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71.
Todd Wojtowicz Zacchaeus G. Compson Louis J. Lamit Thomas G. Whitham Catherine A. Gehring 《Oecologia》2014,176(3):799-810
The effects of plant genetics on predators, especially those not living on the plant itself, are rarely studied and poorly understood. Therefore, we investigated the effect of plant hybridization and genotype on litter-dwelling spiders. Using an 18-year-old cottonwood common garden, we recorded agelenid sheet-web density associated with the litter layers of replicated genotypes of three tree cross types: Populus fremontii, Populus angustifolia, and their F1 hybrids. We surveyed 118 trees for agelenid litter webs at two distances from the trees (0–100 and 100–200 cm from trunk) and measured litter depth as a potential mechanism of web density patterns. Five major results emerged: web density within a 1-m radius of P. angustifolia was approximately three times higher than within a 1-m radius of P. fremontii, with F1 hybrids having intermediate densities; web density responded to P. angustifolia and F1 hybrid genotypes as indicated by a significant genotype × distance interaction, with some genotypes exhibiting a strong decline in web density with distance, while others did not; P. angustifolia litter layers were deeper than those of P. fremontii at both distance classes, and litter depth among P. angustifolia genotypes differed up to 300 %; cross type and genotype influenced web density via their effects on litter depth, and these effects were influenced by distance; web density was more sensitive to the effects of tree cross type than genotype. By influencing generalist predators, plant hybridization and genotype may indirectly impact trophic interactions such as intraguild predation, possibly affecting trophic cascades and ecosystem processes. 相似文献
72.
Cottonwoods are well known as foundation riparian trees that support diverse communities and drive ecosystem processes. Although hybridization naturally occurs when the distributions of two or more cottonwood species overlap, few cottonwood hybrid zones have been genetically characterized. We use genetic and genomic analyses to characterize patterns of admixture and introgression for a newly described hybrid zone at the intersection of three species (Populus L. Salicaceae—Populus deltoides, Populus fremontii, and Populus angustifolia) in southwestern Colorado, USA. Analysis of nuclear and chloroplast microsatellite marker data detected substantial genetic variation among individuals, revealing that (1) hybridization is occurring between two, not three, species (P. deltoides and P. angustifolia); (2) gene flow is bidirectional; (3) hybrids are not abundant (admixture detected in only 34 of 270 trees), with most being early-generation F1 hybrids; (4) cytonuclear disequilibria exists and F1 hybrids tend to retain P. deltoides—like chloroplasts; and (5) roughly 30 % of the nuclear markers deviated from a neutral pattern of introgression, suggesting that selection may play a role in shaping the genetic structure of the hybrid zone in this region. Overall, our results show that despite strong selection maintaining species divergence, transfer of allelic variants across species boundaries can occur. Our study assesses the fine-scale genetic structure of hybridization between P. angustifolia and P. deltoides and lays the foundation for examining how geographic differences in hybrid zone dynamics arise and may influence subsequent ecological and evolutionary processes. 相似文献
73.
74.
Bangert RK Allan GJ Turek RJ Wimp GM Meneses N Martinsen GD Keim P Whitham TG 《Molecular ecology》2006,15(13):4215-4228
We tested the hypothesis that leaf modifying arthropod communities are correlated with cottonwood host plant genetic variation from local to regional scales. Although recent studies found that host plant genetic composition can structure local dependent herbivore communities, the abiotic environment is a stronger factor than the genetic effect at increasingly larger spatial scales. In contrast to these studies we found that dependent arthropod community structure is correlated with both the cross type composition of cottonwoods and individual genotypes within local rivers up to the regional scale of 720,000 km(2) (Four Corner States region in the southwestern USA). Across this geographical extent comprising two naturally hybridizing cottonwood systems, the arthropod community follows a simple genetic similarity rule: genetically similar trees support more similar arthropod communities than trees that are genetically dissimilar. This relationship can be quantified with or without genetic data in Populus. 相似文献
75.
