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991.
It is observed that the harmonic balance (HB) method of parametric identification of nonlinear system may not give right identification
results for a single test data. A multiple-trial HB scheme is suggested to obtain improved results in the identification,
compared with a single sample test. Several independent tests are conducted by subjecting the system to a range of harmonic
excitations. The individual data sets are combined to obtain the matrix for inversion. This leads to the mean square error
minimization of the entire set of periodic orbits. It is shown that the combination of independent test data gives correct
results even in the case where the individual data sets give wrong results. 相似文献
992.
A. S. Bansode Siddharth Patel T. Rajesh Kumar B. Muralidhar T. Sundararajan Sarit Kumar Das 《Heat and Mass Transfer》2007,43(10):1037-1047
A 3D numerical study was carried out to analyze flow, heat and mass transfer first in a single half-cell cathode channel of
proton exchange membrane (PEM) fuel cell. From practical point of view, it is necessary to put the appropriate number of cells
in a stack. Hence, the above study on a single half-cell is extended to a stack of channels. Due to stacking, the assumption
of uniform flow distribution would no longer hold true. Therefore, the channel flow-maldistribution is considered. The water
formed at the active surface due to the electrochemical reaction diffuses through the porous layer and eventually enters the
gas flow duct. The higher gas velocities in the duct result in faster water vapour removal which leads to a lower value of
water vapour into the duct and hence a lower Nusselt number. 相似文献
993.
Jaume Llibre Paulo R. da Silva Marco A. Teixeira 《Journal of Dynamics and Differential Equations》2007,19(2):309-331
Singular perturbations problems in dimension three which are approximations of discontinuous vector fields are studied in
this paper. The main result states that the regularization process developed by Sotomayor and Teixeira produces a singular
problem for which the discontinuous set is a center manifold. Moreover, the definition of sliding vector field coincides with
the reduced problem of the corresponding singular problem for a class of vector fields.
相似文献
994.
Morphological measurements in 3D for pore space characterization (connectivity pore-body/throat classification, shape factors,
virtual fluid intrusion) are based on computed intensive digital-thinning operations for skeletonization and medial axis extraction
from 3D digital images. We present an alternative method that is measurably faster and allows sub-voxel definition of the
pore space network. The method allows extracting—based on morphological considerations only—the centered and shortest stream-lines—i.e.,
the paths—to follow in order to go through the pore space from one given point to another and to exit. In addition the method
penalizes long and narrow pore-throats in favor of short stubby/ones—i.e., it has a built-in exemplification capacity. It
exploits well-established mathematical methods successfully applied in medical endoscopy. 相似文献
995.
Ugo AndreausPaolo Casini 《International Journal of Non》2002,37(1):117-133
The dynamics of non-smooth oscillators has not yet sufficiently been investigated, when damping is simultaneously due to friction and impact. Because of the theoretical and practical interest of this type of systems, an effort is made in this paper to lighten the behaviour of a single-degree-of-freedom oscillator colliding with an obstacle and excited by a moving base, which transfers energy to the system via friction. The different nature of discontinuities arising in the combined problem of friction and impact has been recognized and discussed. Closed-form solutions are presented for both transient and steady-state response, assuming Coulomb's friction law and a rigid stop-limiting motion. Furthermore, a deformable (hysteretic) obstacle has been considered, and its influence on the response has been investigated. 相似文献
996.
Analytical and experimental investigations are performed in order to characterize the dynamic behaviour of a non-smooth rotational oscillator, which exhibits multiple discontinuity boundaries in the phase space. The physical system consists of a rotating body subjected to an elastic restoring force and in contact with one or two rough discs rotating with constant driving velocities. The presence of multiple discontinuity boundaries caused by frictional contacts leads to non-standard bifurcations that are studied by means of a simple mechanical model.A test set-up has then been built to investigate the correctness of modelling of the friction force and the validity of the proposed model for technical applications: the experimental measurements qualitatively and quantitatively capture the basic scenarios anticipated by the model while a strong robustness of the phenomena pointed out by the theoretical analyses has been revealed in the experiments. 相似文献
997.
