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231.
232.
We studied the orientation of plaice (Pleuronectes platessa L.) in the open sea (Southern Bight of the North Sea) during May and June of 1979 and 1980, using continuous, on-line data from 6 fish equipped with transponding acoustic compass tags. During the day, fish swimming in midwater did not maintain their heading. At night, the same fish maintained their heading in a way that was consistent with active orientation to some external directional clue, but inconsistent with the use of an inertial guidance system. We believe this to be the first analysis to demonstrate the use of external guidance clues by fish in the open sea. Because fish were able to maintain a consistent heading in midwater by night, in the apparent absence of both visual and tactile clues, the external reference is likely to be geophysical. Possible clues include the electrical field generated by the flow of sea water through the geomagnetic field and the earth's magnetic field itself. 相似文献
233.
David H. Arnold Glendon W. Smalley Edward R. Buckner 《Environmental monitoring and assessment》1996,39(1-3):339-352
Relationships between forest communities and landtypes (the most detailed level of a hierarchical land classification system) were determined for the Prentice Cooper State Forest (PCSF), located on the southern tip of Walden Ridge, west of Chattanooga, Tennessee.Four extensive landtypes within the Mullins Cove area of PCSF were sampled: 1) broad sandstone ridges-south aspect (LT-3), 2) north sandstone slopes (LT-5), 3) south sandstone slopes (LT-6), and 4) plateau escarpment and upper sandstone slopes and benches-south aspect (LT-17). Rectangular, 0.04-hectare plots specified sub-plots for sampling overstory, midstory, sapling/shrub, seedling/herb forest strata, and physical site characteristics. Plots (139) were allocated by landtype using a random start with subsequent systematic location.Multivariate statistical techniques were used to 1) examine the distinctness of forest communities occurring among landtypes (discriminant analysis), 2) describe the forest communities occurring within landtypes (cluster analysis), and 3) determine factors controlling the spatial distribution of forest communities on the landscape (factor analysis).Different relative importance values of species among communities along with different community combinations among landtypes resulted in distinct forest vegetation among landtypes.Chestnut oak (Quercus prinus L.), white oak (Quercus alba L.), and shortleaf pine (Pinus echinata Miller) communities occurred on all four landtypes. Scarlet oak (Quercus coccinia Muenchh.) communities occurred on LT-5, LT-6, and LT-17. Black oak (Quercus velutina Lam.) communities occurred on LT-3 and LT-5. Yellow-poplar (Liriodendron tulipifera L.), northern red oak (Quercus rubra L.), and eastern hemlock (Tsuga canadensis (L.) Carr.), communities occurred only on LT-17.Landscape scale factors that varied along an elevation gradient were dominant in controlling spatial distribution of forest communities. Microsite factors were secondary controllers. Specific ecological factors could not be determined by factor analysis.Relatively distinct vegetation occurs among sampled landtypes on the PCSF. This study provides additional evidence that the land classification system divides the Mid-Cumberland Plateau landscape into distinct ecological units. 相似文献
234.
235.
Arnold Münster 《Die Naturwissenschaften》1948,35(11):343-344
236.
237.
Manoj Jha Jeffrey G. Arnold Philip W. Gassman Filippo Giorgi Roy R. Gu 《Journal of the American Water Resources Association》2006,42(4):997-1015
ABSTRACT: The Soil and Water Assessment Tool (SWAT) model was used to assess the effects of potential future climate change on the hydrology of the Upper Mississippi River Basin (UMRB). Calibration and validation of SWAT were performed using monthly stream flows for 1968–1987 and 1988–1997, respectively. The R2 and Nash‐Sutcliffe simulation efficiency values computed for the monthly comparisons were 0.74 and 0.69 for the calibration period and 0.82 and 0.81 for the validation period. The effects of nine 30‐year (1968 to 1997) sensitivity runs and six climate change scenarios were then analyzed, relative to a scenario baseline. A doubling of atmospheric CO2 to 660 ppmv (while holding other climate variables constant) resulted in a 36 percent increase in average annual streamflow while average annual flow changes of ?49, ?26, 28, and 58 percent were predicted for precipitation change scenarios of ?20, ?10, 10, and 20 percent, respectively. Mean annual streamflow changes of 51,10, 2, ?6, 38, and 27 percent were predicted by SWAT in response to climate change projections generated from the CISRO‐RegCM2, CCC, CCSR, CISRO‐Mk2, GFDL, and HadCMS general circulation model scenarios. High seasonal variability was also predicted within individual climate change scenarios and large variability was indicated between scenarios within specific months. Overall, the climate change scenarios reveal a large degree of uncertainty in current climate change forecasts for the region. The results also indicate that the simulated UMRB hydrology is very sensitive to current forecasted future climate changes. 相似文献
238.
