全文获取类型
收费全文 | 7907篇 |
免费 | 1567篇 |
国内免费 | 2349篇 |
专业分类
测绘学 | 911篇 |
大气科学 | 1321篇 |
地球物理 | 1977篇 |
地质学 | 4284篇 |
海洋学 | 1277篇 |
天文学 | 229篇 |
综合类 | 761篇 |
自然地理 | 1063篇 |
出版年
2024年 | 68篇 |
2023年 | 194篇 |
2022年 | 428篇 |
2021年 | 519篇 |
2020年 | 387篇 |
2019年 | 487篇 |
2018年 | 481篇 |
2017年 | 500篇 |
2016年 | 534篇 |
2015年 | 479篇 |
2014年 | 553篇 |
2013年 | 554篇 |
2012年 | 603篇 |
2011年 | 605篇 |
2010年 | 642篇 |
2009年 | 548篇 |
2008年 | 508篇 |
2007年 | 461篇 |
2006年 | 393篇 |
2005年 | 314篇 |
2004年 | 267篇 |
2003年 | 230篇 |
2002年 | 229篇 |
2001年 | 263篇 |
2000年 | 191篇 |
1999年 | 233篇 |
1998年 | 161篇 |
1997年 | 162篇 |
1996年 | 114篇 |
1995年 | 121篇 |
1994年 | 119篇 |
1993年 | 110篇 |
1992年 | 76篇 |
1991年 | 52篇 |
1990年 | 41篇 |
1989年 | 40篇 |
1988年 | 39篇 |
1987年 | 21篇 |
1986年 | 18篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 15篇 |
1979年 | 4篇 |
1976年 | 2篇 |
1964年 | 1篇 |
1958年 | 4篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
153.
154.
从网络文本中抽取地理实体间空间关系和语义关系要求高时效性和强鲁棒性。本文提出一种开放式地理实体关系的自动抽取方法,通过bootstrapping技术统计词语的词性、位置和距离特征来计算语境中词语权值,据此确定描述地理实体关系的关键词,最终组织成结构化实例,并使用百度百科和Stanford CoreNLP开展了试验。研究结果表明,本文方法能自动挖掘自然语言的部分词法特征,无须领域专家知识和大规模标注语料,适用于未知关系类型的信息抽取任务;较之经典的Frequency、TFIDF和PPMI频率统计方法,精度和召回率分别提升约5%和23%。 相似文献
155.
156.
Pattern recognition in road networks can be used for different applications, including spatiotemporal data mining, automated map generalization, data matching of different levels of detail, and other important research topics. Grid patterns are a common pattern type. This paper proposes and implements a method for grid pattern recognition based on the idea of mesh classification through a supervised learning process. To train the classifier, training datasets are selected from worldwide city samples with different cultural, historical, and geographical environments. Meshes are subsequently labeled as composing or noncomposing grids by participants in an experiment, and the mesh measures are defined while accounting for the mesh’s individual characteristics and spatial context. The classifier is generated using the C4.5 algorithm. The accuracy of the classifier is evaluated using Kappa statistics and the overall rate of correctness. The average Kappa value is approximately 0.74, which corresponds to a total accuracy of 87.5%. Additionally, the rationality of the classifier is evaluated in an interpretation step. Two other existing grid pattern recognition methods were also tested on the datasets, and comparison results indicate that our approach is effective in identifying grid patterns in road networks. 相似文献
157.
Light Detection and Ranging (LiDAR) waveforms are being increasingly used in many forest and urban applications, especially for ground feature classification. However, most studies relied on either discretizing waveforms to multiple returns or extracting shape metrics from waveforms. The direct use of the full waveform, which contains the most comprehensive and accurate information has been scarcely explored. We proposed to utilize the complete waveform to test its ability to differentiate between objects having distinct vertical structures using curve matching approaches. Two groups of curve matching approaches were developed by extending methods originally designed for pixel-based hyperspectral image classification and object-based high spatial image classification. The first group is based on measuring the curve similarity between an unknown waveform and a reference waveform, including curve root sum squared differential area (CRSSDA), curve angle mapper (CAM), and Kullback–Leibler (KL) divergence. The second group assesses the curve similarity between an unknown and reference cumulative distribution functions (CDFs) of their waveforms, including cumulative curve root sum squared differential area (CCRSSDA), cumulative curve angle mapper (CCAM), and Kolmogorov–Smirnov (KS) distance. When employed to classify open space, trees, and buildings using ICESat waveform data, KL provided the highest average classification accuracy (87%), closely followed by CCRSSDA and CCAM, and they all significantly outperformed KS, CRSSDA, and CAM based on 15 randomized sample sets. 相似文献
158.
159.
从海量影像数据中查找所需数据是正射影像制作中的一个重要步骤,本文利用天绘影像提供的XML文件自动提取坐标信息,根据图号自动计算图幅角点坐标,研究了自动识别点和面位置关系的算法,实现了根据图号自动搜索天绘影像数据,根据天绘影像数据自动搜索参考影像数据的功能. 相似文献
160.