全文获取类型
收费全文 | 1400篇 |
免费 | 132篇 |
国内免费 | 70篇 |
专业分类
测绘学 | 742篇 |
大气科学 | 45篇 |
地球物理 | 189篇 |
地质学 | 258篇 |
海洋学 | 199篇 |
综合类 | 88篇 |
自然地理 | 81篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 35篇 |
2021年 | 80篇 |
2020年 | 86篇 |
2019年 | 76篇 |
2018年 | 66篇 |
2017年 | 97篇 |
2016年 | 123篇 |
2015年 | 116篇 |
2014年 | 108篇 |
2013年 | 137篇 |
2012年 | 80篇 |
2011年 | 93篇 |
2010年 | 49篇 |
2009年 | 60篇 |
2008年 | 53篇 |
2007年 | 54篇 |
2006年 | 40篇 |
2005年 | 21篇 |
2004年 | 29篇 |
2003年 | 28篇 |
2002年 | 33篇 |
2001年 | 12篇 |
2000年 | 16篇 |
1999年 | 8篇 |
1998年 | 17篇 |
1997年 | 13篇 |
1996年 | 19篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有1602条查询结果,搜索用时 31 毫秒
151.
A computational canopy volume (CCV) based on airborne laser scanning (ALS) data is proposed to improve predictions of forest biomass and other related attributes like stem volume and basal area. An approach to derive the CCV based on computational geometry, topological connectivity and numerical optimization was tested with sparse-density, plot-level ALS data acquired from 40 field sample plots of 500–1000 m2 located in a boreal forest in Norway. The CCV had a high correspondence with the biomass attributes considered when derived from optimized filtrations, i.e. ordered sets of simplices belonging to the triangulations based on the point data. Coefficients of determination (R2) between the CCV and total above-ground biomass, canopy biomass, stem volume, and basal area were 0.88–0.89, 0.89, 0.83–0.97, and 0.88–0.92, respectively, depending on the applied filtration. The magnitude of the required filtration was found to increase according to an increasing basal area, which indicated a possibility to predict this magnitude by means of ALS-based height and density metrics. A simple prediction model provided CCVs which had R2 of 0.77–0.90 with the aforementioned forest attributes. The derived CCVs always produced complementary information and were mainly able to improve the predictions of forest biomass relative to models based on the height and density metrics, yet only by 0–1.9 percentage points in terms of relative root mean squared error. Possibilities to improve the CCVs by a further analysis of topological persistence are discussed. 相似文献
152.
Canada is dominated by forested ecosystems which are subject to various inventory and management practices, with more northern boreal forests subject to neither. Our objectives were to measure the capacity of temporal trajectory metrics for estimating selected forest attributes in a northern Canadian boreal forest context using Landsat imagery and investigate the importance of different types of temporal trajectory metrics. Results indicated that Wetness was the best Tasseled Cap (TC) component for aboveground biomass estimation (R2 = 50%, RMSE% = 56%), and the combination of simple and complex metrics from all TC components produced the highest R2 (62%) and lowest RMSE% (49%). Using a similar combination of variables, other forest attributes were estimated equally reliably with lower RMSE% values. The most important temporal trajectory metrics were simple and described TC component values at each point of change in the temporal trajectory, however the most important variables overall were environmental variables. 相似文献
153.
The development of robust and accurate methods for automatic registration of optical imagery and 3D LiDAR data continues to be a challenge for a variety of applications in photogrammetry, computer vision and remote sensing. This paper proposes a new approach for the registration of optical imagery with LiDAR data based on the theory of Mutual Information (MI), which exploits the statistical dependency between same- and multi-modal datasets to achieve accurate registration. The MI-based similarity measures quantify dependencies between aerial imagery, and both LiDAR intensity data and 3D point cloud data. The needs for specific physical feature correspondences, which are not always attainable in the registration of imagery with 3D point clouds, are avoided. Current methods for registering 2D imagery to 3D point clouds are first reviewed, after which the mutual MI approach is presented. Particular attention is given to adoption of the Normalised Combined Mutual Information (NCMI) approach as a means to produce a similarity measure that exploits the inherently registered LiDAR intensity and point cloud data so as to improve the robustness of registration between optical imagery and LiDAR data. The effectiveness of local versus global similarity measures is also investigated, as are the transformation models involved in the registration process. An experimental program conducted to evaluate MI-based methods for registering aerial imagery to LiDAR data is reported and the results obtained in two areas with differing terrain and land cover, and with aerial imagery of different resolution and LiDAR data with different point density are discussed. These results demonstrate the potential of the MI and especially the CMI methods for registration of imagery and 3D point clouds, and they highlight the feasibility and robustness of the presented MI-based approach to automated registration of multi-sensor, multi-temporal and multi-resolution remote sensing data for a wide range of applications. 相似文献
154.
