PTC热敏电阻及其应用研究

本文对PTC热敏电阻的电阻温度、电压电流和电流时间三大特性进行了分析,同时介绍了PTC热敏电阻在自动消磁、电机启动、过流保护、恒温加热、灯丝预热等方面的应用     

济宁16号小麦等量氮肥不同时期追施与产量的关系

本试验是在小麦新品种济宁16号通过省审后，所做的一项高产配套栽培技术研究。本试验用等量标准氮肥，做了3种不同处理追施。结果为：以标准氮肥的50％作为底肥，50％作为拔节肥，小麦群体变化最合理；以标准氮肥50％作为底肥，50％作为拔节肥追施，小麦增产达极显著水平，此处理下的小麦产量比以标准氮肥的50％作为底肥，50％作为起身肥处理下的产量增产显著；以标准氮肥50％作为底肥，50％作为拔节肥的小麦灌浆时间最长，千粒重最大；以标准氮肥50％作为底肥，40％作为起身肥，10％作为挑旗肥为处理的倒伏最严重，以标准氮肥50％作为底肥，50％作为拔节肥的小麦倒伏最轻。     

糊化淀粉尿素对山羊消化代谢和增重的效果

选择３６只本地白山羊随机分成３组进行饲养试验。配制３种分别含有豆粕、糊化淀粉尿素和尿素并达到等能等氮水平的混合材料，定量饲喂，干草自由采食。３５天饲养试验后，每组选３只阉公羊作上述３种日粮的消化代谢试验。结果表明：（１）３种日粮的粗纤维表现消化率分别为６４．６５±５．５８％、６６．１０±３．７２％和６１．４９±７．６１％。（２）３种日粮的氮代谢率分别为２５．８３±４．８６％、２２．２５±７．０％和１９．３６±３．９８％，糊化淀粉尿素日粮比尿素日粮提高１４．９３％。（３）与尿素日粮相比，动物采食含糊化淀粉尿素日粮后外周血液尿素浓度有所下降，且动态变化也相对平稳。（４）３个日粮组的日增重分别为６８．４５±３５．８４、７０．８３±３１．２８和６１．９１±３１．８０ｇ／只，差异不显著（Ｐ＞０．０５）；每千克增重所需日粮粗蛋白质分别为９２６．５、９５２．２和１１３３．２ｇ，尿素日粮的饲喂效果最差。结果分析指出：糊化淀粉尿素产品能有效改善尿素氮的利用率，并能达到与豆粕相同的增重效果。     

Flow through sharp-crested rectangular side orifices under free flow condition in open channels

Side orifices are widely used in irrigation and environmental engineering to spill or divert water from a channel. Flow characteristic of sharp-crested rectangular orifices under free flow condition in open channels is studied in the present paper. Existing discharge equations are checked for their accuracy using the data collected in the present study and available data in the literature and a new discharge equation has been proposed. The coefficient of discharge mainly depends on the approach flow Froude number and ratio of the size of orifice and bed width of the channel. Relationships for the coefficient of discharge, treating the orifice as large and small were developed. The computed discharges using these relationships were within ±5% of the observed ones. Measurement of three-dimensional velocities and visualisation of streamlines in a horizontal plane at the centerline of the orifice indicates that for the flow of low Froude number, almost all the streamlines divert towards the orifice. However, in the case of high Froude number flows, only those streamlines which are close to the side orifice are diverted towards the orifice. The opposite side of the boundary has significant effect on the diverted discharge of low Froude number compared to the flow of high Froude number. Circular orifice has been found to be more efficient compared to the rectangular orifice of the same opening area.     

