全文获取类型
收费全文 | 329篇 |
免费 | 21篇 |
国内免费 | 1篇 |
专业分类
351篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 11篇 |
2021年 | 14篇 |
2020年 | 16篇 |
2019年 | 23篇 |
2018年 | 16篇 |
2017年 | 10篇 |
2016年 | 10篇 |
2015年 | 20篇 |
2014年 | 25篇 |
2013年 | 27篇 |
2012年 | 27篇 |
2011年 | 21篇 |
2010年 | 15篇 |
2009年 | 11篇 |
2008年 | 13篇 |
2007年 | 12篇 |
2006年 | 14篇 |
2005年 | 9篇 |
2004年 | 8篇 |
2003年 | 14篇 |
2002年 | 11篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1994年 | 1篇 |
1990年 | 4篇 |
1984年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有351条查询结果,搜索用时 15 毫秒
41.
Immunohistochemical, ultrastructural and pathological studies were carried out on the gills of bream Abramis brama (L.) from Lake Mondsee, Austria, that were naturally infected with Ergasilus sieboldi Nordmann, 1832. Of a total of 14 specimens of bream examined, the gills of 7 (50%) were parasitized with this copepod and the intensity of infection ranged from 1 to 23 crustaceans per host. Histopathological investigations of infected gill showed extensive tissue damage due to attachment and feeding of the crustacean. Parasites attached close to the base of filaments near the gill arch. Pressure exerted by the ectoparasite attached to the lateral margin of the gill filaments induced atrophy of the secondary lamellae. Tissue reactions included hyperplasia and mucous cell proliferation of the respiratory epithelium. Mucous cells displayed an intense immunohistochemical reactivity with the anti-nitric oxide synthase antibody. In parasitized primary and secondary lamellae, a high number of eosinophilic granular cells and rodlet cells were noticed. Rodlet cells represent an inflammatory cell type closely linked to other piscine inflammatory cells. Presence of a high number of inflammatory cells at the site of E. sieboldi attachment is related to intense host cellular reaction. 相似文献
42.
Hannan MA Faraji B Tanguma J Longoria N Rodriguez RC 《Biological trace element research》2009,127(1):6-15
The dietary intake of zinc (Zn), iron (Fe), selenium (Se), and iodine (I) of 31 lactating Mexican–American women attending
the Hidalgo County WIC program in Rio Grande Valley (RGV), Texas was estimated from 24-h dietary recall interviews. Milk samples
were obtained from lactating mothers who had infants 3 months of age and younger. Milk samples were collected in two visits
to assess change in breast milk composition after 1–3 months postpartum: group A—after 30–45 days and group B—75–90 days.
Dietary intakes indicated that the study participants had significantly inadequate percent energy intakes than the DRI (Dietary
Recommended Intakes) percent recommended kilocalorie values but protein intakes were substantially higher than the percent
recommended values. The estimated percent Zn, Fe, Se, and I intakes were also significantly lower than the DRI percent recommended
values. The lactating mothers consumed significantly less Zn, Se, and I when compared to the Recommended Dietary Allowances
(RDA) even though Fe intake was higher than the RDA value. Breast milk concentration of Zn, Fe, and Se were in agreement within
the range of representative values for Constituents of Human Milk but I has significantly less concentration than the representative
value. There was no statistically significant correlation observed between dietary intake and milk concentration of Zn, Fe,
Se, and I. This study compares the estimated dietary intake of zinc, iron, selenium, and iodine to the concentration of these
trace elements in the maternal milk of lactating women of Mexican–American heritage who attend the Rio Grande Valley WIC clinic. 相似文献
43.
We examined the molecular basis of ddNTP selectivity in archaeal family B DNA polymerases by randomly mutagenizing the gene encoding Thermococcus sp. JDF-3 DNA polymerase and screening mutant libraries for improved ddNTP incorporation. We identified two mutations, P410L and A485T, that improved ddNTP uptake, suggesting the contribution of P410 and A485 to ddNTP/dNTP selectivity in archaeal DNA polymerases. The importance of A485 was identified previously in mutagenesis studies employing Pfu (A486) and Vent (A488) DNA polymerases, while the contribution of P410 to ddNTP/dNTP selectivity has not been reported. We demonstrate that a combination of mutations (P410L/A485T) has an additive effect in improving ddNTP incorporation by a total of 250-fold. To assess the usefulness of the JDF-3 P410L/A485T in fluorescent-sequencing applications, we compared the archaeal mutant to Taq F667Y with respect to fidelity and kinetic parameters for DNA and dye-ddNTPs. Although the Taq F667Y and JDF-3 P410L/A485T mutants exhibit similar K(m) and V(max) values for dye-ddNTPs in single-base extension assays, the archaeal mutant exhibits higher fidelity due to a reduced tendency to form certain (ddG:dT, ddT:dC) mispairs. DNA polymerases exhibiting higher insertion fidelity are expected to provide greater accuracy in SNP frequency determinations by single-base extension and in multiplex minisequencing assays. 相似文献
44.
