收费全文 | 15990篇 |
免费 | 1634篇 |
国内免费 | 2611篇 |
2024年 | 63篇 |
2023年 | 268篇 |
2022年 | 562篇 |
2021年 | 840篇 |
2020年 | 635篇 |
2019年 | 808篇 |
2018年 | 699篇 |
2017年 | 526篇 |
2016年 | 667篇 |
2015年 | 1103篇 |
2014年 | 1266篇 |
2013年 | 1320篇 |
2012年 | 1616篇 |
2011年 | 1444篇 |
2010年 | 1031篇 |
2009年 | 950篇 |
2008年 | 1054篇 |
2007年 | 918篇 |
2006年 | 826篇 |
2005年 | 663篇 |
2004年 | 584篇 |
2003年 | 546篇 |
2002年 | 467篇 |
2001年 | 247篇 |
2000年 | 206篇 |
1999年 | 184篇 |
1998年 | 153篇 |
1997年 | 90篇 |
1996年 | 83篇 |
1995年 | 61篇 |
1994年 | 79篇 |
1993年 | 43篇 |
1992年 | 42篇 |
1991年 | 28篇 |
1990年 | 20篇 |
1989年 | 16篇 |
1988年 | 11篇 |
1987年 | 24篇 |
1986年 | 11篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1979年 | 5篇 |
1976年 | 3篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1966年 | 2篇 |
1965年 | 2篇 |
Cuticular wax is an important factor that affects storage quality of fruits and vegetables. Previous studies have shown that cuticular wax of pears changes significantly during storage, whereas there are few studies on the effects of different storage methods on the wax changes and the relationship with storage quality. Cuticular wax of Korla pear stored using different methods, was measured to analyze its total wax content, chemical compositions and their relationship with storage quality. At the end of storage, the highest cuticular wax content was observed in controlled atmosphere (CA) storage and the lowest in room temperature storage. The substances of the primary components with higher contents were nonacosane, (E, E)-ɑ-farnesene, dodecan-1-ol, 1,1-dimethoxynonane, nonanal, palmitic acid, and oleic acid. Total wax content, olefins and fatty acids were most significantly with the storage quality, followed by alkanes and esters. Moreover, total wax content, wax composition and weight loss were closely related to postharvest senescence. Overall, an understanding of variations in the cuticular wax under different storage methods could provide theoretical basis for further study on the storage and preservation technology of pears.
相似文献The imbalance between excess reactive oxygen species (ROS) generation and insufficient antioxidant defenses contribute to a range of neurodegenerative diseases. High ROS levels damage cellular macromolecules such as DNA, proteins and lipids, leading to neuron vulnerability and eventual death. However, the underlying molecular mechanism of the ROS regulation is not fully elucidated. Recently, an increasing number of studies suggest that microRNAs (miRNAs) emerge as the targets in regulating oxidative stress. We recently reported the neuroprotective effect of miR-137-3p for brachial plexus avulsion-induced motoneuron death. The present study is sought to investigate whether miR-137-3p also could protect PC12 cells against hydrogen peroxide (H2O2) induced neurotoxicity. By using cell viability assay, ROS assay, gene and protein expression assay, we found that PC-12 cells exposed to H2O2 exhibited decreased cell viability, increased expression levels of calpain-2 and neuronal nitric oxide synthase (nNOS), whereas a decreased miR-137-3p expression. Importantly, restoring the miR-137-3p levels in H2O2 exposure robustly inhibited the elevated nNOS, calpain-2 and ROS expression levels, which subsequently improved the cell viability. Furthermore, the suppressive effect of miR-137-3p on the elevated ROS level under oxidative stress was considerably blunted when we mutated the binding site of calpain-2 targted by miR-137-3p, suggesting the critical role of calpain-2 involving the neuroprotective effect of miR-137-3p. Collectively, these findings highlight the neuroprotective role of miR-137-3p through down-regulating calpain and NOS activity, suggesting its potential role for combating oxidative stress insults in the neurodegenerative diseases.
相似文献