全文获取类型
收费全文 | 190篇 |
免费 | 10篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 31篇 |
地球物理 | 44篇 |
地质学 | 62篇 |
海洋学 | 17篇 |
天文学 | 7篇 |
综合类 | 2篇 |
自然地理 | 32篇 |
出版年
2022年 | 1篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 2篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 7篇 |
2014年 | 9篇 |
2013年 | 14篇 |
2012年 | 12篇 |
2011年 | 10篇 |
2010年 | 13篇 |
2009年 | 7篇 |
2008年 | 11篇 |
2007年 | 3篇 |
2006年 | 3篇 |
2005年 | 7篇 |
2004年 | 5篇 |
2003年 | 8篇 |
2002年 | 12篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1973年 | 3篇 |
1965年 | 1篇 |
1959年 | 1篇 |
1948年 | 2篇 |
排序方式: 共有202条查询结果,搜索用时 15 毫秒
71.
ABSTRACTThe purpose of the article is to explore the role of participation in organized leisure activities in young teenagers’ emotional place relations. Data from a survey of students in lower secondary schools were analysed using multivariate linear regression models to address the research questions concerning whether participation in organized leisure activities was associated with more positive community assessments in youths in line with early Nordic welfare theory and the role played by socio-economic hardships and gender in the association. The results showed that for boys there were no indications of a general positive association between participation in organized leisure activities and community assessments, while for girls the association was modest. Students who experienced socio-economic hardships had more negative assessments of community compared with well-off students, even when they participated in organized leisure activities. The author discusses the results according to a welfare theory approach to emotional place relations, supplemented by other theoretical perspectives. From a theoretical perspective, the findings point to social exclusion and inclusion dynamics instead of early Nordic welfare theory approaches to leisure participation. The author concludes that gender, class and school relations are strongly associated with young teenagers’ emotional place relations. 相似文献
72.
73.
SONG Yanling Elisabeth SIMELTON CHEN Deliang DONG Wenjie 《Acta Meteorologica Sinica》2005,19(4):501-510
1. IntroductionChinese agriculture has undergone tremendousstructural changes over the last decades. The averagestaple crop productivity has doubled in 25 yr while thepopulation increased by 25 % [China Statistical Year-book (CSY), 2003]. Winter wheat is one of China'smost important staple food crops, with a total farm-ing area of nearly 24 million hectares and a produc-tion exceeding 92 million ton in 2002 (CSY, 2003).Although China has been the world's largest wheatproducer since 1983 (… 相似文献
74.
Temporal and spatial information on land use/cover is a prerequisite for effective planning decisions in the context of social and economic development. Satellite remote sensing data have become increasingly important in the study of land use/cover changes. This paper uses multitemporal satellite data to measure and spatially characterize land use/cover changes in the Jaffna Peninsula, northern Sri Lanka over the two decades from 1984 to early 2004 in terms of potential drivers. Over this period, the Jaffna Peninsula has been impacted severely by armed conflict between the government of Sri Lanka and the Liberation Tigers of Tamil Eelam. A postclassification method is used to compare land use/cover classes from satellite images using Geographical Information Systems (GIS) to analyze the spatial pattern of land use/cover changes over the study period. Results indicate that the land use/cover pattern has been very dynamic since early the 1980s, showing a remarkable decrease in agricultural land use and concomitant increase in non-agricultural land uses. The ethnic conflict and its consequences, particularly large-scale population migrations, have been the main driving forces for such land use/cover changes in the Jaffna Peninsula. The results of this study are not only important in aiding efforts to reconstruct this area after decades of physical and socioeconomic devastation, but should also prompt similarly urgent studies in other inaccessible war-torn areas of the world. 相似文献
75.
