全文获取类型
收费全文 | 301篇 |
免费 | 31篇 |
出版年
2023年 | 5篇 |
2022年 | 12篇 |
2021年 | 15篇 |
2020年 | 7篇 |
2019年 | 3篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 7篇 |
2015年 | 7篇 |
2014年 | 12篇 |
2013年 | 13篇 |
2012年 | 12篇 |
2011年 | 15篇 |
2010年 | 14篇 |
2009年 | 4篇 |
2008年 | 10篇 |
2007年 | 10篇 |
2006年 | 19篇 |
2005年 | 12篇 |
2004年 | 11篇 |
2003年 | 9篇 |
2002年 | 7篇 |
2001年 | 9篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1995年 | 10篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 7篇 |
1987年 | 1篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1953年 | 1篇 |
排序方式: 共有332条查询结果,搜索用时 15 毫秒
101.
102.
Background
Extensive focus is placed on the comparative analyses of consensus genotypes in the study of West Nile virus (WNV) emergence. Few studies account for genetic change in the underlying WNV quasispecies population variants. These variants are not discernable in the consensus genome at the time of emergence, and the maintenance of mutation-selection equilibria of population variants is greatly underestimated. The emergence of lineage 1 WNV strains has been studied extensively, but recent epidemics caused by lineage 2 WNV strains in Hungary, Austria, Greece and Italy emphasizes the increasing importance of this lineage to public health. In this study we explored the quasispecies dynamics of minority variants that contribute to cell-tropism and host determination, i.e. the ability to infect different cell types or cells from different species from Next Generation Sequencing (NGS) data of a historic lineage 2 WNV strain.Results
Minority variants contributing to host cell membrane association persist in the viral population without contributing to the genetic change in the consensus genome. Minority variants are shown to maintain a stable mutation-selection equilibrium under positive selection, particularly in the capsid gene region.Conclusions
This study is the first to infer positive selection and the persistence of WNV haplotype variants that contribute to viral fitness without accompanying genetic change in the consensus genotype, documented solely from NGS sequence data. The approach used in this study streamlines the experimental design seeking viral minority variants accurately from NGS data whilst minimizing the influence of associated sequence error. 相似文献103.
The rise and fall of arbuscular mycorrhizal fungal diversity during ecosystem retrogression
下载免费PDF全文
![点击此处可从《Molecular ecology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Manuela Krüger François P. Teste Etienne Laliberté Hans Lambers Megan Coghlan Graham Zemunik Michael Bunce 《Molecular ecology》2015,24(19):4912-4930
Ecosystem retrogression following long‐term pedogenesis is attributed to phosphorus (P) limitation of primary productivity. Arbuscular mycorrhizal fungi (AMF) enhance P acquisition for most terrestrial plants, but it has been suggested that this strategy becomes less effective in strongly weathered soils with extremely low P availability. Using next generation sequencing of the large subunit ribosomal RNA gene in roots and soil, we compared the composition and diversity of AMF communities in three contrasting stages of a retrogressive >2‐million‐year dune chronosequence in a global biodiversity hotspot. This chronosequence shows a ~60‐fold decline in total soil P concentration, with the oldest stage representing some of the most severely P‐impoverished soils found in any terrestrial ecosystem. The richness of AMF operational taxonomic units was low on young (1000's of years), moderately P‐rich soils, greatest on relatively old (~120 000 years) low‐P soils, and low again on the oldest (>2 000 000 years) soils that were lowest in P availability. A similar decline in AMF phylogenetic diversity on the oldest soils occurred, despite invariant host plant diversity and only small declines in host cover along the chronosequence. Differences in AMF community composition were greatest between the youngest and the two oldest soils, and this was best explained by differences in soil P concentrations. Our results point to a threshold in soil P availability during ecosystem regression below which AMF diversity declines, suggesting environmental filtering of AMF insufficiently adapted to extremely low P availability. 相似文献
104.
105.
106.
