对高校图书馆功能的思考     

金颖华  刘艳波  朴恩姬 《农业网络信息》2012,(6):50-52

高校图书馆是文献信息中心是高校的重要组成部分。高校图书馆保存和传播着人类的文化成果,促进科学发展中起着重要的作用。从图书馆最基本的功能出发,结合研究性教学改革,分析当代高校图书馆该如何有效地提高本身功能,提出了一些新的思路,为提高高校图书馆功能提供新的理论依据。  相似文献   

一类半定规划问题的最优性条件     

吕雄  李月鲜  吴国荣 《内蒙古农业大学学报(自然科学版)》2012,33(2):211-216

先引入向量值函数的广义凸性,研究了向量值不变凸函数与不变预凸函数的关系.接着证明了当一类函数是局部Lipschitz的不变凸函数时的广义Fakars引理.最后利用广义Fakars定理,研究了一类半定规划问题的最优性条件.  相似文献   

酸枣活性成分分析及药理作用研究进展     

田秀红  黎梅 《安徽农业科学》2012,40(23):11555-11557,11690

对酸枣中的主要活性成分黄酮类、皂苷类、生物碱类物质、脂肪酸、氨基酸及矿物质等进行分析,并对其主要药理作用的研究进展进行综述,为酸枣仁的进一步开发利用提供依据。  相似文献   

农产品质量安全监管系统的功能和复杂性及其化解路径   总被引：5，自引：2，他引：3  

张蓓  文晓巍 《农业现代化研究》2012,33(1):59-63

农产品质量安全监管是一项复杂的系统工程。系统科学的基本原理与系统复杂性理论,为农产品质量安全监管系统工程建设提供了理论依据。农产品质量安全监管系统包括物理、事理和人理三类,实现农业经济发展和社会和谐稳定功能,呈现出系统要素、系统关系、系统规模、系统特征和系统演进的复杂性。从法制框架、追溯信息系统、技术支撑体系、多方联动机制,从定性到定量综合集成方法和整体最优原则等维度,提出推进我国农产品质量安全监管系统工程的关键环节和策略建议。  相似文献   

农民专业合作社功能对社员农业现代化贡献性实证研究     

孙琳  高建中  赵金燕 《北方园艺》2012,(6):194-196

农民专业合作社是走中国特色农业现代化道路的重要选择。为了研究农民专业合作社的各分功能对农业现代化水平的贡献程度,现通过对陕西省55个合作社及275个社员进行一对一调研获得数据,运用多元回归方法进行实证分析。结果表明:农民专业合作社的提供信息功能和销售功能对提高农业现代化水平有显著影响,在总结分析基础上提出了相应的对策建议。  相似文献   

Distribution of biomass and carbon in even‐aged stands of Norway spruce (Picea abies (L.) Karst.): A case study on spacing and thinning effects in northern Denmark     

《Scandinavian Journal of Forest Research》2012,27(6):470-488

The main objective of this case study was to explore the possible influence of forest management on the levels and distribution of biomass and carbon (C) in even-aged stands of Norway spruce [Picea abies (L.) Karst.] in Denmark. Data originated from a long-term thinning experiment and an adjacent spacing experiment at stand ages of 58 and 41 years, respectively. Biomass of 16 trees from different thinning and spacing treatments was measured or partly estimated, and soils were sampled for determination of C stocks. All trees in each plot were measured for stem diameter and some for total height, to allow for scaling-up results to stand-level estimates. For trees of similar size, foliage biomass tended to be higher in the spacing experiment, which was located on slightly more fertile land. Foliage biomass increased with increasing thinning grade, but the effect could not be separated from that of tree size. At stand level, foliage biomass tended to increase with increasing spacing as well as with increasing thinning grade. For branchwood, stems and roots (including below-ground stump), the biomass increased with increasing tree size and stand volume at tree and stand level, respectively, but no differences between stands, spacings or thinning grades were observed, apart from that expressed by tree size or stand volume. At stand level, C stocks of all biomass compartments decreased with increasing thinning grade, while the distribution between compartments was hardly influenced. The ratio between above-ground and stem biomass was about 1.21 at stand level, while the ratio between below- and above-ground biomass was about 0.17. Thinning influenced the C stock of the forest floor and mineral soil oppositely, resulting in no effect of thinning on total soil C.  相似文献   

