排序方式： 共有44条查询结果，搜索用时 15 毫秒
1.
2.
RP Andres T Bein M Dorogi S Feng JI Henderson CP Kubiak W Mahoney RG Osifchin R Reifenberger 《Science (New York, N.Y.)》1996,272(5266):1323-1325
Double-ended aryl dithiols [alpha,alpha'-xylyldithiol (XYL) and 4,4'-biphenyldithiol] formed self-assembled monolayers (SAMs) on gold(111) substrates and were used to tether nanometer-sized gold clusters deposited from a cluster beam. An ultrahigh-vacuum scanning tunneling microscope was used to image these nanostructures and to measure their current-voltage characteristics as a function of the separation between the probe tip and the metal cluster. At room temperature, when the tip was positioned over a cluster bonded to the XYL SAM, the current-voltage data showed "Coulomb staircase" behavior. These data are in good agreement with semiclassical predictions for correlated single-electron tunneling and permit estimation of the electrical resistance of a single XYL molecule (approximately18 ± 12 megohms). 相似文献
3.
The local effects of isolated magnetic adatoms on the electronic properties of the surface of a superconductor were studied with a low-temperature scanning tunneling microscope. Tunneling spectra obtained near magnetic adsorbates reveal the presence of excitations within the superconductor's energy gap that can be detected over a few atomic diameters around the impurity at the surface. These excitations are locally asymmetric with respect to tunneling of electrons and holes. A model calculation based on the Bogoliubov-de Gennes equations can be used to understand the details of the local tunneling spectra. 相似文献
4.
Miele M Dondero R Ciarallo G Mazzei M 《Journal of agricultural and food chemistry》2001,49(1):517-521
Ocimum basilicum cv. Genovese Gigante is the basil cultivar used the most in the production of a typical Italian sauce called pesto. The aromatic composition of plants at different growth stages was determined. Plants from different areas of northwestern Italy were analyzed at 4 and 6 weeks after sowing and showed methyleugenol and eugenol as the main components. The content of these compounds was correlated with plant height rather than plant age. Particularly, methyleugenol was predominant in plants up to 10 cm in height, whereas eugenol was prevalent in taller plants. These results are important in the evaluation of risk to human health posed by dietary ingestion of methyleugenol contained in pesto. 相似文献
5.
Siani AC Tappin MR Ramos MF Mazzei JL Ramos MC De Aquino Neto FR Frighetto N 《Journal of agricultural and food chemistry》2002,50(12):3518-3521
A new chemotype of the aromatic Verbenaceae species Lippia alba Mill. N. E. Br. from southeastern Brazil has recently been shown to have a high content of linalool in the leaf essential oil. Vegetative propagation of this chemotype was conducted at six different locations in Brazil, and the variation of the content and the optical purity of linalool in the oils were verified. Yields (0.6-0.9%, hydrodistillation), chemical composition, linalool content, and optical purity of the oils from all the plants were compared, using GC-FID, GC-MS, chiral chromatography, and retention index calculation. No plant exceeded the matrix in linalool content (46.5 to 90.7%), and the chemical profile of the oils was the same for all the samples. Purification of linalool to a content close to 100% was effected by vacuum distillation of the crude oil. Chiral analysis showed exclusively the presence of S-linalool in all the crude oils and in the distilled samples. 相似文献
6.
7.
8.
