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排序方式: 共有2100条查询结果,搜索用时 15 毫秒
71.
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74.
Hans Eschenlohr 《Forstwissenschaftliches Centralblatt》1921,43(10):376-391
Ohne Zusammenfassung 相似文献
75.
The optimum conditions for pigment production by Ae. liquefaciens was found to be 30 °C and aerobic incubation, and the properties of the pigment are shown to be similar to those of the synthetic dopa-melanin referred to. The enzyme phenol oxidase was demonstrated in the culture filtrates, but not in extracts of disintegrated cells. As precursors for the pigment production, which was shown to be strictly pH dependent, DL-tyrosine, DL-dopa and catechol were used with success, while numerous other amino acids failed. The significance of the pigment as a criterium for the identification of strains which are pathogenic to certain animals or fishes, is not known. 相似文献
76.
Abstract – Effects of local environmental influences on the structure of fish assemblages were evaluated from 159 sites in two regions of the Great Plains with limited anthropogenic disturbance. These regions offered an opportunity to evaluate the structure and variation of streams and fish assemblages within the Great Plains. We used canonical correspondence analyses to determine the influence of environmental conditions on species abundances, species occurrences and assemblage characteristics. Analysis of regions separately indicated that similar environmental factors structured streams and fish assemblages, despite differences in environmental conditions and species composition between regions. Variance in fish abundance and assemblage characteristics from both regions was best explained by metrics of stream size and associated metrics (width, depth, conductivity and instream cover). Our results provide a framework and reference for conditions and assemblage structure in North American prairie streams. 相似文献
77.
Summary Wood storage has a great influence on the efficiency of a pulpmill. Great problems arise when using outside chip storage, especially in processing hardwoods, in that hardwood chips discolorate after a few days, which is not the case with spruce chips. The causes of such a different behavior of beech and spruce were investigated. It could be shown that a sufficient amount of active peroxidase, malate dehydrogenase and oxygen are prerequisites for the formation of phenoxy radicals within the beech lignin. This causes formation of new chromophores that discolorize the wood. Sufficient amounts of such enzymes are present in beech wood after harvesting. 相似文献
78.
Hans Jürgen Bestmann Beate Classen Uwe Kobold Otto Vostrowsky Fred Klingaup 《Journal of pest science》1987,60(2):31-34
The essential oil ofChrysanthemum balsamita L. revealed insecticidal properties when tested againstM. dirhodum aphids. The insecticidal activity was attributed to the presence of pyrethrine I in the oil. By an appropriate testing procedure, the dependence of the activity upon the time of harvesting of the plants was determined. Furthermore, the insecticidal effect of the oil was compared with that of a commercially available pyrethrum preparation. 相似文献
79.
Gerhard?WieserEmail author Thomas?Gigele Hans?Pausch 《European Journal of Forest Research》2005,124(1):1-8
We investigated carbon (C) uptake and respiratory losses of an adult Pinus cembra tree at the alpine timberline throughout an entire year by means of an automated, multiplexing gas exchange system. These chamber measurements were then combined with biomass data for scaling up the C budget to the tree level. Integrated over an entire year, the cumulative C gain of the tree under study was 23.5 kg of C in 2002. The daily C balance was negative for 5 months and the estimated total wintertime respiratory losses were 9% of the amount of C fixed during the growing season. The total annual C loss of the tree consumed 55% of the annual net C gain and the remaining surplus was stored in new tissues (36%) and used for fine root growth (9%). Thus, the overall C budget of P. cembra at the upper timberline is balanced fairly well, although the C sink strength in fine roots is strongly limited owing to low root zone temperatures when compared to conifers at lower elevation sites. 相似文献
80.
Stefan Fleck Nathalie Cools Bruno De Vos Henning Meesenburg Richard Fischer 《Annals of Forest Science》2016,73(4):945-957