喜马拉雅东部主要边界冲断层上的微震活动和现今构造模型     

Kayal  JR 胡凤珍 《地壳构造与地壳应力》1994,(1):21-24

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强化掩埋矿床附近异常的运积层土壤酶浸析法     

Clark  JR 周国华 《物探化探译丛》1994,(2):63-65

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降水的同位素组成中令人难以捉摸的气候信号     

Lawr.  JR 郑成华 《地质地球化学》1994,(4):25-31,37

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地表形状的数字化表示     

Cart.  JR 李跃进 《北京测绘》1990,(4):40-43,26

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Migration and the transformation of employment and household structures     

Heaton TB  Hawley AH  Udry JR  Boonlert-leoprapai 《Singapore journal of tropical geography》1982,3(1):34-43

Data collected in Colombia and Thailand in 1977 are used to "compare the employment and household characteristics of migrants before and after the move in order to assess the degree of change which accompanies migration. Moreover, these comparisons [are] made for migration streams between places at different levels in the urban hierarchy with the intention of determining within which streams the greatest transformations occur."  相似文献   

Population trends and the status of population policy in Africa     

Rogge JR 《The Journal of geography》1982,81(5):164-174

There is every indication that Africa's population growth will remain well above the world average for the remainder of this decade and probably for the rest of this century. With the exception of the island states and parts of North Africa, fertility levels show little indication of change. This is in part a reflection of little desire for small families, as well as a consequence of limited or even restricted family planning services. Great diversity in attitudes regarding population policy prevails among African governments, ranging from extreme pronatal to committed antinatal. Even with antinatal policies, however, many African states have yet to attain any significant success in depressing their rates of growth. To date, Mauritius can be cited as the only state to have almost achieved the transition from high to low fertility. The consequence of these continuing trends is that Africa will see further increases in its youth dependency ratio. Pressures on infrastructural services will therefore increase, and the problems of generating employment will intensify. While demographic factors are by no means the only ones creating economic stress on the continent, they clearly are contributory. Unlike Asia or parts of Latin America, Africa's problem is less a matter of too many people but rather 1 of excessive growth in too short a time frame. A realistic and effective long-term population policy, therefore, is an immediate need. Several countries including Nigeria (with a pouplation of over 80 million) are experiencing a crude birth rate of 50 or more/1,000. At least 4 countries, including Kenya, are currently doubling their population in 20 years or less. With these current population trends, a demographic transition to low vital rates must assume passage through an even higher growth phase than is currently being experienced because the fall in birth rates tends to occur much later than the fall in death rates. Government population policies and the status of family planning activities are illustrated according to natal sentiments and attitudes. Trends in national vital rates and of population structures in Africa are illustrated.  相似文献   

Clay-mineral suites,sources, and inferred dispersal routes: Southern California continental shelf     

Hein JR  Dowling JS  Schuetze A  Lee HJ 《Marine environmental research》2003,56(1-2):79-102

Clay mineralogy is useful in determining the distribution, sources, and dispersal routes of fine-grained sediments. In addition, clay minerals, especially smectite, may control the degree to which contaminants are adsorbed by the sediment. We analyzed 250 shelf sediment samples, 24 river-suspended-sediment samples, and 12 river-bed samples for clay-mineral contents in the Southern California Borderland from Point Conception to the Mexico border. In addition, six samples were analyzed from the Palos Verdes Headland in order to characterize the clay minerals contributed to the offshore from that point source. The <2 microm-size fraction was isolated, Mg-saturated, and glycolated before analysis by X-ray diffraction. Semi-quantitative percentages of smectite, illite, and kaolinite plus chlorite were calculated using peak areas and standard weighting factors. Most fine-grained sediment is supplied to the shelf by rivers during major winter storms, especially during El Ni?o years. The largest sediment fluxes to the region are from the Santa Ynez and Santa Clara Rivers, which drain the Transverse Ranges. The mean clay-mineral suite for the entire shelf sediment data set (26% smectite, 50% illite, 24% kaolinite+chlorite) is closely comparable to that for the mean of all the rivers (31% smectite, 49% illite, 20% kaolinite+chlorite), indicating that the main source of shelf fine-grained sediments is the adjacent rivers. However, regional variations do exist and the shelf is divided into four provinces with characteristic clay-mineral suites. The means of the clay-mineral suites of the two southernmost provinces are within analytical error of the mineral suites of adjacent rivers. The next province to the north includes Santa Monica Bay and has a suite of clay minerals derived from mixing of fine-grained sediments from several sources, both from the north and south. The northernmost province clay-mineral suite matches moderately well that of the adjacent rivers, but does indicate some mixing from sources in adjacent provinces.  相似文献   

