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131.
J. Crain S. R. Meeker W. J. Hossack R. J. Lavery W. C. K. Poon 《Molecular Crystals and Liquid Crystals》2013,570(1):951-956
Abstract The mechanical properties of concentrated dispersions of sterically-stabilised colloidal particles in nematic hosts are explored using a combination of optical microscopy and viscoelastic shear measurements. Starting from an initially homogeneous dispersion in an isotropic host, it is found that the kinetics of the isotropic-nematic transition lead to the formation of a percolated particle network that imparts surprising mechanical rigidity to the resulting colloid/liquid crystal composite. Specifically, the viscoelastic storage modulus G′ is observed to rise by approximately 5 orders of magnitude within a few degrees of the bulk isotropic-nematic transition temperature. Using 4-4′pentyl cyano-biphenyl as the solvent, the composite at room temperature is a self-supporting soft solid over a wide range of particle concentrations. The particle microstructure depends sensitively on thermal treatment and particle concentration and it is found that faster cooling enhances the visoelastic moduli of the composite. Also, several classes of network topology have been identified. In all cases studied to date, the particles can be redispsersed upon heating the solvent through the nematic-isotropic transition. The formation of the composite is therefore thermally reversible. A rigorous theory to account for the observed mechanical properties is not currently available. 相似文献
132.
Chuen Y. Poon Julie M. Edwards C. John Evans Ashley D. Harris Beverly Tsai-Goodman Charlotte E. Bolton John R. Cockcroft Richard G. Wise Sailesh Kotecha 《Magnetic resonance imaging》2013
Purpose
To assess the feasibility of measuring pulmonary artery (PA) pulse wave velocity (PWV) in children breathing ambient air and 12% oxygen.Methods
Velocity-encoded phase-contrast MR images of the PA were acquired in 15 children, aged 9–12 years, without evidence of cardiac or pulmonary diseases. PWV was derived as the ratio of flow to area changes during early systole. Each child was scanned twice, in air and after at least 20 minutes into inspiratory hypoxic challenge. Intra-observer and inter-observer variability and repeatability were also compared.Results
PA PWV, which was successfully measured in all subjects, increased from 1.31 ± 0.32 m/s in air to 1.61 ± 0.58 m/s under hypoxic challenge (p = 0.03). Intra- and inter-observer coefficients of variations were 9.0% and 15.6% respectively. Good correlation within and between observers of r = 0.92 and r = 0.72 respectively was noted for PA PWV measurements. Mean (95% limit of agreement) intra- and inter-observer agreement on Bland–Altman analysis were − 0.02 m/s (− 0.41–0.38 m/s) and -0.28 m/s (− 1.06–0.49 m/s).Conclusion
PA PWV measurement in children using velocity-encoded MRI is feasible, reproducible and sufficiently sensitive to detect differences in PA compliance between normoxia and hypoxia. This technique can be used to detect early changes of PA compliance and monitor PAH in children. 相似文献133.
134.
Gang Chen Miguel A. Modestino Billy K. Poon André Schirotzek Stefano Marchesini Rachel A. Segalman Alexander Hexemer Peter H. Zwart 《Journal of synchrotron radiation》2012,19(5):695-700
A fluctuation X‐ray scattering experiment has been carried out on platinum‐coated gold nanoparticles randomly oriented on a substrate. A complete algorithm for determining the electron density of an individual particle from diffraction patterns of many particles randomly oriented about a single axis is demonstrated. This algorithm operates on angular correlations among the measured intensity distributions and recovers the angular correlation functions of a single particle from measured diffraction patterns. Taking advantage of the cylindrical symmetry of the nanoparticles, a cylindrical slice model is proposed to reconstruct the structure of the nanoparticles by fitting the experimental ring angular auto‐correlation and small‐angle scattering data obtained from many scattering patterns. The physical meaning of the refined structure is discussed in terms of their statistical distributions of the shape and electron density profile. 相似文献
135.
