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71.
ABSTRACT: Decisionmaking associated with the Nation's 1.7 billion acres of forest and range land has become increasingly complicated because of the rise in competition for resource use and in the awareness of environmental and social effects. This system analysis approach uses four models to synthesize pertinent masses of information into measures of economic, environmental, and social impacts. The system results can be used to help evaluate alternative national programs. The models are:
72.
    
We present a method for estimating the mean vector from a bivariate skew distribution that includes some unobserved data below the detection limits. The method uses a Box‐Cox transformation, of which the parameters are found by maximizing the likelihood function over a fixed power transformation set. To estimate the mean vector and the covariance matrix, we develop an E‐M algorithm solution. Given a transformation, we obtain expressions for the mean vector, covariance matrix, and the asymptotic covariance of the vector of means in the original scale. Expressions are obtained for a confidence region for the vector of means. The performance of the maximum likelihood estimation (MLE) method in selecting the correct power transformation and the coverage rate of the confidence region under several conditions are investigated in a simulation study. This method gives reliable results for finding effective transformations and the coverage rate for highly skew data sets. The method is applied to water quality monitoring data. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
73.
Municipal solid waste landfills pose a threat on environment and human health, especially old landfills which lack facilities for collection and treatment of landfill gas and leachate. Consequently, missing information about emission flows prevent site-specific environmental risk assessments. To overcome this gap, the combination of waste sampling and analysis with statistical modeling is one option for estimating present and future emission potentials. Optimizing the tradeoff between investigation costs and reliable results requires knowledge about both: the number of samples to be taken and variables to be analyzed.This article aims to identify the optimized number of waste samples and variables in order to predict a larger set of variables. Therefore, we introduce a multivariate linear regression model and tested the applicability by usage of two case studies. Landfill A was used to set up and calibrate the model based on 50 waste samples and twelve variables. The calibrated model was applied to Landfill B including 36 waste samples and twelve variables with four predictor variables.The case study results are twofold: first, the reliable and accurate prediction of the twelve variables can be achieved with the knowledge of four predictor variables (Loi, EC, pH and Cl). For the second Landfill B, only ten full measurements would be needed for a reliable prediction of most response variables. The four predictor variables would exhibit comparably low analytical costs in comparison to the full set of measurements. This cost reduction could be used to increase the number of samples yielding an improved understanding of the spatial waste heterogeneity in landfills.Concluding, the future application of the developed model potentially improves the reliability of predicted emission potentials. The model could become a standard screening tool for old landfills if its applicability and reliability would be tested in additional case studies.  相似文献   
74.
    
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75.
水环境中铬的存在形态及迁移转化规律   总被引:15,自引:0,他引:15  
综合评述了水环境中铬的存在形态、污染特征及其迁移转化规律的研究现状.水体中铬主要是三价和六价,存在形态分为溶解态、离子交换态、有机结合态、无机沉淀态、残留态,迁移转化过程主要是水解、沉淀、络合、吸附和氧化还原等.对铬在水体中迁移和转化过程的动力学模型进行了论述.  相似文献   
76.
循环经济国内外立法研究   总被引:15,自引:0,他引:15  
二十世纪九十年代以来,由于传统线性经济带来的恶性结果,发展循环经济在国际社会上蔚为风潮.许多西方国家纷纷进行循环经济立法活动,德国和日本建立了较为完善的循环经济法律体系.从西方国家的立法经验我们可以看出,要发展循环经济,建立一个完善的法律保障体系至关重要.我国的循环经济立法还处在初级阶段,要吸收和借鉴先进经验,制定修改一批法律、法规,建立完善的循环经济法律体系,以促进循环经济发展.  相似文献   
77.
"两山"理论,即"绿水青山就是金山银山",是习近平新时代中国特色社会主义思想的重要内容。浙江是"两山"理论的发源地,思考探寻基于浙江情境的"两山"转化路径,意义重大且十分迫切。本研究从顶层设计、高质量发展、营商环境、协同治理、技术创新等方面,总结浙江"两山"转化的实践经验及其实践特征,探讨其"两山"转化路径,以期为在全国范围内推广"两山"转化与践行提供参考。  相似文献   
78.
磷石膏中磷、氟和重金属等元素的存在严重威胁生态环境安全。通过分析磷石膏渣场不同空间位置的pH及磷、氟、重金属分布情况发现:含水率随土壤深度的增加而呈现先增加后降低的趋势,pH随土壤深度的增加表现出先碱性后酸性的趋势,不同深度含水率不同,导致有毒有害物质的分布规律不同,含水率上升导致磷、氟及重金属浸出毒性升高,对氟、锰、铅3种元素的影响最明显。研究发现:在不同土壤深度处重金属各种赋存形态的含量变化规律不仅取决于磷石膏本身的特性,还受外界环境的影响及重金属本身的性质差异影响。该研究为分析磷石膏的污染特性提供重要的研究基础,并为磷石膏的定向处理提供参考。  相似文献   
79.
构建了包气带土壤水分运动和溶质运移耦合模型,模拟特定降雨条件下“三氮”在沿江地区污染场地包气带垂向的迁移转化过程。结果表明:“三氮”在包气带0 m~2 m范围内以吸附和硝化作用为主,在2 m~8 m范围内以反硝化作用为主,越接近包气带底部反硝化作用越强烈;包气带确对饱水带能起到一定的防护作用,考虑吸附、生物降解作用,模拟应力期内NH+4并未迁移至地下潜水面,NO-2可忽略不计,NO-3最终以36 mg/L迁移至地下水并发生环境污染行为。  相似文献   
80.
ABSTRACT. Unit hydrographs derived by using two methods, linear programming and least squares, are compared. Test data comprise rainfall and runoff information from four storms over the North Branch Potomac River near Cumberland, Maryland. The mathematical bases of these methods for unit-hydrograph derivation are explained. The linear programming method minimizes the sum of absolute deviations, and the least squares method minimizes the sum of the squares of deviations. Computer subroutines are readily available for application of these methods. The unit hydrographs derived with the two methods are practically the same for storms 2 and 3, but differ somewhat for storms 1 and 4. However, the reconstituted direct surface runoff hydrographs are similar to those observed with the exception of the hydrograph for storm 4 which had a relatively more non-uniform rainfall excess of a considerably larger duration.  相似文献   
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