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821.
822.
基于遥感和GIS的天津城市空间形态变化分析 总被引:5,自引:0,他引:5
选用分维数和紧凑度作为城市形态指数,与城市土地利用变化相结合研究城市扩展的过程和特征。以天津市为例,利用遥感提取26年内9个时相的数据进行研究,结果表明,天津市近26年内有2次快速城市扩展,但两阶段的特征不同,后期虽然扩展速率高于前期,但形态指数变化速率却低于前期,反映出后期城市扩展更趋于理性和有序。城市形态指数与土地利用变化指标有很好的互补性,两者结合可以更充分描述城市扩展的特征和过程。 相似文献
823.
In contrast to typical planktonic hydromedusae, Cladonema medusae are mostly benthic, with specialised adhesive branches to adhere to the substrate. In this study, a Cladonema species discovered in a laboratory aquarium in Fuzhou, China, was confirmed as a new species, based on morphological and molecular analyses.The species was named Cladonema multiramosum sp. nov. Its medusa is distinct from that of congeners possessing substantially more adhesive branches(8–24, rarely 5–7), and tiny branches... 相似文献
824.
825.
黄土高原"千沟万壑"的地貌形态,在多尺度空间下表现出显著自相似性,具有"局部无规则,宏观有规律"的纹理特征.目前,黄土高原地形纹理的提取方法及应用已经得到初步发展,但依然缺乏在理论层面的框架体系.本文在已有学者研究成果的基础上,限定黄土高原为研究范围,明确提出黄土高原地形纹理的概念模型,即内涵、特征、分类及表达.将内涵... 相似文献
826.
IINTRODUCTIONDebrisflowisaphenomenonhappeninginextremeseveresit'Uationofsoilerosion(Guan,1996).ItoccursfrequentlyanddistributesdenselyinupperreachesoftheYangtzeRiverandtransportsahugeamountofsedimentilltotheriver.Debrisflowdepositinfluencesthecompositionofsedimentandthemorphologyoftheriverbedfromupstreamt6downstreamandthenaffectsthedynamiccharactersandsedimentbudgetoftheYangtzeRiver.Furthermore,itimpactsonthefloodandwaterconservancyengineering.2DEBRISFLOWGULLY--HIGHWAYOFSEDI… 相似文献
827.
Two large groups of rodents inhabit South America: the hystricognaths and the murids. It has been postulated that while the former show a high degree of specialization to desert habitats, the murids are not well adapted to xeric conditions. We studied the renal structure and function of selected desert-dwelling murid and octodontid (hystricognath) rodents from Argentina to evaluate levels of adaptation to aridity. Our results show that the murids Salinomys, Andalgalomys, Calomys and Eligmodontia have the highest renal indices and urine concentration among Argentine desert rodents. The octodontid Tympanoctomys barrerae shows higher renal indices and urine osmolarity than those of its close relativesOctomys mimax and Octodontomys gliroides . We compare the renal traits of the Argentine desert murids with those of other world-desert rodents such as North American heteromyid rodents. The results show that these Argentine murid rodents posses renal adaptations to conditions which are as impressive as those of both octodontids and the classic desert-adapted heteromyids. 相似文献
828.
WANG Wenkui ZHAO Shanrong LEI Xinrong WU Youcai China University of Geosciences Wuhan Hubei 《《地质学报》英文版》2000,74(2):190-193
The research on morphology of mineral crystals in China includes classical goniometry of 100 minerals such as hsianghualite, orthobrannerite, jamesonite and bertrandite and surface microtopography of 20 minerals such as wolframite and diamond, among which 5 new minerals and 34 uranium minerals were discovered and measured by Chinese mineralogists. These have enriched mineralogy and crystal morphology and strengthened the study of information of morphological genesis. 相似文献
829.
锆石柱面中Hf、Y的配位差异性及其对晶型的控制效应 总被引:1,自引:0,他引:1
天然锆石的形态并不简单地依照PBC理论发育,它同时受到生长温度 、熔体扩散系数等物理参数的影响,以及置换Zr的杂质离子的种类和浓度等化学因素的制约 ,即杂质离子选择性地置换Zr而降低晶面的生长速度。通过对{100}和{110}柱面的半定量分 析发现,Hf4+、Y3+离子同O2-离子的成键数目在{100}与{110}生长层 上是不同的,且Hf-O的键强比Zr-O的大,而Y-O的键强比Zr-O的小。如果假定晶体与岩浆熔体并未达到真正的平衡,而是各晶面与岩浆熔体分别达到平衡,按热力学中浓度与能量变化的指数律去处理Hf和Y在{100}与{110}晶面上的配分可以得到,{100}晶面上趋于富Hf贫 Y,{110}晶面上趋于富Y贫Hf,从而导致富Hf的锆石上{100}优先发育,富Y的锆石上{110}优 先发育。 相似文献
830.
The morphodynamics of fluvial sand dunes in the River Rhine, near Mainz, Germany. I. Sedimentology and morphology 总被引:2,自引:0,他引:2
The dynamics of large isolated sand dunes moving across a gravel lag layer were studied in a supply‐limited reach of the River Rhine, Germany. Bed sediments, dune geometry, bedform migration rates and the internal structure of dunes are considered in this paper. Hydrodynamic and sediment transport data are considered in a companion paper. The pebbles and cobbles (D50 of 10 mm) of the flat lag layer are rarely entrained. Dunes consist of well‐sorted medium to coarse sand (D50 of 0·9 mm). Small pebbles move over the dunes by ‘overpassing’, but there is a degree of size and shape selectivity. Populations of ripples in sand (D50 < 0·6 mm), and small and large dunes are separated by distinct breaks in the bedform length data in the regions of 0·7–1 m and 5–10 m. Ripples and small dunes may have sinuous crestlines but primarily exhibit two‐dimensional planforms. In contrast, large dunes are primarily three‐dimensional barchanoid forms. Ripples on the backs of small dunes rarely develop to maximum steepness. Small dunes may achieve an equilibrium geometry, either on the gravel bed or as secondary dunes within the boundary layer on the stoss side of large dunes. Secondary dunes frequently develop a humpback profile as they migrate across the upper stoss slope of large dunes, diminishing in height but increasing in length as they traverse the crestal region. However, secondary dunes more than 5 m in length are rare. The dearth of equilibrium ripples and long secondary dunes is probably related to the limited excursion length available for bedform development on the parent bedforms. Large dunes with lengths between 20 m and 100 m do not approach an equilibrium geometry. A depth limitation rather than a sediment supply limitation is the primary control on dune height; dunes rarely exceed 1 m high in water depths of ≈4 m. Dune celerity increases as a function of the mean flow velocity squared, but this general relationship obscures more subtle morphodynamics. During rising river stage, dunes tend to grow in height owing to crestal accumulation, which slows downstream progression and steepens the dune form. During steady or falling stage, an extended crestal platform develops in association with a rapid downstream migration of the lee side and a reduction in dune height. These diminishing dunes actually increase in unit volume by a process of increased leeside accumulation fed by secondary dunes moving past a stalled stoss toe. A six‐stage model of dune growth and diminution is proposed to explain variations in observed morphology. The model demonstrates how the development of an internal boundary layer and the interaction of the water surface with the crests of these bedload‐dominated dunes can result in dunes characterized by gentle lee sides with weak flow separation. This finding is significant, as other studies of dunes in large rivers have attributed this morphological response to a predominance of suspended load transport. 相似文献