[R] Any functions available for significant increment in R-square?

[Xingwang Ye]

Dear all,
Are there any functions available for calculate significant increment in 
R-square?
Following is a link for what's "significant increment in R2".
 http://www.psy.jhu.edu/~ashelton/courses/stats315/week2.pdf

Thank you.

Yours, sincerely,
Xingwang Ye