發送短信

數:

提供者:

CAPTCHA:

  _  __     ___      ______   _    _    _    _   
 | |/ //   / _ \\   /_   _// | || | || | |  | || 
 | ' //   / //\ \\  `-| |,-  | || | || | |/\| || 
 | . \\  |  ___  ||   | ||   | \\_/ || |  /\  || 
 |_|\_\\ |_||  |_||   |_||    \____//  |_// \_|| 
 `-` --` `-`   `-`    `-`'     `---`   `-`   `-`

Please enter what you see:

發送短信 : Retention and attrition among African Americans in the STAR*D study: What causes research volunteers to stay or stray?