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331.
Land-use changes on the Sheyenne Delta in southeastern North Dakota, USA, have prompted research on impacts to the unconfined
Sheyenne Delta aquifer (SDA). This study examines effects of the saline discharge of a flowing artesian well that taps the
Dakota aquifer (DAK) on SDA groundwater chemistry and soil salinity. Objectives were to map the saline plume in the SDA using
induction techniques, to assess chloride migration in the SDA, and to evaluate induction sensitivity to moderately saline
sands. Induction data, collected in a 2.9-ha grid, were compared to 31 soil profiles analyzed for gravimetric moisture, electrical
conductivity, and chloride. Soil salinization is widespread, but only 7% of the area meets the 4-dS/m threshold for saline
soils. SDA chloride distribution was determined on transects oriented with and perpendicular to the flow path determined from
induction readings. Chloride was detected in the aquifer 550 m from the source, indicating a transport rate of 21 m/yr. Complex
recharge and discharge patterns and hummocky relief contribute to a wide chloride plume at this site. A mass balance based
on soil-water content and chloride concentration shows that only 4% of the chloride from the DAK well remains in the grid
volume.
Received, January 1998 · Revised, January 1999 · Accepted, March 1999 相似文献
332.
Modeling alternative paths of chemical evolution of Na-HCO3-type groundwater near Oak Ridge, Tennessee, USA 总被引:2,自引:0,他引:2
This paper demonstrates that both cation exchange, a commonly invoked mechanism, and silicate hydrolysis, which is less commonly
considered, can produce Na-HCO3-type water in sedimentary rocks. Evolution of Na-HCO3 groundwater beneath the Oak Ridge Reservation, Tennessee, USA, was studied by comparing observed end-member groundwater composition
from multiport samplers to compositions generated by reaction-path geochemical models. Observed groundwater compositions could
be reproduced by either the silicate-hydrolysis model or the cation-exchange model. Secondary minerals precipitated in the
silicate-hydrolysis model are similar to those present along fractures in the shale and carbonate host rocks, and observed
molar Sr2+/Ca2+ ratios more closely resemble evolution from shale weathering. Both mechanisms should be considered to understand the evolution
of Na-HCO3 groundwater.
Received, April 1998 · Revised, January 1999 · Accepted, March 1999 相似文献
333.
PATRICK J. MULHOLLAND G. RONNIE BEST CHARLES C. COUTANT GEORGE M. HORNBERGER JUDY L. MEYER PETER J. ROBINSON JOHN R. STENBERG R. EUGENE TURNER FRANCISCO VERA-HERRERA ROBERT G. WETZEL 《水文研究》1997,11(8):949-970
The south-eastern United States and Gulf Coast of Mexico is physiographically diverse, although dominated by a broad coastal plain. Much of the region has a humid, warm temperate climate with little seasonality in precipitation but strong seasonality in runoff owing to high rates of summer evapotranspiration. The climate of southern Florida and eastern Mexico is subtropical with a distinct summer wet season and winter dry season. Regional climate models suggest that climate change resulting from a doubling of the pre-industrial levels of atmospheric CO2 may increase annual air temperatures by 3–4°C. Changes in precipitation are highly uncertain, but the most probable scenario shows higher levels over all but the northern, interior portions of the region, with increases primarily occurring in summer and occurring as more intense or clustered storms. Despite the increases in precipitation, runoff is likely to decline over much of the region owing to increases in evapotranspiration exceeding increases in precipitation. Only in Florida and the Gulf Coast areas of the US and Mexico are precipitation increases likely to exceed evapotranspiration increases, producing an increase in runoff. However, increases in storm intensity and clustering are likely to result in more extreme hydrographs, with larger peaks in flow but lower baseflows and longer periods of drought. The ecological effects of climate change on freshwaters of the region include: (1) a general increase in rates of primary production, organic matter decomposition and nutrient cycling as a result of higher temperatures and longer growing seasons: (2) reduction in habitat for cool water species, particularly fish and macroinvertebrates in Appalachian streams; (3) reduction in water quality and in suitable habitat in summer owing to lower baseflows and intensification of the temperature–dissolved oxygen squeeze in many rivers and reservoirs; (4) reduction in organic matter storage and loss of organisms during more intense flushing events in some streams and wetlands; (5) shorter periods of inundation of riparian wetlands and greater drying of wetland soils, particularly in northern and inland areas; (6) expansion of subtropical species northwards, including several non-native nuisance species currently confined to southern Florida; (7) expansion of wetlands in Florida and coastal Mexico, but increase in eutrophication of Florida lakes as a result of greater runoff from urban and agricultural areas; and (8) changes in the flushing rate of estuaries that would alter their salinity regimes, stratification and water quality as well as influence productivity in the Gulf of Mexico. Many of the expected climate change effects will exacerbate current anthropogenic stresses on the region's freshwater systems, including increasing demands for water, increasing waste heat loadings and land use changes that alter the quantity and quality of runoff to streams and reservoirs. Research is needed especially in several critical areas: long-term monitoring of key hydrological, chemical and biological properties (particularly water balances in small, forested catchments and temperature-sensitive species); experimental studies of the effects of warming on organisms and ecosystem processes under realistic conditions (e.g. in situ heating experiments); studies of the effects of natural hydrological variation on biological communities; and assessment of the effects of water management activities on organisms and ecosystem processes, including development and testing of management and restoration strategies designed to counteract changes in climate. © 1997 John Wiley & Sons, Ltd. 相似文献