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前苏联是世界上铁路运输利用率最高的国家。本文从其铁路发展的背景条件出发，分析了铁路成为前苏联最主要运输方式的原因，并进一步探讨了前苏联铁路网的建设、发展和分布特点，对我国正在进行的大规模铁路建设有一定借鉴意义。 相似文献
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Benjamin M. Rau Dale W. Johnson Bruce A. Roundy Richard F. Miller Todd G. Caldwell Annmarie Lucchesi 《Journal of Arid Environments》2011,75(9):827-835
Vegetation changes associated with climate shifts and anthropogenic disturbance can have major impacts on biogeochemical cycling and soils. Much of the Great Basin, U.S. is currently dominated by sagebrush (Artemisia tridentate (Rydb.) Boivin) ecosystems. Sagebrush ecosystems are increasingly influenced by pinyon (Pinus monophylla Torr. & Frém and Pinus edulis Engelm.) and juniper (Juniperus osteosperma Torr. and Juniperus occidentalis Hook.) expansion. Some scientists and policy makers believe that increasing woodland cover in the intermountain western U.S. offers the possibility of increased organic carbon (OC) storage on the landscape; however, little is currently known about the distribution of OC on these landscapes, or the role that nitrogen (N) plays in OC retention. We quantified the relationship between tree cover, belowground OC, and total below ground N in expansion woodlands at 13 sites in Utah, Oregon, Idaho, California, and Nevada, USA. One hundred and twenty nine soil cores were taken using a mechanically driven diamond tipped core drill to a depth of 90 cm. Soil, coarse fragments, and coarse roots were analyzed for OC and total N. Woodland expansion influenced the vertical distribution of root OC by increasing 15-30 cm root OC by 2.6 Mg ha−1 and root N by 0.04 Mg ha−1. Root OC and N increased through the entire profile by 3.8 and 0.06 Mg ha−1 respectively. Woodland expansion influenced the vertical distribution of soil OC by increasing surface soil (0-15 cm) OC by 2.2 Mg ha−1. Woodland expansion also caused a 1.3 Mg ha−1 decrease in coarse fragment associated OC from 75-90 cm. Our data suggests that woodland expansion into sagebrush ecosystems has limited potential to store additional belowground OC, and must be weighed against the risk of increased wildfire and exotic grass invasion. 相似文献
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Local labor market policies of the federal government are critically evaluated with respect to their target efficiency and underlying theoretical assumptions. Policies of the Economic Development Administration are considered to be target inefficient compared to those of the Comprehensive Employment Training Act. Experimental mobility policies of the Department of Labor appear to be have questionable impact locally as opposed to nationally. Some local hybrid programs offer improved place and people targeting. 相似文献
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19世纪末20世纪初,美国成为世界第一大经济体,亟须开辟海外新市场。为了争夺当时被认为是潜在的“最大的世界市场”,美国侵占西班牙在南海东岸的殖民地菲律宾,将其作为进入中国市场的据点,这是美国对南海地缘的最初认知。在以后的30多年时间里,美国都没有染指南海,直到日本侵略东南亚。日本把东南亚纳入“大东亚共荣圈”,利用南海地缘优势攻击美军,使南海首次呈现重要的地缘战略价值。南海地缘的新变化促使美国重新认知南海。此后,随着“边缘地带论”的兴起,美国越发重视南海的地缘战略价值,并谋求为自己的国家利益服务。进入20世纪50年代,亚太形成了截然对立的以中国为首的社会主义阵营和以美国为首的资本主义阵营。遏制共产主义在亚太扩张成为美国推行霸权战略的总方针。这直接影响美国对南海的地缘战略认知,利用南海的地缘战略价值围堵遏制中国就成为美国对华政策的必然选项。 相似文献
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Internal migration within the United States continues to transform both the magnitude and composition of population at all geographic scales. During 1994 ‐ 1995, the majority of counties gained both people and income, largely as a consequence of net outmigration by higher income migrants from the nation's most populous cities. Regionally, net gainers of both people and income included counties in the West and South as well as other areas renowned for environmental amenities. Spatially, net migration flowed down the urban hierarchy from large central cities to adjacent suburbs which, in turn, exported migrants to exurban areas. Large cities tended to exchange migrants with nearby counties as well as other large cities. Migration patterns such as these are contributing to spatial deconcentration and economic disparity. 相似文献
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Records of terminus positions for the 1960s to 1980s have been obtained for 51 glaciers in the Greater Caucasus Mountains between the Black Sea and Caspian Sea, between latitude 40° and 44° N and longitude 40° and 49° E. These records have been analyzed as percentage of glaciers observed retreating, advancing, and stationary, displayed as a five-year moving average. The main result is the absence of the clear trend towards glacier advance found in the Alps between the 1960s and 1980s by both Patzelt (1985) and Wood (1988), suggesting a phase difference in the climates of the Alps and the Caucasus. [Key words: glaciers, glaciology, Greater Caucasus Mountains, Alps.] 相似文献
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Rohan G. Clark 《The Australian geographer》1989,20(1):65-73
