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231.
关于陕西电子农务体系创新的思考 总被引:1,自引:0,他引:1
崔岩 《中国农业科技导报》2006,8(6):61-65
电子农务对于农业实现现代化、农民致富、农村繁荣至关重要。在此背景下,本文对陕西电子农务发展的现状、运行机制进行了分析,井进一步对其存在的问题进行了探讨,提出了以市场运作为主、政府引导为辅、多元化投资的电子农务服务创新体系,并对完善创新体系提出了相应的对策和建议。 相似文献
232.
河流地貌对构造活动的响应 总被引:15,自引:0,他引:15
以前人的研究工作为例,讨论了河流地貌对构造活动的响应.对河流阶地、河流冲洪积扇、河谷形态、水系格式与河道变迁等对构造活动响应的模式、机理进行了分析.这对于我们通过河流地貌研究活动构造有重要意义,同时对河流演化的研究,水土保持研究也有积极的意义. 相似文献
233.
The transport processes of solutes in two soil columns filled with undistrubed soil material collected from an unsaturated sandy aquifer formation in Belgium subjected to a variable upper boundary condition were identified from breakthrough curves measured by means of time domain reflectometry(TDR),Solute breakthrough was measured with 3 TDR probes inserted into each soil column at three different depths at a 10 minutes time interval.In addition,soil water content and pressure head were measured at 3 different depths.Analyteical solute transport models were used to estimate the solute disperison coefficient and average pore-water velocity from the observed breakthrough curves,the results showed that the analytical solutions were suitable in fitting the observed solute transport,The dispersion coefficient was found to be a function of the soil depth and average proe-water velocity,imposed by the soil water flux.the mobile moistrue content on the other hand was not correlated with the average pore-water velocity and the dispersion coefficient. 相似文献
234.
In this paper, taking the hydraulic mechanism of auto unloading truck as an example, the author discussed mainly how to analyze the movement of mechanism by the optimization method. 相似文献
235.
J. HEGGENES & P. K. OMHOLT J. R. KRISTIANSEN & J. SAGEIE F. ØKLAND J. G. DOKK M. C. BEERE 《Fisheries Management and Ecology》2007,14(5):333-342
Abstract Radio transmitters were implanted in wild brown trout, Salmo trutta L., in the River Måna at low summer water flows ( n = 18), higher flow in summer ( n = 20), and variable, peaking flows in autumn ( n = 20), and tracked two to four times day and night for 4–5 weeks. Individuals were caught and released in a 4-km uniformly channelised section, and in a 4-km natural diverse river section. Substantial individual variation in home range and total movement (924–85 818 m2 and 295–7014 m) suggested flexibility to adapt to local environmental conditions. Fish were stationary most of the time (median movement 0 m), but some individuals undertook few and apparently sporadic longer movements, sometimes involving shifts in home range. No consistent diurnal pattern in movements was found. Trout in the uniform habitat section appeared to have larger home ranges and moved more than trout in the natural section. Differences were, however, not statistically significant in most comparisons, due to large individual variation. Similarly, larger home ranges and movements between trials related to higher flow were found, but differences were generally not significant. No consistent effects of sudden, extreme peaking flows on area use or movements by the brown trout were observed. 相似文献
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单坑变水头入渗条件下均质土壤水分运动的数值模拟 总被引:5,自引:2,他引:3
变水头入渗条件下的土壤水分运动是蓄水坑灌的基本理论问题。该文根据土壤水动力学的基本理论,分析了蓄水坑变水头入渗的复杂边界条件,并推导了其坑水位变化与坑壁变水头入渗关系的数学表达式,进而建立了蓄水坑灌单坑变水头入渗及土壤水分运动的数学模型。采用ADI交替方向隐式差分格式将土壤水分运动方程离散,用Gauess-Seidel迭代算法求解非线性差分方程,实现了单坑变水头条件下的土壤水分运动的数值模拟。实验验证表明,数值计算结果与实测值有着较好的一致性。 相似文献
240.
Understanding insect movement and distribution is critical for developing an effective insect pest management protocol. Movement and distribution of adult Cryptolestes ferrugineus (Stephens) in response to nominal temperature differences of 5, 10, 15, and 20°C in 1- and 2-m horizontal columns filled with 12.5% moisture content wheat were studied in 24, 48, and 72 h of movement times. In the wheat columns without temperature differences, adults had a diffusion distribution pattern caused by their random movement. Adults showed bias movement to the warmer grain in wheat columns with temperature differences and preferred the warmer grain regardless of the magnitude of temperature differences in less than 24 h. Their distribution did not have significant differences among different movement times in 1- or 2-m columns. About 40% of adults moved to the warmer wheat located at 0.4 to 0.5 m in the 1 m column but did not move to the warmer wheat located at 0.9 to 1 m in the 2-m column. Therefore, length of grain column influenced detection of warmer grain by insects. Adults under different temperatures had a similar response as that under linear temperature gradients. 相似文献