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   663篇
  免费   63篇
  国内免费   124篇
安全科学   90篇
废物处理   25篇
环保管理   144篇
综合类   322篇
基础理论   90篇
污染及防治   53篇
评价与监测   25篇
社会与环境   81篇
灾害及防治   20篇
  2024年   5篇
  2023年   8篇
  2022年   31篇
  2021年   28篇
  2020年   32篇
  2019年   31篇
  2018年   28篇
  2017年   39篇
  2016年   38篇
  2015年   32篇
  2014年   26篇
  2013年   45篇
  2012年   46篇
  2011年   66篇
  2010年   33篇
  2009年   40篇
  2008年   29篇
  2007年   53篇
  2006年   45篇
  2005年   30篇
  2004年   21篇
  2003年   24篇
  2002年   19篇
  2001年   19篇
  2000年   15篇
  1999年   12篇
  1998年   10篇
  1997年   7篇
  1996年   7篇
  1995年   3篇
  1994年   6篇
  1993年   1篇
  1992年   4篇
  1991年   1篇
  1988年   2篇
  1986年   2篇
  1985年   1篇
  1984年   2篇
  1981年   1篇
  1980年   3篇
  1978年   1篇
  1977年   1篇
  1972年   1篇
  1971年   1篇
  1970年   1篇
排序方式: 共有850条查询结果,搜索用时 968 毫秒
351.
为探明新集矿区深层地下水离子组成及其演化特征,采集了研究区砂岩水和太灰水等共20个水样,测试分析常规离子和氢氧同位素数据,采用Piper三线图、相关性分析、离子比例系数与饱和指数等方法,探讨了研究区深层地下水水化学特征及其成因。结果表明:(1)研究区砂岩水为高矿化度水,平均矿化度为2 743. 73mg/L,水化学类型主要为Cl-Na型,太灰水多为中矿化度水,平均矿化度为1 468. 33mg/L,水化学类型主要为HCO3·Cl-Na型和Cl-Na型;(2)研究区地下水的补给不仅有大气降水和地表水,还有古气候条件下形成的古溶滤-渗入水,且由于矿物质与深层地下水的水岩作用使得氧同位素发生漂移;(3)含水层中主要发生的水岩相互作用有硅酸盐和蒸发盐岩的溶解及阳离子交替吸附作用,盐岩和石膏在研究区地下水中是反应性矿物,白云石和方解石的溶解在矿区地下水中呈过饱和状态。  相似文献   
352.
洱海流域乡镇尺度上人类活动对净氮输入量的影响   总被引:1,自引:0,他引:1  
人类活动引起的氮素过量输入已经成为引起水体富营养化及其他生态危害的主要原因.为了研究人类活动对流域氮素的影响,本文基于洱海流域16个乡镇行政单元的统计数据,考虑流动人口的影响,利用NANI模型估算洱海流域乡镇尺度的人类活动净氮输入量(net anthropogenic nitrogen inputs,NANI).结果表明,2014年洱海流域NANI总量为29.81×10~3t,单位面积输入强度(以氮计)为10 986 kg·(km~2·a)-1,显著高于我国平均水平.当地旅游人口带入的食品氮输入为0.26×10~3t,占到了流域居民食品氮输入的8%.从氮素的输入量的构成来看,肥料输入是最大的贡献源,占到了流域净氮输入的47%,其次为食品饲料的净氮输入.在空间分布上,乡镇单元的NANI分布呈现明显区域化特征,从流域整体上看呈现北高南低的特点.耕地或人口集中的乡镇NANI强度偏高,洱海流域具有较大的氮素污染风险.  相似文献   
353.
