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521.
网站信息的安全策略研究 总被引:10,自引:3,他引:10
网站是信息的发布中心 ,其数据库中存放着大量的供用户共享的重要信息 ,因此 ,网站信息安全是网站建设和运行过程中应该充分考虑和重视的问题。笔者从信息之源 (数据库 )、数据库运行环境 (操作系统 )以及信息发布平台 (Web服务器 ) 3个方面 ,论述了网站信息安全问题 ,并结合当前流行的实用系统 ,阐述了网站信息的安全策略 相似文献
522.
Scott W. Ator Anthony R. Olsen Ann M. Pitchford Judith M. Denver 《Journal of the American Water Resources Association》2003,39(4):873-885
ABSTRACT: A stratified, spatially balanced sample with unequal probability selection was used to design a multipurpose survey of headwater streams in the Mid‐Atlantic Coastal Plain. Objectives for the survey include unbiased estimates of regional stream conditions, and adequate coverage of unusual but significant environmental settings to support empirical modeling of the factors affecting those conditions. The design and field application of the survey are discussed in light of these multiple objectives. A probability (random) sample of 175 first‐order nontidal streams was selected for synoptic sampling of water chemistry and benthic and riparian ecology during late winter and spring 2000. Twenty‐five streams were selected within each of seven hydrogeologic subre‐gions (strata) that were delineated on the basis of physiography and surficial geology. In each subregion, unequal inclusion probabilities were used to provide an approximately even distribution of streams along a gradient of forested to developed (agricultural or urban) land in the contributing watershed. Alternate streams were also selected. Alternates were included in groups of five in each subregion when field reconnaissance demonstrated that primary streams were inaccessible or otherwise unusable. Despite the rejection and replacement of a considerable number of primary streams during reconnaissance (up to 40 percent in one subregion), the desired land use distribution was maintained within each hydrogeologic subregion without sacrificing the probabilistic design. 相似文献
523.
524.
福岛核事故对中国核电站厂址选择影响研究 总被引:1,自引:0,他引:1
日本福岛核事故源于两个直接因素--地震和海啸,以及两因素的叠加,并导致放射性泄漏对周围居民产生重大影响。针对这些问题,分析中国大陆核电站厂址的地震发生概率、海啸发生概率和人口分布因素,由此评价我国核电站厂址选择的安全性。结果证明:我国大陆核电站远离地震带;沿海不会发生特大海啸;核电站周围人口分布密度符合安全标准,我国核电站具有较高的固有安全性。同时,此次福岛事故也是对我国核电发展的警示,要求不可忽视小概率的超基准设计事故以及多个超基准设计事故叠加的情况;要重新审查中国抗震和海啸等极限事故的标准;要考虑人口密度;要避免两个核电站建设过密的情况。目前,我国已经采取安全检查等措施确保核电站的安全性。这次福岛事故对我国乃至世界核电的发展都是宝贵的经验教训。 相似文献
525.
分析了生活垃圾填埋场渗滤液产生、污染成分及特点,介绍了监测方案制定的基本原则和工作程序,明确了生活垃圾填埋场封场前后渗滤液环境监测的要求,并实证分析两种监测方案的异同。 相似文献
526.
527.
Arzarello M Marcolini F Pavia G Pavia M Petronio C Petrucci M Rook L Sardella R 《Die Naturwissenschaften》2007,94(2):107-112
Some flint lithic artifacts were discovered in the fissure fillings of the well-known Pirro Nord site (Apulia, Southern Italy).
The lithic industry, composed by three cores and some flakes, has been found to be associated to an Early Pleistocene vertebrate
fossil assemblage. The fossil association contains a wide range of micromammals, including Allophaiomys ruffoi and Episoriculus gibberodon and large mammals including Bison degiulii and Equus altidens together with African elements as the gelada baboon Theropithecus and the saber-toothed cat Megantereon whitei. It defines the latest Villafranchian chronological unit (Pirro Nord Faunal Unit) in the Western European mammal biochronology.
The lithic industry of Pirro Nord represents the oldest occurrence of the genus Homo in Europe as it is attributable to a chronological interval between 1.3 and 1.7 Ma. This supports the hypothesis that the
genus Homo, with Oldowaian technology, extended its range in Europe, probably from western Asia, during the first half of the Early
Pleistocene. The new discovery from Pirro Nord changes the chronology of the first arrival of hominids in Europe and offers
new perspectives in the debate about the human dispersal in the Early Pleistocene. 相似文献
528.
Natural regeneration and the height-age structure of small-leaved linden (Tilia cordata Mill.) under a forest canopy were studied with regard to specific features of forest typology on the Ufa Plateau. For the first time, the height-age structure of linden undergrowth was analyzed by an anatomical method, which allowed accurate determination of the actual plant age and linear increment. The results of this analysis made it possible to reveal three periods in the development of linden undergrowth with respect to the linear growth rate and abundance of plants. More successful regeneration of linden was observed in open elements of relief. 相似文献
529.
层次分析法作为一种定性分析与定量计算相结合的多目标决策分析方法,在环境规划、管理和评价领域已有较广泛的应用,比如在城市垃圾填埋场选址、POPs污染物处理处置技术优选、生态环境质量评价等领域。然而,层次分析法在污染场地管理领域的应用尚未见报道。本研究在考虑我国现有修复技术种类、成本费用、环境友好程度、技术成熟度、公共接受程度等方面,建立综合考虑修复方法的技术、经济、社会、环境等因素的层次分析模型,为修复技术优选提供科学依据。 相似文献
530.