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991.
Jeffrey R. Lehman 《School science and mathematics》1995,95(2):69-77
Science teacher educators from 205 colleges/universities completed a questionnaire concerning the nature and extent of microcomputer offerings in their secondary science teacher preparation programs. These data are reported and compared to a similar sample surveyed in 1984. Seventy-seven percent of reporting institutions now require either a microcomputer course or completion of a microcomputer competency within their secondary science certification program. The most common applications in these courses are simulations, word processing, databases, and spreadsheet use. Chi-square analysis revealed that more institutions in 1992 were requiring a microcomputer course than in 1984. However, only 23.4% of the institutions offered a microcomputer course designed solely for secondary science majors, and 10.6% of the institutions offered such a course taught by a science teacher educator. Preservice science teachers were also more likely in 1992 than in 1984 to be using microcomputers in instruction during supervised field experiences in secondary schools. Finally, college/university science teacher educators perceived that microcomputer use in secondary science classrooms has increased during the past five years. 相似文献
992.
993.
C W Ponton J J Eggermont S G Coupland R Winkelaar 《The Journal of the Acoustical Society of America》1992,91(3):1576-1586
Previous studies of human auditory development using frequency-specific auditory brain-stem responses (ABRs) have reported that maturation for both peak and interpeak latencies occurs earlier for responses generated by low-frequency stimuli. In two of these studies, low-frequency ABRs presumed to originate from apical locations in the cochlea were likely dominated by activity from higher frequency regions closer to the base. In the present study, the high-pass noise-masking technique was used to generate derived ABRs that represent activity from isolated place specific regions along the basilar membrane. Analysis of auditory brain-stem maturation based on I-V interpeak latency differences with adult means revealed a frequency-specific pattern of development. Developmental changes occurred faster and mature function was attained earlier for ABRs from the mid-center-frequency (CF) derived conditions than from either the highest or lowest CF derived conditions. The differential maturation of mid-CF derived ABRs may reflect the delayed effects of the pattern of development that occurs in the cochlea. 相似文献
994.
R. Szymczak K. Zaveta H. Szymczak H. -Q. Guo H. Kronmü ller 《Journal of magnetism and magnetic materials》1994,130(1-3):363-366
The temperature dependence of magnetization of a nanocrystalline Fe60Co30Zr10 alloy annealed at various temperatures to varying crystal sizes was investigated down to 5 K in the field range up to 5 T. The fitting procedure gave T3/2 as the leading term irrespective of the crystal size. We suggest that the increase of the coefficient by this term for smaller crystals may be connected to an increased relative volume of their surface. 相似文献
995.
Sulfide cluster-derived ensembles are promising models of the active sites in commercial hydrotreatment catalysts. A series of sulfide clusters were adsorbed intact onto high-surface-area γ-alumina, magnesium oxide and activated carbon supports, then pretreated to produce highly dispersed catalytic ensembles with sizes similar to those of their precursor clusters. The activities of the bimetallic cluster-derived catalysts were significantly higher than those of the monometallic catalysts. We took this as evidence that direct interactions between molybdenum and the promoter element cause the promotional effect observed in commercial hydrotreatment catalysts. The hydrodesulfurization and hydrodenitrogenation activities correlated with the extent of molybdenum reduction. Our results suggested that the active sites in promoted hydrotreatment catalysts are centered on molecular-scale ensembles containing molybdenum, sulfur and the promoter element. 相似文献
996.
997.
The nature of the propagation center in the cationic polymerization of N-benzoyl-8-octanelactam initiated by octanoylium hexachlcroantimonate, SbCl5, and Ph3CAsF6 in perdeuterated tetrachloroethane or its mixture with o-dichlorobenzene was studied using 1H, 13C, 19F, 31P, 75As, and 121Sb nuclear magnetic resonance (NMR) of model oligomers and the products of their end-capping with triphenylphosphine. In all cases, the nature of the propagation center has been found to be of an acylium ion pair with an SbCl6? or AsF6? counterion coordinated with the nearest benzoylamide group and cosolvated by the solvent. © 1994 John Wiley & Sons, Inc. 相似文献
998.
M. R. Nuriddinova V. M. Malikov A. Yu. Kushmuradov A. I. Saidkhodzhaev 《Chemistry of Natural Compounds》1992,28(6):551-552
A microcolumn HPLC fingerprint method has been developed for the epigeal organs ofFerula kuhistanica andF. tenuisecta. The possibility has been shown of control by the microcolumn HPLC method of the qualitative and quantitative yields of ferutinin
in the initial plant raw material and in preparations extracted from it, and also at each stage of the isolation of the desired
product. The method is universal and does not depend on species and chemical composition of the plant.
Institute of the Chemistry of Plant Substances, Uzbekistan Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh
Soedinenii, No. 6, pp. 635–636, November–December, 1992. 相似文献
999.
The complexation of Ho3+ in HoCl3 and KOH solutions at 25°C and saturated vapor pressure was studied by an indicator spectrophotometric technique, and the pH values of the investigated solutions were determined. The stability constants of the hydroxo complexes of Ho3+ were measured over a range of pH 9.25–10.10 and at μ≤ 4 × 10?4 and extrapolated to zero ionic strength. 相似文献
1000.
Lahiouel R. Pierre J. Siaud E. Galera R. M. Besnus M. J. Kappler J. P. Murani A. P. 《Zeitschrift für Physik B Condensed Matter》1987,67(2):185-191
Magnetic properties, electrical resistivity, specific heat and magnetic excitations have been investigated in Heusler phases CeInAg2–xCux. The hybridization continuously increases from CeInAg2 (antiferromagnetic Kondo lattice) to CeInCu2 (heavy fermion compound). The specific heat coefficient for this last compound is found to reach 1.2 J/mole. K2 at 1.4 K, the Kondo temperature is 6 K and the Wilson ratio is close to 2. 相似文献