研究了以粉煤灰和氧化铁皮为原料制备聚硅酸铝铁混凝剂的影响因素及产品微观结构和形貌,选取碱化度、nAl:nFe、聚合温度、反应时间对透光率进行4因素3水平响应面实验.得出制备优化方案:碱化度为0.5,nAl:nFe为1.38,聚合温度为39.2℃,反应时间为1.36h,透光率预测值达90.24%,验证试验均值相对误差1.20%,表明RSM优化模型可靠.结合产品表征测试,XRD分析主要物相为氯化钠,大范围衍射驼峰预示着浸出液聚合形成了新的无定形物;FT-IR测试表明聚硅酸与Al3+、Fe3+之间存在较多金属-OH等非离子键络合态;TEM测试结果显示产品为高聚集度和枝化度的网状结构;TG分析表明产品在400℃以前失去结合水和羟基,700℃左右产品主要化学键断裂,对应DSC图中均出现较强吸热峰,产品具有较好的稳定性.  相似文献   
354.
我国沿海地区是土地资源供需矛盾最突出的区域,经济园区超前、超大规划空间规模,加剧了城市的土地矛盾,为解决沿海经济园区合理规划空间扩张的问题,论文以16个沿海经济园区为样本,根据其与城市的区位关系划分为远离城市型、城市边缘型、城市内部型三类园区,分别就三类园区扩张的空间特征及其经济特征进行研究。结果表明:就目前我国经济发展环境及土地政策下,园区发展25 a,最大扩张规模不超过60 km2,园区扩张节奏与经济发展阶段有关,园区建设初期以及“二次创业”阶段是园区扩张的高峰期;不同区位的园区扩张方向与形态存在差异,远离城市型园区扩张形态为多方向扩张与沿交通线路扩张相结合,城市边缘型园区可由宽幅扇形扩张到半圆形,城市内部型园区为内生式与窄小扇形外延式扩张相结合。远离城市的经济园区,空间扩张所需的投资更高,但其为经济发展保证了更大的发展空间,经济产出也相对较高。因此沿海各地规划建设园区时,应结合当地资本实力、园区布局区位、园区所处发展阶段等,合理规划园区扩张规模与扩张节奏。  相似文献   
355.
ABSTRACT: When faced with practical forest land management issues such as the impacts of logging or forest conversion to other land uses, planners ideally require a comprehensive understanding of within drainage basin hydrological processes to determine the most vulnerable areas to increased storm runoff and erosion. Land managers in particular need to know the source areas and magnitude of inputs to the storm hydrograph, in terms of water quantity, sediment and solute transport; and the routing of such hydrographs from headwater to larger drainage basins. The latter includes an overall assessment at various scales of the impacts of forest disturbance and conversion on the water balance. This paper will focus on runoff generation in terms of identifying the various pathways and source areas. Such aspects will be linked with the need for a more comprehensive effort towards the field testing of so-called ‘physically based’ models of runoff generation. Some of the controversial issues arising from the difficulties in reconciling results from hydrochemical investigations with complementary hydrometric studies will be highlighted. Subsequently, attention will be given to topographic-wetness models, which have promising applications in forestland management. In addition, alternative simple models for application at the catchment scale will be assessed. The latter is in recognition that at smaller scales, heterogeneity both in time and space of soil hydraulic properties demand a greater number of parameters in modelling. Such considerations can even prove an obstacle in terms of the confident application of ‘physically based’ models.  相似文献   
356.
从分析小型污水处理厂实验室现状入手,指出当前污水处理厂实验室存在的问题,并就其规范化管理的重要性进行了探讨。  相似文献   
357.
Local-scale and large-scale factors can affect the presence of a species of understory vegetation in the forest. Local-scale factors may be the influence of surrounding trees, while climate and latitude are typically considered large-scale factors. A model for the presence of a species needs to take into account both scales. A conditional logistic model is proposed for those studies where only the local-scale factors are of interest and that avoids estimating the large-scale parameters. Conditioning is carried out by the number of quadrats in the plot where the vegetation is found. As the latter is a sufficient statistic for the large-scale factors, a model free from these parameters is obtained. Data gathered in the permanent sample plots of the 1985–1986 National Forest Inventory of Finland is used for illustration, where the local-scale factor of interest is the influence of the trees, quantified by an index based on the size and location of the trees. The model fitted to Vaccinium vitis-idaea showed a significant and positive influence of Scots pine on the presence of this species, while for Calamagrostis arundinacea, a decrease in the odds ratio was observed due to the influence of Norway spruce.  相似文献   
358.
