全文获取类型
收费全文 | 254578篇 |
免费 | 5176篇 |
国内免费 | 3347篇 |
专业分类
测绘学 | 6847篇 |
大气科学 | 18876篇 |
地球物理 | 53472篇 |
地质学 | 88152篇 |
海洋学 | 21158篇 |
天文学 | 55791篇 |
综合类 | 1005篇 |
自然地理 | 17800篇 |
出版年
2021年 | 2219篇 |
2020年 | 2584篇 |
2019年 | 2836篇 |
2018年 | 3185篇 |
2017年 | 2820篇 |
2016年 | 5539篇 |
2015年 | 4184篇 |
2014年 | 6879篇 |
2013年 | 14189篇 |
2012年 | 6359篇 |
2011年 | 7561篇 |
2010年 | 6570篇 |
2009年 | 9218篇 |
2008年 | 8113篇 |
2007年 | 7488篇 |
2006年 | 9624篇 |
2005年 | 7605篇 |
2004年 | 7561篇 |
2003年 | 7056篇 |
2002年 | 6688篇 |
2001年 | 5982篇 |
2000年 | 5925篇 |
1999年 | 5196篇 |
1998年 | 5216篇 |
1997年 | 5026篇 |
1996年 | 4671篇 |
1995年 | 4423篇 |
1994年 | 4089篇 |
1993年 | 3841篇 |
1992年 | 3624篇 |
1991年 | 3583篇 |
1990年 | 3749篇 |
1989年 | 3508篇 |
1988年 | 3301篇 |
1987年 | 3844篇 |
1986年 | 3404篇 |
1985年 | 4216篇 |
1984年 | 4733篇 |
1983年 | 4400篇 |
1982年 | 4307篇 |
1981年 | 3923篇 |
1980年 | 3634篇 |
1979年 | 3504篇 |
1978年 | 3478篇 |
1977年 | 3275篇 |
1976年 | 3044篇 |
1975年 | 2956篇 |
1974年 | 2914篇 |
1973年 | 3073篇 |
1972年 | 2024篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
781.
T. T. Chia 《Astrophysics and Space Science》1985,114(1):151-156
In any theory of gravitation that predicts the existence of gravitational waves, it is shown that, in the absence of mass
exchange and mass loss and subjected to a condition, a circular binary system with spherically-symmetrical components cannot
evolve in such a way that the spin angular velocity is always a linear function of the orbital velocity. Probably this relation
between the angular velocities cannot be realized in any time interval. In particular, the system cannot remain in a synchronized
state. Of eight special cases of evolution of this binary system, three cases, where the separation increases, are shown to
be kinematically impossible while a restriction on the variation of a parameter governing the evaluation of the system can
be made in another.
In one of the kinematically allowed special cases the separation increases. 相似文献
782.
P. G. Niarchos 《Astrophysics and Space Science》2005,296(1-4):359-370
A new method for the determination of the proximity effects and gravity darkening exponents in contact binaries of W UMa type
is presented. The method is based on Kopal’s method of Fourier analysis of the light changes of eclipsing variables in the
Frequency Domain. The method was applied to 36 W UMa systems for which geometric and photometric elements have been derived
by the most powerful techniques. The derived values are very close to those predicted by the existing theory of radiative
transfer or convective equilibrium. 相似文献
783.
K.A. MAASCH P.A. MAYEWSKI E.J. ROHLING J.C. STAGER W. KARLEN L.D. MEEKER E.A. MEYERSON 《Geografiska Annaler: Series A, Physical Geography》2005,87(1):7-15
ABSTRACT. Although considerable attention has been paid to the record of temperature change over the last few centuries, the range and rate of change of atmospheric circulation and hydrology remain elusive. Here, eight latitudinally well-distributed (pole-equator-pole), highly resolved (annual to decadal) climate proxy records are presented that demonstrate major changes in these variables over the last 2000 years. A comparison between atmospheric 14 C and these changes in climate demonstrates a first-order relationship between a variable Sun and climate. The relationship is seen on a global scale. 相似文献
784.
785.
786.
The steady flow expansions of monatomic gases consisting of Maxwellia molecules into a vacuum moving under external forces with a source of spherical symmetry are investigated. The analysis is based on the B-G-K model of the Boltzmann equation with the approximation in hypersonic limit. The kinetic equation is solved by using the moment method. Analytical forms for the density and temperature are obtained for small and large distances from the source. The results show that the temperature in free expansion is less than that in the case of the expansion under the influence of external field of forces. 相似文献
787.
Skylab EUV observations of an active region near the solar limb were analyzed. Both cool (T < 106 K) and hot (T > 106 K) loops were observed in this region. For the hot loops the observed intensity variations were small, typically a few percent over a period of 30 min. The cool loops exhibited stronger variations, sometimes appearing and disappearing in 5 to 10 min. Most of the cool material observed in the loops appeared to be caused by the downward flow of coronal rain and by the upward ejection of chromospheric material in surges. The frequent EUV brightenings observed near the loop footpoints appear to have been produced by both in situ transient energy releases (e.g. subflares) and the infall/impact of coronal rain. The physical conditions in the loops (temperatures, densities, radiative and conducting cooling rates, cooling times) were determined. The mean energy required to balance the radiative and conductive cooling of the hot loops is approximately 3 × 10–3 erg cm–3 s–1. One coronal heating mechanism that can account for the observed behavior of the EUV emission from McMath region 12634 is heating by the dissipation of fast mode MHD waves. 相似文献
788.
789.
V. Maupin 《Geophysical Journal International》1985,83(2):379-398
Summary. Surface wave behaviour in flat anisotropic structures is first illustrated by performing an exact computation on a simple two-layer model. The variational procedure of Smith & Dahlen is then used to compute the partial derivatives of surface wave phase velocities with respect to the elastic parameters in more realistic earth models. Linear relationships between the partial derivatives for a general anisotropic structure and those for a transversely isotropic structure are derived. When considering waves propagating in a fixed direction, there are only four independent derivatives for Rayleigh waves, and two for Love waves. To avoid the lack of resolution in an inverse method, we propose to use physically constrained models. These results are illustrated by using a model with hexagonal symmetry and a symmetry axis oriented either vertically or horizontally. Quasi-Love- and quasi-Rayleigh-wave partial derivatives are computed for both axis orientations. Modes up to the second overtone and periods ranging between 45 and 130 s have been considered. Finally, anomalies of phase velocity are computed in an oceanic model made of 1/6 oriented olivine crystals with horizontal or vertical preferred orientations of the a -axis. 相似文献
790.
The lifetimes, characteristics of the shapes as well as lengths and perimeters of artificial solar granules (Nordlund, 1982, 1984a) are compared with data from the literature and parameters determined from two different sets of observed granules. No significant differences of the parameters for these sets of granules are detectable.Mitteilungen aus dem Kiepenheuer-Institut Nr. 251. 相似文献