Genetic and antigenic characterization of the matrix protein of two genetically distinct ovine lentiviruses 总被引：1，自引：0，他引：1
Grego E Bertolotti L Carrozza ML Profiti M Mazzei M Tolari F Rosati S 《Veterinary microbiology》2005,106(3-4):179-185
Small Ruminant Lentiviruses (SRLV) are a group of non-oncogenic retroviruses including Maedi-Visna virus (MVV) and Caprine Arthritis-Encephalitis virus (CAEV), which cause a chronic, multisystemic disease in sheep and goats, respectively. Phylogenetic analyses of SRLV are based in most cases on partial pol sequences. Several reports indicate that the species specificity of these viruses is not as strict as previously thought; MVV-like viruses have been found in goat populations and vice versa. Recently, the sequencing of some Italian ovine isolates has shown the presence of a new cluster more similar to classical caprine isolates (CAEV-like). Few data are available on the variability of structural proteins involved in the antibody response of infected animals. In this study, the gag gene of two genetically distinct ovine isolates, namely the MVV-like It-561 and the CAEV-like It-Pi1, was sequenced and the epitopes of matrix protein (MA) were mapped. Recombinant MAs and their subunits from both ovine aforementioned strains were tested against a panel of sheep and goat sera. Reactive epitopes were found in all three subunits of MA, although the central subunit displayed a more consistent reactivity. Epitope mapping of this subunit demonstrated that the amino acid sequence of at least one immunodominant epitope was quite different in the two strains. This antigenic variability may affect the sensitivity of a single strain-based immunoassay and suggests that both SRLV genotypes should be used in the development of future diagnostic tests, to avoid viral strain selection during the eradication programmes. 相似文献
9.
Francesco Tolari Wafa’a Al-Ramadneh Maurizio Mazzei Maria Luisa Carrozza Mario Forzan Patrizia Bandecchi Elena Grego Sergio Rosati 《Tropical animal health and production》2013,45(6):1335-1340
Small ruminant lentiviruses infect sheep and goats worldwide, causing chronic progressive diseases and relevant economic losses. Disease eradication and prevention is mostly based on serological testing. The goal of this research was to investigate the presence of the small ruminant lentiviruses (SRLVs) in Jordan and to characterize the serological response in sheep and goat populations. A panel of sera were collected from flocks located in Northern Jordan and Jordan Valley. The samples were tested using three ELISA assays: a commercially available ELISA based on p25 recombinant protein and transmembrane peptide derived from British maedi–visna virus (MVV) EV1 strain, an ELISA based on P16-P25 recombinant protein derived from two Italian strains representative of MVV- and caprine arthritis encephalitis virus (CAEV)-like SRLVs, and an ELISA based on SU5 peptide from the same two Italian isolates. The results indicate that both MVV- and CAEV-like strains are present in Jordan and that the majority of the viruses circulating among sheep and goat populations belong to the MVV-like genotype. 相似文献
10.
CP Bianchi A Meikle MA Alvarez MA Benavente MV Cavilla E Rodríguez MA Aba 《Reproduction in domestic animals》2013,48(4):681-690
Endometrial expression of oestrogen (ERα), progesterone (PR) and oxytocin receptor (OR) and cyclooxygenase‐2 (COX‐2) was evaluated from the induction of ovulation to luteolysis in llamas. Ovarian activity was daily assessed by ultrasonography in five females. Ovulation was induced immediately after the detection of an ovulatory follicle by a GnRH injection (Day 0). Endometrial samples were obtained by transcervical biopsies from the left and right horns on day 0 and days 4, 8, 10 and 12 post‐GnRH. Blood samples were collected daily for progesterone and estradiol‐17β determinations by RIA. An immunohistochemical technique was used to study receptors population and COX‐2 expression which were then evaluated by two independent observers. The expression of ERα and PR was highest on day 0 in the luminal epithelium and stroma in association with high plasma estradiol‐17β concentrations. Thereafter, a decrease in ERα population was registered on day 4 and a new increase of its expression was observed between days 8 and 12 in those cell types. Conversely, PR population was gradually down‐regulated until its lowest expression was reached on day 10 post‐GnRH in the luminal epithelium. Content of OR was similar throughout the study in all cell types. The expression of COX‐2 was highest from day 8 to 12 post‐GnRH in the luminal epithelium, in relation to the time of maximal PGF2α release. Both steroid receptors populations and COX‐2 expression were similar between horns. Meanwhile, OR expression was higher in the right than in the left uterine horn. In summary, this study showed that the loss of endometrium sensitivity to progesterone by days 8–10 post‐induction of ovulation and the concomitant increase of COX‐2 expression could play a key role in the mechanism of luteolysis and somehow be related to the short corpus luteum lifespan of llamas. 相似文献