全文获取类型
| 收费全文 | 130篇 |
| 免费 | 14篇 |
| 国内免费 | 27篇 |
专业分类
| 测绘学 | 44篇 |
| 大气科学 | 10篇 |
| 地球物理 | 24篇 |
| 地质学 | 53篇 |
| 海洋学 | 11篇 |
| 天文学 | 7篇 |
| 综合类 | 16篇 |
| 自然地理 | 6篇 |
出版年
| 2023年 | 1篇 |
| 2022年 | 3篇 |
| 2021年 | 7篇 |
| 2020年 | 1篇 |
| 2019年 | 10篇 |
| 2018年 | 9篇 |
| 2017年 | 8篇 |
| 2016年 | 12篇 |
| 2015年 | 7篇 |
| 2014年 | 9篇 |
| 2013年 | 7篇 |
| 2012年 | 9篇 |
| 2011年 | 4篇 |
| 2010年 | 3篇 |
| 2009年 | 6篇 |
| 2008年 | 8篇 |
| 2007年 | 5篇 |
| 2006年 | 10篇 |
| 2005年 | 10篇 |
| 2004年 | 3篇 |
| 2003年 | 6篇 |
| 2002年 | 3篇 |
| 2001年 | 6篇 |
| 2000年 | 2篇 |
| 1999年 | 2篇 |
| 1998年 | 7篇 |
| 1997年 | 3篇 |
| 1995年 | 2篇 |
| 1994年 | 3篇 |
| 1993年 | 2篇 |
| 1992年 | 1篇 |
| 1991年 | 1篇 |
| 1990年 | 1篇 |
排序方式： 共有171条查询结果，搜索用时 15 毫秒
101.
Attenuation of P,S, and coda waves in Koyna region,India 总被引：1，自引：0，他引：1
The attenuation properties of the crust in the Koyna region of the Indian shield have been investigated using 164 seismograms
from 37 local earthquakes that occurred in the region. The extended coda normalization method has been used to estimate the
quality factors for P waves and S waves , and the single back-scattering model has been used to determine the quality factor for coda waves (Q
c). The earthquakes used in the present study have the focal depth in the range of 1–9 km, and the epicentral distance vary
from 11 to 55 km. The values of
and Q
c show a dependence on frequency in the Koyna region. The average frequency dependent relationships (Q = Q
0
f
n) estimated for the region are , and . The ratio is found to be greater than one for the frequency range considered here (1.5–18 Hz). This ratio, along with the frequency
dependence of quality factors, indicates that scattering is an important factor contributing to the attenuation of body waves
in the region. A comparison of Q
c and in the present study shows that for frequencies below 4 Hz and for the frequencies greater than 4 Hz. This may be due to the multiple scattering effect of the medium. The outcome of this
study is expected to be useful for the estimation of source parameters and near-source simulation of earthquake ground motion,
which in turn are required in the seismic hazard assessment of a region. 相似文献
102.
Assessment of different topographic corrections in AWiFS satellite imagery of Himalaya terrain 总被引：2，自引：0，他引：2
V. D. Mishra J. K. Sharma K. K. Singh N. K. Thakur M. Kumar 《Journal of Earth System Science》2009,118(1):11-26
The influence of topographic effects in optical satellite imagery is not investigated very extensively in the Himalayan terrain.
The topographic variability causes a problem of differential illumination due to steep and varying slopes in rugged Himalayan
terrain. Therefore, topographic corrections are essential for qualitative and quantitative analysis of snow cover applications.
The present paper discusses the implementation of different topographic correction models on AWiFS sensor onboard IRS P6 satellite
images and the qualitative and quantitative comparative analysis in detail. Both the Lambertian and non-Lambertian assumptions
have been considered in the present analysis with the aim to explore best suitable empirical model for rugged terrain. The
main topographic methods implemented are:
Lambertian assumptions are found to be very unrealistic over Himalayan terrain as these lead to either underestimation or
overestimation of physical parameters significantly both on sunlit slopes as well as the slopes away from the Sun. This problem
is overcome by considering non-Lambertian assumption. Minneart constant and C-correction coefficients for all AWiFS satellite
bands are estimated using regression analysis. All the results due to topographic effects are investigated qualitatively and
quantitatively using four criteria namely visual analysis, validation with field measurements (in-situ observations), spectral reflectance of training samples of snow on the south and north aspects and graphically. The visual
analysis confirms the minimization of three dimensional relief effects in two-stage normalization and slope matching methods
and retrieves some of the information under mountain shadow. Due to the very bright surface of snow fields there is likely
to be more diffuse reflected light in these areas than over darker vegetated surfaces. The qualitative analysis in other methods
does not extract any information on shady slopes. The quantitative validation of topographic results in satellite imagery
with in-situ observations shows underestimation of spectral reflectance of snow significantly except for slope matching technique. It
is also apparent that although all the topographic methods correct the reflectance of training snow samples on the south and
north aspects but most acceptable values are achieved using slope matching. The results obtained from graphical analysis reveal
that mean reflectance after all topographic corrections are independent of illumination. This study also suggests that the
suitability of topographic models can not be concluded as successful based on single criterion. Slope matching technique is
the only technique which satisfies all the four criteria successfully and produces the best result for Himalayan terrain. 相似文献
| • | C-correction |
| • | Minneart corrections |
| • | Civco’s modified version of cosine correction |
| • | two-stage normalization and |
| • | slope matching technique. |
103.
