共查询到20条相似文献，搜索用时 343 毫秒
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三峡工程对坝下长江流量影响研究 总被引：1，自引：0，他引：1
根据长江水情的具体特点,采用Ｐｒｅｉｓｍａｎｎ隐式格式,建立了一个描述长江情的水动力学数值模式。以最佳拟合历史水文资料,重演历史水文过程为原则,率定数值模式中的各参数;并运行率定后的模式,进行三峡工程对坝下长江若干断面处流量影响的模拟预测。 相似文献
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风场对藻类在太湖中迁移影响的动力学研究 总被引：36，自引：10，他引：26
在Ｗｅｂｓｔｅｒ等人工作的基础上,以三维湖流为背景,考虑了波浪及藻类自身浮力的影响,建立了一个太湖梅梁湾三维藻类迁多模型,以研究在不同几场作用下藻类在湖泊中的迁移过程。模拟结果表明,不同风场对于藻类在湖泊中的水平及垂直分布影响很大,并且存在着一临界风速,其范围在２－３ｍ／ｓ之间,当几速小于临床风速时,水面可以拟看作水动力学光滑,没有波浪产生,在水表面藻类顺着风向迅速的向迎风岸的边漂移,形成藻类大量 相似文献
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Nigel Wreford 《CT理论与应用研究》2000,9(Z1):145-147
男性和女性的生育控制问题是本世纪一个重要的生物学研究领域。女性生育的有效控制方法已存在好多年了，然而，用于男性的有效的方法还没有找到。近年来，人们试图确定荷尔蒙对精子产生的调节作用，期望找到与女性避孕同样有效并可接受的方法。睾丸包括生精管和裂隙腔，生精管中容纳的是滋养幼芽上皮细胞的Sertoli细胞，裂隙腔中容纳的是产生睾丸激素的Leydig细胞。在精子产生过程中，精原细胞通过有丝分裂繁殖，其下一代经过减数分裂产生单倍体圆形精子细胞，接着发生一系列复杂的形态变化成为成熟的长形精子细胞，成熟后的精子就具有受精能力。 维持幼芽上皮细胞的Sertoli细胞在人的一生中不发生大的变化。Sertoli细胞维持幼雅细胞的能力是有限的，但在不同人之间其能力有一个较大的变化范围。因而，Sertoli细胞的数目决定了睾丸产生精子的最大能力。对于精子产生的调节涉及到内分泌、副分泌和自分泌机制。体视学和各种形态测定工具已成为实验条件和自然条件下睾丸生物学研究的一把钥匙，这些研究包括了解Sertoli细胞的繁殖以及调节精原细胞转变为成熟细胞的效率的因素。从而提出精子发育的规律性，由荷尔蒙对精子产生调节作用的模型。 相似文献
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简要介绍同车公司地裂缝观测站情况,以2013年至2016年数字化改造后的观测数据为基础,结合仪器工作原理,分析三维断层形变测量仪测值与观测仪两端辅助温度测值的关系。结果表明,地裂缝三维断层形变观测中,垂直向DFG观测受地裂缝两端辅助温度影响较显著,地裂缝垂直形变变化是热形变效应和断层运动信息的综合反映。 相似文献
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川东地区平均构造应力场反演研究 总被引：1，自引：0，他引：1
本文运用断面滑动矢量分析，定量反演了川东地区的平均构造应力场，结果表明：川东地区构造应力场自第四纪以来一直稳定，主压应力轴方向为ＮＷ－ＮＷＷ，倾角由陡变缓，与震源机制解反映的现代构造应力场接近，局部应力状态随内部构造特点而发生变化。 相似文献
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四川地震震级与烈度区面积和震源深度的关系 总被引：2，自引：0，他引：2
本文按照地震地质分区,同时考虑7级以上地震的空间分布特征,分四川为鲜水河、松潘—龙门山及马边地震带等几个区带,对四川1900年以来既有仪器测定参数、又有宏观烈度考查的33个地震资料,应用多元线性回归分析方法,统计拟合出了震级与不同烈度区面积、烈度值、震源深度之间的多组关系式,其一般形式为:■相关系数R大都在0.90左右,用部分地震检验的结果表明,震级误差一般小于0.3,震源深度误差一般小于5公里,基本消除了离散情况,笔者用求得的关系式对1900年以前的有三条以上等震线的部分历史地震的震级、震源深度进行了标定,结果也比较令人满意。 相似文献
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This paper reviews original and published data on the abundance and composition of pyroclastics due to explosive discharges
by volcanoes on the Iceland Plume. The pyroclastics were deposited in the Cenozoic sediments in the North Atlantic Ocean and
in the Norwegian-Greenland basin. The DSDP and ODP initial reports (70 deep wells), 100 geologic columns sampled during cruises
of the R/Vs Akademik Kurchatov and Mikhail Lomonosov furnished the database from which we constructed stratigraphic and areal-maps of pyroclastics abundance and computed the
distribution of the volumes and amounts of pyroclastic layers over the stratigraphic intervals of the Cenozoic sedimentary
sequence. The distribution of these layers was found to be cyclic; the highest frequency occurred during the Quaternary. Basaltoid
pyroclastics prevailed in the late Paleocene and Early Eocene. The Oligocene has typically subalkaline ankaramite pyroclastics.
