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81.
82.
The most common approach to establish a set of window coefficients, representing the discrete time window (data window), is to select a suitable one from the well-known collections of continuous time window functions by simply sampling techniques. The simplicity of this approach has its price in certain complications which become more and more obvious as the number N of window coefficients decreases to small values (N about 20 or less). It can be shown, that the DFT-even sampling technique as proposed by Harris [1] is not the most suitable one. Since both the aliasing effects as well as the relative position of the sampling raster gain influence on the resulting window magnitude spectrum in such a way that they must be checked individually, it turns out to be better to change the whole design strategy. The design of discrete windows is changed into an optimization problem within the set of all potential window coefficient vectors of given dimension. We apply the optimization criterion of Landau and Pollak [9]. One important advantage of this approach is that the optimization of the window coefficients is reduced to the proper selection of one single parameter which in a monotonic manner controls the trade-off between the two relevant window features mainlobe width and sidelobe level. 相似文献
83.
The windowed Fourier transform is a useful technique for fringe pattern analysis. It has been shown that the proper selection of the window size is a balance between the linear phase approximation error and the influence of noise [Q. Kemao, On widow size selection in windowed Fourier ridges algorithm. Opt Lasers Eng, 2007, accepted for publication]. Since the fringe intensity and noise level usually vary spatially, the window size should also be spatially adaptive in order to reach a good balance for each pixel of the fringe pattern. This addendum first shows that the windowed Fourier transform with a spatially fixed window size (SFWS) is still practically useful and then discusses the window size competition strategies for the windowed Fourier transform with a spatially adaptive window size (SAWS). The windowed Fourier transform with a SAWS is theoretically better than that with a SFWS but it is also more challenging in use. The windowed Fourier ridges algorithm is used for analysis throughout this paper. This analysis is also applicable to the windowed Fourier filtering algorithm. 相似文献
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85.
比较了乳糖等3种双糖或核糖等3种单糖及其复配物对近中性范围共轭亚油酸(CLA)形成脂肪酸囊泡(FAV)的影响. 用激光丁达尔效应确定FAV的pH窗口及各相区, 用透射电子显微镜及动态光散射表征其形貌和尺寸, 用浊度法研究了其稳定性, 用等温滴定量热证明各种糖及其复配物与FAV表面的弱非共价键合作用, 并经理论计算获得结合能. 实验和计算结果表明, 各种糖及其复配物均可以双向拓宽CLA形成FAV的pH窗口, 且拓宽其近中性pH窗口的能力按照双糖<单糖≈双糖/单糖≤单糖/单糖的顺序依次增强. 主要归结为单糖在FAV表面的强竞争吸附, 以及双糖可能因多结合位点吸附而减少其自由羟基与环境水分子的缔合作用, 从而影响多羟基小分子依靠自由羟基增强囊泡表面亲水性的效果. 相似文献
86.
Well-acknowledged problems associated with modeling the history force in large, many-particle simulations are related to the need to store and integrate over the entire lifetime of the particle. To address this concern, a computationally efficient method for calculating the history force (the “window model”) was developed based on the assumption of weak changes in acceleration in the recent relevant history of the particle. This assumption leads to the design of a model with a truncated integration interval which requires storage of and integration over a much shorter period of the particle’s history compared to other history force models. The truncation of the integration window can yield more than an order of magnitude savings in CPU time. In a related study, the two empirical coefficients of the Mei & Adrian history force kernel have been optimized (based on comparison with experimental data for falling particles) to give improved predictions of the data. Both the new history force kernel and the window model have been investigated for a large range of experimental data yielding, to the authors’ knowledge, the most extensive comparison yet conducted. For falling particles, the new history force kernel shows good predictions for particle Reynolds numbers ranging from 9 to 853 and density ratios from 1.17 to 9.32. Good predictions were also obtained using the window model when changes in particle relative acceleration over the window period were modest. For particles under forced oscillating in a quiescent fluid, the history kernel was generally reasonable but did not predict the peak forces well in all cases. This may be explained by noting that the assumption of a t−2 long-time dependence for the finite Reynolds number history force kernel may become invalid during rapid deceleration and wake ingestion (which can lead to exponential or t−1 behavior). However, the finite Reynolds number kernel gives better predictions in all cases than those made using the Basset history force. The window model was only reasonable for the oscillating particle cases when the changes in the relative particle acceleration over the integration window were small. 相似文献
87.
This study investigates the use of high resolution 1H NMR as a suitable alternative to the standard chromatographic method for the determination of adulteration of orange juice (Citrus sinensis) with grapefruit juice (Citrus paradisi) based on flavonoid glycoside content. Fifty-nine orange juices (OJ), 23 grapefruit juices (GJ) and 10 blends (OG), obtained from local retail outlets were used to assess the performance of the 1H NMR method. The work presented here introduces the Evolving Window Zone Selection (EWZS) function that holds promise for the automatic detection of spectral regions tailored to discriminate predefined groups. This technique was applied on the pre-processed 1H NMR spectra of the 92 juices. Independent Component Analysis (ICA) is a good alternative to Principal Component Analysis (PCA) for recovering linearly-mixed unobserved multidimensional independent signals and has been used in this study to build supervised models that classify the samples into three categories, OJ, GJ, OG. The regions containing the known flavonoid glycoside markers were selected as well as another zone containing the signals of sucrose, α-glucose and other components that were tentatively attributed. ICA was applied on three different groups of selected variables and showed good results for both discrimination and interpretation of the signals. Up to 97.8% of the juices were correctly attributed. This method gave better results than the commonly used PCA method. In addition, the time required to carry out the 1H NMR analysis was less than half the time of the standard chromatographic method. 相似文献
88.
本文研究了几种微波电路或元件和FIR数字滤波器的直接结构形式的内在关系。从而将FIR数字滤波器的窗函数设计技术引用到微波电路的设计中,提出了这些微波电路的时域设计方法。该方法具有简捷,有闭合形式公式可循等优点,尤其适合于工程设计。 相似文献
89.
本文给出(n,6,m)(m6)等重等距码的一种构造方法,侧重讨论了(n,6,m)等重等距码的基本结构形式,设计了几类可以用来构造(n,6,m)等重等距码的基本单元子块,并分析了构造原则和实现结果,以及置换个数和性能分析。 相似文献
90.