全文获取类型
收费全文 | 246篇 |
免费 | 32篇 |
国内免费 | 6篇 |
专业分类
化学 | 97篇 |
力学 | 10篇 |
综合类 | 1篇 |
数学 | 47篇 |
物理学 | 129篇 |
出版年
2023年 | 1篇 |
2022年 | 7篇 |
2021年 | 2篇 |
2020年 | 8篇 |
2019年 | 2篇 |
2018年 | 5篇 |
2017年 | 6篇 |
2016年 | 13篇 |
2015年 | 10篇 |
2014年 | 17篇 |
2013年 | 21篇 |
2012年 | 14篇 |
2011年 | 12篇 |
2010年 | 19篇 |
2009年 | 17篇 |
2008年 | 16篇 |
2007年 | 14篇 |
2006年 | 13篇 |
2005年 | 5篇 |
2004年 | 13篇 |
2003年 | 8篇 |
2002年 | 12篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 1篇 |
1998年 | 4篇 |
1997年 | 11篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 5篇 |
1981年 | 1篇 |
排序方式: 共有284条查询结果,搜索用时 328 毫秒
101.
Wenbin Gao 《Chinese Journal of Lasers》1992,1(2):159-164
This paper reports that the actual fluorescence lifetime 7.64±0.06ns of a10%-glyoxal water solution is determined for the first time from the laser-induced fluores-cence decay curve detected by the system with a response time in the order of magnitude ofnanosecond and processed by deconvolution on combination with phase plane method and iter-ative convolution method.The experimental method presented in this paper is regarded as aneffective method for measuring the fluorescence lifetime in nanoseconds or even in sub-nanoseconds by means of a detecting system with an order of magnitude of nanosecond. 相似文献
102.
Y. P. Mack
Norman S. Matloff
《Statistics & probability letters》1990,10(5):369-376Given unobservable i.i.d. r.v.'s Mi with c.d.f. F, and observable r.v.'s Yij with E(Yij|Mi) = Mi; we study a nonparametric estimate of F based on the Yij's by conditioning and kernel techniques. This investigation extends previous works of Blischke (1965) and James (1978). 相似文献
103.
Per Christian Hansen 《Numerical Algorithms》2002,29(4):323-378
By deconvolution we mean the solution of a linear first-kind integral equation with a convolution-type kernel, i.e., a kernel that depends only on the difference between the two independent variables. Deconvolution problems are special cases of linear first-kind Fredholm integral equations, whose treatment requires the use of regularization methods. The corresponding computational problem takes the form of structured matrix problem with a Toeplitz or block Toeplitz coefficient matrix. The aim of this paper is to present a tutorial survey of numerical algorithms for the practical treatment of these discretized deconvolution problems, with emphasis on methods that take the special structure of the matrix into account. Wherever possible, analogies to classical DFT-based deconvolution problems are drawn. Among other things, we present direct methods for regularization with Toeplitz matrices, and we show how Toeplitz matrix–vector products are computed by means of FFT, being useful in iterative methods. We also introduce the Kronecker product and show how it is used in the discretization and solution of 2-D deconvolution problems whose variables separate. 相似文献
104.
105.
The rotational motion and orientational distribution of ellipsoidal particles in turbulent flows are of significance in environmental and engineering applications. Whereas the translational motion of an ellipsoidal particle is controlled by the turbulent motions at large scales, its rotational motion is determined by the fluid velocity gradient tensor at small scales, which raises a challenge when predicting the rotational dispersion of ellipsoidal particles using large eddy simulation (LES) method due to the lack of subgrid scale (SGS) fluid motions. We report the effects of the SGS fluid motions on the orientational and rotational statistics, such as the alignment between the long axis of ellipsoidal particles and the vorticity, the mean rotational energy at various aspect ratios against those obtained with direct numerical simulation (DNS) and filtered DNS. The performances of a stochastic differential equation (SDE) model for the SGS velocity gradient seen by the particles and the approximate deconvolution method (ADM) for LES are investigated. It is found that the missing SGS fluid motions in LES flow fields have significant effects on the rotational statistics of ellipsoidal particles. Alignment between the particles and the vorticity is weakened; and the rotational energy of the particles is reduced in LES. The SGS-SDE model leads to a large error in predicting the alignment between the particles and the vorticity and over-predicts the rotational energy of rod-like particles. The ADM significantly improves the rotational energy prediction of particles in LES. 相似文献
106.
