共查询到14条相似文献,搜索用时 12 毫秒
1.
为研究土壤分形维数是否会影响草原植物生长,本文多角度地剖析了草原土壤分形维数与植物生物量的相关性。2012年在锡林浩特地区采集了88个土样,分别计算分形维数值,采用线性回归、相关性分析等统计方法,分析土壤分形维数与土壤各粒级颗粒含量、植物生物量之间的关系。结果表明:①土壤分形维数与粗砂粒含量存在显著负相关,与细砂粒含量不相关,与粉粒、黏粒含量呈显著正相关,说明土壤分形维数对于各粒级含量的反映程度不同,主要反映黏粒含量;②根据植物的形态特征和适应方式,将草原植物划分为不同类型的功能群,生活型功能群中多年生丛生禾草、小半灌木、一、二年生植物的生物量与土壤分形维数呈正相关(R值分别为0.345,0.674,0.238,P<0.05),说明土壤分形维数可以表征这三类功能群植物的生物量累积情况;生态类型功能群中,旱生植物、旱中生植物与分形维数并无直接相关性,而旱生植物生物量与黏粒含量呈正相关,旱中生植物生物量与粉粒含量呈显著正相关,鉴于颗粒含量与分形维数间的关系,即其生长与土壤分形维数呈正相关,多年生根茎禾草、多年生杂类草、中旱生植物、中生植物的生物量与土壤分形维数并无明显相关性。 相似文献
2.
3.
4.
农业科技资源配置公平性对提高农业科技资源配置能力至关重要。文章利用Dagum分解的基尼系数分析中国农业科技资源配置能力的区域差异,并对其驱动因子进行分解。研究发现,中国农业科技资源配置能力差异明显,仅14个省市区农业科技资源配置能力不断提升;东北与西北2区农业科技资源配置能力总体呈下降趋势,华北、华东、中南、及西南4区则呈上升趋势。中国农业科技资源配置能力总体差距呈波动上升的趋势,且具有"波动上升"、"波动下降"及"稳定上升"的阶段特征。区域内(间)农业科技资源配置能力差异明显,且中国农业科技资源配置能力的差距主要来自于区域间的差异。 相似文献
5.
6.
由江苏科技资源配置现状与问题入手,通过文献阅读遴选科技资源市场化配置影响因素,基于测量模型验证性分析,构建区域科技资源市场化配置结构方程模型,得出系统和环境因素确对科技资源配置能力具有正向影响的结论。基此,运用广义设计思想,联系实际提出协同治理策略建议。 相似文献
7.
随着全球生态危机加剧,森林的生态环境功能日益突出,全球森林数量持续减少、质量不断下降,使涉嫌消耗大量木材的经济发展、林产品贸易备受争议。本文以木材消耗作为森林资源的压力指标,分析了影响木材消耗的关键因素,以世界具有代表性的61个国家2010年的相关截面数据,运用多元线性回归模型,进行了实证分析,结果表明:经济发展对木材消耗的影响为正,人均木材消耗指标与经济发展指标呈现一种向右上方倾斜的N形关系;林产品出口贸易与木材消耗的关系为负向,有利于减少人均木材消耗;林产品进口贸易与木材消耗的关系为正向,但相较于使用本国木材来说更有利于减少人均木材消耗;木材产量与木材消耗同方向变化,是影响人均木材消耗的最为显著的因素;林产品贸易规模、森林资源的丰富程度以及技术进步因素的影响不显著。据此,本文从世界和中国林业发展的角度提出了林产品贸易自由化、保持木材供应适度偏紧等相关建议。 相似文献
8.
土地市场运行对经济增长的影响:作用机理与实证评价 总被引:1,自引:1,他引:1
本文基于一个城市土地市场运行对经济增长影响的理论框架,系统探讨和实证评价了中国土地市场运行对经济增长的作用机理和影响程度。研究结果指出,土地市场运行对经济增长的影响主要是通过经济要素投入与配置的改变展现出来的,包括土地一级市场运行对经济要素投入的规模扩张效应,土地二级市场运行对经济要素配置的结构优化效应,以及土地市场化程度发展对经济要素利用的经济激励效应。这三大效应在目前中国土地市场的运行过程中存在着明显的结构差异,其对经济增长的贡献率分别为5.07%、0.20%和2.65%,即规模扩张效应>经济激励效应>结构优化效应。因此,为更好地促进土地市场运行的经济增长作用效应的发挥,中国政府仍需采取必要的政策措施,以进一步完善土地市场结构和规范土地市场的运行。 相似文献
9.
10.
文章概括了组织种群灭绝的现象及其原因,分别从组织种群密度与环境承载力方面分析了组织种群灭绝的机理。运用系统动力学方法,对组织种群密度与环境承载力影响组织种群灭绝的交互作用进行仿真模拟。结果发现:(1)在组织种群发展的初始阶段,种群密度的增长速度慢于环境承载力的增长速度;(2)种群密度对环境承载力的变动存在滞后效应。环境承载力减小后,种群密度需要四年的时间才开始呈现下降趋势。环境承载力等于零时,种群密度要在三年后才会等于零;(3)环境承载力略微下降能提升组织种群的资源利用效率,有利于组织种群存活。 相似文献
11.
