Different types of search are available from a drop-down menu on the left hand side of the search bar.
Some special types are:
- Modification/Publication date This allows the narrowing of results to a particular range of dates specified as [MM] [YYYY]. For example 08 2016 to 08 2016 returns results published from the first day in August 2016 to the last day in August 2016.
- Strategy Provides an additional drop-down list of types of experiments e.g., RNA-Seq, ChIP-Seq, etc.
- Library Selection Provides an additional drop-down list of known library preparation methods, e.g. Poly(A) and Size fractionation.
- Platform Provides an additional drop-down list of NGS sequencing platforms e.g., Illumina, Ion Torrent. Note that download of data from some platforms such as Complete Genomics is not supported.
- Instrument Provides an additional drop-down list of individual NGS sequencing machines e.g., HiSeq X Ten, Ion Torrent PGM.
- Paired Status Choose between paired end and single end runs.
- Availability Choose between dbGaP or public. dbGaP refers to confidential data that can be searched through the tool and accessed upon request at NCBI.
- PubMed Choose between "has abstract" or "has full-text article" to find results that have a PubMed abstract or entire publication available.
Any number of search parameters may be added to refine a search, for example to construct a query for "paired-end RNA-Seq data from an Illumina HiSeq2500", but the return search must satisfy every search parameter. In other words, search parameters work as "A and B" and not as "A or B". In consequence, searches performed with two platform parameters for example "Platform = Illumina and Platform = Ion Torrent" will not return any results.
Note also that searches rely on metadata provided by the depositor of the SRA runs. This means that if, for example, an RNA-Seq run was not annotated as being RNA-Seq during submission, it won't be returned by a search for "Strategy = RNA-Seq".
Finally, the search tool uses NCBI's e-utilities, which occasionally experience downtime. If no searches return any results, check https://www.ncbi.nlm.nih.gov/sra/ to see the status of the service.