对农村老年人口养老的主要问题分析     

李恒锐 《湖南农机》2007,(11):142

目前农村老年人养老现状不容乐观.家庭养老功能弱化,社区养老机制滞后,社会福利、政府救济和低保投入严重不足等,导致绝大多数农村老年人处在家庭边缘和社会保障体系之外.  相似文献   

中国沙棘的性状变异与演化趋势   总被引：5，自引：2，他引：5  

黄铨 《国际沙棘研究与开发》2003,1(2):6-12

在中国沙棘天然分布区的主轴线上,自西南向东北,选择5个有代表性的地段,用样地调查和统计分析方法.研究了中国沙棘主要性状变异及性状间的组配情况;比较了不同地段的异同;统计了各主要经济性状的变异参数;探索了几个主要性状的演化趋势。认为中国沙棘乃是多态型的种群系统,即存在很大幅度的随机变异,也存在着地理种群间的差异。种群变异的主要特征是各主要性状出现频率随生态——地理条件而递变,但群内变异幅度小,而群间差异显著。  相似文献   

An Evidential Analysis on the Rural Urbanization Development in Chongqing     

WU Pei-lin~ 《保鲜与加工》2004,(6):6-12

The rural urbanization process in Chongqing is much slower than that in other metropolitans and most of the provinces in eastern China, which can't adapt to its important function as the economic and cultural center in southwestern China.It is urgent for Chongqing to accelerate the rural urbanization for improving its whole urbanization level and speeding up its economy development to catch up with other metropolitans and some advanced provinces.Compared with the urbanization in other metropolitans and some provinces, the authors demonstrated the rural urbanization situation and its characteristics in Chongqing in details, analyzed the reasons for the poor urbanization and its influences on the social-economic development especially that in the rural area.Inferior position of Chongqing's small towns in the market competition with those from other provinces is one of the results of its poor urbanization development.At last, the authors suggested a few practical countermeasures to improve the rural urbanization in order to get a rapid and sustainable rural development and to increase the whole economic effects of the metropolitan.  相似文献   

THE INDUSTRIAL ORGANIZATIONS AND THE L-S-BUSINESS STRATEGIES     

He Zonglu 《保鲜与加工》1992,(4):111-117

This papar presents an evolution model in business behaviors-the L-S Business Strategies,gives some examples and predictions which support these strategies,and analyzes the relationship between the industrial organizations in China and the L-S Business strategies.  相似文献   

水科学中应用数理统计方法应注意   总被引：1，自引：0，他引：1  

张子贤 《中国农村水利水电》2005,(12):13-15

对回归方程误差的影响因素进行了分析，导出了回归方程的均方误差与其影响因素之间的关系式。分析表明，复相关系数(或相关系数)一定时，倚变量的变差系数越大，回归方程的均方误差就越大；回归分析时，应对回归方程的误差进行分析。对于样本均值估计总体均值，给出了基于误差限制的样本容量的计算式。研究表明，应考虑样本变差系数对估计精度的影响。  相似文献   

保种群体遗传结构变化的模拟研究     

芒来 《内蒙古农业大学学报(自然科学版)》1991,(2)

本文运用电子计算机模拟的方法,分析了影响畜禽保种的主要因素,并通过不同参数组合(包括起始基因频率、群体有效含量和世代数等)的模拟试验得出三个主要结论: 1 在有性繁殖的有限群体中,原封不动地保存群体基因库中的每个基因(包括频率很低的基因)是根本不可能的。 2 在完全实行随机交配的情况下,长期保存频率较高的基因也需要相当大的群体才有可能。 3 频率较高基因的保存也不能单纯依靠群体大小,还需借助于选择。只有这样才能在小群体内长期保存频率较高的基因。  相似文献   

