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1.
We conducted a study to investigate the role of aggregates in the stabilization of residue‐ and root‐derived C in an illitic Mollisol and a kaolinitic Oxisol under the following treatments: (i) incorporated residue, (ii) growing plants, and (iii) both incorporated residue and growing plants. Residue‐C dynamics were followed in soils incubated with 13C‐labelled wheat residue with and without unlabelled growing wheat plants. Root‐C was traced by growing wheat plants with and without unlabelled wheat residue in a 13CO2‐labelling chamber. After 46 and 76 incubation days, residue‐ and root‐C were measured in four aggregate size classes and in microbial‐C. Both soils had greater residue‐derived than root‐derived total aggregate‐associated C at day 76, which we attributed to the larger residue‐C than root‐C inputs at the start of the experiment. On an aggregate basis, the ratio of residue‐derived over root‐derived C decreased in most size fractions over time, indicating a greater potential for longer‐term root‐C than residue‐C stabilization by aggregates in both soils. At both sampling days, all aggregates > 53 µm had greater residue‐C concentrations in the illitic soil than in the kaolinitic soil and this difference increased with increasing aggregate size. This suggested a greater affinity of illite clay than kaolinite clay to bind with fresh residue‐derived compounds into larger aggregates and hence a greater importance of aggregates in stabilizing residue‐C in illitic compared with kaolinitic soils. The stabilization of root‐C by aggregates was less affected by clay mineralogy and thus less dependent on the affinity of clay minerals to bind with root‐derived compounds.  相似文献   
2.
Pit-1 is a pituitary-specific POU-domain DNA binding factor, which binds to and trans-activates promoters of growth hormone- (GH), prolactin- (PRL) and thyroid stimulating hormone-beta- (TSHbeta) encoding genes. Thyrotropin-releasing hormone (TRH) is located in the hypothalamus and stimulates TSH, GH and PRL release from the pituitary gland. In the present study, we successfully used the cell aggregate culture system for chicken pituitary cells to study the effect of TRH administration on the ggPit-l* (chicken Pit-1), GH and TSHbeta mRNA expression in vitro. In pituitary cell aggregates of 11-day-old male broiler chicks the ggPit-l * mRNA expression was significantly increased following TRH administration, indicating that the stimulatory effects of TRH on several pituitary hormones are mediated via its effect on the ggPit-l* gene expression. Therefore, a semiquantitative RT-PCR method was used to detect possible changes in GH and TSHbeta mRNA levels. TRH affected both the GH and TSHbeta mRNA levels. The results of this in vitro study reveal that ggPit-1 * has a role in mediating the stimulatory effects of TRH on pituitary hormones like GH and TSHbeta in the chicken pituitary.  相似文献   
3.
East Coast fever, an acute lymphoproliferative disease of cattle, is caused by the apicomplexan parasite Theileria parva. Protective immunity is mediated by CD8(+) cytotoxic T lymphocytes directed against schizont-infected cells. The polymorphic immunodominant molecule, although an antibody-inducing surface molecule of the schizont, has been hypothesized to play a role in protective immunity. In order to evaluate the immunogenicity of PIM for inducing CTL, cattle were immunized with PIM in isolation from other T. parva antigens, forcing the presentation of PIM-derived epitopes on the MHC class I molecules. Although parasite-specific cytotoxicity was induced in both vaccinated animals, their immune response was clearly different. One animal generated MHC-restricted parasite-specific CTL against PIM while the other calf exhibited a strong PIM-specific proliferative response but non-MHC-restricted parasite-specific cytotoxicity. Only calf 1 survived a lethal sporozoite challenge. This DNA immunization technique with an antigen in isolation of CTL-immunodominant antigens might open possibilities for directing CTL responses against predefined antigens, such as strain cross-reacting CTL antigens.  相似文献   
4.
