全文获取类型
收费全文 | 941篇 |
免费 | 26篇 |
国内免费 | 23篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 72篇 |
地球物理 | 236篇 |
地质学 | 332篇 |
海洋学 | 74篇 |
天文学 | 161篇 |
综合类 | 2篇 |
自然地理 | 99篇 |
出版年
2023年 | 3篇 |
2021年 | 6篇 |
2020年 | 11篇 |
2019年 | 7篇 |
2018年 | 24篇 |
2017年 | 20篇 |
2016年 | 34篇 |
2015年 | 27篇 |
2014年 | 23篇 |
2013年 | 57篇 |
2012年 | 34篇 |
2011年 | 45篇 |
2010年 | 36篇 |
2009年 | 44篇 |
2008年 | 38篇 |
2007年 | 40篇 |
2006年 | 46篇 |
2005年 | 36篇 |
2004年 | 46篇 |
2003年 | 35篇 |
2002年 | 27篇 |
2001年 | 28篇 |
2000年 | 26篇 |
1999年 | 19篇 |
1998年 | 26篇 |
1997年 | 18篇 |
1996年 | 13篇 |
1995年 | 17篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 16篇 |
1991年 | 13篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 13篇 |
1983年 | 12篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 11篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1972年 | 4篇 |
排序方式: 共有990条查询结果,搜索用时 15 毫秒
941.
942.
Stuart A. Harris 《寒旱区科学》2016,8(6):451-460
The latest available data for mean annual air temperature at sites away from the Arctic coast in both Alaska and the Yukon Territory show no significant warming in the last 30~50 years. However, around the Arctic coast of northwest North America centered on Prudhoe Bay, the weather stations show significant warming of both the air and the ocean water, resulting in substantial losses in sea ice west of Prudhoe Bay. These changes appeared shortly after the commencement of shipment of oil through the Trans-Alaska Pipeline in 1977, but have now reached a quasi-stable thermal state. Since more than 17 trillion barrels of oil have passed through the pipeline after being cooled by the adjacent air, which in turn, can then result in the melting of the adjacent sea ice, there appears to be a very strong relationship between these events, and a marked lack of correlation with the changes of the content of greenhouse gases in the atmosphere. This contrasts with the IPCC interpretation of the available climatic data, which assumes that the maximum climatic warming at Prudhoe Bay is typical of the entire region and is the result of increasing greenhouse gases. Engineers need to consider heat advection by oil or gas from underground when designing pipeline facilities, and to take account of the potential environmental consequences that they may cause. 相似文献
943.
Stuart A. Harris 《寒旱区科学》2016,8(3):177-186
Cryogenic block streams consist of a stream of rocks superficially resembling a stream deposit but lacking a matrix, usually occurring on a valley or gully floor or on slopes that are less steep than the maximum angle of repose of coarse sediments. They are usually formed on perennially frozen ground, but can also occur as relict landforms. There are three main active kinds forming today, viz., Siberian and Tibetan dynamic rock streams and lag block streams. During their formation, the blocks in the active Siberian and Tibetan dynamic block streams move downslope at up to 1 m/a. They are forming today on the Tibetan Plateau and in the more arid parts of south-central Siberia, although the processes involved in the movement are different. In the case of the Tibetan type, individual blocks slide downslope over the substrate in winter on an icy coating in areas of minimal winter precipitation. The Siberian type develops in areas of 15–80 cm of winter snow cover and an MAAT(mean annual air temperature) of-4 °C to-17 °C. The movement is due to creep of snow and ice and collapse of the blocks downslope during thawing. Lag block streams are formed by meltwater flowing over the surface of sediment consisting primarily of larger blocks with a limited amount of interstitial sediment. The erosion of the matrix is primarily in the spring in areas of higher winter precipitation on 10°–30° slopes. The blocks remain stationary, but the interstitial sediment is washed out by strong seasonal flows of meltwater or rain to form an alluvial fan. The boulders undergo weathering and become more rounded in the process. Lag block streams can also develop without the presence of permafrost in areas with cold climates or glaciers. Block streams also occur as relict deposits in older deposits under various climatic regimes that are unsuitable for their formation today. An example of relict lag block streams with subangular to subrounded blocks occurs in gullies on the forested mountainsides at Felsen in Germany, and is the original "felsenmeer". Similar examples occur near Vitosha Mountain in Bulgaria. The "stone runs" in the Falkland Islands are examples of the more angular relict lag block streams. In both Tasmania and the Falkland Islands, they mask a more complex history, the underlying soils indicating periods of tropical and temperate soil formation resulting from weathering during and since the Tertiary Period. Block streams have also been reported from beneath cold-based glaciers in Sweden, and below till in Canada, and when exhumed, can continue to develop. 相似文献
944.
