对书写工具的选择与预防近视的认识和建议

从字迹是视觉信号这个角度来说,中小学生写字时最好使用较软质的铅笔或用钢笔。如果说低头歪头写字达不到书写＂三个一＂的要求,是孩子们＂喜欢低头歪头＂,那么众多家庭从孩子小的时候就手把手地教孩子怎样握笔写字、上学后老师又是那么耐心地教学生如何正确执笔书写,反而还有如此多的学生还是很难达到书写＂三个一＂的要求呢？     

期权博弈理论在不确定性投资决策中的应用

应用期权博弈理论方法分析了存在竞争条件下的不确定性投资决策问题。建立了一个双寡头模型，用实物期权方法计算了模型中2个公司的价值，并分析了模型的均衡状态，给出了影响产品需求的随机因素位于不同区间上时。2公司的均衡状态及其最优的投资决策。分析结果表明，随着影响产品需求的随机因素值的变化2公司的最优策略是。做领导者、跟随者或者采取对二者无差别的态度；只有当随机变动值非常大时，同时投资对2公司而言才可能是最优的策略。     

从嘉莉妹妹的三次选择看女性意识的觉醒

嘉莉妹妹是一个从农村出来、未谙世事的小姑娘,她到大都市芝加哥追求美好生活.她的人生先后经历了三次选择,从三次选择的内在联系可以看出嘉莉妹妹的女性意识逐步增强,人生从依附走向独立.     

The use of compensatory and non-compensatory multi-criteria analysis for small-scale forestry

Small-scale farm forestry has the potential to offer many benefits both to landholders and the wider community. As with all changes in land-use practices, there are associated benefits and costs and these are not uniformly distributed. They have varying impacts on the different values, aspirations, goals and objectives that exist within the community. Furthermore, the community does not consider these values, aspirations, goals and objectives of equal importance. The degree of concern can vary from minor to high and overriding all other considerations. When evaluating farm forestry options it is necessary to address all of these concerns. This paper examines the combined use compensatory and non-compensatory multi-criteria analyses to evaluate forestry options, in a case study for the Darling Downs region of Queensland, Australia. These aggregation techniques are found to be highly complementary and together provide a comprehensive analysis. The compensatory technique provides a sound measure of overall performance of a forestry system, whereas the non-compensatory technique alerts decision-makers to presence of particularly poor performance with respect to individual criteria. The compensatory technique used is simple and understandable even for those with non-mathematical backgrounds. This analysis can identify and aid communication of the relative benefits and costs, and trade-offs, between economic, environmental and social considerations.     

黄土丘陵沟壑区不同退耕类型径流、侵蚀效应及其时间变化特征

在自然降水条件下,连续14年对半干旱黄土丘陵沟壑区坡耕地及其4种退耕类型径流、侵蚀进行观测实验。结果表明:坡耕地退耕显著减少地表径流和土壤侵蚀,退耕类型之间径流量和侵蚀量存在显著差异,其大小次序为:农耕坡地>牧草地>乔木林地>自然草地>灌木林地。地表径流和侵蚀具有明显的季节分布特征,减流、减沙效应主要发生于7月和8月。牧草地累积减流、减沙效应随年度增加逐步下降,乔木林地的累积减流效应逐渐下降而减沙效应则逐步增加,灌木林地累积减流、减沙效应持续提高,自然草地则为先增长后降低的过程。14年观测结果表明:累积减流、减沙效应次序为:灌木林地>自然草地>乔木林地>牧草地。牧草地和乔木林地在短期具有较好的减流、减沙效应,而灌木林地和自然草地具有较好稳定持久的水土保持功能。     

一种亚式风格可重置执行价格期权设计

本文设计了一种亚式风格的可重置执行价格期权;严格证明了可重置执行边界的存在性,以及连续区域与重置区域的单连通性;利用Hartman-Watson分布,写出了可重置期权的定价公式,并利用此公式给出了可重置执行边界的一种新的数值算法.     

Promoting and preserving biodiversity in the urban forest

Efforts at mitigating global biodiversity loss have often focused on preserving large, intact natural habitats. However, preserving biodiversity should also be an important goal in the urban environment, especially in highly urbanized areas where little natural habitat remains. Increasingly, research at the city/county scale as well as at the landscape scale reveals that urban areas can contain relatively high levels of biodiversity. Important percentages of species found in the surrounding natural habitat, including endangered species, have been found in the urban forest.

This contribution concisely highlights some examples of urban biodiversity research from various areas of the world. Key issues involved in understanding the patterns and processes that affect urban biodiversity, such as the urban–rural gradient and biotic homogenization, are addressed. The potential for urban areas to harbor considerable amounts of biodiversity needs to be recognized by city planners and urban foresters so that management practices that preserve and promote that diversity can be pursued. Management options should focus on increasing biodiversity in all aspects of the urban forest, from street trees to urban parks and woodlots.     

当前我国农村税费改革面临的主要问题及其政策选择

在分析当前我国农村税费改革存在的四大主要问题的基础上，有针对性地提出了政策建议和主张。     

中国发展现代农业的对策选择

中国加入WTO后农业产业发展面临一个全新的国际环境。论述了发展现代农业的特征、分析了制约中国发展现代农业的症结因素,并提出了创新农业知识,建立现代农业科技体系,发展农业科技企业与农业产业化,将农业科技推向广度、深度,提高农民素质,培养知识型农民,优化生态系统,倡导持续、标准化农业和重视国际农业科技交流与合作等五个方面的对策选择。