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71.
72.
J Galicek F Seow J M Lingard 《The Australian journal of experimental biology and medical science》1981,59(4):383-391
Since the few data available concerning the effect of acid/base disturbances on renal amino acid reabsorption were conflicting, and there were sound theoretical reasons for an effect, we have studied the clearance of endogenous amino acids in the rat in vivo under control conditions and after induction of either metabolic acidosis or alkalosis by administration of NH4Cl or NaHCO3, respectively. The effectiveness of treatment was assessed by examination of plasma and urinary levels of HCO3, Cl, Na and K. It was found that the renal clearance of amino acids, measured during acidosis or alkalosis, did not differ from those found under control conditions, the majority of values being less than 1% of the glomerular filtration rate. Thus, the amino acid reabsorptive mechanism appears unaffected by changes in the pH of the glomerular filtrate and/or by changes in tubular hydrogen ion secretion which would accompany such disturbances. These data are thus in agreement with findings during acidosis in man and in both acidosis and alkalosis in the dog. The findings are contrary to earlier reports from in vitro studies in the rat, and suggest the presence of severe functional impairment in the isolated perfused kidneys used in these earlier studies where very large changes in amino acid clearance were obtained. 相似文献
73.
We examined annual variation in the timing of conception andparturition in the African buffalo (Syncerus caffer) and thesynchrony of birth timing with resource cues, using 8 yearsof monthly birth, rainfall, and vegetation data, measured asNormalized Difference Vegetation Index (NDVI). Monthly birthshad the strongest significant correlations with NDVI and rainfalllevels 12 and 13 months in the past, respectively. In addition,the synchrony of current year births corresponds most stronglyto the synchrony of the previous year's NDVI distribution. Becausethe gestation period of buffalo has been estimated to be around11 months, these findings suggest that improved protein levels,occurring approximately a month after the first green flushof the wet season, are either a trigger for conception or conceptionhas evolved to be synchronous with correlated environmentalcues that ensure females enter a period of peak body conditionaround the time of conception and/or parturition. With a gestationperiod of approximately 340 days, parturition occurs to takeadvantage of the period when forage has its highest proteincontent. A comparative analysis of gestation periods withinthe subfamily Bovinae indicates that African buffalo have aprotracted gestation for their body size, which we suggest isan adaptation to their seasonal environment. We also found thatinterannual variation in the birth distribution suggests a degreeof plasticity in the date of conception, and variation in thenumber of calves born each year suggest further synchrony ata timescale longer than a single year. 相似文献