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   366篇
  免费   43篇
  国内免费   71篇
安全科学   77篇
环保管理   27篇
综合类   222篇
基础理论   32篇
污染及防治   3篇
评价与监测   44篇
社会与环境   21篇
灾害及防治   54篇
  2024年   2篇
  2023年   7篇
  2022年   14篇
  2021年   20篇
  2020年   17篇
  2019年   16篇
  2018年   11篇
  2017年   12篇
  2016年   24篇
  2015年   24篇
  2014年   18篇
  2013年   24篇
  2012年   42篇
  2011年   48篇
  2010年   25篇
  2009年   25篇
  2008年   12篇
  2007年   23篇
  2006年   19篇
  2005年   16篇
  2004年   8篇
  2003年   10篇
  2002年   10篇
  2001年   7篇
  2000年   9篇
  1999年   4篇
  1998年   4篇
  1997年   5篇
  1996年   1篇
  1995年   7篇
  1994年   7篇
  1993年   1篇
  1992年   1篇
  1991年   3篇
  1990年   2篇
  1988年   1篇
  1987年   1篇
排序方式: 共有480条查询结果,搜索用时 15 毫秒
191.
本文通过百花湖沉积物柱芯不同化学相磷含量分布,孔隙水地球化学及早期成岩模式和通量估算等研究,揭示了磷在早期成岩过程中迁移,转化和富集规律,揭示某些湖泊表层沉积物几厘米磷蓄积浓度的增加与磷在早期成岩过程中的行为有关。  相似文献   
192.
In the `Des Vieux Arbres' ecological reserve situated within northwestern Québec, 40 band dendrometers were installedon 7 of the major boreal tree species. The late Spring–early Summer daily radial activity registered in 1997 was related todaily weather variables. For each tree species, the daily mean i) cumulative radial increment and ii) radial activity indexedseries obtained by first-difference standardization were analyzed. The results indicate the existence of strong similarities among the 7 species. All showed strong synchronousfluctuations in radius during late winter and early spring. Thisperiod ended with a short but sharp increase in radial increments that marked the passage of water into the stem. Thisinitial swelling, less obvious in Pinus species was followed by a prolonged period of little change in radial activity. Meteorological data indicated that air temperature waspositively related to stem swelling during the late winter–earlyspring period. Both air and soil temperatures became negatively related to radial expansion once the passage of water has occurred in the stem. Starting in early June, all species registered a sustained increase in radial increments possiblyassociated with active cell division. After this, radial expansion was negatively related to air temperature and positively to rainfall.  相似文献   
193.
Analysis of summer and winter vegetable samples during 2002–2003 for pesticidal contamination was carried out on Gas Chromatograph-Electron Capture Detector with capillary columns. The contamination levels of winter vegetables (average concentration of 4.57, 6.80 and 5.47 ppb respectively for Lindane, Endosulphan and DDT) were found to be slightly higher than the summer vegetables (average concentration of 4.47, 3.14 and 2.82 ppb respectively for Lindane, Endosulphan and DDT). The concentration of these organochlorine pesticides in summer and winter vegetables were well below the established tolerances but continuous consumption of such vegetables even with moderate contamination level can accumulate in the receptor's body and may lead to chronic effects that could be fatal.  相似文献   
194.
基于国家干线公路交通量信息,运用GIS的路网线性参考系统,计算珠三角地区夏季NOx和VOCs排放量,使用最大增量反应活性(MIR)和经验公式,分别估算VOCs和NOx的O3生成及其强度的空间分布特征.结果表明,夏季VOCs的排放量占比总体上与各类型车辆数占比一致,而汽油车的NOx排放量占比与车辆数差异较大;VOCs排放的分布与NOx基本相似,广州市是NOx和VOCs排放量最高的城市,珠海、中山和江门3个城市的排放量较小;NOx的O3生成总量与生成能力成反比,所有车型中烯烃和芳香烃对O3生成贡献率都是最大的,而排放量较大的烷烃生成O3量最低;路网密度大的广州市、深圳市,汽车排放的NOx和VOCs量相对较高,其产生的O3浓度也较高,对于路网密度较小的城市(如珠海市),其O3污染主要以交通干线为中心,向外扩散,O3生成量较小.  相似文献   
195.
