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在国家实施林权制度改革的大形势,对原料林基地建设的影响、较适宜的造林模式、新的造林模式所需要的条件进行阐述,并以合作造林中订单林业的具体实施方案为例详析. 相似文献
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The antioxidant -tocopherol (vitamin E), applied in a basal trunk band to the green ash tree,Fraxinus pennsylvanica var.subintergerrinia, elicited an alteration of foliar feeding byMalacosoma disstria larvae (Lepidoptera: Lasiocampidae). The bioassayed effects were dependent on the dosage of elicitor, the time after elicitation, and the position in the tree. Leaves for chemical analysis were collected from trees receiving two dosages and at two intervals after elicitation. Compounds in the ethyl acetate extractables from the ash tree leaves were separated by TLC and HPLC. TLC separations showed differences in the nonhydrolyzed extractables attributable to elicitor dosage and time after elicitation. TLC-resolved differences were also evident among acid-hydrolyzed samples. HPLC-resolved profiles revealed eight peaks in the nonhydrolyzed extractables that were quantitatively negatively correlated with larval feeding preference between elicited versus control foliage on at least one of the two sampling dates. Results from this study and other investigations reported in the literature indicate that the antioxidant-tocopherol (vitamin E) can function as an environmental-stress elicitor of alterable defensive chemistry in green ash and other plants. 相似文献
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In arid regions, large-scale water diversion from rivers leads to significant changes in river flow regimes, which may have large impacts on ecological water uses of river-dependent ecosystems, such as river, lake, wetland, and riparian ecosystems. To assess the integrated impact of water diversion on ecological water uses, we proposed a hierarchy evaluation model composed of four layers representing the evaluation goal, sub-areas of the influenced region, evaluation criteria, and water diversion schemes, respectively. The evaluation criteria for different types of ecological water uses were proposed, and the analytical hierarchy process was used for the integrated assessment. For a river ecosystem, the percentage of mean annual flow was used to define the grade of environmental flow. For a lake ecosystem, water recharge to the lake to compensate the lake water losses was used to assess the ecological water use of a lake. The flooding level of the wetland and the groundwater level in the riparian plain were used to assess the wetland and riparian ecological water uses, respectively. The proposed model was applied to a basin in northern Xinjiang in northwest China, where both water diversion and inter-basin water transfer projects were planned to be carried out. Based on assessment results for the whole study area and two sub-areas, an appropriate scheme was recommended from four planning schemes. With the recommended scheme, ecological water uses of the influenced ecosystems can be maintained at an acceptable level. Meanwhile, economical water requirements can be met to a great extent. 相似文献
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森林植被截留降雨实验与模拟 总被引:1,自引:0,他引:1
根据半干旱地区樟子松林冠截留降雨的实测资料,对林冠截留与大气降雨之间的关系进行了分析。在几个假设的基础上,建立林冠截留及林内雨量的半理论半经验公式,并介绍了参数确定方法。经检验,公式的计算值与实测值取得较好的一致性,基本上反映出林冠截留降雨的一般规律,揭示了林冠对降雨截留作用的数量关系和客观实质。 相似文献
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Budimir Popovic 《Nutrient Cycling in Agroecosystems》1985,6(2):139-147
The effect of fertilization with urea and ammonium nitrate on nitrogen mineralization was studied in a series of laboratory incubation experiments. The samples (humus layer) were collected from field experiments with different applications of fertilizers during a period of 11–14 years. The nitrogen fertilization influenced some chemical properties of the humus layer such as pH, N-Kjeldahl content and the content of inorganic nitrogen, especially in the samples from North Sweden. Nitrate nitrogen was formed in humus samples classified as non-nitrifying in several cases, usually after urea fertilization. 相似文献
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Reneilson Santos Danilo Souza Walter Santo Admilson Ribeiro Edward Moreno 《Concurrency and Computation》2020,32(16)
Summary Software‐Defined Networking (SDN) is an emerging network paradigm that has gained significant traction from many researchers to address the requirement of current data centers. Although central control is the major advantage of SDN, it is also a single point of failure if it is made unreachable by a Distributed Denial of Service (DDoS) attack. Despite the large number of traditional detection solutions that exist currently, DDoS attacks continue to grow in frequency, volume, and severity. This paper brings an analysis of the problem and suggests the implementation of four machine learning algorithms (SVM, MLP, Decision Tree, and Random Forest) with the purpose of classifying DDoS attacks in an SDN simulated environment (Mininet 2.2.2). With this goal, the DDoS attacks were simulated using the Scapy tool with a list of valid IPs, acquiring, as a result, the best accuracy with the Random Forest algorithm and the best processing time with the Decision Tree algorithm. Moreover, it is shown the most important features to classify DDoS attacks and some drawbacks in the implementation of a classifier to detect the three kinds of DDoS attacks discussed in this paper (controller attack, flow‐table attack, and bandwidth attack). 相似文献