Tree diversity and species identity effects on soil fungi,protists and animals are context dependent
Leho Tedersoo Mohammad Bahram Tomá? Cajthaml Sergei P?lme Indrek Hiiesalu Sten Anslan Helery Harend Franz Buegger Karin Pritsch Julia Koricheva Kessy Abarenkov 《The ISME journal》2016,10(2):346-362
Plant species richness and the presence of certain influential species (sampling effect) drive the stability and functionality of ecosystems as well as primary production and biomass of consumers. However, little is known about these floristic effects on richness and community composition of soil biota in forest habitats owing to methodological constraints. We developed a DNA metabarcoding approach to identify the major eukaryote groups directly from soil with roughly species-level resolution. Using this method, we examined the effects of tree diversity and individual tree species on soil microbial biomass and taxonomic richness of soil biota in two experimental study systems in Finland and Estonia and accounted for edaphic variables and spatial autocorrelation. Our analyses revealed that the effects of tree diversity and individual species on soil biota are largely context dependent. Multiple regression and structural equation modelling suggested that biomass, soil pH, nutrients and tree species directly affect richness of different taxonomic groups. The community composition of most soil organisms was strongly correlated due to similar response to environmental predictors rather than causal relationships. On a local scale, soil resources and tree species have stronger effect on diversity of soil biota than tree species richness per se. 相似文献
45.
Temporal variation of Bistorta vivipara‐associated ectomycorrhizal fungal communities in the High Arctic 下载免费PDF全文
Sunil Mundra Mohammad Bahram Leho Tedersoo Håvard Kauserud Rune Halvorsen Pernille Bronken Eidesen 《Molecular ecology》2015,24(24):6289-6302
Ectomycorrhizal (ECM) fungi are important for efficient nutrient uptake of several widespread arctic plant species. Knowledge of temporal variation of ECM fungi, and the relationship of these patterns to environmental variables, is essential to understand energy and nutrient cycling in Arctic ecosystems. We sampled roots of Bistorta vivipara ten times over two years; three times during the growing‐season (June, July and September) and twice during winter (November and April) of both years. We found 668 ECM OTUs belonging to 25 different ECM lineages, whereof 157 OTUs persisted throughout all sampling time‐points. Overall, ECM fungal richness peaked in winter and species belonging to Cortinarius, Serendipita and Sebacina were more frequent in winter than during summer. Structure of ECM fungal communities was primarily affected by spatial factors. However, after accounting for spatial effects, significant seasonal variation was evident revealing correspondence with seasonal changes in environmental conditions. We demonstrate that arctic ECM richness and community structure differ between summer (growing‐season) and winter, possibly due to reduced activity of the core community, and addition of fungi adapted for winter conditions forming a winter‐active fungal community. Significant month × year interactions were observed both for fungal richness and community composition, indicating unpredictable between‐year variation. Our study indicates that addressing seasonal changes requires replication over several years. 相似文献
46.
Mohammad Hassanzadeh Saber Shahrouz Baradaran Noveiri Mohammad Pourkazemi Mahtab Yarmohammadi Jalil Jalilpour Mohammadreza Nowruz Fashkhami Bahram Falahatkar 《Zeitschrift fur angewandte Ichthyologie》2019,35(4):843-849
In sturgeons, the induction of gynogenesis and sex reversal could be important for potential production of neomale sturgeon and all‐female progeny for caviar production. The aim of this study was sex reversal of ship sturgeon (Acipenser nudiventris Lovetsky, 1828) gynogen into male sex. Five‐month‐old gynogens were sex reversed into male by including 17α‐methyl testosterone in their food for 7 months. Three treatments were considered as follows: (a) without treated (gynogen control), (b) 10 mg MT/kg diet, and (c) 50 mg MT/kg diet. All treatments (60 individuals) were sampled both the 30 and 36 months old and their sex was determined using classical histology method of gonad. The sex ratio of the progenies in the gynogen control were 73.3% female and 26.7% male. In treatment of 10 mg MT/kg feed, 18 specimens were studied that half of them (50%) showed pseudo‐testicular structure in the female gonad. That is 50% of the specimens were intersex, 27.7% were male and 22.3% were female. All of the fish fed by 50 mg MT/kg feed had been sex reversed to male. Sexual maturation of these fish had been recognized in stage III at 36 months old. In conclusion, 50 mg MT/kg feed found as effective dose for successful sex reversal in gynogenetic ship sturgeon. 相似文献
47.
