全文获取类型
收费全文 | 433篇 |
免费 | 20篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 46篇 |
地球物理 | 84篇 |
地质学 | 145篇 |
海洋学 | 32篇 |
天文学 | 61篇 |
综合类 | 1篇 |
自然地理 | 78篇 |
出版年
2022年 | 2篇 |
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 3篇 |
2018年 | 11篇 |
2017年 | 13篇 |
2016年 | 9篇 |
2015年 | 12篇 |
2014年 | 12篇 |
2013年 | 20篇 |
2012年 | 17篇 |
2011年 | 22篇 |
2010年 | 26篇 |
2009年 | 31篇 |
2008年 | 24篇 |
2007年 | 22篇 |
2006年 | 23篇 |
2005年 | 18篇 |
2004年 | 20篇 |
2003年 | 20篇 |
2002年 | 15篇 |
2001年 | 11篇 |
2000年 | 12篇 |
1999年 | 11篇 |
1998年 | 12篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 8篇 |
1989年 | 5篇 |
1988年 | 1篇 |
1987年 | 6篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1969年 | 1篇 |
1952年 | 1篇 |
1947年 | 1篇 |
排序方式: 共有459条查询结果,搜索用时 31 毫秒
431.
432.
Glacial Geology of Cape Bird, Ross Island, Antarctica 总被引:1,自引:0,他引:1
433.
In the summer of 2010/2011 Chile suffered the third most severe energy and water supply crisis in only one decade.This may be surprising as the Andes which accompany the country along 4,200 km are a water tower and could provide more electricity and water than needed.On top of that,it has to be mentioned that Chile also counts with sunny and windy climates and with excellent geothermal energy resources and thus has a huge potential as far as renewable energies are concerned.After analyzing the existing natural conditions,the infrastructure and the present challenges of climate change,it has to be asked in which way Chile can make use of this potential in the near future,considering the legal and political situation and the technological opportunities.It seems that the resources are still hidden in the Andes,and only the key is missing to realize the country’s natural potential.This research has been based on the analysis of existing literature,media,quantitative data from government institutions and other antecedents obtained by the authors in field work done in the South of Chile in 2010.The added value of this compilation lies in the comprehensive perspective,linking the knowledge of climatologists,hydrologists,mountain researchers and energy experts in order to support a sustainable energy and water supply for the future in Chile.From this present research,it can be concluded that Chile necessarilyhas to adopt new energy-related strategies,particularly those aimed at diminishing the strong dependence on traditional sources of energy and establishing new techniques and technologies for generating electricity and utilizing the vast potential that the country is ready to offer,such as that provided by the Andes along 4,200 kilometers. 相似文献
434.
Stefan H. Doerr Rob R. Davies Alexander Lewis Graham Pilkington John A. Webb Peter J. Ackroyd Owen Bodger 《地球表面变化过程与地形》2012,37(3):253-261
The Australian Nullarbor Plain, one of the world's largest limestone platforms (~200 000 km2), has few distinctive surface karst features for its size, but is known for its enigmatic ‘blowholes’, which can display strong barometric draughts. Thousands of these vertical tubes with decimetre–metre (dm–m) scale diameter puncture the largely featureless terrain. The cause and distribution of these has remained unclear, but they have been thought to originate from downward dissolution and/or salt weathering. To elucidate blowhole distribution and mode of formation we (i) correlated existing location data with Shuttle Radar Topography Mission (SRTM) data, which distinguishes the subtle undulations (< 10 m per km) of the landscape, (ii) surveyed blowhole morphology and (iii) determined their rock surface hardness. Over a sampled area of 4200 km2, the distribution of 615 known blowholes is not correlated with present topography. Blowholes are often connected to small or, in some cases extensive, but typically shallow cavities, which exhibit numerous ‘cupolas’ (dome‐shaped pockets) in their ceilings. Statistical arguments suggest that cavities with cupolas are common, but in only a few cases do these puncture the surface. Hardness measurements indicate that salt weathering is not their main cause. Our observations suggest that blowholes do not develop downwards, but occur where a cupola breaks through the surface. Lowering of the land surface is suggested to be the main cause for this breakthrough. Although cupolas may undergo some modification under the current climate, they, as well as the shallow caves they are formed in, are likely to be palaeokarst features formed under a shallower water table and wetter conditions in the past. The findings presented have implications for theories of dissolutional forms development in caves worldwide. The environmental history of the Nullarbor platform allows testing of such theories, because many other factors, which complicate karst evolution elsewhere, have not interfered with landform evolution here. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
435.
