首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   134篇
  免费   35篇
化学   28篇
数学   3篇
物理学   138篇
  2023年   1篇
  2022年   10篇
  2021年   11篇
  2020年   5篇
  2019年   8篇
  2018年   14篇
  2017年   18篇
  2016年   11篇
  2015年   6篇
  2014年   19篇
  2013年   21篇
  2012年   10篇
  2011年   8篇
  2010年   3篇
  2009年   2篇
  2008年   7篇
  2007年   8篇
  2006年   2篇
  2004年   1篇
  2003年   3篇
  2002年   1篇
排序方式: 共有169条查询结果,搜索用时 31 毫秒
1.
基于NIR高光谱成像技术的长枣虫眼无损检测   总被引:5,自引:2,他引:3       下载免费PDF全文
为了研究快速识别虫眼枣与正常枣的有效方法,利用特征波长主成分分析法结合波段比算法进行虫眼枣识别。首先,利用NIR高光谱成像系统采集130个长枣(50个正常、80个虫眼枣)图像,提取并分析不同类型长枣特征区域的平均光谱曲线,对970~1 670 nm范围内的光谱数据进行主成分分析,确定7个特征波长(990,1 028,1 109,1 160,1 231,1 285,1 464 nm)。然后,对长枣图像做主成分分析,选择PC2图像进行虫眼识别,虫眼与正常枣的识别率分别为67.5%、100%。为了进一步提高虫眼枣的识别率,采用波段比(R1231/R1109)对未识别的虫眼枣进行再次识别,识别率提高到90%。结果表明,基于NIR高光谱成像技术的检测方法对虫眼枣识别是可行的,同时也为多光谱成像技术应用于在线检测长枣品质提供了理论依据。  相似文献   
2.
针对高光谱图像中背景及目标先验知识未知条件下的异常目标检测问题,提出了一种基于独立成分分析(ICA)的异常探测算法.首先估计原始数据的虚拟维(VD)以确定要分离的独立成分个数,在此基础上进行快速独立成分分析(FastICA),然后基于平均局部奇异度选择含异常信息较多的独立成分,最后使用丰度量化算法得到异常目标的丰度图像...  相似文献   
3.
A porcelain insulator is an important part to ensure that the insulation requirements of power equipment can be met. Under the influence of their structure, porcelain insulators are prone to mechanical damage and cracks, which will reduce their insulation performance. After a long-term operation, crack expansion will eventually lead to breakdown and safety hazards. Therefore, it is of great significance to detect insulator cracks to ensure the safe and reliable operation of a power grid. However, most traditional methods of insulator crack detection involve offline detection or contact measurement, which is not conducive to the online monitoring of equipment. Hyperspectral imaging technology is a noncontact detection technology containing three-dimensional (3D) spatial spectral information, whereby the data provide more information and the measuring method has a higher safety than electric detection methods. Therefore, a model of positioning and state classification of porcelain insulators based on hyperspectral technology is proposed. In this model, image data were used to extract edges to locate cracks, and spectral information was used to classify the surface states of porcelain insulators with EfficientNet. Lastly, crack extraction was realized, and the recognition accuracy of cracks and normal states was 96.9%. Through an analysis of the results, it is proven that the crack detection method of a porcelain insulator based on hyperspectral technology is an effective non-contact online monitoring approach, which has broad application prospects in the era of the Internet of Things with the rapid development of electric power.  相似文献   
4.
