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61.
Theory of large-signal direct modulation of extended cavitysemiconductor lasers with dispersive loss
We present a model of coupled semiconductor diode-dispersive extended cavity lasers that describes arbitrarily large current modulation, does not assume uniform photon and carrier densities within the semiconductor diode gain medium, and is simple to implement numerically. In particular, we look at the fiber grating laser, an example of such a coupled system that has been studied as a possible optical communications source. We find simple expressions for the instantaneous frequency and intensity in terms of a few parameters characterizing the dispersion, allowing for the design of the system to minimize chirp. From these expressions we also recover Kazarinov and Henry's adiabatic chirp formula in the limit of slow modulation and Petermann's dynamical chirp formula in the limit of uniform carrier and photon densities. We show that in typical cases, where nonuniformity is important, the instantaneous frequency modulation is quantitatively and qualitatively different than is predicted by previous models 相似文献
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Gregory J. McCarthy Carol A. Sipe Kenneth E. McIlvried 《Materials Research Bulletin》1974,9(10):1279-1283
All REVO3 phases have been prepared and characterized by x-ray powder diffraction for symmetry and unit cell parameters. LaVO3 and CeVO3 have tetragonal variations of the perovskite structure while all remaining REVO3 phases are orthorhombic and isostructural with GdFeO3. The variation of cell parameters with RE3+ ionic radius shows a steady contraction with decreasing radius for ao, co and V while bo goes through a maximum. 相似文献
64.
Feature space trajectory methods for active computer vision 总被引:2,自引:0,他引:2
Sipe M.A. Casasent D. 《IEEE transactions on pattern analysis and machine intelligence》2002,24(12):1634-1643
We advance new active object recognition algorithms that classify rigid objects and estimate their pose from intensity images. Our algorithms automatically detect if the class or pose of an object is ambiguous in a given image, reposition the sensor as needed, and incorporate data from multiple object views in determining the final object class and pose estimate. A probabilistic feature space trajectory (FST) in a global eigenspace is used to represent 3D distorted views of an object and to estimate the class and pose of an input object. Confidence measures for the class and pose estimates, derived using the probabilistic FST object representation, determine when additional observations are required as well as where the sensor should be positioned to provide the most useful information. We demonstrate the ability to use FSTs constructed from images rendered from computer-aided design models to recognize real objects in real images and present test results for a set of metal machined parts. 相似文献
65.
Novel multimode fiber for narrow-band Bragg gratings 总被引:1,自引:0,他引:1
Szkopek T. Pasupathy V. Sipe J.E. Smith P.W.E. 《IEEE journal of selected topics in quantum electronics》2001,7(3):425-433
We propose a novel multimode fiber structure with modal propagation characteristics tailored to facilitate the creation of narrow-band high-reflectivity fiber Bragg gratings. The fiber structure proposed consists of concentric cylindrical shells of higher and lower refractive index material. A full vector second-order finite-element method is used to analyze the proposed multimode fiber structure. Simulations of the modal profiles show that high-order modes are localized to particular high-refractive index shells. We present the theoretical characterization of the modal propagation constant as a function of inner shell radius, shell separation, and harmonic-mode parameter. It is shown that a fiber with a minimum inner shell radius of at least 25λ (where λ is the vacuum wavelength), and a minimum shell separation of at least 10λ provides a reasonable tradeoff between fiber size and grating performance. A simulation of the multimode fiber grating shows that a grating with a full-width at half-maximum bandwidth on the order of 10-4λ is theoretically possible, if optical power is launched strictly into modes with angular harmonic parameter p=1 相似文献
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