Use double quotes ("") for exact terms and ampersand (&) for AND queries. All spaces yield OR queries.
Examples:
human&"ESC" mouse&"ESC" (human or mouse embryonic stem cells)
"H. Sapiens"&"DMSO" humanðanol (human samples treated with DMSO or ethanol)
GRO-seq&"blood" PRO-seq&lymphoblast&DMSO (GRO-seq samples from blood or DMSO-treated PRO-seq from lymphoblasts)