全文获取类型
收费全文 | 119667篇 |
免费 | 3307篇 |
国内免费 | 1051篇 |
专业分类
测绘学 | 3037篇 |
大气科学 | 8727篇 |
地球物理 | 25630篇 |
地质学 | 41785篇 |
海洋学 | 10261篇 |
天文学 | 26323篇 |
综合类 | 311篇 |
自然地理 | 7951篇 |
出版年
2021年 | 964篇 |
2020年 | 1172篇 |
2019年 | 1324篇 |
2018年 | 2676篇 |
2017年 | 2586篇 |
2016年 | 3360篇 |
2015年 | 2246篇 |
2014年 | 3366篇 |
2013年 | 6398篇 |
2012年 | 3487篇 |
2011年 | 4788篇 |
2010年 | 4112篇 |
2009年 | 5484篇 |
2008年 | 5104篇 |
2007年 | 4683篇 |
2006年 | 4557篇 |
2005年 | 3770篇 |
2004年 | 3790篇 |
2003年 | 3564篇 |
2002年 | 3334篇 |
2001年 | 3006篇 |
2000年 | 2926篇 |
1999年 | 2402篇 |
1998年 | 2448篇 |
1997年 | 2346篇 |
1996年 | 2006篇 |
1995年 | 1957篇 |
1994年 | 1765篇 |
1993年 | 1604篇 |
1992年 | 1527篇 |
1991年 | 1394篇 |
1990年 | 1596篇 |
1989年 | 1373篇 |
1988年 | 1227篇 |
1987年 | 1506篇 |
1986年 | 1311篇 |
1985年 | 1646篇 |
1984年 | 1841篇 |
1983年 | 1750篇 |
1982年 | 1628篇 |
1981年 | 1508篇 |
1980年 | 1344篇 |
1979年 | 1252篇 |
1978年 | 1314篇 |
1977年 | 1194篇 |
1976年 | 1139篇 |
1975年 | 1069篇 |
1974年 | 1070篇 |
1973年 | 1064篇 |
1972年 | 683篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
A. Quirrenbach J. Larkin M. Barczys T. Gasaway C. Iserlohe A. Krabbe M. McElwain I. Song J. Weiss S. Wright 《New Astronomy Reviews》2006,49(10-12):639
OSIRIS (OH-Suppressing Infra-Red Integral-field Spectrograph) is a new facility instrument for the Keck Observatory. After seeing first light in February 2005, OSIRIS is currently undergoing commissioning. OSIRIS provides the capability of performing three-dimensional spectroscopy in the near-infrared z, J, H, and K bands at the resolution limit of the Keck II telescope, which is equipped with adaptive optics and a laser guide star. The science case for OSIRIS is summarized, and the instrument and associated data reduction software are described. 相似文献
102.
J. M. Diego J. Mohr J. Silk G. Bryan 《Monthly notices of the Royal Astronomical Society》2003,341(2):599-608
We develop a new method to estimate the redshift of galaxy clusters through resolved images of the Sunyaev–Zel'dovich effect (SZE). Our method is based on morphological observables which can be measured by actual and future SZE experiments. We test the method with a set of high-resolution hydrodynamical simulations of galaxy clusters at different redshifts. Our method combines the observables in a principal component analysis. After calibrating the method with an independent redshift estimation for some of the clusters, we show – using a Bayesian approach – how the method can give an estimate of the redshift of the galaxy clusters. Although the error bars given by the morphological redshift estimation are large, it should be useful for future SZE surveys where thousands of clusters are expected to be detected; a first preselection of the high-redshift candidates could be done using our proposed morphological redshift estimator. Although not considered in this work, our method should also be useful to give an estimate of the redshift of clusters in X-ray and optical surveys. 相似文献
103.
104.
S.J Weidenschilling 《Icarus》2003,165(2):438-442
For standard cosmic abundances of heavy elements, a layer of small particles in the central plane of the solar nebula cannot attain the critical density for gravitational instability. Youdin and Shu (2002, Astrophys. J. 580, 494-505) suggest that the local surface density of solids can be enhanced by radial migration of particles due to gas drag. However, they consider only motions of individual particles. Collective motion due to turbulent stress on the particle layer acts to inhibit such enhancement and may prevent gravitational instability. 相似文献
105.
