Hope this e-mail finds you well.
My name is XXX and I'm a researcher from XX/XX.（先进行自我介绍）
Recently our group are performing a systematic review and meta-analysis testing the hypothesis that XXXX.（表明你在做什么） Your paper entitled "XXXX. (杂志,年代,期卷,页码,PMID)" is of significant importance in this topic. Of course, your excellent work will be included into the meta-analysis. However, some important information and data have not been reported in the apaper.（表示对方的文章的重要性，切记文章一定要注明清楚，有些文章很多的大牛不一定记得清是那篇！）
We would appreciate it if you could provide us the following data: （需要的数据，要列清楚）
By the way, on behalf of our group we will add your contribution in the acknowledgement part of the article (on behalf of ourgroup we kindly invite you to participate in this project; your assignments will be to provide the data of your study, review and revisingof the paper and, in the final, joining us as a co-author of the paper 到底是在致谢部分进行感谢，还是邀请作为共同作者，小编认为主要取决于原始研究的数据量大小！) We believe that this paper will result in a good publication.
Your help is of great importance, and the results of the meta-analysis may be useful for future studies.（再次强调对方文章数据的重要性）
We are looking forward to hearing from you.