全文获取类型
收费全文 | 642篇 |
免费 | 97篇 |
国内免费 | 83篇 |
专业分类
测绘学 | 46篇 |
大气科学 | 80篇 |
地球物理 | 151篇 |
地质学 | 289篇 |
海洋学 | 113篇 |
天文学 | 6篇 |
综合类 | 24篇 |
自然地理 | 113篇 |
出版年
2024年 | 4篇 |
2023年 | 22篇 |
2022年 | 18篇 |
2021年 | 15篇 |
2020年 | 32篇 |
2019年 | 29篇 |
2018年 | 24篇 |
2017年 | 31篇 |
2016年 | 29篇 |
2015年 | 36篇 |
2014年 | 46篇 |
2013年 | 49篇 |
2012年 | 37篇 |
2011年 | 38篇 |
2010年 | 33篇 |
2009年 | 42篇 |
2008年 | 39篇 |
2007年 | 35篇 |
2006年 | 34篇 |
2005年 | 47篇 |
2004年 | 21篇 |
2003年 | 21篇 |
2002年 | 22篇 |
2001年 | 13篇 |
2000年 | 12篇 |
1999年 | 14篇 |
1998年 | 9篇 |
1997年 | 12篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有822条查询结果,搜索用时 15 毫秒
131.
132.
133.
134.
Alena Gessert Janetta Nestorová–Dická Ivo Sninčák 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):173-183
Show caves are one of the most important targets in developing local ecotourism strategies. This work focuses on a tourism visit rate incidence through an Attractiveness Index concerning 12 selected show caves in Slovakia. Our study focuses on visitor counts published from 2000 to 2014. A set of eight criteria were selected in order to analyse and determine the appeal that each cave may have for visitors. Establishing the “degree” of appeal as an indicator of the tourism and geographic absolute attractiveness value is based on a principal components factor analysis; the resultant single factor was correlated with our selected criteria. We find a strong correlation between touristic cave attractiveness and cave locations, ease of cave passage access (vehicle and trail) infrastructures, cave location in main tourism regions, and the growth of urban areas as they encroach on show cave locations. Similar studies in valorization of show caves tourism have not been attempted in Slovakia or Eastern Europe. The data and result from this study are also clearly important from a managerial perspective. This general framework could be easily expanded to include additional attributes that might be relevant for other market segments or other vacation experiences. 相似文献
135.
In this article, we use local indicators of spatial association (LISA) and other spatial analysis techniques to analyze the distribution of centers with high employment density within metropolitan areas. We examine the 359 metropolitan areas across the United States at three points in time (1990, 2000, and 2010) to provide a spatio-temporal panoramic of urban spatial structure. Our analysis highlights three key findings. (1) The monocentric structure persists in a majority of metropolitan areas: 56.5% in 1990, 64.1% in 2000, and 57.7% in 2010. (2) The pattern of employment centers remains stable for most metropolitan areas: the number of centers remained the same for 74.9% of metropolitan areas between 1990 and 2000 and for 85.2% between 2000 and 2010. (3) Compared with monocentric metropolitan areas, polycentric metros are larger and more dense, with higher per-capita incomes and lower poverty rates. 相似文献
136.
