全文获取类型
收费全文 | 84篇 |
免费 | 1篇 |
国内免费 | 1篇 |
专业分类
化学 | 28篇 |
力学 | 3篇 |
数学 | 7篇 |
物理学 | 48篇 |
出版年
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 4篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2017年 | 3篇 |
2016年 | 1篇 |
2013年 | 7篇 |
2012年 | 2篇 |
2011年 | 5篇 |
2010年 | 2篇 |
2009年 | 2篇 |
2008年 | 2篇 |
2006年 | 5篇 |
2005年 | 2篇 |
2004年 | 3篇 |
2003年 | 1篇 |
2002年 | 25篇 |
2001年 | 6篇 |
1999年 | 1篇 |
1996年 | 1篇 |
1994年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1984年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有86条查询结果,搜索用时 46 毫秒
1.
Emily S. Tepe Ellen S. Deutsch MD Quiana Sampson Stephen Lawless James S. Reilly Robert Thayer Sataloff 《Journal of voice》2002,16(2):244-250
The objective of this study was to determine the incidence of vocal problems in young choir singers and to correlate vocal problems with demographic and behavioral information. A questionnaire addressing vocal habits and hygiene was offered to 571 young choir singers, up to 25 years of age, who sing at least weekly; 129 (22.6%) responded. More than one-half of the respondents had experienced vocal difficulty, particularly older adolescents. Detrimental behaviors and circumstances surveyed were not reflective of the incidence of vocal difficulty, except for morning hoarseness, chronic fatigue, insomnia, and female gender after puberty. Voice care professionals should be aware that self-reported voice difficulties are common among young choral singers, especially postpubescent girls, and children with symptoms consistent with reflux (morning hoarseness) and emotional stress (insomnia). Laryngologists should communicate with choral conductors and singing teachers to enhance early identification and treatment of children with voice complaints, and to develop choral educational strategies that help decrease their incidence. 相似文献
2.
3.
4.
Chloroacetaldehyde reacts with viral M13mp18 single and double stranded DNA to form the highly fluorescent adducts, etheno-AMP and etheno-CMP. Absorbance and fluorescence spectroscopy can be used to monitor and characterize these reactions. Both single and double stranded DNA showed increases in the absorbance following reaction with the aldehyde. The fluorescence also increased in these two groups and continued to rise with increasing time of incubation until a point of saturation was reached. The fluorescence of the double stranded moiety was considerably enhanced following reaction with the aldehyde while that of the single stranded population was not, making this method appropriate for the separation of small quantities of the two populations of DNA. 相似文献
5.
Reza MD. Sultanur Taniguchi Rihito Kaneko Jyunya Oura Yasuji 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(6):2609-2619
Journal of Radioanalytical and Nuclear Chemistry - Instrumental photon activation analysis (IPAA) is nondestructive and multi-elemental analysis method like instrumental neutron activation... 相似文献
6.
Dr. Rebecca Walker Dr. Magdalena Majewska Dr. Damian Pociecha Dr. Anna Makal Prof. John MD Storey Prof. Ewa Gorecka Prof. Corrie T. Imrie 《Chemphyschem》2021,22(5):461-470
A selection of pyrene-based liquid crystal dimers have been prepared, containing either methylene-ether or diether linked spacers of varying length and parity. All the diether linked materials, CBOnO.Py (n=5, 6, 11, 12), exhibit conventional nematic and smectic A phases, with the exception of CBO11O.Py which is exclusively nematic. The methylene-ether linked dimer, CBnO.Py, with an even-membered spacer (n=5) was solely nematogenic, but odd-members (n=6, 8, 10) exhibited both nematic and twist-bend nematic phases. Replacement of the cyanobiphenyl fragment by cyanoterphenyl giving CT6O.Py, gave elevated melting and nematic-isotropic transition temperatures, and SmA and SmCA phases were observed on cooling the nematic phase. Intermolecular face-to-face associations of the pyrene moieties drive glass formation, and all these materials have a glass transition temperature at or above room temperature. The stability of the glassy twist-bend nematic phase allowed for its study using AFM, and the helical pitch length, PTB, was measured as 6.3 and 6.7 nm for CB6O.Py and CB8O.Py, respectively. These values are comparable to the shortest pitch of a twist-bend nematic phase measured to date. 相似文献
7.
Shozo Kawamura Makoto Suzuki Hossain MD. Zahid Hirofumi Minamoto 《Applied Acoustics》2009,70(11-12):1393-1399
Machine condition monitoring and fault diagnosis of rotating machinery are very important because of the wide use of rotating machinery in industry. Couplings and gears are used in many mechanical systems to connect elements and transmit power. The system is usually modeled as a single-degree-of-freedom system with a piecewise linear spring property, where the mass of main machine is only considered. In the present study, the dynamic behavior of a system with an unsymmetrical nonlinearity and a significant mass of the connecting part was investigated both experimentally and by numerical simulation. In the experiment, a 1/3 sub-harmonic oscillation was observed, but this oscillation was not found in the simulation using a single-degree-of-freedom system, in which the mass of the connecting part was ignored. However, when a two-degrees-of-freedom system was used that considered both the mass of the connecting part and the impact property, the 1/3 sub-harmonic oscillation was observed. Thus it is recognized that an adequate mathematical model for diagnosis in the early stage of abnormality must be selected on the basis of the mass ratio between the connecting part and the main body. 相似文献
8.
