3 Ways to Find Research Articles in PubMed
1. Filter (Limit) to Article Type
Most citations in PubMed are for journal articles. However, you may limit your retrieval based on the type of material the article represents. Use the Filters on the Results page sidebar and look at the Article Types checklist which contains a list of frequently searched publication types.
For example, choose Randomized Controlled Trial or Clinical Trial or Meta-Analysis from the list.
2. PubMed Clinical Queries 
Enter your search terms and evidence-filtered citations will appear under Clinical Study Categories. Systematic Reviews or Medical Genetics. The Clinical Queries link is found on the PubMed home page or under the More Resources drop-down at the top of the Advanced Search page.
This specialized search query with built-in research methodology search filters is intended for clinicians. Five study categories or filters are provided: etiology, diagnosis, therapy, prognosis, and clinical prediction guides. Two emphasis categories or filters are provided: broad, sensitive search (includes relevant articles but probably some less relevant) and narrow, specific search (more precise articles, with less retrieval).
NOTE: We suggest changing to Narrow scope rather than Broad.
Systematic Reviews
This feature is provided to help clinicians locate systematic reviews and similar articles. It combines your search term(s) with citations identified as systematic reviews, meta-analyses, reviews of clinical trials, evidence-based medicine, consensus development conferences, and guidelines.
The resulting retrieval in PubMed Clinical Queries can be further refined using PubMed's Filters, e.g., English language, humans.
3. Limit to Articles with Structured Abstracts
Many abstracts that are added to PubMed include section labels such as BACKGROUND, OBJECTIVE, METHODS, RESULTS, and CONCLUSIONS. These 'structured' abstracts appear in many different article types such as review articles, original research, and practice guidelines and facilitate skimming of citations for relevance and specific information such as research design within the Methods section. The presence of structured abstracts in citations are a searchable feature in PubMed. To limit to citations containing structured abstracts, include the term hasstructuredabstract in the search box.
For example: valerian AND sleep AND hasstructuredabstract
NOTE: Click here to discover how to find Full-Text Articles on PubMed.