全文获取类型
收费全文 | 192篇 |
免费 | 8篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 6篇 |
2015年 | 15篇 |
2014年 | 15篇 |
2013年 | 13篇 |
2012年 | 14篇 |
2011年 | 21篇 |
2010年 | 12篇 |
2009年 | 8篇 |
2008年 | 8篇 |
2007年 | 9篇 |
2006年 | 6篇 |
2005年 | 10篇 |
2004年 | 6篇 |
2003年 | 9篇 |
2002年 | 5篇 |
2001年 | 4篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有200条查询结果,搜索用时 62 毫秒
71.
Ecosystem processes in agricultural landscapes are often triggered by resource availability in crop and noncrop habitats.
We investigated how oilseed rape (OSR; Brassica napus, Brassicaceae) affects noncrop plants in managed systems and semi-natural habitat, using trophic interactions among wild
mustard (Sinapis arvensis, Brassicaceae), rape pollen beetles (Meligethes aeneus, Nitidulidae) and their parasitoids (Tersilochus heterocerus, Ichneumonidae). We exposed wild mustard as phytometer plants in two cropland habitat types (wheat field, field margin) and
three noncrop habitat types (fallow, grassland, wood margin) across eight landscapes along a gradient from simple to complex
(quantified as % arable land). Both landscape and local factors affected the abundance of rape pollen beetles and parasitoids.
Rape pollen beetle infestation and parasitism rates on these plants were lower in noncrop habitats and higher in wheat fields
and field margins, whereas beetles and parasitoids responded differently to landscape scale parameters. We found the hypothesized
spillover from OSR crop onto wild plants in surrounding habitats only for parasitoids, but not for pollen beetles. Parasitism
rates were not related to landscape simplification, but benefited from increasing proportions of OSR. In contrast, rape pollen
beetles benefited from simple landscape structures, presumably due to multi-annual population build-ups resulting from long-term
OSR planting (as part of the crop rotation). In conclusion, we showed that spillover from cropland affects parasitism rates
on related wild plants outside cropland, which has not been shown so far, but can be expected to be a widespread effect shaping
noncrop food webs. 相似文献
72.
73.
Contrasting effects of natural habitat loss on generalist and specialist aphid natural enemies 总被引:1,自引:0,他引:1
The greater susceptibility of higher trophic levels to habitat loss has been demonstrated to disrupt important trophic interactions such as consumer control of prey populations. This pattern is predicted to break down for generalist species that can use matrix habitats, yet empirical studies comparing generalist and specialist enemy pressure in response to natural habitat loss are lacking. Here we examined the effects of landscape simplification resulting from habitat conversion to agriculture on nettles, Urtica dioica , their specialized aphid herbivore, Microlophium carnosum , and associated natural enemies that varied broadly in their degree of specialization. Both nettles and their specialized aphid herbivore were significantly more abundant in complex than simple landscapes. Different enemy groups showed contrasting responses. Aphid specialists (parasitic wasps and cecidomyiid midges) reached higher densities in complex than simple landscapes, and this effect was primarily related to shifts in local resource abundance (i.e. nettle aphid densities). In contrast, densities of generalists (coccinellid beetles and spiders) were significantly higher in simple landscapes, presumably due to spillover of generalists from surrounding cropland habitats. Natural enemy-prey ratios did not differ significantly across landscape types for specialist groups but were significantly higher in simple than complex landscapes for generalist groups, suggesting that enemy pressure on nettle aphids likely increases with landscape simplification. This was supported by our finding that aphid population growth rates were lower in simple than complex landscapes, and declined significantly with increasing coccinellid densities. Thus, in marked contrast to previous work, our results suggest that natural habitat loss may augment rather than disrupt consumer–prey interactions, and this will depend greatly on the degree of specialization of functionally dominant natural enemies. 相似文献
74.