Scale is important to consider when investigating effects of the environment on a species. Breeding Bird Survey (BBS) data and landscape metrics derived from aerial photographs were evaluated to determine how relationships of bird abundances with landscape variables changed over a continuous range of 16 spatial scales. We analyzed the average number of birds per stop (1985–1994) for five songbird species (family Cardinalidae) for each of 50 stops on 198 BBS transects throughout six states in the Central Plains, USA. Land along each transect was categorized into six cover types, and landscape metrics of fractal dimension (a measure of shape complexity of habitat patches), edge density, patch density, and percent area were calculated, with principal components used to construct composite environmental variables. Associations of bird abundances and landscape variables changed in accordance with small scale changes. Abundances of three species were correlated with edge density and one with component I, which subsumes initial variables of patch density for urban, closed forest, open forest, and open country. Fractal dimension and component II (summarizing amount of closed forest versus open country) were associated with the most species. Correlation patterns of fractal dimension with northern cardinal (Cardinalis cardinalis) and painted bunting (Passerina ciris) abundances were similar, with highest correlations at intermediate to small scales, suggesting indirectly that these species thrive in areas where local habitat conditions are most important. Multiscale analysis can provide insight into the spatial scale(s) at which species respond, a topic of intrinsic scientific interest with applied implications for researchers establishing protocols to assess and monitor avian populations.  相似文献   
359.
针对胶带运输巷火灾时期有毒烟气蔓延严重威胁工作人员的生命安全问题,提出利用水幕阻烟法抑制火灾烟气传播,搭建小尺寸实验台研究水幕对矿井巷道火灾烟气的阻挡效果。通过分析火灾烟气的运移规律,测量温度分布、非水溶性火灾烟气体积分数的变化,检验矿井运输巷内设置水幕阻烟的有效性。实验结果表明:水幕开启后,其下游空间烟气体积分数降低,能够有效阻止火灾烟气的扩散;水幕远离烟气源、增加水幕层数、水幕向上喷射、喷头压力增大均能够提高水幕的阻烟效果。实验为矿井巷道等地下建筑的防排烟设计提供了思路,对火灾的救援与人员的疏散具有重要意义。  相似文献   
360.
Urban areas are generally regarded as major sources of some semivolatile organic compounds and other persistent organic pollutants(POPs) to the surrounding regions. Huge differences in contaminant emissions between urban and rural areas directly affect their fate in environmental media. Little is known about POPs behavior between urban and rural areas at a regional scale. A spatially resolved Berkeley-Trent-Urban-Rural Fate Model(BETR-UR) was designed by coupling land cover information to simulate the transport of POPs between urban and rural areas, and the Bohai Rim was used as a case study to estimate Polycyclic Aromatic Hydrocarbon(PAH) fate. The processes of contaminant fate including emission, inter-compartmental transfer, advection and degradation in urban and rural areas were simulated in the model. Simulated PAH concentrations in environmental media of urban and rural areas were very close to measured values. The model accuracy was highly improved, with the average absolute relative error for PAH concentrations reduced from 37% to 3% compared with unimproved model results. PAH concentrations in urban soil and air were considerably higher than those in rural areas. Sensitivity analysis showed temperature was the most influential parameter for Phen rather than for Bap, whose fate was more influenced by emission rate, compartment dimension, transport velocity and chemical persistence. Uncertainty analysis indicated modeled results in urban media had higher uncertainty than those in rural areas due to larger variations of emissions in urban areas. The differences in urban and rural areas provided us with valuable guidance on policy setting for urban–rural POP control.  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