重新认识土地收益递减规律

本文在确认土地收益递减规律在农业中普遍存在的基础上,阐述了土地收益递减规律的实质内涵及其与土地肥力递减规律的本质区别:同时,又进一步根据生产要素结构理论,指出了土地收益递减规律存在的经济和技术原因;为防止农业生产中土地收益递减现象的存在,本文在最后还指出了重新认识土地收益递减规律的现实意义,尤为强调不断提高农业科学技术水平,改善农业生产生态环境条件对农业生产的促进作用。     

Developing effective sampling designs for monitoring natural resources in Alaskan national parks: An example using simulations and vegetation data

Monitoring natural resources in Alaskan national parks is challenging because of their remoteness, limited accessibility, and high sampling costs. We describe an iterative, three-phased process for developing sampling designs based on our efforts to establish a vegetation monitoring program in southwest Alaska. In the first phase, we defined a sampling frame based on land ownership and specific vegetated habitats within the park boundaries and used Path Distance analysis tools to create a GIS layer that delineated portions of each park that could be feasibly accessed for ground sampling. In the second phase, we used simulations based on landcover maps to identify size and configuration of the ground sampling units (single plots or grids of plots) and to refine areas to be potentially sampled. In the third phase, we used a second set of simulations to estimate sample size and sampling frequency required to have a reasonable chance of detecting a minimum trend in vegetation cover for a specified time period and level of statistical confidence. Results of the first set of simulations indicated that a spatially balanced random sample of single plots from the most common landcover types yielded the most efficient sampling scheme. Results of the second set of simulations were compared with field data and indicated that we should be able to detect at least a 25% change in vegetation attributes over 31 years by sampling 8 or more plots per year every five years in focal landcover types. This approach would be especially useful in situations where ground sampling is restricted by access.     

不同类型玉米笋营养成分在罐藏期间变化规律的研究

不同类型玉米笋糖含量随着罐藏时间（３～１２个月）的长短而有所变化，但不太明显；玉米笋各类维生素和胡萝卜素含量随着罐藏时间而变化较明显，可作为玉米笋营养成分在罐藏时间的一些参考指标。     

山东省耕地变化与人口增长及经济发展间的关系初探

选择GDP增长率、人口增长率和耕地面积减少率作为主要分析指标,分析了1978—2000年山东经济增长,人口增长和耕地面积减少之间的关系,并选用1991—2000年的数据以市为单位探讨了区域差异。发现改革开放以来的20多年,耕地面积大量减少的时间和经济过热的增长阶段基本同步,具体受固定资产投资规模的牵动。认为经济增长是耕地面积减少的主要宏观驱动因子。     

Determination of suitable chemical extraction methods for available zinc content of paddy soils at Thrace Region

This research was carried out in order to determine the zinc status of the paddy soils with different physical and chemical properties of Thrace region as well as to determine the most suitable method for chemical extraction of available zinc content of soils for plant. As a result of the investigation with 12 paddy soils representing the region, it was estimated that the application of increasing amounts of zinc to the soil of pot grown maize to increasing the zinc uptake, dry matter and zinc content of the plant was determined. Nine chemical extraction methods for available zinc contents of soil were used and the reliability of the investigated methods was ranked as: 0.005 r M DTPA+0.01 r M CaCl 2 +0.1 r M TEA; 0.005 r M DTPA+1 r M NH 4 HCO 3 ; 0.01 r M Na 2 EDTA+1 r M (NH 4 ) 2 CO 3 ; 0.01 r N Na 2 EDTA+1 r N NH 4 Oac; 0.01 r N Na 2 EDTA; 1 r N NH 4 Oac; 2 r N MgCl 2 ; 0.05 r N HCl+0.025 r N H 2 SO 4 ; 0.01 r M Hidrocinon. The method for extraction with 0.005 r M DTPA+0.01 r M CaCl 2 +0.01 r M TEA solution which not only owns the highest correlation coefficient but also enables determination of Fe, Mn and Cu concentrations in addition to Zn amount, could be recommended as the most suitable one for the investigated soils.     

浙江北部岛礁周围海域鱼类优势种及其种间关系的初步研究

本文用定量张网渔获物组成资料，研究了浙江北部岛礁周围海域鱼类的群聚生态学。着重分析了优势种的区域及逐月和年间变化，以及优势种时空分布上的关系，还对鱼类群聚的食物关系进行了探讨。