首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1238篇
  免费   62篇
  国内免费   89篇
安全科学   87篇
废物处理   19篇
环保管理   258篇
综合类   638篇
基础理论   79篇
污染及防治   51篇
评价与监测   89篇
社会与环境   116篇
灾害及防治   52篇
  2024年   5篇
  2023年   13篇
  2022年   23篇
  2021年   25篇
  2020年   35篇
  2019年   21篇
  2018年   16篇
  2017年   27篇
  2016年   46篇
  2015年   43篇
  2014年   50篇
  2013年   55篇
  2012年   89篇
  2011年   95篇
  2010年   63篇
  2009年   57篇
  2008年   61篇
  2007年   74篇
  2006年   66篇
  2005年   66篇
  2004年   59篇
  2003年   64篇
  2002年   50篇
  2001年   41篇
  2000年   48篇
  1999年   35篇
  1998年   21篇
  1997年   26篇
  1996年   10篇
  1995年   10篇
  1994年   8篇
  1993年   12篇
  1992年   10篇
  1991年   10篇
  1990年   5篇
  1989年   3篇
  1988年   9篇
  1987年   3篇
  1986年   6篇
  1985年   4篇
  1984年   5篇
  1983年   3篇
  1982年   9篇
  1980年   2篇
  1978年   1篇
  1977年   1篇
  1974年   1篇
  1972年   2篇
  1968年   1篇
排序方式: 共有1389条查询结果,搜索用时 503 毫秒
881.
During the past decade, Norway has become an important oil and gas producer. Annual production is six times national consumption. Development policies of the national government have been cautious, and future policies will probably follow a similar pattern. The government recently opened offshore areas poleward of 62°N latitude, a decision likely to have a significant impact on Norway's future as an oil producer. Norway maintains a tight reign on foreign oil company participation, domestic downstream processing of crude, oil company taxation and oil revenue investment within the national economy. Norway's large inflow of oil-related capital investments and production revenues have contributed to significant inflation and to changes in local labour supplies. Norway has always used its petroleum industry to further the country's overall development goals, a policy that will continue in the years ahead.  相似文献   
882.
公路建设作为国家基础设施建设发展迅速。公路建设对社会经济的发展贡献巨大,然而当公路建成后便捷的交通对加剧人口迁移流动造成的社会生态环境影响,却没有引起有关部门的足够重视,尤其在干旱地区脆弱的生态环境下,这种影响更为深远。本文分析了这种不利影响并提出了防治对策和建议。  相似文献   
883.
ABSTRACT: Nitrate levels in the Ocklawaha River Basin in north central Florida were reviewed over a 50‐year period. Data were obtained from the literature, U.S. Environmental Protection Agency (USEPA) STOrage and RETrieval (STORET), and U.S. Geological Survey (USGS) databases. The study objective was to determine whether nitrate concentrations are increasing and if so, whether this increase is linked to land use changes. Increasing nitrate levels were seen at 5 of the 14 stations, while other stations showed no trend or a decreasing trend. Median nitrate concentrations in the Ocklawaha River increased from 0.07 mg‐N/L to 0.78 mg‐N/L at sites downstream from the Silver River. Throughout the Rodman Reservoir, median nitrate concentrations decreased from 0.48 mg‐N/L to 0.01 mg‐N/L and increased to 0.04 mg‐N/L after the Kirkpatrick Dam. Flow and concentration relationships were correlated for five stations. At four of the five stations nitrate concentrations decreased in response to increasing flow, likely the result of dilution with nitrate poor water. Changes in land use over a 20‐ year period (1970 to 1990) also were monitored. Sources of nitrate have been linked by isotopic analysis to organic and inorganic fertilizers, which appear to be related to increased urbanization and an increase in lawns that require nutrient fertilization.  相似文献   
884.
环境与发展综合决策是实现可持续发展战略的重要举措。本文在总结城市环境管理实践的基础上,探讨了建立和实施环境与发展综合决策制度的必要性和完善该项制度应当强化的一些相关制度,以及在城市环境管理过程中围绕该项制度实施各相关部门的具体职责的一般程序。  相似文献   
885.
