全文获取类型
收费全文 | 547篇 |
免费 | 32篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 15篇 |
大气科学 | 47篇 |
地球物理 | 135篇 |
地质学 | 192篇 |
海洋学 | 41篇 |
天文学 | 67篇 |
综合类 | 2篇 |
自然地理 | 85篇 |
出版年
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 17篇 |
2018年 | 15篇 |
2017年 | 14篇 |
2016年 | 13篇 |
2015年 | 17篇 |
2014年 | 22篇 |
2013年 | 26篇 |
2012年 | 18篇 |
2011年 | 30篇 |
2010年 | 11篇 |
2009年 | 15篇 |
2008年 | 17篇 |
2007年 | 18篇 |
2006年 | 17篇 |
2005年 | 16篇 |
2004年 | 19篇 |
2003年 | 21篇 |
2002年 | 14篇 |
2001年 | 10篇 |
2000年 | 8篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 13篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1993年 | 4篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 15篇 |
1984年 | 7篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 10篇 |
1972年 | 5篇 |
1969年 | 4篇 |
1967年 | 3篇 |
排序方式: 共有584条查询结果,搜索用时 687 毫秒
81.
Stream temperature is a complex function of energy inputs including solar radiation and latent and sensible heat transfer. In streams where groundwater inputs are significant, energy input through advection can also be an important control on stream temperature. For an individual stream reach, models of stream temperature can take advantage of direct measurement or estimation of these energy inputs for a given river channel environment. Understanding spatial patterns of stream temperature at a landscape scale requires predicting how this environment varies through space, and under different atmospheric conditions. At the landscape scale, air temperature is often used as a surrogate for the dominant controls on stream temperature. In this study we show that, in regions where groundwater inputs are key controls and the degree of groundwater input varies in space, air temperature alone is unlikely to explain within-landscape stream temperature patterns. We illustrate how a geologic template can offer insight into landscape-scale patterns of stream temperature and its predictability from air temperature relationships. We focus on variation in stream temperature within headwater streams within the McKenzie River basin in western Oregon. In this region, as in other areas of the Pacific Northwest, fish sensitivity to summer stream temperatures continues to be a pressing environmental issue. We show that, within the McKenzie, streams which are sourced from deeper groundwater reservoirs versus shallow subsurface flow systems have distinct summer temperature regimes. Groundwater streams are colder, less variable and less sensitive to air temperature variation. We use these results from the western Oregon Cascade hydroclimatic regime to illustrate a conceptual framework for developing regional-scale indicators of stream temperature variation that considers the underlying geologic controls on spatial variation, and the relative roles played by energy and water inputs. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
82.
83.
Grant Ian Thrall 《The Professional geographer》1981,33(4):450-456
Because the property tax is structurally tied to market values of dwellings through the assessment function, rapidly increasing market values may beget rapid increases in property taxes. Public awareness of this process was instrumental in California's 1978 passage of the Jarvis-Gann Amendment. Millage rates should be indexed to counterbalance changes in market values. 相似文献
84.
Summary. The governing equation derived by England & M c Kenzie for the deformation of a thin viscous shell contains an error. We give the correct derivation here and correct those figures where the change makes a visible difference. The correct results differ quantitatively from those of England & M c Kenzie but their conclusions are not affected. 相似文献
85.
Abstract The uniform stretching model has been applied to seismic reflection profiles and well-log information from the Pearl River Mouth Basin on the northern flank of the South China Sea. Stretching factors were calculated from subsidence curves determined from the stratigraphy by using the backstripping technique to remove the effects of compaction and sediment loading. Variations in rift topography, palaeobathymetry and global sea-level v/ere taken into account. We argue that the Pearl River Mouth Basin formed by lithospheric extension by a factor of about 1.8, lasting from Late Cretaceous to late Oligocene times. Stretching factors calculated from subsidence agree with those determined from the geometry of normal faulting and from crustal thinning. Thus there is no indication of a significant discrepancy between the different estimates of stretching. The geometry of faulting suggests that considerable amounts of local footwall uplift occurred during the rifting period. Small differences between the observed and calculated subsidence curves (∽ 400 m in the middle Miocene) are best explained by minor amounts of extension ( β ∽ 1.1). The time-temperature history of sediments within the basin has also been calculated so that expected vitrinite reflectance and oil abundance could be determined. The results are consistent with each other and are in reasonable agreement with observations from wells. 相似文献
86.
