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221.
微尾鼩种群繁殖的年龄和季节特征 总被引:2,自引:0,他引:2
2003年9月~2004年8月对四川南充地区微尾鼩种群不同年龄组繁殖的差异以及各年龄组在不同季节的差异进行研究.结果表明,微尾鼩总性比为1.05,经χ2检验,两性差异不显著,繁殖个体性比为1.08,两性差异不显著.雄性微尾鼩1、2月份各年龄组的睾丸大小(长径与短径)和重量差异不显著,3~12月份差异极显著.微尾鼩各年龄组睾丸大小和重量在12mo内季节变化为1、2月差异均不明显,3~12月份未成体组(Ⅰ)季节变化明显,而成体Ⅰ组(Ⅱ)和成体Ⅱ组(Ⅲ)差异不明显.雌性子宫斑数在1~10之间,平均胎仔数为4.05±0.14只(N=76),4、9月份为繁殖高峰期,繁殖指数分别为2.37和1.45,4~10月份成体Ⅰ组(Ⅱ)和成体Ⅱ组(Ⅲ)的繁殖力和平均胎仔数年龄差异不明显,成体Ⅱ组(Ⅲ)繁殖力和平均胎仔数在4~12月份季节变化不显著.1、2月份均为雌雄微尾鼩非繁殖期,3~12月份为繁殖期.表2参24 相似文献
222.
粤西残斑岩的锆石U-Pb年龄及其地质意义 总被引:1,自引:0,他引:1
粤西残斑岩脉是由花岗斑岩脉遭受后期地质作用改造而成的 ,具有片状构造 ,片理产状与地层围岩一致。通过对该残斑岩的颗粒锆石U -Pb年龄测定 ,莸得两条不一致线 ,它们的下交点年龄分别为 40 4±6Ma和 42 8± 17Ma ,从而确定残斑岩脉的侵入年龄为 40 4~ 42 8Ma ,属加里东期。根据上交点年龄和2 0 7Pb/2 0 6Pb年龄推断 ,其源区物质较复杂 ,包含有 1737Ma、2 16 5Ma和 2 494Ma的物质 ,暗示粤西云开隆起区存在中、古元古代以及太古宙基底。 相似文献
223.
Modeling of residual chlorine in water distribution system 总被引:2,自引:0,他引:2
Water quality within water distribution system may vary with both location and time.Water quality models are used to predict the spatial and temporal variation of water quality throughout water system.A model of residual chlorine decay in water pipe has been developed, given the consumption of chlorine in reactions with chemicals in bulk water,bio-films on pipe wall, in corrosion process, and the mass transport of chlorine from bulk water to pipe wall.Analytical methods of the flow path from water sources to the observed point and the water age of every observed node were proposed .Model is used to predict the decay of residual chlorine in an actual distribution system.Good agreement between calculated and measured values was obtained. 相似文献
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M. G. J. Jahoda H. Brandenburg A. Reuss T. E. Cohen-Overbeek J. W. Wladimiroff F. J. Los E. S. Sachs 《黑龙江环境通报》1991,11(8):559-561
Data from 3611 consecutive CVS (TC, N= 1780; TA, N= 1831) were analysed with emphasis put on influence of maternal and gestational age at CVS on the fetal loss rate < 28 weeks. For TC-CVS the gestational age varied from 9.3–11.6 weeks, for TA-CVS from 9.3–20 weeks. Sampling efficacy at first attempt was 86.5 per cent and 95 per cent respectively. In 4.6 per cent an abnormal result was established. In older mothers (N=2362) the fetal loss rate was significantly higher (p = <0.05) when sampled before 12 weeks (TC-CVS 6.2 per cent, TA-CVS 5.8 per cent). When the CVS (TA) was performed after 12 weeks the fetal loss rate decreased to 2.4 per cent. In 1079 younger women the fetal loss rate remained low (TC 2.8 per cent; TA < 12 weeks 1.8 per cent; TA > 12 weeks 1.7 per cent) and was not influenced by gestational age at the time of sampling. We concluded both methods safe and reliable when the choice of application considers maternal age. 相似文献
227.
Between 1981 and 1991, 461 pregnant women between 15 and 40 weeks of gestation (mean 30 weeks) with completed follow-up were referred to our centre for prenatal diagnosis because of a small-for-gestational age (SGA) fetus or combined SGA and structural abnormality. The referral diagnosis was based either on biparietal diameter measurements or on measurement of the upper-abdominal circumference. SGA in our centre was defined as a fetal upper-abdominal circumference below the tenth centile. SGA was confirmed by ultrasound in 75 per cent of the fetuses, whilst combined SGA and fetal structural abnormality was substantiated in only 16 per cent of the fetuses. However, in our centre structural abnormality was detected in 34 fetuses who were referred because of SGA alone. Nearly half of the structurally normal SGA fetuses displayed a normal head-to-abdomen (H/A), ratio, whereas an increased H/A ratio was found in 13/15 fetuses with an abnormal karyotype. An abnormal karyotype was present in 20 fetuses, which is 7 per cent of the total SGA population. Nearly 50 per cent represented triploidy associated with oligohydramnios. SGA was confirmed by a birth weight below the tenth centile in 89 per cent, below the fifth centile in 77 per cent, and below the 2·3rd centile in 55 per cent of infants. Structural abnormality was confirmed in 65 per cent of infants, whereas in 19 per cent of infants the abnormality was missed or a misclassification was made. Perinatal mortality was 31 per cent for all SGA fetuses, 27 per cent for SGA fetuses without anomalies, and 64 per cent for SGA fetuses with structural abnormality. 相似文献
228.
Natural regeneration and the height-age structure of small-leaved linden (Tilia cordata Mill.) under a forest canopy were studied with regard to specific features of forest typology on the Ufa Plateau. For the first time, the height-age structure of linden undergrowth was analyzed by an anatomical method, which allowed accurate determination of the actual plant age and linear increment. The results of this analysis made it possible to reveal three periods in the development of linden undergrowth with respect to the linear growth rate and abundance of plants. More successful regeneration of linden was observed in open elements of relief. 相似文献
229.
空间站密封舱空气龄分布数值模拟及试验研究 总被引:1,自引:0,他引:1
介绍了空气龄理论,阐述了空气龄在空间站密封舱内空气品质评价方面的作用,对国内外在空间站密封舱内空气龄数值模拟、空气龄分布验证试验的研究进展进行了综述,并给出了对空间站密封舱进行空气龄数值模拟及试验研究的建议。 相似文献
230.
Hair samples were collected randomly from 110 subjects (55 male and 55 female) ranging in age from (<15–60) years. Each subject was asked to complete a personal questionnaire describing his/her sex, age, general health, smoking, use of hair dyes, occupational area, and living habits. Concentrations of Pb, Cd, Cu, Zn, Fe, and Ca in human hair samples were evaluated using atomic absorption spectrometry. Results indicated that concentrations of Pb, Cd, Cu, and Zn in the hair of smokers were higher than those in the hair of non-smokers, whereas, Fe and Ca concentrations in hair of smokers were lower than those in hair of non-smokers. Moreover, the concentrations of these elements are higher in dyed hair compared with undyed hair. 相似文献