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991.
992.
A low-background germanium spectrometer was used to measure the gamma-ray spectra of the three parts of the Swanscombe skull. Detailed studies of the method showed that it was possible to make accurate measurements of the content of 226 Ra and 231 Pa but less accurate ones of 238U and 235U. Results from the three samples were inconsistent, showing that their exposure to radioactive ground water must have been very different, although they were found close together. The uncertainty in the ratio of 234U to 238U in the ground water and the lack of knowledge of the time at which the bones acquired the uranium also prevented the deduction of any reliable dates for these specimens. 相似文献
993.
994.
A new method is proposed to map firms' principal market areas using shipment data. The new method is a general one which could prove just as useful in mapping the incidence of disease as in mapping market areas. This method is applied to agricultural data for feeder cattle sales at a video cattle auction. Transportation costs appear to be the main determinant of market area boundaries, but there are many cases where transportation costs alone cannot explain the market areas found. The size and shape of market areas for feeder cattle buyers are large, irregularly shaped, and extensively overlapping. 相似文献
995.
Estimating Relative Standard of Living in the United States Using Cross-Migration Data 总被引:2,自引:0,他引:2
Stratford Douglas 《Journal of regional science》1997,37(3):411-436
A new estimator links migration data to a random utility "voting with your feet" model to compare the relative living standards of pairs of regions. It is argued that this estimator has a firmer theoretical basis and uses migration information more efficiently than previous methods. An algorithm converts pairwise comparisons into rankings of the U.S. states for 1970, 1980, and 1990. The rankings indicate living standards were highest in the Northwest (1970, 1980) and the south Atlantic coast (1990). A nonparametric test suggests that the system was in disequilibrium in 1980 (probably due to energy price shocks), but near equilibrium in 1970 and 1990. 相似文献
996.
997.
998.
Setlow B 《Journal of the history of the neurosciences》1997,6(2):181-192
The idea that memories could be transferred from one organism to another by administration of a "trained" donor brain to a naive recipient seized both scientific and public attention in the 1960's and early 1970's. Georges Ungar was one of the earliest and strongest proponents of this idea, and he provided it extensive theoretical and experimental support. This paper reviews Ungar's work on memory transfer (and in particular on the scotophobin molecule), with an analysis of its successes and failures. 相似文献
999.
1000.
THOMAS KB 《Journal of the history of medicine and allied sciences》1957,12(4):449-458