全文获取类型
收费全文 | 1147篇 |
免费 | 96篇 |
国内免费 | 184篇 |
专业分类
安全科学 | 132篇 |
废物处理 | 29篇 |
环保管理 | 230篇 |
综合类 | 559篇 |
基础理论 | 182篇 |
污染及防治 | 59篇 |
评价与监测 | 74篇 |
社会与环境 | 82篇 |
灾害及防治 | 80篇 |
出版年
2024年 | 6篇 |
2023年 | 9篇 |
2022年 | 29篇 |
2021年 | 33篇 |
2020年 | 29篇 |
2019年 | 31篇 |
2018年 | 24篇 |
2017年 | 31篇 |
2016年 | 62篇 |
2015年 | 51篇 |
2014年 | 54篇 |
2013年 | 70篇 |
2012年 | 101篇 |
2011年 | 80篇 |
2010年 | 72篇 |
2009年 | 68篇 |
2008年 | 56篇 |
2007年 | 76篇 |
2006年 | 93篇 |
2005年 | 60篇 |
2004年 | 48篇 |
2003年 | 36篇 |
2002年 | 42篇 |
2001年 | 38篇 |
2000年 | 39篇 |
1999年 | 29篇 |
1998年 | 28篇 |
1997年 | 21篇 |
1996年 | 22篇 |
1995年 | 9篇 |
1994年 | 15篇 |
1993年 | 9篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 3篇 |
排序方式: 共有1427条查询结果,搜索用时 265 毫秒
601.
602.
603.
Applications of Total Maximum Daily Load (TMDL) criteria for complex estuarine systems like Chesapeake Bay have been limited by difficulties in estimating precisely how changes in input loads will impact ambient water quality. A method to deal with this limitation combines the strengths of the Chesapeake Bay's Water Quality Sediment Transport Model (WQSTM), which simulates load response, and the Chesapeake Bay Program's robust historical monitoring dataset. The method uses linear regression to apply simulated relative load responses to historical observations of water quality at a given location and time. Steps to optimize the application of regression analysis were to: (1) determine the best temporal and spatial scale for applying the WQSTM scenarios, (2) determine whether the WQSTM method remained valid with significant perturbation from calibration conditions, and (3) evaluate the need for log transformation of both dissolved oxygen (DO) and chlorophyll a (CHL) datasets. The final method used simple linear regression at the single month, single WQSTM grid cell scale to quantify changes in DO and CHL resulting from simulated load reduction scenarios. The resulting linear equations were applied to historical monitoring data to produce a set of “scenario‐modified” DO or CHL concentration estimates. The utility of the regression method was validated by its ability to estimate progressively increasing attainment in support of the 2010 Chesapeake Bay TMDL. 相似文献
604.
Lewis C. Linker Carl F. Cerco 《Journal of the American Water Resources Association》2013,49(5):986-1006
Nutrient load allocations and subsequent reductions in total nitrogen and phosphorus have been applied in the Chesapeake watershed since 1992 to reduce hypoxia and to restore living resources. In 2010, sediment allocations were established to augment nutrient allocations supporting the submerged aquatic vegetation resource. From the initial introduction of nutrient allocations in 1992 to the present, the allocations have become more completely applied to all areas and loads in the watershed and have also become more rigorously assessed and tracked. The latest 2010 application of nutrient and sediment allocations were made as part of the Chesapeake Bay total maximum daily load and covered all six states of the Chesapeake watershed. A quantitative allocation process was developed that applied principles of equity and efficiency in the watershed, while achieving all tidal water quality standards through an assessment of equitable levels of effort in reducing nutrients and sediments. The level of effort was determined through application of two key watershed scenarios: one where no action was taken in nutrient control and one where maximum nutrient control efforts were applied. Once the level of effort was determined for different jurisdictions, the overall load reduction was set watershed‐wide to achieve dissolved oxygen water quality standards. Further adjustments were made to the allocation to achieve the James River chlorophyll‐a standard. 相似文献
605.