Different theories have been brought forward to explain the commonly observed δ15N enrichment with depth in soil profiles, including the discrimination against 15N during N decomposition and the buildup of 15N-enriched microbial residues. A combination of soil organic matter (SOM) size and density fractionations, 15N determinations, and phospholipid fatty acid (PLFA) analyses was conducted on soils from a pristine N-limited Nothofagus forest in southern Chile. The purpose of this study was to investigate which SOM fractions mostly reflect the 15N-enrichment pattern and to link 15N SOM enrichment with microbial community composition. Nitrogen-15 enrichments were greater for the microaggregate (<150 μm) than for the macroaggregate (>150 μm) size fraction, with Rayleigh isotope enrichment factors averaging −8.5‰ and −3.7‰, respectively. The macro-organic matter density fractions (>150 μm) showed intermediate enrichment factors of −5.1‰ and −7.3‰ for the light (<1.37 g cm−3) and heavy (>1.37 g cm−3) fraction, respectively. The abundance of fungal and bacterial PLFAs was significantly higher in the microaggregate compared to the macroaggregate size fraction, but their relative abundance did not change between aggregate size fractions. Our data link differential 15N enrichment of SOM fractions to “total” microbial abundance and, as such, corroborates existing theories of microbial-induced 15N enrichment. Isotopic fractionation during microbial N decomposition processes alone could not explain the large 15N enrichment in the microaggregate size fraction (−8.5‰) and the heavy density fraction (−7.3‰). We therefore suggest that microbial turnover and accretion of 15N-enriched microbial (especially fungal) compounds was an additional driver for 15N enrichment of this soil profile.  相似文献   
5.
Plant residues, living roots and microbial activity play an important role in aggregate formation and the stabilization of soil organic carbon (SOC), but their impact might differ among soils with different clay mineralogy. We investigated the effect of these organic agents on aggregation and SOC during a 76‐day incubation of 2‐mm sieved soil from an illitic Kastanozem and a kaolinitic Ferralsol, subjected to the following treatments: (i) control (no residue input or plant growth), (ii) residue input, (iii) living plants, and (iv) residue input and living plants. After 46 and 76 days, aggregate size distribution, aggregate‐associated SOC and microbial‐C were measured. In both soils, microbial‐C was less in the control than in the residue and/or plant treatments. After 46 days, new large macroaggregates (> 2000 µm) were formed in the control treatment of the kaolinitic soil, but not of the illitic soil. Control macroaggregates in the kaolinitic soil were formed out of silt and clay particles without accumulating C. Residue input and plant growth had a greater positive effect on macroaggregate formation in the illitic than in the kaolinitic soil. A stronger relation was found between microbial‐C and amount of large macroaggregates in the illitic than in the kaolinitic soil. We conclude that kaolinitic soils can rapidly form macroaggregates independent of biological processes due to physical or electrostatic interactions between the 1:1 clay minerals and oxides. However, biological processes led to stronger organic bonds between the illite compared with the kaolinite clay, resulting in more macroaggregates with long‐term stability in the illitic than in the kaolinitic soil.  相似文献   
6.
The development of routine analyses to allow for the handling of large amounts of samples and to avoid cost and time expensive analytical techniques is of high value. These routine analyses most often require calibration using the detailed analyses as reference values. A representative subset reflecting the complete range of the variables of interest is required for this purpose. In this paper this subset selection problem is tackled for multi-experiment data sets. Conventional techniques such as the Kennard and Stone algorithm and OptiSim are compared to a new approach based on Genetic Algorithms. The challenge here is to find an adequate objective function and to modify the standard crossover and mutation operators to keep the number of desired samples fixed. These techniques are applied on a data set containing the concentration of 45 fatty acids, determined by a simplified reference method, in 1033 milk samples, stemming from six different experiments. The objective is to select a subset of 100 samples in which each of the six different experiments is sufficiently represented. While there is no obvious way to generalize the conventional methods for multi-experiment data sets, this can quite easily be accomplished for Genetic Algorithms by modifying the objective function. Our results indicate that Genetic Algorithms are very capable of handling the subset selection problem for multi-experiment data sets.  相似文献   
7.
When used in bread dough systems, glucose oxidase (GO) and pyranose oxidase (P2O) generate H2O2 from O2. We here studied their potential to improve dough and bread characteristics. Neither GO nor P2O significantly affected the volume of straight dough bread produced with fermentation and proofing times of respectively 90 and 36 min at dosages up to 0.50 nkat/g flour. Supplementation with 1.00 nkat/g flour of GO or P2O significantly decreased bread loaf volume. The resistance of dough (fermented for 20 min and proofed for 56 min) to an applied shock was substantially improved by inclusion of 0.08, 0.25, 0.50 or 1.00 nkat/g flour of GO or P2O in the dough recipe. Thus, the proofed doughs showed significantly less collapse and the resultant breads had higher loaf volumes than did the reference breads. Yeast probably exerts an oxidizing effect on dough, which, depending on the exact breadmaking protocol used, might veil the positive oxidizing effect of the enzymes on dough properties during prolonged fermentation.  相似文献   
8.
