全文获取类型
收费全文 | 152篇 |
免费 | 23篇 |
国内免费 | 10篇 |
专业分类
化学 | 11篇 |
力学 | 19篇 |
综合类 | 8篇 |
数学 | 49篇 |
物理学 | 98篇 |
出版年
2023年 | 1篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 10篇 |
2013年 | 8篇 |
2012年 | 6篇 |
2011年 | 12篇 |
2010年 | 11篇 |
2009年 | 12篇 |
2008年 | 14篇 |
2007年 | 15篇 |
2006年 | 12篇 |
2005年 | 9篇 |
2004年 | 6篇 |
2003年 | 4篇 |
2002年 | 7篇 |
2001年 | 1篇 |
2000年 | 8篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有185条查询结果,搜索用时 46 毫秒
81.
James W. Cooley 《Mikrochimica acta》1987,93(1-6):33-45
The discovery of the fast Fourier transform (FFT) algorithm and the subsequent development of algorithmic and numerical methods based on it have had an enormous impact on the ability of computers to process digital representations of signals, or functions. At first, the FFT was regarded as entirely new. However, attention and wide publicity led to an unfolding of its pre-electronic computer history going back to Gauss. The present paper describes the author's own involvement and experience with the FFT algorithm.The author is grateful for permission from the Association for Computing Machinery to allow the present paper to bear some similarity with the paper,How the FFT Gained Acceptance, ref. [28] 相似文献
82.
P. Norouzi M. R. Ganjali A. Mirabi-Semnakolaii B. Larijani 《Russian Journal of Electrochemistry》2008,44(9):1015-1023
A novel method for determining perphenazine in flow-injection systems has been developed in this work. The method was successfully
applied for fast determination of perphenazine in its pharmaceutical formulations. Being very simple, precise, accurate, time-saving,
and economical, this method has many advantages compared to all of the previously reported methods. Some investigations were
also performed to find the effects of various parameters on the sensitivity of the proposed method. The conditions responsible
for the performance were a pH value of 2, a scan rate value of 30 V/s, an accumulation potential of 500 mV, and an accumulation
time of 0.8 s. Some of the advantages of the proposed method are as follows: the removal of oxygen from the test solution
is not required anymore, the detection limit of the method is subnanomolar, and finally, the method is fast enough to determine
such compounds in a wide variety of chromatographic methods. We also introduce a special computer-based numerical method to
calculate the analyte signal and noise reduction. After subtraction of the background current from noise, the electrode response
was calculated based on partial and total charge exchanges at the electrode surface. The integration range of currents was
set for all the potential scan ranges, including oxidation and reduction of the Au surface electrode, to obtain a sensitive
determination. The waveform potential was continuously applied on an Au disk microelectrode (a radius of 12.5 μm). The detention
limit of the method for perphenazine was 15 pg/ml. For eight runs, the relative standard deviation of the method at 1.1 ×
10−8 M was 2.1%.
Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 9, pp. 1093–1102.
The text was submitted by the authors in English. 相似文献
83.
84.
二维小波变换及在青藏高原地形重构中的应用 总被引:1,自引:0,他引:1
计算和检验了4种不同小波基底和不同阶小波基底对单脉冲和尖峰两个信号的分解及重构的性质,结果表明双正交小波的精度最高,Coifman小波的精度最低.通过设阈值对小波和快速Fourier变换进行截断后再重构,说明小波具有重构精度高、所用非零系数少以及误差被局域化等优点,这就削弱了"Gibbs现象",限制了它的影响范围.在此基础上,用二维快速Fourier和二维离散小波变换对实际青藏高原及其附近地形做了分解、重构及截断后重构等,说明二维小波变换能以较之FFT更少的非零系数和误差局域化等重构大地形,表明了二维小波变换在未来大气环流数值模式中的应用潜力. 相似文献
85.