Katarzyna A. Rejniak Shizhen E. Wang Nicole S. Bryce Hang Chang Bahram Parvin Jerome Jourquin Lourdes Estrada Joe W. Gray Carlos L. Arteaga Alissa M. Weaver Vito Quaranta Alexander R. A. Anderson 《PLoS computational biology》2010,6(8)
Most tumors arise from epithelial tissues, such as mammary glands and lobules, and their initiation is associated with the disruption of a finely defined epithelial architecture. Progression from intraductal to invasive tumors is related to genetic mutations that occur at a subcellular level but manifest themselves as functional and morphological changes at the cellular and tissue scales, respectively. Elevated proliferation and loss of epithelial polarization are the two most noticeable changes in cell phenotypes during this process. As a result, many three-dimensional cultures of tumorigenic clones show highly aberrant morphologies when compared to regular epithelial monolayers enclosing the hollow lumen (acini). In order to shed light on phenotypic changes associated with tumor cells, we applied the bio-mechanical IBCell model of normal epithelial morphogenesis quantitatively matched to data acquired from the non-tumorigenic human mammary cell line, MCF10A. We then used a high-throughput simulation study to reveal how modifications in model parameters influence changes in the simulated architecture. Three parameters have been considered in our study, which define cell sensitivity to proliferative, apoptotic and cell-ECM adhesive cues. By mapping experimental morphologies of four MCF10A-derived cell lines carrying different oncogenic mutations onto the model parameter space, we identified changes in cellular processes potentially underlying structural modifications of these mutants. As a case study, we focused on MCF10A cells expressing an oncogenic mutant HER2-YVMA to quantitatively assess changes in cell doubling time, cell apoptotic rate, and cell sensitivity to ECM accumulation when compared to the parental non-tumorigenic cell line. By mapping in vitro mutant morphologies onto in silico ones we have generated a means of linking the morphological and molecular scales via computational modeling. Thus, IBCell in combination with 3D acini cultures can form a computational/experimental platform for suggesting the relationship between the histopathology of neoplastic lesions and their underlying molecular defects. 相似文献
48.
European minnows, Phoxinus phoxinus L., are commonly infected with Diplostomum phoxini Faust, 1918 metacercariae. A sub-sample of 34 minnows collected from the River Endrick, Stirlingshire, Scotland revealed that 50% of the population were infected (n = 17), with the cerebellum, medulla oblongata and the optic lobe regions of the minnow brain bearing the heaviest infections (13.7 +/- 2.6 mean +/- S.E.; 1-38 range). Serial histological sections through the brains of both uninfected and infected minnows revealed the presence of rodlet cells in the latter, which were occasionally observed in close proximity to the tegument of a metacercaria. Rodlet cells were the only type of host inflammatory cells found in this study and their role in the host's immune response to parasitic infection is commented upon. 相似文献
49.
Reproductive or neotenic soldiers of the Archotermopsid Zootermopsis nevadensisnevadensis (Hagen) are compared to sterile soldiers and primary male reproductives. Several head capsule morphometrics correlate significantly with gonad size across all forms and both sexes of soldiers. The easily observed field character of ratio of mandible length to labrum length is a consistent and reliable feature of head capsule external morphology for predicting gonad development and reproductive potential of soldier forms regardless of age, sex, or live weight. 相似文献
50.
Mohan Babu Roland Arnold Cedoljub Bundalovic-Torma Alla Gagarinova Keith S. Wong Ashwani Kumar Geordie Stewart Bahram Samanfar Hiroyuki Aoki Omar Wagih James Vlasblom Sadhna Phanse Krunal Lad Angela Yeou Hsiung Yu Christopher Graham Ke Jin Eric Brown Ashkan Golshani Philip Kim Gabriel Moreno-Hagelsieb Jack Greenblatt Walid A. Houry John Parkinson Andrew Emili 《PLoS genetics》2014,10(2)
Large-scale proteomic analyses in Escherichia coli have documented the composition and physical relationships of multiprotein complexes, but not their functional organization into biological pathways and processes. Conversely, genetic interaction (GI) screens can provide insights into the biological role(s) of individual gene and higher order associations. Combining the information from both approaches should elucidate how complexes and pathways intersect functionally at a systems level. However, such integrative analysis has been hindered due to the lack of relevant GI data. Here we present a systematic, unbiased, and quantitative synthetic genetic array screen in E. coli describing the genetic dependencies and functional cross-talk among over 600,000 digenic mutant combinations. Combining this epistasis information with putative functional modules derived from previous proteomic data and genomic context-based methods revealed unexpected associations, including new components required for the biogenesis of iron-sulphur and ribosome integrity, and the interplay between molecular chaperones and proteases. We find that functionally-linked genes co-conserved among γ-proteobacteria are far more likely to have correlated GI profiles than genes with divergent patterns of evolution. Overall, examining bacterial GIs in the context of protein complexes provides avenues for a deeper mechanistic understanding of core microbial systems. 相似文献