全文获取类型
收费全文 | 20486篇 |
免费 | 4125篇 |
国内免费 | 2649篇 |
专业分类
测绘学 | 945篇 |
大气科学 | 1781篇 |
地球物理 | 13275篇 |
地质学 | 5676篇 |
海洋学 | 968篇 |
天文学 | 1587篇 |
综合类 | 1439篇 |
自然地理 | 1589篇 |
出版年
2024年 | 110篇 |
2023年 | 316篇 |
2022年 | 542篇 |
2021年 | 770篇 |
2020年 | 706篇 |
2019年 | 803篇 |
2018年 | 691篇 |
2017年 | 709篇 |
2016年 | 674篇 |
2015年 | 825篇 |
2014年 | 1013篇 |
2013年 | 1093篇 |
2012年 | 1046篇 |
2011年 | 1079篇 |
2010年 | 996篇 |
2009年 | 1395篇 |
2008年 | 1183篇 |
2007年 | 1327篇 |
2006年 | 1287篇 |
2005年 | 1204篇 |
2004年 | 1061篇 |
2003年 | 1014篇 |
2002年 | 880篇 |
2001年 | 820篇 |
2000年 | 741篇 |
1999年 | 726篇 |
1998年 | 697篇 |
1997年 | 568篇 |
1996年 | 573篇 |
1995年 | 536篇 |
1994年 | 464篇 |
1993年 | 369篇 |
1992年 | 296篇 |
1991年 | 183篇 |
1990年 | 151篇 |
1989年 | 116篇 |
1988年 | 104篇 |
1987年 | 53篇 |
1986年 | 34篇 |
1985年 | 19篇 |
1984年 | 22篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1979年 | 25篇 |
1978年 | 3篇 |
1977年 | 10篇 |
1976年 | 3篇 |
1972年 | 1篇 |
1954年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
基于矩阵论的空间相似变换分析 总被引:1,自引:0,他引:1
根据空间相似变换的线性化公式,利用矩阵论分析误差方程的系数矩阵,给出求解空间相似变换参数所需控制点的具体要求。 相似文献
42.
Downscaling has an important role to play in remote sensing. It allows prediction at a finer spatial resolution than that of the input imagery, based on either (i) assumptions or prior knowledge about the character of the target spatial variation coupled with spatial optimisation, (ii) spatial prediction through interpolation or (iii) direct information on the relation between spatial resolutions in the form of a regression model. Two classes of goal can be distinguished based on whether continua are predicted (through downscaling or area-to-point prediction) or categories are predicted (super-resolution mapping), in both cases from continuous input data. This paper reviews a range of techniques for both goals, focusing on area-to-point kriging and downscaling cokriging in the former case and spatial optimisation techniques and multiple point geostatistics in the latter case. Several issues are discussed including the information content of training data, including training images, the need for model-based uncertainty information to accompany downscaling predictions, and the fundamental limits on the representativeness of downscaling predictions. The paper ends with a look towards the grand challenge of downscaling in the context of time-series image stacks. The challenge here is to use all the available information to produce a downscaled series of images that is coherent between images and, thus, which helps to distinguish real changes (signal) from noise. 相似文献
43.
44.
High-resolution satellite gravity data have been generated and utilized to infer subsurface geological structures in the area of devastating earthquake that struck the Bhuj region in Gujarat on 26 January 2001. Latitudinal gravity profiles have been generated in the Bhuj, Anjar and IBF regions across the epicentres (23.5° N, 69.8° E/Mw 7.0 in 2001; 23.2° N, 70° E/Mw 7.0 in 1956; 24.2° N, 69.2° E/Mw 7.8 in 1819). Substantial differences in gravity anomaly patterns as high as 37 mGal could be observed existing near the epicentre regions. These gravitational differences might have caused due to the plate tectonic processes and due to the changes in densities of different lithospheric zones/sedimentary layers. Temporal variations of the satellite-derived gravity and their probable relations with already occurred major earthquakes in this region have been studied. Hence we conclude that drastic changes in gravity anomalies can be considered as a precursor for occurrences of substantially large earthquakes. 相似文献
45.
