全文获取类型
收费全文 | 92篇 |
免费 | 35篇 |
国内免费 | 7篇 |
专业分类
化学 | 15篇 |
力学 | 12篇 |
数学 | 9篇 |
物理学 | 98篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 5篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 2篇 |
2014年 | 7篇 |
2013年 | 13篇 |
2012年 | 9篇 |
2011年 | 4篇 |
2010年 | 6篇 |
2009年 | 10篇 |
2008年 | 4篇 |
2007年 | 4篇 |
2006年 | 9篇 |
2005年 | 9篇 |
2004年 | 5篇 |
2003年 | 6篇 |
2002年 | 1篇 |
2001年 | 1篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1989年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有134条查询结果,搜索用时 78 毫秒
31.
In the present paper, the algorithm of Binary Image Cross-Correlation (BICC) was developed to measure the unsteady flow field.
A vortex flow field was used to test the algorithm by numerical simulation. The results show that BICC is an effective algorithm
for particle identification from consecutive images, the accurate velocity vector field can be obtained. The real velocity
field in a valve chamber was measured by BICC in this study. From the full-field velocity information, the pressure and vorticity
fields were also extracted by post-processing.
The project supported by the National Natural Science Foundation of China 相似文献
32.
通过理论分析指出啁啾脉冲光谱仪探测法探测THz辐射存在时间分辨率极限,实验也得到了与理论分析相一致的结果.提出使用啁啾脉冲互相关法探测THz辐射,给予了一定的理论分析,实验结果证明此方法探测THz辐射的时间分辨率与传统的时间扫描延迟方法的时间分辨率相当.
关键词:
啁啾脉冲
THz辐射
互相关 相似文献
33.
Andrs F. Almeida-
auay Rosa María Benito Miguel Quemada Juan Carlos Losada Ana M. Tarquis 《Entropy (Basel, Switzerland)》2021,23(5)
Multiple studies revealed that pasture grasslands are a time-varying complex ecological system. Climate variables regulate vegetation growing, being precipitation and temperature the most critical driver factors. This work aims to assess the response of two different Vegetation Indices (VIs) to the temporal dynamics of temperature and precipitation in a semiarid area. Two Mediterranean grasslands zones situated in the center of Spain were selected to accomplish this goal. Correlations and cross-correlations between VI and each climatic variable were computed. Different lagged responses of each VIs series were detected, varying in zones, the year’s season, and the climatic variable. Recurrence Plots (RPs) and Cross Recurrence Plots (CRPs) analyses were applied to characterise and quantify the system’s complexity showed in the cross-correlation analysis. RPs pointed out that short-term predictability and high dimensionality of VIs series, as well as precipitation, characterised this dynamic. Meanwhile, temperature showed a more regular pattern and lower dimensionality. CRPs revealed that precipitation was a critical variable to distinguish between zones due to their complex pattern and influence on the soil’s water balance that the VI reflects. Overall, we prove RP and CRP’s potential as adequate tools for analysing vegetation dynamics characterised by complexity. 相似文献
34.
光码分多址系统中, 光编解码器是影响系统性能的关键因素之一.自相关峰值旁瓣比(P/W)、自互相关峰值比(P/C)是衡量编解码器性能的两个重要指标.以硅基SOI微环谐振腔为载体, 提出了一种串联三环阵列的二维相干OCDMA编解码器模型.详细研究了耦合系数、损耗系数、阵列间距以及通道间隔对微环谐振腔编解码器性能的影响.结果表明, 半径为50 μm的微环, 环与直波导间耦合系数在0.6–0.7之间, 环与环间耦合系数在0.1–0.2之间, 损耗系数 < 2 dB/cm, 阵列间距大于3 mm, 通道间隔在25–36 GHz间时, 编解码器能够获得良好的性能. 相似文献
35.
Multiplicative Difference Sets via Additive Characters 总被引:1,自引:0,他引:1
J. F. Dillon 《Designs, Codes and Cryptography》1999,17(1-3):225-235
We use Fourier analysis on the additive group of
to give an alternative proof of the recent theorem of Maschietti and to prove recent conjectures of No, Chung and Yun and No, Golomb, Gong, Lee and Gaal on difference sets in the multiplicative group of
, m odd. Along the ay e prove a stronger form of a celebrated theorem of Welch on the 3-valued cross-correlation of maximal length sequences. 相似文献
36.