Bart Makaske Ben H. P. Maathuis Carlos R. Padovani Chris Stolker Erik Mosselman Rob H. G. Jongman 《地球表面变化过程与地形》2012,37(12):1313-1326
Avulsion, the natural relocation of a river, is a key process in the evolution of subaerial fans, river floodplains and deltas. The causes of avulsion are poorly understood, which is partly due to the scarcity of field studies of present avulsions. At present, two avulsions are occurring on the middle and lower Taquari megafan, Pantanal basin, south‐western Brazil. Here we present an analysis of the causes of these avulsions based on field and remote sensing data and show that avulsions on megafans can be controlled by both upstream and downstream processes. The middle fan avulsion (started in 1997–1998) is a result of upstream control: overbank aggradation was caused by the (variable) input of sandy sediment into the system, which caused channel‐belt superelevation and also created an easily erodible subsurface favouring bank retreat, crevassing, and scour of deep floodplain channels. The sandy subsurface in this area is inferred to have been a major factor in the causation of this avulsion under conditions of little gradient advantage. The lower fan avulsion (started c. 1990) results from interplay of upstream and downstream controls, the latter being related to the local base level (the Paraguay River floodplain) at the toe of the fan. Channel and overbank aggradation on the lower fan was influenced by fan sub‐lobe progradation and channel backfilling. Fan sub‐lobe progradation caused a significant gradient advantage of the avulsion channel over the parent channel. Avulsions are commonly supposed to be preferentially triggered by high‐magnitude floods, when there is considerable channel‐belt superelevation. However, both avulsions studied by us were triggered by small to average floods, with modest channel‐belt superelevation. We conclude that flood magnitude and channel‐belt superelevation have been overrated as causes of avulsion, and demonstrate additional causes that influence the growth of crevasses into avulsions. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
436.
437.
Kees Van Beek Rob Breedveld Martijn Tas René Kollen 《Ground Water Monitoring & Remediation》2010,30(4):81-89
Wellfield “Tull en ’t Waal” (water utility Vitens Midden Nederland) suffers extensively from wellbore (or mechanical) clogging. To prevent this type of clogging, wells have been operated intermittently since August 2005 using a carrousel well operation schedule. Since the introduction of this schedule, wellbore clogging has become minimal. 相似文献
438.
Long-period seismicity during magma movement at Volcán de Colima 总被引:1,自引:1,他引:0
Nick R. Varley Raúl Arámbula-Mendoza Gabriel Reyes-Dávila John Stevenson Rob Harwood 《Bulletin of Volcanology》2010,72(9):1093-1107
During the period from February to September 2005, Volcán de Colima produced 30 Vulcanian explosions of sufficient magnitude
to produce pyroclastic flows of variable size, with a total volume of at least 2.5 × 106 m3. Swarms of long-period events were associated with each event, their duration ranging from about 6 h to 3 days and each swarm
containing up to 886 events. The characteristics of the swarms have been studied to understand the source mechanism and their
relationship with the Vulcanian explosions. In total, 12,548 long-period events were analysed using various comparative and
statistical methods. Patterns were not apparent in the data with no correlation between different properties of the swarms
(duration, magnitude or frequency of occurrence of LP events) and the magnitude of the associated Vulcanian explosion, whether
recorded by seismicity, volume of pyroclastics or altitude of the eruption column. This, along with other characteristics
of the swarms, such as the continuation of the swarm after the explosion, with an increase in long-period event amplitude
in some cases, suggests that the mechanism is not merely associated with the pressurization under an impermeable cap and resulting
pressure differentials between adjacent volumes within the system. It is more likely that the production of long-period events
is dominated by brittle fracturing on the margins of an ascending magma body. A model is proposed whereby the unloading above
the ascending magma column produced by a Vulcanian explosion resulted in an increase in ascent rate, reflected in the increasing
amplitude of long-period events. The results reflect the complexity of non-linear processes involved during magma ascent,
degassing, crystallization and rupture of the impermeable plug during the Vulcanian process. At Volcán de Colima, as at many
volcanoes, long-period events represent a useful precursor for eruptive activity. For monitoring, this paper highlights some
useful analyses that can be carried out, which could illustrate certain characteristics of an eruptive episode. A preliminary
model is presented of the conduit processes at work during the cyclic extrusive and explosive activity during 2005. 相似文献
439.
Environmental indicators are being increasingly used to emphasise the relevance of monitoring. However, indicators must also be effective. In particular, they must be able to answer management questions, be accessible to the target audience and be sufficiently precise. Here, we use a time series of mercury levels in plaice from Liverpool Bay to illustrate how specific management questions can be formulated, answered, and the precision of these answers assessed. We also show how a programme design can incorporate a series of management questions that are likely to arise over time in response to observed changes in a time series. 相似文献
440.
Landscape-Scale Analysis of Interactions between Insect Defoliation and Forest Fire in Central Canada 总被引:6,自引:0,他引:6
Analysis of Ontario's historical records from 1941–1996 showed that spruce budworm, Choristoneura fumiferana (Clem.) caused whole tree mortality within 389×103 km2. This amounted to 9.2% of the annually cumulative area with moderate-severe defoliation. Large (>2 km2) fires were reported in approximately 65,000 km2 and overlapped only 2.8% of the area of reported spruce budworm (SBW) caused tree mortality. Within the 417×103 km2 defoliated by SBW at least once in 1941–1996, the maximum total area recorded as defoliated in any year was over 20 times the maximal area burnt. In the 19,950 km2 experiencing both wildfire and SBW defoliation, analysis of the spectra of time lags between the two disturbance types indicated that fires occurred 3–9 years after a SBW outbreak disproportionately often. This window of opportunity for wildfire varies geographically: it starts later after SBW outbreak and lasts longer in western than in eastern Ontario. In addition, 7.5% of the areas containing SBW killed trees were burnt in western compared to 4.8% in eastern Ontario. These geographical differences may result at least partly from slower decomposition of dead fuels in the drier climates of the western SBW belt compared to the eastern SBW belt. The implications for climatic change are discussed. 相似文献