MD. Daloar Hossain Le Thi Bao Tran Jong Myung Park Kwon Taek Lim 《Journal of polymer science. Part A, Polymer chemistry》2010,48(22):4958-4964
A new, efficient method for synthesizing stable nanoparticles with poly(ethylene oxide) (PEO) functionalities on the core surface, in which the micellization and crosslinking reactions occur in one pot, has been developed. First, amphiphilic PEO‐b‐PS copolymers were synthesized by reversible addition fragmentation chain transfer (RAFT) radical polymerization of styrene using (PEO)‐based trithiocarbonate as a macro‐RAFT agent. The low molecular weight PEO‐b‐PS copolymer was dissolved in isopropyl alcohol where the block copolymer self‐assembled as core‐shell micelles, and then the core‐shell interface crosslink was performed using divinylbenzene as a crosslinking agent and 2,2′‐azobisisobutyronitrile as an initiator. The design of the amphiphilic RAFT agent is critical for the successful preparation of core‐shell interface crosslinked micellar nanoparticles, because of RAFT functional groups interconnect PEO and polystyrene blocks. The PEO functionality of the nanoparticles surface was confirmed by 1H NMR and FTIR. The size and morphology of the nanoparticles was confirmed by scanning electron microscopy, transmission electron microscopy, and dynamic laser light scattering analysis. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
9.
MD. Anwarul Hasan Carlos F. Lange Malcolm L. King 《ournal of non Newtonian Fluid Mechanics》2010,165(21-22):1431-1441
The effect of viscoelastic properties and surface tension of artificial mucus simulant samples on the size distribution and volume concentration of bioaerosol droplets generated during simulated coughing was investigated through in vitro experiments. The mucus simulant samples had viscoelastic properties in a similar range as those of real human airway mucus. The mucus simulant gels were prepared by mixing various proportions of 0.5–1.7% locust bean gum solution and 0.1 M sodium tetraborate (XLB) solution. Surface tension of one set of samples was varied by adding different amounts of SDS (sodium dodecyl sulfate) surfactant while the measurement of surface tension was performed using ADSA (axisymmetric drop shape analysis) method. The viscoelastic properties of the samples were measured using a Bohlin Gemini 200 HR (Malvern, UK) nano-rheometer with peltier plate assembly. An artificial cough machine was used to simulate human cough, generating aerosol droplets in a model trachea attached to the front of the cough machine. The size distribution and volume concentration of the droplets generated through simulated cough were measured using a laser diffraction particle sizer (SprayTec, Malvern, USA). The surface tension was found to have negligible effect on the characteristic of generated droplets within the range of this investigation. The experimental results showed a decrease in particle size as the samples changed from a viscous fluid type to a viscoelastic to an elastic solid type sample. The volume concentration also changed significantly as the viscoelasticity of the samples was varied. 相似文献
10.
We report the electrogenerated chemiluminescence (ECL) of 2,2'-bis(10-phenylanthracen-9-yl)-9,9'-spirobifluorene (spiro-FPA), a dichromophoric molecule composed of two phenylanthracenes linked by a spirobifluorene moiety (PA-X-PA). The results are compared to those for 9,10-diphenylanthracene (DPA), a related molecule with a single chromophore. Cyclic voltammetry (CV) of spiro-FPA shows two reversible, closely spaced, one-electron transfers on both reduction and oxidation, occurring at E(o)(1,red) = -2.02, E(o)(2,red) = -2.07 V vs SCE and E(o)(1,ox) = 1.14, E(o)(2,ox) = 1.20 V vs SCE. The potentials for each pair are close enough to appear as a single peak in CV, indicating that the spirobifluorene moiety interrupts conjugation between the redox centers. The potentials observed are similar to those of DPA, which shows E(o)(red) = -2.06 V vs SCE and E(o)(ox) = 1.15 V vs SCE. The absorbance spectrum of spiro-FPA shows lambda(max,abs) = 377 nm, with 377 = 25,700 M(-1) s(-1), while DPA exhibited lambda(max,abs) = 374 nm, with 374 = 13,800 M(-1) s(-1), demonstrating that spiro-FPA has twice the available chromophores as DPA. Photoluminescence (PL) data for spiro-FPA shows lambda(max,PL) = 434 nm, with Phi(PL) = 0.74, while DPA fluoresces at 420 nm with Phi(PL) = 0.91; thus, there is greater solvent or structural relaxation in the spiro-FPA excited state, which may account for the greater internal conversion. Unlike DPA, the ECL spectrum of spiro-FPA exhibits long-wavelength emission not observed in the PL. We attribute this emission to excimers formed during annihilation ECL. Steric hindrance prevents DPA from forming excimers, even in ECL, but spiro-FPA annihilation can occur between pairs of di-ions (PA(*-)-X-PA(*-) and PA(*+)-X-PA(*+)), which are electrostatically more strongly attracted to one another than the mono-ions. This greater electrostatic attraction may be sufficient to overcome the steric hindrance to excimer formation. Lowering the electrolyte concentration decreases the electrostatic shielding of the ions from one another; thus, the increase in longer wavelength ECL accompanying a decrease in electrolyte concentration supports the role of the di-ions in excimer formation. Additionally, simulations show, consistent with experiment, a more rapid decrease in excimer concentration than in excited monomer concentration as a function of time after each potential pulse. This is probably due to the greater number of scavenging reactions available for di-ions. The simulations are confirmed experimentally when lower potential pulsing frequencies yield lower relative excimer emission. Since an excited state created by one-electron transfer between two di-ions should be rapidly quenched via electron transfer by the other PA moiety, the existence of excimers suggests the possibility of simultaneous, two-electron transfer to generate the excimer. 相似文献