Jasmin Jung Kristina Loy Eva-Maria Schilling Mareike Röther Jan M. Brauner Tobias Huth Ursula Schlötzer-Schrehardt Christian Alzheimer Johannes Kornhuber Oliver Welzel Teja W. Groemer 《Molecular neurobiology》2014,49(2):916-930
Effects of the antidepressant fluoxetine in therapeutic concentration on stimulation-dependent synaptic vesicle recycling were examined in cultured rat hippocampal neurons using fluorescence microscopy. Short-term administration of fluoxetine neither inhibited exocytosis nor endocytosis of RRP vesicular membranes. On the contrary, acute application of the drug markedly increased the size of the recycling pool of hippocampal synapses. This increase in recycling pool size was corroborated using the styryl dye FM 1-43, antibody staining with αSyt1-CypHer?5E and overexpression of synapto-pHluorin, and was accompanied by an increase in the frequency of miniature postsynaptic currents. Analysis of axonal transport and fluorescence recovery after photobleaching excluded vesicles originating from the synapse-spanning superpool as a source, indicating that these new release-competent vesicles derived from the resting pool. Super resolution microscopy and ultrastructural analysis by electron microscopy revealed that short-term incubation with fluoxetine had no influence on the number of active synapses and synaptic morphology compared to controls. These observations support the idea that therapeutic concentrations of fluoxetine enhance the recycling vesicle pool size and thus the recovery of neurotransmission from exhausting stimuli. The change in the recycling pool size is consistent with the plasticity hypothesis of the pathogenesis of major depressive disorder as stabilization of the vesicle recycling might be responsible for neural outgrowth and plasticity. 相似文献
75.
Lukas Wisgrill Simone Schüller Markus Bammer Angelika Berger Arnold Pollak Teja Falk Radke Gesine K?gler Andreas Spittler Hanns Helmer Peter Husslein Ludwig Gortner 《PloS one》2014,9(9)
Background
In the last decades, human full-term cord blood was extensively investigated as a potential source of hematopoietic stem and progenitor cells (HSPCs). Despite the growing interest of regenerative therapies in preterm neonates, only little is known about the biological function of HSPCs from early preterm neonates under different perinatal conditions. Therefore, we investigated the concentration, the clonogenic capacity and the influence of obstetric/perinatal complications and maternal history on HSPC subsets in preterm and term cord blood.Methods
CD34+ HSPC subsets in UCB of 30 preterm and 30 term infants were evaluated by flow cytometry. Clonogenic assays suitable for detection of the proliferative potential of HSPCs were conducted. Furthermore, we analyzed the clonogenic potential of isolated HSPCs according to the stem cell marker CD133 and aldehyde dehydrogenase (ALDH) activity.Results
Preterm cord blood contained a significantly higher concentration of circulating CD34+ HSPCs, especially primitive progenitors, than term cord blood. The clonogenic capacity of HSPCs was enhanced in preterm cord blood. Using univariate analysis, the number and clonogenic potential of circulating UCB HSPCs was influenced by gestational age, birth weight and maternal age. Multivariate analysis showed that main factors that significantly influenced the HSPC count were maternal age, gestational age and white blood cell count. Further, only gestational age significantly influenced the clonogenic potential of UCB HSPCs. Finally, isolated CD34+/CD133+, CD34+/CD133– and ALDHhigh HSPC obtained from preterm cord blood showed a significantly higher clonogenic potential compared to term cord blood.Conclusion
We demonstrate that preterm cord blood exhibits a higher HSPC concentration and increased clonogenic capacity compared to term neonates. These data may imply an emerging use of HSPCs in autologous stem cell therapy in preterm neonates. 相似文献76.
Iris Berent Hong Pan Xu Zhao Jane Epstein Monica L. Bennett Vibhas Deshpande Ravi Teja Seethamraju Emily Stern 《PloS one》2014,9(4)
It is well known that natural languages share certain aspects of their design. For example, across languages, syllables like blif are preferred to lbif. But whether language universals are myths or mentally active constraints—linguistic or otherwise—remains controversial. To address this question, we used fMRI to investigate brain response to four syllable types, arrayed on their linguistic well-formedness (e.g., blif≻bnif≻bdif≻lbif, where ≻ indicates preference). Results showed that syllable structure monotonically modulated hemodynamic response in Broca''s area, and its pattern mirrored participants'' behavioral preferences. In contrast, ill-formed syllables did not systematically tax sensorimotor regions—while such syllables engaged primary auditory cortex, they tended to deactivate (rather than engage) articulatory motor regions. The convergence between the cross-linguistic preferences and English participants'' hemodynamic and behavioral responses is remarkable given that most of these syllables are unattested in their language. We conclude that human brains encode broad restrictions on syllable structure. 相似文献
77.
