全文获取类型
收费全文 | 41篇 |
免费 | 8篇 |
国内免费 | 8篇 |
专业分类
大气科学 | 1篇 |
地球物理 | 8篇 |
地质学 | 23篇 |
海洋学 | 11篇 |
天文学 | 6篇 |
自然地理 | 8篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 1篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2015年 | 6篇 |
2014年 | 2篇 |
2013年 | 4篇 |
2012年 | 4篇 |
2011年 | 2篇 |
2010年 | 3篇 |
2009年 | 2篇 |
2008年 | 1篇 |
2007年 | 3篇 |
2006年 | 3篇 |
2004年 | 5篇 |
2003年 | 3篇 |
2001年 | 1篇 |
1998年 | 1篇 |
1995年 | 3篇 |
1993年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1927年 | 1篇 |
排序方式: 共有57条查询结果,搜索用时 15 毫秒
1.
P. Persi M. Ferrari-Toniolo A. R. Marenzi M. Busso L. Corcione M. Marengo M. Tapia 《Astrophysics and Space Science》1995,224(1-2):535-536
We present the results of direct mid-IR images of the luminous young stellar objects GL 2591, S140-IRS1, and W51-IRS2. The sources show an extended mid-IR emission at the limit of our spatial resolution indicating the presence of dense circumstellar dust disks. 相似文献
2.
Agust Gudmundsson 《Comptes Rendus Geoscience》2004,336(1):85-92
Elastic crack models predict a linear relationship between displacement (u) and rupture (trace) length (L) during slip in a fault zone. Attempts to find universal-scaling laws for L/u, however, have generally failed. Here I propose that these attempts have failed because they do not take into account the changes in the mechanical properties, in particular Young's modulus (stiffness), of the fault zone as it evolves. I propose that Young's modulus affects fault displacement both spatially and temporally: spatially when the trace of a fault at a given time dissects host rocks of different stiffnesses, and temporally when the stiffness of the fault zone itself changes. During the evolution of an active fault zone, the effective Young's modulus of its damage zone and fault core normally decreases, and so does the L/u ratio of the fault. By contrast, during inactive periods sealing and healing of the damage zone and core may increase the stiffness, hence the L/u ratio in subsequent slips. This model predicts that not only will the scaling of L/u within a given fault population vary in space and time, but also that of individual faults. To cite this article: A. Gudmundsson, C. R. Geoscience 336 (2004). 相似文献
3.
Roger M. Downs 《The Journal of geography》2016,115(1):3-11
The history of K–12 geography education has been characterized by recurrent high hopes and dashed expectations. There have, however, been moments when the trajectory of geography education might have changed to offer students the opportunity to develop a thorough working knowledge of geography. Lucy Sprague Mitchell’s geography program developed in the 1920s and 1930s was brilliant in its conception and execution but it did not lead to large-scale systemic change. Analyzing the origins, development, and outcome of her program suggests the conditions that facilitate and inhibit systemic change, and therefore perhaps we can learn to capitalize on comparable moments in the future. 相似文献
4.
