全文获取类型
收费全文 | 2181篇 |
免费 | 269篇 |
国内免费 | 779篇 |
专业分类
测绘学 | 211篇 |
大气科学 | 354篇 |
地球物理 | 395篇 |
地质学 | 1205篇 |
海洋学 | 255篇 |
天文学 | 409篇 |
综合类 | 135篇 |
自然地理 | 265篇 |
出版年
2024年 | 8篇 |
2023年 | 44篇 |
2022年 | 72篇 |
2021年 | 72篇 |
2020年 | 91篇 |
2019年 | 101篇 |
2018年 | 60篇 |
2017年 | 69篇 |
2016年 | 83篇 |
2015年 | 86篇 |
2014年 | 91篇 |
2013年 | 117篇 |
2012年 | 128篇 |
2011年 | 152篇 |
2010年 | 133篇 |
2009年 | 146篇 |
2008年 | 137篇 |
2007年 | 157篇 |
2006年 | 158篇 |
2005年 | 136篇 |
2004年 | 152篇 |
2003年 | 144篇 |
2002年 | 107篇 |
2001年 | 108篇 |
2000年 | 97篇 |
1999年 | 95篇 |
1998年 | 80篇 |
1997年 | 68篇 |
1996年 | 58篇 |
1995年 | 55篇 |
1994年 | 49篇 |
1993年 | 45篇 |
1992年 | 30篇 |
1991年 | 33篇 |
1990年 | 30篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 7篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有3229条查询结果,搜索用时 15 毫秒
31.
We study the existence of invariant tori in a neighbourhood of the collinear equilibrium points of the planar three-body problem. To this end some properties of the normal form of the Hamiltonian reduced to the 4D central manifold are proved. Using this normal form, we show that the nondegeneracy conditions of KAM theorem are satisfied for all positive masses, including the 2:1 resonance case. The evaluation of the conditions is done numerically. 相似文献
32.
Douglas Soldan de Oliveira Othon Cabo Winter Ernesto Vieira Neto Gislaine de Felipe 《Earth, Moon, and Planets》2007,100(3-4):233-239
The irregular satellites of Jupiter are believed to be captured asteroids or planetesimals. In the present work is studied
the direction of capture of these objects as a function of their orbital inclination. We performed numerical simulations of
the restricted three-body problem, Sun-Jupiter-particle, taking into account the growth of Jupiter. The integration was made
backward in time. Initially, the particles have orbits as satellites of Jupiter, which has its present mass. Then, the system
evolved with Jupiter losing mass and the satellites escaping from the planet. The reverse of the escape direction corresponds
to the capture direction. The results show that the Lagrangian points L1 and L2 mainly guide the direction of capture. Prograde
satellites are captured through these two gates with very narrow amplitude angles. In the case of retrograde satellites, these
two gates are wider. The capture region increases as the orbital inclination increases. In the case of planar retrograde satellites
the directions of capture cover the whole 360° around Jupiter. We also verified that prograde satellites are captured earlier
in actual time than retrograde ones.
This paper was presented at the Asteriods, Comets and Meteors meeting held at Búzios, Rio de Janeiro, Brazil in August 2005
and could not be included in the special issue related to that conference. 相似文献
33.
An analytical proof of the existence of some kinds of periodic orbits of second species of Poincaré, both in the Circular and Elliptic Restricted three-body problem, is given for small values of the mass parameter. The proof uses the asymptotic approximations for the solutions and the matching theory developed by Breakwell and Perko. In the paper their results are extended to the Elliptic problem and applied to prove the existence of second-species solutions generated by rectilinear ellipses in the Circular problem and nearly-rectilinear ones in the Elliptic case. 相似文献
34.
Mutual Potential of Homogeneous Polyhedra 总被引:2,自引:0,他引:2
Robert A. Werner Daniel J. Scheeres 《Celestial Mechanics and Dynamical Astronomy》2005,91(3-4):337-349
The mutual gravitational potential between a pair of homogeneous polyhedra is expressed using an infinite series. The nested
volume integrals are evaluated analytically and result in simple tensor expressions containing no special functions. However,
complexity increases as O(6
n
), where n is the term degree. An alternate formulation due to Liebenthal is also presented. 相似文献
35.
