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181.
L. M. Shown G. C. Lusby F. A. Branson 《Journal of the American Water Resources Association》1972,8(6):1265-1272
Precipitation, soil moisture, runoff, and vegetation were measured on two, 5- to 10-acre, big sagebrush (Artemisia tridentata) watersheds and two, equally small, beardless bluebunch wheatgrass (Agrophron inerme) watersheds that were converted from big sagebrush in 1967. The watersheds are located near Wolcott, Colorado, at an elevation of 7,200 feet, and are mantled with 2 to 3 feet of silty clay soils. Annual precipitation was about 13.5 inches; about 9 inches occurred as rain or snow from April through October and about 4.5 inches accumulated as a snowpack from November through March. Evapotranspiration was about 2 inches greater in 1968 and 1 inch greater in 1969 from the sagebrush watersheds than from the grass watersheds. With a mature stand of grass in 1970 and 1971 the differences in evapotranspiration were within the range of differences measured during the 3-year calibration period when all four watersheds were sagebrush. Water use was similar in the top 1 foot of soil but slightly more water was used by the grass in the 1- to 2-foot zone and more water being used by the sagebrush below 2 feet. Soil-water potential data indicated that only the big sagebrush used a small amount of water from the fractured shale at depths below 40 inches. Sagebrush used more water in August and September than the grass. 相似文献
182.
ABSTRACT: A framework for sensitivity and error analysis in mathematical modeling is described and demonstrated. The Lake Eutrophication Analysis Procedure (LEAP) consists of a series of linked models which predict lake water quality conditions as a function of watershed land use, hydrolgic variables, and morphometric variables. Specification of input variables as distributions (means and standard errors) and use of first-order error analysis techniques permits estimation of output variable means, standard errors, and confidence ranges. Predicted distributions compare favorably with those estimated using Monte-Carlo simulation. The framework is demonstrated by applying it to data from Lake Morey, Vermont. While possible biases exist in the models calibrated for this application, prediction variances, attributed chiefly to model error, are comparable to the observed year-to-year variance in water quality, as measured by spring phosphorus concentration, hypolimnetic oxygen depletion rate, summer chlorophyll-a, and summer transparency in this lake. Use of the framework provides insight into important controlling factors and relationships and identifies the major sources of uncertainty in a given model application. 相似文献
183.
David F. Kibler John M. Hrubovcak David C. Froehlich 《Journal of the American Water Resources Association》1981,17(3):458-465
The lack of uniform techniques for estimating design discharges in ungaged areas is a source of growing concern in the courts now faced with challenges to floodplain boundaries and culvert design for highway crossings. This paper summarizes a court case in which calculations of the design discharge and the hydraulic backwater effects of a major highway culvert were contested by the plaintiff. Emphasis in the paper is placed on the variation in computed flows and the interpretation of the court in the face of diverse hydrologic methods for the ungaged watershed. The results of a preliminary evaluation of ungaged watershed methods applicable to Pennsylvania are also reported in terms of standard error and bias. 相似文献
184.
G. Aron D. F. Kibler C. J. Tagliati 《Journal of the American Water Resources Association》1981,17(4):691-698
: The construction of a flood peak index map was attempted for use by hydrologists in the simple format of rainfall maps. Since flood peaks are highly dependent on watershed area, the effect of area was removed. By regression analysis flood peaks of 2.33 and 100-year return periods were found to be proportional to watershed area to the 0.8 and 0.7 powers, respectively. Therefore, indices C2 33= Q2 33/A0.7 were completed at each gage and plotted on a Pennsylvania map. It was attempted to further remove some of the scatter by regression of C with several other watershed parameters like slope, percent forest cover, and watershed shape, but no significant correlation could be found. The index maps, drawn without attenuation of the scatter, can be used by hydrologists to compute flood peaks as Q = CAn (with n = 0.8 and 0.7 for the 2.33 and 100-year flood peaks, respectively). Flood peak safety factors can be based on visual observation of the index variation in the vicinity of the location for which the flood peak estimate is needed. 相似文献
185.
David F. Kibler David C. Froelich Gert Aron 《Journal of the American Water Resources Association》1981,17(2):270-274
ABSTRACT: The impact of man made change on the hydrology of developing watersheds is frequently measured in terms of the ratio: flood peak after development to flood peak before development over a range of return periods. However, the analysis of urbanization effects on flood frequency presents a vexing problem because of a general lack of flood data in urban areas and also because of nonstationarity in the development process. Clearly, the flood peak ratio depends on the impervious fraction and percent of basin sewered and these factors have been taken into account in recent urban flood peak models. In genral, these models are developed either by: (1) split sample analysis of available annual flood data, or (2) by computer simulation using mathematical watershed models capable of representing man made changes. The present paper discusses the results of work in progress to characterize the impact of urbanization on small developing watersheds in Pennsylvania. 相似文献
186.
Global nitrogen (N) emission and deposition have been increased rapidly due to massive mobilization of N which may have longreaching
impacts on ecosystems. Many agricultural and forest ecosystems have been identified as secondary N sources. In the present
study, the input-output budget of inorganic N in a small forested watershed of subtropical China was investigated. Inorganic N wet
deposition and discharge by stream water were monitored from March, 2007 to February, 2009. The concentrations and fluxes of
inorganic N in wet precipitation and stream water and net retention of N were calculated. Global N input by dry deposition and
biological fixation and N output by denitrification for forested watersheds elsewhere were reported as references to evaluate whether
the studied forested watershed is a source or a sink for N. The results show that the inorganic N output by the stream water is mainly
caused by NO3??-N even though the input is dominated by NH4
+-N. The mean flux of inorganic N input by wet precipitation and
output by stream water is 1.672 and 0.537 g N/(m2 yr), respectively, which indicates that most of inorganic N input is retained in the
forested watershed. Net retention of inorganic N reaches 1.135 g N/(m2 yr) considering wet precipitation as the main input and stream
water as the main output. If N input by dry deposition and biological fixation and output by denitrification are taken into account, this
subtropical forested watershed currently acts as a considerable sink for N, with a net sink ranging from 1.309 to 1.913 g N/(m2 yr)
which may enhance carbon sequestration of the terrestrial ecosystem. 相似文献
187.