全文获取类型
收费全文 | 1076篇 |
免费 | 88篇 |
国内免费 | 167篇 |
专业分类
测绘学 | 355篇 |
大气科学 | 153篇 |
地球物理 | 144篇 |
地质学 | 201篇 |
海洋学 | 88篇 |
天文学 | 15篇 |
综合类 | 134篇 |
自然地理 | 241篇 |
出版年
2024年 | 27篇 |
2023年 | 63篇 |
2022年 | 165篇 |
2021年 | 185篇 |
2020年 | 157篇 |
2019年 | 122篇 |
2018年 | 65篇 |
2017年 | 67篇 |
2016年 | 35篇 |
2015年 | 35篇 |
2014年 | 30篇 |
2013年 | 59篇 |
2012年 | 79篇 |
2011年 | 31篇 |
2010年 | 24篇 |
2009年 | 24篇 |
2008年 | 27篇 |
2007年 | 22篇 |
2006年 | 21篇 |
2005年 | 14篇 |
2004年 | 12篇 |
2003年 | 9篇 |
2002年 | 5篇 |
2001年 | 11篇 |
2000年 | 8篇 |
1999年 | 11篇 |
1998年 | 2篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有1331条查询结果,搜索用时 489 毫秒
871.
Interest in the role that cities can play in climate change as sites of transformation has increased but research has been limited in its practical applications and there has been limited consideration of how policies and technologies play out. These challenges necessitate a re-thinking of existing notions of urban governance in order to account for the practices that emerge from governments and a plethora of other actors in the context of uncertainty. We understand these practices to constitute adaptive governance, underpinned by social learning guiding the actions of the multiplicity of actors. The aim here is to unpack how social learning for adaptive governance requires attention to competing understandings of risk and identity, and the multiplicity of mechanisms in which change occurs or is blocked in urban climate governance. We adopt a novel lens of ‘environmentalities’ which allows us to assess the historical and institutional context and power relations in the informal settlements of Maputo, Mozambique. Our findings highlight how environmental identities around urban adaptation to climate change are constituted in the social and physical divisions between the formal and informal settlements, whilst existing knowledge models prioritise dominant economic and political interests and lead to the construction of new environmental subjects. While the findings of this study are contextually distinct, the generalizable lessons are that governance of urban adaptation occurs and is solidified within a complex multiplicity of socio-ecological relations. 相似文献
872.
《International Journal of Digital Earth》2013,6(9):1083-1097
ABSTRACTUnderstanding and detecting the intended meaning in social media is challenging because social media messages contain varieties of noise and chaos that are irrelevant to the themes of interests. For example, conventional supervised classification approaches would produce inconsistent solutions to detecting and clarifying whether any given Twitter message is really about a wildfire event. Consequently, a renovated workflow was designed and implemented. The workflow consists of four sequential procedures: (1) Apply the latent semantic analysis and cosine similarity calculation to examine the similarity between Twitter messages; (2) Apply Affinity Propagation to identify exemplars of Twitter messages; (3) Apply the cosine similarity calculation again to automatically match the exemplars to known training results, and (4) Apply accumulative exemplars to classify Twitter messages using a support vector machine approach. The overall correction ratio was over 90% when a series of ongoing and historical wildfire events were examined. 相似文献
873.
Spectral sparse Bayesian learning reflectivity inversion 总被引:4,自引:0,他引:4
A spectral sparse Bayesian learning reflectivity inversion method, combining spectral reflectivity inversion with sparse Bayesian learning, is presented in this paper. The method retrieves a sparse reflectivity series by sequentially adding, deleting or re‐estimating hyper‐parameters, without pre‐setting the number of non‐zero reflectivity spikes. The spikes with the largest amplitude are usually the first to be resolved. The method is tested on a series of data sets, including synthetic data, physical modelling data and field data sets. The results show that the method can identify thin beds below tuning thickness and highlight stratigraphic boundaries. Moreover, the reflectivity series, which is inverted trace‐by‐trace, preserves the lateral continuity of layers. 相似文献
874.