The application of ecohydrological groundwater indicators to hydrogeological conceptual models 总被引:1,自引:0,他引:1
Lewis J 《Ground water》2012,50(5):679-689
This article reviews the application of ecohydrological indicators to hydrogeological conceptual models for earth-scientists with little or no botanical training. Ecohydrological indicators are plants whose presence or morphology can provide data about the hydrogeological setting. By examining the literature from the fields of ecohydrology, hydrogeology, geobotany, and ecology, this article summarizes what is known about groundwater indicator plants, their potential for providing information about the aquifer, and how this data can be a cost-effective addition to hydrogeological conceptual models. We conclude that the distribution and morphology of ecohydrological groundwater indicator plants can be useful to hydrogeologists in certain circumstances. They are easiest to evaluate in arid and semiarid climates. Ecohydrological groundwater indicators can provide information about the absolute depth to the water table, patterns of groundwater fluctuation, and the mineralization of the aquifer. It is shown that an understanding of the meteorological conditions of a region is often necessary to accurately interpret groundwater indicator plants and that useful data is usually obtained by observing patterns of vegetation behavior rather than interpreting individual plants. The most serious limitations to applying this source of information to hydrogeological conceptual models are the limited data in the literature and the regional nature of many indicator plants. The physical and physiological indications of the plants exist, but little effort has been made to interpret them. This article concludes by outlining several potential lines of research that could further the usefulness of ecohydrological groundwater indicators to the hydrogeological community. 相似文献
945.
Bernard O. Bauer Robin G. D. Davidson‐Arnott Ian J. Walker Patrick A. Hesp Jeff Ollerhead 《地球表面变化过程与地形》2012,37(15):1661-1677
Evidence from a field study on wind flow and sediment transport across a beach–dune system under onshore and offshore conditions (including oblique approach angles) indicates that sediment transport response on the back‐beach and stoss slope of the foredune can be exceedingly complex. The upper‐air flow – measured by a sonic anemometer at the top of a 3·5 m tower located on the dune crest – is similar to regional wind records obtained from a nearby meteorological station, but quite different from the near‐surface flow field measured locally across the beach–dune profile by sonic anemometers positioned 20 cm above the sand surface. Flow–form interaction at macro and micro scales leads to strong modulation of the near‐surface wind vectors, including wind speed reductions (due to surface roughness drag and adverse pressure effects induced by the dune) and wind speed increases (due to flow compression toward the top of the dune) as well as pronounced topographic steering during oblique wind approach angles. A conceptual model is proposed, building on the ideas of Sweet and Kocurek (Sedimentology 37 : 1023–1038, 1990), Walker and Nickling (Earth Surface Processes and Landforms 28 : 111–1124, 2002), and Lynch et al. (Earth Surface Processes and Landforms 33 : 991–1005, 2008, Geomorphology 105 : 139–146, 2010), which shows how near‐surface wind vectors are altered for four regional wind conditions: (a) onshore, detached; (b) onshore‐oblique, attached and deflected; (c) offshore, detached; and (d) offshore‐oblique, attached and deflected. High‐frequency measurements of sediment transport intensity during these different events demonstrate that predictions of sediment flux using standard equations driven by regional wind statistics would by unreliable and misleading. It is recommended that field studies routinely implement experimental designs that treat the near‐surface wind field as comprising true vector quantities (with speed and direction) in order that a more robust linkage between the regional (upper air) wind field and the sediment transport response across the beach–dune profile be established. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
946.
947.
This special issue of Continental Shelf Research contains 20 papers giving research results produced as part of Australia's Torres Strait Co-operative Research Centre (CRC) Program, which was funded over a three-year period during 2003–2006. Marine biophysical, fisheries, socioeconomic-cultural and extension research in the Torres Strait region of northeastern Australia was carried out to meet three aims: 1) support the sustainable development of marine resources and minimize impacts of resource use in Torres Strait; 2) enhance the conservation of the marine environment and the social, cultural and economic well being of all stakeholders, particularly the Torres Strait peoples; and 3) contribute to effective policy formulation and management decision making. Subjects covered, including commercial and traditional fisheries management, impacts of anthropogenic sediment inputs on seagrass meadows and communication of science results to local communities, have broad applications to other similar environments. 相似文献
948.
