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41.
液压技术的应用已成为现代化农业机械的典型标志。为此,介绍了农机液压技术的应用现状;并根据科学技术的发展,简要分析了农机液压技术的发展趋势。 相似文献
42.
对以QY系列为主体的农用潜水电泵修复可靠性低、寿命短的问题,提出了改进措施,从而有效提高潜水电泵修复可靠性,并延长使用寿命。 相似文献
43.
44.
对使用Windows 2000 Server操作系统,以及MS SQL Server数据库的农机监理计算机管理系统的维护,进行了较为详细的分析,并针对不同的情况提出了相应的处理措施,总结了保证农机监理系统可靠运行的办法。 相似文献
45.
46.
茭白主茎地上部养分积累和转运规律 总被引:1,自引:0,他引:1
以两个有代表性的茭白品种为试材,测定了植株主茎生育过程中地上各部位干、鲜质量的积累及叶片净光合速率的变化。结果表明在田间封行前,植株主茎叶和短缩茎的干、鲜质量持续缓慢增加;封行后至肉质茎快速膨大前,短缩茎的物质积累超过叶片和叶鞘;肉质茎快速膨大期间,干物质积累主要在其前期,同时短缩茎等其余部位干、鲜质量明显下降;之后肉质茎干、鲜质量增加趋缓,叶片、叶鞘质量仍持续下降,而短缩茎质量回升,进入新一轮物质积累期;主茎的总干物质量在封行后迅速提高,在肉质茎充分膨大后下降。功能叶片净光合速率在生育进程中总体呈持续缓慢下降的趋势,肉质茎快速膨大期间迅速大幅上升,紧接着又快速回落。 相似文献
47.
结合重庆市地形地貌特点和山区农业面源污染发生的因子,提出山区农业面源污染的防治对策。一方面必需结合当地的自然环境条件和经济发展水平提出农业面源污染的防治规划;另一方面必需结合生态农业建设这一主线,使物质、能量在生态系统内良性循环。紧紧抓住产生农业面源污染源的因子——化肥、农药、农田秸杆、畜禽粪便、农村生活废物等,提出科学的防治和减少途径。 相似文献
48.
Effects of land ownership and landscape-level factors on rare-species richness in natural areas of southern Ontario,Canada 总被引:5,自引:0,他引:5
Lovett-Doust J. Biernacki M. Page R. Chan M. Natgunarajah R. Timis G. 《Landscape Ecology》2003,18(6):621-633
Surprisingly few studies have considered the extent to which the nature of the ownership of land is associated with differences
in biodiversity. We analysed ownership and other landscape-level effects on rare-species richness for both globally- and regionally-rare
biota (including birds, herpetofauna, butterflies, mammals, and plants) in 289 designated natural areas (NAs) in southern
Ontario, Canada. Information about each NA −including area, number of plant communities, ownership status and details of species
diversity were collected from published sources. Length of perimeter of NA, relative isolation, and an estimate of fragmentation
were measured using image analysis and GIS techniques. NAs were in general relatively small, with mean area of 158 ha (median
85 ha, range from 0.9 to 1278 ha) for private NAs; public NAs had mean area of 132 ha (median 16 ha, range from 0.1 to 1481
ha). Mean number of plant communities was 4.6 (median 4, range 1- 13) at private NAs and 3.8 (median 3, range 1-16) at public
NAs. Our results show that, of several landscape-level factors, area had the greatest effects on rare-species richness and
other biotic indices. Effects of area were followed by effects of plant community diversity, however this was itself significantly
affected by area and the extent of perimeter of the NA. Both these factors were followed by effects of ownership of the NA
and by effects of isolation of the NA (represented by minimum distance to nearest NA and by number of NAs in 10 km radius).
Other landscape- level factors did not appear to have overall significant effects. Variation in area accounted for 0.1% to
29% of variation in number of rare species, with lower values for globally-rare, than for regionally-rare taxa. For all biotic
groups, public ownership of NAs was associated with significantly greater rare-species richness compared to private ownership,
even after other factors such as area were controlled. For all globally-rare biota except butterflies, area of NA had greater
effects on rare-species richness than did ownership. Richness of regionally- rare birds was more affected by plant community
diversity than by area of NA. Number of recorded plant communities accounted from 2.1% of variation in number of globally-rare
plant species to as high as 31% of variation in regionally-rare butterflies. The diversity of plant communities was itself
influenced by total site area (accounting for 45% of variation), extent of elongation of the NA, and both external- and interior-
edge perimeters. Public NAs had greatest numbers of rare biota and so should be a significant focus for conservation programs.
Smaller, privately-owned patches of natural area dominate (by number and area) in this densely populated region and their
significance should not be overlooked.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
49.
50.
Ecology and non-chemical control of Rumex crispus and R. obtusifolius (Polygonaceae): a review 总被引:1,自引:1,他引:1
J G Zaller 《Weed Research》2004,44(6):414-432