Работа с базой данных PubMed

Для получения списка айдишников статей по ключевому слову можно использовать get-запрос:

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/esearch.fcgi?db=pmc&tool=[название вашего скрипта]&email=[контактный email]&format=json&term=[ключевое слово]

Результат будет примерно такой:

{
  "header": {
    "type":"esearch", 
    "version":"0.3"},
  "esearchresult": {
    "count":"556850", 
    "retmax":"20", 
    "retstart":"0",
    "idlist":["7956338","7956337","7956317","7956313","7956301","7956298","7956293","7956291","7956287","7956282","7956276","7956270","7956269","7956239","7956238","7956234","7956232","7956215","7956214","7956207"],
    "translationset":[{
      "from":"eye",
      "to":"\"eye\"[MeSH Terms] OR \"eye\"[All Fields]"}],
    "translationstack":[
      { 
        "term":"\"eye\"[MeSH Terms]",
        "field":"MeSH Terms",
        "count":"49929",
        "explode":"Y"},
      {
        "term":"\"eye\"[All Fields]",
        "field":"All Fields",
        "count":"557471",
        "explode":"N"},
      "OR",
      "GROUP"],
    "querytranslation":"\"eye\"[MeSH Terms] OR \"eye\"[All Fields]"}
}