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101.
树轮稳定同位素记录:进展、问题及展望 总被引:1,自引:0,他引:1
树轮稳定同位素比率(δ13 C、δ18O 和δD)变化与树木生长季的气候和环境条件密切相关。控制实验表明, 树轮稳定同位素比率变化可较好地记录树木叶片气孔活动、水分来源、水分利用效率等相关信息, 已成为古气候和全球变化生态学研究的重要代用指标和手段之一。树轮稳定同位素记录能够较好地保留低频气候环境变化信息, 与年轮宽度相结合, 可有效地进行区域古气候重建和全球变化生态学方面的研究。文章综述了树轮稳定同位素的分馏机理及其发展, 系统阐述和评价了利用树轮稳定同位素指标进行古气候和古环境的相关研究成果, 并指出树轮稳定同位素研究在中国未来亟须着重发展的方向。 相似文献
102.
Lei Xing Huaishan Liu Xilai Zheng Xueqin Liu Jin Zhang Linfei Wang Zhihui Zou Yiming Xu 《中国海洋大学学报(英文版)》2016,15(5):815-824
Air guns are important sources for marine seismic exploration. Far-field wavelet of air gun arrays, as a necessary parameter for pre-stack processing and source models, plays an important role during marine seismic data processing and interpretation. When an air gun fires, it generates a series of air bubbles. Similar to onshore seismic exploration, the water forms a plastic fluid near the bubble; the farther the air gun is located from the measurement, the more steady and more accurately represented the wavelet will be. In practice, hydrophones should be placed more than 100 m from the air gun; however, traditional seismic cables cannot meet this requirement. On the other hand, vertical cables provide a viable solution to this problem. This study uses a vertical cable to receive wavelets from 38 air guns and data are collected offshore Southeast Qiong, where the water depth is over 1000 m. In this study, the wavelets measured using this technique coincide very well with the simulated wavelets and can therefore represent the real shape of the wavelets. This experiment fills a technology gap in China. 相似文献
103.
Neolithic culture series in the Yishu River Basin developed in the order of Beixin culture-Dawenkou culture-Longshan culture-Yueshi culture. During the early and middle stage of Longshan culture (4600-4300 cal. yr BP), the climate in the Yishu River Basin was warm and wet. Paddy-oriented agriculture planted paddy was very developed. The society was flourishing with great amount of archaeological sites. The cooling starting in 4200 cal. yr BP made the paddies shortfall in output or even no seeds were gathered. This situation intensified the discrepancy between population and resource. The scarcity in natural resource led to substantial decrease in population and subsequent drop in archaeological sites. About 4000 cal. yr BP Longshan culture was displaced by Yueshi culture which was relatively un- derdeveloped, simple and unsophisticated. 相似文献
104.
105.
中国煤炭资源供应格局演变及流动路径分析 总被引:1,自引:0,他引:1
利用1949—2008年的相关统计数据,分析中国煤炭资源供应格局和流动路径,结果表明:(1)国家政策变动对中国煤炭资源消费规模影响深刻,每一次政策变化都会造成能源消费规模的波动,近年来强烈的能源需求使得我国煤炭供应不得不面临进口的现实;(2)受能源需求和资源禀赋的双重压力,大规模、跨区域、长距离的煤炭运输成为我国能源运输体系的重要特征;(3)尽管煤炭运输方式在向铁路、水路和公路组合并用的多元化发展,但仍然不能满足旺盛的能源需求,煤炭运输瓶颈始终存在,变输煤为输电是缓解当前煤炭运输困难的一个途径。 相似文献
106.
A new species from the caridean family Hippolytidae, Eualus heterodactylus sp. nov. is described and illustrated based on the specimens collected from Chinese coast of the Yellow Sea. The new species is a part of an informal species group characterized by the possession of epipods on the anterior three pairs of pereopods, and is distinguished from other species of this group by the dactyli of the third to fifth pereopods possessing distinctly stair-like flexor margins in males. 相似文献
107.
YU Shanshan KONG Xiaoyu LI Yulong XU Hui 《中国海洋大学学报(英文版)》2007,6(2):187-192
The complete mitochondrial cytochrome oxidase subunit Ⅱ (COⅡ) gene of Penaeinae shrimp Fenneropenaeus chinensis was cloned and sequenced. The gene is 688 bp in length and codes for 229 amino acids. It shows 83.2%, 87.0% and 83.8% sequence similarity to Marsupenaeus Japonicus, Penaeus monodon and Farfantepenaeus notialis, respectively. The A+T content of the whole gene and that at the third position of codons are 64.7% and 78.2%, respectively. The phylogenetic relationship between F. chinensis and three other species representing genera Farfanatepenaeus, Marsupenaeus and Penaeus was analyzed. Results showed that the genetic distances among the four taxa ranged from 0.144 0 to 0.200 5, exceeding those estimated with COⅠ and partial 16S rRNA gene sequences among Marsupenaeus, Litopenaeus and Melicertus, and being therefore larger than the value among subgenera. It has been suggested that the COⅡ gene has a faster evolutionary rate than that of the COⅠ gene and partial 16S rRNA gene and could be used for phylogenetic analysis at genus or species level. The results of the present study indicated that Farfantepenaeus, Fenneropenaeus, Marsupenaeus and Penaeus are at a higher phylogenetic level than subgenus, which supports the opinion of the elevation of phylogenetic status of the four subgenera to genus level. 相似文献
108.
109.
Natural Resources Research - Coal and gas outbursts often result in a large number of casualties and economic losses. Its complex processes involve the multi-field coupling of gas flow, coal... 相似文献
110.
XiaoNing Zhang XueLu Liu Ghanney Philip XiaoDan Li QuanXi Wang YaNan Xu TingTing Hui 《寒旱区科学》2020,(1):22-33
Yanchi County is located in the agro-pastoral ecotone and belongs to the ecologically fragile area of Northwest China.It is important to study the evolution of landscape pattern to curb its environmental degradation.In order to intuitively show how the landscape pattern of the study area changes over time,Landsat Thematic Mappers(TM)and Landsat Operational Land Imager(OLI)data of 1991,2000,2010 and 2017 were used.This paper attempts to apply niche theories and methods into landscape ecology,and constructs a niche model of landscape components by using"n-dimentional hypervolume niche theory"and landscape pattern indices.By evaluating the spatial and temporal evolution of niche from the perspective of two-dimensional space to reflect the changes of landscape pattern in the study area over the past 26 years,new theories and methods were introduced for the characterization of landscape pattern.The results indicate that:1)The larger the attribute and dominance value of landscape components,the higher the ecological niche and the stronger the control effect on the overall landscape.2)The ecological niche of each landscape component was significantly different,just as its control effect on the overall landscape.3)The dynamic change of the ecological niche of each landscape component was different,with grassland,unused land and arable land always in a high dominant position,although the ecological niche of construction land and water area was always low.In general,the introduction of niche theory into the landscape ecology provided a new method to study the changes in regional landscape pattern. 相似文献