We present X-ray images from the P78-1 satellite for a long-lasting burst at 20 cm wavelength mapped with the Very Large Array on 19 May, 1979 by Velusamy and Kundu (1981). The decimeter wave observations were originally interpreted in terms of two models, one invoking thermal electrons radiating at low harmonics of the gyrofrequency, and the other invoking mildly relativistic electrons emitting gyrosynchrotron radiation. If indeed the 20 cm source is thermal, it should also be visible in soft X-rays, while if it is nonthermal, the soft X-ray emission should be weak or spatially or temporally distinct from the 20 cm burst. We find that only one of the three 20 cm sources was approximately co-spatial with the soft X-ray source, and that it was only partially thermal. The 20 cm burst is therefore primarily decimeter type IV emission from mildly relativistic electrons of the post-flare phase. The long lifetime (? 2h) and smooth temporal variation of the burst belie its nonthermal nature and suggest continuous acceleration as well as long term storage of energetic electrons. 相似文献
87.
Austin T.C. Edson J.B. McGillis W.R. Purcell M. Petitt R.A. Jr. McElroy M.K. Grant C.W. Ware J. Hurst S.K. 《Oceanic Engineering, IEEE Journal of》2002,27(2):228-234
Underwater observatories with real-time data and virtually unlimited power transmission capabilities compared to traditional oceanographic moorings are beginning to provide scientists with continuous access to the coastal and open ocean. However, for any coastal observatory to serve as a cost-effective system for the collection of long-term scientific and environmental data, it must have a simple, upgradeable power and telemetry system and an instrument interface that is compatible with existing standards. It must be designed for extended environmental exposure and ease of service to avoid high maintenance costs. Most importantly, the observatory must be accessible to all potential users, including students, scientists, engineers, and policy makers. This strategy was applied to the design of the Martha's Vineyard Coastal Observatory on the south shore of the island of Martha's Vineyard. The new facility, and in particular its system architecture, as developed by the Woods Hole Oceanographic Institution with support from the National Science Foundation, are described 相似文献
88.
Active Tectonics of the Mediterranean Region 总被引:32,自引:0,他引:32
Dan McKenzie 《Geophysical Journal International》1972,30(2):109-185
89.
Adrian Gilli Flavio S. Anselmetti Daniel Ariztegui† Milan Beres† Judith A. McKenzie Vera Markgraf‡ 《Sedimentology》2005,52(1):1-23
The results of a seismic stratigraphic analysis of a closed lake basin, Lago Cardiel, in southernmost South America are reported. Very few high-resolution, continental records spanning the Late Quaternary have been obtained from this region. Seismic sequence stratigraphic analysis allows a reconstruction of lake level variations. Two major hiatuses of unknown age occurred during the early evolution of the basin with the deposition of an alluvial fan in a restricted area in the intervening time period. Following the development of a relatively shallow lake during the late Pleistocene and a short desiccation pulse around 11 220 14C yr BP, a transgression of over 135 m occurred at the beginning of the Holocene. The transgression was associated with the formation of beach ridges preserved in the lake stratigraphy on the floor of the modern Lago Cardiel at four different elevations. The preservation of largely unreworked beach ridges indicates a stepwise rise in the lake level. There is no seismic evidence of a major lowering of the lake below modern level during the entire Holocene. Deposition since the mid-Holocene is marked by strong lateral differences in sediment accumulation with a depocentre slightly to the north of the basin midpoint and a pronounced mounded distribution. Seismic reflection geometries, as well as sedimentological characteristics indicate a lacustrine contourite drift covering an area of 80–100 km2. As Lago Cardiel is under the influence of westerly winds, these most likely drove lake circulation. The identification of drowned beach ridges and of contourite drifts illustrates that high-resolution seismic stratigraphy is not only a powerful tool in reconstructing past lake level elevations for closed lake basins, but it can also provide information about the rate of lake level changes and the presence and strength of lake currents. 相似文献
90.
Summary. A simplified model of convection in the mantle is used to investigate the transient effect of cooling a fluid layer from above, The model, representing the mantle overlain by the lithosphere, consists of a two-dimensional fluid layer overlain by a solid conducting lid. The initial temperature of both layers is the same, with the top surface of the lid kept at 0°C throughout. We observe the onset of small-scale flow in the model. In the absence of internal heating the behaviour of the system is controlled by the Rayleigh number, R , and the ratio of the thicknesses of the two layers, a . The onset time of convection as defined by reference to conduction temperature profiles is related simply to a boundary layer critical Rayleigh number. The mean temperature profiles for the convection model are also compared with the observed depth—age relation for oceanic lithosphere and the results are used to estimate the viscosity of the mantle. 相似文献