共查询到20条相似文献，搜索用时 78 毫秒
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华南地区小流域水污染控制规划初探 总被引：1，自引：2，他引：1
随着经济和城市化进程的快速发展，华南地区小流域水环境污染日趋严重，因此以规划的方法控制该区小流域水污染成为了一种重要的途径。从水环境污染控制规划的基本定义出发，重点分析了小流域水环境污染控制规划的一般规范及其在实施中存在的一些问题，并就这些问题提出了相应的对策，指出小流域进行水环境污染控制时必须加强环境意识，提高环境工作者素质，结合自身实际，走出一条既符合中国国情更符合华南地区小流域的水污染控制规划道路，为华南地区的持续，快速发展创造条件。 相似文献
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我国水环境非点源污染研究与展望 总被引：79，自引：5，他引：79
剖析土地利用方式与污染负荷之间的内在联系是非点源污染研究的基本出发点，采用大区域调查分析与小区实测相结合，引入新技术，并进行模型化研究。今后应完善非点源污染总量控制与排污权交易工作，开发非点源污染信息系统与专家系统，加强人工模拟实验研究，开展污染控制、管理对策研究。 相似文献
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云南元谋土地荒漠化特征及原因分析 总被引：22，自引：1，他引：22
元谋地区由于青藏高原隆起而产生的气候变化和人类活动强烈干扰而形成的土壤加速侵蚀，使土地荒漠化加速发展，主要表现在土地资源不断被蚕食和土壤退化而导致的土地质量下降，最终使土地荒废．因此，控制人口增长，调整区域农林牧结构布局，增加地表覆盖度，是控制区域土地荒漠化发展的主要措施。 相似文献
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下面介绍一种变形的方格法——“231”几何图形控制法的作图步骤：一、建立“231”几何图形控制网：用方格法缩放地图，关键是建立方格控制网。但在图形弯曲多变处，又可在有关方格内加绘对角线、中位线等，从而将“方格”变形为三角形、长方形等。依据这一原理，在画中国轮廓图时，我们只要按一定的比例关系，建立一套由2个正方形、3个三角形，1个长方形组成的控制网即可(如图1)。其画图顺序为： 相似文献
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发菜贸易对内蒙古草地生态环境的影响及政策建议 总被引：2，自引：0，他引：2
本文就发菜贸易对内蒙古草地生态的影响进行了经济学评价，并从环境经济学角度进行了原因分析，得出其根本原因是市场失灵和干预失灵导致环境成本外部化的结论，为此提出运用经济手段，按照控制、干扰、引导的思路，控制野生发菜贸易，大力发展发菜的人工培植和寻找并研制发菜的代用品的政策建议。 相似文献
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区域环境变迁与持续发展的互动关系 总被引：1，自引：0，他引：1
区域历史进程中持续发展与环境变迁表现出了复杂的互动关系，两种动态过程紧密地交织在一起，通过人类活动互相作用，互相影响，持续发展，环境变迁与人类活动的内容在不同时代表现出不同的主题，并受到自然和人为因素的调节与控制，文中还简要阐明了当代可持续发展的主题，指出解决PRED问题要注意控制人口数量，提高人口素质；消除贫困，达到全球环境共有共治共保共享。 相似文献
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STRATIGRAPHY, DENSITY AND CRYSTAL STRUCTURE OF FIRN-ICE AT DE08-A VERY HIGH ACCUMULATION SITE ON LAW DOME, ANTARCTICA 
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下载免费PDF全文 《极地研究》1991,2(2):83-85
An approximately 195 mm diameter firn/ice core, 234 m long, was thermally drilled in 1987 austral summer at DE08 (66°43′S, 113°12′E) on Law Dome, East Antarctica, where the accumulation rate is about 1200kg/(m~2. a); 10m ice temperature is about-18.8℃. Analysis was mainly made at the site immediately after drilling. The snow stratigraphy at DE08 is characterised by the lack of coarse-grained snow and other distinct visible feature normally corresponding to annual layers. There is a smooth transformation from fine-grained snow at shallow depth to ice at about 80-90m which is greater than that at most other polar locations due to its abnormally high accumulation rate. According to the marked change in the trend of density with depth and in the crystal properties four stages of the transformation of snow to ice and development of crystal structure can be distinguished; settling stage (0-10m); sintering stage (10-90m); rapid crystal growth stage (90-170m); and dynamic metamorphism stage (170-234m). The 相似文献
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大阿尔玛京卡河流域的雪崩与治理 总被引：1，自引：0，他引：1
大阿尔玛京卡河流域危险主要出现在中山森林－草原带和高山雪冰带。受局地气候、地貌与环境的综合作用，流域雪崩规模小、路程短，多见全程雪崩；雪崩类型单调，以干、湿雪崩占统治地位，在９０％以上，雪崩发生地点集中，而且每年都有出现，只有数量上的差异性。在西风气流的控制下，冬季积雪层的变质过程具温度梯度变质特征。积雪层负温梯度大，雪层深霜的发育和生长迅速，呈出“干寒型”积雪的基本特征。雪崩对道路、居民点和建筑 相似文献
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The fabrics and crystals of Bohai one year ice show that the noncontinuous ice growth rate enables the level ice layers with different amount of air bubbles to be formed in lower part of an ice sheet which was clearly seen from CT technology; typical grain ice and columnar ice occur in the grey ice which grows in stable water; thaw refrozen ice and rafted ice have their specific crystal characters. On the Arctic sea ice, the ice core located at 72°24.037′N, 153°33.994′W and 2.2 m in length was a 3 year ice floe and a new sort of crystal was found, which is defined as refrozen clastic pieces. The crystal profile of the ice core 4.86 m in length located at 74°58.614′N, 160°31.830′W shows the evidence that ice ridge changed into hummock. 相似文献
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SIGNE KJELSTRUP RATKJE 《Polar research》1985,3(2):141-143