Brett Harper Elizabeth K. Neumann Sarah M. Stow Jody C. May John A. McLean Touradj Solouki 《Analytica chimica acta》2016
Ion mobility (IM) is an important analytical technique for determining ion collision cross section (CCS) values in the gas-phase and gaining insight into molecular structures and conformations. However, limited instrument resolving powers for IM may restrict adequate characterization of conformationally similar ions, such as structural isomers, and reduce the accuracy of IM-based CCS calculations. Recently, we introduced an automated technique for extracting “pure” IM and collision-induced dissociation (CID) mass spectra of IM overlapping species using chemometric deconvolution of post-IM/CID mass spectrometry (MS) data [J. Am. Soc. Mass Spectrom., 2014, 25, 1810–1819]. Here we extend those capabilities to demonstrate how extracted IM profiles can be used to calculate accurate CCS values of peptide isomer ions which are not fully resolved by IM. We show that CCS values obtained from deconvoluted IM spectra match with CCS values measured from the individually analyzed corresponding peptides on uniform field IM instrumentation. We introduce an approach that utilizes experimentally determined IM arrival time (AT) “shift factors” to compensate for ion acceleration variations during post-IM/CID and significantly improve the accuracy of the calculated CCS values. Also, we discuss details of this IM deconvolution approach and compare empirical CCS values from traveling wave (TW)IM-MS and drift tube (DT)IM-MS with theoretically calculated CCS values using the projected superposition approximation (PSA). For example, experimentally measured deconvoluted TWIM-MS mean CCS values for doubly-protonated RYGGFM, RMFGYG, MFRYGG, and FRMYGG peptide isomers were 288.8 Å2, 295.1 Å2, 296.8 Å2, and 300.1 Å2; all four of these CCS values were within 1.5% of independently measured DTIM-MS values. 相似文献
107.
The probability density function (pdf) valid for the Gaussian case is often applied for describing the convolutional noise pdf in the blind adaptive deconvolution problem, although it is known that it can be applied only at the latter stages of the deconvolution process, where the convolutional noise pdf tends to be approximately Gaussian. Recently, the deconvolutional noise pdf was approximated with the Edgeworth Expansion and with the Maximum Entropy density function for the 16 Quadrature Amplitude Modulation (QAM) input but no equalization performance improvement was seen for the hard channel case with the equalization algorithm based on the Maximum Entropy density function approach for the convolutional noise pdf compared with the original Maximum Entropy algorithm, while for the Edgeworth Expansion approximation technique, additional predefined parameters were needed in the algorithm. In this paper, the Generalized Gaussian density (GGD) function and the Edgeworth Expansion are applied for approximating the convolutional noise pdf for the 16 QAM input case, with no need for additional predefined parameters in the obtained equalization method. Simulation results indicate that improved equalization performance is obtained from the convergence time point of view of approximately 15,000 symbols for the hard channel case with our new proposed equalization method based on the new model for the convolutional noise pdf compared to the original Maximum Entropy algorithm. By convergence time, we mean the number of symbols required to reach a residual inter-symbol-interference (ISI) for which reliable decisions can be made on the equalized output sequence. 相似文献
108.
109.
In inertial confinement fusion (ICF), X-ray coded imaging is considered as the most potential means to diagnose the compressed core. The traditional Richardson-Lucy (RL) method has a strong ability to deblur the image where the noise follows the Poisson distribution. However, it always suffers from over-fitting and noise amplification, especially when the signal-to-noise ratio of image is relatively low. In this paper, we propose an improved deconvolution method for X-ray coded imaging. We model the image data as a set of independent Gaussian distributions and derive the iterative solution with a maximum-likelihood scheme. The experimental results on X-ray coded imaging data demonstrate that this method is superior to the RL method in terms of anti-overfitting and noise suppression. 相似文献
110.
Microscopic information on the complexation of Be2+ with cyclo-tri-μ-imidotriphosphate anions in aqueous solution has been gained by both 9Be and 31P NMR techniques at −2.3 °C. Separate NMR signals corresponding to free and complexed species have been observed in both spectra. Based on an empirical additivity rule, i.e., proportionality observed between the 9Be NMR chemical shift values and the number of coordinating atoms of ligand molecules, the 9Be NMR spectra have been deconvoluted. By precise equilibrium analyses, the formation of [BeX(H2O)3]+ and [BeX2(H2O)2]0 (X = non-bridging oxygen donor as a coordination atom in the phosphate groups) has been verified, and the formation of complexes coordinating with the nitrogen atoms of the cyclic framework in the ligand molecule has been excluded. Instead, the formation of one-to-one (ML) complexes, one-to-two (ML2), together with two-to-one (M2L) complexes (L = cP3O6(NH)3) has been disclosed, the stability constants of which have been evaluated as log KML = 3.87 ± 0.03 (mol dm−3)−1, log KML2 = 2.43 ± 0.03 (mol dm−3)−2 and log KM2L = 1.30 ± 0.02 (mol dm−3)−2, respectively. 31P NMR spectra measured concurrently have verified the formation of the complexes estimated by the 9Be NMR measurement. Intrinsic 31P NMR chemical shift values of the phosphorus atoms belonging to ligand molecules complexed with Be2+, together with the 31P-31P spin-spin coupling constants have been determined. 相似文献