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971.
The purpose of this paper is to elaborate a procedure, based on a mathematical model, for the setting of the pulling rate, capillary and thermal conditions, in order to grow a cylindrical rod with prescribed radius and length, by edge-defined film-fed growth (EFG) method. First, in the case of an axisymmetric meniscus, we use simultaneously the catching and the angle fixation conditions in order to find a formula, which describes the fluctuation of the angle between the horizontal axis Or and the tangent line to the free surface of the meniscus at the three phase point. This angle appears in the system of differential equations which describes the evolution of the radius of the rod. During the growth this angle can fluctuate due to the fluctuations of the crystal radius, or crystallization front level, or pressure, respectively. In the second part of the paper it is shown in which kind this formula together with the energy balance equation at the crystallization front level can be used for setting the pulling rate, the thermal and capillary conditions to grow a cylindrical rod with prescribed radius and length. Numerical illustration and simulation are presented for rods having thermo-physical properties similar to NdYAG and InSb. This type of results can be useful for the experiment planning, since personal computer simulation is less expensive than experiment. With this aim the present study was undertaken. 相似文献
972.
Using molecular dynamics simulations, we investigate the oscillatory behaviors of carbon nanotube oscillators containing sp3-hybridized defects formed by hydrogen chemisorption. It is found that the presence of these defects significantly affects the kinetic and potential energies of the nanotube systems, which in turn affects their oscillation periods and frequencies. We have also studied the oscillatory characteristics of the oscillators containing sp3-hybridized Stone-Wales defects. Our results show that it is possible to control the motion of the inner nanotube by introducing sp3-hybridized defects on the outer nanotube, which provides a potential way to tune the oscillatory behavior of nanotube oscillators. 相似文献
973.
A new optimal control problem that incorporates the residual of the Eikonal equation into its objective is presented. The formulation of the state equation is based on the level set transport equation but extended by an additional source term, correcting the solution so as to minimize the objective functional. The method enforces the constraint so that the interface cannot be displaced at least in the continuous setting. The system of first‐order optimality conditions is derived, linearized, and solved numerically. The control also prevents numerical instabilities, so that no additional stabilization techniques are required. This approach offers the flexibility to include other desired design criteria into the objective functional. The methodology is evaluated numerically in three different examples and compared with other PDE‐based reinitialization techniques. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
974.
In this paper, special emphasis is given to the inclusion of uncertainties in the evaluation of structural behaviour aiming at a better representation of the system characteristics and the quantification of the importance of these uncertainties in the project. It deals with the structural reliability analysis problem accounting the effect of spatial variability of material properties. To this end it is proposed a finite element model to represent the behaviour of reinforced concrete for short and long-term loads, which includes the main features observed in this material. It was developed a model for the generation of multidimensional non-Gaussian stochastic fields for the material properties that is independent of the finite element mesh. First, an example of a two-dimensional non-Gaussian stochastic field generation in a square steel plate is presented. Latter, the reliability analysis is performed to a limit state function based on prescribed values of mid-span displacements on a simply-supported reinforced beam. Finally, the influence of long-term effects on the reliability of a reinforced concrete beam is studied considering the effect of steel reinforcement corrosion. 相似文献
975.
976.
In a magneto-Archimedes levitation device, a polymer can be levitated in a paramagnetic medium, and its equilibrium levitated height is mainly related to its density. Here, a novel density measurement method for polymers via magneto-Archimedes levitation is proposed, in which the relationship between the density and the levitated height is determined through numerical simulation. COMSOL software is employed to simulate the distribution of magnetic field in the device, and FLUENT-EDEM multiphase software is adopted to predict the polymer's levitated height. A 3rd-order polynomial equation is fitted by simulation results for density calculation. Several experiments with different devices, different magnets, different mediums, and various polymers were carried out to verify the proposed method. Experimental results showed that the proposed method has high accuracy (0.0060–0.0130 g/cm3) in density measurements for small polymer samples (∼25 mm3). In general, the proposed method has prospects of broad application in polymer density-based testing. 相似文献
977.
We develop a microscopic pedestrian-simulation model in which pedestrian positions are updated at discrete time steps. At each time step, each pedestrian probabilistically selects a direction of movement from a predetermined set according to a logit-type function that considers the dynamics of other pedestrians around, and then selects a step size that satisfies a certain distribution. We perform a number of field experiments on real intersecting pedestrian flows with four different angles. We then validate and calibrate the model using sample data on the deviation angles, step velocities, and velocity–density relations obtained from the experiments. 相似文献
978.
Niti Nipun Sharma 《Journal of nanoparticle research》2008,10(2):333-340
Emissive power per unit area of a blackbody has been modeled as a function of frequency using quantum electrodynamics, semi-classical
and classical approaches in the available literature. Present work extends the classical lumped-parameter systems model of
Brownian motion of nanoparticle to abstract an emissive power per unit area model for nanoparticle radiating at temperature
greater than absolute zero. The analytical model developed in present work has been based on synergism of local deformation
leading to local motion of nanoparticle due to photon impacts. The work suggests the hypothesis of a free parameter f′ characterizing the damping coefficient of resistive forces to local motion of nanoparticle and the manipulation of which
is possible to realize desired emissivity from nanoparticles. The model is validated with the well established Planck’s radiation
law. 相似文献
979.
We study theoretically, by means of layer-multiple scattering techniques, the propagation of elastic waves through finite slabs of phononic crystals consisting of metallic spheres in polyester matrix, embedded in air. We focus on the study of modes localized on the surfaces of the structure, investigating the physical parameters which influence and determine their appearance. Our results reveal the existence of absolute phononic frequency gaps in these finite structures, and point out the possibility, under an appropriate choice of the parameters, of tunable regions of frequency free of propagating and/or surface-localized modes. This could be very useful in the design of devices related to frequency filtering, waveguiding, etc. 相似文献
980.
Yoshiyuki Shirakawa Yusuke Hayashi Kazunori Kadota Hiroshi Mio Hiroto Ohtsuki Atsuko Shimosaka Jusuke Hidaka 《Journal of nanoparticle research》2008,10(4):577-584
In our previous paper, structural changes of selenium powders ground by a planetary ball mill at various rotational speeds
were investigated for the nanostructural modification of particles using mechanical grinding process. The experimental results
indicated that the amorphisation of Se by grinding accompanies lattice strain, and the lattice strain arises from impact energy
which is more than an energy related to intermolecular interaction. In this paper, molecular dynamics simulations of selenium
have been carried out under compressing conditions of various pressure strengths for obtaining information of the lattice
strain at atomic level. Then, dynamical behaviour of atomic configuration has been discussed in this process. The structural
disordering and formation of the structural defects were estimated by deviations of bond length and angle and the number of
created defects before and after compressing from simulated results. The disordering took place during compressing at various
pressure strengths, and the disordered atoms return to their initial positions at lower pressure. Stable disordered state
and defects after the compression can however remain by compression at more than a certain pressure strength mainly associated
with binding energy of selenium. 相似文献