Andrew J. L. Harris Massimiliano Favalli Francesco Mazzarini Christopher W. Hamilton 《Bulletin of Volcanology》2009,71(4):459-474
We use a kinematic GPS and laser range finder survey of a 200 m-long section of the Muliwai a Pele lava channel (Mauna Ulu,
Kilauea) to examine the construction processes and flow dynamics responsible for the channel–levee structure. The levees comprise
three packages. The basal package comprises an 80–150 m wide ′a′a flow in which a ∼2 m deep and ∼11 m wide channel became
centred. This is capped by a second package of thin (<45 cm thick) sheets of pahoehoe extending no more than 50 m from the
channel. The upper-most package comprises localised ′a′a overflows. The channel itself contains two blockages located 130 m
apart and composed of levee chunks veneered with overflow lava. The channel was emplaced over 50 h, spanning 30 May–2 June,
1974, with the flow front arriving at our section (4.4 km from the vent) 8 h after the eruption began. The basal ′a′a flow
thickness yields effusion rates of 35 m3 s−1 for the opening phase, with the initial flow advancing across the mapped section at ∼10 m/min. Short-lived overflows of fluid
pahoehoe then built the levee cap, increasing the apparent channel depth to 4.8 m. There were at least six pulses at 90–420 m3 s−1, causing overflow of limited extent lasting no more than 5 min. Brim-full flow conditions were thus extremely short-lived.
During a dominant period of below-bank flow, flow depth was ∼2 m with an effusion rate of ∼35 m3 s−1, consistent with the mean output rate (obtained from the total flow bulk volume) of 23–54 m3 s−1. During pulses, levee chunks were plucked and floated down channel to form blockages. In a final low effusion rate phase,
lava ponded behind the lower blockage to form a syn-channel pond that fed ′a′a overflow. After the end of the eruption the
roofed-over pond continued to drain through the lower blockage, causing the roof to founder. Drainage emplaced inflated flows
on the channel floor below the lower blockage for a further ∼10 h. The complex processes involved in levee–channel construction
of this short-lived case show that care must be taken when using channel dimensions to infer flow dynamics. In our case, the
full channel depth is not exposed. Instead the channel floor morphology reflects late stage pond filling and drainage rather
than true channel-contained flow. Components of the compound levee relate to different flow regimes operating at different
times during the eruption and associated with different effusion rates, flow dynamics and time scales. For example, although
high effusion rate, brim-full flow was maintained for a small fraction of the channel lifetime, it emplaced a pile of pahoehoe
overflow units that account for 60% of the total levee height. We show how time-varying volume flux is an important parameter
in controlling channel construction dynamics. Because the complex history of lava delivery to a channel system is recorded
by the final channel morphology, time-varying flow dynamics can be determined from the channel morphology. Developing methods
for quantifying detailed flux histories for effusive events from the evidence in outcrop is therefore highly valuable. We
here achieve this by using high-resolution spatial data for a channel system at Kilauea. This study not only indicates those
physical and dynamic characteristics that are typical for basaltic lava flows on Hawaiian volcanoes, but also a methodology
that can be widely applied to effusive basaltic eruptions. 相似文献
949.
This paper studies knowledge production in complex, collaborative research projects that brought together academics from different disciplines, research users and agricultural businesses. It takes a comparative approach, studying the interactions within interdisciplinary research teams from ten case studies, considering the process of collaboration from initial idea through to publication. The research developed a typology of participants in these projects, and identified the motivations and challenges of each. Our results analyse the process of research teams coming together and the relationships that are built up during the research. A particular challenge identified was the building of cooperation and trust. This issue is explored alongside issues of communication, methodology, data analysis and the process of drawing and publicising conclusions. 相似文献
950.
Massimiliano Favalli Andrew J. L. Harris Alessandro Fornaciai Maria Teresa Pareschi Francesco Mazzarini 《Bulletin of Volcanology》2010,72(1):119-127
Etna’s 2001 basaltic lava flow provided a good example of the distal flow segment between the flow front and stable channel,
across which the flow evolves from channel-contained to dispersed. This zone was mapped with meter precision using LIDAR data
collected during 2004 and 2005. These data, supported by field mapping, show that the flow front comprised eight lobes each
10 to 20 m high. The flow front appears to have advanced not as a single unit, but as a series of lobes moving forward one
lobe at a time. Primary lobes were centered on the channel axis and marginal lobes were off-axis. The lobes advanced as breakouts
of low-yield-strength lava from the flow core of the stalled flow front. Marginal lobes were abandoned and contributed to
marginal levees flanking the transitional channel. For Etna’s 2001 flow, the transitional channel is 140 m wide, 700 m long
and fed a 240-m-long zone of dispersed flow; the change from stable to transitional channel occurred at a major reduction
in slope. Above this, the stable channel is 5.2 km long, 55 to 105 m wide and bounded by 15- to 25-m-high levees, and the
stable channel is located over a previous channel. In a final stage of activity, lava ponding at the break-in-slope that marks
the terminus of the stable channel put pressure on the eastern levee, causing it to fail. Liberated lava then fed a final
break-out to the east. Similar flow front-features occur at other volcanoes, indicating that similar processes are characteristic
of dispersed flow zones. 相似文献