急找两篇外文文献。题目在内容里，谢谢

http://www.scribd.com/doc/62695/Population-Trends这是外文原文地址。

The individual income tax is uniquely suited for raising revenue in a democratic country where the distribution of income, and therefore of ability to pay,is unequal. Theoreticians may disagree about the meaningfulness of the term “ability to pay,” but the close association between a man’s income and taxpaying ability is commonly accepted. There is also general acceptance of the idea of progression in income taxation.

查外文文献当然最好进入专业的数据库网站，比如blackwell或者sciencedirect等，这些数据库一般好点的大学或图书馆都会有，如果没有这种数据库，那可以上google scholar，也就是google的学术搜索，在这里你可以查到相关的文献，不过可能有一部分只能看到摘要，看不到全文。这是网站：http://scholar.google.cn/schhp?hl=zh-CN，你可以输入微生物絮凝剂的英文单词进行搜索。