全文获取类型
收费全文 | 587篇 |
免费 | 21篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 49篇 |
地球物理 | 121篇 |
地质学 | 217篇 |
海洋学 | 69篇 |
天文学 | 68篇 |
综合类 | 1篇 |
自然地理 | 76篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 12篇 |
2019年 | 7篇 |
2018年 | 19篇 |
2017年 | 19篇 |
2016年 | 26篇 |
2015年 | 16篇 |
2014年 | 21篇 |
2013年 | 46篇 |
2012年 | 24篇 |
2011年 | 43篇 |
2010年 | 33篇 |
2009年 | 30篇 |
2008年 | 36篇 |
2007年 | 30篇 |
2006年 | 17篇 |
2005年 | 16篇 |
2004年 | 26篇 |
2003年 | 26篇 |
2002年 | 21篇 |
2001年 | 12篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有612条查询结果,搜索用时 31 毫秒
391.
392.
'Earthlearningidea' will be putting up a new idea for learning about the Earth every week during 2008—the International Year of Planet Earth. The ideas are aimed at teacher trainers in science and geography who will be training teachers in the teaching of Earth science—but we hope they will be widely used by classroom teachers who have access to the internet too. A blog runs alongside them aiming to build up a worldwide discussion network of Earth science educators. Help us circulate Earthlearningideas around the globe! 相似文献
393.
Elizabeth P. TURTLE Elisabetta PIERAZZO David P. O'BRIEN 《Meteoritics & planetary science》2003,38(2):293-303
Abstract— Large meteorite impacts, such as the one that created the Vredefort structure in South Africa?2 Ga ago, result in significant heating of the target. The temperatures achieved in these events have important implications for post‐impact metamorphism as well as for the development of hydrothermal systems. To investigate the post‐impact thermal evolution and the size of the Vredefort structure, we have analyzed impact‐induced shock heating in numerical simulations of terrestrial impacts by projectiles of a range of sizes thought to be appropriate for creating the Vredefort structure. When compared with the extent of estimated thermal shock metamorphism observed at different locations around Vredefort, our model results support our earlier estimates that the original crater was 120–160 km in diameter, based on comparison of predicted to observed locations of shock features. The simulations demonstrate that only limited shock heating of the target occurs outside the final crater and that the cooling time was at least 0.3 Myr but no more than 30 Myr. 相似文献
394.
395.
Earlier views regarding the relative insignificance of Antarctic science have been rudely shattered by recent developments. The International Geophysical Year (IGY) of 1957–1958 represented a major turning point for research in Antarctica, even if it is a mistake to believe that no useful scientific work was performed during the pre-IGY period. The IGY provided a sound foundation for the development of Antarctic scientific activity in a wide range of disciplines, including glaciology, atmospheric sciences and medicine. The intrinsic value of research in Antarctica is reinforced by its relevance to an improved understanding of global environmental systems; stratospheric ozone depletion was first identified at Halley base station. Minerals, as yet unproven, have highlighted the conservation problems inherent in the utilization of any Antarctic resources. Marine living resources are at present under threat of over-exploitation in some areas. The 1990s hold the promise for a brighter scientific future for Antarctica, but only as long as the Antarctic Treaty system continues in operation. 相似文献
396.
397.
Yu Jingjing Li Xiao-Feng Lewis Elizabeth Blenkinsop Stephen Fowler Hayley J. 《Climate Dynamics》2020,54(5):2919-2940
Climate Dynamics - There is an urgent need for high-quality and high-spatial-resolution hourly precipitation products around the globe, including the UK. Although hourly precipitation products... 相似文献
398.
A four‐antenna GPS attitude determination system was used to estimate roll, pitch, and heading parameters of a 52‐meter surveying vessel in an operational marine environment. The least squares algorithm for platform attitude estimation using multiple baseline vector observables is presented. An efficient on‐the‐fly carrier phase ambiguity searching method is derived, which utilizes the Cholesky decomposition method and the known baseline constraints between the GPS antennas to construct the potential ambiguity sets on the sphere. The accuracy of the estimated attitude parameters from the GPS multi‐antenna system was assessed with an independent inertial navigation system (INS). Results from sea trials show that the proposed GPS multi‐antenna system and processing algorithms delivered a satisfactory performance under various ship maneuvers. The accuracy of GPS estimated ship attitude parameters is better than 0.06 degrees at an output rate of 10 Hz. Such a performance demonstrates a new alternative means to provide accurate, reliable, and cost‐effective ship attitude information for hydrographic applications. 相似文献
399.
Currently, the largest tidal wetlands restoration project on the US Pacific Coast is being planned and implemented in southern San Francisco Bay; however, knowledge of baseline conditions of salt marsh extent in the region prior to European settlement is limited. Here, analysis of 24 sediment cores collected from ten intact southern San Francisco Bay tidal marshes were used to reconstruct spatio-temporal patterns of marsh expansion to provide historic context for current restoration efforts. A process-based marsh elevation simulation model was used to identify interactions between sediment supply, sea-level rise, and marsh formation rates. A distinct age gradient was found: expansion of marshes in the central portion of southern San Francisco Bay dated to 500 to 1500 calendar years before present, while expansion of marshes in southernmost San Francisco Bay dated to 200 to 700 calendar years before present. Thus, much of the tidal marsh area mapped by US Coast Survey during the 1853–1857 period were in fact not primeval tidal marshes that had persisted for millennia but were recently formed landscapes. Marsh expansion increased during the Little Ice Age, when freshwater inflow and sediment influx were higher than during the previous millennium, and also during settlement, when land use changes, such as introduction of livestock, increased watershed erosion, and sediment delivery. 相似文献
400.
This paper uses investment data for the period 1994–2008 and information from in-depth interviews with key informants in Ethiopian government agencies and 15 entrepreneurs who returned to Ethiopia to start business ventures, to assess the success of the Ethiopian government in attracting diaspora investment. The study found that diaspora investment was highly concentrated geographically and sectorally. Among the significant issues facing diasporan investors were access to land, access to finance, lack of reliable information, poor contract enforcement and frequent changes in government policies and sectoral priorities. The authors recommend the development of frameworks for the enforcement of laws and standards to make investing in Ethiopia more attractive. They also propose that the government consider the long-term sustainability of policies before they are implemented, foster diversification and the better use of the country’s natural resource clusters, and establish policies that facilitate the circulation of knowledge and skills through input from expatriate professionals and experts. 相似文献