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101.
We present a Fourier analysis of multigrid for the two-dimensional discrete convection-diffusion equation. For constant coefficient
problems with grid-aligned flow and semi-periodic boundary conditions, we show that the two-grid iteration matrix can be reduced
via a set of orthogonal transformations to a matrix containing individual 4×4 blocks. This enables a trivial computation of
the norm of the iteration matrix demonstrating rapid convergence in the case of both small and large mesh Peclet numbers,
where the streamline-diffusion discretisation is used in the latter case. We also demonstrate that these results are strongly
correlated with the properties of the iteration matrix arising from Dirichlet boundary conditions.
AMS subject classification (2000) 65F10, 65N22, 65N30, 65N55 相似文献
102.
Per Lötstedt Stefan Söderberg Alison Ramage Lina Hemmingsson-Frändén 《BIT Numerical Mathematics》2002,42(1):134-158
Adaptivity in space and time is introduced to control the error in the numerical solution of hyperbolic partial differential equations. The equations are discretised by a finite volume method in space and an implicit linear multistep method in time. The computational grid is refined in blocks. At the boundaries of the blocks, there may be jumps in the step size. Special treatment is needed there to ensure second order accuracy and stability. The local truncation error of the discretisation is estimated and is controlled by changing the step size and the time step. The global error is obtained by integration of the error equations. In the implicit scheme, the system of linear equations at each time step is solved iteratively by the GMRES method. Numerical examples executed on a parallel computer illustrate the method. 相似文献
103.
104.
Xuefei Zhong Rong Yi Alison E. Holliday David D. Y. Chen 《Rapid communications in mass spectrometry : RCM》2009,23(5):689-697
Three‐dimensional computer models of electrospray ionization sources were constructed in COMSOL Multiphysics? to solve the static electric fields using finite element methods. The magnitude of the electric field strength for onset of electrospray and optimum signal was calculated under various conditions. The modification of the electric field distribution in the ion source by an atmospheric pressure ion lens was also investigated by plotting the equipotential surfaces, electric field lines and trajectories of charged droplets. Both the calculated and the experimental results demonstrate that the changes in the ion signal detected by the mass spectrometer are attributable to the focusing effect of the ion lens when appropriate voltages are applied on the sprayer and ion lens. The optimum signal was found by setting the sprayer voltage from 3000 to 5000 V while scanning the ion lens voltage. The calculated strengths of the electric field at the sprayer tip for optimum signals are similar although the applied voltages at the sprayer and ion lens are significantly different. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
105.
Previous results for 12C16O chemisorbed on a Pt“111” recrystallised ribbon revealed that the infrared absorption band due to the CO stretch appears at low coverages at 2063 cm?1 and shifts to ~2100 cm?1 at saturation coverage at 300 K. The cause of this shift is studied in the present work, by investigating the vibrational spectra from a variety of mixtures of 12C16O and 12C16O. The results show that there is a strong dipole-dipole coupling interaction between adsorbate molecules in the overlayer, and provide conclusive evidence that the 35 cm?1 frequency shift observed with increasing coverage for 12C16O is attributable to coupling. 相似文献
106.
107.
Previous research has shown that a region of the midbrain, the periaqueductal gray matter (PAG), is critical for vocalization. In this review, we describe the results of previous investigations in which we sought to find out how PAG neurons integrate the activity and precise timing of respiratory, laryngeal, and oral muscle activity for natural-sounding vocalization using the technique of excitatory amino acid microinjections in cats. In these studies, all surgical procedures were carried out under deep anaesthesia. In the precollicular decerebrate cat two general types of vocalization, classified as voiced and unvoiced, could be evoked by exciting neurons in the lateral part of the intermediate part of the PAG. The patterns of evoked electromyographic activity were strikingly similar to previously reported patterns of human muscle activity. Coordinated patterns of activity were evoked with just-threshold excitation leading to the conclusion that patterned muscle activity corresponding to the major categories of voiced and voiceless sound production are represented in the PAG. In a parallel series of human and animal experiments, we also determined that the speech and vocalization respiratory patterns are integrated and coordinated with afferent signals related to lung volume. These data have led to the proposal of a new hypothesis for the neural control of vocalization: that the PAG is a crucial brain site for mammalian voice production, not only in the production of emotional or involuntary sounds, but also as a generator of specific respiratory and laryngeal motor patterns essential for human speech and song 相似文献
108.
We present an approach to providing broad-based accessibility to graphical applications by employing the capabilities of the
Eclipse platform and aspect-oriented programming (AOP) in a way that leverages the strengths of each. We first describe the
Eclipse platform and the variety of frameworks that can be useful to the effort. We also present the advantages of aspect-oriented
programming and contrast aspect-oriented programming with object-oriented programming (OOP). Then, we discuss how to use the
Eclipse frameworks and AOP in the design of accessible Eclipse-based applications and share some situations of when to leverage
these frameworks and when we do not from the perspective of robustness and efficiency. 相似文献
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110.