Environmental and genetic effects on the formation of ectomycorrhizal and arbuscular mycorrhizal associations in cottonwoods 总被引:1,自引:0,他引:1
Although both environment and genetics have been shown to affect the mycorrhizal colonization of host plants, the impacts of these factors on hosts that can be dually colonized by both ectomycorrhizal (EM) and arbuscular mycorrhizal (AM) fungi are less understood. We examined the influence of environment and host crosstype on the EM and AM colonization of cottonwoods (Populus angustifolia and natural hybrids) by comparing levels of colonization of trees growing in common gardens that differed in elevation and soil type. We also conducted a supplemental watering experiment to determine the influence of soil moisture on AM and EM colonization. Three patterns emerged. First, garden location had a significant impact on mycorrhizal colonization, such that EM colonization was 30% higher and AM colonization was 85% lower in the higher elevation garden than the lower elevation garden. Second, crosstype affected total (EM + AM) colonization, but did not affect EM or AM colonization. Similarly, a significant garden × crosstype interaction was found for total colonization, but not for EM or AM colonization. Third, experimental watering resulted in 33% higher EM colonization and 45% lower AM colonization, demonstrating that soil moisture was a major driver of the mycorrhizal differences observed between the gardens. We conclude that environment, particularly soil moisture, has a larger influence on colonization by AM versus EM fungi than host genetics, and suggest that environmental stress may be a major determinant of mycorrhizal colonization in dually colonized host plants. 相似文献
76.
Sohini Mukherjee Carrie L. Partch Rebecca E. Lehotzky Cecilia V. Whitham Hiutung Chu Charles L. Bevins Kevin H. Gardner Lora V. Hooper 《The Journal of biological chemistry》2009,284(8):4881-4888
Members of the RegIII family of intestinal C-type lectins are directly
antibacterial proteins that play a vital role in maintaining host-bacterial
homeostasis in the mammalian gut, yet little is known about the mechanisms
that regulate their biological activity. Here we show that the antibacterial
activities of mouse RegIIIγ and its human ortholog, HIP/PAP, are tightly
controlled by an inhibitory N-terminal prosegment that is removed by trypsin
in vivo. NMR spectroscopy revealed a high degree of conformational
flexibility in the HIP/PAP inhibitory prosegment, and mutation of either
acidic prosegment residues or basic core protein residues disrupted prosegment
inhibitory activity. NMR analyses of pro-HIP/PAP variants revealed distinctive
colinear backbone amide chemical shift changes that correlated with
antibacterial activity, suggesting that prosegment-HIP/PAP interactions are
linked to a two-state conformational switch between biologically active and
inactive protein states. These findings reveal a novel regulatory mechanism
governing C-type lectin biological function and yield new insight into the
control of intestinal innate immunity.The gastrointestinal tracts of mammals are heavily colonized with vast
symbiotic microbial communities and are also a major portal of entry for
bacterial pathogens. To cope with these complex microbial challenges,
intestinal epithelial cells produce a diverse repertoire of protein
antibiotics from multiple distinct protein families
(1). These proteins are
secreted apically into the luminal environment of the intestine where they
play a pivotal role in protecting against enteric infections
(2,
3) and may also function to
limit opportunistic invasion by symbiotic bacteria
(4).We previously identified lectins as a novel class of secreted antibacterial
proteins in the mammalian intestine. RegIIIγ is a member of the RegIII
subgroup of the C-type lectin family and is expressed in the small intestine
in response to microbial cues
(5), stored in epithelial cell
secretory granules, and released into the small intestinal lumen
(5). Similarly, HIP/PAP
(hepatointestinal pancreatic/pancreatitis-associated protein; the human
ortholog of
RegIIIγ)6 is
expressed in the human intestine
(6) and is up-regulated in
patients with inflammatory bowel disease
(7). These proteins are
produced in multiple epithelial lineages, including enterocytes and Paneth
cells (5,
6). Both RegIIIγ and
HIP/PAP are directly bactericidal at low micromolar concentrations for
Gram-positive bacteria (5),
revealing a previously unappreciated biological function for mammalian
lectins. The antibacterial functions of RegIIIγ and HIP/PAP are
dependent upon binding bacterial targets through interactions with
peptidoglycan (5). As
peptidoglycan is localized on surfaces of Gram-positive bacteria but is buried
in the periplasmic space of Gram-negative bacteria, this binding activity
provides a molecular explanation for the Gram-positive specific bactericidal
effects of these lectins. Although the mechanism of lectin-mediated
antibacterial activity remains unclear, RegIIIγ and HIP/PAP have been
shown to elicit extensive damage to the cell surfaces of targeted bacteria
(5).In this study, we show that C-type lectin bactericidal activity is under
stringent post-translational control. RegIIIγ and HIP/PAP each undergo
in vivo proteolytic removal of a flexible anionic N-terminal
prosegment that maintains the proteins in a biologically inactive state. NMR
spectroscopy suggests that the prosegment functions by controlling a two-state
conformational switch between the biologically active and inactive states of
the protein. We propose that this regulatory mechanism allows the host to
restrict expression of RegIII lectin antibacterial activity to the intestinal
lumen. Together, our findings represent a unique example of post-translational
control of C-type lectin biological activity, and provide novel insight into
the regulation of lectin-mediated innate immunity in the mammalian
intestine. 相似文献
77.
