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881.
发头裸腹溞休眠卵发育的温度因子分析 总被引:2,自引:0,他引:2
测定了不同温度下发头裸腹溞(Moina irrasa)体眠卵的孵化时间及孵化率;取最先孵出和过半数孵出的两组数据依莱奥姆积温法则求得种群休眠卵最低临界温度为12.00℃,最低有效积温为441.61℃·h;最低亚致死高温点(即最适温度)为35.16℃,以及最低死亡高温点39.44℃。种群中过半数的临界温度为12.88℃,过半数有效积温为557.10℃·h,过半数的亚致死高温点为35.56℃以及过半数死亡高温点为39.49℃。讨论了这些参数在枝角类集约化培养中休眠卵的有效保存与启用所具有的实践意义。 相似文献
882.
伊乐藻—草鱼圈养复合生态系统中水生生物的变化和影响 总被引:2,自引:1,他引:2
从细菌、浮游植物、浮游动物、底栖动物和有机碎屑等几个方面分析了养鱼对伊乐藻种植区(以下简称为有草区)和无草区水域环境的影响。结果表明:两个区域存在着显著的差异性。有草区由于生长着茂密的水生植被,对环境压迫的缓冲能力增强,水生生物的群落结构较为稳定,物种多样性指数高于无草区,有机物的沉降速率也大大低于无草区。与此相比,无草区对环境压迫的缓冲能力较差,水体浮游植物数量增加,富营养化加剧。通过本项实验可以看出,人工种植伊乐藻对养鱼区水质有着明显地控制作用,是发展生态渔业的一条有效途径。 相似文献
883.
884.
885.
ICSED (Improved Cluster Shade Edge Detection) algorithm and other various methods to accurately and efficiently detect edges on satellite data are presented. Error rate criterion is used to statistically evaluate the perform-ances of these methods in detecting oceanic features for both noise free and noise contaminated AVHRR (Advanced Very High Resolution Radiometer) IR image with Kuroshio. Also, practical experiments in detecting the eddy of Kuroshio with these methods are carried out for comparison. Results show that the ICSED algorithm has more advantages than other methods in detecting mesoscale features of ocean. Finally, the effectiveness of window size of ICSED method to oceanic features detection is quantitatively discussed. 相似文献
886.
本文分析了30例肺癌的 MRI 及手术病理分期的结果。结果表明:MRI 能够比较准确地显示肿块的大小、范围、部位及叶以上支气管的受累情况;容易显示胸壁、纵隔、隔肌及远处转移,对胸壁受侵犯诊断准确率为86.7%;无需使用造影剂能直接显示肺门及纵隔区大血管的受累与否、诊断准确率为83.3%;对肺门及纵隔淋巴结转移诊断准确率为90%,敏感性为91.3%,特异性为85.7%;与手术病理分期结果比较,MRI 对肺癌分期准确率为80%。故认为 MRI 是对肺癌分期癌一种准确的无创性新方法。 相似文献
887.
888.
Precambrian Geochronology, Chronotectonic Framework and Model of Chronocrustal Structure of the Zhongtiao Mountains 总被引:8,自引:0,他引:8
The Zhongtiao Mountains, a typical exposure area of Precambrian rocks, are a concentration area of vari-ous types of copper deposit. The rocks were dated using several dating methods. Based on the age data ob-tained by means of three methods, several aspects are dealt with: (1) the dating results obtained by differentmethods and their geological implications have been compared; (2) a chronotectonic framework has been con-structed by means of these reliable ages, which indicates that the ages of the rocks of the Proterozoic mobilebelt fall in a time span of 2400 to 2000 Ma during which global magmatic records are lacking and reflects theages of important events in the mobile belt; (3) according to the ages of inherited zircons, neodymium modelage of the depleted mantle sources (T_(DM)) and geochemical and geological data, a model of Precambrianchronocrustal structure has been constructed, representing a typical for the North China craton. 相似文献
889.
890.
Jiangchuan Ni Yuntai Chen Ming Wang Mingxi Wu Jiayu Zhou Peide Wang Francis T. Wu 《地震学报(英文版)》1992,5(3):459-467
Based on the three component accelerograms, recorded at near-field distance by a temporary seismic network consisting of digital
cassette tape recording accelerographs, the focal mechanisms of three aftershocks of the April 18, 1985, Luquan, Yunnan Province,
China, earthquake ofM
S=6.1, are calculated using seismic moment tensor inversion technique. The phases of direct P, S and converted SP waves in
the displacement seismograms, produced by twice integrations of the observed accelerograms, are identified via forward calculation
using Green’s functions for homogeneous semi-infinite elastic medium, and used in the inversion. The results of inversion
show that a better fit of synthetic to the observed seismograms of direct as well as converted phases can be achieved if appropriate
weighting functions are used in solving the over definite linear equations. While these aftershocks are of different magnitudes
(M
L=4.8, 3.2 and 3.5, respectively) and hypocentral locations, their focal mechanisms are very similar and consistent with that
of the main shock. This feature demonstrates the intrinsic correlation between the occurrence of aftershocks and the seismogenic
fault of main shock. Our experimentations show that using the near field accelerogram obtained from the digital seismic network
with appropriate azimuthal coverage on the focal sphere, with the aid of even simple medium model, not only the shear dislocation
source, but also the isotropic part and CLVD (compensated linear vector dipole) can be retrieved by the technique of moment
tensor inversion.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 412–419, 1991.
This work is supported by the Chinese Joint Seismological Sciences Foundation and the Western Yunnan Earthquake Prediction
Test Site (WYEPTS), State Seismological Bureau. 相似文献