全文获取类型
收费全文 | 260篇 |
免费 | 13篇 |
国内免费 | 20篇 |
专业分类
测绘学 | 87篇 |
大气科学 | 46篇 |
地球物理 | 52篇 |
地质学 | 15篇 |
海洋学 | 52篇 |
天文学 | 6篇 |
综合类 | 20篇 |
自然地理 | 15篇 |
出版年
2023年 | 2篇 |
2022年 | 10篇 |
2021年 | 9篇 |
2020年 | 13篇 |
2019年 | 14篇 |
2018年 | 3篇 |
2017年 | 15篇 |
2016年 | 13篇 |
2015年 | 8篇 |
2014年 | 12篇 |
2013年 | 24篇 |
2012年 | 15篇 |
2011年 | 14篇 |
2010年 | 16篇 |
2009年 | 11篇 |
2008年 | 15篇 |
2007年 | 18篇 |
2006年 | 19篇 |
2005年 | 10篇 |
2004年 | 11篇 |
2003年 | 13篇 |
2002年 | 8篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1994年 | 2篇 |
1990年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有293条查询结果,搜索用时 15 毫秒
21.
多回击负地闪先导通道的辐射和光学特征 总被引:1,自引:0,他引:1
利用闪电VHF窄带干涉仪辐射源定位系统和高速摄像系统,对青海大通地区一次有5次回击的负地闪放电过程进行了同步观测,对比分析了通道传输过程的辐射和光学特征.结果表明,光学通道亮度能补充VHF干涉仪定位先导通道的电流特征,VHF干涉仪定位弥补了光学设备拍摄弱放电和云内流光通道的不足;在通道分枝结构上,干涉仪定位的通道和光学通道呈现出很好对应.干涉仪定位分枝通道的辐射源点较明显,但分枝光学通道的出现明显落后于干涉仪定位辐射源通道.对用两种不同观测手段探测的先导通道进行速度计算,发现两者计算的直窜先导和直窜梯级先导速度量级一致,均为106m·s-1,但干涉仪在时间的获取及精确量化上有优势,干涉仪定位计算先导速度的精确度高于光学通道定位. 相似文献
22.
23.
Meteor44 is a software system developed at MSFC for the calibration and analysis of video meteor data. The photometric range
of the (8 bit) video data is extended from a visual magnitude range of from 8 to 3 to from 8 to −8 for both meteors and stellar
images using saturation compensation. Camera and lens specific saturation compensation coefficients are derived from artificial
variable star laboratory measurements. Saturation compensation significantly increases the number of meteors with measured
intensity and improves the estimation of meteoroid mass distribution. Astrometry is automated to determine each image's plate
coefficient using appropriate star catalogs. The images are simultaneously intensity calibrated from the contained stars to
determine the photon sensitivity and the saturation level referenced above the atmosphere. The camera's spectral response
is used to compensate for stellar color index and typical meteor spectra in order to report meteor light curves in traditional
visual magnitude units. Recent efforts include improved camera calibration procedures and long focal length "streak" meteor
photometry. Meteor44 has been used to analyze data from the 2001, 2002 and 2003 MSFC Leonid observational campaigns as well
as several lesser showers. 相似文献
24.
《The Journal of geography》2012,111(6):235-246
Learning about climate change is tangible when it addresses impacts that can be observed close to home. In this program, sixty-four diverse middle and high school students produced videos about locally relevant climate change topics. Graduate and undergraduate students provided mentorship. The program engaged students in research and learning about climate change, and sparked their interest in science careers. Evaluation results showed that students were highly motivated by the experience, developed a genuine interest in their science topic, learned about the scientific process, and developed twenty-first century skills. The program provided a unique and authentic approach to science learning and communication. 相似文献
25.
26.