我国东北黑土富含养分,随着土壤数字制图、精确农业和土壤资源调查等研究的深入,引入航空高光谱数据并提供科学的预测结果成为研究热点。硒元素相对于黑土土壤的主要成分属于微量元素,但其对作物的正常生长的作用与大量元素是同等重要的,亦是人体健康所必要的营养元素。针对硒含量反演,建立了一个基于主要成分的间接提取模型,该模型能够显著提升硒含量回归系数,降低实测值与预测值的误差。数据源自CASI-1500航空高光谱成像系统,光谱范围380~1 050 nm,空间分辨率1.5 m。在黑龙江建三江地区采集60个土壤样本,化验获得硒、有机质、全铁、pH和氧化钙含量数据,选择BP神经网络,建立光谱与含量的反演模型。分析不同含量的黑土成分在可见-近红波段范围内光谱变换规律,掌握了硒元素随着含量升高,光谱反射率会逐步升高的规律。但当硒含量较低时,在其他成分的干扰下,这一规律会逐渐减弱,直至不显著。有机质的光谱特征与硒元素相反,总体上随着含量的增高,反射率整体下降,这与有机质的光谱特性紧密相关。全铁光谱呈现出与有机质光谱类似的规律,说明二者具有较高的相关性。不同pH值和氧化钙含量的光谱特征与检测值没有呈现出明显的特征规律,反射规律不明显。对60个采样点不同养分含量进行逐波段求反射率对养分的相关系数。结果表明,pH值各个波段相关系数最高,均值达到0.63;其次是全铁的相关系数,为0.54;有机质和氧化钙的相关系数接近,分别为0.42和0.47;而硒元素含量与逐波段的平均相关系数最低,为0.38。选取相关系数较高的前5个波段,作为建模波段。硒特征波段为447,437,456,466和475 nm;有机质特征波段为447,456,466,437和475 nm;全铁特征波段为752,695,800,762和733 nm;pH特征波段为905,752,800,943和695 nm;氧化钙特征波段为752,695,800,523和762 nm。通过计算样本点硒含量与其他成分的相关系数,硒与有机质呈正相关,相关系数为0.79;与全铁、pH、氧化钙呈负相关,相关系数分别为-0.80,-0.94和-0.69。针对有机质、全铁、pH和氧化钙反演精度较高,而硒元素含量较低,直接反演精度不足的问题,设计了一种先提取4种成分含量,再根据其提取结果建立硒元素函数关系,间接反演硒元素含量的方法。首先将五种成分与特征光谱进行神经网络分析,计算每种成分的回归系数R2和RMSE。显示全铁和pH具有较高的反演精度,有机质和氧化钙归系数虽低于0.8,但也显著高于硒元素的反演精度。建立硒元素与其他4种成分含量的回归模型,得出Se=0.522 9+0.041 8Som-0.016 6Fe2O3-0.035 6pH-0.005CaO,进行硒元素间接提取,回归系数从0.516增长到0.724,均方根误差从0.182降低到0.136,显著改进了反演硒含量的精度,为硒元素大范围精确制图提供了一种新技术。  相似文献   
5.
This study attempts to model snow wetness and snow density of Himalayan snow cover using a combination of Hyperspectral image processing and Artificial Neural Network (ANN). Initially, a total of 300 spectral signature measurements, synchronized with snow wetness and snow density, were collected in the field. The spectral reflectance of snow was then modeled as a function of snow properties using ANN. Four snow wetness and three snow density models were developed. A strong correlation was observed in near‐infrared and shortwave‐infrared region. The correlation analysis of ANN modeled snow density and snow wetness showed a strong linear relationship with field‐based data values ranging from 0.87–0.90 and 0.88–0.91, respectively. Our results indicate that an Artificial Intelligence (AI) approach, using a combination of Hyperspectral image processing and ANN, can be efficiently used to predict snow properties (wetness and density) in the Himalayan region. Recommendations for resource managers
  • Snow properties, such as snow wetness and snow density are mainly investigated through field‐based survey but rugged terrains, difficult weather conditions, and logistics management issues establish remote sensing as an efficient alternative to monitor snow properties, especially in the mountain environment.
  • Although Hyperspectral remote sensing is a powerful tool to conduct the quantitative analysis of the physical properties of snow, only a few studies have used hyperspectral data for the estimation of snow density and wetness in the Himalayan region. This could be because of the lack of synchronized snow properties data with field‐based spectral acquisitions.
  • In combination with Hyperspectral image processing, Artificial Neural Network (ANN) can be a useful tool for effective snow modeling because of its ability to capture and represent complex input‐output relationships.
  • Further research into understanding the applicability of neural networks to determine snow properties is required to obtain results from large snow cover areas of the Himalayan region.
  相似文献   
6.
Near-infrared (NIR) hyperspectral imaging system was used to detect five concentration levels of ochratoxin A (OTA) in contaminated wheat kernels. The wheat kernels artificially inoculated with two different OTA producing Penicillium verrucosum strains, two different non-toxigenic P. verrucosum strains, and sterile control wheat kernels were subjected to NIR hyperspectral imaging. The acquired three-dimensional data were reshaped into readable two-dimensional data. Principal Component Analysis (PCA) was applied to the two dimensional data to identify the key wavelengths which had greater significance in detecting OTA contamination in wheat. Statistical and histogram features extracted at the key wavelengths were used in the linear, quadratic and Mahalanobis statistical discriminant models to differentiate between sterile control, five concentration levels of OTA contamination in wheat kernels, and five infection levels of non-OTA producing P. verrucosum inoculated wheat kernels. The classification models differentiated sterile control samples from OTA contaminated wheat kernels and non-OTA producing P. verrucosum inoculated wheat kernels with a 100% accuracy. The classification models also differentiated between five concentration levels of OTA contaminated wheat kernels and between five infection levels of non-OTA producing P. verrucosum inoculated wheat kernels with a correct classification of more than 98%. The non-OTA producing P. verrucosum inoculated wheat kernels and OTA contaminated wheat kernels subjected to hyperspectral imaging provided different spectral patterns.  相似文献   
7.
