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981.
姜修道 《地球科学与环境学报》1995,(2)
驾鹿金矿床是小秦岭金矿带中一个比较特殊的矿床类型,产于古老韧性剪切带中,围岩蚀变强烈而广泛,尤其是成脉前的钾长石化。蚀变带及其中的石英脉控制了金矿体的产出,矿床属蚀变岩型金矿,成矿时代为燕山晚期.本文在论述矿床地质特征的基础上,通过稳定同位素研究,认为燕山期构造热事件是成矿的主导控制因素,成矿溶液来自大气降水,成矿物质则部分来自太华群,部分来自上覆中元古界高山河组,矿床成因属大气降水热液矿床. 相似文献
982.
We used the tropical oceanic planktonic diatom species Nitzschia marina, Rhizosolenia bergonii and Azpeitia africana/Azpeitia neocrenulata, most commonly found in the surface sediments of the northeasternmost South China Sea (SCS) where the Kuroshio Current enters the SCS through the Bashi Strait north of Luzon, to analyse the influence of the the Kuroshio Current on the SCS. The impact of the Kuroshio Current seems to be relatively strong during major warm periods and, to a lesser degree, in minor warm periods during the last 115 000 years. The strongest influence took place during the main part of the Holocene and during the very late phase of Marine Isotope Stage (MIS) 5e. It is possible to distinguish two magnitudes of change in the impact of the Kuroshio Current on the SCS: large changes occurred at shifts between glacial and interglacial conditions, while smaller changes seem to have recurred in both glacial and interglacial episodes as well as during the Holocene. Climatic/oceanographic changes and sea‐level variations were possibly the two most important mechanisms for the varying influences of the Kuroshio Current on the SCS. The interaction between the Kuroshio Current and monsoon‐related processes may also have played a role. However, because of restricted knowledge of the present‐day Kuroshio Current and the absence of a modern analogue to the ancient SCS due to the marked changes in palaeogeography, this relationship is difficult to establish. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
983.
在简要回顾GIS软件和组件式GIS的发展之后,经过对比分析,提出同时支持两大主流开发平台——.NET和Java EE是新一代GIS组件的必然选择,并对可能实现的几种模式加以讨论.提出基于“共相”思想的C++扩展模式是最为彻底和完关的解决方案,最后介绍在“共相”思想指导下的新一代组件式SuperMap GIS的设计和开发。 相似文献
984.
Using a 2.5-D, time-dependent ideal MHD model in Cartesian coordinates, we carried out numerical simulations to investigate
the equilibrium and evolution properties of a magnetic configuration that consists of a coronal magnetic flux rope and a partly
open photospheric background field, which is equivalent to that produced by a two-patch magnetic source on the photospheric
surface. The axial and annular magnetic fluxes of the flux rope are given and fixed. The global magnetic configuration evolves
in response to three types of changes of the background field: decreasing of the distance between the two sources, shrinking
of the size of each source, and increasing of the shear in the closed component of the background field. As a result, the
geometrical parameters of the flux rope, i.e. the height of the rope axis, the half-width of the rope and the length of the
vertical current sheet below the rope, change due to the variation of the background field. It is shown that for a given coronal
magnetic flux rope in a partly open background field, the variation of the geometrical parameters of the flux rope displays
a catastrophic behavior, namely, there exists a critical point for each case, at which an infinitesimal change of the background
field leads to a loss of equilibrium, and thus a jump of the flux rope. The implication of such a catastrophe in solar active
phenomena is briefly discussed. 相似文献
985.
采用低温—盐形成法对蓝圆 Scombermorusniphonius(Cuvier)、马鲛鱼Decapternsmaruadsi(TemmincketSchleget)、海蛇三种海产动物油中高度不饱和脂肪酸进行提取,经皂化、冷冻、过滤、酸化、离心等工序反复处理后,可得碘价为220~250的高度不饱和脂肪酸混和物。探讨了提取过程中的最适工艺条件,并比较了该三种海产动物脂质中的高度不饱和脂肪酸的含量。 相似文献
986.
V. I. Slysh M. A. Voronkov V. Migenes K. M. Shibata T. Umemoto V. I. Altunin I. E. Val'Tts B. Z. Kanevsky M. V. Popov A. V. Kovalenko E. B. Fomalont B. A. Poperechenko YU. N. Gorshenkov B. R. Carlson S. M. Dougherty J. E. Reynolds D. R. Jiang A. I. Smirnov V. G. Grachev 《Monthly notices of the Royal Astronomical Society》2001,320(2):217-223
We report on the first space–VLBI observations of the OH 34.26+0.15 maser in two main-line OH transitions at 1665 and 1667 MHz. The observations involved the space radio telescope on board the Japanese satellite HALCA and an array of ground radio telescopes. The map of the maser region and images of individual maser spots were produced with an angular resolution of 1 mas, which is several times higher than the angular resolution available on the ground. The maser spots were only partly resolved and a lower limit to the brightness temperature was obtained. The maser seems to be located in the direction of low interstellar scattering, an order of magnitude lower than the scattering of a nearby extragalactic source and pulsar. 相似文献
987.
THE CORRESPONDING ANALYSIS OF HEAVY-METAL POLLUTION OF SOIL IN ZHUZHOU CITY ShangJincheng(尚金城);LongAimin(龙爱民)LiBin(李斌);JiangJ... 相似文献
988.
989.
A neural-network approach to classification of sidescan-sonar imagery is tested on data from three distinct geoacoustic provinces of a midocean-ridge spreading center: axial valley, ridge flank, and sediment pond. The extraction of representative features from the sidescan imagery is analyzed, and the performance of several commonly used texture measures are compared in terms of classification accuracy using a backpropagation neural network. A suite of experiments compares the effectiveness of different feature vectors, the selection of training patterns, the configuration of the neural network, and two widely used statistical methods: Fisher-pairwise classifier and nearest-mean algorithm with Mahalanobis distance measure. The feature vectors compared here comprise spectral estimates, gray-level run length, spatial gray-level dependence matrix, and gray-level differences. The overall accurate classification rates using the best feature set for the three seafloor types are: sediment ponds, 85.9%; ridge flanks, 91.2%; and valleys, 80.1%. While most current approaches are statistical, the significant finding in this study is that high performance for seafloor classification in terms of accuracy and computation can be achieved using a neural network with the proper combination of texture features. These are preliminary results of our program toward the automated segmentation and classification of undersea terrain 相似文献
990.
根据几年来对嵩山地区的考察和研究 ,通过对夷平面、河流阶地、串珠状洪积扇等诸多地貌现象的分析 ,论述了嵩山地区新构造运动以间歇性抬升运动和掀斜运动为主的特征。 相似文献