基于多核学习的高分辨率遥感图像目标检测方法 总被引:1,自引:0,他引:1
为更有效地实现复杂场景中的多类目标同时检测,本文提出了一种基于多核学习算法进行目标检测的框架。该方法由特征提取和模型训练2个阶段组成。特征提取阶段,引入了多尺度下的点特征、表观特征同时对多类目标进行综合描述;模型训练阶段,分别采用加权相加和相乘2种方法将提取的各个基础特征组合起来,在支持向量机的框架下对各特征所代表的基础核权重进行学习。将训练所得的分类器结合滑动窗搜索技术对遥感图像进行目标检测实验,结果表明,与传统单核支持向量机相比,准确率更高。 相似文献
875.
Q. Guo W. Li Y. Liu D. Tong 《International journal of geographical information science》2013,27(10):1697-1715
One common problem with geographic data is that, for a specific geographic event, only occurrence information is available; information about the absence of the event is not available. We refer to these specific types of geospatial data as geographic one-class data (GOCD). Predicting the potential spatial distributions that a particular geographic event may occur from GOCD is difficult because traditional binary classification methods that require availability of both positive and negative training samples cannot be used. The objective of this research is to define GOCD and propose novel approaches for modelling potential spatial distributions of geographic events using GOCD. We investigate the effectiveness of one-class support vector machine (OCSVM), maximum entropy (MAXENT) and the newly proposed positive and unlabelled learning (PUL) algorithm for solving GOCD problems using a case study: species distribution modelling from synthetic data. Our experimental results indicate that generally OCSVM, MAXENT and PUL are effective in modelling the GOCD. Each method has advantages and disadvantages, but PUL seems to be the most promising method. 相似文献
876.
Julian Hagenauer Marco Helbich 《International journal of geographical information science》2013,27(6):963-982
In the context of OpenStreetMap (OSM), spatial data quality, in particular completeness, is an essential aspect of its fitness for use in specific applications, such as planning tasks. To mitigate the effect of completeness errors in OSM, this study proposes a methodological framework for predicting by means of OSM urban areas in Europe that are currently not mapped or only partially mapped. For this purpose, a machine learning approach consisting of artificial neural networks and genetic algorithms is applied. Under the premise of existing OSM data, the model estimates missing urban areas with an overall squared correlation coefficient (R 2) of 0.589. Interregional comparisons of European regions confirm spatial heterogeneity in the model performance, whereas the R 2 ranges from 0.129 up to 0.789. These results show that the delineation of urban areas by means of the presented methodology depends strongly on location. 相似文献
877.
Anne Godlewska 《The Professional geographer》2013,65(3):384-389
This article describes an experiment in learning with a course on “research and philosophies of place and space” in which students were repeatedly dislocated from an environment familiar to them and replaced in key locations about the city with local place experts as their guide. The article begins with a review of the meaning of place and the opportunities offered by the City of Kingston for reflective engagement. It briefly hints at some of the social trends devaluing place learning and the consequently political nature of this pedagogy. Finally, it summarizes the lessons learned in five of the ten classes. 相似文献
878.
Dragos Simandan 《The Professional geographer》2013,65(3):390-395
Wisdom is at once one of the most elusive and most valued kinds of knowledge. Empirical research shows that, indeed, across cultures, people hope that life experience will eventually make them wiser. The problem is that, to date, the academic study of wisdom and of the processes by which it can be learned has been dominated by psychologists. The first part of the article reviews the state-of-the-art psychological scholarship on wisdom to show how that conceptualization lacks geographical sensitivity and therefore misses some of the crucial geographical mechanisms by which people become wiser. The second part of the article singles out and focuses on one such mechanism, namely, the learning of wisdom through geographical dislocations. By drawing on insights from the study of international migration, exile, and transculturation in postcolonial contexts, the final part of the article suggests specific learning processes that might strengthen the hypothesis that geographical dislocations and the attendant cross-cultural experiences they generate are often conducive to wisdom. 相似文献
879.
《The Professional geographer》2013,65(1):108-109
Electromap World Atlas, Version 1.1. Interactive Population Statistical System, Version 1.0. Jerry W. Wicks and Jose Luiz Pereira de Almeida MATHCAD, Version 2.5. Memory Mate. Micro DEM+, Version 5.21. Peter Guth NCSS – Number Cruncher Statistical System, Version 5.02. Dr. Jerry L. Hintze 相似文献
880.