共查询到20条相似文献，搜索用时 222 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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介绍了几种GPS控制网平差方法的优缺点，通过大连金州区航测数字化成图任务时所实施的的基础控制为例，介绍大面积GPS控制网在平差时应选用的方法。 相似文献
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GPS全球空间定位技术，已广泛地应用在许多不同领域，由于空间卫星构成的前方交会信息不受时间、气候、通视等因素的影响，大大地提高了作业效率，大大地降低了劳动强度，使内外业的衔接更有机和有时效，受到了广泛的欢迎。目前从多等级的控制作业及图根控制，都在采用这种先进的技术。下面仅就接收和转换时，控制其长度变形谈点看法。 相似文献
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控制论是研究各类系统的调节和控制规律的科学，是具有方法论意义的科学理论。整个控制过程就是一个信息流通的过程，控制就是通过信息的传输、变换、加工、处理来实现系统高效运转。控制论注重系统运行的严密性，信息流动的通畅性和进程的实时可控性；还注重过程信息的反馈，只有通过对反馈信息的分析，找出其中负面反馈的结症，才能使系统的目标指向减少偏移，趋于完备的状态。 相似文献
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有害植物金钟藤的隔离带式化学控制研究初报 总被引：1，自引：0，他引：1
有害植物治理是生态学面临的重要难题．为控制危害广州市龙眼洞林场的大型木质藤本金钟藤（Merremia boisiana van Ooststr），本研究进行了治理技术的探索．通过比较大面积化学除莠、人工清除和隔离带式化学控制3种方法对金钟藤及环境的影响，阐明了各种方法的利与弊．大面积化学除莠和人工清除虽能清除金钟藤，但都造成了地表长期大面积裸露，从而引起严重的水土流失，同时前者还引起环境污染．隔离带式化学控制既能在较长时期内有效遏制金钟藤的扩散，为林地由外到内恢复创造条件，又避免了水土流失．隔离带式化学控制试用了斩荒（草甘膦．乙羧氟草醚混剂）、国产草甘膦、农达、2－甲-4-氯4种农药，综合控制效果以斩荒最优，有效控制时间180d以上，第180d对地上部分、绿枝条和老茎鲜重的抑制率分别为85．8％、99．7％和70．0％，明显高于单一使用草甘膦．国产草甘膦与进口农达无显著差异．金钟藤老茎占地上部分近一半的鲜重，老茎受抑制率低、抗药性强，是金钟藤抗除草剂能力强的主要原因． 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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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