ISI 只统计 SCI 文章，非 SCI 和其他语言的文章可能搜不到，因此引用次数比 Google Scholar 要少。
Google Scholar 虽然搜到引用文章比较多，但是有些涉及到非英语语种，可能需要翻译、比较麻烦些。
我们最后在参考两个搜索情况后，再对比了一下文章具体的引用情况，最后主要采用 Google Scholar 统计结果（如下图），同时用到了一些 ISI 统计数据。
我在最后提交的 Petition Letter 正文中并没有使用以上图表，只是简单阐述了一下杂志影响因子和所在领域的排名，把统计图表在 Exhibits 里边。当然，Petition Letter 使用图表有独特的优势，可以想象移民官天天看材料比较枯燥劳累，如果文中有漂亮的图表、再配以流畅和言简意赅措辞，会使得申请人的闪光点变得更加有说服力。「油灯图」是大家常用的引用文章统计图，可选择 ISI Web of Knowledge，Google Maps 和 Batchgeo 来做。
Subject: Volunteer to peer review manuscripts for xx Journal
Dear Dr. xxx (Editors),
My name is xxx, a (job title) at xx University in Dr. xxx’s group. I am writing to ask for an opportunity to serve as a reviewer for xxx Journal.
My main interests are in xx, xx, and xx. I got my xx degree at xx under the supervision of Dr. xx. During that time, I mainly focused on xx. After that I did my post-doctoral training in xx University. My current projects focus on xx.
I find manuscript reviewing very helpful to my career, in terms of both improving professional expertise and taking responsibilities in scientific communities. I have published xx articles in peer-reviewed journals from xx to xx (see attached CV), and reviewed xx manuscripts from xx to xx for xx Journal. I also reviewed some manuscripts on behalf of Dr. xx.
Enclosed please find my CV that details my educational and professional background. Please feel free to let me know if you have any questions or need more information.