收费全文 | 11107篇 |
免费 | 658篇 |
国内免费 | 2篇 |
2023年 | 96篇 |
2022年 | 167篇 |
2021年 | 343篇 |
2020年 | 258篇 |
2019年 | 304篇 |
2018年 | 364篇 |
2017年 | 307篇 |
2016年 | 486篇 |
2015年 | 640篇 |
2014年 | 650篇 |
2013年 | 837篇 |
2012年 | 917篇 |
2011年 | 869篇 |
2010年 | 583篇 |
2009年 | 478篇 |
2008年 | 607篇 |
2007年 | 595篇 |
2006年 | 555篇 |
2005年 | 443篇 |
2004年 | 368篇 |
2003年 | 345篇 |
2002年 | 317篇 |
2001年 | 157篇 |
2000年 | 139篇 |
1999年 | 131篇 |
1998年 | 94篇 |
1997年 | 58篇 |
1996年 | 49篇 |
1995年 | 46篇 |
1994年 | 40篇 |
1993年 | 28篇 |
1992年 | 43篇 |
1991年 | 43篇 |
1990年 | 34篇 |
1989年 | 36篇 |
1988年 | 23篇 |
1987年 | 24篇 |
1986年 | 27篇 |
1985年 | 22篇 |
1984年 | 22篇 |
1983年 | 23篇 |
1982年 | 17篇 |
1981年 | 20篇 |
1980年 | 12篇 |
1979年 | 23篇 |
1978年 | 12篇 |
1977年 | 10篇 |
1976年 | 10篇 |
1975年 | 11篇 |
1974年 | 13篇 |
Although branched-chain amino acids (BCAA) are commonly used as a strategy to recover nutritional status of critically ill patients, recent findings on their role as immunonutrients have been associated with unfavorable outcomes, especially in obese patients. The present study aimed to explore the effects of different BCAA supplementation protocols in the inflammatory response of LPS-stimulated RAW 264.7 macrophages. Cell cultures were divided into five groups, with and without BCAA supplementation, (2 mmol/L of each amino acid). Then, cell cultures followed three different treatment protocols, consisting of a pretreatment (PT), an acute treatment (AT), and a chronic treatment (CT) with BCAA and LPS stimulation (1 µg/mL). Cell viability was analyzed by MTT assay, NO production was assessed by the Griess reaction and IL-6, IL-10, TNF-α and PGE2 synthesis, was evaluated by ELISA. BCAA significantly increased cell viability in AT and CT protocols, and NO and IL-10 synthesis in all treatment protocols. IL-6 synthesis was only increased in PT and CT protocols. TNF-α and PGE2 synthesis were not altered in any of the protocols and groups. BCAA supplementation was able to increase both pro and anti-inflammatory mediators synthesis by RAW 264.7 macrophages, which was influenced by the protocol applied. Moreover, these parameters were significantly increased by isoleucine supplementation, highlighting a potential research field for future studies.
相似文献Winter is a challenging period for aquatic research—weather is uncomfortable, ice is hazardous, equipment fails, and daylength is short. Consequently, until recently relatively little research on freshwater fishes has included winter. Telemetry methods for tracking fish and observing movement behavior are an obvious solution to working in harsh conditions because much of the data can be collected remotely, and passive methods collect data year-round without winter maintenance. Yet, many telemetry studies do not collect data during winter or, if they do, only report data from the ice-free seasons while the remaining data are unused. Here, we briefly summarize the advantages and limitations of using telemetry methods in winter, including acoustic and radio telemetry and passive integrated transponder technology, then review the range of questions related to fish ecology, behavior, bioenergetics, and habitat use that can be addressed in winter using telemetry. Our goals are to highlight the untapped potential of winter fish biology and to motivate scientists to revisit their four-season telemetry data and incorporate objectives specific to winter biology in future study plans.
相似文献