GIS在山东省震后早期应急系统中的应用   总被引:4,自引:2,他引:4  
本文将地理信息系统(GIS)应用于震后早期地震形势判定,地震灾情快速了解,地震监测能力汇总显示等地震应急工作,建立了山东省震后早期地震应急信息系统,实现以历史地震活动信息和地震地质构造背景为基础,以最大概率法给出地震早期形势的判定。同时快速给出震中附近各种历史地震特点,快速给出灾害的影响范围和震区地震监测能力的统计分析结果,为地震早期应急工作提供高显示度的综合信息。  相似文献   
886.
黄土高原地区农林牧业生态系统中主要灾害及减灾对策   总被引:1,自引:1,他引:1  
彭珂珊  张彬 《灾害学》1993,8(3):31-35
农林牧业在黄土高原地区国民经济发展中占有十分重要的位置。本文根据全区的生态特点,对农业系统的生态环境恶化的几种主要形式进行了分析,同时提出了农林牧业整体建设的综合整治对策。  相似文献   
887.
Traditional approaches to metropolitan management have placed stress upon the achievement of physical and economic growth. In recent years attention has turned to environmental concerns and the achievement of sustainable urban development. It is important to define the objectives for the sustainable development of cities and to identify the principles upon which such development can be based.  相似文献   
888.
ABSTRACT: Water quality data collected at inflows to Everglades National Park (ENP) are analyzed for trends using the seasonal Kendall test (Hirsch et al., 1982; Hirsch and Slack, 1984). The period of record is 1977–1989 for inflows to Shark River Slough and 1983–1989 for inflows to Taylor Slough and ENP's Coastal Basin. The analysis considers 20 water quality components, including nutrients, field measurements, inorganic species, and optical properties. Significant (p<0.10) increasing trends in total phosphorus concentration are indicated at eight out of nine stations examined. When the data are adjusted to account for variations in antecedent rainfall and water surface elevation, increasing trends are indicated at seven out of nine stations. Phosphorus trend magnitudes range from 4 percent/year to 21 percent/year Decreasing trends in the Total N/P ratio are detected at seven out of nine stations. N/P trend magnitudes range from -7 percent/year to -15 percent/year. Trends in water quality components other than nutrients are observed less frequently and are of less importance from a water-quality-management perspective. The apparent nutrient trends are not explained by variations in marsh water elevation, antecedent rainfall, flow, or season.  相似文献   
889.
ABSTRACT: An assumption of scale is inherent in any environmental monitoring exercise. The temporal or spatial scale of interest defines the statistical model which would be most appropriate for a given system and thus affects both sampling design and data analysis. Two monitoring objectives which are strongly tied to scale are the estimation of average conditions and the evaluation of trends. For both of these objectives, the time or spatial scale of interest strongly influences whether a given set of observations should be regarded as independent or serially correlated and affects the importance of serial correlation in choosing statistical methods. In particular serial correlation has a much different effect on the estimation of long-term means than it does on the estimation of specific-period means. For estimating trends, a distinction between serial correlation and trend is scale dependent. An explicit consideration of scale in monitoring system design and data analysis is, therefore, most important for producing meaningful statistical information.  相似文献   
890.
ABSTRACT: Parts of the Raritan River basin in central New Jersey have undergone increasing development over the last several decades. The increasing population relies on the region's ground water and surface water sources for its residential, commercial, and industrial water supply. Urbanization, regionalized wastewater-treatment facilities, stream channel alterations, and interbasin transfers of water can all affect water availability. This pilot study was conducted to determine whether significant trends exist in the base-flow and overland-runoff characteristics of streams in two subbasins with different percentages of urban/built-up land (Anderson et at., 1976). Changes in flow characteristics that could indicate future reductions in safe water yield of the Raritan River basin were examined. Flow and flow variability of the steams draining these two subbasins have increased over time. Many of the flow measures studied experienced pronounced trend shifts about 1960. The cause of these changes cannot be readily determined from the data, nor is it clear whether the increased flow variability lies outside the natural range of flow variability of the streams draining the subbasins.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号