甘肃省人口预测与可持续发展研究   总被引：1，自引：1，他引：0  

石培基  祝璇 《干旱区资源与环境》2007,21(9):1-5

人口问题是一个国家或地区可持续发展的前提。人口规模是否合理,对一个国家或地区未来的经济、社会和生态环境可持续发展影响深远。本文运用马尔萨斯人口模型和Logistic增长模型,利用《甘肃年鉴》统计数据对甘肃省2005~2020年的人口发展规模做出预测,取马尔萨斯人口模型和Logistic增长模型的预测结果的平均值作为预测结果,并在预测的基础上对人口与水、耕地、矿产和能源的可持续发展进行了分析,提出了可持续发展的人口对策,为甘肃省科学地制定国民经济和社会发展战略、实现人口与资源环境的可持续发展提供参考。  相似文献   

人口发展与城市化水平预测——以乌兰察布市为例     

金良  宝音  李百岁 《干旱区资源与环境》2007,21(3):23-27

科学预测人口城市化水平,对相关政策的制定、制度的改革、城市配套设施的建设以及解决就业问题都具有重要意义。本文以乌兰察布市为例,对地区总人口进行预测的基础之上,运用劳动力结构模型、劳动力地域转移模型等多种数学模型,预测了城镇人口城市化水平和非农业人口的城市化水平。最后,选取与城市化相关的七项指标,对城市化水平进行了综合预测。  相似文献   

Resistance and resilience of soil biological indicators: A case study with multi-walled carbon nanotube     

Shagufta YASMEEN  Nintu MANDAL  Anupam DAS  Pritam GANGULY  Sanjay KUMAR  Rajiv RAKSHIT 《土壤圈》2024,34(3):664-675

Soil ecosystem is experiencing stresses due to climate change, and soil inhabitants try to demonstrate their inherent resistance and resilience against those stresses. Application of nanomaterials as agricultural inputs could bring shifts in resistance and resilience patterns of soil microbes and associated enzymes, especially under short-term heat stress. With this background, the impacts of multi-walled carbon nanotube (MWCNT) on the resistance and resilience of soil biological indicators were evaluated. An incubation experiment was conducted with varied MWCNT concentrations (0, 50, 100, 250, and 500 mg kg^-1 soil) for 90 d after 24-h heat stress at 48 ±2 ℃ to assess the impacts of MWCNT on soil enzyme activities and microbial populations vis-à-vis their resistance and resilience indices under short-term exposure to heat stress. Enzyme activities were reduced after exposure to heat stress. Resistance indices of enzyme activities were enhanced by MWCNT application on day 1 after heat stress, whereas there was no recovery of enzyme activities after 90-d incubation. Like soil enzyme activities, resistance index values of soil microbial populations followed the similar trend and were improved by MWCNT application. Multi-walled carbon nanotube has the potential to improve resistance indices of soil enzyme activities and microbial populations under heat stress, although they could not recover to their original state during periodical incubation after heat stress. This study helps to understand the relative changes of biological indicators under MWCNT and their ability to withstand heat stress.  相似文献   

中国粮食生产发展特征及土地资源承载力空间格局现状   总被引：17，自引：4，他引：17  

刘东  封志明  杨艳昭  游珍 《农业工程学报》2011,27(7):1-6

首先分析了1949－2008年中国粮食生产发展过程特点,随后以粮食为判据,基于人口与粮食关系,建立土地资源承载力模型和土地资源承载指数模型,从分县尺度对中国土地资源承载力空间格局现状进行了分析。结果表明： 1949－2008年中国粮食生产呈台阶式上升特征,且伴随周期性波动,具有明显的不稳定性;人口增幅小于粮食产量增幅,人均粮食占有量从建国初期的不足209 kg,增长至21世纪初期的400 kg,呈稳步提升态势;2007年我国分县土地资源承载力主要以人口超载、粮食短缺为主要特征。东北平原、华北平原、长江中下游、河西走廊、河套地区及四川盆地等主要粮食生产区表现为粮食盈余,而人口压力较大的东南沿海以及粮食生产水平较低的西北干旱半干旱地区则表现为人口超载。国家尺度上,中国粮食尚处于盈余状态,因此粮食短缺地区需通过贸易、调配来满足超载人口的粮食需求。东、中部城市密集地区人粮关系尤为紧张,随着城市化进程不断加快,这些地区人粮矛盾会进一步加剧,粮食贸易和调配趋势也会越来越明显。该研究可为国家粮食安全与区域可持续发展提供科学依据和决策支持。  相似文献