全文获取类型
收费全文 | 1929篇 |
免费 | 63篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 43篇 |
大气科学 | 140篇 |
地球物理 | 933篇 |
地质学 | 492篇 |
海洋学 | 27篇 |
天文学 | 321篇 |
综合类 | 5篇 |
自然地理 | 41篇 |
出版年
2021年 | 25篇 |
2020年 | 29篇 |
2019年 | 21篇 |
2018年 | 47篇 |
2017年 | 61篇 |
2016年 | 78篇 |
2015年 | 66篇 |
2014年 | 74篇 |
2013年 | 101篇 |
2012年 | 37篇 |
2011年 | 55篇 |
2010年 | 77篇 |
2009年 | 60篇 |
2008年 | 59篇 |
2007年 | 52篇 |
2006年 | 45篇 |
2005年 | 20篇 |
2004年 | 39篇 |
2003年 | 40篇 |
2002年 | 42篇 |
2001年 | 32篇 |
2000年 | 27篇 |
1999年 | 21篇 |
1998年 | 32篇 |
1997年 | 17篇 |
1996年 | 34篇 |
1995年 | 19篇 |
1994年 | 30篇 |
1993年 | 26篇 |
1992年 | 27篇 |
1991年 | 23篇 |
1990年 | 24篇 |
1989年 | 20篇 |
1988年 | 28篇 |
1987年 | 25篇 |
1986年 | 29篇 |
1984年 | 33篇 |
1983年 | 30篇 |
1982年 | 35篇 |
1981年 | 24篇 |
1980年 | 22篇 |
1979年 | 37篇 |
1978年 | 29篇 |
1977年 | 24篇 |
1975年 | 20篇 |
1974年 | 23篇 |
1973年 | 23篇 |
1972年 | 24篇 |
1971年 | 24篇 |
1967年 | 16篇 |
排序方式: 共有2002条查询结果,搜索用时 31 毫秒
1.
Axel Wittmann Randy L. Korotev Bradley L. Jolliff Paul K. Carpenter 《Meteoritics & planetary science》2019,54(2):379-394
Magnesium‐rich spinel assemblages occur in the two lunar vitric breccia meteorites—Dhofar (Dho) 1528 and Graves Nunataks (GRA) 06157. Dho 1528 contains up to ~0.7 mm cumulate Mg‐rich spinel crystals associated with Mg‐rich olivine, Mg‐ and Al‐rich pyroxene, plagioclase, and rare cordierite. Using thermodynamic calculations of these mineral assemblages, we constrain equilibration depths and discuss an origin of these lithologies in the upper mantle of the Moon. In contrast, small, 10 to 20 μm spinel phenocryst assemblages in glassy melt rock clasts in Dho 1528 and GRA 06157 formed from the impact melting of Mg‐rich rocks. Some of these spinel phenocrysts match compositional constraints for spinel associated with “pink spinel anorthosites” inferred from remote sensing data. However, such spinel phenocrysts in meteorites and Apollo samples are typically associated with significant amounts of olivine ± pyroxene that exceed the compositional constraints for pink spinel anorthosites. We conclude that the remotely sensed “pink spinel anorthosites” have not been observed in the collections of lunar rocks. Moreover, we discuss impact‐excavation scenarios for the spinel‐bearing assemblages in Dhofar 1528 and compare the bulk rock composition of Dho 1528 to strikingly similar compositions of Luna 20 samples that contain ejecta from the Crisium impact basin. 相似文献
2.
Brigitta von Rekowski Axel Brandenburg Wolfgang Dobler Anvar Shukurov 《Astrophysics and Space Science》2004,292(1-4):493-500
An axisymmetric model of a cool, dynamo-active accretion disc is applied to protostellar discs. Thermally and magnetically driven outflows develop that are not collimated within 0.1 AU. In the presence of a central magnetic field from the protostar, accretion onto the protostar is highly episodic, which is in agreement with earlier work. 相似文献
3.
New determination of the Earth orientation parameters (EOP), based on optical astrometry observations since the beginning of the century, is now under preparation by the Working group established by Commission 19 of the IAU. The Hipparcos catalog is to define the celestial reference frame in which the new series of EOP are to be described, The novelties of the prepared solution are the higher resolution (5 days) and more parameters estimated from the solution (celestial pole offsets, rheological parameters of the Earth, certain instrumental constants). The mathematical model of the solution is described, and the results based on the observations made with 46 instruments at 29 observatories and a preliminary Hipparcos catalog are presented. 相似文献
4.