Many infectious gram-negative bacteria, including Salmonella typhimurium, require a Type Three Secretion System (T3SS) to translocate virulence factors into host cells. The T3SS consists of a membrane protein complex and an extracellular needle together that form a continuous channel. Regulated secretion of virulence factors requires the presence of SipD at the T3SS needle tip in S. typhimurium. Here we report three-dimensional structures of individual SipD, SipD in fusion with the needle subunit PrgI, and of SipD:PrgI in complex with the bile salt, deoxycholate. Assembly of the complex involves major conformational changes in both SipD and PrgI. This rearrangement is mediated via a π bulge in the central SipD helix and is stabilized by conserved amino acids that may allow for specificity in the assembly and composition of the tip proteins. Five copies each of the needle subunit PrgI and SipD form the T3SS needle tip complex. Using surface plasmon resonance spectroscopy and crystal structure analysis we found that the T3SS needle tip complex binds deoxycholate with micromolar affinity via a cleft formed at the SipD:PrgI interface. In the structure-based three-dimensional model of the T3SS needle tip, the bound deoxycholate faces the host membrane. Recently, binding of SipD with bile salts present in the gut was shown to impede bacterial infection. Binding of bile salts to the SipD:PrgI interface in this particular arrangement may thus inhibit the T3SS function. The structures presented in this study provide insight into the open state of the T3SS needle tip. Our findings present the atomic details of the T3SS arrangement occurring at the pathogen-host interface. 相似文献
107.
Siti Nurfadilah Nigel D. Swarts Kingsley W. Dixon Hans Lambers David J. Merritt 《Annals of botany》2013,111(6):1233-1241
Background and Aims
Many terrestrial orchids have an obligate requirement for mycorrhizal associations to provide nutritional support from germination to establishment. This study will investigate the ability of orchid mycorrhizal fungi (OMF) to utilize a variety of nutrient sources in the nutrient-impoverished (low organic) soils of the Southwest Australian Floristic Region (SWAFR) in order to effectively compete, survive and sustain the orchid host.Methods
Mycorrhizal fungi representing key OMF genera were isolated from three common and widespread species: Pterostylis recurva, Caladenia flava and Diuris corymbosa, and one rare and restricted species: Drakaea elastica. The accessibility of specific nutrients was assessed by comparing growth including dry biomass of OMF in vitro on basal CN MMN liquid media.Key Results
Each of the OMF accessed and effectively utilized a wide variety of nutrient compounds, including carbon (C) sources, inorganic and organic nitrogen (N) and inorganic and organic phosphorus (P). The nutrient compounds utilized varied between the genera of OMF, most notably sources of N.Conclusions
These results suggest that OMF can differentiate between niches (micro-niche specialization) in a constrained, highly resource-limited environment such as the SWAFR. Phosphorus is the most limited macronutrient in SWAFR soils and the ability to access phytate by OMF indicates a characterizing functional capacity of OMF from the SWAFR. Furthermore, compared with OMF isolated from the rare D. elastica, OMF associating with the common P. recurva produced far greater biomass over a wider variety of nutritional sources. This suggests a broader tolerance for habitat variation providing more opportunities for the common orchid for recruitment and establishment at a site. 相似文献108.
