According to its website, Oppenheimer is a "leading investment bank and full-service investment firm that provides financial services and advice to high net worth investors, individuals, businesses and institutions."

Indeed, Oppenheimer has some pull in the market through its equity ratings, which is why we examined a list of all the U.S. stocks rated "buy" by the firm. This is a highly bullish rating, so we can assume many smart minds from the firm spent time analyzing companies and feel convinced of the stocks' potential.

Encouraging accounts receivable trends
But we wanted more meat -- so we screened Oppenheimer's buy list for the names that have shown encouraging accounts receivable trends relative to sales.

The trend helps to gauge whether the quality of sales, not just the quantity, is increasing over time.

To be more specific, we screened for names with strong sales trends relative to accounts receivable and for increases in revenue that are outpacing increases in accounts receivable year over year, as well as receivables comprising a smaller portion of accounts receivable over the same time period.

These trends are positive because accounts receivable has not yet been received, and there is no guarantee it will be received in full, so the smaller the portion of revenue and current assets, the better.

Business section: Investing ideas
Below are the results of this screen. These stocks have positive sales trends relative to both revenue and current assets. They also have buy ratings from Oppenheimer.

Do you think these stocks are poised to move higher? (Click here to access free, interactive tools to analyze these ideas.)

1. Biogen Idec (Nasdaq: BIIB): Develops, manufactures, and markets therapeutics in the areas of neurology, immunology, hemophilia, and oncology in the United States and internationally. The company has a market cap of $30.87 billion, most recent closing price at $129.55. On Aug. 18, 2011, Oppenheimer had an outperform rating on the stock. Revenue grew by 8.83% during the most recent quarter ($1,326.71 million vs. $1,219.07 million y/y). Accounts receivable grew by -1.04% during the same time period ($831.23 million vs. $839.99 million y/y). Receivables, as a percentage of current assets, decreased from 33.07% to 27.94% during the most recent quarter (comparing three months ending Dec. 31, 2011 to three months ending Dec. 31, 2010).

2. EV Energy Partners (Nasdaq: EVEP): Engages in the acquisition, development, and production of oil and natural gas properties in the United States. The company has a market cap of $1.93 billion, most recent closing price at $63.80. On July 29, 2011, Oppenheimer had an outperform rating on the stock. Revenue grew by 38.07% during the most recent quarter ($66.84 million vs. $48.41 million y/y). Accounts receivable grew by 32.65% during the same time period ($37.38 million vs. $28.18 million y/y). Receivables, as a percentage of current assets, decreased from 26.2% to 23.49% during the most recent quarter (comparing three months ending Dec. 31, 2011 to three months ending Dec. 31, 2010).

3. Fluidigm (Nasdaq: FLDM): Engages in the development, manufacture, and marketing of microfluidic systems for growth markets in the life science and agricultural biotechnology industries. The company has a market cap of $320 million, most recent closing price at $15.57. On Oct. 5, 2011, Oppenheimer had an outperform rating on the stock. Revenue grew by 25.48% during the most recent quarter ($13 million vs. $10.36 million y/y). Accounts receivable grew by 14.2% during the same time period ($9.25 million vs. $8.1 million y/y). Receivables, as a percentage of current assets, decreased from 38.79% to 13.21% during the most recent quarter (comparing 13 weeks ending Dec. 31, 2011 to 13 weeks ending Dec. 31, 2010).

4. MedAssets (Nasdaq: MDAS): Provides technology enabled products and services for hospitals, health systems, and other non-acute health care providers in the United States. The company has a market cap of $744.59 million, most recent closing price at $12.94. On April 26, 2011, Oppenheimer had an outperform rating on the stock. Revenue grew by 46.59% during the most recent quarter ($156.78 million vs. $106.95 million y/y). Accounts receivable grew by 4.02% during the same time period ($104.04 million vs. $100.02 million y/y). Receivables, as a percentage of current assets, decreased from 54.14% to 51.78% during the most recent quarter (comparing three months ending Dec. 31, 2011 to three months ending Dec. 31, 2010).

5. Rex Energy: Operates as an independent oil and gas company in the Appalachian, Illinois, and Denver-Julesburg Basins. The company has a market cap of $515.78 million, most recent closing price at $9.99. On April 4, 2012, Oppenheimer had an outperform rating on the stock. Revenue grew by 62.8% during the most recent quarter ($31.68 million vs. $19.46 million y/y). Accounts receivable grew by -38.58% during the same time period ($17.72 million vs. $28.85 million y/y). Receivables, as a percentage of current assets, decreased from 30.81% to 26.88% during the most recent quarter (comparing three months ending Dec. 31, 2011 to three months ending Dec. 31, 2010).

6. Tempur-Pedic International (NYSE: TPX): Distributes bedding products worldwide. The company has a market cap of $3.97 billion, most recent closing price at $60.51. On Dec. 12, 2011, Oppenheimer had an outperform rating on the stock. Revenue grew by 17.97% during the most recent quarter ($384.39 million vs. $325.84 million y/y). Accounts receivable grew by 13.8% during the same time period ($152.96 million vs. $134.41 million y/y). Receivables, as a percentage of current assets, decreased from 44.61% to 35.91% during the most recent quarter (comparing three months ending March 31, 2012 to three months ending March 31, 2011).

Interactive Chart: Press Play to compare changes in analyst ratings over the last two years for the stocks mentioned above. Analyst ratings sourced from Zacks Investment Research.