全文获取类型
收费全文 | 234篇 |
免费 | 8篇 |
国内免费 | 9篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 27篇 |
地球物理 | 64篇 |
地质学 | 82篇 |
海洋学 | 22篇 |
天文学 | 10篇 |
综合类 | 7篇 |
自然地理 | 33篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 8篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 5篇 |
2016年 | 6篇 |
2015年 | 4篇 |
2014年 | 12篇 |
2013年 | 19篇 |
2012年 | 9篇 |
2011年 | 7篇 |
2010年 | 13篇 |
2009年 | 9篇 |
2008年 | 13篇 |
2007年 | 12篇 |
2006年 | 10篇 |
2005年 | 6篇 |
2004年 | 4篇 |
2003年 | 4篇 |
2002年 | 13篇 |
2001年 | 9篇 |
2000年 | 3篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 6篇 |
1996年 | 2篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 2篇 |
1965年 | 1篇 |
1956年 | 1篇 |
1949年 | 1篇 |
1946年 | 1篇 |
1925年 | 1篇 |
排序方式: 共有251条查询结果,搜索用时 26 毫秒
201.
Geoff A. Wilson 《Geoforum》2009,40(2):269-280
Based on reconceptualisations of multifunctional agriculture as a normative spectrum of decision-making (strong to weak multifunctionality) bounded by productivist and non-productivist action and thought [Hollander, G.M., 2004. Agricultural trade liberalization, multifunctionality, and sugar in the south Florida landscape. Geoforum 35, 299-312; Holmes, J., 2006. Impulses towards a multifunctional transition in rural Australia: gaps in the research agenda. Journal of Rural Studies 22, 142-160; Wilson, G.A., 2007. Multifunctional Agriculture: A Transition Theory Perspective. CAB International, Wallingford], this paper argues that there is currently insufficient research into the geography of multifunctionality. Building on current human geography debates about issues of scale, the paper suggests that we should conceive of multifunctionality as a spatially complex nested hierarchy comprising different interlinked ’layers’ of multifunctional decision-making ranging from the farm level to the national and global levels. It suggests that the notion of multifunctional agriculture only makes sense if it is applied at the farm level as the most important spatial scale for the implementation of multifunctional action ‘on the ground’. Multifunctionality can be interpreted as having ’direct’ expression only at the ’lower’ geographical scales (i.e. farm, community and regional levels in particular) while the regional, national and global levels show ’indirect’ expressions of multifunctionality that are mediated by local level actors in order to find tangible expression on the ground. The notion of global-level multifunctionality is the most challenging, as this level lacks political and ideological coherence about the required directions necessary for implementation of strong multifunctionality pathways. The paper concludes by arguing that much work still awaits those investigating the spatiality of multifunctionality, in particular with regard to the question whether global-level strong multifunctionality is possible, or whether strong multifunctionality in one territory is predicated on weak multifunctionality in others. 相似文献
202.
Jenet Austin Lu Zhang Roger N. Jones Paul Durack Warrick Dawes Peter Hairsine 《Climatic change》2010,100(3-4):607-631
Climate change has potentially significant implications for hydrology and the quantity and quality of water resources. This study investigated the impacts of climate change and revegetation on water and salt balance, and stream salt concentration for catchments within the Murray-Darling Basin, Australia. The Biophysical Capacity to Change model was used with climate change scenarios obtained using the CSIRO DARLAM 125 (125 km resolution) and Cubic Conformal (50 km resolution) regional climate models. These models predicted up to 25% reduction in mean annual rainfall and a similar magnitude of increase in potential evapotranspiration by 2070. Relatively modest changes in rainfall and temperature can lead to significant reductions in mean annual runoff and salt yield and increases in stream salt concentrations within the Basin. The modelled reductions in mean annual runoff were up to 45% in the wetter/cooler southern catchments and up to 64% in the drier/hotter western and northern catchments. The maximum reductions in salt yield were estimated to be up to 34% in the southern catchments and up to 49% in the northern and western catchments. These changes are associated with average catchment rainfall decreases of 13 to 21%. The results suggest that percentage changes in rainfall will be amplified in runoff. This study demonstrates that climate change poses significant challenges to natural resource management in Australia. 相似文献
203.
Julie A. Vano Nathalie Voisin Lan Cuo Alan F. Hamlet Marketa McGuire Elsner Richard N. Palmer Austin Polebitski Dennis P. Lettenmaier 《Climatic change》2010,102(1-2):261-286
Climate change is projected to result, on average, in earlier snowmelt and reduced summer flows in the Pacific Northwest, patterns not well represented in historical observations used in water planning. We evaluate the sensitivities of water supply systems in the Puget Sound basin cities of Everett, Seattle, and Tacoma to historical and projected future streamflow variability and water demands. We simulate streamflow for the 2020s, 2040s, and 2080s using the distributed hydrology–soil–vegetation model (DHSVM), driven by downscaled ensembles of climate simulations archived from the 2007 IPCC Fourth Assessment Report. We use these streamflow predictions as inputs to reservoir system models for the three water supply systems. Over the next century, under average conditions all systems are projected to experience declines and eventual disappearance of the springtime snowmelt peak. How these shifts affect management depends on physical characteristics, operating objectives, and the adaptive capacity of each system. Without adaptations, average seasonal drawdown of reservoir storage is projected to increase in all three systems throughout the 21st century. Reliability of all systems in the absence of demand increases is robust through the 2020s however, and remains above 98% for Seattle and Everett in the 2040s and 2080s. With demand increases, however, reliability of the systems in their current configurations and with current operating policies progressively declines through the century. 相似文献
204.
