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261.
开放条件下重庆地区城镇化对土地利用效率的影响及区位差异 总被引:1,自引:0,他引:1
经济开放和城镇化大幅度促进经济增长是中国30年经济持续增长的重要经验。内陆地区经济赶超更加受到人地耦合系统脆弱性的挑战。在对国内外关于城镇化与土地利用关系相关文献述评的基础上,以重庆40个区县为例,通过对其城镇化水平、开放度、技术水平、区位指数及城镇建设用地综合效率进行测算,采用多元回归方法实证分析了重庆40个区县在开放条件下城镇化对土地利用效率的影响及机制。研究发现:区位因素并不像在沿海地区一样对土地利用效率起着显著性作用;土地利用效率的高低严重依赖于物质资本投入密度,而不是人力资本投入密度;极低的人力资本积累和大量缺乏训练的劳动力涌入城市,降低了城市土地利用效率并提高了经济系统的脆弱性;城镇化极为显著地促进了土地利用效率,而开放度的促进作用却不明显,二者并没有形成理论上提升土地利用综合效率的合力。 相似文献
262.
Unlike other branches of geosciences, exploratory drilling has not been investigated within the framework of an information
system; so, the expression “value of exploratory drilling information” (despite its common usage) is vague. This article presents
a model for the evaluation of value of the information gathered from exploratory drilling after studying different mineral
exploration and exploratory drilling systems within the framework of an “information system.” Although this model does not
present the economic value of information, it is a suitable tool for comparing different drilling patterns. The model was
verified on the basis of drilling data for the Gol-Gohar XIIA anomaly. 相似文献
263.
264.
基于遥感和GIS的黄土高原中阳县土壤侵蚀评价 总被引:4,自引:0,他引:4
黄土高原地区是我国水土流失最严重的地区,定量评价土壤侵蚀量、土壤侵蚀强度及其空间分布特征,可以为水土流失防治措施的制定提供依据.基于遥感和GIS,应用修正的通用土壤流失方程(RUSLE)对山西中阳县土壤侵蚀进行评价.结果表明,中阳县平均土壤侵蚀模数为2 874.25t/(km2·a),属于中度侵蚀地区,年平均土壤侵蚀量408.78×104 t.发生中度以上土壤侵蚀面积占总面积的29.95%,土壤侵蚀量占总侵蚀量的85.61%,这部分土地是土壤侵蚀防治的主要区域.黄土区发生轻度以上土壤侵蚀面积大,所占比例多,侵蚀程度严重.微度土壤侵蚀面积以有林地为主,轻度和中度土壤侵蚀面积主要是未成林造林地和灌木林地,发生强烈以上土壤侵蚀面积主要是疏林地、未利用地、灌木林地和农田,土地类型、植被覆盖与土壤侵蚀有着密切关系,林业生态工程建设对于中阳县控制水土流失和改善生态环境有着重要作用. 相似文献
265.
The Haji-Gak iron deposit of eastern Bamyan Province, eastern Afghanistan, was studied extensively and resource calculations
were made in the 1960s by Afghan and Russian geologists. Recalculation of the resource estimates verifies the original estimates
for categories A (in-place resources known in detail), B (in-place resources known in moderate detail), and C1 (in-place resources estimated on sparse data), totaling 110.8 Mt, or about 6% of the resources as being supportable for the
methods used in the 1960s. C2 (based on a loose exploration grid with little data) resources are based on one ore grade from one drill hole, and P2 (prognosis) resources are based on field observations, field measurements, and an ore grade derived from averaging grades
from three better sampled ore bodies. C2 and P2 resources are 1,659.1 Mt or about 94% of the total resources in the deposit. The vast P2 resources have not been drilled or sampled to confirm their extent or quality. The purpose of this article is to independently
evaluate the resources of the Haji-Gak iron deposit by using the available geologic and mineral resource information including
geologic maps and cross sections, sampling data, and the analog-estimating techniques of the 1960s to determine the size and
tenor of the deposit. 相似文献
266.
267.
