citeulike

One thing is for sure: you can find high quality resources there for sure so forget about Wikipedia, Google and news sites as trustworthy resources are located right there. It's not a very handy tool so I am not entirely pleased with it as searching through the library is a pain, but the quality level of the content is very high so it might be worth the pain.

Searching is a pain with it! If you are covering a wider topic and don't have a very specific thing in mind, you will literally search for hours before hitting that right topic - some more developed keyword search module wouldn't hurt. Actually the whole interface is pretty bad and isn't really good to use, despite the fact you can find great resources there.

I can't say I recommend this tool. If you are in a hurry with finding right content then this is not the tool for you as searching is really hard there - there aren't enough filters to back you up. As far as the content itself goes though, it is high quality so in case there is a need for a very speficic, reliable source, then you might check this one out.