William R. Michaud 《Journal of the American Water Resources Association》2013,49(3):693-699
Does collaborative modeling improve water resource management outcomes? How does collaborative modeling improve these outcomes? Does it always work? Under what conditions is collaborative modeling most appropriate? With support from the U.S. Army Corps of Engineers' Institute for Water Resources (IWR), researchers developed an evaluation framework to help address these questions. The framework links the effects of collaborative modeling on decision‐making processes with improvements in the extent to which resource management decisions, practices, and policies balance societal needs. Both practitioners' and participants' experiences suggest that under the right circumstances, collaborative modeling can generate these beneficial outcomes. Researchers developed performance measures and a survey to systematically capture these experiences and evaluate the outcomes of collaborative modeling processes. The survey can provide immediate feedback during a project to determine whether collaborative modeling is having the desired effect and whether course correction is warranted. Over the longer term, the systematic evaluation of collaborative modeling processes will help demonstrate in what ways and under what circumstances collaborative modeling is effective, inform and improve best practices, and raise awareness among water resource planners regarding the use of collaborative modeling for resource management decisions. 相似文献
606.
ABSTRACTSmall-scale ecological farming and their associated alternative food networks, are increasingly important in China, as a response to poor farm incomes and as a contribution to widespread concerns about environmental degradation and food safety. However, despite the enormous market potential and the notable success of some ventures, this type of farming remains at the margins, with many businesses struggling to develop beyond their start-up phase and consumers struggling to build confidence in the new produce and routes to market. Many of these farms display the classic elements of pioneer businesses, including high reliance on charismatic individuals, insecure land rights, high transaction and monitoring costs and fragile routes to market. Empirically, many of these businesses fail because they cannot grow out of the pioneer phase before the pioneer grows tired of the business. While this is a problem for all small businesses, it is particularly acute in business sectors like ecological farming in China, where there is little evidence of suitable and sustainable developmental models. Using Bernardus Lievegoed's work on organisational development applied to two case study farms, we suggest that there are Western developmental models that are applicable to small-scale ecological farming and that have the potential to offer insights into how this might be achieved with Chinese characteristics. We conclude by arguing that, Chinese ecological farms have to plan explicitly for a form of development that allows them to remain committed to their ideals while moving them away from dependence on charismatic people, family labour and volatile customer bases. 相似文献
607.
为解决铁路综合客运枢纽客流疏解预警忽略旅客心理感知与焦虑问题,基于状态焦虑问卷,定量描述旅客焦虑状态,通过引入心理测量学中积极率划分客流疏解等级阈值,确定枢纽客流疏解预警等级,构建以旅客感知疏解时间为预警指标的回归预测模型。研究结果表明:模型可定量预测枢纽站各种交通接驳方式客流的感知疏解时间,准确描述枢纽站预警等级,研究结果可为管理人员选择相应疏解措施提供依据。 相似文献
608.
609.
ABSTRACT: The parameters of the extreme value type 1 distribution were estimated for 55 annual flood data sets by seven methods. These are the methods of (1) moments, (2) probability weighted moments, (3) mixed moments, (4) maximum likelihood estimation, (5) incomplete means, (6) principle of maximum entropy, and (7) least squares. The method of maximum likelihood estimation was found to be the best and the method of incomplete means the worst. The differences between the methods of principle of maximum entropy, probability weighted moments, moments, and least squares were only minor. The difference between these methods and the method of maximum likelihood was not pronounced. 相似文献
610.
MATTHEW LINKIE ROBERT J. SMITH YU ZHU† DEBORAH J. MARTYR‡ BETH SUEDMEYER§†† JOKO PRAMONO NIGEL LEADER-WILLIAMS 《Conservation biology》2008,22(3):683-690
Abstract: Many of the large, donor-funded community-based conservation projects that seek to reduce biodiversity loss in the tropics have been unsuccessful. There is, therefore, a need for empirical evaluations to identify the driving factors and to provide evidence that supports the development of context-specific conservation projects. We used a quantitative approach to measure, post hoc, the effectiveness of a US$19 million Integrated Conservation and Development Project (ICDP) that sought to reduce biodiversity loss through the development of villages bordering Kerinci Seblat National Park, a UNESCO World Heritage Site in Indonesia. We focused on the success of the ICDP component that disbursed a total of US$1.5 million through development grants to 66 villages in return for their commitment to stop illegally clearing the forest. To investigate whether the ICDP lowered deforestation rates in focal villages, we selected a subset of non-ICDP villages that had similar physical and socioeconomic features and compared their respective deforestation rates. Village participation in the ICDP and its development schemes had no effect on deforestation. Instead, accessible areas where village land-tenure had been undermined by the designation of selective-logging concessions tended to have the highest deforestation rates. Our results indicate that the goal of the ICDP was not met and, furthermore, suggest that both law enforcement inside the park and local property rights outside the park need to be strengthened. Our results also emphasize the importance of quantitative approaches in helping to inform successful and cost-effective strategies for tropical biodiversity conservation. 相似文献