全文获取类型
收费全文 | 354篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 21篇 |
地球物理 | 28篇 |
地质学 | 95篇 |
海洋学 | 24篇 |
天文学 | 174篇 |
自然地理 | 20篇 |
出版年
2023年 | 3篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2017年 | 4篇 |
2016年 | 5篇 |
2015年 | 9篇 |
2014年 | 10篇 |
2013年 | 11篇 |
2012年 | 9篇 |
2011年 | 6篇 |
2010年 | 4篇 |
2009年 | 18篇 |
2008年 | 15篇 |
2007年 | 16篇 |
2006年 | 19篇 |
2005年 | 9篇 |
2004年 | 14篇 |
2003年 | 14篇 |
2002年 | 10篇 |
2001年 | 11篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1985年 | 13篇 |
1984年 | 7篇 |
1983年 | 10篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1975年 | 8篇 |
1974年 | 10篇 |
1973年 | 6篇 |
1972年 | 2篇 |
1971年 | 7篇 |
1970年 | 2篇 |
1969年 | 3篇 |
1967年 | 2篇 |
排序方式: 共有364条查询结果,搜索用时 15 毫秒
61.
The world’s largest coral reef ecosystem, the Great Barrier Reef (GBR), continues to be degraded from land-based pollution. Information about the source of pollutants is critical for catchment management to improve GBR water quality. We report here on an 11-year source to sea study of pollutant delivery in runoff from the Fitzroy River Basin (FRB), the largest GBR catchment. An innovative technique that relates land use to pollutant generation is presented. Study results indicate that maximum pollutant concentrations at basin and sub-catchment scales are closely related to the percentage area of croplands receiving heavy rain. However, grazing lands contribute the majority of the long-term average annual load of most common pollutants. Findings suggest improved land management targets, rather than water quality targets should be implemented to reduce GBR pollution. This study provides a substantial contribution to the knowledge base for the targeted management of pollution ‘hot-spots’ to improve GBR water quality. 相似文献
62.
Ashley J. Williams Aaron C. Ballagh Gavin A. Begg Cameron D. Murchie Leanne M. Currey 《Continental Shelf Research》2008
The reef line fishery (RLF) in eastern Torres Strait (ETS) is unique in that it has both a commercial indigenous sector and a commercial non-indigenous sector. Recently, concerns have been expressed by all stakeholders about the long-term sustainability of the fishery. These concerns have been exacerbated by the lack of detailed catch and effort information from both sectors, which has precluded any formal assessment of the fishery. In this paper, we characterise the harvest patterns and effort dynamics of the indigenous and non-indigenous commercial sectors of the ETS RLF using a range of data sources including commercial logbooks, community freezer records, voluntary logbooks and observer surveys. We demonstrate that bycatch is a significant component of the catch for both sectors and identify substantial differences in harvest patterns and effort dynamics between the sectors. Differences between sectors were observed in species composition and spatial and temporal patterns in catch, effort and catch per unit effort. These results highlight the inherent variation in catch and effort dynamics between the two commercial sectors of the ETS RLF and provide valuable information for the development of future assessments and appropriate management strategies for the fishery. The more reliable estimates of harvest patterns and effort dynamics for both sectors obtained from observer surveys will also assist in resolving issues relating to allocation of reef fish resources in Torres Strait. 相似文献
63.
64.
65.
66.
67.
68.
This paper argues that there is an immanent and evolving relationship between the prevailing form of taxation and the economic geographies of the state. Despite this, the geographic significance of taxation has been obscured by the language in which its historic transformation tends to be couched. Prevailing fiscal systems tend to be presented as essentially static – institutionally and spatially fixed and routinely inscribed within the fixed boundaries and territories of the ‘sovereign’ fiscal state. Any threat to, or change in the nature or geography of the fiscal state tends to be couched in terms of ‘crisis’ – of negative and discontinuous change. This paper contends that these related and essentially conservative discourses of fiscal geography mask the degree to which fiscal spaces are both multiple and continuously evolving. More importantly, it argues, this fluidity and multiplicity does not threaten the stability and viability of state form, but it is an essential process in its maintenance and reproduction. Running counter to the prevailing discourse of the ‘national economy’, the practice of fiscal geography is an under-analysed but key aspect of the historical evolution and transformation of the imagined geographies of economies. 相似文献
69.
Lee Cameron C. Sheridan Scott C. Barnes Brian B. Hu Chuanmin Pirhalla Douglas E. Ransibrahmanakul Varis Shein Karsten 《Theoretical and Applied Climatology》2017,130(1-2):557-569
Theoretical and Applied Climatology - The coastal waters of the southeastern USA contain important protected habitats and natural resources that are vulnerable to climate variability and singular... 相似文献
70.
Low rank coals from two disparate geological settings have been subjected to petrographic and palynological analysis. The stratigraphic units studied and their locations are the Amphitheatre Formation, St Elias Mountains, Yukon Territory, of Eocene to Oligocene age; and the base of the Ravenscrag Formation, south-central Saskatchewan, of latest Cretaceous to earliest Paleocene age.The depositional setting of the Amphitheatre Formation ranges from distal sand-dominated braided stream and lacustrine environments to proximal gravel-dominated fluvial environments. The coals are low in inertinite (< 6%) and mostly high in huminite (> 85%). In localities with a dominance of angiosperm pollen the relative abundance of eu-ulminite B and densinite is greatest whereas in the ones with a dominantly coniferous pollen assemblage eu-ulminite A is the most prominent maceral. These observations suggest as an immediate cause/effect relationship, an at least partial dependance of present maceral content on floral precursors. This in turn probably reflects a certain combination of depositional environment conditions (pH, Eh, temperature, etc.), that likely controlled the plant community and the preservation of vegetal matter.The depositional environment of coals from the basal part of the Ravenscrag Formation contrasts sharply with that of the Amphitheatre. The Ravenscrag coals formed within a low energy, stable, floodplain environment. Palynological and coal maceral profiles for the basal Ravenscrag Formation coal, which spans the Cretaceous-Tertiary boundary, indicates that the environment of deposition progressed from an open canopied swamp forest with areas of open water, through a phase of low-lying to open water swamps with herbaceous, pterophytic vegetation to, at least locally, raised bogs. The change in coal petrography across the Cretaceous-Tertiary boundary is shown to be relatively minor in comparison to subsequent changes in coal petrography in the earliest Paleocene and to changes that occur in the palynological assemblages across the boundary interval. 相似文献