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151.
Researchers aim to design environmental studies that optimize precision and allow for generalization of results, while keeping the costs of associated field and laboratory work at a reasonable level. Ranked set sampling is one method to potentially increase precision and reduce costs by using ‘rough but cheap’ quantitative or qualitative information to obtain a more representative sample before the real, more expensive sampling is done. In this report, we investigate under what conditions ranked set sampling becomes a cost‐effective sampling method for ecological and environmental field studies where the ‘rough but cheap’ measurement has a cost. Ratios of measuring to ranking costs necessary for ranked set sampling to be as cost effective as simple random sampling, for a common precision, are presented for known distributions with and without ranking error. Cost ratios are also presented for a real data set consisting of visually estimated and physically measured stream habitat areas. Results provide specific guidelines for when ranked set sampling is appropriate, and cost effective, for ecological and environmental field sampling. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
152.
153.
The Seymour aquifer region of Texas has been identified as containing elevated levels of nitrate in ground water. Various state and federal agencies are currently studying policy options for the region by gathering more site-specific information. However, because of lack of sufficient information, cause and effect relationships between water quality and agricultural practices have not been well established for the region. Some recently available biophysical simulation models have impressive capabilities in generating large amounts of data on environmental pollution resulting from agricultural production practices. In this study, the data generated by a biophysical simulation model were used to estimate the nitrate percolation response functions for the Seymour aquifer region. Interestingly, nitrate percolation values obtained from simulation models often comprise acensoredsample because the non-zero percolation values are only observed under certain climatic events and input levels. It has been shown in the econometric literature that the use of Ordinary Least Squares (OLS) on censored sample data produces biased and inconsistent parameter estimates. Thus, a sample selection model was used in this study to estimate the response functions for nitrate percolation. The study provides some insight into the relationship between nitrate percolation and agricultural production practices. In particular, the study demonstrates the potential of selected design standards in minimizing agricultural nonpoint-source (NPS) pollution for the study area. 相似文献
154.
Semiu A. Lawal W. Edgar. Watt 《Journal of the American Water Resources Association》1996,32(6):1159-1166
ABSTRACT: The implications of fitting distributions with non-zero lower limits to low flow data are examined. The 3-parameter Weibull distribution is fitted to annual minimum flow series from 60 long term stations in Canada. The relations between the estimated lower limit and three sampling variables (skewness, smallest, and largest observations) were investigated. The lower limit strongly depends on the sample skewness; it varies directly with the sample skewness, which in turn is highly influenced by the largest observation. For a given skewness, the value of the estimated lower limit is determined by the value of the smallest observation. Therefore, the lower limit cannot be accurately determined, and the resulting low flow estimates will be either too small or too high. 相似文献
155.
156.
The separate collection of waste, and especially of recyclables with specific collection systems, would not be possible without
the involvement of the users. Apart from the physical installations such as collection containers, collection points, etc.,
the motivation of the users is an essential component. Motivation can be reinforced through public relations work. In addition
to the underlying technical considerations, this paper describes the difference between communication in general and public
relations and specifically examines public involvement in recycling. Through the use of examples, we look at the targeted
users and typical media employed. Furthermore, we analyzes the development of public involvement. The examples show that public
relations for recycling strategies relies to a great extent on attitudes, habits, and access to the target group. Thus, standardized
procedures cannot be developed. For these reasons, public relation activities must be planned carefully and professionally
and include an analysis of the target group, choice of media, and verification of success. 相似文献
157.
Brett B. Roper Jeffrey L. Kershner Eric Archer Richard Henderson Nicolaas Bouwes 《Journal of the American Water Resources Association》2002,38(6):1637-1646
ABSTRACT: The last few decades have seen an increased reliance on the use of stream attributes to monitor stream conditions. The use of stream attributes has been criticized because of variation in how observers evaluate them, inconsistent protocol application, lack of consistent training, and the difficulty in using them to detect change caused by management activity. In this paper, we evaluate the effect of environmental heterogeneity and observer variation on the use of physical stream attributes as monitoring tools. For most stream habitat attributes evaluated, difference among streams accounted for greater than 80 percent of the total survey variation. To minimize the effect that variation among streams has on evaluating stream conditions, it may be necessary to design survey protocols and analysis that include stratification, permanent sites, and/or analysis of covariance. Although total variation was primarily due to differences among streams, observers also differed in their evaluation of stream attributes. This study suggests that if trained observers conducting a study that is designed to account for environmental heterogeneity can objectively evaluate defined stream attributes, results should prove valuable in monitoring differences in reach scale stream conditions. The failure to address any of these factors will likely lead to the failure of stream attributes as effective monitoring tools. 相似文献
158.
Steve H. Hanke Lennart de Mare 《Journal of the American Water Resources Association》1982,18(4):621-626
Shortcoming associated with past water demand studies are evaluated. To overcome these shortcomings, pooled, time series, cross section data from -6, Sweden, are used in an ordinary Least squares analysis to estimate the demand for residential water. Elasticities for five variables, including price and income, are estimated. An approach for the conduct of future water demand studies is suggested. 相似文献
159.
气溶胶过滤捕集效率的理论研究 总被引:2,自引:1,他引:2
本分析了气溶胶过滤理论的研究与发展,推导了稳定过滤过程捕集效率计算模型,并在此基础上,考虑颗粒在纤维表面的沉积,根据质量守恒定律,建立非稳定过滤过程数学模型,通过理论求解,得出非稳定过滤捕集效率理论计算公式。通过相关实验研究对比表明:该模型可描述非稳定过滤过程随时间的变化趋势,为预测捕集效率、延长滤料使用寿命提供理论依据。 相似文献
160.