全文获取类型
收费全文 | 990篇 |
免费 | 80篇 |
国内免费 | 80篇 |
专业分类
测绘学 | 353篇 |
大气科学 | 73篇 |
地球物理 | 150篇 |
地质学 | 205篇 |
海洋学 | 84篇 |
天文学 | 7篇 |
综合类 | 77篇 |
自然地理 | 201篇 |
出版年
2024年 | 6篇 |
2023年 | 13篇 |
2022年 | 22篇 |
2021年 | 55篇 |
2020年 | 58篇 |
2019年 | 51篇 |
2018年 | 39篇 |
2017年 | 55篇 |
2016年 | 54篇 |
2015年 | 54篇 |
2014年 | 59篇 |
2013年 | 73篇 |
2012年 | 58篇 |
2011年 | 70篇 |
2010年 | 41篇 |
2009年 | 58篇 |
2008年 | 63篇 |
2007年 | 38篇 |
2006年 | 49篇 |
2005年 | 45篇 |
2004年 | 30篇 |
2003年 | 29篇 |
2002年 | 21篇 |
2001年 | 20篇 |
2000年 | 19篇 |
1999年 | 7篇 |
1998年 | 10篇 |
1997年 | 13篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有1150条查询结果,搜索用时 15 毫秒
941.
This study scrutinises the use of terrestrial laser scanning (TLS) to measure diameter at breast height (DBH) and tree height at individual tree species level. LiDAR point cloud scans are collected from uniformly defined control points. The result of processed TLS data demonstrates the precise measurements of tree height and DBH by comparing it with field data (DBH, tree height, tree species and location). The average tree height and DBH obtained through TLS measurements were 9.44?m and 43.30?cm, respectively. A linear equation between TLS derived parameters and field measured values were established, which gave the coefficient of determination (r2) of 0.79 and 0.96 for tree height and DBH, respectively. Further, these parameters were used to calculate above ground biomass (AGB) for individual tree species by considering a non-destructive approach. The total AGB and carbon stock from 80 different trees are computed to be 49.601 and 22.320?tonnes, respectively. 相似文献
942.
With the emergence of very high spatial and spectral resolution data set, the resolution gap that existed between remote-sensing data set and aerial photographs has decreased. The decrease in resolution gap has allowed accurate discrimination of different tree species. In this study, discrimination of indigenous tree species (n?=?5) was carried out using ground based hyperspectral data resampled to QuickBird bands and the actual QuickBird imagery for the area around Palapye, Botswana. The purpose of the study was to compare the accuracies of resampled hyperspectral data (resampled to QuickBird sensors) with the actual image (QuickBird image) in discriminating between the indigenous tree species. We performed Random Forest (RF) using canopy reflectance taking from ground-based hyperspectral sensor and the reflectance delineated regions of the tree species. The overall accuracies for classifying the five tree species was 79.86 and 88.78% for both the resampled and actual image, respectively. We observed that resampled data set can be upscale to actual image with the same or even greater level of accuracy. We therefore conclude that high spectral and spatial resolution data set has substantial potential for tree species discrimination in savannah environments. 相似文献
943.
空间数据索引对于空间数据管理和分析具有重要作用,与数据处理速度和效率密切相关。随着人类社会进入大数据时代,遥感矢量数据具备了大数据的特点,传统的空间索引构建方法无法有效满足矢量大数据处理的需求,为此引入云计算环境来进行空间索引构建,目的是提高空间索引构建速度。首先,对常见的空间索引及现阶段云计算环境下基于MapReduce模型的空间数据管理进行了综述;然后以云计算环境下R树索引构建为例,对云计算环境下空间索引的构建进行了研究;最后,通过实验验证,证明了云计算环境下空间索引构建的速度与单机索引构建相比,加速比为28~40倍;在相同云环境下,网格索引构建速度最快,R+索引构建速度相对较慢。 相似文献
944.
J. Amorós López E. Izquierdo VerdiguierL. Gómez Chova J. Muñoz MaríJ.Z. Rodríguez Barreiro G. Camps VallsJ. Calpe Maravilla 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(1):115-123
Managing land resources using remote sensing techniques is becoming a common practice. However, data analysis procedures should satisfy the high accuracy levels demanded by users (public or private companies and governments) in order to be extensively used. This paper presents a multi-stage classification scheme to update the citrus Geographical Information System (GIS) of the Comunidad Valenciana region (Spain). Spain is the first citrus fruit producer in Europe and the fourth in the world. In particular, citrus fruits represent 67% of the agricultural production in this region, with a total production of 4.24 million tons (campaign 2006-2007). The citrus GIS inventory, created in 2001, needs to be regularly updated in order to monitor changes quickly enough, and allow appropriate policy making and citrus production forecasting. Automatic methods are proposed in this work to facilitate this update, whose processing scheme is summarized as follows. First, an object-oriented feature extraction process is carried out for each cadastral parcel from very high spatial resolution aerial images (0.5 m). Next, several automatic classifiers (decision trees, artificial neural networks, and support vector machines) are trained and combined to improve the final classification accuracy. Finally, the citrus GIS is automatically updated if a high enough level of confidence, based on the agreement between classifiers, is achieved. This is the case for 85% of the parcels and accuracy results exceed 94%. The remaining parcels are classified by expert photo-interpreters in order to guarantee the high accuracy demanded by policy makers. 相似文献
945.
946.
947.
Skillful streamflow forecasts at seasonal lead times may be useful to water managers seeking to provide reliable water supplies and maximize hydrosystem benefits. In this study, a class of data mining techniques, known as tree-structured models, is investigated to address the nonlinear dynamics of climate teleconnections and screen promising probabilistic streamflow forecast models for river–reservoir systems. In a case study of the Lower Colorado River system in central Texas, a number of potential predictors are evaluated for forecasting seasonal streamflow, including large-scale climate indices related to the El Niño–Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO), and others. Results show that the tree-structured models can effectively capture the nonlinear features hidden in the data. Skill scores of probabilistic forecasts generated by both classification trees and logistic regression trees indicate that seasonal inflows throughout the system can be predicted with sufficient accuracy to improve water management, especially in the winter and spring seasons in central Texas. 相似文献
948.
Site specific probabilistic seismic hazard analysis at Dubai Creek on the west coast of UAE 总被引:2,自引:1,他引:1
Ayman A. Shama 《地震工程与工程振动(英文版)》2011,10(1):143-152
A probabilistic seismic hazard analysis (PSHA) was conducted to establish the hazard spectra for a site located at Dubai Creek on the west coast of the United Arab Emirates (UAE). The PSHA considered all the seismogenic sources that affect the site, including plate boundaries such as the Makran subduction zone, the Zagros fold-thrust region and the transition fault system between them; and local crustal faults in UAE. PSHA indicated that local faults dominate the hazard. The peak ground acceleration (PGA) for the 475-year return period spectrum is 0.17 g and 0.33 g for the 2,475-year return period spectrum. The hazard spectra are then employed to establish rock ground motions using the spectral matching technique. 相似文献
949.
政务GIS平台专题网站的建设 总被引:1,自引:1,他引:0
以"中国(云南)一东盟自由贸易区一南亚区域合作联盟空间信息公共平台"中"云南省综合省情"专题为例,阐述政务GIS平台专题页面制作方法,从页面布局、信息组织、地图服务调用等方面对政务专题网站的建设进行探讨,着重介绍了页面中控制内容区对象的方法,并展望其应用前景,以期为政务GIS平台中相关功能的应用与开发提供参考. 相似文献
950.