全文获取类型
收费全文 | 306篇 |
免费 | 15篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 9篇 |
地球物理 | 58篇 |
地质学 | 139篇 |
海洋学 | 33篇 |
天文学 | 35篇 |
综合类 | 2篇 |
自然地理 | 41篇 |
出版年
2023年 | 2篇 |
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 8篇 |
2018年 | 14篇 |
2017年 | 7篇 |
2016年 | 8篇 |
2015年 | 11篇 |
2014年 | 8篇 |
2013年 | 16篇 |
2012年 | 8篇 |
2011年 | 18篇 |
2010年 | 13篇 |
2009年 | 12篇 |
2008年 | 15篇 |
2007年 | 18篇 |
2006年 | 15篇 |
2005年 | 12篇 |
2004年 | 10篇 |
2003年 | 10篇 |
2002年 | 12篇 |
2001年 | 12篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 10篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有321条查询结果,搜索用时 15 毫秒
51.
Impacts of afforestation on groundwater resources and quality 总被引:4,自引:0,他引:4
Plans to double the proportion of land under forest cover in Ireland by the year 2035 have been initiated. The plan, primarily
financially driven, ignores potential environmental impacts of forestry, particularly impacts on groundwater resources and
quality. Since groundwater supplies almost 25% of Ireland's total potable water, these impacts are important. Field investigations
indicate that afforestation leads to a reduction in runoff by as much as 20%, mainly due to interception of rainfall by forest
canopies. Clearfelling has the opposite impact. Implications are that uncoordinated forestry practices can potentially exacerbate
flooding. Groundwater recharge is affected by forestry, largely due to greater uptake of soil water by trees and to increased
water-holding capacity of forest soils, arising from higher organic contents. Recharge rates under forests can be reduced
to one tenth that under grass or heathland. Groundwater quality may be affected by enhanced acidification and nitrification
under forests, due partly to scavenging of atmospheric pollutants by forest canopies, and partly to greater deposition of
highly acid leaf litter. The slower recharge rates of groundwater under forests lead to significant delays in manifestation
of deterioration in groundwater quality.
Electronic Publication 相似文献
52.
Many of the relationships used in coupled land–atmosphere models to describe interactions between the land surface and the atmosphere have been empirically parameterized and thus are inherently dependent on the observational scale for which they were derived and tested. However, they are often applied at scales quite different than the ones they were intended for due to practical necessity. In this paper, a study is presented on the scale-dependency of parameterizations which are nonlinear functions of variables exhibiting considerable spatial variability across a wide range of scales. For illustration purposes, we focus on parameterizations which are explicit nonlinear functions of soil moisture. We use data from the 1997 Southern Great Plains Hydrology Experiment (SGP97) to quantify the spatial variability of soil moisture as a function of scale. By assuming that a parameterization keeps its general form the same over a range of scales, we quantify how the values of its parameters should change with scale in order to preserve the spatially averaged predicted fluxes at any scale of interest. The findings of this study illustrate that if modifications are not made to nonlinear parameterizations to account for the mismatch of scales between optimization and application, then significant systematic biases may result in model-predicted water and energy fluxes. 相似文献
53.
Petrogenesis of calc-alkaline,shoshonitic and associated ultrapotassic Oligocene volcanic rocks from the Northwestern Alps,Italy 总被引:1,自引:0,他引:1
G. Venturelli R. S. Thorpe G. V. Dal Piaz A. Del Moro P. J. Potts 《Contributions to Mineralogy and Petrology》1984,86(3):209-220
Along the Western Alps there is geological evidence of late-Alpine (Oligocene) magmatic activity which clearly postdates the
Lepontine (Eocene-early Oligocene) metamorphism and related deformation of the Alpine nappe pile. This magmatic activity was
notably delayed in relation to the most important convergent processes and may be related to buoyancy of lithosphere, tensional
tectonics and thermal updoming subsequent to the collision between the Eurasian and African plates. The geochemical features
of the rocks and the geophysical characteristics of the Alpine chain, suggest that: (a) shoshonitic and calcalkaline melts
may have been generated by partial melting of metasomatized peridotitic material and subsequent fractional crystallization
and crustal contamination; silicic andesites and latites, however, could have been also derived from metasomatized eclogite
or deep continental crust material; (b) the ultrapotassic lamprophyres with high K, P, LREE, Th, Zr, U and high 87Sr/86Sr ratios were generated by partial melting of strongly metasomatized mantle; the varied Sr-isotopic ratios may partially
also reflect additional radiogenic component from the continental crust following magma segregation from the source. 相似文献
54.