DNA methylation is an important epigenetic strategy for embryo development and survival. The one‐carbon metabolism can be disturbed by inadequate provision of dietary methyl donors. Because of the continuous selection for larger litters, it is relevant to explore if highly prolific sows might encounter periods of methyl donor deficiency throughout their reproductive cycles. This study, therefore, assesses the fluctuation(s) in methylation potential (MP) and aims to link possible methyl donor deficiencies to nutrient metabolism. In total, 15 hybrid sows were followed from weaning of the previous reproductive cycle (d‐5) to weaning of the present cycle. Blood samples were taken at d‐5, 0, 21, 42, 63, 84 and d108 of gestation, the day of parturition (d115), two weeks of lactation (d129) and at weaning (d143). Blood plasma samples were analysed for S‐adenosylmethionine (SAM), S‐adenosylhomocysteine (SAH), free methionine, free glycine, acetylcarnitine and 3‐hydroxybutyrylcarnitine. Serum samples were analysed for urea and creatinine. Generally, MP (i.e. ratio SAM:SAH) increased throughout gestation (p = 0.009), but strongly fluctuated in the period around parturition and weaning. From d108 to parturition, absolute plasma levels of SAM (p < 0.001), SAH (p = 0.031) and methionine (p = 0.001) increased. The first two weeks of lactation were characterised by an increase in MP (p = 0.039) due to a remaining high value of SAM and a distinct decrease in SAH (p = 0.008). During the last two weeks of lactation, MP decreased (p = 0.038) due to a decrease in SAM (p < 0.001) and a stable value for SAH. The methylation reactions seem to continue after weaning, a period crucial for the follicular and embryonic development of the subsequent litter. This study thus demonstrates that the methylation status fluctuates substantially throughout a sow's reproductive cycle, and further research is needed to identify the factors affecting methylation status.  相似文献   
9.
Pyranose oxidase (P2O) improves wheat flour dough stability and bread quality. We related its effect on dough spread behavior to that on dough and bread crumb structure. Increasing P2O addition levels gradually reduced dough flow. High P2O addition levels further increased dough strength, significantly increased dough cell wall thickness, and decreased bread loaf volume. Taken together, affecting dough spread behavior impacts dough and bread (crumb) structure, and dough structure largely determines bread crumb structure.  相似文献   
10.
Carbon stabilization by macroaggregate-occluded microaggregates (Mm) has been proposed as a principal mechanism for long-term soil organic carbon (SOC) sequestration in temperate alternative agricultural and (af)forested systems. The aim of this study was to evaluate the importance of the Mm fraction for long-term C stabilization in Oxisols and to validate its diagnostic properties for total SOC changes upon changes in land use. Soil samples were taken from the 0-5 and 5-20 cm soil layers of native forest vegetation (NV), conventional tillage (CT) and no-tillage (NT) systems at an experimental site near Passo Fundo and one near Londrina in Southern Brazil. After aggregate-size separations by wet-sieving, macroaggregate-occluded water-stable microaggregates (53-250 μm) (Mm) were isolated from large (>2000 μm) and small (>250 μm) macroaggregates. Particulate organic matter located inside the Mm (intra-Mm-POM) and the mineral fraction (< 53 μm) associated with the Mm (mineral-Mm) were separated from the POM fraction located outside the Mm (inter-Mm-POM) by density flotation followed by mechanical dispersion. Sand-free Mm-C concentrations on a macroaggregate basis were generally greater under NV and NT compared to CT in the 0-5 cm depth at both sites. Our findings support the importance of Mm (especially the mineral-Mm fraction) as long-term C-stabilization sites in highly weathered tropical soils under sustainable agricultural and natural systems. At both sites, significant differences in total SOC stocks (g C m−2) among different land use systems were always accompanied by parallel Mm-C stock differences. Though total SOC did not differ among land use systems in the 0-20 cm depth at both sites, Mm-C stocks were greater under NT compared to the CT treatment in the 0-20 cm depth at the Londrina site. We concluded that in these highly weathered tropical soils the Mm-C fraction is a more responsive fraction to management changes than total SOC and represents a diagnostic fraction for present as well as potential total SOC changes upon land-use change.  相似文献   
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