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   365篇
  免费   24篇
  国内免费   37篇
安全科学   3篇
废物处理   2篇
环保管理   93篇
综合类   174篇
基础理论   75篇
污染及防治   26篇
评价与监测   12篇
社会与环境   32篇
灾害及防治   9篇
  2024年   2篇
  2023年   5篇
  2022年   8篇
  2021年   14篇
  2020年   8篇
  2019年   14篇
  2018年   11篇
  2017年   12篇
  2016年   8篇
  2015年   17篇
  2014年   8篇
  2013年   18篇
  2012年   16篇
  2011年   25篇
  2010年   14篇
  2009年   20篇
  2008年   19篇
  2007年   16篇
  2006年   12篇
  2005年   20篇
  2004年   13篇
  2003年   21篇
  2002年   20篇
  2001年   25篇
  2000年   15篇
  1999年   3篇
  1998年   6篇
  1997年   5篇
  1996年   2篇
  1995年   6篇
  1994年   1篇
  1993年   7篇
  1992年   2篇
  1991年   2篇
  1989年   4篇
  1988年   1篇
  1987年   4篇
  1986年   1篇
  1985年   2篇
  1984年   3篇
  1983年   3篇
  1982年   2篇
  1981年   4篇
  1980年   2篇
  1979年   3篇
  1978年   1篇
  1975年   1篇
排序方式: 共有426条查询结果,搜索用时 312 毫秒
391.
渤海湾西岸海平面上升威胁的防治对策   总被引:5,自引:2,他引:5  
因受全球海平面上升和地面沉降的双重影响,在21世纪末渤海湾西岸海平面将相对上升90~260厘米,广大地区(包括天津市区)将处于大潮平均高潮位之下,自然岸线位置将后撤至津浦线附近.我们提出筑堤防潮引黄放淤提高建筑高程三位一体的治理方案。  相似文献   
392.
在瘦西湖选择中试河段,利用太阳能风能绿色能源,研发了风光电能驱动的曝气生物接触氧化水净化系统。系统由风光互补发电子系统、曝气生物接触氧化子系统、植物生态子系统组成。风光电能驱动的曝气生物接触氧化水净化系统运行正常。按照景观娱乐用水水质标准进行水质监测,采用模糊综合评价与贴近度计算方法,进行了系统水净化功能评价。结果表明,在试验段原水水质低于景观水C类,经该系统水净化后,可以达到景观水B类。系统的开发与实验,探索了利用绿色能源河湖水净化的新途径。  相似文献   
393.
杭州西湖水体粪大肠菌的监测及环境意义   总被引:4,自引:0,他引:4  
粪大肠菌群指数是综合评价城市污水,尤其是生活污水污染的一个重要指标.作者于1999.1~1999.7时杭州西湖水体的FC进行了监测,结果表明西湖受到了生活污水的污染,特别是三条入湖溪流污染程度十分严重.三条溪流的FC指数超出我国地表水Ⅲ类标准的10倍.水体中FC指数同TN、TP浓度呈高度正相关.  相似文献   
394.
过渡带中岳桦种群生态特征的研究   总被引:9,自引:0,他引:9  
在长白山北坡halt1525m-1775m的岳桦云冷杉森林过渡带和1990m-2170m的岳桦苔原林线过渡带中,沿海拔高度,采用梯度取样方法,进行岳桦种群生态学研究,分析了岳桦种群存活曲线、种群分布格局和种群竞争指数。同时应用分形分析研究了岳桦种群的分形特征。结果表明:依据岳桦种群的存活曲线,在岳桦云冷杉过渡带中岳桦种群处于由衰退型向稳定型发展的阶段,而在岳桦苔原过渡带中则由稳定型向增长型过渡,从种群分布格局指数分析,岳桦在两个过渡带中的分布格局类型都是杂乱无章的,而且都偏离随机分布,处于由一个生态系统向另一个生态系统转换的相变区,从竞争指数和盒维数来看,在岳桦云冷杉过渡带中,这两项指标都是由小到大迅速递增,而在岳桦苔原过渡 情况刚好相反。  相似文献   
395.