106.
V. J. Mclntyre A. C. Gilmore J. B. Hearnshaw 《Journal of Astrophysics and Astronomy》1990,11(1):81-123
Photographic spectra of SN1987A in the LMC have been obtained from 1987 February 25 to 1988 June 30. Microdensitometer tracings
of these have been reduced to intensity and corrections for instrumental response have been applied to the spectra. This paper
presents these data in an atlas format, discusses the reduction procedures in detail, and presents radial velocity measurements
of selected lines in the spectra 相似文献
107.
An introduction to Maslov's asymptotic method 总被引:3,自引:0,他引:3
Summary. Familiar concepts such as asymptotic ray theory and geometrical spreading are now recognized as an asymptotic form of a more general asymptotic solution to the non-separable wave equation. In seismology, the name Maslov asymptotic theory has been attached to this solution. In its simplest form, it may be thought of as a justification of disc-ray theory and it can be reduced to the WKBJ seismogram. It is a uniformly valid asymptotic solution, though. The method involves properties of the wavefronts and ray paths of the wave equation which have been established for over a century. The integral operators which build on these properties have been investigated only comparatively recently. These operators are introduced very simply by appealing to the asymptotic Fourier transform of Ziolkowski & Deschamps. This leads quite naturally to the result that phase functions in different domains of the spatial Fourier transform are related by a Legendre transformation. The amplitude transformation can also be inferred by this method. Liouville's theorem (the incompressibility of a phase space of position and slowness) ensures that it is always possible to obtain a uniformly asymptotic solution. This theorem can be derived by methods familiar to seismologists and which do not rely on the traditional formalism of classical mechanics. It can also be derived from the sympletic property of the equations of geometrical spreading and canonical transformations in general. The symplectic property plays a central role in the theory of high-frequency beams in inhomogeneous media. 相似文献
108.
Thomas M. Tharp 《Geophysical Journal International》1985,80(2):419-437
Summary. Finite element models for shallow subduction produce realistic behaviour for a wide variety of mechanical strength and density distributions. Characteristic displacements are found to occur even without a discrete low-strength megathrust if there is a high-density subducted plate to localize lithospheric compression. A high-density plate is itself unnecessary in the presence of a low-strength megathrust and regional compression.
Successful finite element models produce an outer arc at the top of the trench slope, and forearc basin with geometry characteristic of natural analogues. These structural features occur by upward inelastic bending of the lithospheric wedge overlying the megathrust. This mechanically unstable behaviour may dissipate significant energy and cause the megathrust to migrate continuously by accretion, tectonic erosion, or abandonment and reinitiation farther offshore. Upward bending in the overriding plate is promoted by low megathrust dip, low megathrust shear strength, and high horizontal compression in the overriding plate. 相似文献
Successful finite element models produce an outer arc at the top of the trench slope, and forearc basin with geometry characteristic of natural analogues. These structural features occur by upward inelastic bending of the lithospheric wedge overlying the megathrust. This mechanically unstable behaviour may dissipate significant energy and cause the megathrust to migrate continuously by accretion, tectonic erosion, or abandonment and reinitiation farther offshore. Upward bending in the overriding plate is promoted by low megathrust dip, low megathrust shear strength, and high horizontal compression in the overriding plate. 相似文献
109.
Richard J. Pike 《The Professional geographer》1987,39(2):131-145
Extraterrestrial geography has become a reality, as we move from Earth's moon to the planets. A broad-scale regional physiography is being established on twenty planets and satellites through remote sensing techniques. Spacecraft images yield most of the information on Solar System landscapes. Topographic measurements are extracted by monoscopic image-processing, stereophotogrammetry, and radar analysis. Invisible parts of the spectrum furnish non-topographic data. 相似文献
110.
Byurakan Astrophysical Observatory. Translated from Astrofizika, Vol. 33, No. 2, pp. 271–281, September–October, 1990. 相似文献