Besseling R Isa L Ballesta P Petekidis G Cates ME Poon WC 《Physical review letters》2010,105(26):268301
We report experiments on hard-sphere colloidal glasses that show a type of shear banding hitherto unobserved in soft glasses. We present a scenario that relates this to an instability due to shear-concentration coupling, a mechanism previously thought unimportant in these materials. Below a characteristic shear rate γ(c) we observe increasingly nonlinear and localized velocity profiles. We attribute this to very slight concentration gradients in the unstable flow regime. A simple model accounts for both the observed increase of γ(c) with concentration, and the fluctuations in the flow. 相似文献
136.
A optical filter based on Sagnac interferometer was proposed to be acted as a comb filter with equal frequency spacing and
good signal to noise ratio (SNR), which was composed of an 8.14 m stress-induced Hi-Bi (high-birefringence) PM (polarization-maintaining)
fiber. Using this multi-wavelength Sagnac comb filter and a gain flattening Sagnac filter that made the output spectra flattening
at different pump powers, a 25-channel multi-wavelength all-fiber source were successfully generated with channel spacing
of 0.8 nm with respect to the center wavelength at 1550 nm and flattened gain about ±1 dB peak deviation. The channel spacing
can be further reduced to 0.4 nm to produce a DWDM (dense wavelength division multiplexing) source, simply by increasing the
Hi-Bi fiber to be 16.28 m. It can be used in many applications such as WDM (wavelength division multiplexing), optical amplifiers
with a high SNR, narrow band filters and optical sensors. 相似文献
137.
Here we obtain various results on the class of axially symmetric harmonic maps from B 3 to S 2. We find some new classes of non-minimizing harmonic maps exhibiting unusual singular behavior. Optimal partial regularity estimates are obtained for mappings which minimize, among axially symmetric maps, various relaxed energies which have been studied in [4]and [11]. 相似文献
138.
Ting-Chung Poon Kyu B. Doh Bradley Schilling Kazunori Shinoda Yoshiji Suzuki Ming Hsien Wu 《Optical Review》1997,4(5):567-571
Three-dimensional (3-D) or holographic information extracted by two-dimensional active optical heterodyne scanning has been demonstrated recently. The technique is called optical scanning holography. To reconstruct the obtainable 3-D holographic information, digital techniques have been used and demonstrated. For real-time applications, we need to investigate spatial-light-modulator-based systems. In this paper, we first briefly review optical scanning holography, and then present experimental results of 3-D image reconstruction using an electron-beam-addressed spatial light modulator. 相似文献
139.
A prototype of an optical-electronic histogram generator has been designed and tested for one-dimensional objects. In this scheme, the object to be analysed is laser scanned. The resulting optical signal is detected by a photodetector, which generates an electrical signal output that is subsequently analysed with a combination of analogue and digital electronics. The system is shown to be fairly modular in design. Various aspects of the extension of the design to two dimensions are discussed. 相似文献
140.
Apomyoglobin was chosen as a model to study the emulsifying properties of proteins. It was cleaved into three peptides using cyanogen bromide and these peptides were purified and tested for emulsifying and interfacial properties. Two of the peptides had improved emulsifying activity compared to the whole protein. The peptide (residues 1-55) with the highest emulsifying activity and whole apomyoglobin were studied further. The amount of protein or peptide adsorbed at the oil-water interface of an emulsion was measured and the surface area occupied per molecule was calculated. For apomyoglobin, at maximal surface coverage each molecule occupied a surface area of approximately 8 nm2. This is consistent with a packed monolayer, based on the approximate dimensions of apomyoglobin. For peptide (1-55), at maximal surface coverage each molecule occupied a surface area of approximately 3 nm2. This is consistent with the area that the two amphipathic alpha-helices which are potentially present in this molecule would cover, if they were aligned along the oil-water interface. The different structural characteristics of these molecules responsible for their emulsifying properties are discussed. Copyright 1999 Academic Press. 相似文献