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1. Predation‐exclusion experiments have highlighted that top‐down control is pervasive in terrestrial communities, but most of these experiments are simplistic in that they only excluded a single group of predators and the effect of removal was evaluated on a few species from the community. The main goal of our study was to experimentally establish the relative effects of ants and birds on the same arthropod assemblage of canopy trees. 2. We conducted 1‐year long manipulative experiments in an organic citrus grove intended to quantify the independent effects of bird and ant predators on the abundance of arthropods. Birds were excluded with plastic nets whereas ants were excluded with sticky barriers on the trunks. The sticky barrier also excluded other ground dwelling insects, like the European earwig Forficula auricularia L. 3. Both the exclusion of ants and birds affected the arthropod community of the citrus canopies, but the exclusion of ants was far more important than the exclusion of birds. Indeed, almost all groups of arthropods had higher abundance in ant‐excluded than in control trees, whereas only dermapterans were more abundant in bird‐excluded than in control trees. A more detailed analysis conducted on spiders also showed that the effect of ant exclusion was limited to a few families rather than being widespread over the entire diverse spectrum of spiders. 4. Our results suggest that the relative importance of vertebrate and invertebrate predators in regulating arthropod populations largely depends on the nature of the predator–prey system.  相似文献   
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Hematopoietic neoplasia other than lymphoma and leukemia is uncommon among non-human primates. Herein, we provide the first evidence of occurrence of leukemic histiocytic sarcoma in a captive common squirrel monkey with Saimiriine Gammaherpesvirus 2 (Rhadinovirus), Saimiri sciureus lymphocryptovirus 2 (Lymphocryptovirus), and Squirrel monkey retrovirus (β-Retrovirus) coinfection.  相似文献   
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We have determined the plasma (p) concentration of gamma-aminobutyric acid (GABA) and the dopamine metabolite homovanillic acid (HVA), and the pHVA/pGABA ratio in schizophrenic and bipolar patients. The research was undertaken in a geographic area with an ethnically homogeneous population. The HVA plasma concentrations were significantly elevated in the schizophrenic patients compared to the bipolar patients. The levels of pGABA was significantly lower in the two groups of patients compared to the control group, while the pHVA/pGABA ratio was significantly greater in the both groups of patients compared to the controls. As the levels of pHVA and pGABA are partially under genetic control it is better to compare their concentrations within an homogeneous population. The values of the ratio pHVA/pGABA are compatible with the idea of an abnormal dopamine-GABA interaction in schizophrenic and bipolar patients. The pHVA/pGABA ratio may be a good peripheral marker in psychiatric research.  相似文献   
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Amphibians may be critically challenged by aquatic contaminants during their embryonic development. Many classes of compounds, including organophosphorus pesticides, are able to cause oxidative stress that affects the delicate cellular redox balance regulating tissue modeling. We determined the progression of antioxidant defenses during the embryonic development of the South American common toad, Bufo arenarum. Superoxide dismutase (SOD) and catalase (CAT) activities were high in the unfertilized eggs, and remained constant during the first stages of development. SOD showed a significant increase when the gills were completely active and opercular folds began to form. Reductase (GR) activity was low in the oocytes and increased significantly when gills and mouth were entirely developed and the embryos presented a higher exposure to pro-oxidant conditions suggesting an environmental control. Reduced glutathione (GSH) content was also initially low, and rose continuously pointing out an increasing participation of GSH-related enzymes in the control of oxidative stress. GSH peroxidases and GSH-S-transferases showed relatively high and constant activities, probably related to lipid peroxide control. B. arenarum embryos have plenty of yolk platelets containing lipids, which provide the energy and are actively transferred to the newly synthesized membranes during the early embryonic development. Exposure to the pro-oxidant pesticide malathion during 48 h did not significantly affect the activity of antioxidant enzymes in early embryos, but decreased the activities of CAT, GR, and the pool of GSH in larvae. Previous work indicated that lipid peroxide levels were kept low in malathion-exposed larvae, thus we conclude that oxidative stress is overcome by the antioxidant defenses. The increase in the antioxidant metabolism observed in the posthatching phase of development of B. arenarum embryo, thus constitutes a defense against natural and human-generated pro-oxidants present in the aquatic environment.  相似文献   
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The location of major quantitative trait loci (QTL) contributing to stem and leaf [Na+] and [K+] was previously reported in chromosome 7 using two connected populations of recombinant inbred lines (RILs) of tomato. HKT1;1 and HKT1;2, two tomato Na+‐selective class I‐HKT transporters, were found to be closely linked, where the maximum logarithm of odds (LOD) score for these QTLs located. When a chromosome 7 linkage map based on 278 single‐nucleotide polymorphisms (SNPs) was used, the maximum LOD score position was only 35 kb from HKT1;1 and HKT1;2. Their expression patterns and phenotypic effects were further investigated in two near‐isogenic lines (NILs): 157‐14 (double homozygote for the cheesmaniae alleles) and 157‐17 (double homozygote for the lycopersicum alleles). The expression pattern for the HKT1;1 and HKT1;2 alleles was complex, possibly because of differences in their promoter sequences. High salinity had very little effect on root dry and fresh weight and consequently on the plant dry weight of NIL 157‐14 in comparison with 157‐17. A significant difference between NILs was also found for [K+] and the [Na+]/[K+] ratio in leaf and stem but not for [Na+] arising a disagreement with the corresponding RIL population. Their association with leaf [Na+] and salt tolerance in tomato is also discussed.  相似文献   
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Anguiano M  Nowak RJ  Lansbury PT 《Biochemistry》2002,41(38):11338-11343
Islet amyloid polypeptide (IAPP) and insulin are copackaged and cosecreted by pancreatic islet beta-cells. Non-insulin-dependent (type II) diabetes mellitus (NIDDM) is characterized by dysfunction and depletion of these beta-cells and also, in more than 90% of patients, amyloid plaques containing fibrillar IAPP. An aggregated but not necessarily fibrillar form of IAPP is toxic in cell culture, suggesting that prefibrillar oligomeric (protofibrillar) IAPP may be pathogenic. We report here that IAPP generates oligomeric species in vitro that are consumed as beta-sheet-rich fibrils grow. Protofibrillar IAPP, like protofibrillar alpha-synuclein, which is implicated in Parkinson's disease pathogenesis, permeabilizes synthetic vesicles by a pore-like mechanism. The formation of the IAPP amyloid pore is temporally correlated to the formation of early IAPP oligomers and its disappearance to the appearance of amyloid fibrils. Neither pores nor oligomers were formed by the nonfibrillogenic rat IAPP variant. The IAPP amyloid pore may be critical to the pathogenic mechanism of NIDDM, as other amyloid pores may be to Alzheimer's disease and Parkinson's disease.  相似文献   
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