排序方式: 共有52条查询结果,搜索用时 15 毫秒
21.
22.
23.
Chen D Albuquerque IF Baublis VV Bondar NF Carrigan RA Cooper PS Lisheng D Denisov AS Dobrovolsky AV Dubbs T Endler AM Escobar CO Foucher M Golovtsov VL Goritchev PA Gottschalk H Gouffon P Grachev VT Khanzadeev AV Kubantsev MA Kuropatkin NP Lach J Lang Pengfei Lebedenko VN Li Chengze Li Yunshan Mahon JR McCliment E Morelos A Newsom C Pommot Maia MC Samsonov VM Schegelsky VA Shi Huanzhang Smith VJ Sun CR Tang Fukun Terentyev NK Timm S Tkatch II Uvarov LN Vorobyov AA Yan Jie Zhao Wenheng 《Physical review letters》1992,69(23):3286-3289
24.
Foucher M Albuquerque IF Bondar NF Carrigan R Chen D Li Chengze Cooper PS Denisov AS Dobrovolsky AV Dubbs T Endler AM Escobar CO Tang Fukun Golovtsov VL Goritchev PA Gottschalk H Gouffon P Grachev VT Shi Huanzhang Yan Jie Khanzadeev AV Kubantsev MA Kuropatkin NP Lach J Luksys M Lebedenko VN Dai Lisheng Mahon JR McCliment E Morelos A Newsom C Lang Pengfei Pommot Maia MC Samsonov VM Zheng Shuchen Smith VJ Terentyev NK Timm S Tkatch II Uvarov LN Vorobyov AA Zhao Wenheng Zhong Yuanyuan 《Physical review letters》1992,68(20):3004-3007
25.
Robert M. Adlington Jack E. Baldwin William MC Coull Gareth J. Pritchard Christopher J. Schofield Nicholas J. Westwood 《合成通讯》2013,43(21):3803-3813
N-Arylsulfonylation of 2-azetidinones can lead to the diastereoselective formation of oligomerization products. However, a simple increase of arylsulfonyl chloride concentration minimized oligomerization and allowed preparation of 1-arylsulfonyl-2-azetidinones in good yield. 相似文献
26.
Lelio Zoccolillo Carlo Abete Luca Amendola Roberta Ruocco Andrea Sbrilli Marco Termine 《International journal of environmental analytical chemistry》2013,93(6-7):513-522
Aqueous matrices from Antarctica were analysed for three volatile chlorinated hydrocarbons (VCHCs): tetrachloromethane (CCl4), trichloroethylene (C2HCl3) and tetrachloroethylene (C2Cl4). The matrices analysed were snow from Rennick Nèvè and Rennick Glacier sampled during the Italian Expeditions of 1995/96 and 1996/97, respectively, and seawater, pack ice, sea-microlayer, subsuperficial water and freshwater, collected during the Italian Expedition of 1997/98. Extractions from the aqueous matrices were carried out in Antarctica (the laboratories of the Italian Base, Terra Nova Bay). Because of the critical space–time conditions in these laboratories, an extraction procedure was developed, suitable for large volumes of water (10?L), in order to combine the extraction of other classes of organic compounds (polychlorinated biphenyls, polycyclic aromatic hydrocarbons and chlorinated pesticides) with those of our direct interest. The VCHC organic extracts were analysed in Italy by GC-ECD and GC-MS. The analyses confirmed the presence of the three halocarbons in Antarctica in quantities ranging from units to some dozens of nanograms per kilogram. The results were evaluated with respect to the local distribution of these compounds and their diffusion on a global scale. 相似文献
27.
The behaviour of the total energy for a semi-infinite piezoelectricbeam, with uniform or variable cross-section, in dynamical conditionsis investigated. Precisely, we obtain some estimates in termsof the data for the energy of the portion of the body at distancegreater than z from the base and for its norm in L1(0,t) (wheret is an arbitrary positive time). We obtain some estimates whichdepend on the initial data if t z/V (where V is a computablepositive material constant); if t > z/V, by using also theKorn inequality, we show that the bounds depend on all the data.Under mild hypotheses on the initial data we derive the asymptoticbehaviour of the energy as z +. All possible combinations ofboundary conditions are examined and the kind of the estimateis formally the same for all the problems whether the beam isa cylinder or not. 相似文献
28.
We study a model for the gel degradation by an enzyme, where the gel is schematized as a cubic lattice, and the enzyme as a random walker, that cuts the bonds over which it passes. The model undergoes a (reverse) percolation transition, which for low density of enzymes falls in a universality class different from random percolation. In particular, we have measured a gel fraction critical exponent beta=1.0+/-0.1, in excellent agreement with experiments made on the real system. 相似文献
29.
M. POPEM. MAGNUSSON R. LUNDSTRÖMC. HULSHOF J. VERBEEKM. BOVENZI 《Journal of sound and vibration》2002,253(1):131-167
There is strong epidemiological evidence that occupational exposure to WBV is associated with an increased risk of low back pain (LBP), sciatic pain, and degenerative changes in the spinal system, including lumbar intervertebral disc disorders. A prototype health surveillance scheme for WBV is presented in this paper. Surveillance is the collection, analysis, and dissemination of data for the purpose of prevention. The aims are to assess health status and diagnose vibration-induced disorders at an early stage, to inform the workers on the potential risk associated with vibration exposure, to give preventive advice to employers and employees and to control whether preventive measures which have been taken, were successful. It is suggested that a pre-placement health examination should be offered to each worker who will be exposed to WBV so as to make the worker aware of the hazards, to obtain baseline health data, and to identify medical conditions that may increase the risk due to WBV. The case history should focus on personal history, work history, and leisure activities involving driving of vehicles. The personal medical history should detail back pain complaints, disorders in the spine, any injuries or surgery to the musculoskeletal system. A physical examination on the lower back should be performed on workers who have experienced LBP symptoms over the past 12 months. The preplacement examination should be followed by periodic health reassessment with a regular interval according to the legislation of the country. It is suggested that periodic medical examination should be made available at least every 2 years to all workers who are exposed to WBV. Any change in vibration exposure at the workplace should be reported by the employer. If an increase in vibration exposure or a change in health status have occurred, the medical re-examination should be offered at shorter intervals at the discretion of the attending physician. There should be a periodic medical examination, which includes recording any change in exposure to WBV. The findings for the individual should be compared with previous examinations. Group data should also be compiled periodically. Medical removal may be considered along with re-placement in working practices without exposure to WBV. This paper presents opinions on health surveillance for whole-body vibration developed within a working group of partners funded on a European Community Network (BIOMED2 concerted action BMH4-CT98-3251: Research network on detection and prevention of injuries due to occupational vibration exposures). The health surveillance protocol and the draft questionnaire with explanation comments are presented for wider consideration by the science community and others before being considered appropriate for implementation. 相似文献
30.
Alajarin M Vidal A Tovar F Ramirez De Arellano MC Cossio FP Arrieta A Lecea B 《The Journal of organic chemistry》2000,65(22):7512-7515
Efficient 1,4-asymmetric induction has been achieved in the highly stereocontrolled intramolecular [2 + 2] cycloadditions between ketenimines and imines, leading to 1,2-dihydroazeto[2, 1-b]quinazolines. The chiral methine carbon adjacent to the iminic nitrogen controls the exclusive formation of the cycloadducts with relative trans configuration at C2 and C8. The stepwise mechanistic model, based on theoretical calculations, fully supports the stereochemical outcome of these cycloadditions. 相似文献