In the present study, prediction of agricultural drought has been addressed through prediction of agricultural yield using a model based on NDVI-SPI. It has been observed that the meteorological drought index SPI with different timescale is correlated with NDVI at different lag. Also NDVI of current fortnight is correlated with NDVI of previous lags. Based on the correlation coefficients, the Multiple Regression Model was developed to predict NDVI. The NDVI of current fortnight was found highly correlated with SPI of previous fortnight in semi-arid and transitional zones. The correlation between NDVI and crop yield was observed highest in first fortnight of August. The RMSE of predicted yield in drought year was found to be about 17.07 kg/ha which was about 6.02 per cent of average yield. In normal year, it was 24 kg/Ha denoting about 2.1 per cent of average yield. 相似文献
46.
Mousa Abedini Bahareh Ghasemian Ataollah Shirzadi Himan Shahabi Kamran Chapi Binh Thai Pham 《国际地球制图》2013,28(13):1427-1457
AbstractA novel artificial intelligence approach of Bayesian Logistic Regression (BLR) and its ensembles [Random Subspace (RS), Adaboost (AB), Multiboost (MB) and Bagging] was introduced for landslide susceptibility mapping in a part of Kamyaran city in Kurdistan Province, Iran. A spatial database was generated which includes a total of 60 landslide locations and a set of conditioning factors tested by the Information Gain Ratio technique. Performance of these models was evaluated using the area under the ROC curve (AUROC) and statistical index-based methods. Results showed that the hybrid ensemble models could significantly improve the performance of the base classifier of BLR (AUROC?=?0.930). However, RS model (AUROC?=?0.975) had the highest performance in comparison to other landslide ensemble models, followed by Bagging (AUROC?=?0.972), MB (AUROC?=?0.970) and AB (AUROC?=?0.957) models, respectively. 相似文献
47.
土地利用/覆盖变化是目前研究全球及区域环境的一个重要领域,在城镇化加速的今天,城镇的土地利用格局也发生了飞速的变化。本文通过其一研究区内的Landsat TM遥感影像进行处理,获取了2007~2016年10个时相土地利用/覆盖信息,通过不同的预测模型对监测到的数据进行处理及比较,根据相应的最优预测方法预测了2017~2019年南昌市各土地类型的数据,由此研究并探讨了南昌市土地利用/覆盖的时空格局变化。 相似文献
48.
苏里格气田为一致密沙岩气田,油气富集区的预测优选为气藏开发奠定基础。常规的油气富集区预测方法存在着多学科成果综合分析困难、预测过程复杂、效率低下等弊端,本文针对苏里格120区块开展了基于GIS的油气富集区多因素综合预测方法的研究。首先借助GIS的空间数据库,实现多学科成果图件的集成管理;然后基于空间定位,从多学科成果图件中提取预测多因子,构建油气多因素综合预测模型;再次,运用GIS强大的叠加分析方法进行多因素综合预测,自动生成油气富集区预测平面图。本文的研究,为油气富集区的预测提供了新的技术方法,有效地提高了预测效率。 相似文献
49.
近年来,旨在与注册测绘师制度相衔接的测绘地理信息类专业认证开启了我国高校测绘教育改革的新思路。测绘类专业认证的核心是使毕业生的能力达成度目标必须符合专业认证标准的各项要求。课程作为整个教学体系的基本单元,对毕业生各项能力的达成起着基本的支撑作用。误差理论与测量平差基础课程作为测绘工程本科专业的主干课程之一,是培养学生有关工程测绘数据处理基本能力的根本保证。本文结合贵州大学办学实际,讨论了测绘专业认证背景下误差理论与测量平差基础课程的建设问题。 相似文献
50.