全文获取类型
收费全文 | 403篇 |
免费 | 8篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 58篇 |
地球物理 | 94篇 |
地质学 | 106篇 |
海洋学 | 44篇 |
天文学 | 82篇 |
综合类 | 2篇 |
自然地理 | 19篇 |
出版年
2021年 | 2篇 |
2019年 | 7篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 4篇 |
2014年 | 14篇 |
2013年 | 24篇 |
2012年 | 12篇 |
2011年 | 26篇 |
2010年 | 17篇 |
2009年 | 21篇 |
2008年 | 20篇 |
2007年 | 14篇 |
2006年 | 11篇 |
2005年 | 13篇 |
2004年 | 14篇 |
2003年 | 12篇 |
2002年 | 10篇 |
2001年 | 6篇 |
2000年 | 12篇 |
1999年 | 8篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 10篇 |
1983年 | 11篇 |
1982年 | 2篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 5篇 |
1972年 | 2篇 |
1970年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有414条查询结果,搜索用时 15 毫秒
321.
David L. Morse Edwin D. Waddington Hans-Peter Marshall Tomas A. Neumann Eric J. Steig Jack E. Dibb Dale P. Winebrenner & Robert J. Arthern 《Geografiska Annaler: Series A, Physical Geography》1999,81(4):683-694
Accumulation rate measurements on the East Antarctic plateau are challenging due to both spatial and temporal variability. Annual stratigraphy is often not reliably or consistently preserved in the firn, and so accumulation cannot be determined from snow pit stratigraphy. We present a suite of accumulation rate measurements collected over several seasons at Taylor Dome, East Antarctica. We compare net accumulation results from direct burial rate measurements and β -activity firn cores along a 35 km traverse. The two methods are consistent and show that the net accumulation varies from greater than 10 cm a−1 to about 1 cm a−1 (ice equivalent) southwest to northeast across the dome. We map the depth of shallow radar layering to interpolate and extrapolate these point-location measurements and show that considerable variations occur over kilometer scales resulting from subtle surface topography. We also present accumulation rates estimated from concentration of the cosmogenic isotope 10 Be and from activity profiles of 210 Pb. Finally, satellite passive microwave data are used to estimate spatially averaged accumulation rates on the regional to continental scale to provide a context for these local observations. We show that robust mass balance measurements in this environment must rely on spatial and/or temporal averaging. 相似文献
322.
Models of the climatic perturbation caused by a large scale extraterrestrial impact predict an injection of dust into the stratosphere. This would cause the onset of environmental conditions whose two principal characteristics are a prolonged period of darkness and reduced global temperatures. Similar scenarios follow large scale volcanic eruptions, wildfires and they are predicted for a nuclear winter following a protracted nuclear exchange. A significant drop in temperature and solar insolation are also characteristics of the polar winter. In this paper the onset and emergence from the polar winter is examined as a potential biological framework for studying immediate biological effects following transition into and out of a dark/cold catastrophe. Limitations of the conceptual model, particularly with respect to the fact that polar organisms are well adapted to a regular and severe dark/cold climatic change (which the rest of the Earth's biota is not) are discussed. The model has implications for the poles as an extinction refuge during such climatic changes. 相似文献
323.
The outline and trend of 6566 subglacial bedforms in the New York Drumlin Field have been digitized from digital elevation data. A spatial predictive model has been used to extend values of bedform elongation over an area measuring 200 km × 110 km. The resulting surface is used in conjunction with depth‐to‐bedrock data and an assumed duration of ice residence to test three proposed controls on bedform elongation. Upon comparison, the resulting display of morphometry is best explained by differences in ice velocity across the field of study. The existence of multiple zones of fast‐moving ice located along the southern margin of the Laurentide Ice Sheet is implied by the observed patterns of bedform elongation and orientation. We present two interpretations that are consistent with the observations. First, enhanced basal sliding caused by decreasing effective pressure near a calving margin is suggested as a possible mechanism by which localized fast ice flow is initiated and maintained. Second, topographically controlled ice streams likely occupied the fjord‐like troughs of the Appalachian Upland northern rim. Contrary to previous understanding of the Laurentide southern margin in New York State, the resulting palaeoglaciological reconstruction illustrates a dynamic mosaic of ice stream and/or outlet glacier activity. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
324.
