全文获取类型
收费全文 | 801篇 |
免费 | 59篇 |
国内免费 | 9篇 |
专业分类
测绘学 | 42篇 |
大气科学 | 45篇 |
地球物理 | 203篇 |
地质学 | 306篇 |
海洋学 | 64篇 |
天文学 | 149篇 |
综合类 | 2篇 |
自然地理 | 58篇 |
出版年
2024年 | 4篇 |
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 17篇 |
2020年 | 14篇 |
2019年 | 24篇 |
2018年 | 33篇 |
2017年 | 28篇 |
2016年 | 36篇 |
2015年 | 30篇 |
2014年 | 29篇 |
2013年 | 42篇 |
2012年 | 36篇 |
2011年 | 49篇 |
2010年 | 39篇 |
2009年 | 60篇 |
2008年 | 34篇 |
2007年 | 44篇 |
2006年 | 38篇 |
2005年 | 37篇 |
2004年 | 28篇 |
2003年 | 22篇 |
2002年 | 28篇 |
2001年 | 15篇 |
2000年 | 16篇 |
1999年 | 13篇 |
1998年 | 16篇 |
1997年 | 9篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1976年 | 4篇 |
1973年 | 2篇 |
1965年 | 2篇 |
1964年 | 3篇 |
排序方式: 共有869条查询结果,搜索用时 31 毫秒
81.
Guillermo Tenorio-Tagle & Casiana Muñoz-Tuñón 《Monthly notices of the Royal Astronomical Society》1998,293(3):299-305
Two-dimensional calculations of the hydrodynamics produced by nuclear starbursts, taking into consideration the accretion or infall of disc matter on to the heart of the starburst, are here shown to lead to stationary solutions that naturally account for the kpc-scale biconical X-ray and optically detected filamentary structure. The calculated flows are critically compared with former models and with observations of nuclear starbursts. For the infall models, we find that the mechanical energy power of the nuclear cluster must exceed a threshold value, imposed by the rate of disc mass accretion, to undergo blowout. This, combined with an initial mass function (IMF), is shown to regulate the minimum amount of mass that a starburst needs to generate kpc-scale outflows. 相似文献
82.
Andrew Harrison Phil Puxley Adrian Russell & Peter Brand 《Monthly notices of the Royal Astronomical Society》1998,297(2):624-632
We present measurements of several near-infrared emission lines from the nearby galaxy NGC 253. We have been able to measure four H2 lines across the circumnuclear starburst, from which we estimate the ortho- to para- ratio of excited H2 to be ∼2. This indicates that the bulk of the H2 emission arises from photodissociation regions (PDRs), rather than from shocks. This is the case across the entire region of active star formation.
As the H2 emission arises from PDRs, it is likely that the ratio of H2 to Brγ (the bright hydrogen recombination line) is a measure of the relative geometry of O and B stars and PDRs. Towards the nucleus of NGC 253 the geometry is deduced to be tightly clustered O and B stars in a few giant H II regions that are encompassed by PDRs. Away from the nuclear region, the geometry becomes that of PDRs bathed in a relatively diffuse ultraviolet radiation field.
The rotation curves of 1–0 S(1) and Brγ suggest that the ionized gas is tracing a kinetic system different from that of the molecular gas in NGC 253, particularly away from the nucleus. 相似文献
As the H
The rotation curves of 1–0 S(1) and Brγ suggest that the ionized gas is tracing a kinetic system different from that of the molecular gas in NGC 253, particularly away from the nucleus. 相似文献
83.
Orbit classification in arbitrary 2D and 3D potentials 总被引:1,自引:0,他引:1
Daniel D. Carpintero & Luis A. Aguilar 《Monthly notices of the Royal Astronomical Society》1998,298(1):1-21
A method of classifying generic orbits in arbitrary 2D and 3D potentials is presented. It is based on the concept of spectral dynamics introduced by Binney &38; Spergel that uses the Fourier transform of the time series of each coordinate. The method is tested using a number of potentials previously studied in the literature and is shown to distinguish correctly between regular and irregular orbits, to identify the various families of regular orbits (boxes, loops, tubes, boxlets, etc.), and to recognize the second-rank resonances that bifurcate from them. The method returns the position of the potential centre and, for 2D potentials, the orientation of the principal axes as well, should this be unknown. A further advantage of the method is that it has been encoded in a FORTRAN program that does not require user intervention, except for 'fine tuning' of search parameters that define the numerical limits of the code. The automatic character makes the program suitable for classifying large numbers of orbits. 相似文献
84.
85.
86.
We presented a finite‐element‐based algorithm to simulate plane‐strain, straight hydraulic fractures in an impermeable elastic medium. The algorithm accounts for the nonlinear coupling between the fluid pressure and the crack opening and separately tracks the evolution of the crack tip and the fluid front. It therefore allows the existence of a fluid lag. The fluid front is advanced explicitly in time, but an implicit strategy is needed for the crack tip to guarantee the satisfaction of Griffith's criterion at each time step. We enforced the coupling between the fluid and the rock by simultaneously solving for the pressure field in the fluid and the crack opening at each time step. We provided verification of our algorithm by performing sample simulations and comparing them with two known similarity solutions. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
87.
88.
89.
90.
Joaquín Tintoré Raúl Medina Lluís Gómez-Pujol Alejandro Orfila Guillermo Vizoso 《Ocean & Coastal Management》2009,52(10):493-505
Coastal zones and beach management practices, regulatory decisions, and land use planning activities along coastal zones have historically been made with insufficient information concerning the dynamic coastal environment. In this study we address and integrate an interdisciplinary scientific approach to Coastal Management in a scenario where lack of this information has resulted in the alteration of the natural dune system of the beach of Cala Millor (Mallorca, Balearic Islands, Spain), and also in the perception of the beach retreat and in a parallel way, a risk for the tourism resources. In this work the detailed studies on beach morphodynamics have been developed as a basis for integrating proper beach management, beach natural dynamics and local users and economic agent interests. From this point of view a set of solutions are considered as the basis for a management policy that links beach science and beach use as a tourism resort resource. 相似文献