This note shows how the rate of ice crystal growth during temperature gradient metamorphosis can be calculated using irreversible thermodynamics. The method describes the transfer of mass as a consequence. of heat transfer. The main heat transfer is the latent heat change by condensing and freezing. Local equilibrium and no convection is assumed. The transport equation, with the temperature gradient as the force of transport, predicts mass transfer measurements. 相似文献
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碳酸氢钠(NaHCO_3)俗称小苏打,其产品质量取决于颗粒的大小,晶体的形貌和样品的纯度等诸多因素。本论文基于连续稳态MSMPR结晶器原理,研究了不同停留时间下,碳酸氢钠从碳酸钠溶液中冷却结晶过程动力学。利用实验数据建立了NaHCO_3的结晶动力学操作模型。实验和计算结果表明,随停留时间的增加,NaHCO_3过饱和度降低,晶体生长速率和成核速率均减小,相应的平均粒径增加,细颗粒含量减小;适当延长停留时间是制取高品质小苏打产品的有效途径。冷却结晶过程可有效增加小苏打产量,小苏打收率维持在55%左右。此外,一定Na_2CO_3存在下冷却结晶碳酸氢钠晶体形态由细长的针状变为规整的片状。 相似文献
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Based on the case study of peripheral urban areas in Beijing, this paper aims to identify the factors which will influence the spatial distribution of peri-urban recreation areas, by analyzing the collected data from questionnaires, online survey, documentation and field investigations (2007). In order to achieve sound information, relevant data from different management departments, owners and land-use types involved in the case study area are collected. A sampling database for peri-urban recreation areas in Beijing is established, and GIS spatial analyses as well as statistic analyses are applied. The result indicates that spatial distribution of recreation areas is majorly influenced by four factors, e.g. tourism attractions and environmental conditions, policy and spatial governance, consumption demand and preference, land price and availability. Tourism attractions and environmental conditions are dominant factors for public recreation areas. Commercial recreation areas are highly related with accessibility. Agricultural recreation areas are usually attached to special farmlands near large-scaled scenic areas. Meanwhile, recreational business clusters have appeared in suburbs influenced by mass recreation market growth. Controlled by the land price, commercial recreation areas are differentiated on their scales and developing intensity. Policy and spatial governance have made arrangements of recreation areas more balancing and more human- oriented. A peri-urban recreation area model is therefore established on the basis of this analysis, which can guide urban planning and designing, land-use planning and recreation resource development. 相似文献
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Based on the case study of peripheral urban areas in Beijing, this paper aims to identify the factors which will influence
the spatial distribution of peri-urban recreation areas, by analyzing the collected data from questionnaires, online survey,
documentation and field investigations (2007). In order to achieve sound information, relevant data from different management
departments, owners and land-use types involved in the case study area are collected. A sampling database for peri-urban recreation
areas in Beijing is established, and GIS spatial analyses as well as statistic analyses are applied. The result indicates
that spatial distribution of recreation areas is majorly influenced by four factors, e.g. tourism attractions and environmental
conditions, policy and spatial governance, consumption demand and preference, land price and availability. Tourism attractions
and environmental conditions are dominant factors for public recreation areas. Commercial recreation areas are highly related
with accessibility. Agricultural recreation areas are usually attached to special farmlands near large-scaled scenic areas.
Meanwhile, recreational business clusters have appeared in suburbs influenced by mass recreation market growth. Controlled
by the land price, commercial recreation areas are differentiated on their scales and developing intensity. Policy and spatial
governance have made arrangements of recreation areas more balancing and more human-oriented. A peri-urban recreation area
model is therefore established on the basis of this analysis, which can guide urban planning and designing, land-use planning
and recreation resource development. 相似文献