排序方式: 共有50条查询结果,搜索用时 15 毫秒
21.
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
22.
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
23.
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
24.
Serena Gabrielli Alessandro Palmieri Deepak S. Panmand Daniela Lanari Luigi Vaccaro Roberto Ballini 《Tetrahedron》2012,68(39):8231-8235
The reaction of ylidene malononitriles with β-nitroacrylates, in Et3N/MeCN, affords the one-pot synthesis of a new class of penta-substituted, densely functionalized anilines in satisfactory to good overall yields. The method represents a very important improvement of the recent strategy for the preparation of anilines from conjugated nitroalkenes. 相似文献
25.
A new solvent-free, TBD-catalyzed protocol for the synthesis of 3-formyl-2H-chromenes is presented. Substituted salicylaldehydes 1 and 3-methyl-2-butenal 2 in the presence of 10 mol % of TBD underwent a domino oxa Michael/aldol reaction to effectively yield the corresponding 2H-chromene derivatives 3. The methodology represents an improvement either in terms of efficiency and sustainability as a small amount of catalyst is required and the work-up procedure is simple and straightforward. 相似文献
26.
Hou H Leung KC Lanari D Nelson A Stoddart JF Grubbs RH 《Journal of the American Chemical Society》2006,128(48):15358-15359
A trifurcated template, containing three secondary dialkylammonium ion recognition sites for encirclement by a dibenzo [24]crown-8-containing acyclic diene, is used to promote acyclic diene metatheses (ADMET) catalyzed by ruthenium-alkylidene complexes, affording a cyclic trimer in 55% yield. Following this one-step, threefold ADMET reaction, the resulting cyclic trimer was isolated by preparative HPLC and characterized by NMR spectroscopy and mass spectrometry. 相似文献
27.
South CR Higley MN Leung KC Lanari D Nelson A Grubbs RH Stoddart JF Weck M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(14):3789-3797
Poly(norbornene)-based block copolymers containing side chains of palladated pincer complexes/dibenzo[24]crown-8 or palladated pincer complexes/dibenzylammonium salts were synthesized. Noncovalent functionalization was accomplished with their corresponding recognition units through simple 1:1 addition with association constants (Ka) greater than 10(5) m(-1). The self-assembly processes were monitored by using both 1H NMR spectroscopy and isothermal titration calorimetry. In all cases, we found that the self-assembly of the recognition units along each polymer block does not preclude the self-assembly processes along the other block. 相似文献
28.
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
29.
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
30.