We study the stability of motion in the 3-body Sitnikov problem, with the two equal mass primaries (m
1 = m
2 = 0.5) rotating in the x, y plane and vary the mass of the third particle, 0 ≤ m
3 < 10−3, placed initially on the z-axis. We begin by finding for the restricted problem (with m
3 = 0) an apparently infinite sequence of stability intervals on the z-axis, whose width grows and tends to a fixed non-zero value, as we move away from z = 0. We then estimate the extent of “islands” of bounded motion in x, y, z space about these intervals and show that it also increases as |z| grows. Turning to the so-called extended Sitnikov problem, where the third particle moves only along the z-axis, we find that, as m
3 increases, the domain of allowed motion grows significantly and chaotic regions in phase space appear through a series of
saddle-node bifurcations. Finally, we concentrate on the general 3-body problem and demonstrate that, for very small masses, m
3 ≈ 10−6, the “islands” of bounded motion about the z-axis stability intervals are larger than the ones for m
3 = 0. Furthermore, as m
3 increases, it is the regions of bounded motion closest to z = 0 that disappear first, while the ones further away “disperse” at larger m
3 values, thus providing further evidence of an increasing stability of the motion away from the plane of the two primaries,
as observed in the m
3 = 0 case. 相似文献
36.
P. P. Hallan Sanjay Jain K. B. Bhatnagar 《Celestial Mechanics and Dynamical Astronomy》2000,77(3):157-184
The non-linear stability of L
4 in the restricted three-body problem has been studied when the bigger primary is a triaxial rigid body with its equatorial
plane coincident with the plane of motion. It is found that L
4 is stable in the range of linear stability except for three mass ratios:
where A1, A2 depend upon the lengths of the semi axes of the triaxial rigid body.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
37.
The accelerated Kepler problem (AKP) is obtained by adding a constant acceleration to the classical two-body Kepler problem.
This setting models the dynamics of a jet-sustaining accretion disk and its content of forming planets as the disk loses linear
momentum through the asymmetric jet-counterjet system it powers. The dynamics of the accelerated Kepler problem is analyzed
using physical as well as parabolic coordinates. The latter naturally separate the problem’s Hamiltonian into two unidimensional
Hamiltonians. In particular, we identify the origin of the secular resonance in the AKP and determine analytically the radius
of stability boundary of initially circular orbits that are of particular interest to the problem of radial migration in binary
systems as well as to the truncation of accretion disks through stellar jet acceleration. 相似文献
38.
When μ is smaller than Routh’s critical value μ
1 = 0.03852 . . . , two planar Lyapunov families around triangular libration points exist, with the names of long and short
period families. There are periodic families which we call bridges connecting these two Lyapunov families. With μ increasing from 0 to 1, how these bridges evolve was studied. The interval (0,1) was divided into six subintervals (0, μ
5), (μ
5, μ
4), (μ
4, μ
3), (μ
3, μ
2), (μ
2, μ
1), (μ
1, 1), and in each subinterval the families B(pL, qS) were studied, along with the families B(qS, qS′). Especially in the interval (μ
2, μ
1), the conclusion that the bridges B(qS, qS′) do not exist was obtained. Connections between the short period family and the bridges B(kS, (k + 1)S) were also studied. With these studies, the structure of the web of periodic families around triangular libration points
was enriched. 相似文献
39.
New doubly-symmetric families of comet-like periodic orbits in the spatial restricted (N + 1)-body problem 总被引:1,自引:0,他引:1
For any positive integer N ≥ 2 we prove the existence of a new family of periodic solutions for the spatial restricted (N +1)-body problem. In these solutions the infinitesimal particle is very far from the primaries. They have large inclinations
and some symmetries. In fact we extend results of Howison and Meyer (J. Diff. Equ. 163:174–197, 2000) from N = 2 to any positive integer N ≥ 2.
相似文献
40.
第四纪冰期大型山岳冰川运动遗留下的大型冰水堆积体是我国西南高山峡谷地区一类重要的第四系堆积物.本世纪以来,随着该地区大型基础工程的陆续上马,这种大型冰水堆积体的存在常常成为工程建设必须面临的工程地质问题,这些冰水堆积体因其形成演化过程的特殊性,使得其在结构、物质组成、力学特性、水理特性等诸多方面与一般松散堆积体存在显著差别,因而研究其结构特征、形成演化过程以及带来的工程地质问题具有重要意义.以澜沧江某电站坝前冰水堆积体为例,在调查分析其结构特征的基础上,对冰水堆积体的形成演化过程进行分析和研究,并对冰水堆积体的工程特性,以及带来的工程地质问题进行了探讨,认为该冰水堆积体的工程特性明显好于其他第四系松散堆积体,电站蓄水后整体失稳的可能性较小,但其前缘仍存在局部失稳的可能. 相似文献