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351.
天津地区六六六的归宿和跨界面迁移 总被引:6,自引:0,他引:6
以天津市为研究区域,以80年代有机氯农药禁用前为时限,利用稳态非平衡逸度模型估算了稳态条件下六六六的四种异构体在环境各相中的迁移和分布。模型估算结果用同期各主要介质的实测浓度加以验证。结果表明,农业施用和农药厂排放是该地区环境中六六六的主要来源,最大的汇则是土壤和水体沉积物,该地区最主要的界面迁移过程包括大气向土壤的沉降、水体向沉积物的沉降以及气相平流输出等,发生在土壤和沉积物中的降解则是六六六消失的最主要途径。 相似文献
352.
Karasek's (1979) demand–discretion model of occupational stress has been highly influential but has been criticized as confounding social class variables (Payne and Fletcher, 1983), ignoring the curvilinearity of relationships (Warr, 1991), and because it has inconsistently predicted heart disease (Ganster and Fusilier, 1989). The present study examines the ability of the model to predict raised blood pressure (a risk factor in the development of CHD), anxiety, depression, job and life satisfaction, in a large heterogeneous sample of over 3000 people. It examines the predictability of the model for men and women, taking occupational classification (manual and non-manual workers) into account, to allow some control over social class confounding. It also examines nonlinear relationships in the data. The study showed that demands and discretion do separately predict psychological strain, job and life satisfaction, though they account for a very small percentage of the variance. There was no evidence of interactive effects which are central to the model. Where the model was able to predict blood pressure, relationships were consistently in the opposite direction to that hypothesized. There was also little evidence of curvilinear relationships. Interpersonal support was found to add significantly to the predictability of the dependent variables. The findings cast doubt on Karasek's model and suggest that emphasis should be shifted to those models which are more encompassing of support factors. 相似文献
353.
Ben Dziegielewski John J. Boland 《Journal of the American Water Resources Association》1989,25(1):101-109
ABSTRACT: In the current forecasting practice, future water requirements of a growing urban area are often represented as the product of the number of people to be served by the water system and an assumed quantity of gross per capita water use. This paper describes a forecasting approach that differs from the per capita method in two important aspects. First, it disaggregates urban water use into a large number of categories, each consisting of a relatively homogeneous group of water users. Second, it links water use in each category to factors that determine both the need for water as well as the intensity of water use. This approach is incorporated into a computerized forecasting system referred to as IWR-MAIN. The advantages of the IWR.MAIN model over the traditional per capita method are illustrated in a case study of Anaheim, California. 相似文献
354.
355.
Ronald C. Flemal Donovan C. Wilkin Ben B. Ewing 《Journal of the American Water Resources Association》1979,15(4):996-1003
ABSTRACT: A great deal of information can be derived from study of standard stream monitoring data, if these are properly ordered and organized. This information may then be used to make decisions about water quality management. Among critical information items are evaluation of performance to standards, determination of seasonality and time-trends of water quality conditions, and estimation of the effects on water quality to be expected from load reductions or standards modifications. Additional information on the magnitude of individual pollution sources is also critical to water quality management. Each of these items can be derived within the water quality information system which is currently under development for the State of Illinois. 相似文献
356.
A mass balance model was applied to simulate the long-term fate of PAHs in San Francisco Bay. The model treats the Bay as a single box with interacting water and sediment compartments, and includes loading, volatilization, outflow to the ocean, degradation, and burial in deep sediment. The estimated time required for loss of one-half of the mass in the Bay in the absence of loading ranged from 20 d for naphthalene to 5 yr for benzo(b)fluoranthene. Uncertainty analysis using Monte Carlo simulation indicated a high degree of influence and uncertainty for degradation rates, suggesting that improved estimates of degradation would significantly improve the predictive ability of the model. A comparison of model calculations to literature values suggested that external PAH loading to San Francisco Bay was at or above previous estimates of 3600 kgyr(-1), and that degradation in the Bay was within the range of commonly published estimates for high molecular weight PAHs (4.0 x 10(-5) to 4.0 x 10(-4)d(-1)). 相似文献
357.