Michael Kessler Dietrich Hertel Hermann F. Jungkunst Jürgen Kluge Stefan Abrahamczyk Merijn Bos Damayanti Buchori Gerhard Gerold S. Robbert Gradstein Stefan K?hler Christoph Leuschner Gerald Moser Ramadhanil Pitopang Shahabuddin Saleh Christian H. Schulze Simone G. Sporn Ingolf Steffan-Dewenter Sri S. Tjitrosoedirdjo Teja Tscharntke 《PloS one》2012,7(10)
Managing ecosystems for carbon storage may also benefit biodiversity conservation, but such a potential ‘win-win’ scenario has not yet been assessed for tropical agroforestry landscapes. We measured above- and below-ground carbon stocks as well as the species richness of four groups of plants and eight of animals on 14 representative plots in Sulawesi, Indonesia, ranging from natural rainforest to cacao agroforests that have replaced former natural forest. The conversion of natural forests with carbon stocks of 227–362 Mg C ha−1 to agroforests with 82–211 Mg C ha−1 showed no relationships to overall biodiversity but led to a significant loss of forest-related species richness. We conclude that the conservation of the forest-related biodiversity, and to a lesser degree of carbon stocks, mainly depends on the preservation of natural forest habitats. In the three most carbon-rich agroforestry systems, carbon stocks were about 60% of those of natural forest, suggesting that 1.6 ha of optimally managed agroforest can contribute to the conservation of carbon stocks as much as 1 ha of natural forest. However, agroforestry systems had comparatively low biodiversity, and we found no evidence for a tight link between carbon storage and biodiversity. Yet, potential win-win agroforestry management solutions include combining high shade-tree quality which favours biodiversity with cacao-yield adapted shade levels. 相似文献
78.
79.
Hepatoma-derived growth-factor-related protein 2 (HRP-2) belongs to a family with five additional members: hepatoma-derived growth factor (HDGF); lens epithelium-derived growth factor; and the HDGF-related proteins -1, -3 and -4. Very little is known regarding the function of HRP-2 in particular. This study shows for the first time heteromer formation of different members of the HRP family; HDGF and HRP-2. In addition, we discovered a previously unknown splice variant of HRP-2 mRNA encoding for a protein with a 53-amino acid deletion in its hath region. This HRP-2 isoform c interacts preferentially with a processed form of HDGF probably because of the loss of an α helix of HRP-2. Furthermore, in contrast to other isoforms of HRP-2, isoform c binds to chromatin similar to its most closely related family member lens epithelium-derived growth factor with potential consequences regarding its function in HIV integration. Interestingly, only the new HRP-2 isoform c and a processed form of HDGF are displaced from condensed mitotic metaphase chromatin. In conclusion, these observations provide a new perspective for understanding the biological functions of HDGF and related proteins. 相似文献
80.
Marc Srour Germano Leão Demolin Leite Torsten Wappler Teja Tscharntke Christoph Scherber 《Insect Science》2012,19(6):705-705
Retraction: The following article from Insect Science, ‘Diversity of ants across an altitudinal gradient in and outside a spruce forest in the Harz Mountains, Germany’ by Marc Srour, Germano Leão Demolin Leite, Torsten Wappler, Teja Tscharntke and Christoph Scherber, published online on 2 August 2012 in Wiley Online Library ( http://wileyonlinelibrary.com ), has been retracted by agreement between the authors, the journal Editor in Chief, Le Kang, and Wiley Publishing Asia Pty Ltd. The retraction has been agreed due to concerns having been raised about the validity of the species richness values derived by the authors, and regarding the validity of the species determinations. 相似文献