全文获取类型
收费全文 | 20585篇 |
免费 | 532篇 |
国内免费 | 200篇 |
专业分类
测绘学 | 449篇 |
大气科学 | 202篇 |
地球物理 | 538篇 |
地质学 | 1887篇 |
海洋学 | 256篇 |
天文学 | 17368篇 |
综合类 | 95篇 |
自然地理 | 522篇 |
出版年
2024年 | 46篇 |
2023年 | 76篇 |
2022年 | 157篇 |
2021年 | 96篇 |
2020年 | 96篇 |
2019年 | 165篇 |
2018年 | 58篇 |
2017年 | 46篇 |
2016年 | 75篇 |
2015年 | 178篇 |
2014年 | 160篇 |
2013年 | 156篇 |
2012年 | 242篇 |
2011年 | 235篇 |
2010年 | 298篇 |
2009年 | 1617篇 |
2008年 | 1561篇 |
2007年 | 1841篇 |
2006年 | 1841篇 |
2005年 | 1716篇 |
2004年 | 1788篇 |
2003年 | 1540篇 |
2002年 | 1344篇 |
2001年 | 1162篇 |
2000年 | 946篇 |
1999年 | 891篇 |
1998年 | 1060篇 |
1997年 | 240篇 |
1996年 | 108篇 |
1995年 | 295篇 |
1994年 | 306篇 |
1993年 | 129篇 |
1992年 | 77篇 |
1991年 | 93篇 |
1990年 | 91篇 |
1989年 | 146篇 |
1988年 | 97篇 |
1987年 | 96篇 |
1986年 | 79篇 |
1985年 | 45篇 |
1984年 | 30篇 |
1983年 | 28篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1977年 | 6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
51.
52.
53.
On the origins of part-time radio pulsars 总被引:1,自引:0,他引:1
Bing Zhang Janusz Gil Jaroslaw Dyks 《Monthly notices of the Royal Astronomical Society》2007,374(3):1103-1107
54.
Masatoshi Taga & Masanori Iye 《Monthly notices of the Royal Astronomical Society》1998,299(1):111-117
In this paper we show the positional oscillation of a massive object in a dense stellar system by numerical N -body simulations. We found that the central massive object, which at first is placed at rest at the centre of the surrounding spherical stellar system, promptly departs from the centre and rotates in accordance with the rotation of the stellar system, if the stellar system has an appreciable rotation. This oscillatory motion continues for a long time because of the absence of dynamical friction. Such a long-lasting oscillation may explain the asymmetric structure observed in the centres of M31 and NGC 4486B, may cause the secular flow of gaseous elements distributed in the central regions of galaxies on to the massive object, and may ignite activity in the centres of galaxies. 相似文献
55.
Rui-Xiang Chang Cheng-Gang Shu Jin-Liang Hou Shanghai Astronomical Observatory Chinese Academy of Sciences Shanghai CAS-Peking University Joint Beijing Astronomical Center Beijing 《中国天文和天体物理学报》2002,2(3)
Based on a physical treatment of the star formation law similar to that given by Efstathiou, we have improved our two-component chemical evolution model for the Milky Way disk. Two gas infall rates are compared, one exponential, one Gaussian. It is shown that the star formation law adopted in this paper depends more strongly on the gas surface density than that in Chang et al. It has large effects on the history of star formation and gas evolution of the whole disk. In the solar neighborhood, the history of chemical evolution and star formation is not sensitive to whether the infall rate is Gaussian or exponential. For the same infall time scale, both forms predict the same behavior for the current properties of the Galactic disk. The model predictions do depend on whether or not the infall time scale varies with the radius, but current available observations cannot decide which case is the more realistic. Our results also show that it would be inadequate to describe the gradient evolution along the Gala 相似文献
56.
We use the Hubble Ultra Deep Field to study the galaxy luminosity–size ( M – R e ) distribution. With a careful analysis of selection effects due to both detection completeness and measurement reliability, we identify bias-free regions in the M – R e plane for a series of volume-limited samples. By comparison to a nearby survey also having well-defined selection limits, namely the Millennium Galaxy Catalogue, we present clear evidence for evolution in surface brightness since z ∼ 0.7 . Specifically, we demonstrate that the mean, rest-frame B -band 〈μ〉 e for galaxies in a sample spanning 8 mag in luminosity between M B =−22 and −14 mag increases by ∼1.0 mag arcsec−2 from z ∼ 0.1 to 0.7. We also highlight the importance of considering surface brightness-dependent measurement biases in addition to incompleteness biases. In particular, the increasing, systematic underestimation of Kron fluxes towards low surface brightnesses may cause diffuse, yet luminous, systems to be mistaken for faint, compact objects. 相似文献
57.
58.
59.
P. F. L. Maxted C. K. J. Moran T. R. Marsh A. A. Gatti 《Monthly notices of the Royal Astronomical Society》2000,311(4):877-880
We have used the radial velocity variations of two sdB stars previously reported to be binaries to establish their orbital periods. They are PG 0940+068 ( P =8.33 d) and PG 1247+554 ( P =0.599 d). The minimum masses of the unseen companions, assuming a mass of 0.5 M⊙ for the sdB stars, are 0.090±0.003 M. for PG 1247+554 and 0.63±0.02 M⊙ for PG 0940+068. The nature of the companions is not constrained further by our data. 相似文献
60.
We investigate the dynamical evolution of 210 hypothetical massless bodies initially situated between 10 and 30 au from the Sun in order to determine the general characteristics of the evolved system. This is of particular relevance to the understanding of the origin of Edgeworth–Kuiper belt objects on scattered intermediate orbits, such as 1996 TL 66 , which have high eccentricity and semimajor axis but nevertheless have perihelion in the region between 30 and 50 au from the Sun. 相似文献