全文获取类型
收费全文 | 745篇 |
免费 | 114篇 |
国内免费 | 99篇 |
专业分类
测绘学 | 69篇 |
大气科学 | 79篇 |
地球物理 | 274篇 |
地质学 | 200篇 |
海洋学 | 228篇 |
天文学 | 41篇 |
综合类 | 28篇 |
自然地理 | 39篇 |
出版年
2024年 | 2篇 |
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 9篇 |
2020年 | 14篇 |
2019年 | 15篇 |
2018年 | 12篇 |
2017年 | 26篇 |
2016年 | 31篇 |
2015年 | 17篇 |
2014年 | 32篇 |
2013年 | 52篇 |
2012年 | 36篇 |
2011年 | 35篇 |
2010年 | 50篇 |
2009年 | 58篇 |
2008年 | 59篇 |
2007年 | 61篇 |
2006年 | 46篇 |
2005年 | 34篇 |
2004年 | 30篇 |
2003年 | 41篇 |
2002年 | 29篇 |
2001年 | 19篇 |
2000年 | 28篇 |
1999年 | 26篇 |
1998年 | 26篇 |
1997年 | 17篇 |
1996年 | 11篇 |
1995年 | 16篇 |
1994年 | 23篇 |
1993年 | 18篇 |
1992年 | 14篇 |
1991年 | 7篇 |
1990年 | 12篇 |
1989年 | 17篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有958条查询结果,搜索用时 15 毫秒
82.
Abstract Using a contour dynamical algorithm, we have found rotating tripolar V-state solutions for the inviscid Euler equations in two-dimensions. We have studied their geometry as a function of their physical parameters. Their stability was investigated with the aid of contour surgery, and most of the states were found to be stable. Under finite-amplitude perturbations, tripoles are shown to either fission into two asymmetric dipoles or to evolve into a shielded axisymmetric vortex, demonstrating the existence of two new ‘‘reversible transitions'’ between topologically distinct coherent vortex structures. These dynamical results are confirmed by pseudo-spectral simulations, with which we also show how continuous tripolar long-lived coherent vortex structures can be generated in a variety of ways. 相似文献
83.
The finite element (FE) simulation of large‐scale soil–structure interaction problems (e.g. piled‐raft, tunnelling, and excavation) typically involves structural and geomaterials with significant differences in stiffness and permeability. The symmetric quasi‐minimal residual solver coupled with recently developed generalized Jacobi, modified symmetric successive over‐relaxation (MSSOR), or standard incomplete LU factorization (ILU) preconditioners can be ineffective for this class of problems. Inexact block diagonal preconditioners that are inexpensive approximations of the theoretical form are systematically evaluated for mitigating the coupled adverse effects because of such heterogeneous material properties (stiffness and permeability) and because of the percentage of the structural component in the system in piled‐raft foundations. Such mitigation led the proposed preconditioners to offer a significant saving in runtime (up to more than 10 times faster) in comparison with generalized Jacobi, modified symmetric successive over‐relaxation, and ILU preconditioners in simulating piled‐raft foundations. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
84.
85.
Lambert problem solution in the hill model of motion 总被引:1,自引:0,他引:1
Alexander Sukhanov Antonio F. Bertachini A. Prado 《Celestial Mechanics and Dynamical Astronomy》2004,90(3-4):331-354
The goal of this paper is obtaining a solution of the Lambert problem in the restricted three-body problem described by the
Hill equations. This solution is based on the use of pre determinate reference orbits of different types giving the first
guess and defining the sought-for transfer type. A mathematical procedure giving the Lambert problem solution is described.
This procedure provides step-by-step transformation of the reference orbit to the sought-for transfer orbit. Numerical examples
of the procedure application to the transfers in the Sun–Earth system are considered. These examples include transfer between
two specified positions in a given time, a periodic orbit design, a halo orbit design, halo-to-halo transfers, LEO-to-halo
transfer, analysis of a family of the halo-to-halo transfer orbits. The proposed method of the Lambert problem solution can
be used for the two-point boundary value problem solution in any model of motion if a set of typical reference orbits can
be found. 相似文献
86.
The SMF algorithms were recently developed by the authors as a multistep generalization of the ScheifeleG-functions one-step method. Like the last, the proposed codes integrate harmonic oscillations without truncation error and the perturbing parameter appears as a factor of that error when integrating perturbed oscillations. Therefore they seemed to be convenient for the accurate integration of orbital problems after the application of linearizing transformations, such as KS or BF. In this paper we present several numerical experiments concerning the propagation of Earth satellite orbits, that illustrate the performance of the the SMF method. In general, it provides greater accuracy than the usual standard algorithms for similar computational cost. 相似文献
87.
We present a time-transformed leapfrog scheme combined with the extrapolation method to construct an integrator for orbits in N-body systems with large mass ratios. The basic idea can be used to transform any second-order differential equation into a form which may allow more efficient numerical integration. When applied to gravitating few-body systems this formulation permits extremely close two-body encounters to be considered without significant loss of accuracy. The new scheme has been implemented in a direct N-body code for simulations of super-massive binaries in galactic nuclei. In this context relativistic effects may also be included. 相似文献
88.
N. H. Gray 《Mathematical Geology》1973,5(3):225-236
A rigorous treatment of the least-squares estimation of the parameters in petrologic materials balance equations is developed to take into account the uncertainties inherent in the chemical analyses. The choice of the optimal estimation procedure for a particular problem is dependent upon the extent of the petrogenetic understanding of the exact nature of the materials balance involved. Some of the complications entailed in obtaining least-squares estimates are illustrated by the examples of magmatic differentiation and metamorphic reactions. 相似文献
89.
王行翔 《中国天文和天体物理学报》1988,(3)
本文在假设荷电球体内部物质密度为ρ_m=μγ~α,电荷密度为ρ_e=ρ_0γ~(b_e-λ/2)的情况下,严格求解Einstein-Maxwell场方程,求得了静态荷电球体的一个较为普遍的内部解。这个解可以看作是Wyman得到的内部解推广到荷电情况下的结果,并且将Wilson,李鉴增,Santos,Pant和Sah等人给出的许多结果作为自己的特例包括在内。 相似文献
90.
In this article the charged analogues of recently derived Buchdahl’s type fluid spheres have been obtained by considering a particular form of electric field intensity. In this process, Einstein–Maxwell field equations yield eight different classes of solutions, joining smoothly with the exterior Reissner–Nordstrom metric at the pressure free intersurface. Out of the eight solutions only seven could be utilized to represent superdense star models with ultrahigh surface density of the order 2×1014 gm cm−3. The maximum masses of the star models were found to be 8.223931MΘ and 8.460857MΘ subject to strong and weak energy conditions, respectively, which are much higher than the maximum masses 3.82MΘ and 4.57MΘ allowed in the neutral cases. The velocity of sound seen to be less than that of light throughout the star models. 相似文献