Mark J. Potts 《Contributions to Mineralogy and Petrology》1972,36(4):249-264
The Preacher Creek ultramafic body is a small, lenticular-shaped intrusion of peridotite exposed in an ancient (2400–2500 m.y.), regionally metamorphosed terrane in southeastern Wyoming, U.S.A. The central core of the body consists of clinopyroxene-olivine peridotite and is surrounded by a marginal rim of peridotite in which orthopyroxene and plagioclase also occur as primary minerals. Alteration of primary minerals is relatively minor. However, at the contact with the country rock progressive alteration of the peridotite to actinolite and chlorite is locally severe. Chemical study of the effect of this alteration indicates that no more than minor changes from the primary composition of the peridotite have occurred. Petrographic studies reveal accumulative textures characteristic of stratiform complexes. Cryptic layering in the body is indicated by partial chemical analyses of the two major primary minerals, olivine and clinopyroxene.The body is inferred to have formed within the earth's crust by fractional crystallization and gravity accumulation of mafic minerals from a gabbroic magma that was differentiating along a tholeiitic trend. Subsequent to (or during) crystallization the body was remobilized, folded, and emplaced in its present site as a tectonic intrusion. Ultramafic intrusions with chemical, mineralogical, and structural features similar to the Preacher Creek body may be best explained perhaps as crystalline accumulates formed in volcanic magma chambers. 相似文献
55.
John Stamatakos Rob Van Der Voo Ben Van Der Pluijm Stephen Potts Trond Torsvik 《Geophysical Journal International》1994,119(3):1009-1013
56.
57.
58.
Spatially enabled bushfire recovery 总被引:1,自引:0,他引:1
Over the last decade growth in spatial information use for disaster management has been considerable. Maps and spatial data are now recognized as critical elements in each of the four phases of disaster management: mitigation, preparedness, response, and recovery. The use of spatial information to support the phases of mitigation, preparedness and response to bushfires is widely understood. Less attention, however, has been given to the role of spatial information in the recovery. Moreover, the application of the spatially enabled society concept to bushfire recovery has not been explored. This paper explores the role that spatial information plays and could play in the recovery phase of a bushfire disaster. The bushfires in Victoria, Australia that took place during February 2009 are used as the primary case study. It is found that: Spatial information for recovery requires a pre-existing infrastructure; Spatial capacity must be developed across agencies dealing with recovery; Spatially enabled address and parcel information are the key dataset required to support all recovery tasks; Spatial integration of bushfire datasets (spread and intensity) require linking with planning regimes, and Spatial information that is volunteered could be incorporated into recovery activities. 相似文献
59.
This article uses accessibility as an analytical tool to examine health care access among immigrants in a multicultural urban setting. It applies and improves on two widely used accessibility models—the gravity model and the two-step floating catchment area model—in measuring spatial accessibility by Mainland Chinese immigrants in the Toronto Census Metropolitan Area. Empirical data on physician-seeking behaviors are collected through two rounds of questionnaire surveys. Attention is focused on journey to physician location and utilization of linguistically matched family physicians. Based on the survey data, a two-zone accessibility model is developed by relaxing the travel threshold and distance impedance parameters that are traditionally treated as a constant in the accessibility models. General linear models are used to identify relationships among spatial accessibility, geography, and socioeconomic characteristics of Mainland Chinese immigrants. The results suggest a spatial mismatch in the supply of and demand for culturally sensitive care, and residential location is the primary factor that determines spatial accessibility to family physicians. The article yields important policy implications. 相似文献
60.
Edmund M. Harris Deborah G. Martin Colin Polsky Lillian Denhardt Abigail Nehring 《The Professional geographer》2013,65(2):345-361
Many recent studies have applied satellite remote sensing data to large-scale hydrologic and biospheric modeling. It is widely accepted that the thermal infrared observations from the Advanced Very High Resolution Radiometer (AVHRR) have the potential to estimate land surface conditions, such as surface temperature, near surface air temperature, and near surface water vapor. In this study, algorithms to estimate all three variables are presented and applied to an area covering the state of Oklahoma for a six day period in August, 1994. The results were validated using ground observations from the 111 station Oklahoma Mesonet. Validation of the remote sensing algorithms with Mesonet observations produced comparable results to previous validation studies. In addition, the validation process revealed inadequacies in thermal modeling that had not been detected in previous validation studies leading to the development of a new approach to estimate atmospheric water vapor. 相似文献