As you have seen, this directory contains hundreds links. To find easily what you

are looking for,

you have three main possibilities:

1) you navigate in categories and sub-categories, till you find what you need

2) you can use the search option, to find quicklier.

For example, if you are keen on astronomy and you are looking for a specific

article by P. Jacobs,

just type "jacobs" in the "research" field. This way you will get focused results

and a short list

of sites that contain this name.

3) you can  use the advanced search to select the options you need.