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排序方式： 共有10000条查询结果，搜索用时 15 毫秒
991.
The cleistogamous species Collomia grandiflora produces dimorphic cross-incompatible flowers on a single plant. The open or chasmogamous flower has smaller, flask-shaped stigmatic papillae, larger pollen grains, longer styles, and faster pollen tube growth rates down the style than the closed or cleistogamous flower. In intermorph crosses, pollen tube growth rates are greatly decreased and fertilization does not occur. 相似文献
992.
993.
994.
Bird SJ 《Science (New York, N.Y.)》1984,224(4649):595-596
995.
996.
Mahoney MS 《Science (New York, N.Y.)》1984,226(4670):39-40
997.
Effects of pretreatment solutions containing varying concentrations of calcium, potassium, ammonium and nitrate were evaluated by measuring fluxes of the same ions during a subsequent 4-hour uptake by Douglas-fir seedlings. Maximal rate of ammonium uptake (11 microeq g(-1) root dry weight h(-1)) was about 5 times faster than that of nitrate (2 microeq g(-1) root dry weight h(-1)). Ammonium uptake was most rapid after pretreatment with low potassium levels and was unaffected by ammonium pretreatment. Nitrate uptake was most rapid after pretreatment with high levels of nitrate and low levels of potassium. Calcium uptake was greater when nitrate replaced ammonium as the N source. High calcium pretreatment levels depressed subsequent calcium uptake or resulted in calcium release in both ammonium and nitrate experiments. Potassium efflux occurred with both N sources, but the release was less during nitrate uptake than during ammonium uptake. Efflux of potassium is probably associated with the high potassium status of the seedlings and the exchange between potassium and other cations. High levels of potassium in the pretreatment solutions enhanced potassium efflux and caused a reduction in the subsequent rates of uptake of both ammonium and nitrate. Length of pretreatment and seedling size generally did not affect uptake rates. 相似文献
998.
Alexandrov YN Crymov AA Kotelnikov VA Petrov GM Rzhiga ON Sidorenko AI Sinilo VP Zakharov AI Akim EL Basilevski AT Kadnichanski SA Tjuflin YS 《Science (New York, N.Y.)》1986,231(4743):1271-1273
From October 1983 to July 1984, the north hemisphere of Venus, from latitude 30 degrees to latitude 90 degrees , was mapped by means of the radar imagers and altimeters of the spacecraft Venera 15 and Venera 16. This report presents the results of the radar mapping of the Maxwell Montes region, one of the most interesting features of Venus' surface. A radar mosaic map and contour map have been compiled. 相似文献
999.
1000.
Crawford M 《Science (New York, N.Y.)》1986,234(4774):275-277