高质量的海底声强图是多波束海底底质分类的基础。在系统分析了多波束声强图像中沿测船航迹灰度异常值和区域性明暗差异成因的基础上,提出了基于加权最小二乘估计的多波束声强数据归一化方法。实例计算结果表明:该方法在不损失原有强度变化信息的基础上,有效地抑制了声强图中灰度异常值对海底底质分类的影响,提高了区域底质分类的质量。 相似文献
104.
A nonlinear function approach for the normalized complementary relationship evaporation model that is different from the methodology maintaining the symmetric complementary relationship with appropriate definitions of potential and wet‐environment evaporation is proposed and verified. This approach employs the definitions used in the advection‐aridity model, wherein the potential is estimated using the Penman equation. Normalized by Penman potential evaporation, the complementary relationship model is expressed as a function describing the relationship between the evaporation ratio (the ratio of the actual to the Penman potential evaporation) and the proportion of the radiation term in Penman potential evaporation. The new nonlinear function proposed in the current study is approximately equivalent to the advection‐aridity and the modified Granger models under conditions that are neither too wet nor too dry, but is more reasonable under arid and wet conditions. The new nonlinear function model performs well in estimating actual evaporation, as verified by the observed data from four sites under different land covers. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
105.
106.
遥感数字图像直方图的标准化常用于不同时相相邻遥感图像的拼接和进行土地利用变化监测的预处理,还可以消除不同成像条件对图像分析的影响,部分纠正由于太阳/传感器位置或大气影响造成的相邻图像的辐射误差,从而达到相同成像条件的效果。由于常用的基于数值统计学的直方图的标准化方法不能达到理想效果,该文提出了基于无变化像素进行图像标准化的方法,通过多光谱图像差异直方图及每一波段黑灰白像素的相关系数计算,自动选择无变化像素,进而进行直方图的标准化。将该方法应用于2期TM图像遥感数据,明显减小了成像条件差异,提高了数字图像标准化的有效性。 相似文献
107.
用质控图和稳健统计-迭代法评估环境检测实验室测量不确定度 总被引：3，自引：0，他引：3
基于实验室长期积累的质控数据评估测量不确定度的方法具有广泛应用前景,但常见的质控图法只能处理单一浓度,而处理多浓度水平的线性校准法建立模型时需要成套、完整的质控数据,不利于基层实验室的应用。稳健统计是指不用识别、剔除离群值,直接应用全部测量数据,将离群值对统计分析结果影响降低到最小的统计分析方法。本文尝试用回收率将不同浓度数据归一化,然后用质控图方法处理。如果存在离群数据时,可用稳健统计法计算期间精密度s R'。利用本实验室积累的5套和其他实验室提供的19套环境检测领域常规项目质控数据验证了新方法的可行性。验证结果表明,对单一浓度数据,不经任何处理,稳健统计-迭代法可得到与质控图法基本相符的结果,s R'(相对值)平均偏差为0.15%。对于多浓度水平数据,经归一化后,质控图法、稳健统计-迭代法与线性校准法的结果平均偏差分别为0.43%和0.20%,质控图法与稳健统计-迭代法的结果平均偏差为0.26%,三种方法计算结果基本相符;稳健统计-迭代法更接近于线性校准法计算结果,且方法原理简单,计算步骤明显简化,适用于线性校准法比例模型数据的处理。 相似文献
108.
研究区延长组沉积为陆相三角洲沉积,主要含油气层位为长6油层组.受沉积环境及泥岩中有机质含量的影响,该区非渗透层段测井曲线响应差异较大,使得测井曲线标准化效果不佳.针对此情况,在借助自然伽马、井径测井、声波测井、感应测井等曲线构建"视标准层"的基础上,利用ΔlgR方法剔除受有机质影响明显的非渗透层段,进而选取不受井眼条件、岩性、物性、含油气性等因素影响的非渗透层段作为"视标准层",最后采用直方图法对研究区测井曲线进行标准化,并结合孔隙度计算模型进行了检验.研究结果表明,ΔlgR方法可以较为有效地消除非渗透层段有机质含量的影响,提高陆相地层中"视标准层"构建的质量,为后期储层参数的确定奠定基础. 相似文献
109.
小波变换在遥感图像相对辐射校正中的应用 总被引：1，自引：0，他引：1
邢宇 《测绘与空间地理信息》2015,(6)
采用小波分析将ASTER图像的低频分量和高频分量进行分离;对低频分量差值计算得到伪不变特征点,采用最小二乘法对低频分量进行线性变换;然后将原始待校正图像的高频分量与校正后的低频分量进行图像重构,实现多时相ASTER遥感图像的相对辐射校正。结果表明,该方法有效地保留了源图像中由于地物变化引起的辐射差异,相对辐射校正的整体效果较好。 相似文献
110.