Advances in vibrational spectroscopy have propelled new insights into the molecular composition and structure of biological tissues. In this review, we discuss common modalities and techniques of vibrational spectroscopy, and present key examples to illustrate how they have been applied to enrich the assessment of connective tissues. In particular, we focus on applications of Fourier transform infrared (FTIR), near infrared (NIR) and Raman spectroscopy to assess cartilage and bone properties. We present strengths and limitations of each approach and discuss how the combination of spectrometers with microscopes (hyperspectral imaging) and fiber optic probes have greatly advanced their biomedical applications. We show how these modalities may be used to evaluate virtually any type of sample (ex vivo, in situ or in vivo) and how “spectral fingerprints” can be interpreted to quantify outcomes related to tissue composition and quality. We highlight the unparalleled advantage of vibrational spectroscopy as a label-free and often nondestructive approach to assess properties of the extracellular matrix (ECM) associated with normal, developing, aging, pathological and treated tissues. We believe this review will assist readers not only in better understanding applications of FTIR, NIR and Raman spectroscopy, but also in implementing these approaches for their own research projects.  相似文献   
8.
近红外高光谱图像结合CARS算法对鸭梨SSC含量定量测定   总被引:3,自引:0,他引:3  
高光谱数据量大、维数高且原始光谱噪声明显、散射严重等特征导致光谱建模时关键波长变量提取困难。基于此,提出采用竞争性自适应重加权算法(CARS)对近红外高光谱数据进行关键变量选择。鸭梨作为研究对象。采用决定系数r2、预测均方根误差RMSEP和验证集标准偏差和预测集标准偏差的比值RPD值进行模型性能评估。基于选择的关键变量建立PLS模型(CARS-PLS)与全光谱变量建立的PLS模型进行比较发现CARS-PLS模型仅仅使用原始变量中15.6%的信息获得了比全变量PLS模型更好的鸭梨SSC含量预测结果,r2pre,RMSEP和RPD分别为0.908 2,0.312 0和3.300 5。进一步与基于蒙特卡罗无信息变量MC-UVE和遗传算法(GA)获得的特征变量建立的PLS模型比较发现,CARS不仅可以去除原始光谱数据中的无信息变量,同时也能够对共线性的变量进行压缩去除,该方法能够有效地用于高光谱数据变量的选择。结果表明,近红外高光谱技术结合CARS-PLS模型能够用于鸭梨可溶性固形物SSC含量的定量预测。从而为基于近红外高光谱技术预测水果内部品质的研究提供了参考。  相似文献   
9.
The use of near infrared (NIR) hyperspectral imaging and hyperspectral image analysis for distinguishing between hard, intermediate and soft maize kernels from inbred lines was evaluated. NIR hyperspectral images of two sets (12 and 24 kernels) of whole maize kernels were acquired using a Spectral Dimensions MatrixNIR camera with a spectral range of 960-1662 nm and a sisuChema SWIR (short wave infrared) hyperspectral pushbroom imaging system with a spectral range of 1000-2498 nm. Exploratory principal component analysis (PCA) was used on absorbance images to remove background, bad pixels and shading. On the cleaned images, PCA could be used effectively to find histological classes including glassy (hard) and floury (soft) endosperm. PCA illustrated a distinct difference between glassy and floury endosperm along principal component (PC) three on the MatrixNIR and PC two on the sisuChema with two distinguishable clusters. Subsequently partial least squares discriminant analysis (PLS-DA) was applied to build a classification model. The PLS-DA model from the MatrixNIR image (12 kernels) resulted in root mean square error of prediction (RMSEP) value of 0.18. This was repeated on the MatrixNIR image of the 24 kernels which resulted in RMSEP of 0.18. The sisuChema image yielded RMSEP value of 0.29. The reproducible results obtained with the different data sets indicate that the method proposed in this paper has a real potential for future classification uses.  相似文献   
10.
The purpose of this paper was to investigate the feasibility of a newly developed hyperspectral fundus imaging camera with a liquid crystal tunable filter. The intensities of different wavelengths of light transmitted through an artery, vein, and the area surrounding these vessels and reflected out were measured, and the differential spectral absorptions were analyzed. Measurements were made from 16 normal eyes and from two artificial capillaries. The ratios of absorption (ROA) of arteries to veins from 500 to 580 nm (range 1) and from 600 to 720 nm (range 2) were calculated. For all eyes, the ROArange1 was larger than ROArange2. The ROA obtained from the artificial capillary filled with blood saturated with oxygen or nitrogen was similar to that of simulated data of oxy- and deoxyhemoglobin extinction rate. Most ROAs of human eyes were lower than those of the simulated data and the artificial capillaries. Oxygen saturation analysis by hyperspectral fundus imaging of retinal vessels were qualitatively in agreement with thein vitro analysis or simulated values. However, further improvements are necessary to evaluate the oxygen saturation quantitatively in the retinal blood vessels.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号