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991.
We used the molecular dynamics simulation with interatomic potentials of the embedded atom method to calculate the high-index surface energies of the surfaces containing the 〈0 0 1〉 axis or 〈−1 1 0〉 axis in f.c.c. metal Al, Cu and Ni at zero temperature. We generalized an empirical formula based on structural unit model for high-index surfaces and present some new formulas that can be used to estimate the surface energy and structural feature of high-index surfaces very well. The results show that the closest surfaces have the lowest surface energy and the surface energies of the closest (1 1 1) surface and the next closest (1 1 0), (1 0 0) surfaces are the extremum on the curve of surface energy versus orientation angle. We also calculated the b.c.c. metal Fe and obtained a similar result. The difference is that in the b.c.c. metal the surface energies of the closest (1 1 0) surface and the next closest (1 0 0), (1 1 2) surfaces are the extremum on the curve of surface energy versus orientation angle. The results of theoretical simulation and the empirical formula consist well with the experiment data. 相似文献
992.
The structure and dynamics of amorphous surfaces are poorly understood. The present work develops methods employing classical molecular dynamics (MD) simulations to elucidate these phenomena on amorphous silicon. Careful relaxation of the initial ensemble and taking account of exchange with the bulk yield surface diffusion coefficients in good agreement with experiment. Randomly oriented dimer pairs dominate the surface structure. Diffusion proceeds by several pathways, which all differ in basic character from those typically observed on crystalline silicon. The primary pathways involve single atoms and dimer pairs, which typically move only one or two atomic diameters before reincorporating into the surface. Frequent vertical migration takes place between the first two atomic layers. 相似文献
993.
Classical ion trajectory simulations using the scattering and recoiling imaging code (SARIC) have been applied to study the low energy ion surface hyperchanneling phenomenon. It was found that the ion-surface interaction geometry, projectile type, surface chemisorbed hydrogen, and phonon amplitudes had a profound effect on the scattered ion trajectories. It is possible to determine the surface Debye temperature through analysis of the scattering yields and angular distributions. The simulations will find application in delineation of classical ion trajectories for specific as well as generic ion surface interactions. 相似文献
994.
Giovanna Longhi Sergio Abbate Claudio Zagano Giovanni Botto Laure Ricard-Lespade 《Theoretical chemistry accounts》1992,82(3-4):321-337
Summary The system consisting of two Morse oscillators coupled via either a potential or a kinetic quadratic term is considered. The corresponding classical equations of motion have been numerically integrated and the initial conditions have been systematically analyzed in the regime of low total excitation energy of the system. Particular attention was paid to the full characterization of an intermediate type of motion, herein called transition mode, which appears at total energy values in between those typical of normal modes and those where local and normal modes coexist. A previously proposed perturbative approach (Jaffé C, Brumer P (1980) J Chem Phys 73:5646) is reanalyzed and compared with the results of numerical experiments, with the purpose of lending further support to the existence of transition modes. 相似文献
995.
Alessandro Savo 《Annals of Global Analysis and Geometry》2001,19(2):133-151
We prove lower bounds for the length of the zero set of aneigenfunction of the Laplace operator on a Riemann surface; inparticular, in non-negative curvature, or when the associated eigenvalueis large, we give a lower bound which involves only the square root ofthe eigenvalue and the area of the manifold (modulo a numericalconstant, this lower bound is sharp). 相似文献
996.
Raphaël Cerf goston Pisztora 《Annales de l'Institut Henri Poincaré (B) Probabilités et Statistiques》2001,37(6):193
We study phase coexistence (separation) phenomena in Ising, Potts and random cluster models in dimensions d3 below the critical temperature. The simultaneous occurrence of several phases is typical for systems with appropriately arranged (mixed) boundary conditions or for systems satisfying certain physically natural constraints (canonical ensembles). The various phases emerging in these models define a partition, called the empirical phase partition, of the space. Our main results are large deviations principles for (the shape of) the empirical phase partition. More specifically, we establish a general large deviation principle for the partition induced by large (macroscopic) clusters in the Fortuin–Kasteleyn model and transfer it to the Ising–Potts model where we obtain a large deviation principle for the empirical phase partition induced by the various phases. The rate function turns out to be the total surface free energy (associated with the surface tension of the model and with boundary conditions) which can be naturally assigned to each reasonable partition. These LDP-s imply a weak law of large numbers: asymptotically, the law of the phase partition is determined by an appropriate variational problem. More precisely, the empirical phase partition will be close to some partition which is compatible with the constraints imposed on the system and which minimizes the total surface free energy. A general compactness argument guarantees the existence of at least one such minimizing partition. Our results are valid for temperatures T below a limit of slab-thresholds
conjectured to agree with the critical point Tc. Moreover, T should be such that there exists only one translation invariant infinite volume state in the corresponding Fortuin–Kasteleyn model; a property which can fail for at most countably many values and which is conjectured to be true for every T≠Tc. 相似文献
997.
Paolo Stellari 《Geometriae Dedicata》2004,108(1):1-14
In this paper we describe some results about K3 surfaces with Picard number 1 and 2. In particular, we give a new simple proof of a theorem due to Oguiso which shows that,
given an integer N, there is a K3 surface with Picard number 2 and at least N non-isomorphic FM-partners. We describe also the Mukai vectors of the moduli spaces associated to the FM-partners of K3 surfaces with Picard number 1. 相似文献
998.
Rigid-plastic reinforced shells of revolution with a piecewise linear condition of plasticity are considered. It is shown
that, in solving problems on their limit equilibrium, the application of linearized yield surfaces or the approximation of
derivatives by finite differences restricts the set of possible solutions. In this paper, an asymptotic method for solving
the problems by constructing a convergent sequence of solutions is offered. Each of these solutions is constructed numerically,
and to approximate the derivatives, special finite differences coordinated with suppositions of the theory of thin shells
are used. A feature of this method is that, with piecewise smooth yield surfaces, it is not necessary to determine a sequence
of various plastic states, because the approximating yield surfaces are constructed during solution of the problem. Shells
of revolution with positive and negative Gaussian curvatures and compound constructions of shells with various structures
of reinforcement are examined. It is shown that the junction boundaries of rigid and plastic regions and the sequence of realization
of plastic hinges greatly depend on the accuracy of approximation of the surfaces. With these approximations tending to the
true yield surface, the sizes of the rigid regions decrease, and the range of structural and geometrical parameters of the
shells grows when the yield state is reached through out their span. It is noted that, for closed constructions of shells
reinforced only with spiral fibers at placement angles less that 55°, all possible mechanisms of plastic flow correspond to
the direction of operating forces, whereas for other reinforcement structures, mechanisms of plastic flow with the opposite
direction of velocities are possible.
Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 5, pp. 613–632, September–October, 2008. 相似文献
999.
1000.
We discuss the influence of polymer adsorption on the curvature energy of an interface. Following an article by Clement and
Joanny (J. Phys. II 7, 973 (1997)), a mean-field theory is used to calculate the surface tension, rigidity constants and spontaneous curvature
associated with both reversible and irreversible polymer adsorption. In the case of irreversible polymer adsorption it is
assumed that the amount of adsorbed polymer remains constant upon curving the interface. Unfortunately, constraining the amount
of polymer by adding a Lagrange multiplier affects the thermodynamic state of the (free) polymer far away from the interface.
Clement and Joanny solve this problem by removing the polymers in the bulk. We allow for the presence of free polymers, but
to achieve this we have to apply a local external field to keep the adsorbed amount fixed. The results of the two approaches
are compared and a physical interpretation is given.
Received 25 July 2001 and Received in final form 5 December 2001 相似文献