全文获取类型
收费全文 | 1930篇 |
免费 | 144篇 |
国内免费 | 116篇 |
专业分类
测绘学 | 484篇 |
大气科学 | 112篇 |
地球物理 | 278篇 |
地质学 | 468篇 |
海洋学 | 94篇 |
天文学 | 406篇 |
综合类 | 129篇 |
自然地理 | 219篇 |
出版年
2024年 | 2篇 |
2023年 | 6篇 |
2022年 | 16篇 |
2021年 | 25篇 |
2020年 | 38篇 |
2019年 | 43篇 |
2018年 | 30篇 |
2017年 | 42篇 |
2016年 | 43篇 |
2015年 | 50篇 |
2014年 | 62篇 |
2013年 | 79篇 |
2012年 | 94篇 |
2011年 | 82篇 |
2010年 | 58篇 |
2009年 | 83篇 |
2008年 | 100篇 |
2007年 | 123篇 |
2006年 | 162篇 |
2005年 | 114篇 |
2004年 | 122篇 |
2003年 | 106篇 |
2002年 | 100篇 |
2001年 | 77篇 |
2000年 | 70篇 |
1999年 | 69篇 |
1998年 | 54篇 |
1997年 | 53篇 |
1996年 | 50篇 |
1995年 | 39篇 |
1994年 | 40篇 |
1993年 | 37篇 |
1992年 | 27篇 |
1991年 | 33篇 |
1990年 | 27篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有2190条查询结果,搜索用时 31 毫秒
841.
The one-dimensional Newtonian three-body problem is known to have stable (quasi-)periodic orbits when the masses are equal. The existence and size of the stable region is discussed here in the case where the three masses are arbitrary. We consider only the stability of the periodic (generalized) Schubart's (1956) orbit. If this orbit is linearly stable it is almost always surrounded by a region of stable quasi-periodic orbits and the size and shape of this stable region depends on the masses. The three-dimensional linear stability of the periodic orbits is also determined. Final results show that the region of stability has a complicated shape and some of the stable regions in the mass-plane are quite narrow. The non-linear three-dimensional stability is studied independently by extensive numerical integrations and the results are found to be in agreement with the linear stability analysis. The boundaries of stable region in the mass-plane are given in terms of polynomial approximations. The results are compared with a similar work by Héenon (1977).We thank the referee for pointing out this reference to us. 相似文献
842.
Kiyotaka Tanikawa Hiroaki Umehara Hiroshi Abe 《Celestial Mechanics and Dynamical Astronomy》1995,62(4):335-362
A numerical procedure is devised to find binary collision orbits in the free-fall three-body problem. Applying this procedure, families of binary collision orbits are found and a sequence of triple collision orbits are positioned. A property of sets of binary collision orbits which is convenient to search triple collision orbits is found. Important numerical results are formulated and summarized in the final section. 相似文献
843.
T. J. Kalvouridis 《Celestial Mechanics and Dynamical Astronomy》1994,58(4):309-315
In this paper we present for the first time simple symmetric motions in the planar magnetic-binary problem where both primaries are spherical bodies or oblate spheroids. From the study of this case it follows that there is a dense and complicated distribution of the families of such motions in the phase space. Our results also show that the orbital characteristics of the particle and the configuration of the phase space are appreciably affected by the oblateness of the primaries only if these parameters become sufficiently large. 相似文献
844.
本文总结出地下水资源管理模型实际应用中存在的三大问题:第一,管理模型建立自身存在问题;第二,模型研制者和决策管理者合作不够;第三,地下水资源管理比较混乱。对三大问题进行了详细的论述,并提出了解决问题采取的措施。 相似文献
845.
Masanori Sakamoto Kiyoji Shiono Shinji Masumoto Kiyoshi Wadatsumi 《Natural Resources Research》1993,2(2):140-147
In this article we describe the basic framework of the computerized geologic mapping system cigma. The system, whic is based on a mathematical formulation of geologic concepts, consists of the following six subsystems: (1) input of geologic data set; (2) inference of stratigraphic sequence; (3) construction of logical models of geologic structures; (4) determination of three-dimensional geologic boundary surfaces; (5) construction of three-dimensional solid model of geologic structures; and (6) graphical presentation. Geologic structures are summarized in several tables called logical models of geologic structures. Each model is constructed automatically from input data on structural relations between geologic bodies. The model interprets the data automatically to create data files necessary to determine the shapes of geologic boundaries; it also provides a threedimensional solid model of geologic structures referring to the shapes of boundaries. As a prototype, we introduce two types of contacts corresponding to conformity and unconformity into the logical model and show that it is possible to draw a geologic map automatically. More complex geologic structures can be introduced into the geologic mapping system through further formulation of geologic structures. 相似文献
846.
Michèle Moons Alessandro Morbidelli 《Celestial Mechanics and Dynamical Astronomy》1993,57(1-2):99-108
We study the motion of asteroids in the main mean motion commensurabilities in the frame of the planar restricted three-body problem. No assumption is made about the size of the eccentricity of the asteroid. At small to moderate eccentricity, we recover existing results (shape of the phase space and location of secondary resonances). We also provide global pictures of the dynamics in the region of secondary resonances. At high eccentricity, the phase space portraits of the integrable part of the Hamiltonian show new families of stable orbits for the 3:2 and 2:1 cases and the secular resonances 5 and 6 are located. 相似文献
847.
For a given family of orbits f(x,y) = c
* which can be traced by a material point of unit in an inertial frame it is known that all potentials V(x,y) giving rise to this family satisfy a homogeneous, linear in V(x,y), second order partial differential equation (Bozis,1984). The present paper offers an analogous equation in a synodic system Oxy, rotating with angular velocity . The new equation, which relates the synodic potential function (x,y), = –V(x, y) + % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaSqaaSqaai% aaigdaaeaacaaIYaaaaaaa!3780!\[\tfrac{1}{2}\]2(x
2 + y
2) to the given family f(x,y) = c
*, is again of the second order in (x,y) but nonlinear.As an application, some simple compatible pairs of functions (x,y) and f(x, y) are found, for appropriate values of , by adequately determining coefficients both in and f. 相似文献
848.
Krzysztof Goździewski Andrzej J. Maciejewski Zuzanna Niedzielska 《Celestial Mechanics and Dynamical Astronomy》1991,52(2):195-201
Nonlinear stability of the triangular libration point in the photogravitational restricted three body problem was investigated in the whole range of the parameters. Some results obtained earlier are corrected. The method for proper determination of cases when stability cannot be determined by four order terms of the hamiltonian was proposed. 相似文献
849.
850.