Streamflow values are commonly synthesized for locations where flow measurement stations are lacking or where only intermittent measurements are available. In an Appalachian Mountains dataset comprised of 29 watersheds, the most appropriate among geomorphic, geologic, and hydrogeologic datasets were selected for use in prediction of streamflow at watershed scale. A statistical model was developed using principal components analysis (PCA) and cluster analysis (CA) for. Using CA on variables derived from the PCA, an optimum set of variables was derived for predicting streamflow. Results indicate there are two categories of watersheds in the study area. The first is strongly correlated with climatic variables (precipitation, temperature, elevation, and groundwater recharge). The second is strongly correlated with two geomorphic variables (watershed slope and percentage of forested area). The spatial distribution of cluster classifications shows that watersheds dominated by the climatic component are located along the Allegheny Front while watersheds dominated by the geomorphic component are located in the Allegheny Plateau and Valley and Ridge physiographic provinces. These variations between the Allegheny Plateau and Valley and Ridge physiographic provinces suggest that, to accurately model streamflow, modeling needs be done based on natural physiographic boundaries rather than political boundaries. In this physiographic setting, elevation seems to be a major control.  相似文献   
396.
West Nile virus (Flaviviridae: Flavivirus) is a serious infectious disease that recently spread across the North America continent. A spatial analysis tool was developed on the ArcMap 9.x platform to estimate potential West Nile virus activity using a spatially explicit degree-day model. The model identifies when the virus Extrinsic Incubation Period (EIP) is completed within the vector longevity during mid-summer months. The EIP is treated as a threshold indicator of the potential for virus emergence and activity. Comparing the number of West Nile virus cases in Wyoming reported from 2003 to 2005 with model results, actual cases and predicted events of West Nile virus activity match relatively well. The model represents a useful method for estimating potential West Nile virus activity in a large spatial scale.  相似文献   
397.
Abstract:  Habitat degradation alters the dynamics and composition of anuran assemblages in tropical forests. The effects of forest fragmentation on the composition of anuran assemblages are so far poorly known. We studied the joint influence of forest fragmentation and degradation on leaf-litter frogs. We specifically asked whether the processes structuring leaf-litter anuran assemblages in fragmented forests are the same as those in continuous forests. We analyzed anuran assemblages with respect to habitat characteristics, including fragmentation and degradation parameters. In comparison with continuous forests, species richness and diversity were lower and assemblage composition was altered in forest fragments. These changes seemed to be mainly caused by habitat degradation rather than forest fragmentation. Availability of aquatic sites for breeding, vegetation structure (including those variables indicating degradation), and leaf-litter cover had the most influence on the presence of single species. The comparatively small impact of fragmentation on anurans might be due to the location of the study area; it still possessed large tracts of continuous forest. These forest blocks may stabilize the regional rainforest climate and thus weaken the effects of fragmentation .  相似文献   
398.
生物燃料与西部开发   总被引:2,自引:0,他引:2  
傅尧信 《四川环境》2001,20(1):55-57
本文介绍了生物燃料的概况,对国家战略安全,环境保护和区域经济发展的意义,以及技术和应用可行性,把四川建成中国生物燃料的基地。  相似文献   
399.
During the Mesoscale Alpine Programme (MAP) special observation period (SOP) between 7 September and 15 November 1999, ground-based and airborne measurements have been conducted in the Rhine valley south of the Lake of Constance to investigate the unstationary aspects of Foehn and related phenomena, like the impact of Foehn on the ozone concentrations in the valley. Foehn events occurred with above-average frequency and high diversity. Foehn induced ozone peaks in October and November are found to be much lower than the September Foehn case of the period. An inversion layer in the lake area with ozone concentrations below 10 ppb often shields the monitoring stations from the Foehn air aloft. Trajectory calculations for the Foehn period between 19 and 24 October 1999 reveal that the Foehn air originated from below 1 to 1.5 km above the Po Basin and the Mediterranean Sea. Tethered balloon soundings in the source area south of the Alps, ozone measurements at the mountain station Jungfraujoch (3580 m a.s.l.) and airborne measurements across the Alpine crests reveal that the ozone levels found in the Foehn air correspond to the concentrations just above the mixing height in the Po Basin and are transported across the Alpine crest within the lowest flow layer.  相似文献   
400.
在杭州西湖总磷模型及其治理应用(Ⅰ)的研究基础上,再用平面二维水动力方程、对流扩散方程(其中考虑了底泥沉降及底泥释放同时发生的水与底泥双层介质的交换)数值解,对一个进出水口,引水量2000万t/a8个点浓度的平面分布进行了验证,并研究了多个进水、出水口的布局和引水增加后对西湖各水域水质改善程度。又用最新水质资料作了预测验证。  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