高频地波雷达海洋回波数据采集及其处理 总被引:3,自引:0,他引:3
根据线性调频雷达技术雷达和Donald E.Barrick提出FM/CW雷达信号的处理方法,研究雷达数据采集系统的组成和领带处理板(TMS320C50和ADSP2181 DSP)的结构、工作原理,以及程序编写。同时分析了提取海洋表面距离的FFT(Cooley-Tukey)算法、数据结构。数据采集系统采用流水线工作方式,由DSP硬件和PC微机组成,应用C/C++高级语言和汇编语言混合编程,实现了数据的实时采集及处理,满足了雷达系统工作要求。 相似文献
86.
After discussing Schofield's fast Fourier transform (FFT) algorithm, a (weighted) discrete-cosine-transform-based (DCT-based) phase-unwrapping (PU) algorithm is described. The algorithm could unwrap some high-phase-variation map which the FFT algorithm could not solve. Although the DCT algorithm is derived from Schofield's FFT PU algorithm, unlike FFT, it avoids the mirroring operation in implementing the boundary conditions so that it has higher efficiency in PU. Furthermore, in order to improve the reliability and noise robustness, we introduce the phase derivative variance (PDV) quality weight extracted from quality map into the DCT algorithm. The unwrapped results of both the computer-simulated and interferometric synthetic aperture radar (IFSAR) data demonstrate that the (weighted) DCT PU algorithm is generally effective, especially in dealing with the high-phase-variation and/or irregular-phase-distribution maps. 相似文献
87.
88.
G. Lotti 《Numerical Linear Algebra with Applications》2007,14(8):645-657
A direct algorithm is presented for the solution of linear systems having banded Toeplitz coefficient matrix with unbalanced bandwidths. It is derived from the cyclic reduction algorithm, it makes use of techniques based on the displacement rank and it relies on the Morrison–Sherman–Woodbury formula. The algorithm always equals and sometimes outperforms the already known direct ones in terms of asymptotic computational cost. The case where the coefficient matrix is a block banded block Toeplitz matrix in block Hessenberg form is analyzed as well. The algorithm is numerically stable if applied to M‐matrices that are point diagonally dominant by columns. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
89.
A spectrally accurate fast method for electrostatic calculations under periodic boundary conditions is presented. We follow the established framework of FFT-based Ewald summation, but obtain a method with an important decoupling of errors: it is shown, for the proposed method, that the error due to frequency domain truncation can be separated from the approximation error added by the fast method. This has the significance that the truncation of the underlying Ewald sum prescribes the size of the grid used in the FFT-based fast method, which clearly is the minimal grid. Both errors are of exponential-squared order, and the latter can be controlled independently of the grid size. We compare numerically to the established SPME method by Essmann et al. and see that the memory required can be reduced by orders of magnitude. We also benchmark efficiency (i.e. error as a function of computing time) against the SPME method, which indicates that our method is competitive. Analytical error estimates are proven and used to select parameters with a great degree of reliability and ease. 相似文献
90.
Farhad Fakhar‐Izadi Mehdi Dehghan 《Mathematical Methods in the Applied Sciences》2013,36(12):1485-1511
The pseudo‐spectral Legendre–Galerkin method (PS‐LGM) is applied to solve a nonlinear partial integro‐differential equation arising in population dynamics. This equation is a competition model in which similar individuals are competing for the same resources. It is a kind of reaction–diffusion equation with integral term corresponding to nonlocal consumption of resources. The proposed method is based on the Legendre–Galerkin formulation for the linear terms and interpolation operator at the Chebyshev–Gauss–Lobatto (CGL) points for the nonlinear terms. Also, the integral term, which is a kind of convolution, is directly computed by a fast and accurate method based on CGL interpolation operator, and thus, the use of any quadrature formula in its computation is avoided. The main difference of the PS‐LGM presented in the current paper with the classic LGM is in treating the nonlinear terms and imposing boundary conditions. Indeed, in the PS‐LGM, the nonlinear terms are efficiently handled using the CGL points, and also the boundary conditions are imposed strongly as collocation methods. Combination of the PS‐LGM with a semi‐implicit time integration method such as second‐order backward differentiation formula and Adams‐Bashforth method leads to reducing the complexity of computations and obtaining a linear algebraic system of equations with banded coefficient matrix. The desired equation is considered on one and two‐dimensional spatial domains. Efficiency, accuracy, and convergence of the proposed method are demonstrated numerically in both cases. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献