Molecular and isotopic analyses of the hydroxy acids, dicarboxylic acids, and hydroxicarboxylic acids of the Murchison meteorite     

Cronin JR  Pizzarello S  Epstein S  Krishnamurthy RV 《Geochimica et cosmochimica acta》1993,57(19):4745-4752

The hydroxymonocarboxylic acids, dicarboxylic acids, and hydroxydicarboxylic acids of the Murchison meteorite were analyzed as their tert-butyldimethylsilyl derivatives using combined gas chromatography-mass spectrometry. The hydroxydicarboxylic acids have not been found previously in meteorites. Each class of compounds is numerous with carbon chains up to C8 or C9 and many, if not all, chain and substitution position isomers represented at each carbon number. The alpha-hydroxycarboxylic acids and alpha-hydroxydicarboxylic acids correspond structurally to many of the known meteoritic alpha-aminocarboxylic acids and alpha-aminodicarboxylic acids, a fact that supports the proposal that a Strecker synthesis was involved in the formation of both classes of compounds. Isotopic analyses show these acids to be D-rich relative to terrestrial organic compounds as expected; however, the hydroxy acids appear to be isotopically lighter than the amino acids with respect to both carbon and hydrogen. The latter finding would not be expected if both classes of compounds came exclusively from common precursors as would have been the case for a Strecker synthesis.  相似文献   

Genetic diversity and metal tolerance of two marine species: a comparison between populations from contaminated and reference sites     

Ross K  Cooper N  Bidwell JR  Elder J 《Marine pollution bulletin》2002,44(7):671-679

Long-term contamination of the marine environment surrounding a lead smelter offered a unique opportunity to examine how pollutants might have acted to alter genetic characteristics of populations of organisms in the receiving system. This study used random amplified polymorphic DNA analysis to compare the genetic diversity of populations of the prawn, Leander intermedius, and the isopod, Platynympha longicaudata from the smelter discharge site with reference populations. The genetic diversity of the prawn population from the smelter discharge site (Port Pirie) was lower than that found in one reference population, and not significantly different from the other two reference populations. Genetic diversity of the Port Pirie population of isopods was found to be significantly lower than that of all reference populations. Prawns and isopods were also exposed to metal mixtures in the laboratory in a similar ratio to that found in seston near the smelter effluent discharge site. Both pre-exposed and reference populations of prawns tolerated elevated levels of metals and exhibited no significant difference in response. This contrasted with the isopods, with the pre-exposed isopod population showing greater tolerance to elevated metal levels compared with the reference population. These results highlight the need to include a number of reference populations for comparative purposes in genetic diversity studies, and the need to assess the influence of pollution on the genetic diversity of more than one species if genetic diversity analyses are to be used to gauge remediation success.  相似文献   

Seasonal and spatial distribution of nonylphenol and IBP in Saemangeum Bay, Korea     

Li D  Dong M  Shim WJ  Hong SH  Oh JR  Yim UH  Jeung JH  Kanan N  Kim ES  Cho SR 《Marine pollution bulletin》2005,51(8-12):966-974

In order to investigate spatial and temporal distribution of organic pollutants in the Saemangeum Bay, organophosphorus pesticides (10), alkylphenols (8), chlorophenols (2), bisphenol A were analyzed from the surface seawater taken in 2002–2003. Most of the analytes were not detected in all stations except nonylphenol and S-benzyl-O,O-di-isopropyl phosphorothioate (IBP). Concentrations of nonylphenol and IBP ranged from ND to 298 ng/l and from ND to 1840 ng/l, respectively. The high levels of nonylphenol and IBP were found in the estuary areas of Mangyeong and Dongjin River. The levels of nonylphenol and IBP in surface seawater varied through seasons and the high levels of nonylphenol and IBP were in summer season (August). Based on real time monitoring of IBP and on correlation between concentrations of target compounds and contents of salinity in seawater, physical mixing and diffusion of seawater were found to be the major factors that affect the spatial distribution of IBP and nonylphenol in the Saemangeum Bay environment.  相似文献