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排序方式: 共有127条查询结果,搜索用时 312 毫秒
81.
利用DFT相位的矢量地理空间数据水印方法 总被引:1,自引:0,他引:1
基于矢量地理空间数据自身的特点,运用离散傅立叶变换(DFT)技术研究了基于DFT相位的矢量地理空间数据数字水印算法。由于DFT相位的较小变化也会导致原始数据的较大改变,因此引入自相关检测来辅助判定数字水印的存在。实验表明,DFT相位水印算法在抗矢量地理空间数据处理中常见的删点、数据格式转换、平移、旋转等攻击方面具有较好的效果,并且针对浮点型数据的效果要明显优于整数型数据的结果。 相似文献
82.
运用逻辑分块和量化思想,提出了一种矢量地理数据自检测水印算法,对此算法的鲁棒性进行了实验和分析。实验结果表明,该算法鲁棒性较好,且能有效提高矢量地理数据水印检测的效率。 相似文献
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84.
提出了一种适合于二值栅格地理数据版权保护的数字水印算法。首先,对二值栅格地理数据及其水印特征进行分析;在此基础上,引入游程长度编码思想,对二值栅格地理数据进行游程长度编码;最后,结合人类视觉系统特征,通过修改游程长度奇偶性的方式,将有意义的水印信息嵌入到二值栅格地理数据中。实验结果表明,所提出的算法能较好地保持二值栅格地理数据的视觉特征,有效地解决了目前所存在的二值栅格地理数据水印嵌入难、水印容量低等问题,且对压缩、加噪、裁剪等水印攻击具有较好的鲁棒性。 相似文献
85.
JIA Peihong CHEN Yunzhen MA Jinsong ZHU Dakui 《中国地理科学(英文版)》2006,16(3):276-281
1 Introduction Geo-spatial graphics data, as fundamental data in build- ing the Digital Earth, their security poses a big problem and draw much attention of many researchers all over the world. Digital Watermarking, which is based on theories of steganography, is a novel technique for data security developed in the recent years. A digital watermark is defined as an identifiable digital signal or mode that is permanently embedded into other data, namely host data, while it does not affect the … 相似文献
86.
2004年9月12日—2006年10月31日,在河北省香河县对太阳辐射(包括光合有效辐射PAR、可见光辐射VIS和总辐射Q等)、气象参数等进行了综合测量,初步得到了PAR、VIS等的变化特征。观测表明,小时累计之比PAR/Q、VIS/Q、PAR/VIS相对稳定,2004—2006年的平均值分别为2.164、0.434 mol8226;MJ-1和4.967 mol8226;MJ-1,同时它们表现出明显的日、逐日和季节变化特征,并受到水汽、气溶胶、云等因素的影响。建立了实际天气条件计算PAR、VIS小时累计值的经验公式以及PAR与VIS转换关系式,计算值与观测值符合得较好。在考虑水汽和散射因子时,PAR、VIS计算值与观测值的相对偏差分别为9.9%和10.8%。限于实际情况,也可以只考虑水汽因子的作用来计算PAR和VIS小时累计值,它们的相对偏差分别为11.1%和11.8%。对于PAR、VIS的传输和计算来说,水汽因子的作用至关重要。散射因子的作用虽然弱于水汽因子,但它的作用不容忽视。 相似文献
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88.
We present new wind measurements in Venus’ lower mesosphere from visible spectroscopy during the 2007 worldwide coordinated ground campaign in support of ESA's Venus Express mission. These observations consisted of high-resolution spectra of Fraunhofer lines in the entire visible range (0.37-1.05 μm) to measure the winds near 68 km using the Doppler shift of solar radiation scattered by clouds toward the observer's direction. The observations included various points of the dayside hemisphere at a phase angle of ∼109°. We took advantage of two symmetrical elongations in July and September 2007 at Canada-France-Hawaii's 3.6-m telescope. Kinematical fits to the Doppler winds provide a mean equatorial velocity of (104±10) m s−1 for the zonal retrograde flow. This velocity agrees quite well with the mean value obtained by tracking the UV markings from several spacecraft. 相似文献
89.
90.
A Modified Becker''s Split-Window Approach for Retrieving Land Surface Temperature from AVHRR and VIRR 总被引:1,自引:0,他引:1
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QUAN Weijun CHEN Hongbin HAN Xiuzhen LIU Yonghong YE Caihua 《Acta Meteorologica Sinica》2012,26(2):229-240
In order to provide a long time-series, high spatial resolution, and high accuracy dataset of land surface
temperature (LST) for climatic change research, a modified Becker and Li's split-window approach is pro-
posed in this paper to retrieve LST from the measurements of Advanced Very High Resolution Radiometer
(AVHRR) onboard National Oceanic and Atmospheric Administration (NOAA)-7 to -18 and the Visible and
InfraRed Radiometer (VIRR) onboard FY-3A. For this purpose, the Moderate Resolution Transmittance
Model (MODTRAN) 4.1 was first employed to compute the spectral radiance at the top of atmosphere
(TOA) under a variety of surface and atmosphere conditions. Then, a temperature dataset consists of
boundary temperature Ts (which is one of the input parameters to MODTRAN), and channels 4 and 5
brightness temperatures (T4 and T5) were constructed. Note that channels 4 and 5 brightness tempera-
tures were simulated from the MODTRAN output spectral radiance by convolving them with the spectral
response functions (SRFs) of channels 4 and 5 of AVHRRs and VIRR. The coefficients of modified Becker
and Li's split-window approach for various AVHRRs and VIRR were subsequently regressed based on this
temperature dataset using the least square method. As an example of validation, one AVHRR satellite image
over Beijing acquired at 0312 UTC 27 April 2008 by AVHRR onboard NOAA-17 was selected to retrieve
the LST image using the modified Becker and Li's approach. The comparison between this LST image and
that from the MODIS level-2 LST product provided by the University of Tokyo in Japan indicates that
the correlation coefficient is 0.88, the bias is 0.6 K, and the root mean square deviation (RMSD) is 2.1 K.
Furthermore, about 70% and 37% pixels in the LST difference image, which is the result of retrieved LST
image from AVHRR minus the corresponding MODIS LST image, have the values within ±2 and ±1 K,
respectively. 相似文献