全文获取类型
收费全文 | 1505篇 |
免费 | 213篇 |
国内免费 | 136篇 |
专业分类
化学 | 159篇 |
晶体学 | 1篇 |
力学 | 271篇 |
综合类 | 71篇 |
数学 | 665篇 |
物理学 | 687篇 |
出版年
2023年 | 7篇 |
2022年 | 29篇 |
2021年 | 26篇 |
2020年 | 29篇 |
2019年 | 32篇 |
2018年 | 37篇 |
2017年 | 52篇 |
2016年 | 58篇 |
2015年 | 29篇 |
2014年 | 66篇 |
2013年 | 74篇 |
2012年 | 82篇 |
2011年 | 96篇 |
2010年 | 66篇 |
2009年 | 100篇 |
2008年 | 121篇 |
2007年 | 144篇 |
2006年 | 113篇 |
2005年 | 126篇 |
2004年 | 106篇 |
2003年 | 95篇 |
2002年 | 77篇 |
2001年 | 67篇 |
2000年 | 65篇 |
1999年 | 47篇 |
1998年 | 53篇 |
1997年 | 24篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1987年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1959年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有1854条查询结果,搜索用时 15 毫秒
101.
紧支撑三元正交小波滤波器的参数化 总被引:1,自引:0,他引:1
高维小波分析是分析和处理多维数字信号的有力工具.非张量积多元小波被广泛地应用在模式识别、纹理分析和边缘检测等领域.本文给出方体域上三元正交滤波器的一种参数化构造算法,三元小波滤波器的这种构造方法使我们能更方便地研究非张量积的三元正交小波.最后给出数值算例. 相似文献
102.
The trend prediction of the stock is a main challenge. Accidental factors often lead to short-term sharp fluctuations in stock markets, deviating from the original normal trend. The short-term fluctuation of stock price has high noise, which is not conducive to the prediction of stock trends. Therefore, we used discrete wavelet transform (DWT)-based denoising to denoise stock data. Denoising the stock data assisted us to eliminate the influences of short-term random events on the continuous trend of the stock. The denoised data showed more stable trend characteristics and smoothness. Extreme learning machine (ELM) is one of the effective training algorithms for fully connected single-hidden-layer feedforward neural networks (SLFNs), which possesses the advantages of fast convergence, unique results, and it does not converge to a local minimum. Therefore, this paper proposed a combination of ELM- and DWT-based denoising to predict the trend of stocks. The proposed method was used to predict the trend of 400 stocks in China. The prediction results of the proposed method are a good proof of the efficacy of DWT-based denoising for stock trends, and showed an excellent performance compared to 12 machine learning algorithms (e.g., recurrent neural network (RNN) and long short-term memory (LSTM)). 相似文献
103.
Magnetic-resonance image segmentation based on improved variable weight multi-resolution Markov random field in undecimated complex wavelet domain
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
To solve the problem that the magnetic resonance (MR) image has weak boundaries, large amount of information, and low signal-to-noise ratio, we propose an image segmentation method based on the multi-resolution Markov random field (MRMRF) model. The algorithm uses undecimated dual-tree complex wavelet transformation to transform the image into multiple scales. The transformed low-frequency scale histogram is used to improve the initial clustering center of the K-means algorithm, and then other cluster centers are selected according to the maximum distance rule to obtain the coarse-scale segmentation. The results are then segmented by the improved MRMRF model. In order to solve the problem of fuzzy edge segmentation caused by the gray level inhomogeneity of MR image segmentation under the MRMRF model, it is proposed to introduce variable weight parameters in the segmentation process of each scale. Furthermore, the final segmentation results are optimized. We name this algorithm the variable-weight multi-resolution Markov random field (VWMRMRF). The simulation and clinical MR image segmentation verification show that the VWMRMRF algorithm has high segmentation accuracy and robustness, and can accurately and stably achieve low signal-to-noise ratio, weak boundary MR image segmentation. 相似文献
104.
We study the approximation of the inverse wavelet transform using Riemannian sums.We show that when the Fourier transforms of wavelet functions satisfy some moderate decay condition,the Riemannian sums converge to the function to be reconstructed as the sampling density tends to infinity.We also study the convergence of the operators introduced by the Riemannian sums.Our result improves some known ones. 相似文献
105.
106.
107.
基于小波域扩散滤波的弱小目标检测 总被引:1,自引:0,他引:1
分析了基于小波变换进行弱小目标检测的基本思想,利用小波变换的多尺度多分辨率特性,结合小波变换系数的方向特性和扩散滤波扩散方向的可选择性,提出了基于小波域扩散滤波的弱小目标检测算法。采用该算法对不同尺度、不同方向的小波系数分别进行扩散滤波,取得了较好的效果。仿真试验结果表明:该算法能在Gaussian噪声背景和不均匀背景下实现对对比度为2%的微弱目标的检测。 相似文献
108.
109.
《Communications in Nonlinear Science & Numerical Simulation》2014,19(3):483-493
A Haar wavelet operational matrix method (HWOMM) was derived to solve the Riccati differential equations. As a result, the computation of the nonlinear term was simplified by using the Block pulse function to expand the Haar wavelet one. The proposed method can be used to solve not only the classical Riccati differential equations but also the fractional ones. The capability and the simplicity of the proposed method was demonstrated by some examples and comparison with other methods. 相似文献
110.