Héctor Gómez Ignasi Colominas Fermín Navarrina Manuel Casteleiro 《Heat and Mass Transfer》2008,45(2):219-226
A number of contributions have been made during the last decades to model pure-diffusive transport problems by using the so-called hyperbolic diffusion equations. These equations are used for both mass and heat transport. The hyperbolic diffusion equations are obtained by substituting the classic constitutive equation (Fick’s and Fourier’s law, respectively), by a more general differential equation, due to Cattaneo (C R Acad Sci Ser I Math 247:431–433, 1958). In some applications the use of a parabolic model for diffusive processes is assumed to be accurate enough in spite of predicting an infinite speed of propagation (Cattaneo, C R Acad Sci Ser I Math 247:431–433, 1958). However, the use of a wave-like equation that predicts a finite velocity of propagation is necessary in many other calculations. The studies of heat or mass transport with finite velocity of propagation have been traditionally limited to pure-diffusive situations. However, the authors have recently proposed a generalization of Cattaneo’s law that can also be used in convective-diffusive problems (Gómez, Technical Report (in Spanish), University of A Coruña, 2003; Gómez et al., in An alternative formulation for the advective-diffusive transport problem. 7th Congress on computational methods in engineering. Lisbon, Portugal, 2004a; Gómez et al., in On the intrinsic instability of the advection–diffusion equation. Proc. of the 4th European congress on computational methods in applied sciences and engineering (CDROM). Jyväskylä, Finland, 2004b) (see also Christov and Jordan, Phys Rev Lett 94:4301–4304, 2005). This constitutive equation has been applied to engineering problems in the context of mass transport within an incompressible fluid (Gómez et al., Comput Methods Appl Mech Eng, doi: 10.1016/j.cma.2006.09.016, 2006). In this paper we extend the model to compressible flow problems. A discontinuous Galerkin method is also proposed to numerically solve the equations. Finally, we present some examples to test out the performance of the numerical and the mathematical model. 相似文献
998.
Numerical simulation of the steady and laminar convection in the thermal entry region of the finned annulus is carried out
for the case of hydrodynamically fully developed flow when subjected to uniform heat flux thermal boundary condition. Finite
difference based marching procedure is used to compute the numerical solution of the energy equation. The results to be presented
include Nusselt number, as a function of dimensionless axial length and thermal entrance length for various configurations
of the finned double-pipe. The numerical results show that Nusselt number has complex dependence on the geometric variables
like ratio of radii, fin height, and number of fins. A comparison of the computed results for certain limiting cases with
the results available in the literature validates the numerical procedure used in this work. 相似文献
999.
Boiling in a porous layer heated from below at constant heat flux and cooled at constant temperature from the upper permeable
surface leads below the critical flux of appearance of a vapor zone at the bottom in the approximation of dominated reservoirs
to two solutions: a liquid-dominated one and a vapor-dominated one. The stability of these two situations is analyzed. The
approach allows to understand the respective roles played by the gravitational instability, natural convection in the liquid
upper layer, and movement of the interface between the two regions. Taking into account the confinement allows the comparison
of these theoretical results with experimental results obtained in the laboratory. 相似文献
1000.
The controllability for switched linear system with time-delay in controls was first investigated. The whole work contains
three parts. This is the first part, including problem formulation and some preliminaries. Firstly, the mathematical model
of switched linear systems with time-delay in control functions was presented. Secondly, the concept of column space, cyclic
invariant subspace and generalized cyclic invariant subspace were introduced. And some basic properties, such as separation
lemma, were presented. Finally, a basic lemma was given to reveal the relation between the solution set of a centain integral
equations and the generalized cyclic invariant subspace. This lemma will play an important role in the determination of controllability.
All these definitions and lemmas are necessary research tools for controllability analysis.
Contributed by YE Qing-kai
Foundation items: the National Natural Science Foundation of China (69925307, 60274001); the National Key Basic Reasearch and Development
Program (2002CB312200); the Postdoctoral Program Foundation of China
Biography: XIE Guang-ming (1972∼), Doctor (E-mail: xiegming@mech.pku.edu.cn) 相似文献