From the Miocene until the Quaternary the pyroclastics became bimodal (basalt-rhyolite) and high potassium rhyolite pyroclastics
appeared. This evolution seems to have been caused by crystallization differentiation of basaltoid magmas in magma chambers
that came into being in prespreading grabens where a thick (> 20 km) sequence of volcanic rocks accumulated to produce a dipping
reflector. 相似文献
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基于CBS的违禁品目标凸现 总被引：1，自引：1，他引：0
本文在分析基于CBS的人身安检图像基础上,提出了基于数学形态学膨胀累加、双阈值分割的违禁品分割算法.采用形态学的膨胀累加算法可以有效抑制噪声并提高目标能量;利用连通性判断获得违禁品候选区域;最后通过获得的数据对违禁品目标进行有效地凸现. 相似文献
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L. Villari 《Bulletin of Volcanology》1970,34(3):758-766
The central part of the Island of Pantelleria is occupied by a caldera depression of ellipsoidal form, the major diameter of which is about 7 kilometers. The collapse causing the caldera to form seems to have taken place after a complex eruption which led to the extrusion of a great endogenous dome, the formation of which was followed by a localized explosive activity. The succession of the acid volcanites of Pantelleria shows periodical evolutions of the magmas, undergoing various cycles of differentiation. After a period of quiescence a new cycle of differentiation started again. This may be explained by admitting that the differentiation was accompanied by an increase in the gas content. The violent degassing re-established conditions analogous to those which had existed at the beginning of the previous cycle. 相似文献
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Coastal developments in Venezuela are leading to the rapid destruction of the mangrove forests. Population pressure leads to an overcrowding of public recreational beaches and the wealthy are increasingly seeking out previously deserted coasts. A rash of summer houses built on stilts over the shallow water is now extending around the mangrove areas, causing pollution, erosion and a progressive deterioration of the coastal environment. 相似文献
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There are many unanswered astronomical questions about the chemical basis of life; a meeting held in August this year by the Astrophysical Chemistry Group of the RAS and the Royal Society of Chemistry took as its starting point the understanding of a number of questions, and reviews of progress towards the answers, report Anita Richards and Peter Sarre . 相似文献
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J A Jacobs 《Astronomy& Geophysics》2001,42(6):6.30-6.31
Superchrons – long periods in the geomagnetic record when the Earth's magnetic field did not reverse its polarity – are a challenge to observers and theorists. Jack Jacobs outlines the problems and some possible solutions.
Reversals of polarity are a feature of the geomagnetic record for all the time it has been documented. Although not regular, reversals are sufficiently frequent for their absence to be noticeable. When the Earth's magnetic field retains the same polarity for over 20 million years, a superchron is established. Superchrons demand the attention of geophysicists concerned with the generation of the Earth's field: either they must result from an intrinsic feature of the geodynamo, or they reflect the influence of some external force. Here I discuss internal and external mechanisms for the formation of superchrons, including the role of the inner core, true polar wander, Earth's orbital variations and tides. 相似文献
Reversals of polarity are a feature of the geomagnetic record for all the time it has been documented. Although not regular, reversals are sufficiently frequent for their absence to be noticeable. When the Earth's magnetic field retains the same polarity for over 20 million years, a superchron is established. Superchrons demand the attention of geophysicists concerned with the generation of the Earth's field: either they must result from an intrinsic feature of the geodynamo, or they reflect the influence of some external force. Here I discuss internal and external mechanisms for the formation of superchrons, including the role of the inner core, true polar wander, Earth's orbital variations and tides. 相似文献
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P C W Davies 《Astronomy& Geophysics》2005,46(1):1.26-1.29
Why does time apparently fly one way, when the laws of physics are actually time-symmetrical? Paul Davies proposes a quantum solution, in the Whitrow Lecture 2004, given on 8 October 2004. 相似文献