78.
Background
Verrucae are a common, infectious and sometimes painful problem. The optimal treatment for verrucae is unclear due to a lack of high quality randomised controlled trials. The primary objective of this study is to compare the clinical effectiveness of two common treatments for verrucae: cryotherapy using liquid nitrogen versus salicylic acid. Secondary objectives include a comparison of the cost-effectiveness of the treatments, and an investigation of time to clearance of verrucae, recurrence/clearance of verrucae at six months, patient satisfaction with treatment, pain associated with treatment, and use of painkillers for the treatments.Methods/Design
This is an open, pragmatic, multicentre, randomised controlled trial with two parallel groups: cryotherapy using liquid nitrogen delivered by a healthcare professional for a maximum of 4 treatments (treatments 2-3 weeks apart) or daily self-treatment with 50% salicylic acid for a maximum of 8 weeks. Two hundred and sixty-six patients aged 12 years and over with a verruca are being enrolled into the study. The primary outcome is complete clearance of all verrucae as observed on digital photographs taken at 12 weeks compared with baseline and assessed by an independent healthcare professional. Secondary outcomes include self-reported time to clearance of verrucae, self-reported clearance of verrucae at 6 months, cost-effectiveness of the treatments compared to one another, and patient acceptability of both treatments including possible side effects such as pain. The primary analysis will be intention to treat. It is planned that recruitment will be completed by December 2009 and results will be available by June 2010.Trial registration
Current Controlled Trials ISRCTN18994246. 相似文献79.
Björn Schulte-Herbrüggen J. Marcus Rowcliffe Katherine Homewood Laura A. Kurpiers Charlotte Whitham Guy Cowlishaw 《Human ecology: an interdisciplinary journal》2013,41(6):795-806
Unsustainable hunting is a threat to conservation and rural livelihoods that depend on bushmeat for food and income. To reduce the pressure on forest-dependent vulnerable species, hunting in farmland might complement offtake from forests and provide a sustainable source of bushmeat. To explore this possibility, we investigated patterns of hunting and wildlife depletion, and integration of hunting into agricultural livelihoods, in an intensively managed farm-forest mosaic landscape. Surveys were conducted across 63 households over a year in a Ghanaian cocoa-farming community surrounded by a timber production forest. The findings indicated a high level of wildlife depletion in the landscape and the local extinction of the largest species, especially in farmland. Most hunting occurred in forests and offtake from farmland was low, yet hunting in farmland was disproportionately common relative to its coverage in the landscape. Most farmland hunting was opportunistic and integrated with agricultural activities. Our findings suggest that intensively used farmland provides little opportunity to reduce hunting pressure in forests. 相似文献
80.
Hybridization among dominant tree species correlates positively with understory plant diversity 总被引:1,自引:0,他引:1
Adams RI Goldberry S Whitham TG Zinkgraf MS Dirzo R 《American journal of botany》2011,98(10):1623-1632