https://ethos.bl.uk/Home.do may be useful to you

I collected this list before, it may help you

Google Scholar (http://scholar.google.com/)

CiteSeerx (http://citeseerx.ist.psu.edu)

ScienceDirect (http://www.sciencedirect.com/)

GetCITED (http://www.getcited.org/)

Microsoft Academic Research (http://academic.research.microsoft.com/)

Bioline International (http://www.bioline.org.br/)

Directory of Open Access Journals (http://www.doaj.org/)

BioOne (http://www.bioone.org/)

PLOS ONE (http://www.plosone.org/)

Science and Technology of Advanced Materials (http://iopscience.iop.org/1468-6996/)

Other website for research

http://education.iseek.com/iseek/home.page

http://www.refseek.com

http://m.wolframalpha.com/

http://academic.research.microsoft.com/

https://www.highbeam.com/

http://www.siris.si.edu/

http://www.worldcat.org/

http://archiveshub.ac.uk/index.html

http://www.archiefnet.nl/index.asp?taal=en

http://worldwidescience.org/indextext

http://www.sciseek.com/

https://openlibrary.org/

http://www.ojose.com/

http://link.springer.com/

Good luck

Samaa

For literature search

1- https://www.scopus.com

2- http://webofknowledge.com

3- https://scholar.google.com

If you want search thesis , maybe following links helpful for you

1- https://pqdtopen.proquest.com/search.html

2- https://oatd.org/

3- https://www.caul.edu.au/

4- http://www.collectionscanada.ca/thesescanada/