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821.
Gary M. Russell Mark Stewart Aaron L. Higer 《Journal of the American Water Resources Association》1987,23(5):863-866
ABSTRACT: Areas of low topographic relief have low water-table gradients and make the direction of movement of contaminants from land fills in the ground water difficult to predict from regional gradients alone. The landfill, nearby free-flowing ditches or canals, variations in hydraulic conductivity, and the influence of nearby pumping wells can all affect the direction of flow. In low-gradient areas the concepts of “upgradient” and “downgradient” are less useful in planning the location of monitoring wells than in areas of higher relief. Low-relief areas also may be affected by the discharge of mineralized water from deeper aquifers, naturally or through irrigation, which can mask geochemical surveys intended to detect landfill leachate. Examples of effects of low topographic relief are noted in southeast Florida where water-table gradients are 7×10?-4 to 5×10?-4 feet per foot. Water-table mounding beneath the landfill and the drainage effects of nearby ditches and well have created multiple leachate plumes in Stuart where one plume migrated in a direction opposite to the apparent regional gradient. In Coral Springs analysis suggests a bifurcating plume migrating along two narrow zones. In Fort Pierce it was difficult to detect leachate because of mineralized irrigation water and fertilizer runoff from an adjacent citrus grove. 相似文献
822.
Keith W. Hipel 《Journal of the American Water Resources Association》1985,21(4):609-623
ABSTRACT: By employing a set of criteria for classifying the capabilities of time series models, recent developments in time series analysis are assessed and put into proper perspective. In particular, the inherent attributes of a wide variety of time series models and modeling procedures presented by the authors of the 18 papers contained in this volume are clearly pointed out. Additionally, it is explained how these models can address many of the time series problems encountered when modeling hydrologic, water quality and other kinds of time series. For instance, families of time series models are now available for modeling series which may contain nonlinearities or may follow nonGaussian distributions. Based upon a sound physical understanding of a problem and results from exploratory data analyses, the most appropriate model to fit to a data set can be found during confirmatory data analyses by following the identification, estimation and diagnostic check stages of model construction. Promising future research projects for developing flexible classes of time series models for use in water resources applications are suggested. 相似文献
823.
Fernando Camacho A. Ian McLeod Keith W. Hipel 《Journal of the American Water Resources Association》1985,21(4):709-720
ABSTRACT: The Contemporaneous Autoregressive-Moving Average (CARMA) model is a simple and efficient model that can be used to fit many multivariate hydrological time series. For certain types of multistation river flow systems, the CARMA model is naturally obtained when the physical restrictions of the system or the characteristics of the data are taken in consideration during the formulation of the model. It is shown how the CARMA model can optimally be used to handle multiple time series where the number of observations in each series may be different. Adequate model building techniques, as well as computational and statistical efficient algorithms to estimate the parameters of the model, are given. The methodologies and applications of the CARMA model are illustrated with three examples. It is also shown how the full multivariate ARMA model may lead to losses in efficient of the estimators when the CARMA model is adequate. 相似文献
824.
Walter T. Sittner 《Journal of the American Water Resources Association》1973,9(4):655-659
The National Weather Service is nearing the conclusion of a five year period of transition from index type catchment modelling to the use of conceptual hydrologic models. The decision to make this technological change was based on an extensive research project in which various catchment models were tested in a wide variety of basins and their strong and weak points ascertained. This project is described. Some of the problems involved in the changeover, which are discussed, are practical parameter optimization methods, computer requirements for the more complex technology, data requirements, fitting of the catchment model to major river systems, training of personnel and staffing problems. 相似文献
825.
Joseph M. Colonell George R. Higgins 《Journal of the American Water Resources Association》1973,9(4):793-800
Hydrologic response, defined as the annual direct runoff divided by the annual precipitation, was computed for twenty-one watersheds in or near western Massachusetts, using a total of 232 years of hydrologic records. Variability of the results over the period of analysis was greater than is desirable to inspire confidence in the usefulness of the hydrologic response function; however, the results do suggest that the hydrologic response concept, with appropriate refinements, could be applied successfully to the problem of delineating hydrologic provinces and determination of drainage and storage in unregulated watersheds. 相似文献
826.
