解决的问题等。接着对文献进行回顾。然后介绍自己的研究动机、目的和主要内容。至于研究方法、研究结果及论文的组成部分则可以完全省略，如图8．2所示。
第一层: Introducing the importance of the research area and reviewing previous Research………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………第二层: Indicating the problem that has not been solved by previous research, raising a relevant question ………………………………………… ..................................................………………..............................................................................................................................第三层: Specifying the purpose of your research……………………….............................................
图8.2 引言的结构布局模式之二
例2
Forest Decline and Tree Mortality in a Southeastern Ohio Oak(橡树) -Hickory( 山核桃树) ForestGRETCHEN M. WALTERS AND BRIAN C. MCCARTRY INTRODUCTION[1] Forest decline results from a reduction in growth and vigor and may be accompanied by widespread mortality of trees over a relatively large geographic area. There has been a considerable increase in the reporting of forest decline throughout the hardwood forest of eastern North America and thus possible cause for concern. The source of decline is often much more difficult to pinpoint and is frequently the result of multiple stresses including ozone, atmospheric pollution, climatic extremes, and pests. 分析：第一层(第1—3段)：提出森林资源减少和树木死亡这一值得关注的问题，以及有关这一问题的研究状况。第1段：共三句话，提出问题并简单介绍造成这一问题的几种因素。
[2] The condition of eastern hardwood species and ecosystems of the United States has been summarized by Weiss and Rizzo (1987) and Millers et al. (1989). One of the more prominent examples of large scale species decline in northeastern North America is the sugar maple (糖槭树). Observed patterns of decline stimulated the creation of the North American Sugar Maple Decline Project, a joint endeavor between the United States and Canada, to monitor the changing conditions in sugar maples (Hertel and MeKinney- Mcomeal 1991 ). Concurrently, the Forest Response Program was created to examine the effects of and ozone on forest health and productivity. Since then, numerous studies have been completed and many regions are establishing long-term forest health surveys to better monitor changes occurring in the eastern forest (Loncks 1992). [3]Througout the eastern United States, large scale compositional changes have been observed in forests dominated by oak and hickory (Christensen 1977, Lorimer 1984, McCarthy et al. 1987, Pallardy et al. 1988). Many of these changes are believed to be successional in nature and appear to be linked to regeneration problems (Lorimer 1993). Failure of the oaks to regenerate has been tied to a variety of factors including competition (e. g., shade intolerance), altered disturbance regimes (e.g., fire), wildlife populations (e.g., insects, deer), and a variety of influences over the past century ( Lorimer 1993). Certainly, increased stress or decline in the oaks would adversely affect tree reproduction (Marion 1991). 第2段：回顾并评述该领域的研究与发展过程。以糖槭树作为例子，说明树种的减少所引起的关注以及对该问题的研究项目等。第3段：关于美国东部地区森林结构的观察研究状况。以橡树和山核桃树为主的森林在结构上发生了变化。原因是多种多样的。橡树与山核桃树的减少会对树木的再生长造成不良影响。
[4] In Ohio, there have been few specific reports in the literature of oak and hickory decline (Millers et al. 1989). Regionally, oak mortality has been linked to a variety of causes including drought, insects, and diseases. Hickory mortality has usually been associated with insect outbreaks (e.g., hickory bark beetle and gypsy moth) (Millers et al. 1989). Hanson et al. (1976) noted oak mortality and decline associated with drought and insects throughout a multi-s

上一页  [1] [2] [3] [4] [5] [6] [7] [8]  下一页