Elisabeth A. Parfitt Tracy K. P. Gregg Deborah K. Smith 《Journal of Volcanology and Geothermal Research》2002,113(1-2)
Eruption styles on the subaerial East Rift Zone (ERZ) of Kilauea volcano are reviewed and a classification scheme for the different types of eruption is proposed. The various eruption types are produced by differing thermal and driving pressure behaviour in the feeder dikes. Existing evidence is reviewed and new evidence presented of the types and volumes of eruptions on the Puna Ridge, which is the submarine extension of the ERZ. Eruptions on the Puna Ridge fall into the same five classes as, and are of comparable volume to, those on the subaerial ERZ. Evidence is presented which suggests that feeder dikes for Puna Ridge eruptions are more thermally viable than those feeding subaerial eruptions, and this difference causes long-lived, large-volume eruptions to be more common on the Puna Ridge than on the subaerial ERZ. This systematic variation in thermal viability may be due to increased dike width for Puna Ridge dikes or increased pressure gradients driving magma flow. Lateral dike emplacement is common to many basaltic systems including on other Hawaiian volcanoes, in Iceland and at mid-ocean ridges. The systematic trend inferred for the ERZ of Kilauea implies that in the other systems large-volume eruptions may also be more common at great distances than they are close to the magma centre. 相似文献
76.
Benoît Viguier Hervé Jourde Véronique Leonardi Elisabeth Lictevout Linda Daniele 《水文科学杂志》2020,65(9):1606-1613
ABSTRACT Using a statistical approach, Scheihing attempts to demonstrate the direct influence of recharge events in the Precordillera and the Andean Piedmont on water table variations in downstream alluvial fans. The author “unquestionably” discards the existence of ephemeral recharge processes in alluvial fans although they are frequently impacted by major floods. However, the author does not consider previous publications about recharge processes in arid alluvial fans, the hydraulic setting of the Pampa del Tamarugal Aquifer (PTA) and anthropogenic pressure changes in the PTA. Because the sustainable management of groundwater resources in drylands depends on a good understanding of hydrogeological processes, we propose a thorough reinterpretation of the short- and long-term PTA water table variations addressed by the author. In this comment, we illustrate the limits of the sole use of a statistical approach for characterizing both recharge processes and factors controlling the water table variations in the Atacama Desert. 相似文献
77.
This work analyses the potential consequences of two tsunami scenarios and their impacts on an oil refinery located in Sicily. Two credible tsunamis originating in the Tyrrhenian Sea were selected based on historical data. The potential for damage and hazardous materials releases resulting from the tsunami impacts to a refinery was assessed. The results obtained by the JRC tsunami propagation and inundation code HyFlux2 indicate that in both scenarios there would be eighteen storage tanks (of 43 located within 400 m from the shoreline) at the refinery subject to flooding. Water flow velocities were found to be generally low, <1 m/s, except for a central section of the refinery near the shoreline where the water flow velocities reach 3?C4 m/s. These results indicate that any damage would most likely occur due to buoyancy loads particularly in the western part of the facility where inundation levels are higher and storage tanks are less protected. Potential damage caused by impact of floating debris may be a problem in the central area of the refinery near the shoreline due to high flow velocities (3?C4 m/s) in both tsunami scenarios. Small hazardous materials releases could occur due to breakage of connected pipes and flanges caused by floating off of almost empty storage tanks or other equipment. Salt water intrusion could affect electrical equipment, such as control panels, pumps, and motors that are not raised above the inundation level. We conclude that in the two tsunami scenarios analysed, the risk to nearby residents and neighbouring facilities from potential hazardous materials releases, fires or explosions triggered by the tsunamis is likely to be small. Nonetheless, recommendations are made on prevention measures to reduce the risk of tsunami-triggered accidents and to mitigate their consequences if they do occur. The results of this study are limited by the uncertainty in the input data and most importantly by the accuracy of the elevation data and the model resolution. 相似文献
78.