Australian road funding in the 1970s and 1980s has been characterised by conflict between federal and state governments over control of spending. This has influenced both total funds made available and spending priorities between national, arterial and local roads. Having the constitutional responsibility for roads, state governments have refused to discuss priorities with the Commonwealth, have not stated policies, have given the Australian government as little public acknowledgement as possible, have spent money on markedly different priorities, and yet are changing their means of determining priorities to reflect changing community wishes. Interestingly, at neither state nor federal level is there evidence of pursuance of a single, dominant policy objective. 相似文献
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Nufar Avni 《Urban geography》2019,40(4):488-505
In the last decade, justice has been revived as a primary criterion for the analysis and evaluation of planning policies. This paper continues this line of research by examining a proposed redevelopment project in Washington, D.C. that sets equitable development as its goal . The proposed 11th Street Bridge Park would be a top-notch elevated park, physically and symbolically connecting D.C’s wealthy west with the disadvantaged east. The project is managed by a nonprofit organization and seemingly stands out in its progressive vision: An Equitable Development Plan has been developed in an attempt to secure the future of the local residents in light of the neighborhood's anticipated gentrification. However, preliminary findings show that despite explicit commitment to equity, the planning of the park also resurfaces racial and class tensions . The analysis of procedural and substantive aspects of justice in this case suggests that issues of recognition, power and representation are instrumental to fully understand urban (in)justices. 相似文献
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《Urban geography》2013,34(1):24-48
This paper investigates the spatial and hierarchical patterns of interstate banking, major interstate-banking command and control centers, and the spatial structure of the major interstate-banking organizations in the early 1990s. The research has identified a distinct geographical pattern of interstate banking, a spatially skewed and regionally focused pattern of interstate-banking command and control fields, 15 interstate-banking hierarchical systems, and dominance of regional and western centers over New York and Chicago in interstate banking. In addition, determination of major interstate-banking command and control centers is discussed and the 26 largest centers are identified. Finally, this paper demonstrates that spatial networks of major bank holding companies, especially those of regionals and super-regionals, are the foundation of the spatial structure of interstate banking. 相似文献
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Kent M. McGregor 《自然地理学》2013,34(3):288-301
The Palmer Index was used to compare the droughts of the 1930s and the 1950s in the central United States. A series of maps was produced to compare the droughts in terms of location, severity, and duration. The results indicated the 1930s drought lasted longer and consisted of three distinct waves. The 1950s drought, although shorter in overall duration, was actually more intense over a larger area for a longer period. There were changes in the size and configuration of the drought-affected area, but both droughts were especially persistent in a core region on the High Plains. A simple index of overall drought impact was developed based on the drought-affected area and the Palmer value from each climatic division. The probability of drought occurrence was calculated for each of the 76 climatic divisions in the study area. [Key words: drought, Palmer Index, Great Plains.] 相似文献
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Bjarne Kjøllmoen & Gunnar Østrem 《Geografiska Annaler: Series A, Physical Geography》1997,79(3):195-200
When the Norwegian State Power Board decided to plan an extensive water power development in the mountainous areas southeast of Narvik in northern Norway, a large mapping project was started. Detailed maps were constructed at a scale of 1:10 000 from aerial photographs taken in 1960. Several hydrometric stations were installed, and three glaciers were selected for mass balance observations. Storsteinsfjellbreen was the largest of these, and a special glacier map with 10 m contours was printed in four colours, to be used in the field work. Mass balance studies were carried out initially during one 5-year period (1964–68), and also later during another 5-year period (1991–95).
Results from these periods are compared with similar data from the Swedish glacier Storglaciären, about 45 km to the southeast. For all the years except one (1968), the net balance of these glaciers shows a similar pattern: positive years and negative years are synchronous.
A new glacier map was made from a special aerial survey in 1993 at the same scale and of similar accuracy as the first map, so a comparison could be made to calculate the change in glacier volume from 1960 to 1993. From digital terrain models it could be shown that the glacier surface had dropped more than 60 m vertically on the tongue, while the thickness increased above the equilibrium line by up to 20 m. The overall mass loss amounted to 16.8×106 m3 water during 33 years, which corresponds to an extra 2.6 l·s−1 ·km−2 (litres per sec. per sq. km) delivered to the river, in addition to the "normal" discharge
due to annual precipitation, which is 36 l·s−1 ·km−2 in the area.