利用LiDAR数据进行电力设施提取与建模可以克服传统工程测量电力巡线工作量大,危险性高,效率低下等缺点,但现有的电力线提取研究主要集中在电力线的分离与提取,并且拟合的精度不高。针对此问题本文提出了一种精度较高的电力线拟合方法。首先,根据电力线两端悬挂、中间自然下垂的特点,求解电力线拟合的最佳几何模型;然后,通过电力线的走向和端点,建立电力线拟合的最佳平面坐标系;最后,采用基于二次多项式限制的最小二乘法拟合电力线,解算出最优参数,生成最终电力线模型。对真实数据的处理和精度评价表明,本文方法不仅能够实现电力线的快速3维重建,而且能够达到较高的拟合精度。 相似文献
155.
为了能更好地理解激光雷达技术工作原理与三维信息采集全过程,规避现有激光雷达技术,尤其是机载激光雷达,在实践教学中受场地限制的不利条件,本文依托于中国矿业大学(北京)沙河校区的航空模拟平台,自主研发了一套基于单线激光雷达与行程测距仪集成的三维激光扫描装备,阐述了该装备集成的数学原理,设计了三维数据采集实践教学方法,并进行了三维数据采集的实践体验与数据质量评价。结果表明,该装备采集三维点云的精度优于99%,可为激光雷达技术的实践教学、创新训练及本科毕业设计等环节提供有效的硬件支撑,并可在仓储方量核算等工程应用方面进行推广。 相似文献
156.
157.
158.
海洋电磁中浅海作业由于受到空气波的干扰而难于进行,而如果于空中接收电偶极子的磁场响应则可避免空气波的干扰,是一种新的海洋电磁勘探思路。用一维频率域程序,对水中电偶极子在空中的磁场响应进行了计算分析,比较了海底有高阻异常层和低阻异常层时空中磁场响应的变化规律。分别计算测线布置、发射信号频、海水深度、异常储层埋深、异常储层厚度、储层电阻率、空中测量高度等多种因素对空中磁场响应的影响,结果表明,海底有低阻层时空中磁场有更强的响应,归一化幅度异常变化约为10%~60%,而海底有高阻异常储层时响应较弱,归一化异幅度常变化约为2%~8%。因此海洋电磁勘探中于空中接收磁场的模式,更适合浅海区低阻矿产资源的大面积调查。 相似文献
159.
目前框幅式航空摄影飞行质量检查依旧采用先冲印纸质像片,然后人工作业的方法。该方法耗时较长,限制了数字航空摄影快速高效优势的发挥。为此,研究出一套全数字航空摄影飞行质量的检查方法。该方法的整个实现过程完全在计算机上进行:首先,利用数字航空摄影生成的浏览影像完成影像质量检查;然后,应用飞行质量检查软件和机载POS(position and orientation system)数据检查影像的重叠度、像片旋偏角、航线弯曲度以及航高保持等质量因子;最后,根据检查结果整理和编写各类文档。为验证该方法的科学性和可靠性,以湖南省衡阳市实验区影像的人工质量检查结果与其进行对比分析,结果表明,二者具有很好的一致性,说明该方法能较好地反映航空摄影飞行成果质量,并且操作简单、效率高、成本低。 相似文献
160.
分形维数法是分析空间结构分布的一种典型方法,但它对于区分不同的分布形式还存在缺陷。针对这一问题,该文介绍了空隙度指数的定义和树冠空隙度的计算方法;以模拟的树冠点云数据为对象,提出了一种基于三维凸包和三维滑动盒算法的激光雷达(Li DAR)点云数据空隙度分析方法,详尽分析了不同冠型产生的空隙度指数差异;并利用4棵实测的树冠点云数据做检验;最后阐述了空隙度指数在树冠空间异质性分析研究中的作用,并对其应用范围和前景作了展望。结果表明:划分尺度相同时,在一定的尺度范围内,锥型树冠、半球型和半椭球型树冠的差别可以通过空隙度指数曲线有效地区分,实测树冠的结果也体现了空隙度指数对于判断树冠空间结构的有效性。 相似文献