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161.
网络地图或网上地图是指在因特网上浏览、制作和使用的地图,越来越多的人从网络上获取地图和相关信息,但是,它在方便大众的同时也存在很多问题,文章分析和总结了当前网络地图的主要特点和存在的问题,并在此基础上,讨论网络地图相关问题的解决方案以及可以采取的措施。 相似文献
162.
163.
164.
蒋邦远 《物探化探计算技术》2007,(Z1)
双定源回线装置的水平场Hx,其强度大、均匀,有利于探测深部陡倾斜金属矿藏,并可用作远距离井中测量的场源。此方案可用于危机矿山的找矿工作。 相似文献
165.
166.
We consider the inverse problem of permeability estimation for two-phase porous-media flow. The novel approach is based on
regularization by zonation, where the geometry and size of the regions are chosen adaptively during the optimization procedure.
To achieve this, we have utilized level-set functions to represent the permeability. The available data are sparsely distributed
in space; hence, it is reasonable to confine the estimation to coarse-scale structures. The level-set approach is able to
alter the boundaries between regions of different permeability without strict restrictions on their shape; however, when the
data are sparse, a reasonable initial guess for the permeability is required. For this task, we use adaptive multiscale permeability
estimation, which has the potential of identifying main permeability variations. These are described by a piecewise constant
function, where the constant values are attained on rectangular zones. In the current work, we develop a level-set corrector
strategy, assuming adaptive multiscale permeability estimation as a predictor. 相似文献
167.
D. J. Scheeres 《Celestial Mechanics and Dynamical Astronomy》1998,70(2):75-98
Starting from the four-body problem a generalization of both the restricted three-body problem and the Hill three-body problem
is derived. The model is time periodic and contains two parameters: the mass ratio ν of the restricted three-body problem
and the period parameter m of the Hill Variation orbit. In the proper coordinate frames the restricted three-body problem
is recovered as m → 0 and the classical Hill three-body problem is recovered as ν → 0. This model also predicts motions described
by earlier researchers using specific models of the Earth–Moon–Sun system. An application of the current model to the motion
of a spacecraft in the Sun perturbed Earth–Moon system is made using Hill's Variation orbit for the motion of the Earth–Moon
system. The model is general enough to apply to the motion of an infinitesimal mass under the influence of any two primaries
which orbit a larger mass.
Using the model, numerical investigations of the structure of motions around the geometric position of the triangular Lagrange
points are performed. Values of the parameter ν range in the neighborhood of the Earth–Moon value as the parameter m increases
from 0 to 0.195 at which point the Hill Variation orbit becomes unstable. Two families of planar periodic orbits are studied
in detail as the parameters m and ν vary. These families contain stable and unstable members in the plane and all have the
out-of-plane stability. The stable and unstable manifolds of the unstable periodic orbits are computed and found to be trapped
in a geometric area of phase space over long periods of time for ranges of the parameter values including the Earth–Moon–Sun
system.
This model is derived from the general four-body problem by rigorous application of the Hill and restricted approximations.
The validity of the Hill approximation is discussed in light of the actual geometry of the Earth–Moon–Sun system.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
168.
A method for determining the main families of isolated periodic orbits and their characteristic exponents in planar potentials
which are separated by a point transformation is proposed. Since these orbits are continued analytically with the same stability,
these results are persistent under small perturbations. The method is applied to the two fixed centers problem, the Paul trap
and the dipole expansion of an electrostatic potential.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
169.
Mass-weighted symplectic forms provide a unified framework for the treatment of both finite and vanishingly small masses in
the N-body problem. These forms are introduced, compared to previous approaches, and their properties are discussed. Applications
to symplectic mappings, the definition of action-angle variables for the Kepler problem, and Hamiltonian perturbation theory
are outlined
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
170.
We study the motion of an infinitesimal mass point under the gravitational action of three mass points of masses μ, 1–2μ and
μ moving under Newton's gravitational law in circular periodic orbits around their center of masses. The three point masses
form at any time a collinear central configuration. The body of mass 1–2μ is located at the center of mass. The paper has
two main goals. First, to prove the existence of four transversal ejection–collision orbits, and second to show the existence
of an uncountable number of invariant punctured tori. Both results are for a given large value of the Jacobi constant and
for an arbitrary value of the mass parameter 0<μ≤1/2.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献