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61.
J.C. Zhang M.F. Wu J.F. Wang J.P. Liu Y.T. Wang J. Chen R.Q. Jin H. Yang 《Journal of Crystal Growth》2004,270(3-4):289-294
The strain state of 570 nm AlxGa1−xN layers grown on 600 nm GaN template by metal organic chemical vapor deposition was studied using Rutherford backscattering (RBS)/channeling and triple-axis X-ray diffraction measurements. The results showed that the degree of relaxation (R) of AlxGa1−xN layers increased almost linearly when x0.42 and reached to 70% when x=0.42. Above 0.42, the value of R varied slowly and AlxGa1−xN layers almost full relaxed when x=1 (AlN). In this work the underlying GaN layer was in compressive strain, which resulted in the reduction of lattice misfit between GaN and AlxGa1−xN, and a 570 nm AlxGa1−xN layer with the composition of about 0.16 might be grown on GaN coherently from the extrapolation. The different shape of (0 0 0 4) diffraction peak was discussed to be related to the relaxation. 相似文献
62.
A. Hangleiter S. Heppel J. Off B. Kuhn F. Scholz S. Bader B. Hahn V. H rle 《Journal of Crystal Growth》2001,230(3-4):522-526
Using optical gain measurements and calculated optical gain spectra we analyse the various contributions to the threshold current observed for laser diodes. Our model is based on band-to-band transitions and includes internal polarization fields as well as multiple quantum wells. Besides good agreement between experiment and theory, our model explains the characteristic dependence of the threshold current on emission wavelength and well number. 相似文献
63.
64.
A. Louhadj Mohamed Ghezali F. Badi Noureddine Mehnane Youcef Cherchab Bouhalouane Amrani Hamza Abid Nadir Sekkal 《Superlattices and Microstructures》2009,46(3):435-442
Using the plane wave version of the full potential linear muffin-tin orbital (FPLMTO) method, which enables an accurate treatment of the interstitial regions, the electronic properties of ScN, YN, LaN and GdN rocksalt/rocksalt superlattices are calculated. It is found that apart from YN/ScN, all the other superlattices have negative bandgaps. However, it is shown that these systems can be semiconductors if a correction is made to the local density approximation (LDA). 相似文献
65.
F. Stokker-Cheregi M. Zamfirescu A. Vinattieri M. Gurioli I. Sellers F. Semond M. Leroux J. Massies 《Superlattices and Microstructures》2007,41(5-6):376
We discuss the thermalization of the polariton population from a bulk GaN λ/2 microcavity at room temperature. Simultaneous optical measurements of reflectivity and photoluminescence (PL), as well as time resolved measurements, reveal strong light–matter coupling. Transfer matrix theory is used to calculate reflectivity, absorption, and transmission coefficients for the structure. The PL emission is found to be thermalized, despite its very short lifetime, suggesting the existence of very fast energy relaxation channels. 相似文献
66.
Deuterium and nitrogen depth profiles in Ti with modified surfaces have been measured with Auger electron spectroscopy, secondary ion mass spectroscopy, and D(3He,p)4He nuclear reaction analysis. Nitrogen-rich surfaces layers of varying thicknesses were created on Ti by exposure to N2 gas at 650°C. Deuterium loading was performed by exposure to 1 Torr of D2 gas at 500°C. The deuterium distribution was influenced by nitrogen in the near-surface regions of all samples. Specifically, deuterium solubility was suppressed in surface regions of high (greater than 1%) nitrogen concentration. The deuterium solubility also remained low within the first few microns, well beyond the region of high nitrogen concentration. This effect is attributed to internal elastic stresses imposed by the non-deuterium absorbing nitrogen-rich layer on the Ti. These stresses prohibit the volume expansion associated with deuterium absorption. We estimate stresses on the order of 3–4 GPa are required to suppress the deuterium solubility to the values observed. The deuterium absorption kinetics were observed to depend systematically on the thickness of the nitrogen-rich layer. This is consistent with limited solubility near the surface or a surface poisoning effect influencing the overall deuterium diffusion from the gas phase into the Ti bulk. 相似文献
67.
68.
Chun Shan LU Xiao Nian LI* Yi Feng ZHU Hua Zhang LIU Chun Hui ZHOU Zhejiang Key Laboratory of Heterogeneous Catalysis Catalysis Institute of Zhejiang University of Technology Hangzhou 《中国化学快报》2004,(1)
Transition metal nitrides belong to a class of interstitial compounds, in which nitrogen atoms replace oxygen. They possess some technologically useful properties as packaging materials, structural materials and catalytic materials. Since Boudart1 succeeded to prepare high specific surface area g-Mo2N in 1985 using the NH3 temperatureprogrammed reduction method, transition metal nitrides have attracted much attention as potential catalysts owing to their similarity with the group VIII met… 相似文献
69.
Q. Sun J.C. Zhang J. Chen H. Wang Y.T. Wang H. Yang L.P. Guo 《Applied Surface Science》2006,252(8):3043-3050
Both cracked and crack-free GaN/Al0.55Ga0.45N multiple quantum wells (MQWs) grown on GaN template by metalorganic chemical vapor deposition have been studied by triple-axis X-ray diffraction, grazing-incidence X-ray reflectivity, atomic force microscope, photoluminescence spectroscopy and low-energy positron annihilation spectroscopy. The experimental results show that cracks generation not only deteriorates the surface morphology, but also leads to a period dispersion and roughens the interfaces of MQWs. The mean density of dislocations in MQWs, determined from the average full-width at half-maximum of ω-scan of each satellite peak, has been significantly enhanced by the cracks generation. Furthermore, the measurement of annihilation-line Doppler broadening reveals a higher concentration of negatively charged vacancies in the cracked MQWs. The combination of these vacancies and the high density of edge dislocations are assumed to contribute to the highly enhanced yellow luminescence in the cracked sample. 相似文献
70.
The possibility of forming niobium oxynitride through the nitridation of niobium oxide films in molecular nitrogen by rapid
thermal processing (RTP) was investigated. Niobium films 200 and 500 nm thick were deposited via sputtering onto Si(100) wafers
covered with a thermally grown SiO2 layer 100 nm thick. These as-deposited films exhibited distinct texture effects. They were processed in two steps using an
RTP system. The as-deposited niobium films were first oxidized under an oxygen atmosphere at 450 °C for various periods of
time and subsequently nitridated under a nitrogen atmosphere at temperatures ranging from 600 to 1000 °C for 1 min. Investigations
of the oxidized films showed that samples where the start of niobium pentoxide formation was detected at the surface and the
film bulk still consisted of a substoichiometric NbOx phase exhibited distinctly lower surface roughness and microcrack densities than samples where complete oxidation of the
film to Nb2O5 had occurred. The niobium oxide phases formed at the Nb/substrate interface also showed distinct texture. Zones of niobium
oxide phases like NbO and NbO2, which did not exist in the initial oxidized films, were formed during the nitridation. This is attributed to a “snow-plough
effect” produced by the diffusion of nitrogen into the film, which pushes the oxygen deeper into the film bulk. These oxide
phases, in particular the NbO2 zone, act as barriers to the in-diffusion of nitrogen and also inhibit the outdiffusion of oxygen from the SiO2 substrate layer. Nitridation of the partially oxidized niobium films in molecular nitrogen leads to the formation of various
niobium oxide and nitride phases, but no indication of niobium oxynitride formation was found.
Figure Schematic representation of the phase distribution in 200 nm Nb film on SiO2/Si substrate after two steps annealing using an RTP system. The plot below represents the SIMS depth profiles of the nitridated
sample with the phase assignment 相似文献