语篇衔接理论与大学生英语作文写作的连贯性

连贯是语篇的重要特征。要使语篇具备连贯性,就必须依赖一定的语义衔接手段。我国大学生在英语写作中普遍存在着语篇连贯性差的问题。基于教学经验,本文仅从语篇衔接理论中的"照应"替代"省略"连接"等手段来论述作文的连贯性。     

沙地濒危植物长柄扁桃生物学特性与抗逆性及应用综述

揭示长柄扁桃生物学特性与抗逆性机理并提高其在荒漠化治理中的生态效益和经济效益,是实现西北旱区荒漠化治理可持续发展和提升生态脆弱区生态系统服务功能面临的重要科学问题。本文回顾了长柄扁桃研究所取得的进展,包括建立了长柄扁桃快速育苗和无灌溉水栽培技术,揭示了不同地区长柄扁桃生长规律及其对逆境的适应性,推进了长柄扁桃在荒漠化治理中的应用及其产品开发等;在此基础上,提出了长柄扁桃研究面临的机遇和挑战,包括长柄扁桃的适生土壤类型与耗水量,不同地区长柄扁桃的合理种植密度及其调控和管理措施,长柄扁桃抗逆性机理及其产品开发与高值综合利用等,以期为我国在西北地区推广和建设长柄扁桃林、优化水土资源管理和提高脆弱生态系统的服务功能提供科学依据。     

城市道路绿化带景观的可识别性设计研究

道路绿化带作为城市道路最主要的景观要素,是体现城市道路“可识别性”的重要因素。但在许多实际设计项目中,这一点却往往被忽视,致使许多道路景观呈现出“千人一面”的视觉感受。文章在分析可认别性对于道路绿化带的重要性的基础上,从3个方面,即以道路节点设置独特标志物来增强道路的辨识度、以绿化形式的一致性来加强道路的连续感、并以绿化带映射整个区域的特色来提升场所的归属感和领域感,并以实例论述道路绿化带景观的可识别性营造策略。     

GF-4/PMS与GF-1/WFV两种传感器地表反射率及NDVI一致性分析

2015年12月中国成功发射高分系列中首颗地球静止轨道卫星高分四号(GF-4),实现与高分一号(GF-1)近极地轨道卫星的优势互补,构成了具有多种空间和时间分辨率的对地观测体系。该文研究并分析了GF-4/PMS与GF-1/WFV地表反射率与NDVI的一致性,结果表明:一致性研究的最优空间尺度为50 m;GF-4/PMS与GF-1/WFV地表反射率存在较好的线性关系,各波段相关系数R均在0.7以上,传感器之间反射率的系统性偏差可以通过线性回归模型校正,校正后各波段反射率的RMSE明显降低;NDVI能够消除不同波段地表反射率"同增同减"偏差的影响,在GF-4地表反射率校正前后均表现出与GF-1较好的一致性,校正前后相关系数R分别为0.74和0.77。因此,GF-4在农业和植被遥感中具有较好的高分系列数据延续性和应用潜力。     

浅谈极限与连续概念的非标准陈述

极限和连续是数学分析当中十分重要的两个概念,学生在初学时难以理解和正确把握,教师授课时也明显感觉到不易。借助于极限和函数连续两个概念的非标准陈述,对人们熟知的几个命题和定理给予全面阐述,使学生换一种思路和方法来深入理解这两个概念。     

热媒炉改烧渣油的稳定性与连续性分析

通过分析铁大输油管道使用的热媒炉由烧原油改为渣油后所引起的不稳定连续燃烧的诸因素,提出了相应的解决方法和建议,经实践检验效果显著,可供热煤炉使用单位借鉴。     

C〔a,b〕中集合列紧充要条件推广

本文把C〔a,b〕中集合的列紧性判别法则,在添加了1个条件后,推广到C〔-∞,+∞〕的集合中去。     

换元、分部积分法的归纳

本文对求函数不定积分的两种基本积分法———换元法和分部积分法进行了归纳和总结。     

Transverse Effect of Bottom Continuity Tendons in Continuous PC Box Girder

Bottom continuity tendons induce transverse additive effect while providing longitudinal compression during the construction of PC box girder. Taking a cross-sea bridge for example, the mechanism of bottom continuity tendon is investigated. The transverse effect and parameters study are conducted through a refined model. It is illustrated that the state of bottom flange is in a dynamic changeable process during the tensioning of bottom continuity tendons, and the transverse effect caused by the tendons is much more than that by dead loading and other prestressing tendons. The transverse effect is more sensitive to alignment and thickness of the bottom flange, as well as concrete cover of the ducts. Finally, based on the simplified frame analysis, the design method is proposed by introducing prestressing effect simplified factor and duct modified factor.     

Effects of tillage and liming on macropore networks derived from X‐ray tomography images of a silty clay soil

Soil structure influences water infiltration, aeration and root growth and, thereby, also the conditions for sustainable crop production. Our objective was to quantify the effects of different soil management methods and land uses on the topsoil structure of a silty clay soil. We sampled 32 intact soil columns (18 cm high, 12.7 cm diameter) from an experimental silty clay field with four treatments: conventional tillage (CT ), conventional tillage followed by liming (CTL ), reduced tillage (RT ) and unfertilized fallow (UF ). The columns were analysed using 3‐D X‐ray tomography. The samples were taken in autumn after harvest, 7 yr after quick lime was applied to the CTL plots. Despite a relatively large number of replicates per treatment (8, 8, 8 and 6 (two UF samples were excluded), respectively), there were no significant differences between any of the investigated macropore network properties related to tilled treatments. The UF treatment, in contrast, exhibited more vertically oriented macropores, which were also better connected compared to the other treatments. This confirms previous findings that tillage may disrupt the vertical continuity of macropore clusters. The impact of liming on soil pore network properties may have been limited to pores smaller than the resolution in our X‐ray images. It is also possible that the effects of lime on soil structure were limited to a few years which means that any effect would have diminished by the time of this study. These matters should be further investigated in follow‐up studies to understand better the potential of lime amendments to clay soil.