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   44篇
  免费   2篇
  国内免费   2篇
测绘学   1篇
大气科学   1篇
地球物理   5篇
地质学   12篇
海洋学   2篇
综合类   4篇
自然地理   23篇
  2022年   1篇
  2021年   4篇
  2020年   3篇
  2019年   2篇
  2018年   3篇
  2017年   6篇
  2016年   5篇
  2015年   1篇
  2014年   2篇
  2013年   1篇
  2012年   2篇
  2011年   3篇
  2009年   3篇
  2005年   1篇
  2003年   1篇
  2002年   1篇
  2000年   2篇
  1999年   1篇
  1995年   1篇
  1994年   1篇
  1992年   1篇
  1991年   1篇
  1990年   1篇
  1983年   1篇
排序方式: 共有48条查询结果,搜索用时 15 毫秒
11.
模糊直接识别方法在湘南地区成矿预测中的应用   总被引:2,自引:0,他引:2  
周子勇  程方道 《物探与化探》1995,19(4):271-279,263
本文利用信息量法及模糊直接识别方法对湘南地区的地质、物化探资料进行综合处理来优选找矿靶区,取得了一定的效果,为靶区优选提供了一条新的途径.  相似文献   
12.
Brown shrimp (Farfantepenaeus aztecus) are an important commercial aquatic species experiencing loss of inshore marsh nursery habitat in coastal Louisiana. To study inshore brown shrimp movements and identify aspects of essential habitat important for sustaining brown shrimp populations, we collected juvenile brown shrimp in April and May 2000, the time of annual maximum brown shrimp abundance, in a small 1-km2 marsh area on the central Louisiana coast. Drop sampling showed average shrimp densities of 1.6–2.4 m−2 in shallow marsh ponds and seining indicated lower densities of 0.5–0.9 m−2 in nearby shallow channel and open bay sites. Smaller shrimp (< 50 mm) fed disproportionately on benthic diatoms and small harpacticoid copepods, while large shrimp fed more frequently on larger-bodied amphipods and tanaids. We developed novel chemical approaches to estimate patterns of shrimp residency and movement using carbon and nitrogen stable isotopic determinations. Resident shrimp had isotopic values similar to average foods and showed consistent isotopic spacings between fast and slow turnover tissues. Residency was highest (47–55%) in ponds and shallow channel habitats and much less in open bays and deep channels (4–27%). There was sparse evidence for dietary specialization among individull shrimp. The results support the view that small 10–20 mm postlarval and juvenile brown shrimp arriving in estuaries from offshore waters continue movement through sub-optimal habitats (deep channels and open bays), but exhibit much less movement once an optimal habitat (marsh ponds or shallow channel margins) is reached. This study also indicated that combining estimates of shrimp densities, residency, growth rate, and mortality allows evaluation of the importance of different habitat types for shrimp production. Shallow ponds that in many ways resemble fertile aquaculture ponds appear to be hot spots for brown shrimp production, and coastal preservation and restoration efforts should focus on these areas as important for sustaining shrimp fisheries.  相似文献   
13.
整合脱钩模型、耦合协调模型和工业化城镇空间响应测度模型,采用ESDA和GWR等方法,以镇域为研究单元,分析了2003~2015年徐州市工业化与城镇空间耦合格局及影响因素。结果表明:徐州市工业化与城镇空间的脱钩关系呈现由无脱钩向绝对脱钩状态演化,二者之间的耦合协调程度呈增强趋势,但耦合作用不强;徐州市镇域工业化城镇空间响应程度呈波动性增强之势,各镇域间差异在逐渐增大;徐州工业化城镇空间响应强度差异的“一带”、“两翼”格局正在形成,交通区位优越类镇域尤为显著,表明再生性资源型城市工业化城镇空间响应的禀赋基础正在发生改变; 弱响应镇域主要集中于远离城市且区位不便的区域,持续表现为冷点区域,与经济发展水平的区域格局具有一致性;徐州市工业化城镇空间响应的影响因素作用程度呈现政府调控>投资因素>发展阶段>基础设施的特征,且均呈减弱之势,但各因素的影响作用表现出显著的空间异质性。  相似文献   
14.
In Mediterranean semi‐arid conditions, the availability of studies monitoring channel adjustments as a response to reforestation and check dams over representative observation periods, could help develop new management strategies. This investigation is an integrated approach assessing the adjustments of channel morphology in a typical torrent of southern Italy after land‐use changes and check dam construction across a period of about 60 years. A statistical analysis of historical rainfall records, an analysis of land‐use changes in the catchment area and a geomorphological mapping of channel adjustments were carried out and combined with field surveys of bed surface grain‐size over a 5‐km reach including 14 check dams. The analysis of the historical rainfall records showed a slight decrease in the amount and erosivity of precipitation. Mapping of land‐use changes highlighted a general increase of vegetal coverage on the slopes adjacent to the monitored reaches. Together with the check dam network installation, this increase could have induced a reduction in water and sediment supply. The different erosional and depositional forms and adjustments showed a general narrowing between consecutive check dams together with local modifications detected upstream (bed aggradation and cross‐section expansion together with low‐flow realignments) and downstream (local incision) of the installed check dams. Changes in the torrent bends were also detected as a response to erosional and depositional processes with different intensities. The study highlighted: the efficiency of check dams against the disrupting power of intense floods by stabilizing the active channel and the influence of reforestation in increasing hillslope protection from erosion and disconnectivity of water and sediment flows towards the active channel. Only slight management interventions (for instance, the conversion of the existing check dams into open structures) are suggested, in order to mobilize the residual sediment avoiding further generalized incision of the active channel and coast line erosion. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   
15.
