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41.
Structural determinants that target the hepatitis C virus core protein to lipid droplets 总被引:7,自引:0,他引:7
Boulant S Montserret R Hope RG Ratinier M Targett-Adams P Lavergne JP Penin F McLauchlan J 《The Journal of biological chemistry》2006,281(31):22236-22247
Hepatitis C virus core protein is targeted to lipid droplets, which serve as intracellular storage organelles, by its C-terminal domain, termed D2. From circular dichroism and nuclear magnetic resonance analyses, we demonstrate that the major structural elements within D2 consist of two amphipathic alpha-helices (Helix I and Helix II) separated by a hydrophobic loop. Both helices require a hydrophobic environment for folding, indicating that lipid interactions contribute to their structural integrity. Mutational studies revealed that a combination of Helix I, the hydrophobic loop, and Helix II is essential for efficient lipid droplet association and pointed to an in-plane membrane interaction of the two helices at the phospholipid layer interface. Aside from lipid droplet association, membrane interaction of D2 is necessary for folding and stability of core following maturation at the endoplasmic reticulum membrane by signal peptide peptidase. These studies identify critical determinants within a targeting domain that enable trafficking and attachment of a viral protein to lipid droplets. They also serve as a unique model for elucidating the specificity of protein-lipid interactions between two membrane-bound organelles. 相似文献
42.
43.
Analysis of clinical ostreid herpesvirus 1 (Malacoherpesviridae) specimens by sequencing amplified fragments from three virus genome areas 总被引:1,自引:0,他引:1
Although there are a number of ostreid herpesvirus 1 (OsHV-1) variants, it is expected that the true diversity of this virus will be known only after the analysis of significantly more data. To this end, we analyzed 72 OsHV-1 "specimens" collected mainly in France over an 18-year period, from 1993 to 2010. Additional samples were also collected in Ireland, the United States, China, Japan, and New Zealand. Three virus genome regions (open reading frame 4 [ORF4], ORF35, -36, -37, and -38, and ORF42 and -43) were selected for PCR analysis and sequencing. Although ORF4 appeared to be the most polymorphic genome area, distinguishing several genogroups, ORF35, -36, -37, and -38 and ORF42 and -43 also showed variations useful in grouping subpopulations of this virus. 相似文献
44.
Arumugam Thiagarajan Rajasekaran Lada Steeve Pepin Charles Forney Yves Desjardins Martine Dorais 《Trees - Structure and Function》2012,26(5):1545-1553
To fulfill the US Thanksgiving and Christmas tree markets, balsam fir (Abies balsamea (L.) Mill.) is generally harvested before the cold season, anecdotally leading to premature needle senescence. Accordingly, we tested the hypothesis that LT exposure before harvest induces specific hormonal changes and delays postharvest senescence and/or abscission in balsam fir. Two hundred and six seedlings exposed to two temperature treatments for 48?h, LT at 5?°C and controls at 22?°C were severed off roots and monitored for their postharvest needle senescence. Root and shoot (needles and buds) tissues were examined for major endogenous hormone metabolites. LT increased shoot ABA (2,007?ng?g?1 DW) by 2.5× and decreased GA44 (9.84?ng?g?1 DW) by 3.5× over those in roots. LT did not alter cytokinins, auxins or any root hormonal concentration. With auxins, only IAA, IAA-Asp, IAA-Leu and IAA-Glu were detected and the concentrations of IAA and IAA-Asp in shoots were lower than those found in roots. Among cytokinins, shoot c-ZR (58.95?ng?g?1 DW) and t-ZR (4.17?ng?g?1 DW) were 3× higher than those in roots. Apart from GA44, GA9 (136.76?ng?g?1 DW) was abundant in shoots. The PBL and PNL were 46 and 1.2?%, irrespective of treatments. LT seedlings held needles 11?days longer than the controls (122?days). In balsam fir, short-term LT exposure augmented ABA and decreased GA44 levels in shoots and delayed postharvest needle senescence. 相似文献
45.
Forage abundance, forage quality, and social factors are key elements of the foraging ecology of wild herbivores. For non-ruminant
equids, forage-limited environments are likely to impose severe constraints on their foraging behaviour. We used a multi-scale
approach to study foraging behaviour in kiang (Equus kiang), a wild equid inhabiting the high-altitude rangelands of the Tibetan Plateau. Using behavioural observations and vegetation
sampling, we first assessed how patterns of plant abundance and quality affected (i) the instantaneous forage intake rate
(fine scale) and (ii) the proportion of time spent foraging (coarse scale) across seasons. We also tested whether foraging
behaviour differed among group types, between sex in adults, and between females of different reproductive status. At a fine
scale, intake rate increased linearly with bite size and increased following a type II curvilinear function with biomass on
feeding sites. Forage intake rate also increased linearly with plant quality. Male and female kiangs had similar intake rates.
Likewise, gravid and lactating females had similar intake rates as barren and non-lactating females. At a coarse scale, kiangs
spent longer time feeding in mesic than in xeric habitats, and spent more time feeding in early summer and fall than in late
summer. Groups of adults with foals spent less time feeding than male groups and groups of adults without foals. Our findings
suggest that kiangs use flexible foraging behaviours in relation to seasonal variations of vegetation quality and abundance,
a likely outcome of the extreme seasonal conditions encountered on the Tibetan Plateau. 相似文献
46.
47.
