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661.
Effective receive beamforming in medical ultrasound imaging is important for enhancing spatial and contrast resolution. In current ultrasound receive beamforming, a constant sound speed (e.g., 1540 m/s) is assumed. However, the variations of sound speed in soft tissues could introduce phase distortions, leading to degradation in spatial and contrast resolution. This degradation becomes even more severe in imaging fatty tissues (e.g., breast) and with obese patients. In this paper, a mean sound speed estimation method where phase variance of radio-frequency channel data in the region of interest is evaluated is presented for improving spatial and contrast resolution. The proposed estimation method was validated by the Field II simulation and the tissue mimicking phantom experiments. In the simulation, the sound speed of the medium was set to 1450 m/s and the proposed method was capable of capturing this value correctly. From the phantom experiments, the −18-dB lateral resolution of the point target at 50 mm obtained with the estimated mean sound speed was improved by a factor of 1.3, i.e., from 3.9 mm to 2.9 mm. The proposed estimation method also provides an improvement of 0.4 in the contrast-to-noise ratio, i.e., from 2.4 to 2.8. These results indicate that the proposed mean sound speed estimation method could enhance the spatial and contrast resolution in the medical ultrasound imaging systems. 相似文献
662.
I.IntroductionTheboundaryelementmethod(BEM),basedontheHelmholtzintegralequation(HIE),hasbeenappliedtothesolutionofexternalandinternalacousticradiationandscatteringproblemssincetheearly196Os.Inrecentyears,extensiveworkhasbeenperformedtoaddressthetwomajordrawbacksoftheuseofboundaryelementmethodinacousticprobIems'singularintegralkerneIsanduniquenessofsolution.ThisarticlepresentsanewmethodoftheBEMforexternalsoundradiationthateliminatesthesingularintegrationinasimpleway.TheBEMinsoundradiatio… 相似文献
663.
I.IntroductionIn1979,M.R.S.h.o.der[1]pro-posedanewdesignofsounddiffusorwhoseperiodcomprisesNelements(slotsorwells,referedtoaschannelsinfol1owing)ofequalwidths.ThedepthsofchanneIsvaryaccordingtoapseu-dostochasticsequencewithinonepe-riod.Atypicalstructureofq1ladraticresiduediffusor(N=11)isi1IustratedinFig.1.BychoosingthedePtl1ofchannels,thescatteringcharacteristicsofthestructurecanbeoptirnizeds11chastodistributethescattereden(}rgyequalIyoveralloweddirections.In1992,K.Fuiwaraandothers['repo… 相似文献
664.
Gee-Pinn James Too 《Applied Acoustics》2004,65(3):251-261
The similar source method (SSM) uses an imaginary source distribution to estimate radiated and scattered sound fields. The error analyses in the present study are for possible numerical errors by SSM, solutions of the problem of singularity and non-unique solution by SSM and the effects of possible errors in measurements on the estimation of the sound field by SSM. 相似文献
665.
Harmonic generation measurements typically make use of the plane wave result when extracting values for the nonlinearity parameter, β, from experimental measurements. This approach, however, ignores the effects of diffraction, attenuation, and receiver integration which are common features in a typical experiment. Our aim is to determine the importance of these effects when making measurements of β over different sample dimensions, or using different input frequencies. We describe a three-dimensional numerical model designed to accurately predict the results of a typical experiment, based on a quasi-linear assumption. An experiment is designed to measure the axial variation of the fundamental and second harmonic amplitude components in an ultrasonic beam, and the results are compared with those predicted by the model. The absolute β values are then extracted from the experimental data using both the simulation and the standard plane wave result. A difference is observed between the values returned by the two methods, which varies with axial range and input frequency. 相似文献
666.
In this paper, we propose a more general forecasting method to predict the sound absorption coefficients at six central frequencies and the average sound absorption coefficient of a sandwich structure nonwoven absorber. The kernel assumption of the proposed method is that the acoustics property of sandwich structure nonwoven absorber is determined by some easily measured structural parameters, such as thickness, area density, porosity, and pore size of each layer, if the type of the fiber used in nonwoven is given. By holding this assumption in mind, we will use general regression neural network (GRNN) as a prediction model to bridge the gap between the measured structural parameters of each absorber and its sound absorption coefficient. In experiment section, one hundred sandwich structure nonwoven absorbers are particularly designed with ten different types of meltblown polypropylene nonwoven materials and four types of hydroentangled E-glass fiber nonwoven materials firstly. Secondly, four structural parameters, i.e., thickness, area density, porosity, and pore size of each layer are instrumentally measured, which will be used as the inputs of GRNN. Thirdly, the sound absorption coefficients of each absorber are measured with SW477 impedance tube. The sound absorption coefficient at 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz and their average value are used as the outputs of GRNN. Finally, the prediction framework will be carried out after the desired training set selection and spread parameter optimization of GRNN. The prediction results of 20 test samples show the prediction method proposed in this paper is reliable and efficient. 相似文献
667.
A double-leaf microperforated panel absorber (DLMPP) is composed of a two microperforated panel (MPP) with a air cavity in-between, and without any backing structure. It shows a Helmholtz-type resonance peak absorption and additional low frequency absorption, therefore it can be used as a wideband space sound absorber. In this study, a theoretical study is made to examine the effect of a permeable membrane inside the air-cavity. Permeable membranes are studied in our previous studies and proved to be effective to improve the sound absorption performance of various type MPP sound absorbers. We investigate the absorption characteristics of a DLMPP with a permeable membrane in the cavity through numerical examples, and also studied the effect of honeycomb in the cavity of the same sound absorption structure. 相似文献
668.
669.
本文利用环绕声重发的声像定位理论,对一种受到重视、很可能将被国际上广泛应用的通用环绕声系统—5通路3/2系统的声像特性进行了分析,并对系统进行了声像定位实验.理论和实验结果表明,按目前的信号馈给方式,系统可在倾听者前方产生稳定而明晰的声像;但在侧向和后方只能产生模糊和不稳定的声像(扬声器方向除外);将别是在侧向,存在着一个声像的死区,并且对侧向和后方声像来说,听音区域片不宽阔,因而作为一种通用的系统,虽然将其用作伴随图像的重发时,可获得较好的效果;但用作不伴随图像的重发时,系统并不能很好地再观原声场的空间感。由于系统存在这种不容忽视的缺陷,文中着重强调应设法在这方面对系统加以改进 相似文献
670.