全文获取类型
收费全文 | 4908篇 |
免费 | 571篇 |
国内免费 | 495篇 |
专业分类
化学 | 1690篇 |
晶体学 | 11篇 |
力学 | 158篇 |
综合类 | 149篇 |
数学 | 1387篇 |
物理学 | 2579篇 |
出版年
2024年 | 15篇 |
2023年 | 72篇 |
2022年 | 321篇 |
2021年 | 298篇 |
2020年 | 177篇 |
2019年 | 136篇 |
2018年 | 111篇 |
2017年 | 170篇 |
2016年 | 216篇 |
2015年 | 174篇 |
2014年 | 261篇 |
2013年 | 314篇 |
2012年 | 242篇 |
2011年 | 300篇 |
2010年 | 281篇 |
2009年 | 320篇 |
2008年 | 291篇 |
2007年 | 335篇 |
2006年 | 248篇 |
2005年 | 242篇 |
2004年 | 194篇 |
2003年 | 183篇 |
2002年 | 148篇 |
2001年 | 117篇 |
2000年 | 93篇 |
1999年 | 79篇 |
1998年 | 88篇 |
1997年 | 63篇 |
1996年 | 52篇 |
1995年 | 64篇 |
1994年 | 57篇 |
1993年 | 34篇 |
1992年 | 25篇 |
1991年 | 25篇 |
1990年 | 28篇 |
1989年 | 31篇 |
1988年 | 20篇 |
1987年 | 19篇 |
1986年 | 13篇 |
1985年 | 27篇 |
1984年 | 11篇 |
1983年 | 10篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1972年 | 4篇 |
排序方式: 共有5974条查询结果,搜索用时 15 毫秒
81.
Elena Almaraz Luengo Marcos Brian Leiva Cerna Luis Javier García Villalba Julio Hernandez-Castro Darren Hurley-Smith 《Entropy (Basel, Switzerland)》2022,24(5)
This work presents an analysis of the existing dependencies between the tests of the FIPS 140-2 battery. Two main analytical approaches are utilized, the first being a study of correlations through the Pearson’s correlation coefficient that detects linear dependencies, and the second one being a novel application of the mutual information measure that allows detecting possible non-linear relationships. In order to carry out this study, the FIPS 140-2 battery is reimplemented to allow the user to obtain p-values and statistics that are essential for more rigorous end-user analysis of random number generators (RNG). 相似文献
82.
Carlos Ariel Gil-Barrera Raymundo Santana Carrillo Guo-Hua Sun Shi-Hai Dong 《Entropy (Basel, Switzerland)》2022,24(5)
In this work, we study the quantum information entropies for two different types of hyperbolic single potential wells. We first study the behaviors of the moving particle subject to two different hyperbolic potential wells through focusing on their wave functions. The shapes of these hyperbolic potentials are similar, but we notice that their momentum entropy densities change along with the width of each potential and the magnitude of position entropy density decreases when the momentum entropy magnitude increases. On the other hand, we illustrate the behaviors of their position and momentum entropy densities. Finally, we show the variation of position and momentum entropies and with the change of the potential well depth u and verify that their sum still satisfies the BBM inequality relation. 相似文献
83.
SHANG Yu WANG Gui-Dong WU Xiao-Ning WANG Shi-Kun LAU Yun-Kau 《理论物理通讯》2007,47(4):663-664
An exact solution of the vacuum Einstein's field equations is presented, in which there exists a congruence of null geodesics whose shear behaves like a travelling wave of the KdV equation. On the basis of this exact solution, the feasibility of solitonic information transmission by exploiting the nonlinearity intrinsic to the Einstein field equations is discussed. 相似文献
84.
With the widespread use of emotion recognition, cross-subject emotion recognition based on EEG signals has become a hot topic in affective computing. Electroencephalography (EEG) can be used to detect the brain’s electrical activity associated with different emotions. The aim of this research is to improve the accuracy by enhancing the generalization of features. A Multi-Classifier Fusion method based on mutual information with sequential forward floating selection (MI_SFFS) is proposed. The dataset used in this paper is DEAP, which is a multi-modal open dataset containing 32 EEG channels and multiple other physiological signals. First, high-dimensional features are extracted from 15 EEG channels of DEAP after using a 10 s time window for data slicing. Second, MI and SFFS are integrated as a novel feature-selection method. Then, support vector machine (SVM), k-nearest neighbor (KNN) and random forest (RF) are employed to classify positive and negative emotions to obtain the output probabilities of classifiers as weighted features for further classification. To evaluate the model performance, leave-one-out cross-validation is adopted. Finally, cross-subject classification accuracies of 0.7089, 0.7106 and 0.7361 are achieved by the SVM, KNN and RF classifiers, respectively. The results demonstrate the feasibility of the model by splicing different classifiers’ output probabilities as a portion of the weighted features. 相似文献
85.