The level of Cliff Lake, a small, subalpine, moraine-dammed lake in California’s south central Sierra Nevada, was approximately
5 m lower than present for 50 years or more approximately 600 years ago, this determined by radiocarbon dating of wood recovered
from a submerged tree stump found in the lake. This finding corresponds to commensurate data from throughout much of western
North America, suggesting the duration and magnitude of terminal medieval megadrought was similar throughout the region. Ultimately
this datum helps give credence to the perspective that though late Holocene climate in California was indeed variable, the
effects of terminal Medieval megadrought was similar across both time and broad geographic expanse. 相似文献
268.
W. Earl Bardsley 《Natural Resources Research》2008,17(4):197-204
A sustainable global silicon energy economy is proposed as a potential alternative to the hydrogen economy. This first visualization
of a silicon energy economy is based on large-scale and carbon-neutral metallic silicon production from major smelters in
North Africa and elsewhere, supplied by desert silica sand and electricity from extensive solar generating systems. The resulting
“fuel silicon” is shipped around the world to emission-free silicon power stations for either immediate electricity generation
or stockpiling. The high energy density of silicon and its stable storage make it an ideal material for maintaining national
economic functioning through security of base load power supply from a renewable source. This contrasts with the present situation
of fossil fuel usage with its associated global warming and geopolitical supply uncertainties. Critical technological requirements
for the silicon economy are carbon-neutral silicon production and the development of efficient silicon-fired power stations
capable of high-temperature rapid oxidation of fuel silicon. A call is made for the development of research effort into these
specific engineering issues, and also with respect to large-scale economical solar power generation. 相似文献
269.
Supriyo Kumar Das Joyanto Routh Alakendra N. Roychoudhury J. Val Klump 《Journal of Paleolimnology》2008,39(3):349-360
We used elemental carbon, nitrogen, phosphorus and hydrogen ratios (C/N, N/P and H/C) with total organic carbon (TOC) and
total phosphorus (TP) as well as stable carbon and nitrogen isotopes (δ13C and δ15N) to investigate the source and depositional conditions of organic matter in sediments from Zeekoevlei, the largest freshwater
lake in South Africa. Typical C/N (10–12), H/C ratios (≥1.7) and δ13Corganic values (−22 to −19‰) together with the increase in TOC concentration indicate elevated primary productivity in lower middle
(18–22 cm) and top (0–8 cm) sections of the sediment cores. Seepage of nutrients from a nearby waste water treatment plant,
rapid urbanization and heavily fertilized farming in the catchments are responsible for the increased productivity. Consistent
with this, measured δ15Norganic values (∼11‰) indicate increased raw sewage input towards the top-section of the core. Although cyanobacterial blooms are
evident from the low δ15N values (∼3‰) in mid-section of the core, they did not outnumber the phytoplankton population. Low N/P ratio (∼0) and high
TP (100–2,200 mg l−1) support cyanobacterial growth under N limited condition, and insignificant input of macrophytes towards the organic matter
pool. Dredging in 1983, caused sub-aerial exposure of the suspended and surface sediments, and affected organic matter preservation
in the upper mid-section (12–14 cm) of the core. 相似文献
270.
Dan Hammarlund Anson W. Mackay David M. J. Fallon Gemma Pateman Luisa C. Tavio Melanie J. Leng Neil L. Rose 《Journal of Paleolimnology》2008,39(4):463-475
Detailed stratigraphic analyses of sediments deposited in Lake Botjärnen, a small boreal forest lake in the shield terrain of central Sweden, clearly reflect progressively increasing human impact on terrestrial and aquatic ecosystems following settlement and establishment of an iron industry in the 17th century. Rising frequencies of pollen and spores from light-demanding plants provide evidence of extensive forest clearance for charcoal and timber production, which peaked in the early 20th century. An associated increase in catchment erosion is reflected by changing carbon and nitrogen elemental content and carbon–isotope composition of sediment organic matter and by increased magnetic susceptibility of the sediments. Records of air-borne pollutants (lead, zinc and sulphur) can be correlated to the development of local and regional mining and metal industry as inferred from historical accounts. Rapid recession of the iron industry led to re-forestation and recovery of the aquatic nutrient status to pre-industrial conditions over the past 100 years. The chronology of the sediment succession, which is based on 210Pb and 137Cs radionuclide data in combination with radiocarbon dating, is confirmed by historical lead pollution trends established for the region. 相似文献