Young Sound is a deep-sill fjord in NE Greenland (74°N). Sea ice usually begins to form in late September and gains a thickness of 1.5 m topped with 0–40 cm of snow before breaking up in mid-July the following year. Primary production starts in spring when sea ice algae begin to flourish at the ice–water interface. Most biomass accumulation occurs in the lower parts of the sea ice, but sea ice algae are observed throughout the sea ice matrix. However, sea ice algal primary production in the fjord is low and often contributes only a few percent of the annual phytoplankton production. Following the break-up of ice, the immediate increase in light penetration to the water column causes a steep increase in pelagic primary production. Usually, the bloom lasts until August–September when nutrients begin to limit production in surface waters and sea ice starts to form. The grazer community, dominated by copepods, soon takes advantage of the increased phytoplankton production, and on an annual basis their carbon demand (7–11 g C m−2) is similar to phytoplankton production (6–10 g C m−2). Furthermore, the carbon demand of pelagic bacteria amounts to 7–12 g C m−2 yr−1. Thus, the carbon demand of the heterotrophic plankton is approximately twice the estimated pelagic primary production, illustrating the importance of advected carbon from the Greenland Sea and from land in fuelling the ecosystem.In the shallow parts of the fjord (<40 m) benthic primary producers dominate primary production. As a minimum estimate, a total of 41 g C m−2 yr−1 is fixed by primary production, of which phytoplankton contributes 15%, sea ice algae <1%, benthic macrophytes 62% and benthic microphytes 22%. A high and diverse benthic infauna dominated by polychaetes and bivalves exists in these shallow-water sediments (<40 m), which are colonized by benthic primary producers and in direct contact with the pelagic phytoplankton bloom. The annual benthic mineralization is 32 g C m−2 yr−1 of which megafauna accounts for 17%. In deeper waters benthic mineralization is 40% lower than in shallow waters and megafauna, primarily brittle stars, accounts for 27% of the benthic mineralization. The carbon that escapes degradation is permanently accumulated in the sediment, and for the locality investigated a rate of 7 g C m−2 yr−1 was determined.A group of walruses (up to 50 adult males) feed in the area in shallow waters (<40 m) during the short, productive, ice-free period, and they have been shown to be able to consume <3% of the standing stock of bivalves (Hiatella arctica, Mya truncata and Serripes Groenlandicus), or half of the annual bivalve somatic production. Feeding at greater depths is negligible in comparison with their feeding in the bivalve-rich shallow waters. 相似文献
5.
Christopher M. Wright 《Astrophysics and Space Science》2007,311(1-3):47-55
The position angle of mid-infrared polarisation can be directly related to the magnetic field direction projected onto the
plane of the sky. Such observations, from both ground and space-based platforms, have been used to investigate the relation
between the magnetic field and other “symmetry axes” associated with embedded young stars, such as the interstellar magnetic
field, bipolar outflow and disk/toroid axes. Interpretation of the results in terms of hydromagnetic driving mechanisms of
bipolar outflow is discussed. 相似文献
6.
《Geoforum》2015
Cell phones present new forms of sociality and new possibilities of encounter for young people across the globe. Nowhere is this more evident than in sub-Saharan Africa where the scale of usage, even among the very poor, is remarkable. In this paper we reflect on the inter-generational encounters which are embedded in young people’s cell phone interactions, and consider the wider societal implications, not least the potential for associated shifts in the generational balance of power. An intriguing feature of this changing generational nexus is that while many young people’s phone-based interactions, from their mid-teens onwards, are shifting away from the older generation towards friendship networks in their own age cohort, at the same time they are repositioning themselves – or becoming repositioned – as family information hubs, as a consequence of their phone expertise. The paper draws on mixed-methods research with young people aged c. 9–25 years and in-depth interviews with older age-groups in 24 sites (ranging from high density poor urban to remote rural) across Ghana, Malawi and South Africa. 相似文献
7.
《Geoforum》2015
The paper offers a critical intervention into the debates on research impact, theorising the potential of underpinning research agendas by ethics of care. We explore how a range of vectors of care, both intimate and distant, emerged in collaborative activities between researchers based in the UK and community youth workers and teenage female carers in Slovakia, leading to a series of (un)expected outcomes. We argue that while all research impacts cannot be planned in advance, an ethics of care embedded in relationships within and beyond research settings may form conditions in which outcomes exceeding the initial expectations can be anticipated. To achieve this, we argue for questioning the distinctions between academic and non-academic collaborators, legitimising diverse forms of knowledge, action and impact in institutional policies, and for conceiving research projects from the beginning as “more-than-research” avenues. 相似文献
8.
9.
10.
Shannon McCune 《The Professional geographer》1986,38(4):359-365
The Young Geographers, an informal organization of American geographers, flourished from 1936 to 1943. One of its projects in 1940 and 1941 was the compilation and publication of lists of contemplated research by some 170 Young Geographers. Their listed research interests were relatively narrow in subject and geographical area. The successor of the Young Geographers was the American Society for Professional Geographers which merged with the Association of American Geographers in 1948 under a democratic constitution which assured that young geographers and their research would be recognized. 相似文献