收费全文 | 2081篇 |
免费 | 125篇 |
2023年 | 17篇 |
2022年 | 29篇 |
2021年 | 71篇 |
2020年 | 45篇 |
2019年 | 54篇 |
2018年 | 78篇 |
2017年 | 67篇 |
2016年 | 81篇 |
2015年 | 111篇 |
2014年 | 140篇 |
2013年 | 128篇 |
2012年 | 152篇 |
2011年 | 139篇 |
2010年 | 100篇 |
2009年 | 74篇 |
2008年 | 116篇 |
2007年 | 93篇 |
2006年 | 85篇 |
2005年 | 96篇 |
2004年 | 67篇 |
2003年 | 73篇 |
2002年 | 51篇 |
2001年 | 50篇 |
2000年 | 46篇 |
1999年 | 35篇 |
1998年 | 20篇 |
1997年 | 15篇 |
1996年 | 11篇 |
1995年 | 5篇 |
1994年 | 11篇 |
1993年 | 13篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 11篇 |
1989年 | 11篇 |
1988年 | 4篇 |
1987年 | 11篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1972年 | 4篇 |
1971年 | 4篇 |
1969年 | 3篇 |
1962年 | 2篇 |
The overuse of insecticides to control vector insects such as Diaphorina citri Kuwayama in citrus groves has altered the population dynamics of pest mites. Among phytophagous mites, population outbreaks of citrus leprosis mite, Brevipalpus yothersi Baker, have been increasingly intense and frequent in Brazilian citrus groves. Despite the great importance of the B. yothersi mite for citrus production, the lethal and sublethal effects of insecticides on this mite have not yet been studied. Therefore, in this study, the effects of insecticides commonly used for D. citri control on B. yothersi mortality, reproduction, and instantaneous growth rate were assessed. For this, two experiments were carried out, one under controlled conditions and another in a greenhouse. The insecticides tested were beta-cyfluthrin, bifenthrin, buprofezin, chlorpyrifos, dimethoate, pyriproxyfen, and thiamethoxam at 0 (control), 0.0625, 0.125, 0.25, 0.5, 1, and twofold the recommended insecticide concentration for D. citri control. The pyriproxyfen insecticide provided high mortality of B. yothersi even at low concentrations. Furthermore, this insecticide negatively interfered with the reproduction of this mite. Beta-cyfluthrin, bifenthrin, buprofezin, chlorpyrifos, dimethoate, and thiamethoxam, in the tested concentrations, showed low impact on citrus leprosis mite. Regarding the reproduction of the mite, no significant increase in fecundity was observed on B. yothersi females exposed to insecticide residues, regardless of the concentration tested. Therefore, the application of these insecticides in the management of pest insects is unlikely to promote an increase in the citrus leprosis mite population.
相似文献Niche partitioning occurs among coexisting populations to reduce the effects of competitive exclusion among species of similar niche. The aim of the present study is to verify the trophic niche partitioning and feeding behavior between two mustelids, the Giant otter and the Neotropical otter, through the dry and rainy season hydrologic of the Lower Xingu River. Our results suggest that the diets of both mustelids are composed primarily of fish of the family Anostomidae (Headstanders). Despite extensive niche overlap, our results indicate partitioning is facilitated by differences in niche breadth, with potential implications for conservation of both species in the case of declines in prey abundance and diversity. Both species inhabit an area recently impacted by completion of the Belo Monte Hydropower Plant, resulting in large changes to the hydrologic regime. Thus, our results provide important information for conservation efforts regarding the feeding behavior and co-occurrence of both species, as well as providing a baseline for monitoring future health of these mustelid populations. The present study is the first to test the hypothesis of niche partitioning between these two mustelids outside a protected area in the Amazon.
相似文献