城市燃气管线泄漏极易导致火灾爆炸等重大安全事故,严重威胁城市安全。通过监测预警技术,快速准确地发现泄漏,防止可燃气体聚集,是保障燃气管线安全运行的重要手段。提出了一种燃气管线相邻地下空间安全监测预警方法,构建了风险识别、预测预警、分析推演和决策支持一体化安全监测系统,并应用于合肥市2.5 km燃气管线及其相邻空间高风险区域。结果表明,提出的燃气管线相邻地下空间安全监测方法可用于燃气管线泄漏监测预警,以减少或避免燃气泄漏引发的火灾爆炸事故。  相似文献   
196.
为研究受损钢结构改造施工安全预警状况,建立受损情况下钢结构改造施工安全预警指标体系,并针对BP神经网络算法易陷入局部最优的问题,提出了用改进粒子群算法(IPSO)对BP神经网络权重及阈值进行调整的IPSO-BP安全预警评估模型。通过分析某单层重钢厂房受损现状,针对其结构损伤情况和已构建的安全控制指标体系进行数值模拟分析。研究结果表明:与传统的BP模型相比,IPSO-BP模型具有更好的预测能力,构建的安全预警指标体系及预警模型可以很好地对受损钢结构改造施工过程安全状况进行综合评估,对受损钢结构改造施工安全控制具有一定的参考价值。  相似文献   
197.
Abstract: Climate change will likely have profound effects on cold‐water species of freshwater fishes. As temperatures rise, cold‐water fish distributions may shift and contract in response. Predicting the effects of projected stream warming in stream networks is complicated by the generally poor correlation between water temperature and air temperature. Spatial dependencies in stream networks are complex because the geography of stream processes is governed by dimensions of flow direction and network structure. Therefore, forecasting climate‐driven range shifts of stream biota has lagged behind similar terrestrial modeling efforts. We predicted climate‐induced changes in summer thermal habitat for 3 cold‐water fish species—juvenile Chinook salmon, rainbow trout, and bull trout (Oncorhynchus tshawytscha, O. mykiss, and Salvelinus confluentus, respectively)—in the John Day River basin, northwestern United States. We used a spatially explicit statistical model designed to predict water temperature in stream networks on the basis of flow and spatial connectivity. The spatial distribution of stream temperature extremes during summers from 1993 through 2009 was largely governed by solar radiation and interannual extremes of air temperature. For a moderate climate change scenario, estimated declines by 2100 in the volume of habitat for Chinook salmon, rainbow trout, and bull trout were 69–95%, 51–87%, and 86–100%, respectively. Although some restoration strategies may be able to offset these projected effects, such forecasts point to how and where restoration and management efforts might focus.  相似文献   
198.
While much work has been invested in addressing the economic and technical basis of disaster preparedness, less effort has been directed towards understanding the cultural and social obstacles to and opportunities for disaster risk reduction. This paper presents local insights from five different national settings into the cultural and social contexts of disaster preparedness. In most cases, an early warning system was in place, but it failed to alert people to diverse environmental shocks. The research findings show that despite geographical and typological differences in these locations, the limitations of the systems were fairly similar. In Kenya, people received warnings, but from contradictory systems, whereas in the Philippines and on the island of Saipan, people did not understand the messages or take them seriously. In Bangladesh and Nepal, however, a deeper cultural and religious reasoning serves to explain disasters, and how to prevent them or find safety when they strike.  相似文献   
199.
干沟泥石流是一条典型的下游集中补给型泥石流沟,其物源的启动、流通与堆积在700 m范围内完成.以2005年干沟泥石流过程为例,应用三种计算公式对该沟泥石流的动力学参数进行了计算.通过计算发现,三种公式计算结果差别不大,并取其平均值作为计算结果.根据干沟泥石流流量计算和形态调查对比分析,认为2005年干沟泥石流的形成过程具有明显的堵溃效应,且前期降雨对泥石流的发生影响较为明显.在对干沟泥石流动力学参数计算、物源补给特征及形成过程分析的基础上,认为干沟在2005年后易形成高频泥石流,对该沟泥石流开展监测预警尤为必要,提出了该沟泥石流监测预警方式并予以实施,可为干沟泥石流的防灾减灾提供科学依据.  相似文献   
200.
“万里长江,险在荆江”,民国前期(1912—1927)荆江两岸地区水灾频仍。在荆江两岸地区1912—1927年洪水灾害相关资料的基础上,运用一般统计方法和理论分析了这一时期洪水灾害的若干特征,即普遍性、连续性、积累性和区域性四个特征。对洪水灾害基本特征及其规律的探讨至今对于有效的进行水患治理与防治仍有着深远的影响。  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