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本文在测量的基础上,对热量平衡各分量在大棚内、外的差异,进行了比较与分析,对大棚生产管理有重要参考价值。 相似文献
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随着刻图法和薄膜绘图方法的普及应用，其配套的透明注记法亦被广泛使用。透明注记虽然是上述绘图法的产物，但与相纸注记相比，其本身有着独特的优点。因为透明注记法可以毋需通过照相，而直接用于制版复印，故能节省人力，物力、降低成本，又能大大缩短成图周期。 相似文献
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In the last several decades, the underlying surface conditions on the Qinghai-Tibet Plateau have changed dramatically, causing permafrost degradation due to climate change and human activities. This change severely influenced the cold regions environment and engineering infrastructure built above permafrost. Permafrost is a product of the interaction between the atmosphere and the ground. The formation and change of permafrost are determined by the energy exchange between earth and atmosphere system. Fieldwork was performed in order to learn how land surface change influenced the thermal regime in permafrost regions. In this article, the field data observed in the Fenghuo Mountain regions was used to analyze the thermal conditions under different underlying surfaces on the Qinghai-Tibet Plateau. Results show that underlying surface change may alter the primary energy balance and the thermal conditions of permafrost. The thermal flux in the permafrost regions is also changed, resulting in rising upper soil temperature and thickening active layer. Vegetation could prevent solar radiation from entering the ground, cooling the ground in the warm season. Also, vegetation has heat insulation and heat preservation functions related to the ground surface and may keep the permafrost stable. Plots covered with black plastic film have higher temperatures compared with plots covered by natural vegetation. The reason is that black plastic film has a low albedo, which could increase the absorbed solar radiation, and also decrease evapotranspiration. The ＂greenhouse effect＂ of transparent plastic film might effectively reduce the emission of long-wave radiation from the surface, decreasing heat loss from the earth＇s surface, and prominently increasing ground surface temperature. 相似文献
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吴书敏 《测绘与空间地理信息》1996,(1)
随着刻图法和薄膜绘图方法的普及应用,其配套的透明注记法亦被广泛使用。透明注记虽然是上述绘图法的产物,但与相纸注记相比,其本身有着独特的优点。因为透明注记法可以毋需通过照相,而直接用于制版复印,故能节省人力、物力,降低成本,又能大大缩短成图周期。但是由于透明感光材料的特性不同于照相纸,必然带来操作工艺上的困难。透明感光膜乳剂成份复杂。感光度快、稳定性差、保存期短;片基光滑亲水性强,乳剂层易吸水膨胀而破损和脱落。成品注记经常出现发灰、发黄、退色、字迹外晕、薄膜面脱落等现象,容易造成废品率高。因此,如何改进透明注记的照排工艺技术,提高透明注记的质量,确保优质成图,是地图生产单位急待解决的技术难题。现就如何提高透明注记的质量,笔者浅谈以下几个问题。 相似文献
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塑料大棚,就是顶上用塑料薄膜覆盖的大棚．属于温室的一种。由于棚内的温度和湿度可由人工调节,对于提早或延缓作物生长季节、抵御病虫害有显著作用。我国从60年代起,就已利用塑料大棚种植蔬菜。目前城市郊区蔬菜、副食品基地的建设中,塑料大棚已普遍推广。如上海由于普遍利用塑料大棚种植蔬菜,改变靠天收的局面,提高了抗灾能力,产量比露天生产增加2倍以上一从而使淡季蔬菜供应状况大为改善。 相似文献
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徐贵如 《水文地质工程地质》1989,(6):39-41
山西省平遥县尹回水库加固除险工程,是采用聚乙烯塑料薄膜铺盖方法解决水库坝体和库区渗漏的一项技术改造工程,是我省首次采用塑料薄膜,处理中型水库的渗漏,取得防渗效果好的实例。它具有:工期短、投资少、见效快、经济效益明显等优点。 相似文献
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