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51.
Freddy Alberto Monroy 《Optik》2010,121(22):2049-2052
Experimental features such as wavelength, camera specifications and reconstruction distance determine the theoretical limit for lateral resolution in digital holography. However, the actual experimental resolution limit is about 50% below such theoretical limit due to the high-contrast speckle noise presented in the reconstructed holograms. Recently, a technique has been introduced to reduce the contrast of speckle noise that is based on the superposition of uncorrelated hologram reconstructions of the same static object [5] (Garcia-Sucerquia et al., 2006). By this approach of reducing the contrast of the speckle noise, it is experimentally shown that an improvement of the order of 50% can be reached when 100 reconstructed images are superimposed. 相似文献
52.
In this work, we investigate the electronic structure and vertical electron transport through GaN/AlN/GaN single-barrier structures with different AlN thickness, grown by plasma-assisted molecular beam epitaxy. Conductive and capacitive characterization has been performed, and the experimental results are interpreted by comparison with 1D self-consistent simulations. Capacitive measurements reveal a complete depletion of the top GaN layer, and the formation of a two-dimensional electron gas at the bottom interface of the AlN barrier, even for barrier thicknesses of 0.5 nm (2 monolayers of AlN). Conductive atomic force microscopy reveals discrete leakage current locations with a density of 107 cm−2, more than one order of magnitude lower than the dislocation density in these samples. These results are promising for the fabrication of resonant tunnelling diodes using the GaN/AlN material system. 相似文献
53.
Fiber transmission and generation of ultrawideband pulses by direct current modulation of semiconductor lasers and chirp-to-intensity conversion 总被引:1,自引:0,他引:1
Optical pulses generated by current modulation of semiconductor lasers are strongly frequency chirped. This effect has been considered pernicious for optical communications. We take advantage of this effect for the generation of ultrawideband microwave signals by using an optical filter to achieve chirp-to-intensity conversion. We also experimentally achieve propagation through a 20 km nonzero dispersion shifted fiber with no degradation of the signal at the receiver. Our method constitutes a prospective low-cost solution and offers integration capabilities with fiber-to-the-customer-premise systems. 相似文献
54.
Luz E. González Alvaro Morales Simon Rommel Bo F. Jørgensen N. Porras-Montenegro Idelfonso Tafur Monroy 《Fiber and Integrated Optics》2018,37(2):57-65
A multi-core fiber (MCF) patch panel was designed, allowing easy coupling of individual signals to and from a 7-core MCF. The device was characterized, measuring insertion loss and cross talk, finding highest insertion loss and lowest crosstalk at 1300 nm with values of 9.7 dB and -36.5 dB respectively, while at 1600 nm insertion loss drops to 4.8 dB and crosstalk increases to -24.1 dB. Two MCF splices between the fan-in module, the MCF, and the fan-out module are included in the characterization, and splicing parameters are discussed. 相似文献
55.
S. Valdueza-Felip F.B. Naranjo M. González-Herráez L. Lahourcade E. Monroy S. Fernández 《Journal of Crystal Growth》2010,312(19):2689-2694
We present a detailed investigation on the influence of deposition conditions on morphological, structural and optical properties of InN films deposited on Si(1 1 1) and GaN-on-sapphire templates by reactive radio-frequency (RF) sputtering. The deposition parameters under study are nitrogen content in the sputtering gas, substrate–target distance, substrate temperature and RF power. X-ray diffraction measurements confirm the (0 0 0 1) preferred growth orientation and the wurtzite crystallographic structure of the material. For optimized deposition conditions, InN on Si(1 1 1) substrates presents smooth surface with root-mean-square roughness ∼1 nm. Surface quality of the InN films can be further improved by deposition on GaN-on-sapphire templates, achieving root-mean-square roughness as low as ∼0.4 nm, comparable to that of the underlying substrate. The room-temperature absorption edge is located at 1.70 eV. Intense low-temperature photoluminescence peaking at 1.60 eV is observed. 相似文献
56.
