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961.
Athinodoros Bandis Paul T. Inglefield Alan A. Jones Wen-Yang Wen 《Journal of Polymer Science.Polymer Physics》1995,33(10):1505-1514
The self-diffusion coefficients of toluene in polyisobutylene have been analyzed using the Vrentas-Duda free volume diffusion model. The diffusion coefficients were determined at different temperatures and concentrations, using the pulsed field gradient nuclear magnetic resonance technique. The data were satisfactorily described by the model and the size of the polymer jumping unit was extracted. Comparisons were made with the Fujita free volume theory and the Fujita free volume parameters were extracted from the Vrentas-Duda free volume parameters. From the diffusion data that now available, it can be concluded that for most polymers the jumping unit is about 1.5 times the polymer monomer molecular weight. The activation energy of the toluene diffusion in polyisobutylene is compared with the activation energies of other penetrants in the same polymer. The diffusion data presented in this work show that the energy per mole required to overcome the attractive forces which constrain a diffusing species to its neighbors should be considered to be zero, in order to be able to extract the free volume parameters (from viscosity and diffusion data) with an acceptable uncertainty. ©1995 John Wiley & Sons, Inc. 相似文献
962.
Dynamical systems with nonlinear damping show interesting behavior in the periodic and chaotic phases. The Froude pendulum
with cubical and linear damping is a paradigm for such a system. In this work the driven Froude pendulum is studied by the
harmonic balancing method; the resulting nonlinear response curves are studied further for resonance and stability of symmetric
oscillations with relatively low damping. The stability analysis is carried out by transforming the system of equations to
the linear Mathieu equation. 相似文献
963.
Stefan Siegmund 《Journal of Differential Equations》2002,178(2):541-573
We extend Henry Poincarés normal form theory for autonomous differential equations x=f(x) to nonautonomous differential equations x=f(t, x). Poincarés nonresonance condition λj−∑ni=1 ?iλi≠0 for eigenvalues is generalized to the new nonresonance condition λj∩∑ni=1 ?iλi=∅ for spectral intervals. 相似文献
964.
F. de Luca A. Crescenzi B. Maraviglia B. C. de Simone R. Campanella C. Casieri M. Luzzi 《Il Nuovo Cimento D》1988,10(1):31-41
Summary An analysis of the effect ofB
1 inhomogeneity on spin density andT
1 contrasted images is here given. Distortions both in saturation recovery and inversion recovery sequences are found. The
impact of these distortions onin vivo spectroscopy, where quantitative data are required, is also discussed. In general, these aspects are found to be reduced
at shortertime parameters of the pulse sequences.
Work partially supported by Progetto Finalizzato Tecnologie Biomediche of CNR and by Esacontrol, Genova. 相似文献
965.
Boris N. Khlebtsov Nikolai G. Khlebtsov 《Journal of Quantitative Spectroscopy & Radiative Transfer》2007,107(2):306-314
On the basis of the T-matrix formalism and numerical simulations, we derive an explicit rule for partial multipole contributions to the plasmon resonances of gold nanorods at a fixed or random orientation. The parity of a given spectral resonance number n coincides with the parity of their multipole contributions l, where l is equal to or greater than n, and the total resonance magnitude is determined by the lowest multipole contribution. We also investigate the dependence of multipole plasmons on the size, shape, and orientation of nanorods with respect to the polarized incident light. It is shown that the multipole resonance wavelengths as a function of the aspect ratio divided by the resonance number collapse onto one linear scaling curve. This scaling is explained by using the plasmon standing wave concept introduced by Schider et al. [Plasmon dispersion relation of Au and Ag nanowires. Phys Rev B 2003;68:155427]. 相似文献
966.
