Alimony (called spousal support in California) is calculated differently depending on whether determining temporary support or long term support. Temporary support (also called guideline support) is primarily determined based on the parties respective income and expenses. Temporary support duration lasts until judgement of dissolution. Once judgement of dissolution is entered, then long term support (if any) kicks in.
Long terms support is determined from a number of factors. You can read all such factors by looking up California Family Code section 4320 (via Google or some other source). Duration of long term support is typically half the length of the marriage (and/or registered domestic partnership). If the length of marriage/domestic partnership is over 10 years, duration can be longer than 1/2 such length.
Best to call a local family law lawyer to get a more detailed description based on the circumstances in your case.
The answer to this question will turn on what you mean by "domestic partners":
If the parties were same-sex partners who were STATE-REGISTERED domestic partners in California or other states which permitted "marriage-like" registration, and who then married in the brief period when sax-sex marriages were permitted in California, then the answer is PROBABLY (but not certainly) "Yes".
If the parties were OPPOSITE sex State-registered domestic partners, the answer may not be so clear.
The specific details of this question should be reviewed with an experie3nced family law attorney for a specific answer.