Wenwen Li Sizhe Wang 《International journal of geographical information science》2017,31(8):1562-1582
The increasing research interest in global climate change and the rise of the public awareness have generated a significant demand for new tools to support effective visualization of big climate data in a cyber environment such that anyone from any location with an Internet connection and a web browser can easily view and comprehend the data. In response to the demand, this paper introduces a new web-based platform for visualizing multidimensional, time-varying climate data on a virtual globe. The web-based platform is built upon a virtual globe system Cesium, which is open-source, highly extendable and capable of being easily integrated into a web environment. The emerging WebGL technique is adapted to support interactive rendering of 3D graphics with hardware graphics acceleration. To address the challenges of transmitting and visualizing voluminous, complex climate data over the Internet to support real-time visualization, we develop a stream encoding and transmission strategy based on video-compression techniques. This strategy allows dynamic provision of scientific data in different precisions to balance the needs for scientific analysis and visualization cost. Approaches to represent, encode and decode processed data are also introduced in detail to show the operational workflow. Finally, we conduct several experiments to demonstrate the performance of the proposed strategy under different network conditions. A prototype, PolarGlobe, has been developed to visualize climate data in the Arctic regions from multiple angles. 相似文献
27.
Sébastien Darchen 《Urban geography》2016,37(2):202-222
In this paper, I question whether agglomerations of video game companies in Australia function as clusters (spatially bound) or rather as communities (not spatially bound). The two case studies included in the analysis are the main agglomerations of video companies in Australia—Brisbane and Melbourne. The data have been collected through 21 semi-structured interviews performed between 2012 and 2014. The main findings are as follows: (1) the primary reason that video game companies come together is to share tacit knowledge and skilled labour; (2) these agglomerations do not have the attributes of “creative clusters”; and (3) new technologies enable experienced game developers to operate at the geographic periphery of the main agglomeration of developers. Therefore, to paint a more accurate picture of why some video game companies are successful—beyond simply positive externalities associated with co-localization—I propose the term “networked communities.” This recognizes that social networks at varying scales (local, national, international) are being developed by video game firms in order to thrive and reach a global audience. 相似文献
28.
This paper presents an examination of the timescale of phase transition behaviour of a series of salts known to cause damage
to wall paintings and other cultural property. The rate of deliquescence and crystallisation of single salts (nitromagnesite
and halite) under different RH regimes, and the extent to which this was affected when mixed with other salts (niter, nitratite
and gypsum), was investigated. The study was conducted using simple conventional techniques (mass measurements over time)
and also using an innovative new method: timelapse video imaging with online data annotation. The results demonstrate the
synergy gained from combining video imaging with environmental data in reference to time in the study of salt phase changes:
where it revealed new information concerning the kinetics of deliquescence and crystallisation. The implications of these
results for the implementation of environmental control measures within historic buildings are discussed.
相似文献
Alison SawdyEmail: |
29.
We analyse data obtained by different ground-based video camera systems during the 1999 Leonid meteor storm. We observe similar
activity profiles at nearby observing sites, but significant differences over distances in the order of 4,000 km. The main
peak occured at 02:03 UT (λ⊙=235.286, J2000, corrected for the time of the topocentric stream encounter). At the Iberian peninsula quasi-periodic activity
fluctuations with a period of about 7 min were recorded. The camera in Jordan detected a broad plateau of activity at 01:39–01:53
UT, but no periodic variations. The Leonid brightness distribution derived from all cameras shows a lack of faint meteors
with a turning point close to +3m, which corresponds to meteoroids of approximately 10-3 g. We find a pin-point radiant at αalpha=153.65 ±0.1, δ=21.80 ±0. (λ⊙=235.290). The radiant positionis identical before and after the storm, and also during the storm no driftis observed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
30.
A video analysis method for monitoring sediment transport and sorting processes in a laboratory flume is presented. Video taken through the glass side‐wall of a laboratory flume is captured using a digital CCD (charge‐coupled device) camera and significant movements between individual frames are detected using image analysis. This method involves direct subtraction of the brightness numbers of pixels in sequential video frames, followed by thresholding to produce binarized images of significant change, above the inherent level of system noise. Experimental results showing dilation of a gravel framework and rapid infiltration of fines just prior to entrainment are discussed. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献