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991.
中国前寒武纪金矿的成矿找矿模式 总被引:1,自引:0,他引:1
中国前寒武纪含金岩系密切相关的金矿储量占全国岩金储量的73.85%,它几乎囊括了全国的金产量.已发现的金矿资源基地,基本上沿三条近东西向的槽台边缘构造带成带分布,由于受中生代环太平洋板块的作用影响,产生了一系列北东—北北东向的超壳型深大断裂,使中国前寒武纪金矿产生了极其明显的活化、改造和重就位作用.因此,中国东部金矿具有沿北东向深大断裂成串分布的规律.从10个方面讨论了中国前寒武纪金矿的成矿特点和找矿途径,建立了“三个系统”相统一的成矿找矿模式. 相似文献
992.
Potentilla fruticosa scrub, Kobresia humilis meadow and Kobresia tibetica meadow are widely distributed on the Qinghai-Tibet Plateau. During the grass exuberance period from 3 July to 4 September, based on close chamber-GC method, a study on CO2 emissions from different treatments was conducted in these meadows at Haibei research station, CAS. Results indicated that mean CO2 emission rates from various treatments were 672.09±152.37 mgm^-2h^-1 for FC (grass treatment); 425.41±191.99 mgm^-2h^-1 for FJ (grass exclusion treatment); 280.36±174.83 mgm^-2h^-1 for FL (grass and roots exclusion treatment); 838.95±237.02 mgm^-2h^-1 for GG (scrub+grass treatment); 528.48±205.67 mgm^-2h^-1 for GC (grass treatment); 268.97±99.72 mgm^-2h^-1 for GL (grass and roots exclusion treatment); and 659.20±94.83 mgm^-2h^-1 for LC (grass treatment), respectively (FC, FJ, FL, GG, GC, GL, LC were the Chinese abbreviation for various treatments). Furthermore, Kobresia humilis meadow, Potentilla fruticosa scrub meadow and Kobresia tibetica meadow differed greatly in average CO2 emission rate of soil-plant system, in the order of GG>FC>LC>GC. Moreover, in Kobresia hurnilis meadow,heterotrophic and autotrophic respiration accounted for 42% and 58% of the total respiration of soil-plant system respectively, whereas, in Potentilla fruticosa scrub meadow, heterotrophic and autotrophic respiration accounted for 32% and 68% of total system respiration from GG; 49% and 51% from GC. In addition, root respiration from Kobresia humilis meadow approximated 145 mgCO2m^-2h^-1,contributed 34% to soil respiration. During the experiment period, Kobresia humilis meadow and Potentilla fruticosa scrub meadow had a net carbon fixation of 111.11 gm^-2 and 243.89 gm^-2 respectively. Results also showed that soil temperature was the main factor which influenced CO2 emission from alpine meadow ecosystem, significant correlations were found between soil temperature at 5 cm depth and CO2 emission from GG, GC, FC and FJ treatments. In addition, soil moisture maybe the inhibitory factor of CO2 emission from Kobresia tibetica meadow, and more detailed analyses should be done in further research 相似文献
993.
1 Introduction As a Mesozoic relict terrestrial basin controlled and reformed by fracture activities in themiddle to late stage in Mesozoic, Jiaolai basin is situated in the middle of the Ludong uplift, beingoverthrusted upon Jiaobei uplift in the north, adjoining Jiaonan uplift in the south atWulian-Rongcheng fracture, being connected to Tanlu fracture belt in the west, with its NE partextending into the Yellow Sea and connecting to Qianliyan uplift at Qianliyan fracture. Due totec… 相似文献
994.
One of the significant effects of considering soil-structure interaction in the analysis of structures is the increase in
the fundamental natural period compared to the fundamental natural period of a similar structure, fixed at the base. Applied
Technology Council (ATC) originally set forth some provisions to calculate the fundamental natural period of flexible based
structures using the period of a similar structure, fixed at the base, and lateral and rocking stiffness coefficients of the
foundation. These provisions became the basis of current soil-structure interaction recommendations in several building codes.
The fundamental natural periods of structures founded on different types of foundations computed using recommendations of
the ATC are compared with those computed using a simplified model to perform soil-structure interaction of shear-type structures.
Results show that the provisions given in ATC may be used for structures supported on shallow footings but may not be applicable
for structures supported on pile foundations or foundations having the ratio of lateral to rotational stiffness coefficients
different from those of shallow foundations. An equation, similar to the equation recommended by ATC, is presented to estimate
the fundamental natural period of structures supported on pile foundations.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
995.
Mean return periods, RP, for the site of Roermond, The Netherlands, as calculated by different methods, are compared, and its quality evaluated by a simple two-tail test of hypothesis. Results show that RP values by the EGO-method are statistically more likely. They can be considered, despite their broad 90% probability intervals, and for the site and data used, more reliable, since the Roermond earthquake was not an unusual or surprising event for the Lower Rhine Embayment area, where earthquakes of comparable size have occurred since the 18th century. 相似文献
996.
997.
根据河南城市大型商贸文体活动日益增多的实际需要,按不同活动对气候条件的要求,提出用单项排除和综合舒适指数两种方法来确定气候适宜期,并构建了多要素综合舒适指数的计算方法。在此基础上,以郑州为例,用以上两种方法确定了郑州举办大型社会活动的适宜的季节和日期,为决策机构提供了一项基本的气候依据。 相似文献
998.
面对计算机技术的飞速发展,如何尽可能地延长地震信息系统的生命周期,使有限的投入能在罗长时间发挥更大效益,是地震工作者普遍关心的问题,本文通过介绍河北省地震信息系统(HBEIS)建设与维护的初中和收到的效果,阐述了在系统的规划设计、具体实施、应用开发和维护管理等各阶段应遵从的基本原则。 相似文献
999.
1000.
用西北地区12站1951~1996年月降水量序列,估计了分维数和平均可预报时长,初步结果表明,这些序列为具有低阶自由度(4~6)的动力系统。根据二阶Renyi熵(K2)表征的该地区平均可预报时长在2~3个月,西北地区降水分维特性可能有地域差异。 相似文献