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文章通过对内蒙古大兴安岭林区培育大径材的目的、意义、必要性及方法等方面的分析,论述了大径级材培育是促进林区生态、经济和社会协调发展的有力措施。 相似文献
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We propose an isotopic fractionation mechanism, based on photolytic destruction, to explain the 15N/14N and 18O/16O fractionation of stratospheric nitrous oxide (N2O) and reconcile laboratory experiments with atmospheric observations. The theory predicts that (i) the isotopomers 15N14N16O and 14N15N16O have very different isotopic fractionations in the stratosphere, and (ii) laboratory photolysis experiments conducted at 205 nanometers should better simulate the observed isotopic fractionation of stratospheric N2O. Modeling results indicate that there is no compelling reason to invoke a significant chemical source of N2O in the middle atmosphere and that individual N2O isotopomers might be useful tracers of stratospheric air parcel motion. 相似文献
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Optical emission from individual strained indium arsenide (InAs) islands buried in gallium arsenide (GaAs) was studied. At low excitation power density, the spectra from these quantum dots consist of a single line. At higher excitation power density, additional emission lines appeared at both higher and lower energies, separated from the main line by about 1 millielectron volt. At even higher excitation power density, this set of lines was replaced by a broad emission peaking below the original line. The splittings were an order of magnitude smaller than the lowest single-electron or single-hole excited state energies, indicating that the fine structure results from few-particle interactions in the dot. Calculations of few-particle effects give splittings of the observed magnitude. 相似文献
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AC Assis Neto FTV Pereira TC Santos CE Ambrosio R Leiser MA Miglino 《Reproduction in domestic animals》2010,45(5):760-772
The study is based on 141 pregnant Bos indicus cows, from days 20 to 70 post‐insemination. First, special attention was given to the macroscopically observable phenomena of attachment of the conceptus to the uterus, i.e. the implantation, from about days 20 to 30 post‐insemination up to day 70, and placentome development by growth, vascularization and increase in the number of cotyledons opposite to the endometrial caruncles. Secondly, as for the conceptuses, semiquantitative, statistical analyses were performed of the lengths of chorio‐allantois, amnion and yolk sac; and the different parts of the centre and two extremes of the yolk sacs were also analysed. Thirdly, the embryos/foetuses corresponding to their membranes were measured by their greatest length and by weight, and described by the appearance of external developmental phenomena during the investigated period like neurulation, somites, branchial arcs, brain vesicles, limb buds, C‐form, pigmented eye and facial grooves. In conclusion, all the data collected in this study from days 20 to 70 of bovine pregnancy were compared extensively with corresponding data of the literature. This resulted in an ‘embryo/foetal age‐scale’, which has extended the data in the literature by covering the first 8 to 70 days of pregnancy. This age‐scale of early bovine intrauterine development provides model for studies, even when using slaughtered cows without distinct knowledge of insemination or fertilization time, through macroscopic techniques. This distinctly facilitates research into the cow, which is now being widely used as ‘an experimental animal’ for testing new techniques of reproduction like in vitro fertilization, embryo transfer and cloning. 相似文献
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CE Short 《Veterinary anaesthesia and analgesia》2005,32(4):16-17
There was only limited emphasis on anesthesia and pain management in veterinary colleges in Russia until the last ten years. There is now great interest in improvement by Russia practitioners. This effort is hampered by the lack of approved and available medications and limited instructions. At this time, the small animal practitioners have tranquilizers, alpha2 agonists local anesthetics and NSAID's for their use. Propofol is available through pharmacies and efforts are being made for veterinarians to use ketamine. Only a few practices have inhalant anesthetic units and halothane. During a recent lecture tour of Russia, general clinical principles and specific anesthetic and pain management protocols were taught. The audience, primarily young and progressive veterinarians, actively participated and showed great desire to practice quality anesthesia and pain management for their patients. Teaching young veterinarians how to manage their cases without the availability of opioids, ketamine advanced anesthetic equipment and monitors was indeed challenging. Protocols for perioperative management consisting of medetomidine with or without local anesthesia followed by carprofen for post-operative pain is an improvement. We sometimes spend so much time discussing which of many drug combinations we will use but seldom consider what we would do if we were practicing our specialty in parts of the world where we would have to modify dosages and combinations to achieve humane care with few drug choices. 相似文献
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A 5-month-old female Rottweiler dog was diagnosed to have a neurodegenerative disease that has been recently report ed in Rottweilers from North America and Europe. The dog was presented with progressive signs of ataxia, tetraparesis and inspiratory stridor. The clinical investigation included analysis of CSF, radiography, myelography and electrophysiolog-ical testing. No evidence of vertebral malformation or inflammatory CNS disease was identified. Bilateral laryngeal paraly sis was identified in the lightly anaesthetised dog. Electromyography showed abnormal spontaneous activity from the intrin sic musculature of the larynx. At necropsy there were no gross abnormalities of the nervous system but there was atrophy of the dorsal cricoarytenoid muscles of the larynx. There were widespread histological abnormalities throughout the ner vous system including neuronal vacuolation, spongiform changes in the neuropil and axonal degeneration which was most prominent in the spinal cord. These clinical and pathological findings are consistent with the diagnosis of a new neurode-generative disease reported from North America and Europe. This diagnosis is of particular significance in Australia where transmissible spongiform encephalopathies have not been identified. 相似文献
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