of electrons and reduce the recombination time of the charge carriers. 相似文献
52.
53.
Electronic properties of Ga0.9375Al0.0625As with Ga and As monovacancies are investigated with the density functional theory. A perfect GaAlAs, which specifically produces a radiation wavelength of ~825.6 nm, has been determined in terms of size and number of atoms of substances. We have introduced eight types of vacancies depending on the distance from the Al atom to the vacancy to obtain the changes in charges, band structures, density of states, and optical conductivity. We found that the Fermi level enters into the valence band due to the formations of the Ga or As vacancies so that the vacant materials may show the characteristics of the p-type semiconductor. Interestingly, Ga-vacancy systems make direct band gaps, which are still good for the use in a semiconductor laser. But, As-vacancy systems, where the indirect gaps appear, are not feasible for the same application. It has been found that the latter phenomenon is induced by a newly formed density of state, which comes from the overlapping of hybridised 4s and 4p orbitals of Ga atoms around As vacancy. 相似文献
54.
This paper presents the effect of XeCl laser irradiation on Nd:YAG single crystal samples with various number of pulses at different repetition rates and laser fluences. Effects of the irradiation on the optical and structural properties of the crystal are analyzed by UV–vis-NIR spectroscopy. Annihilation of some point defects of the crystal structure is observed following laser irradiation at a fluence of 100 mJ cm−2 with 100 and 500 pulses. Increasing the laser fluence and pulse numbers leads to saturation and new defects are found to be formed in the crystal. Additional absorption spectra of the irradiated samples show that oxygen vacancies in the Nd:YAG crystals are removed during the low-dose irradiation. The laser irradiation is compared to the thermal annealing process for Nd:YAG crystal modification. Additional absorption spectrum of an annealed sample reveals that induced negative absorption band at 236 nm is correlated with the annihilation of the oxygen vacancy center. Our results also demonstrate that XeCl laser treatment has several advantages upon annealing at high temperatures in the Nd:YAG crystal quality improvement. Thus, the present work can give a new approach to modify Nd:YAG crystals to be used in a wide variety of solid-state laser engineering. 相似文献
55.
In this paper, a high-performance silver-doped titanium dioxide (Ag/TiO2) humidity sensor was synthesized using a hydrothermal synthesis method for respiratory monitoring. The sensing mechanism was studied by the first principles of density functional theory (DFT). Calculations show that the doping of Ag+ ions increases the adsorption energy of TiO2 to water molecules. Furthermore, the Ti–O bond in TiO2 is broken due to the doping of Ag+ ions, which promotes the generation of Ti3+ defects. Experiments show that the doping of Ag+ ions can increase the hydroxide groups, Ti3+ defects and oxygen vacancies on the surface of TiO2, thus effectively improving the responsivity, linearity and hysteresis of the TiO2 humidity sensor. Compared to TiO2, the resistance of the Ag/TiO2 (0.5 mM) humidity sensor reaches 4.5 orders of magnitude with a high response of 39707.1, maximum hysteresis rate of 4.6%, response/recovery time of 31 s/15 s and the best linearity in a range of 11%–95% RH. In addition, the Ag/TiO2 humidity sensor has been successfully used to detect different modes of respiration and determine the respiratory rate under different respiratory states. Significantly, this work demonstrates potential application value in human healthcare and activities monitoring. 相似文献
56.
Xiao Han 《Molecular physics》2013,111(24):3546-3555
The trapping and detection of nitrogen oxide with tungsten trioxide has become a popular research topic in recent years. Knowledge of the complete reaction mechanism for nitrogen oxide adsorption is necessary to improve detector performance. In this work, we used density functional theory (DFT) calculations to study the adsorption characteristics and electron transfer of nitrogen dioxide on an oxygen-deficient monoclinic WO3 (0 0 1) surface. We observed different reactions of NO2 on slabs with different O- and WO-terminated WO3 (0 0 1) surfaces with oxygen vacancies. Our calculations show that the bridging oxygen atom on an oxygen defect on an O-terminated WO3 (0 0 1) surface is the active site where an NO2 molecule is oxidised into nitrate and is adsorbed onto the surface. On a WO-terminated (0 0 1) surface, one of the oxygen atoms from the NO2 molecule fills the oxygen vacancy, and the resulting NO fragment is adsorbed onto a W atom. Both of these adsorption models can cause an increase in the electrical resistance of WO3. We also calculated the adsorption energies of NO2 on slabs with different oxygen-deficient WO3 surfaces. 相似文献
57.
In this study, the semi-empirical and empirical calculations of K X-ray intensity ratios, K-shell fluorescence yields, and vacancy transfer probabilities have been performed for 3d transition elements. Also, σKα, σKβ production cross-sections, Kβ/Kα intensity ratios, ωK fluorescence yields, and ηKL vacancy transfer probabilities of 3d transition elements have been measured. The samples were excited by 59.5 keV γ-rays from a 241Am annular radioactive source. K X-rays emitted by samples were counted by an Ultra-LEGe detector with a resolution of 150 eV at 5.9 keV. 相似文献
58.
C. Paulmann 《Phase Transitions》2013,86(1-3):77-90
High temperature X-ray diffraction and quenching experiments of mullite single crystals with Al2O3:SiO2 ratio 2:1 have been performed to investigate the stability of the oxygen vacancy ordering close to the melting point of mullite. The experiments show that the structure of mullite exhibits an extremely stable, temperature-independent incommensurate modulation. Inspection of satellite reflections at different temperatures leads to the conclusion that the ordering scheme of oxygen vacancies after the crystallization of mullite persists to the melting point and does not show any disordering effects. The experimental results are in agreement with former theoretical calculations using a statistical mechanics approach which yield the critical temperature Tc > 3000°C. 相似文献
59.
The magnetic property induced by neutral Cd and S vacancies in CdS bulk and thin film are investigated, using first principles simulation. For bulk CdS, the magnetism originates from Cd, instead of S, vacancies. The ferromagnetism with a Curie temperature above room temperature can be expected. For CdS thin film, both Cd and S vacancies does not yield any magnetism at the (111) surface, while local magnetic moments at the outermost S plane of the (001) surface is ascribed to the surface effect. The ferromagnetism at S-terminated (001) surface can account for the experimental observation. 相似文献
60.
采用基于密度泛函理论的平面波超软赝势方法研究了 纯的和不同高氧空位浓度金红石型TiO2-x (x=0, 0.083, 0.125, 0.167, 0.25)超胞的能带结构分布、态密度分布.同时, 采用局域密度近似+U方法调准了带隙.结果表明, 高氧空位浓度越高, 金红石型TiO2的最小带隙越变窄、电子有效质量越减小, 自由电子浓度越高, 电子迁移率越低、电导率越低.计算结果与实验结果的变化趋势相符合.
关键词:
高氧空位
2')" href="#">金红石型TiO2
电导率
第一性原理 相似文献