google custom search , and book search

Question

Hi, I am developing a plagiarism system, I am using Google Custom Search , but I found that the results returned are not sufficient  , I need to search in google scholars and google books

My Question is :

Is google custom search is the best way ? i found many sites using google to test plagiarism but there results are better than mine

also , how can i search in google books and sholars

thanks