中国区域经济韧性特征与影响因素分析   总被引:4,自引:2,他引:2  
从经济维持性和恢复性2个方面定量化分析中国31省(市)(未包含港澳台数据)应对1997年亚洲金融危机和2008年全球金融危机的经济韧性特征,并对其主要影响因素进行了研究。结果发现:在亚洲金融危机中,西部地区的经济维持性较高,中部地区的经济维持性普遍较低;经济恢复性较高的省市主要集中在中部地区,而东部和西部地区经济恢复性较低,经济维持性和经济恢复性呈现一定的负相关。各省(市)应对全球金融危机的经济维持性普遍较高,经济维持性较低的区域主要分在东部沿海区域和沿长江经济带地区,而经济维持性较高的区域主要集中在西部地区。在亚洲金融危机中,第二产业表现出了较强的经济韧性,而在全球金融危机中第三产业经济韧性较好。影响2次经济危机中韧性能力的主要因素是不同的,区位条件、人均固定资产投资额和人均GDP的解释力较强,但在2次经济周期中的作用方向不同。  相似文献   
16.
通过构建“多投入-多产出”出口效率测度模型,探讨了2001—2019年中国对49个主要贸易伙伴高端技术产品出口效率的时空分异特征及驱动因素。研究发现:① 中国高端技术产品出口效率整体呈增长趋势,国别间差距逐渐缩小。② 中国高端技术产品出口效率的空间格局明显存在空间集聚特征,高-高型国家集聚于“一带一路”沿线地区并向西蔓延,而低-低型国家分布范围逐年缩小。③ 双边贸易关系对中国高端技术产品出口效率的影响存在空间溢出效应,中国对贸易互竞国家高端技术产品的出口效率要比其对贸易互补国家的出口效率低0.017%,而对贸易互竞国家的邻近国高端技术产品出口效率要比其对贸易互补国家的邻近国出口效率高0.088%。④ 管制性制度差异对出口效率存在直接促进作用,而经济自由度差异对出口效率整体上有阻滞(负溢出)作用。  相似文献   
17.
In this work, we present a new method in designing static output‐feedback H controllers suitable for vibrational control of buildings under seismic excitation. The method produces a Linear Matrix Inequality (LMI) formulation that allows obtaining static output‐feedback controllers with different information structure constraints by imposing a convenient zero–nonzero structure on the LMI variables. The application of the proposed methodology is illustrated by designing centralized and decentralized velocity‐feedback H controllers to mitigate the seismic response of a five‐story building. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   
18.
基于信息熵的海峡西岸经济区城市竞争力分析   总被引:1,自引:0,他引:1  
从宏观经济、社会发展与资源环境三个方面构建城市竞争力评价指标体系,并运用熵值法对海西经济区20个地市的竞争力进行综合分析.在此基础上,运用聚类分析法对海西经济区主要城市的综合竞争力进行分类,并针对各类城市竞争力的增强提出相应的对策,以强化各类中心城市的辐射能力,提升海西经济区在中国东部沿海区域经济发展中的地位,进而推动两岸经济一体化历程.  相似文献   
19.
The generation of electricity has been identified as one of the main pollutant activities, and some studies have established an increment of heavy metals in soil in the areas surrounding these plants. The aim of this study was to evaluate the soil concentrations of heavy metals in the zone surrounding a thermoelectric power in Mexico. Thirty-two top soil samples (0–5 cm) were collected; additionally, four depth profiles (1 m) were investigated. Median concentrations for chromium, vanadium, nickel, mercury, and cadmium were 47, 47, 73, 0.02, and 0.01 mg/kg, respectively. Higher Cr, Ni, and V concentrations were observed in the soil depth profiles located closer to the plant in comparison with the concentrations found in the soil depth profile located further away from the plant; these results may indicate a possible accumulation of these metals. The geoaccumulation index results indicated that most of the sites were in the classifications of unpolluted and unpolluted to moderately polluted (classes 1 and 2). The statistical results showed that downwind of the plant in relation to the prevailing winds, there was a strong correlation between soil concentrations of chromium, copper, nickel, and vanadium. Based on the results of this study, it can be concluded that the use of fuel oil at the thermoelectric plant contributed to the accumulation of vanadium and nickel in the soil of the surrounding areas, as well as chromium and copper.  相似文献   
20.
Based on the adaptive analysis paradigm, this paper constructs an evaluation index system and an evaluation model of the level of industrial ecology of a restricted development zone from the perspective of the industrial system and of the environmental system, and studies the spatial-temporal differentiation characteristics and the driving factors of the level of industrial ecology of the restricted development zone of the Shandong Province, China, by using a variety of measurement methods. The results show that: 1) In the temporal dimension, the level of industrial ecology of the research area increased from 2005 to 2017, while in the regional dimension, it was higher in the eastern coastal areas, followed by the northwestern area and the southwestern area; 2) In the spatial dimension, from2005 to 2017 the level of industrial ecology of the research area had a clear spatial dependence, and the regional spatial agglomeration of the restricted development zones with similar industrial ecology levels become increasingly evident; 3) On the whole, the industrial ecology level in the study area had a clear spatial differentiation pattern, as it was higher in the north and in the east and lower in the south and in the west. Moreover, its evolution model changed from a ‘three-core driven model' to a ‘spatial scattered mosaic distribution model', and then to a ‘single-core driven model'; 4) Industrial ecology was positively correlated with economic development, foreign investment, science and technology, and negatively correlated with the government role, while industrial structure and environmental regulation failed to pass the statistical significance test.  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