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/