Electron cyclotron resonance (ECR) plasma is produced and studied in a small cylindrical system. Microwave power is delivered
by a CW magnetron at 2.45 GHz in TE10 mode and launched radially to have extraordinary (X) wave in plasma. The axial magnetic field required for ECR in the system
is such that the first two ECR surfaces (B = 875.0 G andB = 437.5 G) reside in the system. ECR plasma is produced with hydrogen with typical plasma density ne as 3.2 × 1010 cm-3 and plasma temperature Te between 9 and 15 eV. Various cut-off and resonance positions are identified in the plasma system. ECR heating (ECRH) of the
plasma is observed experimentally. This heating is because of the mode conversion of X-wave to electron Bernstein wave (EBW)
at the upper hybrid resonance (UHR) layer. The power mode conversion efficiency is estimated to be 0.85 for this system. The
experimental results are presented in this paper. 相似文献
967.
Summary Human ceruloplasmin contains several intrinsic copper ions, some of them being paramagnetic. The presence of two classes of
paramagnetic Cu2+ ions (type I and type II) has been suggested, the two types having significantly different spectroscopic features. However,
there are conflicting reports both on the ratio of the number of type-I to type-II Cu2+ and on their EPR spectroscopic parameters. By using a Monte Carlo method we obtained the best fit of the experimental spectrum
with a synthesized composite spectrum generated by two type-I Cu2+ (type I
a
and type I
b
, possessing slightly different spin Hamiltonian parameters) and by one type-II Cu2+. Correspondingly, the EPR spectroscopic parameter (viz. theg-tensors, hyperfine couplings, line widths and molar fractions) together with their accuracies were determined.
Riassunto La ceruloplasmina umana contiene diversi ioni Cu2+ alcuni dei quali sono paramagnetici. Di questi ne sono stati ipotizzati due tipi (tipo I e tipo II), ognuno dei quali con caratteristiche spettroscopiche diverse. Tuttavia esistono nei lavori precedenti discordanze sia sul numero di ioni Cu2+ che sui loro parametri EPR. Si è usato il metodo Montecarlo per ottenere il best fit dello spettro EPR della ceruloplasmina. Lo spettro simulato è risultato la somma di tre spettri, 2 di tipo I (tipo I a e tipo I b ) e 1 di tipo II. Sono stati così determinati i parametri relativi all'hamiltoniana di spin del sistema e le loro deviazioni standard.
Резюме Человеческий церулоплазмин содержит несколяко собственных ионов меди, некоторые из которых являются парамгнитными. Предполагается наличие двух классов парамгнитных Cu2+ ионов (тип I и тип II). Эти два типа имеют существенно различные спектроскопические свойства. Однако имеются противо-речивые публикации об отношении числа ионов Cu2+ типа I к числу ионов Cu2+ типа II и об их ЭПР спектроскопических параметрах. Исполязуя метод Монте-Карло, мы получаем наилучшее согласие экспериментального спектра с синтесированным составным спектром, образованным спектрами Cu2+ типа I (тип I a и тип I b имеющие слегка различные параметры спинового Гамилятониана) и одного спектра Cu2+ типа II. Определяются ЭПР спектроскопические параметы (а именно:g-тензоры, сверхтонкие связи, ширины линий и молярные доли).相似文献
968.
969.
Walter Schempp 《Acta Appl Math》1997,48(2):185-234
Due to its unequalled advantages, the magnetic resonance imaging (MRI) modality has truly revolutionized the diagnosis and evaluation of pathology. Because many morphological anatomic details that may not be visualized by other high tech imaging methods can now be readily shown by diagnostic MRI, it has already become the standard modality by which all other clinical imaging techniques are measured. The unique quantum physical basis of the MRI modality combined with the imaging capabilities of current computer technology has made this imaging modality a target of interdisciplinary interest for clinicians, physicists, biologists, engineers, and mathematicians. Due to the fact that MRI scanners perform corticomorphic processing, this modality is by far more complex than all the other high tech clinical imaging techniques. The purpose of this paper is to outline a phase coherent wavelet approach to Fourier transform MRI. It is based on distributional harmonic analysis on the Heisenberg nilpotent Lie group G and the associated symplectically invariant symbol calculus of pseudodifferential operators. The contour and contrast resolution of MRI scans which is controlled by symplectic filter bank processing gives the noninvasive MRI modality superiority over X-ray computed tomography (CT) in soft tissue differentiation. 相似文献
970.