In this work the authors describe the main characteristics of the velocity field of hydraulic jumps in a very large channel
where lateral shockwaves occur. Experiments were carried out at the Coastal Engineering Laboratory of the Water Engineering
and Chemistry Department of the Technical University of Bari (Italy). Extensive flow velocity measurements were investigated
in order to have a clearer understanding of both hydraulic jump development and lateral shockwave formation in a very large
channel. Eight experiments were performed in a 4m wide rectangular channel; the experiments differed in the inlet Froude number
F
0 and the jump type. Seven tests were carried out with undular jumps and one with a roller jump. The flow velocity and the
flow free surface measurements were taken using a two-dimensional Acoustic Doppler Velocimeter (ADV) and an ultrasonic profiler,
respectively. The experimental results can be summarized as follow: (i) the formation of well developed lateral shockwaves
similar to those of oblique jumps were observed; (ii) the comparison of the experimental and theoretical data shows that the
classic shockwave theory is sufficiently confirmed in the analyzed range of Reynolds number, taking into account the experimental
errors and the difference between the theoretical and experimental assumptions; (iii) the transversal flow velocity profiles
in the recirculating zone show a good agreement with the numerical simulations presented in literature in the case of a separated
turbulent boundary layer over a flat plate. This conclusion enables us to confirm the hypothesis that the lateral shockwaves
in the channel are the result of a boundary layer which, as observed, forms on the channel sidewalls. 相似文献
358.
Prasad VK Ortiz A Stinner B McCartney D Parker J Hudgins D Hoy C Moore R 《Environmental monitoring and assessment》2005,110(1-3):141-169
Ohio is typical among the Midwestern and Eastern United States with high levels of water pollutants, the main sources being
from agriculture. In this study, we used a digital elevation model in conjunction with hydrological indices to determine the
role of landscape complexity affecting the spatial and temporal variation in pollutant levels, in one of the most impaired
headwater streams in Ohio. More than eighty five percent of the study area is dominated by agriculture. Spatial distribution
of slope (S), altitude and wetness index along with other watershed parameters such as flow direction, flow accumulation,
stream networks, flow stream orders and erosion index were used within a Geographic Information Systems framework to quantify
variation in nitrate and phosphate loads to headwater streams. Stream monitoring data for nutrient loads were used to correlate
the observed spatial and temporal patterns with hydrological parameters using multiple linear regressions. Results from the
wetness index calculated from a digital elevation model suggested a range of 0.10–16.39, with more than 35% having values
less than 4.0. A Revised Universal Soil Loss Equation (RUSLE) predicted soil loss in the range of 0.01–4.0 t/ha/yr. Nitrate
nitrogen levels in the study area paralleled precipitation patterns over time, with higher nitrate levels corresponding to
high precipitation. Atmospheric deposition through precipitation could explain approximately 35% of total nitrate levels observed
in streams. Among the different topographic variables and hydrological indices, results from the step-wise multiple regression
suggested the following best predictors, (1) elevation range and upstream flow length for nitrate, (2) flow direction and
upstream flow length for ammonia-nitrogen and slope, and (3) elevation range for phosphate levels. Differences in the landscape
models observed for nitrate, phosphate and ammonia-nitrogen in the surface waters were attributed partly to differences in
the chemical activity and source strengths of the different forms of these nutrients through agricultural management practices.
The results identify geomorphologic and landscape characteristics that influence pollutant levels in the study area. 相似文献
359.
Amanda B. White Praveen Kumar Patricia M. Saco Bruce L. Rhoads Ben C. Yen 《Journal of the American Water Resources Association》2003,39(6):1547-1560
ABSTRACT: The objective of this work is to determine the effects of extension of a stream network through land drainage activities during the late 1800s on the hydrologic response of a watershed. The Mackinaw River Basin in Central Illinois was chosen as the focus and the pre‐land and post‐land drainage activity hydrologic responses were obtained through convolution of the hill slope and channel responses and compared. The hill slope response was computed using the kinematic wave model and the channel response was determined using the geomorphologic instantaneous unit hydrograph method. Our hypothesis was that the hydrologic response of the basin would exhibit the characteristic effects of settlement (i.e., increases in peak discharges and decreases in times to peak). This, indeed, is what occurred; however, the increase in peak discharges diminishes as scale increases, leaving only the decrease in times to peak. At larger scales, the dispersive effects of the longer hill slope lengths in the pre‐settlement scenario seem to balance the depressive effects of the longer path lengths in the post‐settlement scenario, thus the pre‐settlement and post‐settlement peak discharges are approximately equivalent. At small scales, the dispersion caused by the hill slope is larger in the pre‐settlement case; thus, the post‐settlement peak discharges are greater than the pre‐settlement. 相似文献
360.