全文获取类型
收费全文 | 13966篇 |
免费 | 615篇 |
国内免费 | 145篇 |
专业分类
测绘学 | 353篇 |
大气科学 | 1086篇 |
地球物理 | 4125篇 |
地质学 | 4830篇 |
海洋学 | 1003篇 |
天文学 | 2043篇 |
综合类 | 65篇 |
自然地理 | 1221篇 |
出版年
2022年 | 74篇 |
2021年 | 202篇 |
2020年 | 252篇 |
2019年 | 232篇 |
2018年 | 448篇 |
2017年 | 425篇 |
2016年 | 588篇 |
2015年 | 451篇 |
2014年 | 525篇 |
2013年 | 823篇 |
2012年 | 584篇 |
2011年 | 656篇 |
2010年 | 609篇 |
2009年 | 719篇 |
2008年 | 591篇 |
2007年 | 549篇 |
2006年 | 479篇 |
2005年 | 412篇 |
2004年 | 392篇 |
2003年 | 418篇 |
2002年 | 325篇 |
2001年 | 292篇 |
2000年 | 311篇 |
1999年 | 218篇 |
1998年 | 235篇 |
1997年 | 203篇 |
1996年 | 181篇 |
1995年 | 203篇 |
1994年 | 201篇 |
1993年 | 144篇 |
1992年 | 144篇 |
1991年 | 109篇 |
1990年 | 154篇 |
1989年 | 119篇 |
1988年 | 123篇 |
1987年 | 127篇 |
1986年 | 123篇 |
1985年 | 157篇 |
1984年 | 168篇 |
1983年 | 168篇 |
1982年 | 155篇 |
1981年 | 117篇 |
1980年 | 101篇 |
1979年 | 109篇 |
1978年 | 117篇 |
1977年 | 103篇 |
1976年 | 90篇 |
1975年 | 109篇 |
1974年 | 86篇 |
1973年 | 112篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
21.
Jean-Pierre Macquart Kinwah Wu Diana C. Hannikainen Robert J. Sault David L. Jauncey 《Astrophysics and Space Science》2003,288(1-2):105-119
We compare the observational properties of the circular polarization in Galactic jet sources with that observed in AGN, and outline the constraints they place on the mechanism responsible for the circular polarization. We also discuss the implications of the time scale of polarization variations on the mechanism responsible for the circular polarization. 相似文献
22.
Hector Socas-Navarro David Elmore Anna Pietarila Anthony Darnell Bruce W. Lites Steven Tomczyk Steven Hegwer 《Solar physics》2006,235(1-2):55-73
The Spectro-Polarimeter for Infrared and Optical Regions (SPINOR) is a new spectro-polarimeter that will serve as a facility
instrument for the Dunn Solar Telescope at the National Solar Observatory. This instrument is capable of achromatic polarimetry
over a very broad range of wavelengths, from 430 to 1600 nm, allowing for the simultaneous observation of several visible
and infrared spectral regions with full Stokes polarimetry. Another key feature of the design is its flexibility to observe
virtually any combination of spectral lines, limited only by practical considerations (e.g., the number of detectors available, space on the optical bench, etc.).
Visiting Astronomers, National Solar Observatory, operated by the Association of Universities for Research in Astronomy, Inc.
(AURA), under cooperative agreement with the National Science Foundation. 相似文献
23.
24.
25.
We investigate the role of seasonal variations of Titan’s stratospheric composition on the temperature. We use a general circulation model coupled with idealized chemical tracers that reproduce variations of ethane (C2H6), acetylene (C2H2), and hydrogen cyanide (HCN). Enhancement of the mole fractions of these compounds, at high latitudes in the winter hemisphere relative to their equatorial values, induces a relative decrease in temperature above approximately 0.2 mbar, with a peak amplitude around −20 K, and a relative increase in temperature below, around 1 mbar, with a peak amplitude around +7 K. These thermal effects are mainly due to the variations of the cooling to space induced by the varying distributions. The ethane, acetylene, and hydrogen cyanide variations affect the cooling rates in a similar way, with the dominant effect being due to ethane, though its latitudinal variations are small. 相似文献
26.
We present a photometric analysis of the eclipsing binary systemGSC4832.400 based on 732 photometric observations obtained on sixteen clear nights during 1999–2000 in the V-Johnson and yb-Strömgren filters. The observed times of the minima yielded a linear ephemeris showing that the system has a constant period of 0.313150 ± 0.000002days. The light curve corresponds to a circular orbit for the system and clearly shows that GSC4832.400 has the defining characteristics of a W UMa-type eclipsing binary. It also shows a small O'Connell effect, which could be due to the presence of a hot spot in the primary star. A preliminary photometric solution based on the assumption of an over contact systemsatis factorily reproduced the observed light curve. 相似文献
27.
The steady-state population of bodies resulting from a collisional cascade depends on how material strength varies with size. We find a simple expression for the power-law index of the population, given a power law that describes how material strength varies with size. This result is extended to the case relevant for the asteroid belt and Kuiper belt, in which the material strength is described by 2 separate power laws—one for small bodies and one for larger bodies. We find that the power-law index of the small body population is unaffected by the strength law for the large bodies, and vice versa. Simple analytical expressions describe a wave that is superimposed on the large body population because of the transition between the two power laws describing the strength. These analytical results yield excellent agreement with a numerical simulation of collisional evolution. These results will help to interpret observations of the asteroids and KBOs, and constrain the strength properties of those objects. 相似文献
28.
David Lowenthal 《GeoJournal》2006,65(1-2):3-15
Western classical music was long distinctive among the arts for its universality and catholicity. From Greek antiquity on, music uniquely reflected Orphic, mystic, celestial feeling, And unlike painting, architecture, or literature, the standard musical canon came to be breathtakingly inclusive over time as well as space. Yet in recent centuries music has increasingly celebrated national patriotism and period particularism. This essay traces the histories of these antithetical expressive urges, the one universalistic, transcendental, atemporal, the other chauvinist, parochial, historicist. 相似文献
29.
30.
Attila Mészáros 《Astrophysics and Space Science》1985,111(2):399-405
Graviton may, in principle, have a small non-zero mass. In this paper the relevant theory of the massive graviton with six polarisations is developed. The drastic impact of a non-zero mass of the graviton on cosmology is also illustrated. 相似文献