§1Introduction Letpbeaprimenumber,q=pm,andFqdenotethefinitefieldwithqelements.Fo anyn≥1,Trmnm(·)isthetracefunctionfromFqntoFq.LetαbeaprimitiveelementofFq and{α1,α2,...,αn}beabasisofFqnoverFq.Definition1.ForanonlinearfunctionffromFqtoFp,thesequenceS={Si}qn-1i=1withit termdefinedby Si=f(Trmnm(αi))(1iscalledageometricsequence.SuchageometricsequenceShasperioddividingqn-1.Geometricsequences includingm-sequence[1],GMWsequence[2,3],cascadedGMWsequence[4,5]andman others[6],mayhavelar… 相似文献
37.
38.
Moments of the intensity of a single-mode laser driven by coloured pump noises with a cross-correlation between the real and imaginary parts of the quantum noise 总被引:1,自引:0,他引:1 下载免费PDF全文
By means of the unified coloured noise approximation and phase lock, we study in this paper the stationary intensity distribution of the single-mode laser cubic model driven by coloured pump noise with cross-correlation between the real and imaginary parts of the quantum noise. We present a thorough discussion of how the cross-correlation λ_q between the real and imaginary parts of the quantum noise and the self-correlation time τ of the pump noise determine the behaviours of the mean intensity 〈I〉 and variance λ_2 (0) for both below and above the threshold operation, and many new phenomena are discovered. When the laser is operated above the threshold, increasing the cross-correlation intensity λ_q makes the 〈I 〉-τ curves exhibit a "re-entrant phase transition". Whether the laser is above or below the threshold, the whole 〈I 〉-τ curve moves down as
λ_q increases; however, when λ_q=1 (perfect cross-correlation), the curve abruptly runs up. A nonzero value of cross-correlation time τ (τ≠0) leads to the entire λ_2(0)-p′ curve being suppressed (here p′ is the pump noise intensity). This indicates the increasing precision of the laser beam due to the existence of the self-correlation time τ. The behaviour of the λ_2 (0)-p′ curve as a function of λ_q is similar to that of the 〈I 〉-τ curve against λ_q: that is, whether the laser is above or below the threshold, the λ_2 (0)-p′ curve moves up as λ_q increases; however, when λ_q=1, the curve suddenly moves down. Through the study in this paper, we can find a way to optimize for output laser intensity.τ 相似文献
39.
利用混沌激光实现一定浓度脂肪乳液中异质物大小和位置的光学检测,实验采用混沌激光作为光源,并将光信号分为两路,一路信号用于探测脂肪乳液中的异质物信息,另外一路直接经过光电探测器作为参考信号,将两路光信号由光电探测器接收,通过信号处理系统进行互相关,分析混沌激光的互相关峰值信息,可得到异质物的大小和位置信息;通过混沌激光实现异质物信息分析的理论模型,建立混沌相关信号峰值信息与异质物大小和位置之间的关系,并且通过实验验证。结果表明:采用混沌互相关法可以对异质物大小和位置坐标进行探测。 相似文献
40.
Mohammad Arafat Hussain Farzana Alam Sharmin Akhtar Rupa Rayhana Awwal Soo Yeol Lee Md. Kamrul Hasan 《Ultrasonics》2014
Elasticity imaging techniques with built-in or regularization-based smoothing feature for ensuring strain continuity are not intelligent enough to prevent distortion or lesion edge blurring while smoothing. This paper proposes a novel approach with built-in lesion edge preservation technique for high quality direct average strain imaging. An edge detection scheme, typically used in diffusion filtering is modified here for lesion edge detection. Based on the extracted edge information, lesion edges are preserved by modifying the strain determining cost function in the direct-average-strain-estimation (DASE) method. The proposed algorithm demonstrates approximately 3.42–4.25 dB improvement in terms of edge-mean-square-error (EMSE) than the other reported regularized or average strain estimation techniques in finite-element-modeling (FEM) simulation with almost no sacrifice in elastographic-signal-to-noise-ratio (SNRe) and elastographic-contrast-to-noise-ratio (CNRe) metrics. The efficacy of the proposed algorithm is also tested for the experimental phantom data and in vivo breast data. The results reveal that the proposed method can generate a high quality strain image delineating the lesion edge more clearly than the other reported strain estimation techniques that have been designed to ensure strain continuity. The computational cost, however, is little higher for the proposed method than the simpler DASE and considerably higher than that of the 2D analytic minimization (AM2D) method. 相似文献