We re-examine the utility of teleseismic seismic complexity discriminants in a multivariate setting using United Kingdom array
data. We measure a complexity discriminant taken on array beams by simply taking the logarithm of the ratio of the P-wave coda signal to that of the first arriving direct P wave (βCF). The single station complexity discriminant shows marginal performance with shallow earthquakes having more complex signatures
than those from explosions or deep earthquakes. Inclusion of secondary phases in the coda window can also degrade performance.
However, performance improves markedly when two-station complexity discriminants are formed showing false alarm rates similar
to those observed for network mb − Ms. This suggests that multistation complexity discriminants may ameliorate some of the problems associated with mb – Ms discrimination at lower magnitudes. Additionally, when complexity discriminants are combined with mb – Ms there is a tendency for explosions, shallow earthquakes and deep earthquakes to form three distinct populations. Thus, complexity
discriminants may follow a logic that is similar to mb – Ms in terms of the separation of shallow earthquakes from nuclear explosions, although the underlying physics of the two discriminants
is significantly different. 相似文献
325.
Emily B. Voytek Anja Drenkelfuss Frederick D. Day‐Lewis Richard Healy John W. Lane Jr. Dale Werkema 《Ground water》2014,52(2):298-302
A new computer program, 1DTempPro, is presented for the analysis of vertical one‐dimensional (1D) temperature profiles under saturated flow conditions. 1DTempPro is a graphical user interface to the U.S. Geological Survey code Variably Saturated 2‐Dimensional Heat Transport (VS2DH), which numerically solves the flow and heat‐transport equations. Pre‐ and postprocessor features allow the user to calibrate VS2DH models to estimate vertical groundwater/surface‐water exchange and also hydraulic conductivity for cases where hydraulic head is known. 相似文献
326.
Jonathon Dale Tim Holland Roger Powell 《Contributions to Mineralogy and Petrology》2000,140(3):353-362
Calibrations are presented for an independent set of four equilibria between end-members of garnet, hornblende, plagioclase
and quartz. Thermodynamic data from a large internally-consistent thermodynamic dataset are used to determine the ΔG° of the equilibria. Then, with the known mixing properties of garnet and plagioclase, the non-ideal mixing in amphibole is
derived from a set of 74 natural garnet–amphibole–plagioclase–quartz assemblages crystallised in the range 4–13 kbar and 500–800 °C.
The advantage of using known thermodynamic data to calculate ΔG° is that correlated variations of composition with temperature and pressure are not manifested in fictive derived entropies
and volumes, but are accounted for with non-ideal mixing terms. The amphibole is modelled using a set of ten independent end-members
whose mixing parameters are in good agreement with the small amount of data available in the literature. The equilibria used
to calibrate the amphibole non-ideal mixing reproduce pressures and temperatures with average absolute deviations of 1.1 kbar
and 35 °C using an average pressure–temperature approach, and 0.8 kbar with an average pressure approach. The mixing data
provide not only a basis for thermobarometry involving additional phases, but also for calculation of phase diagrams in complex
amphibole-bearing systems.
Received: 8 November 1999 / Accepted: 7 July 2000 相似文献
327.
328.
Earth, Moon, and Planets - 相似文献
329.
Dale R. Lightfoot 《Geoarchaeology》1993,8(5):349-370
Anasazi farmers in northern New Mexico occasionally applied a pebble mulch to their gardens during the 14th and 15th centuries A. D. to increase crop yield and to buffer against drought. Regional variations in surface geology and soils are compared to the distribution of pebble-mulch gardens near Pueblo San Marcos in the Galisteo Basin, south of Santa Fe. The slope angle and aspect of 96 individual garden plots are also examined to determine the role of microenvironment as a siting consideration within the broader geological-pedological context. It is found that Anasazi pebble-mulch gardens were consistently sited on south-facing, relatively flat slopes of erosional benches, within naturally occurring surface/near surface deposits of gravel. This suggests that the Anasazi intentionally exploited regionally scaled variations in geology and soils in their pursuit of agricultural diversification. © 1993 John Wiley & Sons, Inc. 相似文献
330.
Franklin W. Koch Emily B. Voytek Frederick D. Day‐Lewis Richard Healy Martin A. Briggs John W. Lane Jr. Dale Werkema 《Ground water》2016,54(3):434-439
A new version of the computer program 1DTempPro extends the original code to include new capabilities for (1) automated parameter estimation, (2) layer heterogeneity, and (3) time‐varying specific discharge. The code serves as an interface to the U.S. Geological Survey model VS2DH and supports analysis of vertical one‐dimensional temperature profiles under saturated flow conditions to assess groundwater/surface‐water exchange and estimate hydraulic conductivity for cases where hydraulic head is known. 相似文献