Densification of the shrub layer has been reported in many subarctic regions, raising questions about the implication for large herbivores and their resources. Shrubs can tolerate browsing and their level of tolerance could be affected by browsing and soils productivity, eventually modifying resource availability for the caribou. Our objective was to assess the compensatory growth potential of a subarctic shrub, Betula glandulosa Michx., in relation with caribou browsing and nutriment availability for the plants. We used a simulated browsing (0, 25 and 75% of available shoots) and nitrogen-fertilisation (0 and 10 g m−2) experiment to test two main hypotheses linking tolerance to resource availability, the Compensatory Continuum Hypothesis and the Growth Rate Hypothesis as well as the predictions from the Limiting Resource Model. We seek to explicitly integrate the relative browsing pressure in our predictions since the amount of tissues removed could affect the capacity of long-lived plants to compensate. Birches fully compensated for moderate browsing with an overall leaf biomass similar to unbrowsed birches but undercompensated under heavy browsing pressure. The main mechanism explaining compensation appears to be the conversion of short shoots into long shoots. The leaf area increased under heavy browsing pressure but only led to undercompensation. Fertilisation for two consecutive years did not influence the response of birch, thus we conclude that our results support the LRM hypothesis of equal tolerance under both high and low nitrogen availability. Our results highlight that the potential for compensatory growth in dwarf birch is surpassed under heavy browsing pressure independently of the fertilisation regime. In the context of the worldwide decline in caribou herds, the reduction in browsing pressure could act synergistically with global climate change to promote the current shrub expansion reported in subarctic regions. 相似文献
48.
Web-FACE: a new canopy free-air CO<Subscript>2</Subscript> enrichment system for tall trees in mature forests 总被引:2,自引:0,他引:2
The long-term responses of forests to atmospheric CO2 enrichment have been difficult to determine experimentally given the large scale and complex structure of their canopy. We have developed a CO2 exposure system that uses the free-air CO2 enrichment (FACE) approach but was designed for tall canopy trees. The system consists of a CO2-release system installed within the crown of adult trees using a 45-m tower crane, a CO2 monitoring system and an automated regulation system. Pure CO2 gas is released from a network of small tubes woven into the forest canopy (web-FACE), and CO2 is emitted from small laser-punched holes. The set point CO2 concentration ([CO2]) of 500 µmol mol-1 is controlled by a pulse-width modulation routine that adjusts the rate of CO2 injection as a function of measured [CO2] in the canopy. CO2 consumption for the enrichment of 14 tall canopy trees was about 2 tons per day over the whole growing season. The seasonal daytime mean CO2 concentration was 520 µmol mol-1. One-minute averages of CO2 measurements conducted at canopy height in the center of the CO2-enriched zone were within ᆨ% and ᆞ% of the target concentration for 76% and 47% of the exposure time, respectively. Despite the size of the canopy and the windy site conditions, performance values correspond to about 75% of that reported for conventional forest FACE with the added advantage of a much simpler and less intrusive infrastructure. Stable carbon isotope signals captured by 80 Bermuda grass (Cynodon dactylon) seedlings distributed within the canopy of treated and control tree districts showed a clearly delineated area, with some nearby individuals having been exposed to a gradient of [CO2], which is seen as added value. Time-integrated values of [CO2] derived from the C isotope composition of C. dactylon leaves indicated a mean (-SD) concentration of 513ᇓ µmol mol-1 in the web-FACE canopy area. In view of the size of the forest and the rough natural canopy, web-FACE is a most promising avenue towards natural forest experiments, which are greatly needed. 相似文献
49.
The phosphorylation of glucose by polyphosphate glucokinase with both long- and short-chain polyphosphates has been shown to occur by either a nonprocessive mechanism, i.e. with repeated association and dissociation of the polyphosphate from the enzyme after each phosphorylation or by a quasiprocessive mechanism in which several phosphorylations occur prior to the release of polyphosphate and the reassociation with the enzyme. In contrast, the phosphorylation of ADP to ATP by polyphosphate kinase is by a strictly processive mechanism; the phosphorylation occurs without release of the polymer from the enzyme prior to termination of the reaction (Robinson, N. A., Clark, J. E., and Wood, H. G. (1987) J. Biol. Chem. 262, 5216-5222). The demonstration that the mechanism is quasi-or nonprocessive was accomplished by electrophoresis using a variety of concentrations of polyacrylamide gels which made it possible to detect the intermediate sizes formed during the reactions. It also has been shown that all chains longer than about 100 are used simultaneously, but with chains of less than 100 residues, there is preferential utilization of the longest chains. Thus a narrow range of sizes is formed from a heterogeneous mixture of long chains. It is this formation of the narrow range of sizes that makes it possible to use polyphosphate glucokinase for the determination of the average size of long chains (Pepin, C. A., Wood, H. G., and Robinson, N. A. (1986) Biochem. Int. 12, 111-123). 相似文献
50.
Binding surfaces of the type II transforming growth factor (TGF)-beta receptor extracellular domain (TbetaRII-ECD) are mapped by combining scanning-deletion mutagenesis results with knowledge-based modeling of the ectodomain structure. Of the 17 deletion mutants produced within the core binding domain of TbetaRII-ECD, only three retained binding to TGF-beta. Comparative modeling based on the crystal structure of the activin type II receptor extracellular domain (ActRII-ECD) indicates that the TbetaRII mutants which retain TGF-beta binding are deleted in some of the loops connecting the beta-strands in the TbetaRII-ECD model. Interpretation of the mutagenesis data within the structural framework of the ectodomain model allows for the prediction of potential binding sites at the surface of TbetaRII-ECD. 相似文献