Crosslinking effects on hybrid organic–inorganic proton conducting membranes based on sulfonated polystyrene and polysiloxane
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León Guillermo Mendoza‐Reyes Alejandro Gutiérrez‐Sánchez Juan Carlos Ruiz‐Segura Minerva Monroy‐Barreto Julio César Aguilar Eduardo Rodríguez de San Miguel Josefina de Gyves 《先进技术聚合物》2016,27(3):404-413
New hybrid semi‐interpenetrating proton‐conducting membranes were obtained using sulfonated polystyrene (SPS) and inorganic–organic polysiloxane phases with the aim of improving the mechanical and thermal characteristics of the pristine polymer and to study the effects of crosslinking in the latter phase in several of their properties, mainly proton conductivity. Siloxane phases were prepared using poly(dimethylsiloxane) (PDMS) and PDMS with tetraethoxysilane (TEOS) or phenyltrimethoxysilane (PTMS) as crosslinking agents. To study the crosslinking effect, membranes were prepared with different TEOS:PDMS and PTMS:PDMS mole ratios. The films obtained were characterized by FTIR, 29Si‐HPDEC MAS‐NMR, 13C‐CP‐MAS NMR, elemental and thermal analyses. Certain properties, such as water uptake (WU), ion exchange capacity (IEC) and the state of the water, were determined. The proton conductivity was measured at different temperatures (30°C and 80°C) and relative humidities (50–95%). The water content of the hybrid membranes declined significantly, compared with the SPS membranes, depending on the nature and amount of siloxane phase added. Nonetheless, the conductivity values remained relatively high (>100 mS cm?1 at 80°C and 95% RH) when compared to Nafion®117 presumably because of the formation of well developed proton channels, which makes them potentially promising as proton exchange membranes for fuel cells. These membranes proved to be thermally stable up to 350°C. Scanning electron microscopy (SEM) and scanning electrochemical microscopy (SECM) were used to characterize the hybrid membranes microstructures; the latter provided contrast for the conductive domains. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
57.
Doped amorphous silicon films were prepared by plasma-enhanced chemical vapour deposition of silane and hydrogen mixtures, using phosphorus pentafluoride (PF5) and boron trifluoride (BF3) as dopant precursors. The films were studied by UV-vis spectroscopy and their photo and dark conductivity were measured, the latter as a function of temperature. The optical gap of the n-type samples, doped with PF5, diminished as the concentration of this gas in the plasma was increased. However, the optical gap of p-type samples, doped with BF3, did not show any appreciable optical gap decrease as the concentration of BF3 was varied from 0.04% to 4.7%. The dark conductivity of the p-type films at these extremes of the doping range were 7.6 × 10−10 and 3.5 × 10−1 Ω−1 cm−1, respectively. 相似文献
58.
Ramirez F. Monroy O. Favela E. Guyot J. P. Cruz F. 《Applied biochemistry and biotechnology》1998,(1):215-223
Applied Biochemistry and Biotechnology - The methanogenesis of acetamide occurs through a two-step reaction in methanogenic sludges. First, acetamide is hydrolyzed to acetate and ammonia by a... 相似文献
59.
J. L. Pau E. Monroy E. Muoz F. B. Naranjo F. Calle M. A. Snchez-García E. Calleja 《Journal of Crystal Growth》2001,230(3-4):544-548
The fabrication and characterisation of AlxGa1−xN (0x0.35) photodetectors grown on Si(1 1 1) by molecular beam epitaxy are described. For low Al contents (<10%), photoconductors show high responsivities (10A/W), a non-linear dependence on optical power and persistent photoconductivity (PPC). For higher Al contents the PPC decreases and the photocurrent becomes linear with optical power. Schottky photodiodes present zero-bias responsivities from 12 to 5 mA/W (x=0−0.35), a UV/visible contrast higher than 103, and a time response of 20 ns, in the same order of magnitude as for devices on sapphire substrate. GaN-based p–n ultraviolet photodiodes on Si(1 1 1) are reported for the first time. 相似文献
60.
Marangoni stresses and surface compression rheology of surfactant solutions. Achievements and problems 总被引:1,自引:0,他引:1
In the presence of soluble surfactants, the motion of liquid surfaces involves Marangoni effects. As a consequence, the surfaces exhibit elastic responses, even frequently behaving as rigid surfaces, especially at low surfactant concentration. The Marangoni effects can be conveniently quantified introducing surface viscoelastic compression parameters that characterize the mechanical response of the surface near equilibrium. Many experimental techniques allow measuring the viscoelastic parameters. However, many difficulties are encountered during the interpretation of the surface response in the various types of hydrodynamic velocity fields involved in the different techniques. The role of adsorption and desorption energy barriers appears crucial, despite the fact that little is known yet about their values. In this short review, we will present examples illustrating the different problems. 相似文献