全文获取类型
收费全文 | 675篇 |
免费 | 38篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 41篇 |
大气科学 | 108篇 |
地球物理 | 168篇 |
地质学 | 251篇 |
海洋学 | 44篇 |
天文学 | 60篇 |
综合类 | 1篇 |
自然地理 | 50篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 22篇 |
2020年 | 38篇 |
2019年 | 19篇 |
2018年 | 26篇 |
2017年 | 26篇 |
2016年 | 43篇 |
2015年 | 32篇 |
2014年 | 37篇 |
2013年 | 37篇 |
2012年 | 40篇 |
2011年 | 58篇 |
2010年 | 48篇 |
2009年 | 49篇 |
2008年 | 45篇 |
2007年 | 28篇 |
2006年 | 23篇 |
2005年 | 13篇 |
2004年 | 18篇 |
2003年 | 19篇 |
2002年 | 7篇 |
2001年 | 10篇 |
2000年 | 8篇 |
1999年 | 3篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 9篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有723条查询结果,搜索用时 218 毫秒
721.
The patterns of dissolved inorganic C (DIC) and aqueous CO2 in rivers and estuaries sampled during summer and winter in the Australian Victorian Alps were examined. Together with historical (1978–1990) geochemical data, this study provides, for the first time, a multi-annual coverage of the linkage between CO2 release via wetland evasion and CO2 consumption via combined carbonate and aluminosilicate weathering. δ13C values imply that carbonate weathering contributes ∼36% of the DIC in the rivers although carbonates comprise less than 5% of the study area. Baseflow/interflow flushing of respired C3 plant detritus accounts for ∼50% and atmospheric precipitation accounts for ∼14% of the DIC. The influence of in river respiration and photosynthesis on the DIC concentrations is negligible. River waters are supersaturated with CO2 and evade ∼27.7 × 106 mol/km2/a to ∼70.9 × 106 mol/km2/a CO2 to the atmosphere with the highest values in the low runoff rivers. This is slightly higher than the global average reflecting higher gas transfer velocities due to high wind speeds. Evaded CO2 is not balanced by CO2 consumption via combined carbonate and aluminosilicate weathering which implies that chemical weathering does not significantly neutralize respiration derived H2CO3. The results of this study have implications for global assessments of chemical weathering yields in river systems draining passive margin terrains as high respiration derived DIC concentrations are not directly connected to high carbonate and aluminosilicate weathering rates. 相似文献
722.
The October 2005 earthquake triggered several thousand landslides in the Lesser Himalaya of Kashmir in northern Pakistan and
India. Analyses of ASTER satellite imagery from 2001 were compared with a study undertaken in 2005; the results show the extent
and nature of pre- and co-/post-seismic landsliding. Within a designated study area of ~2,250 km2, the number of landslides increased from 369 in 2001 to 2,252 in October 2005. Assuming a balanced baseline landsliding frequency
over the 4 years, most of the new landslides were likely triggered by the 2005 earthquake and its aftershocks. These landslides
mainly happened in specific geologic formations, along faults, rivers and roads, and in shrubland/grassland and agricultural
land. Preliminary results from repeat photographs from 2005 and 2006 after the snowmelt season reveal that much of the ongoing
landsliding occurred along rivers and roads, and the extensive earthquake-induced fissuring. Although the susceptibility zoning
success rate for 2001 was low, many of the co-/post-seismic landsliding in 2005 occurred in areas that had been defined as
being potentially dangerous on the 2001 map. While most of the area in 2001 was (very) highly susceptible to future landsliding,
most of the area in 2005 was only moderate to low susceptible, that is, most of the landsliding in 2005 actually occurred
in the potentially dangerous areas on the 2001 map. This study supports the view that although susceptibility zoning maps
represent a powerful tool in natural hazard management, caution is needed when developing and using such maps. 相似文献
723.
Lynchets are ridges formed by erosion and sediment accumulation downstream of agricultural plots and offer valuable insights into past agricultural activity. These microtopographies cover vast areas and serve as indicators of historical changes in land use. As a result, their ubiquity across Europe makes them particularly interesting. In this study, we propose a geoarchaeological approach to analyze six lynchets, four in the Vosges Mountains and two on the Lorraine Plateau (France). The lynchets can be considered soil archives with no stratigraphic organization or chronological sequence from bottom to top, making it difficult to determine the age of the lynchets and identify changes in land use over time. To this end, we propose the analysis of historical and geo-historical archives combined with the “pedosedimentary” archives of lynchets through charcoal identification and dating combined with near-infrared spectroscopy to determine the age, vegetation, and past land use changes associated with lynchet landscapes. By combining these multiple data sources, we are better able to show the chronological development of these ancient agricultural systems and uncover valuable information on landscape history. Charcoal dating suggests a higher frequency of fires from the Middle Ages. The dating aligns with the regional dynamics of anthropogenic fires, indicating a potential use of fire for cultural purposes. We also demonstrate the difficulty of extrapolating the dating of a lynchet to the entire lynchet system. Our results highlight the difficulties of interpreting the formation and dating of lynchets and the lynchet system on the sole basis of charcoal analysis. However, we highlight the value of applying pedoanthracology to lynchets to determine the dynamics of land use change in former fields. 相似文献