全文获取类型
收费全文 | 122篇 |
免费 | 37篇 |
国内免费 | 41篇 |
专业分类
化学 | 64篇 |
晶体学 | 5篇 |
力学 | 12篇 |
综合类 | 15篇 |
数学 | 15篇 |
物理学 | 89篇 |
出版年
2024年 | 5篇 |
2023年 | 8篇 |
2022年 | 10篇 |
2021年 | 12篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2018年 | 10篇 |
2017年 | 6篇 |
2016年 | 12篇 |
2015年 | 13篇 |
2014年 | 12篇 |
2013年 | 14篇 |
2012年 | 11篇 |
2011年 | 3篇 |
2010年 | 5篇 |
2009年 | 9篇 |
2008年 | 5篇 |
2007年 | 7篇 |
2006年 | 6篇 |
2005年 | 2篇 |
2004年 | 2篇 |
2003年 | 2篇 |
2002年 | 4篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1985年 | 2篇 |
排序方式: 共有200条查询结果,搜索用时 15 毫秒
82.
83.
For the sake of improving the accuracy of forecasting wind speed during typhoon strike in WRF model forecast, a new method for precision forecasting of typhoon wind speed is proposed by combining the data collected from the WRF model forecast and an automatic observation station. The method incorporates many factors influencing the typhoon wind speed. The wind speed which is obtained using the traditional human prediction produces large error when compared with actual wind speed. To address this issue, a fuzzy support vector regression model for wind forecasting is built. Considering the fact that the fuzzy support vector regression model is not adequately efficient in determining the punishment factor and kernel parameter, the fly optimization algorithm is introduced into optimizing the parameters of the fuzzy support vector machine. According to the characteristics of the wind speed regression, the fruit fly optimization algorithm is developed in three dimensional space, combining with the enhancement factor γ for improving the global optimization ability of traditional fruit fly optimization algorithm. The results show that the forecasting wind speed and the actual one is in good agreement with each other, and the correlation is as high as 99%. The presented method of wind speed prediction provides higher accuracy than that of traditional FOA-FSVM model and FOA-SVM model. 相似文献
84.
提出一种基于形态学分量分析的红外云图插值重建方法. 利用平稳小波变换和轮廓波变换在表示平滑分量和纹理分量时各自的优势, 将得到的低分辨率红外云图通过形态学分量分析方法分解为平滑分量和纹理分量; 并针对小波插值使低频能量损失问题, 采用先插值后变换的方法改进平稳小波插值效果, 分别用平稳小波变换和轮廓波变换对平滑分量和纹理分量进行插值; 最后将插值后的平滑分量和纹理分量重新组合实现红外云图的超分辨率重建. 结果表明, 解决了重建图像中的平滑和伪影问题, 在视觉效果和PSNR等指标上均优于其他插值算法. 相似文献
85.
随着纳米加工和制备技术的不断发展,金属纳米粒子的等离激元光学特性已得到了广泛的研究与应用。本文基于金属纳米颗粒等离激元共振特性,分析了金属纳米颗粒等离激元共振对介质谐波的增强机制,综述了该增强机制在近几年所取得的最新研究成果及其在生物成像领域的应用。金属纳米颗粒等离激元共振在增强介质非线性特性领域的发展趋势是从简单的金属纳米颗粒向复杂形状纳米颗粒和金属纳米颗粒组装体的发展,这些新型金属纳米颗粒在非线性光学、生物医学上的疾病诊断和治疗有良好的实际应用前景。 相似文献
86.
Real-time positioning technology of train based on optical fiber coherent Rayleigh backscattering北大核心CSCD 下载免费PDF全文
With the rapid growth of railway mileage in China, the degree of heavy load of railway wagons continues to increase. An interference technology based on Rayleigh backscattering signal in optical fiber was proposed by using existing communication optical cables along railway lines. When the fiber vibrated slightly, the phase and refractive index of the fiber at disturbed position changed, which resulting in the Rayleigh backscattering light. By performing differential calculation on the Rayleigh signal curves before and after the operation, the location of the interference light intensity signal corresponded to the location of the disturbances was obtained. Based on this method, the recognition and positioning of railway vehicles were realized. By collecting and analyzing the time-domain and frequency-domain signal, the signal strength, train length, the number of carriages and other characteristics were extracted, and the model of railway vehicles were accurately recognized. Compared with traditional positioning technologies, this technology could realize long-distance monitoring, and the sensing fiber was buried underground on both sides of the railway, which was conducive to the concealment and protection of optical fiber. Experimental results show that the positioning error of the system is within ±10 m, and the detection of railway speed and position within 25 km can be realized. © 2022 Editorial office of Journal of Applied Optics. All rights reserved. 相似文献
87.
88.
Simulation of crowd dynamics in pedestrian evacuation concerning panic contagion: A cellular automaton approach 下载免费PDF全文
Guan-Ning Wang 《中国物理 B》2022,31(6):60402-060402
The study of the panic evacuation process is of great significance to emergency management. Panic not only causes negative emotions such as irritability and anxiety, but also affects the pedestrians decision-making process, thereby inducing the abnormal crowd behavior. Prompted by the epidemiological SIR model, an extended floor field cellular automaton model was proposed to investigate the pedestrian dynamics under the threat of hazard resulting from the panic contagion. In the model, the conception of panic transmission status (PTS) was put forward to describe pedestrians' behavior who could transmit panic emotions to others. The model also indicated the pedestrian movement was governed by the static and hazard threat floor field. Then rules that panic could influence decision-making process were set up based on the floor field theory. The simulation results show that the stronger the pedestrian panic, the more sensitive pedestrians are to hazards, and the less able to rationally find safe exits. However, when the crowd density is high, the panic contagion has a less impact on the evacuation process of pedestrians. It is also found that when the hazard position is closer to the exit, the panic will propagate for a longer time and have a greater impact on the evacuation. The results also suggest that as the extent of pedestrian's familiarity with the environment increases, pedestrians spend less time to escape from the room and are less sensitive to the hazard. In addition, it is essential to point out that, compared with the impact of panic contagion, the pedestrian's familiarity with environment has a more significant influence on the evacuation. 相似文献
89.
90.
基于水动力学的水体组分垂直结构对遥感信号的影响 总被引:1,自引:0,他引:1
基于水动力模型和辐射传输模型,模拟不同风速条件下水体组分(浮游植物和悬浮颗粒物)垂直分布对遥感反射率的影响,对比分析现有的两种水体光学均一函数(Zaneveld权重函数和Gordon权重函数)在不同层化程度水体中的应用。结果表明,悬浮颗粒物垂直分布对500~650nm范围内的遥感反射率(Rrs)影响较大,随着参考深度悬浮颗粒物质量浓度增加(由5~70mg/L),悬浮颗粒物垂直分布对Rrs的影响不断减小(变异系数由27.46%减小到3.38%),同时Rrs受到悬浮颗粒物影响的最大波长位置向长波方向移动(由585nm逐渐移动到685nm);在浮游植物垂直分布影响下,400~725nm范围内的Rrs值随着风速的增加呈现先增加再逐渐减小趋势,400~450nm范围内的Rrs受浮游植物垂直分布影响较小,变异系数仅为1%;500~600nm范围内的Rrs受浮游植物垂直分布影响较大,最大变异系数可达27.18%。在水体组分层化较弱水体中,Zaneveld与Gordon权重函数对水体光学均一处理效果较为相似;但在水体组分层化较为严重的水体中,Zaneveld权重函数光学均一处理效果要好于Gordon权重函数。 相似文献