E-resources

The Blu-ray Disc -official abbreviation BD- is the optical medium created by Sony at the beginning of 2002 as an evolution of the DVD for high-definition television. It permits a huge storage of data, almost 40 times more than a single-layer DVD-Single Side. Because it's bigger than a USBkey, it's not so easy to lose this kind of E-resource, but careful because the BluRay discs are flimsy ;)

It permits a huge storage of data: I would say: it permits (allows) to store a huge amount of data

single-layer DVD-Single Side: The object is "Side" or "DVD" here?

it's: remember: in formal English writing do not use contraction (but this is not so formal, so it's fine :))

A bibliographic database is an organized collection of bibliographic records or better an organized digital collection of references to journals and newspaper articles, books, conference poroceedings, etc.

They covers only bibliographical information and possibly abstracts.

They generally contain rich subject descriptions such as keywords or subject classification terms

A bibliographic database may be general in scope or cover a specific academic discipline. 

Most of bibliographic databases are proprietary, available by licensing agreement from vendors.

Logical operators (AND - OR - NOT ) that make electronic bibliographic reasearch different from the traditional one set based on a print index. These prepositions operators permit to combine different concepts within the same research, in contrast to the traditional research that allows access to contents using only one word at a time. Every preposition has a specific function and leads to a specific result.  IN - NEAR - WITH can be also be used as boolean operators.

prepositions : AND, OR are conjunctions, NOT an adverb. This in syntax, but here they are "operators", a collective noun including them all.

research: wgìhat about "search string"?

In general: use "allow" rather than "permit".

Another general remark: the operators were NOT born to serve bibliographic research, so maybe you should explain their history (and also something about how they work)

A Web browser, in information technology, is a program that allows you to use the services of Internet connectivity, i.e. a computer network, and to browse the World Wide Web. The most famous are Internet Explorer and Mozilla Firefox. Also Chrome is very good.