A fine-scale model for area-based predictions of tree-size-related attributes derived from LiDAR canopy heights     

《Scandinavian Journal of Forest Research》2012,27(3):312-322

Abstract

We propose a conceptual (generic) allometric (power function) relationship between tree-size-related forest inventory attributes (e.g. biomass, volume, basal area, quadratic mean diameter, Lorey's height) and canopy height (CH) as estimated from first-return airborne light detection and ranging (LiDAR) pulses. A data-driven estimation of the parameters in the power function is complicated, so we recommend an alternative approximation obtained via a linearisation step. Only two predictors appear in the approximation: the mean CH and the variance of CHs within the spatial domain supported by field data. The proposed model eliminates an otherwise complex search for the best predictors amongst a large number of candidate LiDAR metrics. It also facilitates model comparisons and interpretation. Fit statistics estimated for volume, basal area, quadratic mean diameter and Lorey's height – using three separate datasets from Norway – were compelling.  相似文献   

Particle arrangement and internal porosity of coarse fragments affect water retention in stony soils     

Caroline Andrade Pereira  Rodrigo Pivoto Mulazzani  Quirijn de Jong Van Lier  Fabrício de Araújo Pedron  Paulo Ivonir Gubiani 《European Journal of Soil Science》2023,74(3):e13382

Information about water retention in stony soils lags behind due to methodological difficulties. We applied a new strategy to measure the water retention in soils with coarse fragments (CFs) and to get insights into the effect of CFs porosity on water retention. Water retention at zero, 10, and 150 m suction, bulk density, and the mass fraction of six particle size classes were measured in undisturbed blocks from soils with variable CFs contents, originating from three parent materials. The results showed that some soils contain porous CFs (2–250 mm) with a water holding capacity as high as the fine fraction (<2 mm). The water held in the suction range of 1–150 m in a soil with porous CFs was twice as high as in soils with non-porous CFs. Multilinear regressions revealed that both the water retention capacity at 1 m suction and in the range 1–150 m were more dependent on bulk density than on the fraction of CFs and fine particles. In the soil with porous CFs, there was no correlation between their fraction and soil water retention. These results show that the bulk water retention capacity of soils with CFs is underestimated when not considering the internal porosity of the CFs. A better understanding of the effect of the porosity of CFs on bulk soil porosity and water retention is important to propose suitable pedotransfer functions and refine physically-based hydraulic functions for stony soils.  相似文献   

Solving Method for Soil Spring Stiffness of Shallow Shield Tunneling     

Dong Zhengfang  Wang Junjie  Zhao Dongxiao  Wang Wenbiao 《保鲜与加工》2013,(6):28-32

Based on complex variable theory in plane elasticity, the equivalent spring stiffness is derived from the analytical solution by means of simplifying shallow shield tunneling to semi-infinite plane with hole, which is applied to response displacement method. The performances of the analytical solution are evaluated and compared with that of the deep shield tunneling through a series of selected various tunnel depths and soil Poisson's ratios. The relation of compression and shear spring stiffness is discussed. Meanwhile, two factors affected soil spring stiffness, tunnel depth and soil Poisson's ratio, are also analyzed. It is shown that soil spring stiffness of shallow shield tunneling is different from that of deep shield tunneling, and the ratio of compression and shear spring stiffness varies along shallow shield tunneling. It is also found that the value and distribution law of soil spring stiffness of shallow shield tunneling greatly depend on tunnel depth and soil Poisson's ratio.  相似文献   

论农业经济的特点及作用     

马晶晶  姜双双 《绿色科技》2013,(8):287-290

指出了农业是人类的衣食之源,生存之本,是国民经济其他部门独立和进一步发展的基础。农业问题是当前中国最大的经济问题,因为农业问题解决得好与不好,不仅关系到国民经济的发展,而且关系到我们在2020年能否实现全面建设小康社会的宏伟目标,能否推进社会主义现代化的建设。结合我国的实际情况分析我国农业的特点,利用简单的Excel工具,通过数据剖析我国农业的作用,最后得出结论:在推进工业化进程中,农业对国民经济的贡献虽然有所下降,但是它是发展工业化,走现代化道路的基石,它的基础性地位不可动摇。  相似文献