| Acknowledgements | 第1-7页 |
| 摘要 | 第7-8页 |
| Abstract | 第8-10页 |
| List of Tables and Figures | 第10-12页 |
| List of Abbreviations | 第12-13页 |
| Chapter 1 Introduction | 第13-18页 |
| ·Research Background | 第13-14页 |
| ·Notions of Lexical Richness | 第14-15页 |
| ·Lexical Richness | 第14-15页 |
| ·Lexical Variation | 第15页 |
| ·Lexical Sophistication | 第15页 |
| ·Lexical Density | 第15页 |
| ·Research Purposes | 第15-16页 |
| ·Significance of the Present Research | 第16页 |
| ·Feasibility of the Present Research | 第16-17页 |
| ·Organization of the Paper | 第17-18页 |
| Chapter 2 Literature Review | 第18-32页 |
| ·Empirical Studies on Lexical Richness | 第18-26页 |
| ·Studies on Lexical Variation | 第18-22页 |
| ·Studies on Lexical Sophistication | 第22-25页 |
| ·Studies on Lexical Density | 第25-26页 |
| ·Summary of Former Studies | 第26页 |
| ·Lexical Richness Measures | 第26-30页 |
| ·Lexical Variation Measure | 第26-28页 |
| ·Lexical Sophistication Measure | 第28-29页 |
| ·Lexical Density Measure | 第29-30页 |
| ·Holistic Ratings | 第30页 |
| ·Summary | 第30-32页 |
| Chapter 3 Theoretical Framework | 第32-39页 |
| ·Basic Notions | 第32-33页 |
| ·Tokens | 第32页 |
| ·Types | 第32页 |
| ·Lexemes | 第32页 |
| ·Word Families | 第32-33页 |
| ·Relevant Theories | 第33-35页 |
| ·Laufer's Framework | 第33-34页 |
| ·Engber's Framework | 第34-35页 |
| ·Read's Framework | 第35页 |
| ·Theoretical Framework of the Present Study | 第35-38页 |
| ·Summary | 第38-39页 |
| Chapter 4 Research Design | 第39-45页 |
| ·Research Questions | 第39页 |
| ·Subjects | 第39-40页 |
| ·Instruments | 第40-41页 |
| ·Data Collection | 第41-42页 |
| ·Data Analysis | 第42-45页 |
| ·Lexical Variation | 第42页 |
| ·Lexical Sophistication | 第42-43页 |
| ·Lexical Density | 第43页 |
| ·Essay Scoring | 第43-45页 |
| Chapter 5 Results and Discussions | 第45-66页 |
| ·Results in the Three Dimensions of Lexical Richness | 第45-54页 |
| ·Results of Lexical Variation | 第45-47页 |
| ·Results of Lexical Sophistication | 第47-52页 |
| ·Results of Lexical Density | 第52-54页 |
| ·Summary | 第54页 |
| ·Results of the Writing Quality | 第54-56页 |
| ·Correlations | 第56-58页 |
| ·Correlation between Lexical Variation and Lexical Sophistication | 第56-57页 |
| ·Correlation between Lexical Sophistication and Lexical Density | 第57-58页 |
| ·Correlation between Lexical Variation and Lexical Density | 第58页 |
| ·Summary | 第58页 |
| ·Correlations between Lexical Richness and Writing Quality | 第58-61页 |
| ·Correlation between Lexical Variation and Writing Quality | 第59页 |
| ·Correlation between Lexical Sophistication and Writing Quality | 第59-60页 |
| ·Correlation between Lexical Density and Writing Quality | 第60-61页 |
| ·Summary | 第61页 |
| ·Discussions | 第61-64页 |
| ·Discussion of the Results of Lexical Variation,Lexical Sophistication and Lexical Density | 第61-62页 |
| ·Discussion of the Results of Interrelations among Lexical Variation,Lexica #1 Sophistication and Lexical Density | 第62-64页 |
| ·Discussion of the Correlation between Lexical Richness and Writing Quality | 第64页 |
| ·Summary | 第64-66页 |
| Chapter 6 Conclusion | 第66-70页 |
| ·Major Findings of Present Study | 第66页 |
| ·Pedagogical Implications | 第66-68页 |
| ·Limitations of Present Study | 第68-69页 |
| ·Suggestions for Further Study | 第69-70页 |
| References | 第70-75页 |
| Appendix Ⅰ Writing Task | 第75-76页 |
| Appendix Ⅱ Sample Essays | 第76-79页 |
| Appendix Ⅲ 专业四级评分标准 | 第79页 |
