全文获取类型
收费全文 | 20942篇 |
免费 | 721篇 |
国内免费 | 324篇 |
专业分类
测绘学 | 813篇 |
大气科学 | 469篇 |
地球物理 | 1018篇 |
地质学 | 1995篇 |
海洋学 | 356篇 |
天文学 | 16565篇 |
综合类 | 174篇 |
自然地理 | 597篇 |
出版年
2024年 | 46篇 |
2023年 | 96篇 |
2022年 | 164篇 |
2021年 | 133篇 |
2020年 | 140篇 |
2019年 | 185篇 |
2018年 | 101篇 |
2017年 | 93篇 |
2016年 | 110篇 |
2015年 | 218篇 |
2014年 | 201篇 |
2013年 | 215篇 |
2012年 | 277篇 |
2011年 | 288篇 |
2010年 | 317篇 |
2009年 | 1648篇 |
2008年 | 1586篇 |
2007年 | 1859篇 |
2006年 | 1857篇 |
2005年 | 1712篇 |
2004年 | 1792篇 |
2003年 | 1548篇 |
2002年 | 1331篇 |
2001年 | 1200篇 |
2000年 | 968篇 |
1999年 | 912篇 |
1998年 | 1107篇 |
1997年 | 241篇 |
1996年 | 132篇 |
1995年 | 288篇 |
1994年 | 305篇 |
1993年 | 144篇 |
1992年 | 82篇 |
1991年 | 96篇 |
1990年 | 79篇 |
1989年 | 133篇 |
1988年 | 83篇 |
1987年 | 88篇 |
1986年 | 74篇 |
1985年 | 37篇 |
1984年 | 27篇 |
1983年 | 22篇 |
1982年 | 5篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1977年 | 6篇 |
1954年 | 3篇 |
1905年 | 3篇 |
1900年 | 3篇 |
1897年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
A highly automated moving object detection package 总被引:1,自引:0,他引:1
43.
44.
Cygnus A was the first hyper-active galaxy discovered, and it
remains by far the closest of the ultra-luminous radio galaxies. As
such, Cygnus A has played a fundamental role in the study of virtually
all aspects of extreme activity in galaxies. We present a review of jet
theory for powering the double-lobed radio emitting structures in
powerful radio galaxies, followed by a review of observations of Cygnus
A in the radio, optical, and X-ray relevant to testing various aspects
of jet theory. Issues addressed include: jet structure from pc- to
kpc-scales, jet stability, confinement, composition, and velocity, the
double shock structure for the jet terminus and the origin of multiple
radio hotspots, the nature of the filamentary structure in the radio
lobes, and the hydrodynamic evolution of the radio lobes within a dense
cluster atmosphere, including an analysis of pressure balance between
the various gaseous components. Also discussed are relativistic
particle acceleration and loss mechanisms in Cygnus A, as well as
magnetic field strengths and geometries both within the radio source,
and in the intracluster medium. We subsequently review the
classification, cluster membership, and the emission components of the
Cygnus A galaxy. The origin of the activity is discussed.
Concentrating on the nuclear regions of the galaxy, we review the
evidence for an obscured QSO, also given the constraints on the
orientation of the radio source axis with respect to the sky plane. We
present an overview of models of central engines in AGN and observations
of Cygnus A which may be relevant to testing such models. We conclude
with a brief section concerning the question of whether Cygnus A is
representative of powerful high redshift radio galaxies.
Received October 10, 1995 相似文献
45.
46.
47.
48.
George Saklatvala Michael P. Hobson Stafford Withington 《Monthly notices of the Royal Astronomical Society》2006,367(3):1194-1200
We describe a procedure for the numerical modelling of astronomical interferometers, with particular relevance to far-infrared and submillimetre wavelengths. The scheme is based on identifying a set of modes that carry power from the sky to the detector. The procedure is extremely general, and can be used to model scalar or vector fields, in any state of coherence and polarization, the only limitation being that the propagation of a coherent field through the system be described by an integral transform, a constraint that is in practise always met.
We present simulations of ideal, multimode two-dimensional interferometers, and show that the modal theory reproduces the correct behaviour of both Michelson and Fizeau interferometers. We calculate simulated visibility data for a multimode bolometric Michelson interferometer, with a synthesized source, and produce a dirty map, recovering the original source with the usual artefacts associated with interferometers. 相似文献
We present simulations of ideal, multimode two-dimensional interferometers, and show that the modal theory reproduces the correct behaviour of both Michelson and Fizeau interferometers. We calculate simulated visibility data for a multimode bolometric Michelson interferometer, with a synthesized source, and produce a dirty map, recovering the original source with the usual artefacts associated with interferometers. 相似文献
49.
50.