1_http://education.iseek.com/iseek/home.page
2_ http://www.refseek.com/
3_http://m.wolframalpha.com/
4_http://academic.research.microsoft.com/
5_ https://www.highbeam.com/
6_http://www.siris.si.edu/
7_ http://www.worldcat.org/
8_ http://archiveshub.ac.uk/index.html
9_ http://www.archiefnet.nl/index.asp?taal=en
10 _http://worldwidescience.org/indextext
11_http://www.sciseek.com/
12_ https://openlibrary.org/
13_ http://www.ojose.com/
14 _ http://link.springer.com/
15 _ https://scholar.google.com.eg/