Abstract Two‐dimensional pattern matching has been used to delineate raining areas of clouds from GATE and Montreal GOES visible and IR satellite data, with radar as ground truth. For the cases examined, the cloud cover was of the order of 4 times larger than the rain area, requiring skill to separate out low‐thick or high‐thin non‐precipitating clouds from cumulus systems, which is difficult using a single threshold. The more flexible approach described here has allowed useful rain maps to be generated for all the types of weather systems examined. The optimum boundary separating raining from non‐raining areas is relatively insensitive to diurnal and day‐to‐day variations, but is different for the tropical Atlantic and for Montreal. 相似文献
205.
Abstract Twenty‐seven radar cells from the Tropical Atlantic observed during GATE were followed and measurements of their fluxes and areas for initial time increments T0 were fitted to various extrapolation schemes. The extrapolation procedure that gave the smallest error inforecasting the changes influx and area, was found to be the linear one and the optimum increment T0 was about 30 min. However, even though these techniques have the advantage of establishing a trend in the behaviour of the flux and area with time, a comparison of the forecast errors from the linear extrapolation scheme with those from the “status quo” (persistence) assumption shows little if any improvement. A technique including both cell motion and internal changes influx and area of the rain cells was developed to evaluate the accuracy of rain accumulation forecasts. It was found that the errors generated by the “status quo” assumption were of the order of 77% for a 2‐h forecast with little improvement by allowing for the extrapolation of area and flux. 相似文献
206.
Thompson J Roach A Eaglesham G Bartkow ME Edge K Mueller JF 《Marine pollution bulletin》2011,62(12):2869-2875
Perfluorinated alkyl compounds (PFCs) including perfluorooctane sulphonate (PFOS) and perfluorooctanoate (PFOA) were measured in environmental samples collected from around Homebush Bay, an urban/industrial area in the upper reaches of Sydney Harbour and Parramatta River estuary. Water, surface sediment, Sea Mullet (Mugil cephalus), Sydney Rock Oyster (Saccostrea commercialis) and eggs of two bird species; White Ibis (Threskiornis molucca), and Silver Gull (Larus novaehollandiae) were analysed. In most samples PFOS was the dominant PFC. Geometric mean PFOS concentrations were 33 ng/g ww (wet weight) in gull eggs, 34 ng/g ww in ibis eggs, and 1.8 ng/g ww and 66 ng/g ww in Sea Mullet muscle and liver, respectively. In sediment the PFOS geometric mean was 1.5 ng/g, in water average PFOS and PFOA concentrations ranged from 7.5 to 21 ng/L and 4.2 to 6.4 ng/L, respectively. In oysters perfluorododecanoic acid was most abundant, with a geometric mean of 2.5 ng/g ww. 相似文献
207.
Martin J. Austin Gerd Masselink Paul E. Russell Ian L. Turner Chris E. Blenkinsopp 《Coastal Engineering》2011
Field experiments were conducted on a low-gradient, high-energy sandy beach (Truc Vert, France) and a steep, low-energy gravel beach (Slapton, UK) to examine alongshore-directed currents within the swash zone. At Truc Vert, data were collected over 33 tidal cycles with offshore significant wave heights of 1–4 m and periods of 5–12 s. At Slapton data were collected during 12 tides with wave heights of 0.3–1 m and periods of 4–9 s. The swash motion was predominantly at infragravity frequencies at Truc Vert and incident frequencies at Slapton. 相似文献
208.
209.
Oyster Condition Index (CI) was partitioned, using a moving average filter, into seasonal cycles and long-term trends in the James, York, and Rappahannock rivers for the period 1970–1983. Seasonal cyclic fluctuations in CI could be explained partially by changes in salinity and number of days within various temperature regimes. Long-term trends in the James River show a steady increase in CI over the study period, while a concurrent decline was noted in the Rappahannock River. Superimposed on these trends is a 4 to 5 yr cycle that is in synchrony with river discharge (salinity). In the York River, CI peaked in 1975–1976 at all stations. Measured environmental parameters do not sufficiently explain the trends. We speculate that the differences in the Rappahannock and James rivers may be due to a decline in bottom oxygen as a result of gravitational circulation differences. 相似文献
210.
Dale R. Van Stempvoort D. Ross MacKay Geoff Koehler Pamela Collins Susan J. Brown 《水文研究》2021,35(9):e14342
Concepts and terms used in previous multidisciplinary studies of tile-drained aquitard-dominated catchments (TDADC) are inconsistent and confusing. We provide a well-defined, comprehensive conceptual model of the subsurface hydrology of TDADC by selecting seven mutually compatible and consistent concepts. These concepts are: (1) groundwater as the main source of baseflow in headwater streams, (2) dominance of ‘pre-event’ water in stormflow, (3) importance of both macropores and matrix, (4) changes in flowpaths with rate of stream discharge, (5) dominance of shallow, lateral subsurface flow, (6) interactive nature of subsurface water, (7) transpiration of groundwater. This conceptual model was successfully ‘field-tested’ by examining data collected in a TDADC in a rural area of southern Ontario, Canada. The data consist mainly of chemical and isotopes tracers in water samples (headwater streams, groundwater, precipitation, tile water, soil-surface water), supplemented by water levels and meteorological data. 相似文献