林分各器官生物量随林龄的变化规律--以杉木、马尾松人工林为例 总被引:16,自引:0,他引:16
基于中国文献资料的89块生物量样地以及在桂中的6块不同龄级样地实测数据,对南方人工林的代表树种--杉木、马尾松林分及各器官生物量随林龄的变化规律进行了探讨.分析结果表明,杉木、马尾松林分树干、地上生物量及林分总生物量均随林龄的增加而显著增加,枝条、根系生物量在马尾松林分中也随林龄显著增加,但在杉木林中则随林龄的增加逐渐趋向稳定,2种林分叶生物量与林龄的关系不密切.林分生物量的根冠比在杉木林中随林龄增加而逐渐降低并趋于稳定;在马尾松林中二者关系不密切.林分各器官生物量的年龄结构差异表明林龄对于森林植被碳蓄积的准确估算具有重要影响. 相似文献
12.
Business groups in emerging economies frequently use international joint ventures (IJV) as a channel for knowledge acquisition and technology advancement. While IJVs provide a business group with access to new technology, how successful a group is in exploiting that new knowledge for innovative purposes depends on the groups’ ability to recombine new knowledge with its existing pool of knowledge and resources. The more resources a group spends in forming IJVs with foreign partners, the less resources the group has in developing and sustaining organizational mechanisms that facilitate integration of existing ideas and resources. Following this theoretical duality, we view the IJV–innovation relationship not as an “either–or” question, but as a question of whether and how. Specifically, viewing business groups as networks of loosely coupled firms, we examine how intra-group network structure and evolving institutional environment moderates the IJV–patenting relationship in Taiwan between 1981 and 1998. 相似文献
13.
全面停伐背景下国有林区职工主观福祉及其影响因素分析 总被引:2,自引:0,他引:2
在全面停止天然林商品性采伐背景下,准确掌握国有林区职工主观福祉水平,为政府部门精准实施全面停伐后的配套扶持政策提供科学依据。本文首次利用覆盖东北五大森工集团的1004个重点国有林区民生改革监测跟踪调查数据,基于阿玛蒂亚·森的可行能力理论框架和千年生态系统评估福祉要素,构建国有林区职工主观福祉影响因素理论模型,运用多项有序Logit模型展开实证检验。研究结果表明:① 龙江森工、内蒙古森工和长白山森工全面停伐与国有林区改革效果良好,大兴安岭林业集团和吉林森工滞后;全面停伐后国有林区基础设施建设较快,但医疗条件改善缓慢,收入与就业有待提升。② 82.77%国有林区职工生活满意度处于一般满意水平以上,但低于中国农民主观福祉和城镇居民生活满意度水平。③ 身体状况、附属医院、家庭总支出、住房满意度、物价水平满意度、行政服务满意度、社会保障满意度、收入满意度和双重就业满意度对国有林区职工主观福祉有正向影响。④尽管山上林场和山下社区职工主观福祉影响因素不同,但家庭总支出、物价水平、社会保障、双重就业与收入满意度是提升国有林区职工主观福祉的核心要素。 相似文献
14.
Nilima N. Dongre Adinath N. Suryakar Arun J. Patil Indira A. Hundekari Basavaraj B. Devarnavadagi 《Indian journal of clinical biochemistry : IJCB》2013,28(1):65-70
Lead is one of the most widely scattered toxic metals in the environment and used by mankind for over 9,000 years. Lead in the environment may be derived from natural or anthropogenic sources. In humans, lead can cause a wide range of biological effects depending upon the level and duration of exposure. The purpose of this study was to find out the effect of lead exposure on systolic and diastolic blood pressure, serum calcium, ionized calcium, phosphorus, parathyroid hormone and vitamin D and examine the overall effect of all these parameters on the bone mineral density of battery manufacture workers. For this study ninety battery manufacture workers were selected and divided in three groups depending upon duration of lead exposure. Group I—workers with duration of lead exposure 1–5 years, Group II—workers with duration of lead exposure 6–10 years and Group III—workers with duration of lead exposure more than 10 years. Each group consisted of thirty workers. Thirty age matched healthy control subjects were taken for comparison. Demographic, occupational and clinical data were collected by using questionnaire and interview. The venous blood samples were collected from the study groups and normal healthy control group. At the time of blood collection random urine samples were collected in amber coloured bottles. The biochemical parameters were estimated by using standard assay procedures. Statistical analysis of the data was done using independent student‘t’ test for parametric variables. Values were expressed as mean ± standard deviation (SD). P values of 0.05 or less were considered to be statistically significant. The blood lead levels and urinary lead levels of all workers were significantly increased (P < 0.001) in proportion to the duration of lead exposure as compared to controls. Systolic and diastolic blood pressure were significantly raised (P < 0.001) in all three study groups of battery manufacture workers as compared to controls. Serum Calcium, Ionized calcium, phosphorus were significantly decreased (P < 0.001) in all the three study groups. Serum vitamin D levels were lowered (P < 0.01) and serum PTH was increased (P < 0.01) in workers as compared to controls. The results of this study clearly indicate that the absorption of lead is more in these workers which adversely affects blood pressure, disturbs calcium and phosphorus metabolism which further impairs mineralization of bone resulting in decreased bone mineral density observed in these workers. Lead toxicity is still persistent in battery manufacture workers though they are using sophisticated techniques in these industries. There is a need to protect the workers from the health hazards of occupational lead exposure. 相似文献