Google Scholar (which is run by Google and behaves like Google) is a freely available web search engine that indexes the full text or metadata of scholarly literature.
You can find journal articles here as well as conference proceedings and technical reports. Once you've carried out a search, as long as there's a link on the right-hand side, you should be able to get to the full text (instructions to the right of this box!).
Google Scholar recognises advanced searching so, for example, if you typed in the search box "chronic asthma*" child* treat*, you would find articles with the exact phrase "chronic asthma" or "chronic asthmatic" and child or childhood or children etc and treat or treatment or treated etc.
You can refine on the left-hand side to see publications published in the past 5 or 10 years. If you're looking at something historically and how things have changed over time, then you might not want to update this.