86.
采用构造相容分布与非负上鞅的方法研究任意信源随机和相对熵密度的强极限定理,并由此得出若干任意信源,m阶马氏信源,无记忆信源的随机Shannon-Mcmillan定理.将已有的关于离散信源的结果加以推广. 相似文献
87.
基于双混沌置乱和扩频调制的彩色图像盲水印算法 总被引:5,自引:0,他引:5
提出了一种新的适应彩色图像的盲水印算法,先对宿主图像的绿色分量以8×8像素分块进行离散余弦变换(DCT)变换,用logistic映射生成两个混沌序列,然后用混沌序列置乱加密二值水印图像,并用两个互不相关的伪随机序列扩频调制水印,最后将调制好的水印嵌入到DCT变换域的中频子带系数上,进行分块DCT反变换得到水印化图像.提取水印时,通过比较两个伪随机序列和水印化图像的相关性大小来提取水印,不需要原始图像的参与,为盲提取水印算法.实验结果证明本文算法能有效地抵抗JPEG压缩、加噪、剪切等常见攻击,绿色分量嵌入水印比红色和蓝色分量嵌入水印能更好地抵抗JPEG压缩的攻击. 相似文献
88.
基于Arnold变换的图像逆置乱算法 总被引:3,自引:0,他引:3
针对Arnold变换的周期依赖于图像的阶数这一特性,提出了一种反变换算法.该算法通过分析加密图像任一点处两坐标分量间关系,得到原图像相应点的坐标,从而实现图像的解密.该反变换也可作为图像置乱的正变换,相应的反变换就是Arnold变换.在此基础上,把二维反变换算法推广到m维的情形.实验结果表明,对于已应用Arnold变换进行预处理的置乱图像,在无须计算原图像变换周期的前提下可快速实现图像的逆置乱,该过程具有确定性,其迭代次数与预处理置乱次数相等. 相似文献
89.
GAO Li LIU Wen-Biao 《理论物理通讯》2006,46(10)
Hawking radiation is viewed as a process of quantum tunneling. The massive particles‘ tunneling from Garfinkle-Horowitz-Strominger black hole is investigated. Using Jingyi Zhang‘s de Broglie wave method, we get the unthermal spectrum, and the result is consistent with the underlying unitary theory. 相似文献
90.
The age of information (AoI) metric was proposed to measure the freshness of messages obtained at the terminal node of a status updating system. In this paper, the AoI of a discrete time status updating system with probabilistic packet preemption is investigated by analyzing the steady state of a three-dimensional discrete stochastic process. We assume that the queue used in the system is , which represents that the system size is 2 and the packet in the buffer can be preempted by a fresher packet with probability . Instead of considering the system’s AoI separately, we use a three-dimensional state vector to simultaneously track the real-time changes of the AoI, the age of a packet in the server, and the age of a packet waiting in the buffer. We give the explicit expression of the system’s average AoI and show that the average AoI of the system without packet preemption is obtained by letting . When is set to 1, the mean of the AoI of the system with a queue is obtained as well. Combining the results we have obtained and comparing them with corresponding average continuous AoIs, we propose a possible relationship between the average discrete AoI with the queue and the average continuous AoI with the queue. For each of two extreme cases where and , we also determine the stationary distribution of AoI using the probability generation function (PGF) method. The relations between the average AoI and the packet preemption probability , as well as the AoI’s distribution curves in two extreme cases, are illustrated by numerical simulations. Notice that the probabilistic packet preemption may occur, for example, in an energy harvest (EH) node of a wireless sensor network, where the packet in the buffer can be replaced only when the node collects enough energy. In particular, to exhibit the usefulness of our idea and methods and highlight the merits of considering discrete time systems, in this paper, we provide detailed discussions showing how the results about continuous AoI are derived by analyzing the corresponding discrete time system and how the discrete age analysis is generalized to the system with multiple sources. In terms of packet service process, we also propose an idea to analyze the AoI of a system when the service time distribution is arbitrary. 相似文献