A copy of the new glacier map is enclosed with this article. 相似文献
Results from these periods are compared with similar data from the Swedish glacier Storglaciären, about 45 km to the southeast. For all the years except one (1968), the net balance of these glaciers shows a similar pattern: positive years and negative years are synchronous.
A new glacier map was made from a special aerial survey in 1993 at the same scale and of similar accuracy as the first map, so a comparison could be made to calculate the change in glacier volume from 1960 to 1993. From digital terrain models it could be shown that the glacier surface had dropped more than 60 m vertically on the tongue, while the thickness increased above the equilibrium line by up to 20 m. The overall mass loss amounted to 16.8×10
due to annual precipitation, which is 36 l·s
A copy of the new glacier map is enclosed with this article. 相似文献
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A.F. Lotter P.G. Appleby R. Bindler J.A. Dearing J.-A. Grytnes W. Hofmann C. Kamenik A. Lami D.M. Livingstone C. Ohlendorf N. Rose M. Sturm 《Journal of Paleolimnology》2002,28(1):111-127
Sediment cores spanning the last two centuries were taken in Hagelseewli, a high-elevation lake in the Swiss Alps. Contiguous 0.5 cm samples were analysed for biological remains, including diatoms, chironomids, cladocera, chrysophyte cysts, and fossil pigments. In addition, sedimentological and geochemical variables such as loss-on-ignition, total carbon, nitrogen, sulphur, grain-size and magnetic mineralogy were determined. The results of these analyses were compared to a long instrumental air temperature record that was adapted to the elevation of Hagelseewli by applying mean monthly lapse rates.During much of the time, the lake is in the shadow of a high cliff to the south, so that the lake is ice-covered during much of the year and thus decoupled from climatic forcing. Lake biology is therefore influenced more by the duration of ice-cover than by direct temperature effects during the short open-water season. Long periods of ice-cover result in anoxic water conditions and dissolution of authigenic calcites, leading to carbonate-free sediments.The diversity of chironomid and cladoceran assemblages is extremely low, whereas that of diatom and chrysophyte cyst assemblages is much higher. Weak correlations were observed between the diatom and chrysophyte cyst assemblages on the one hand and summer or autumn air temperatures on the other, but the proportion of variance explained is low, so that air temperature alone cannot account for the degree of variation observed in the paleolimnological record.Analyses of mineral magnetic parameters, spheroidal carbonaceous particles and lead suggest that atmospheric pollution has had a significant effect on the sediments of Hagelseewli, but little effect on the water quality as reflected in the lake biota. 相似文献
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Ooi Jin Bee 《Applied geography (Sevenoaks, England)》1984,4(3):187-200
This paper traces the energy transitions in Indonesia: from woodfuels to coal, spanning the period from the establishment of Dutch colonial rule to the 1950s; and from coal to oil, spanning the period from the 1950s to the oil crisis of 1973–1974. It then examines the role of oil in the energy mix of Indonesia, and discusses the reasons — high rates of domestic oil products consumption; the importance of oil as a foreign exchange earner — for the country to move away from oil dependency to alternative forms of energy to meet her domestic needs. 相似文献
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The U.S. Geological Survey periodically makes appraisals of the oil and gas resources of the Nation. In its 1995 National
Assessment the onshore areas and adjoining State waters of the Nation were assessed. As part of the 1995 National Assessment,
274 conventional oil plays and 239 conventional nonassociated-gas plays were assessed. The two datasets of estimates studied
herein are the following: (1) the mean, undiscovered, technically recoverable oil resources estimated for each of the 274
conventional oil plays, and (2) the mean, undiscovered, technically recoverable gas resources estimated for each of the 239
conventional nonassociatedgas plays. It was found that the two populations of petroleum estimates are both distributed approximately
as lognormal distributions. Fractal lognormal percentage theory is developed and applied to the two populations of petroleum
estimates. In both cases the theoretical percentages of total resources using the lognormal distribution are extremely close
to the empirical percentages from the oil and nonassociated-gas data. For example, 20% of the 274 oil plays account for 73.05%
of the total oil resources of the plays if the lognormal distribution is used, or for 75.52% if the data is used; 20% of the
239 nonassociated-gas plays account for 76.32% of the total nonassociated-gas resources of the plays if the lognormal distribution
is used, or for 78.87% if the data is used 相似文献