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排序方式: 共有1586条查询结果,搜索用时 15 毫秒
981.
R. Achiron MD Z. Gottlieb Y. Yaron M. Gabbay U. Gabbay S. Lipitz S. Mashiach 《黑龙江环境通报》1995,15(2):155-160
Our objective was to establish nomograms for fetal eye measurements from 12 weeks' gestation by using transvaginal and transabdominal high-resolution ultrasound techniques. A prospective cross-sectional study was performed on 450 normal singleton pregnancies between 12 and 37 weeks' gestation. Vitreous and lens circumferences were measured by transvaginal ultrasonography until 17 weeks, and by abdominal ultrasound between 18 and 37 weeks' gestation. Regression analyses were used to create nomograms, and several transformations were done to obtain linearity. Eye measurements of 12 fetuses at risk for ocular disturbances were plotted on the constructed nomograms. Linear relationships were fitted between vitreous (r2=0.79) and lens (r2=0.88) circumferences and gestational age. In addition, there was a significant correlation between these measurements and the biparietal diameter. Data of the fetuses at risk showed that disturbances in ocular growth were associated mainly with abnormal cerebral development. These normative data may be helpful in the prenatal diagnosis of suspected congenital syndromes that include, among their manifestations, ocular growth disturbances such as microphthalmos and anophthalmos. 相似文献
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The anaerobic biodegradability of wastewaters from different chemical plants was determined by an integrated test strategy consisting of an anaerobic toxicity test, a static anaerobic biodegradation test and a continuously operated fixed bed reactor test. This integrated procedure offered a useful tool for screening wastewaters for anaerobic biodegradability. Four different wastewaters were tested for anaerobic toxicity and biodegradability. One wastewater was used in subsequent testing in a fixed bed reactor which aimed to illustrate a potential design of an anaerobic treatment plant. 相似文献
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Litter sex ratios in the golden hamster vary with time of mating and litter size and are not binomially distributed 总被引:2,自引:0,他引:2
Summary Pregnancy rates, litter sizes, and litter sex ratios vary strongly with the time in the estrous cycle at which female golden hamsters (Mesocricetus auratus) are mated. Early matings tend to produce relatively high pregnancy rates, large litters, and female-biased sex ratios, while late matings tend to produce low pregnancy rates, small litters, and male-biased sex ratios. Time of mating and litter size are therefore correlated, but each appears to have an independent effect on litter sex ratio: time of mating and sex ratio are positively correlated, holding litter size constant, while litter size and sex ratio are negatively correlated, holding time of mating constant. At each litter size greater than two, the variance of litter sex ratios is less than the binomial variance expected on the hypotheses of independent sampling with a constant probability of producing a male. The main features of the distribution of litter sex ratios can be generated from a causal model in which different probabilities of producing a male apply to early and late conceptions within each litter. The relationship between litter size and mean litter sex ratio is potentially consistent with several different models for the evolution of adaptive sex-ratio variation.
Offrint request to: U.W. Huck 相似文献
990.
U. H. Brockmann G. Kattner G. Hentzschel K. Wandschneider H. D. Junge H. Hühnerfuß 《Marine Biology》1976,36(2):135-146
The physical and chemical properties of the sea surface can be altered considerably by the formation of slicks and the accumulation of particles (including plankton). Investigations of natural slicks near the island of Sylt consisted of analyses of the dissolved and particulate surface-active substances, as well as the identification of plankton and bacteria collected by a surface-film sampler. The analyzed surface material consisted primarily of phytoplankton (Prorocentrum micans in particular), bacteria, detritus and dissolved compounds of fatty acids. These fatty acid compounds alone would not account for the slick. The slick appeared to be caused by the calm weather, the active accumulation of P. micans at the surface, and the increase in bacteria associated with this accumulation. Here a decrease was observed in the dissolved surface-active substances compared with the concentration usually found in normal surface waters, of which the total fatty acid content in a sample was taken as indicator. In some cases a correlation was found between fatty acids and particulate matter in naturally occurring slicks. Particularly large variations were found in the fatty acid patterns in the filtrate and filter residue at a time when no slick was present and no particulate matter had accumulated at the surface.
Diese Arbeit wurde von der Deutschen Forschungsgemeinschaft im Rahmen des SFB 94, Hamburg, unterstützt. 相似文献
Diese Arbeit wurde von der Deutschen Forschungsgemeinschaft im Rahmen des SFB 94, Hamburg, unterstützt. 相似文献