Elisabeth Schoepfer Kristin Spröhnle Olaf Kranz Xavier Blaes Jan Kolomaznik Filip Hilgert 《国际地球制图》2017,32(10):1139-1158
The exploitation of resources, if not properly managed, can lead to spoiling natural habitats as well as to threatening people’s health, livelihoods and security. The paper discusses a multi-scale Earth observation-based approach to provide independent information related to exploitation activities of natural resources for countries which are experiencing armed conflict. The analyses are based on medium to very high spatial resolution optical satellite data. Object-based image analysis is used for information extraction at these different scales. On a subnational level, conflict-related land cover changes as an indication of potential hot spots for exploitation activities are classified. The regional assessment provides information about potential activity areas of resource exploitation, whereas on a local scale, a site-specific assessment of exploitation areas is performed. The study demonstrates the potential of remote sensing for supporting the monitoring and documentation of natural resource exploitation in conflict regions. 相似文献
79.
MERIS and the red-edge position 总被引:1,自引:0,他引:1
Jan G. P. W. Clevers Steven M de Jong Gerrit F Epema Freek van der Meer Wim H Bakker Andrew K Skidmore Elisabeth A Addink 《International Journal of Applied Earth Observation and Geoinformation》2001,3(4):313
The Medium Resolution Imaging Spectrometer (MERIS) is a payload component of Envisat-1. MERIS will be operated over land with a standard 15 band setting acquiring images with a 300 m spatial resolution. The red-edge position (REP) is a promising variable for deriving foliar chlorophyll concentration, which plays an important role in ecosystem processes. The objectives of this paper are: (1) to study which factors effect the REP of vegetation, (2) to study whether this REP can be derived from the MERIS standard band setting and (3) to show what REP represents at the scale of MERIS data. Two different data sets were explored for simulating the REP using MERIS bands: (1) simulated data using reflectance models and (2) airborne reflectance spectra of an agricultural area obtained by the airborne visible-infrared imaging spectrometer (AVIRIS). A “linear method”, assuming a straight slope of the reflectance spectrum around the midpoint of the slope, was a robust method for determining the REP and the MERIS bands at 665, 708.75, 753.75 and 778.75 nm could be used for applying the “linear method” for REP estimation. Results of the translation to the scale of MERIS data were very promising for applying MERIS at, for instance, the ecosystem level. 相似文献
80.
New data support our previously published propagule dispersal hypothesis and show that propagules of some benthic foraminiferal species can survive for two years before growth commences. Following exposure to simulated shallow-water conditions, shallow-water species of benthic foraminifera appeared and grew in large numbers (commonly >100 ind/12 ml sediment) in the <32 µm-size sediment fraction collected from 320 m water depth in the Skagerrak basin (North Sea). None of the shallow-water species that grew abundantly (Planorbulina mediterranensis, Morulaeplecta bulbosa, Bolivina pseudoplicata, Cuneata arctica, Eggerelloides scaber, Gavelinopsis praegeri) seem to grow or reproduce at or in the vicinity of the sampling site. Consequently, they must have been transported there as <32 µm-sized individuals. Their sudden appearance when exposed to shallow-water conditions suggests that they had been transported to the sampling site as propagules and that they could survive in the sediments until conditions became suitable for growth and, for some, reproduction. The lack of agglutination on the proloculi of the agglutinated taxa that appeared in the growth-chambers may enhance their passive transport via currents and, thereby, dispersal. Of all the indigenous foraminiferal species that occur at the sampling site, only Textularia earlandi and Bolivinellina pseudopunctata continued to grow and reproduce when transferred from bathyal (320 m) to simulated shallow-water (0 m) conditions. The former is considered a highly opportunistic species. According to the literature, most of the morphospecies which grew in the experiments are cosmopolitan. Our results indicate substantial inter-specific differences in dispersal potential and support previous suggestions that among free-living species, some serial forms have the potential for long-distance dispersal. Still, oceanographic, physical and ecological boundaries and barriers constrain the distribution of most species. In addition to benthic foraminifera, Gromia spp. (rhizarian protists related to the foraminifera) grew in >60% of the experimental growth-chambers. 相似文献