Marshall Gysi 《Journal of the American Water Resources Association》1972,8(5):957-964
ABSTRACT. Preliminary results from a digital simulation model designed to test time-varying water pricing policies are presented. Stochastic inflows feeding a water supply reservoir are assumed for a hypothetical community with defined demand functions. Prices are allowed to vary as a function of reservoir level, generally rising as reservoir levels fall. Increasing, decreasing and constant rates are tested. It is concluded that varying the price to reflect the increased value of scarce supplies can greatly reduce the risk of water supply shortages. It is also concluded that varying incremental (conservational) pricing policies not only reduces the risk of shortages, but also lowers the average price to the community while rewarding the low consumption user with lower average rates. 相似文献
827.
Carl D. Settergren 《Journal of the American Water Resources Association》1970,6(5):775-783
Extreme rainfall frequency analysis provides one means to predict, within certain limits of probability, the average time interval between the recurrences of storms of a specified duration and magnitude. This in turn furnishes the forest hydrologist a valuable tool for engineering design and runoff and erosion forecast. A modification in the application of the annual maximum and annual exceedance series analysis described by V. T. Chow can, for special purposes, lead to an even more useful estimate of extreme events on a seasonal basis. This can be particularly important on small forested headwater watersheds where the runoff response to extreme rainfall may vary considerably with seasonal changes in canopy cover and soil moisture characteristics. Although the application of data covering a relatively short period of record has produced some inconsistencies among the frequency diagrams, under certain circumstances for short-term recurrence interval forecast and for non-critical application the analysis of extreme rainfall frequency from less than 20 years data seems justified. 相似文献
828.
V. V. Dhruva Narayana J. Paul Riley Eugene K. Israehen 《Journal of the American Water Resources Association》1971,7(1):54-68
ABSTRACT. .A mathematical model for urban watersheds is being developed in stages at the Utah Water Research Laboratory, Utah State University at Logan. In verifying the watershed as a unit, watershed coefficients are determined on the computer, and related to the urbanization characteristics. The second stage of verification consists of dividing the watershed into subzones, and determining the urban parameters within each subzone. Each subzone is then individually modeled, and outflow hydrographs are routed through succeeding downstream subzones to the gaging point. The model thus makes it possible to: (a) develop runoff models for subzone hydrographs within the urban watershed, and (b) account for spatial variations of storm and watershed characteristics. An attempt was also made to analytically model the outflow hydrograph based on storm and watershed characteristics. 相似文献
829.
830.
Wilbert O. Thomas 《Journal of the American Water Resources Association》1982,18(2):221-229
ABSTRACT: An evaluation of flood frequency estimates simulated from a rainfall/runoff model is based on (1) computation of the equivalent years of record for regional estimating equations based on 50 small stream sites in Oklahoma and (2) computation of the bias for synthetic flood estimates as compared to observed estimates at 97 small stream sites with at least 20 years of record in eight eastern states. Because of the high intercorrelation of synthetic flood estimates between watersheds, little or no regional (spatial) information may be added to the network as a result of the modeling activity. The equivalent years of record for the regional estimating equations based totally on synthetic flood discharges is shown to be considerably less than the length of rainfall record used to simulate the runoff. Furthermore, the flood estimates from the rainfall/runoff model consistently underestimate the flood discharges based on observed record, particularly for the larger floods. Depending on the way bias is computed, the synthetic estimate of the 100-year flood discharge varies from 11 to 29 percent less than the value based on observed record. In addition, the correlation between observed and synthetic flood frequency estimates at the same site is also investigated. The degree of correlation between these estimates appears to vary with recurrence interval. Unless the correlation between these two estimates is known, it is not possible to compute a weighted estimate with minimum variance. 相似文献