全文获取类型
收费全文 | 422篇 |
免费 | 46篇 |
国内免费 | 20篇 |
专业分类
化学 | 89篇 |
力学 | 39篇 |
综合类 | 24篇 |
数学 | 45篇 |
物理学 | 291篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 16篇 |
2021年 | 12篇 |
2020年 | 22篇 |
2019年 | 11篇 |
2018年 | 8篇 |
2017年 | 20篇 |
2016年 | 29篇 |
2015年 | 22篇 |
2014年 | 30篇 |
2013年 | 33篇 |
2012年 | 20篇 |
2011年 | 28篇 |
2010年 | 12篇 |
2009年 | 22篇 |
2008年 | 20篇 |
2007年 | 25篇 |
2006年 | 23篇 |
2005年 | 25篇 |
2004年 | 12篇 |
2003年 | 14篇 |
2002年 | 12篇 |
2001年 | 13篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 11篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有488条查询结果,搜索用时 218 毫秒
31.
Target tracking technology that is based on aerial videos is widely used in many fields; however, this technology has challenges, such as image jitter, target blur, high data dimensionality, and large changes in the target scale. In this paper, the research status of aerial video tracking and the characteristics, background complexity and tracking diversity of aerial video targets are summarized. Based on the findings, the key technologies that are related to tracking are elaborated according to the target type, number of targets and applicable scene system. The tracking algorithms are classified according to the type of target, and the target tracking algorithms that are based on deep learning are classified according to the network structure. Commonly used aerial photography datasets are described, and the accuracies of commonly used target tracking methods are evaluated in an aerial photography dataset, namely, UAV123, and a long-video dataset, namely, UAV20L. Potential problems are discussed, and possible future research directions and corresponding development trends in this field are analyzed and summarized. 相似文献
32.
多羰基甾酮的选择性还原反应研究 总被引:8,自引:0,他引:8
在不同金属离子存在下,多羰基甾酮的甾核及支链上都发生了羰基与硼氢化钠的还原反应,得到具有不同的区域选择性和立体选择性的还原产物. 相似文献
33.
Tom Lowrie 《International Journal of Computers for Mathematical Learning》2002,7(3):301-318
This paper explores the way in which young children (6 year olds) made sense of screen-based images on the computer. The participants
were required to interpret 3D-like representations and relate these images to objects in their environment. Both static and
relatively dynamic software programs were used in the investigation. Some of the children could not make links between the
screen representation and the intended three-dimensional (3D) objects. It is argued that young children should be exposed
to activities that establish explicit links between 2D and 3D objects ``away' from the computer before attempting the more
difficult links required to interpret and represent 3D objects in ICT contexts.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
34.
35.
近自然彩色图像融合算法及其实时处理系统的发展 总被引:8,自引:2,他引:8
在军事和生产领域,特别是在极其恶劣的可视条件下,图像融合技术越来越强调融合效果显示的"近自然"感觉,以及人类视觉感知的要求。从彩色图像融合算法的发展概况出发,着重介绍了两种具有代表性的基于视觉特性的近自然彩色图像融合方法,并特别阐述了课题组近期开展的相关算法研究成果。总结了国内外实时彩色图像融合系统的发展现状,概括了课题组已具备的硬件实验基础,综合分析了实时彩色图像融合技术的若干关键技术,如多源图像特征分析、实时图像配准、融合图像后处理等。针对实时图像融合技术的应用状况,提出图像融合系统未来的发展趋势。 相似文献
36.
37.
Road signs must provide a conspicuous signal to a wide variety of drivers over a broad range of environmental and geometric
conditions. Recently, there are an increasing number of applications in which light emitting diodes (LEDs) are used as the
light source, including critical transportation signaling. In the presence of fog, the resulting visual signal is disturbed
due to light scattering by airborne water droplets. By measuring LED brightness with human spectral sensitivity in various
densities and various droplet sizes (10, 30, 50, and 100 μm), it is understood that the particle size distribution (fog droplet
size) and density of fog does affect visibility in fog. The colored LEDs that contain a yellow component had high brightness
evaluation, blue component had low brightness evaluation in all densities and different droplet sizes. The result in this
paper can contribute to air and land traffic safety and the prevention of accidents. 相似文献
38.
Threshold Visual Cryptography Schemes with Specified Whiteness Levels of Reconstructed Pixels 总被引:6,自引:0,他引:6
In 1994, Naor and Shamir introduced an unconditionally secure method for encoding black and white images. This method, known as a threshold visual cryptography scheme (VCS), has the benefit of requiring no cryptographic computation on the part of the decoders. In a
-VCS, a share, in the form of a transparency, is given to ">n users. Any ">k users can recover the secret simply by stacking transparencies, but ">k-1 users can gain no information about the secret whatsoever.In this paper, we first explore the issue of contrast, by demonstrating that the current definitions are inadequate, and by providing an alternative definition. This new definition motivates an examination of minimizing pixel expansion subject to fixing the VCS parameters ">h and ">l. New bounds on pixel expansion are introduced, and connections between these bounds are examined. The best bound presented is tighter than any previous bound. An analysis of connections between (2, ">n) schemes and designs such as BIBD's, PBD's, and (">r, )-designs is performed. Also, an integer linear program is provided whose solution exactly determines the minimum pixel expansion of a (2, ">n)-VCS with specified ">h and >l. 相似文献
39.
The border luminance of the test stimulus between the natural and unnatural object color, yynBu was obtained for different spatial sizes of the immediate surround to prove that nBu can be determined based on a new recognized visual space of illumination (RVSI) that is assumed to be constructed for the immediate surround separately from the RVSI for the subjects room itself. The nBu of five test stimuli were determined for six different sizes covering from zero to 1866 cm2 with four different lightnesses, N4, N6 and N8, while keeping the room illuminance constant at 100 or 600 lx. The results showed that luminance of the border nBu gradually decreased as the size of the immediate surround was increased and that the decrease was larger for immediate surround with lower lightness. The results were interpreted as showing a new RVSI constructed for the spatial extent of the immediate surround of the test stimulus, and the RVSI was more completely constructed for larger spatial size of the immediate surround. © 2005 The Optical Society of Japan 相似文献
40.