Sarah Mubareka Christine Estreguil Claudia Baranzelli Carla Rocha Gomes Carlo Lavalle Barbara Hofer 《International journal of geographical information science》2013,27(9):1740-1763
This article details the process of integrating models to answer a specific policy-driven question: ‘What could be the impact of proposed Natural Water Retention Measures (NWRMs) on Europe’s Green Infrastructure (GI)?’ It describes the new Land Use Modelling Platform (LUMP), now enabling a high spatial scale (100-m) and large coverage (pan-European), whereby several sector-specific models contribute to assessing the impact of regional-level policy on a given spatial topic of concern. The configuration (land claims and land allocations modules) and calibration (accessibility and biophysical suitability) of the LUMP are explained. Four NWRM scenarios (riparian areas, afforestation, grassland and baseline scenario) are configured to run the simulations. For the reference: year 2006, the spatial representation of GI is based on land-use features of a refined version of the CORINE Land Cover (CLC), and resumed as connected components made of nodes and links.Mathematical morphological image processing and network graph theory model, available from the free software package GUIDOS (the Joint Research Center of the European Commission), enabled the measurement of the GI connectivity and identified most critical links. Results show that the competition for land claimed by different economic sectors, combined with policy-driven rule-sets for the implementation of different NWRMs, yields very different results for the 2030 land-use projections, and subsequently for the morphology of GI. Three indicators associated with the morphology of GI are computed in order to assess the model outputs for 2030. The indicators are computed to answer the following questions: (1) How is the quantity of GI affected by each of the NWRM, and what proportion of that GI is most valuable? (2) What is the location of the most critical nodes and connectors of GI, and what land-use conversions occur under these? (3) Are the average components getting larger or smaller?Whereas the grassland measure results in the largest net increase of GI, the afforestation measure results in the overall largest number of hectares of key nodes and links within the network. Land conversions occur under the critical GI nodes and links, with a large increase in agricultural areas, especially for the riparian measure under critical nodes and the grassland measure under critical links. Also predominant is the swapping of land from pasture to forest under critical links with the afforestation measure. The riparian measure most increases the average size of GI components, and all three measures contribute to bridging two large components which were divided in the 2006 land-use map, thus increasing the size of the largest component by more than 50%. 相似文献
137.
[摘 要]山后铅锌矿床位于福建省顺昌县高阳乡境内,目前已发现12 个铅锌矿体和3 个低品位矿体,矿体呈层状、似层状、透镜状产于F13、F14断裂之间的东岩组透辉(透闪) 石岩中,铅+锌品位7.21×10-2,求得铅+锌(332)+(333)金属量12.46 万吨,矿床达中型规模。通过对山后铅锌矿的地层、构造、岩体以及围岩蚀变等地质特征分析,认为铅锌矿体受东岩组绿片岩层位控制,并受热液叠加改造,属海底火山喷发-沉积变质(热液改造)块状硫化物型矿床;总结出中-晚元古代东岩组绿片岩层、地表矿体氧化后常见有黑色的褐铁矿斑点、围岩常伴有绿泥石化、绿帘石化、黄铁矿化、硅化等蚀变以及物化探异常等找矿标志,其对省内乃至华南地区寻找同类型矿床具重要意义。 相似文献
138.
B.K. Bhadra 《Gondwana Research》2000,3(3)
In the eastern part of southern Peninsular India, the charnockitic hills of the Madras block are cut across by the E-W trending Attur shear zone (ASZ) which is characterised by a thick (1 to 1.5 km) phyllonite zone, showing intense mylonitisation due to ductile shearing. Steeply plunging (70°–80°) stretching lineation on steeply dipping mylonitic foliation within this zone indicates a relative vertical upliftment of the adjacent blocks. A dextral shearing event from west to east is envisaged from the kinematic analysis of shear sense indicators such as S-C fabric, asymmetric folds, asymmetric augens and asymmetric porphyroclasts. Simultaneous development of these features, related to vertical and horizontal movements may be explained by the mechanism of transpressional deformation. The Attur shear zone may be correlated with the Moyar shear zone based on distinct lithological and structural similarities. 相似文献
139.
Quantifying the uncertainty associated with monitoring protocols is essential to prevent the misclassification of ecological status and to improve sampling design. We assessed the Posidonia oceanica multivariate index (POMI) bio-monitoring program for its robustness in classifying the ecological status of coastal waters within the Water Framework Directive. We used a 7-year data set covering 30 sites along 500 km of the Catalonian coastline to examine which version of POMI (14 or 9 metrics) maximises precision in classifying the ecological status of meadows. Five factors (zones within a site, sites within a water body, depth, years and surveyors) that potentially generate classification uncertainty were examined in detail. Of these, depth was a major source of uncertainty, while all the remaining spatial and temporal factors displayed low variability. POMI 9 matched POMI 14 in all factors, and could effectively replace it in future monitoring programs. 相似文献
140.