Jaswinder Singh H. Vernon. Knapp J.G. Arnold Misganaw Demissie 《Journal of the American Water Resources Association》2005,41(2):343-360
ABSTRACT: The performance of two popular watershed scale simulation models — HSPF and SWAT — were evaluated for simulating the hydrology of the 5,568 km2 Iroquois River watershed in Illinois and Indiana. This large, tile drained agricultural watershed provides distinctly different conditions for model comparison in contrast to previous studies. Both models were calibrated for a nine‐year period (1987 through 1995) and verified using an independent 15‐year period (1972 through 1986) by comparing simulated and observed daily, monthly, and annual streamflow. The characteristics of simulated flows from both models are mostly similar to each other and to observed flows, particularly for the calibration results. SWAT predicts flows slightly better than HSPF for the verification period, with the primary advantage being better simulation of low flows. A noticeable difference in the models' hydrologic simulation relates to the estimation of potential evapotranspiration (PET). Comparatively low PET values provided as input to HSPF from the BASINS 3.0 database may be a factor in HSPF's overestimation of low flows. Another factor affecting baseflow simulation is the presence of tile drains in the watershed. HSPF parameters can be adjusted to indirectly account for the faster subsurface flow associated with tile drains, but there is no specific tile drainage component in HSPF as there is in SWAT. Continued comparative studies such as this, under a variety of hydrologic conditions and watershed scales, provide needed guidance to potential users in model selection and application. 相似文献
239.
Arnold L. Lum 《Environmental management》1978,2(5):423-430
Numbers of shorebirds visiting the Paiko Lagoon Wildlife Sanctuary, a small tropical estuary located on Oahu, Hawaii, are compared before and after environmental restoration of the lagoon. An attempt is made to examine both the biological impacts and policy implications of the project. The biological results indicate that shorebird abundance did not increase following restoration. On the other hand, public perceptions regarding the ecological value of the lagoon suggest that in spite of a lack of biological benefit to shorebirds, the lagoon was perceived by the public, particularly local residents, as being more ecologically valuable because it had been aesthetically improved. The discussion focuses on the interplay between scientific and non-scientific factors in natural resource decision making. 相似文献
240.
C. Santhi N. Kannan J. G. Arnold M. Di Luzio 《Journal of the American Water Resources Association》2008,44(4):829-846
Abstract: Physically based regional scale hydrologic modeling is gaining importance for planning and management of water resources. Calibration and validation of such regional scale model is necessary before applying it for scenario assessment. However, in most regional scale hydrologic modeling, flow validation is performed at the river basin outlet without accounting for spatial variations in hydrological parameters within the subunits. In this study, we calibrated the model to capture the spatial variations in runoff at subwatershed level to assure local water balance, and validated the streamflow at key gaging stations along the river to assure temporal variability. Ohio and Arkansas‐White‐Red River Basins of the United States were modeled using Soil and Water Assessment Tool (SWAT) for the period from 1961 to 1990. R2 values of average annual runoff at subwatersheds were 0.78 and 0.99 for the Ohio and Arkansas Basins. Observed and simulated annual and monthly streamflow from 1961 to 1990 is used for temporal validation at the gages. R2 values estimated were greater than 0.6. In summary, spatially distributed calibration at subwatersheds and temporal validation at the stream gages accounted for the spatial and temporal hydrological patterns reasonably well in the two river basins. This study highlights the importance of spatially distributed calibration and validation in large river basins. 相似文献