期刊文献+
共找到4篇文章
< 1 >
每页显示 20 50 100
回忆侯德封同志对我国地球化学事业的卓越贡献
1
作者 涂光炽 《第四纪研究》 CAS CSCD 1995年第4期297-300,共4页
侯德封同志是我国早期地球化学事业的开创者、组织者和设计师。他于50年代初提出的化学地史及60年代反复强调的核子地质均蕴育了浓厚的地球化学思维。在50年代我国制定12年科学技术发展规划和60年代创办我国第一个地球化学研... 侯德封同志是我国早期地球化学事业的开创者、组织者和设计师。他于50年代初提出的化学地史及60年代反复强调的核子地质均蕴育了浓厚的地球化学思维。在50年代我国制定12年科学技术发展规划和60年代创办我国第一个地球化学研究机构的过程中,侯老发挥了远见卓识和当机立断的地球化学事业开拓者的关键作用。在领导和组织建国后我国早期的稀有元素地球化学、同位素地球化学和铀钍地球化学科研工作中,侯老是主要的带头人,在学术思想上提出了指导性见解。 展开更多
关键词 地球化学 稀有元素 化学地史
下载PDF
Petrographic characteristics and paleoenvironmental history of Eocene lignites of Cambay basin, Western India 被引量:5
2
作者 Prakash K. Singh Vijay K. Singh +1 位作者 M. P. Singh P. K. Rajak 《International Journal of Coal Science & Technology》 EI 2017年第3期214-233,共20页
Lignite samples collected from Vastan, Rajpardi and Tadkeshwar lignite mines of Cambay basin (Gujarat) were subjected to organic petrographic investigations and geochemical analyses and the data, thus generated, is ... Lignite samples collected from Vastan, Rajpardi and Tadkeshwar lignite mines of Cambay basin (Gujarat) were subjected to organic petrographic investigations and geochemical analyses and the data, thus generated, is used to reconstruct the paleodepositional history of these lignite sequences. The lignites of Cambay basin dominantly comprise huminite maceral group (71.6%-86.3%) followed by liptinite (10.1%-19.3%) and inertinite (3.6%-11.0%) maceral groups. The mineral matter varies from 9.0% to 20.0%. The petrography based facies model indicates that these lignites have high values of gelification index (GI) and low tissue preservation index revealing a continuous wet condition in the basin and a relatively slower rate of subsidence during the decay of organic matter. On several occasions, during the formation of seams in Tadkeshwar, Rajpardi and Vastan mines, the value of GI exceeded 10 which indicates a forest permanently flooded and the cause of pronounced degree of degradation. However, few sections in Tadkeshwar seam had relatively drier spells of environmental conditions due to fluctuation in the water table as revealed by moderately high content of inertinite macerals. This is specially indicated by the occurrence of funginite which normally thrives in the upper oxy- genated peatigenic layer and indicates prevalence of oxic conditions during plant deposition. Such conditions prevailed during a transgressive phase but there were intermittent fluvial activities also giving rise to supratidal flood plain as reflected in the form of associated carbonaceous shales in the basin. 展开更多
关键词 Cambay basin Western India Lignite MACERAL Paleodepositional environment
下载PDF
Late Holocene Environmental History of Lake Victoria Basin: Evidence from Geochemical Proxies
3
作者 Morgan Andama Julius B. Lejju +3 位作者 Casim Umba Tolo Grace Kagoro-Rugunda Immaculate Ssemmanda Janet Ayebare 《Journal of Environmental Science and Engineering(B)》 2012年第9期1054-1063,共10页
Sedimentary TOC (total organic carbon), TN (total nitrogen) and C/N (carbon/nitrogen) at selected sites of Lake Victoria basin have provided evidence of phytoplankton productivity, input of nitrates and allochth... Sedimentary TOC (total organic carbon), TN (total nitrogen) and C/N (carbon/nitrogen) at selected sites of Lake Victoria basin have provided evidence of phytoplankton productivity, input of nitrates and allochthonous (land) plant materials/catchment destruction in the basin during the late Holocene period (last 4,000 years to present). TOC and TN in the sediment cores were determined using EuroEA3000 Series Elemental Analyser and radiocarbon dating done using AMS (accelerator mass spectrometry) standard method. Results showed that TOC (13.45%-20.78%) and TN (1.07%-1.92%) values were higher at Napoleon Gulf from about 4,186 years before present (ca. 4,186 yr. BP) to present than at inlet of river Kagera (TOC: 3.27%-6.32% and TN: 0.30%-0.59%) from about 190 years before present (ca. 190 yr. BP) to present. Generally TOC and TN had a negative correlation (r = -0.37, p = 0.04, n = 32) at Napoleon Gulf in the last 4,186 years to present signifying that C/N ratios were governed mostly by phytoplankton productivity which markedly increased during some periods in the last 370 years to present possibly as a result of increased input of nitrates. However, the periods from about 4,186 years to 1,684 years before present (ca. 4,186 yr. BP to 1,684 yr. BP) and some periods between the last 370 years to present indicated increased input of allochthonous plant materials/catchment destruction. On overall, there was a positive correlation between C/N and TOC at inlet of river Kagera (r = 0.57, p = 0.01, n = 20) in the last 190 years to present possibly signifying that C/N ratios were governed mainly by input of allochthonous plant materials hence increased catchment destruction. Input of land plant materials (catchment destruction) along Kagera basin declined during some period after 1950 AD. However the most recent years have shown increased input of land plant materials (catchment destruction) in Kagera basin. 展开更多
关键词 ENVIRONMENT geochemical proxies Lake Victoria late Holocene.
下载PDF
A coevolutionary framework based on temporal and spatial ecology of host-parasite interactions:A missing link in studies of brood parasitism 被引量:2
4
作者 Anders P.MLLER Juan J.SOLER 《Chinese Birds》 2012年第4期259-273,共15页
A central tenet of coevolutionary theory,including theory of the coevolutionary relationship between brood parasites and their hosts,is that temporal and spatial patterns may reveal important information about ecologi... A central tenet of coevolutionary theory,including theory of the coevolutionary relationship between brood parasites and their hosts,is that temporal and spatial patterns may reveal important information about ecological and evolutionary dynamics.For instance,level of genetic structure of populations provides important information about the role of genetics and gene ow in determining local patterns of selection on hosts due to parasitism(i.e.,egg rejection) and on parasites due to selection by hosts(i.e.,egg mimicry).Furthermore,abiotic(i.e.,climatic conditions) and biotic(phenotypic characteristics of animals) factors that also vary spatially may directly or indirectly a ect populations of hosts and brood parasites and,therefore,their interaction.By reviewing the literature,we found considerable evidence for an e ect of the spatially and temporally structured abiotic environment on the phenotype of both parasite and host eggs and the degree of mimicry.Moreover,we found examples suggesting that speci c life history characteristics of hosts that vary geographically and/or temporally may a ect the probability of initial colonization of a new host species and the direction and the speed of coevolution.We provide an exhaustive review of studies investigating temporal and spatial patterns of the interaction between brood parasites and their hosts.Such temporal and spatial trends in parasite and host traits are,together with genetic information on rejection and signi cant e ects of gene ow,consistent with coevolutionary dynamics.However,gene ow and changes in the temporal and spatial patterns of abundance of both parasites and hosts may result in frequent cases of counter-intuitive relationships between the phenotype of the parasite and that of the host(i.e.,poor or no mimicry),which may suggest limits to the degree of adaptation.We provide a list of scienti c questions in need of further investigation,concluding that studies of brood parasites and their hosts may play a central role in testing the geographic theory of coevolution and several alternative hypotheses. 展开更多
关键词 abiotic environment biotic environment coevolution cuckoos geographic theory of coevolution life history traits limits to adaptation
下载PDF
上一页 1 下一页 到第
使用帮助 返回顶部