Sonja Vrielmann Axel D. Schwope 《Monthly notices of the Royal Astronomical Society》2001,322(2):269-279
We present a new mapping algorithm, the Accretion Stream Mapping (ASM), which uses the full phase-coverage of a light curve to derive spatially resolved intensity distributions along the accretion stream in magnetic cataclysmic variables of AM Herculis type (polars). The surface of the accretion stream is approximated as a 12-sided (duodecadon-shaped) tube. After successfully testing this method on artificial data we applied it to emission-line light curves of H β , H γ and He ii λ 4686 of the bright eclipsing polar HU Aqr. We find hydrogen and helium line emission bright in the threading region of the stream where the stream couples on to magnetic field lines. It is particularly interesting that the stream is bright on the irradiated side facing the white dwarf, which highlights the interplay of collisional and radiative excitation/ionization. 相似文献
5.
G. Djurašević P. Rovithis H. Rovithis-Livaniou E. Fragoulopoulou 《Astrophysics and Space Science》2005,296(1-4):311-314
BV light curves of the eclipsing binary UV Leo obtained at the Kryonerion Astronomical Station of the National Observatory of
Athens, Greece, are analyzed. The analysis is based on a Roche configuration with two spots on the secondary surface. The
elements of the two components of the system are calculated and the spot characteristics are given. 相似文献
6.
Axel Born 《International Journal of Earth Sciences》1930,21(1):1-14
Ohne Zusammenfassung 相似文献
7.
Milan Burša 《Earth, Moon, and Planets》1992,56(1):57-60
The tidal long-term decrease in the angular velocity of the Earth's rotation has been estimated on the basis of the angular momentum tidal balance in the Earth-Moon-Sun system. The observed (LLR) tidal long-term decrease in the Moon's mean motion, the apparent secular acceleration in the mean longitude of the Sun and the long-term decrease in the 2nd degree zonal geopotential parameter were used.Presented at the XXth General Assembly of the I.A.G., Vienna, August 15, 1991. 相似文献
8.
F.Z. Feygin YU.P. Kurchashov V.A. Troitskaya K. Dobeš 《Planetary and Space Science》1985,33(3):271-273
A high resolution numerical sonagram of Pc-1 magnetic record has shown that single narrow lines of Pc-1 spectra produce lower frequency (“red-shifted”) satellite lines more than twice as often as their higher frequency (“violet”) counterparts. The violet satellites usually emerge only when at least two ancestor lines are present simultaneously. 相似文献
9.
The behaviour of the flare in the period of enhancement and maximum of hard X-ray, microwave and decimetric type IV continuum is analysed. The elongation of the H ribbons and microwave source disclose that the energy release site was shifting through a system of loops with a velocity less than 200 km s-1, and that the energy was carried down the field lines with a velocity of about 1000 km s-1, implying the thermal conduction front mechanism of energy transport. Several processes of energy release are considered and it is concluded that an explanation in terms of succeeding interactions of neighbouring loops, involving fast reconnection of their poloidal components is in best agreement with the observations.Proceedings of the Second CESRA Workshop on Particle Acceleration and Trapping in Solar Flares, held at Aubigny-sur-Nère (France), 23–26 June, 1986. 相似文献
10.
Milan Burša 《Studia Geophysica et Geodaetica》1991,35(3):145-150
Summary The estimate of the tidal long-term decrease in the angular velocity of the Earth's rotation due to the Sun is given as –(0.8±0.3)×10
–22
rad s
–2. It was computed on the basis of the observed total long-term decrease in , of the observed tidal deceleration of the Moon and the observed decrease in the second-degree zonal Stokes geopotential harmonic term. Adopting the estimate given, the product of the Love number and the tidal phase lag angle due to the Sun (in degrees) comes out as 0.53±0.20.
am a z nuuu u z mu au u, az : –(0,8±0,3) 10 –22 a¶rt; –2 . ¶rt; ua n a¶rt;a u , n a¶rt;a nuu u ¶rt;z ¶rt;uu u n a¶rt;a u mz az znmuaz naama ma. u num n au, m nu¶rt;u ua a a z u ( za¶rt;a) a z nuua a (0,53±0,20).相似文献