Christopher Lambers Michael Roth Jun Zhong Christoph Campregher Petra Binder Bernhard Burian Ventzislav Petkov Lutz-Henning Block 《PloS one》2013,8(8)
Background
Pulmonary arterial hypertension is characterized by increased thickness of pulmonary vessel walls due to both increased proliferation of pulmonary arterial smooth muscle cell (PASMC) and deposition of extracellular matrix. In patients suffering from pulmonary arterial hypertension, endothelin-1 (ET-1) synthesis is up-regulated and may increase PASMC activity and vessel wall remodeling through transforming growth factor beta-1 (TGF-β1) and connective tissue growth factor.Objective
To assess the signaling pathway leading to ET-1 induced proliferation and extracellular matrix deposition by human PASMC.Methods
PASMC were serum starved for 24 hours before stimulation with either ET-1 and/or TGF-β1. ET-1 was inhibited by Bosentan, ERK1/2 mitogen activated protein kinase (MAPK) was inhibited by U0126 and p38 MAPK was inhibited by SB203580.Results
ET-1 increased PASMC proliferation when combined with serum. This effect involved the mitogen activated protein kinases (MAPK) ERK1/2 MAPK and was abrogated by Bosentan which caused a G1- arrest through activation of p27(Kip). Regarding the contribution of extracellular matrix deposition in vessel wall remodeling, TGF-β1 increased the deposition of collagen type-I and fibronectin, which was further increased when ET-1 was added mainly through ERK1/2 MAPK. In contrast, collagen type-IV was not affected by ET-1. Bosentan dose-dependently reduced the stimulatory effect of ET-1 on collagen type-I and fibronectin, but had no effect on TGF-β1.Conclusion and Clinical Relevance
ET-1 alone does not induce PASMC proliferation and extracellular matrix deposition. However, ET-1 significantly up-regulates serum induced proliferation and TGF-β1 induced extracellular matrix deposition, specifically of collagen type-I and fibronectin. The synergistic effects of ET-1 on serum and TGF-β1 involve ERK1/2 MAPK and may thus present a novel mode of action in the pathogenesis of pulmonary arterial hypertension. 相似文献109.
Lambers TT Oancea E de Groot T Topala CN Hoenderop JG Bindels RJ 《Molecular and cellular biology》2007,27(4):1486-1494
Extracellular pH has long been known to affect the rate and magnitude of ion transport processes among others via regulation of ion channel activity. The Ca(2+)-selective transient receptor potential vanilloid 5 (TRPV5) channel constitutes the apical entry gate in Ca(2+)-transporting cells, contributing significantly to the overall Ca(2+) balance. Here, we demonstrate that extracellular pH determines the cell surface expression of TRPV5 via a unique mechanism. By a comprehensive approach using total internal reflection fluorescence microscopy, cell surface protein labeling, electrophysiology, (45)Ca(2+) uptake assays, and functional channel recovery after chemobleaching, this study shows that upon extracellular alkalinization, a pool of TRPV5-containing vesicles is rapidly recruited to the cell surface without collapsing into the plasma membrane. These vesicles contain functional TRPV5 channels since extracellular alkalinization is accompanied by increased TRPV5 activity. Conversely, upon subsequent extracellular acidification, vesicles are retrieved from the plasma membrane, simultaneously resulting in decreased TRPV5 activity. Thus, TRPV5 accesses the extracellular compartment via transient openings of vesicles, suggesting that rapid responses of constitutive active TRP channels to physiological stimuli rely on vesicular "kiss and linger" interactions with the plasma membrane. 相似文献
110.
Parent presence, delayed dispersal, and territory acquisition in the Seychelles warbler 总被引:1,自引:0,他引:1
The presence of parents in the natal territory may play an important,but often overlooked, role in natal dispersal and the consequentacquisition of a territory. Living with parents in a territorymay confer a fitness advantage to subordinates through, forexample, the nepotistic behavior of the parents or indirectbenefits gained by helping to raise nondescendent kin. Whena parent is replaced by a stepparent, such advantages are reducedor disappear and, as a result, subordinates may disperse. Subordinatesthat disperse after parent replacement may be constrained intheir timing of dispersal, which could have negative fitnessconsequences. In the cooperatively breeding Seychelles warbler,we show that when a parent was naturally replaced or experimentallyremoved and subsequently replaced by a stepparent from outsidethe territory, subordinates were more likely to disperse thanwhen both parents remained in the natal territory. Furthermore,subordinates dispersing from territories in which one or bothparents had been replaced were less likely to acquire a breederposition than subordinates dispersing when both parents werestill on the natal territory. Our findings suggest that thepresence of parents in the natal territory may promote delayeddispersal and facilitate the eventual acquisition of a breederposition outside the natal territory. Our results support theidea that the prolonged parental care, which long-lived speciesare able to provide, may have selected for family living. 相似文献