全文获取类型
| 收费全文 | 42015篇 |
| 免费 | 7528篇 |
| 国内免费 | 7893篇 |
专业分类
| 测绘学 | 4042篇 |
| 大气科学 | 4685篇 |
| 地球物理 | 8640篇 |
| 地质学 | 21350篇 |
| 海洋学 | 4298篇 |
| 天文学 | 4804篇 |
| 综合类 | 3059篇 |
| 自然地理 | 6558篇 |
出版年
| 2024年 | 156篇 |
| 2023年 | 484篇 |
| 2022年 | 1298篇 |
| 2021年 | 1535篇 |
| 2020年 | 1457篇 |
| 2019年 | 1735篇 |
| 2018年 | 1345篇 |
| 2017年 | 1603篇 |
| 2016年 | 1631篇 |
| 2015年 | 1878篇 |
| 2014年 | 2350篇 |
| 2013年 | 2347篇 |
| 2012年 | 2461篇 |
| 2011年 | 2566篇 |
| 2010年 | 2203篇 |
| 2009年 | 2870篇 |
| 2008年 | 2815篇 |
| 2007年 | 3013篇 |
| 2006年 | 2823篇 |
| 2005年 | 2667篇 |
| 2004年 | 2335篇 |
| 2003年 | 2219篇 |
| 2002年 | 1885篇 |
| 2001年 | 1679篇 |
| 2000年 | 1677篇 |
| 1999年 | 1507篇 |
| 1998年 | 1351篇 |
| 1997年 | 981篇 |
| 1996年 | 862篇 |
| 1995年 | 694篇 |
| 1994年 | 662篇 |
| 1993年 | 559篇 |
| 1992年 | 416篇 |
| 1991年 | 338篇 |
| 1990年 | 267篇 |
| 1989年 | 212篇 |
| 1988年 | 173篇 |
| 1987年 | 103篇 |
| 1986年 | 75篇 |
| 1985年 | 44篇 |
| 1984年 | 19篇 |
| 1983年 | 13篇 |
| 1982年 | 15篇 |
| 1981年 | 11篇 |
| 1980年 | 14篇 |
| 1979年 | 10篇 |
| 1978年 | 18篇 |
| 1977年 | 7篇 |
| 1976年 | 4篇 |
| 1954年 | 23篇 |
排序方式： 共有10000条查询结果，搜索用时 515 毫秒
141.
P. A. Patsis 《Monthly notices of the Royal Astronomical Society》2005,358(2):305-315
We investigate the morphological relation between the orbits of the central family of periodic orbits ( x 1 family) and the bar itself using models of test particles moving in a barred potential. We show that different bar morphologies may have as a backbone the same set of x 1 periodic orbits. We point out that by populating initially axisymmetric stellar discs exponentially with test particles in circular, or almost circular motion, we may end up with a response bar which reveals a shape different in crucial details from that of the individual stable x 1 orbits. For example, a bar model in which the x 1 orbits are pure ellipses may have a much more complicated response morphology. This depends on the particular invariant curves around x 1 , which are populated in each model. 相似文献
142.
Motivated by recent high-resolution observations of the solar surface, we investigate the problem of non-linear magnetoconvection in a three-dimensional compressible layer. We present results from a set of numerical simulations which model the situation in which there is a weak imposed magnetic field. This weak-field regime is characterized by vigorous granular convection and spatially intermittent magnetic field structures. When the imposed field is very weak, magnetic flux tends to accumulate at the edges of the convective cells, where it forms compact, almost 'point-like' structures which are reminiscent of those observed in the quiet Sun. If the imposed field is slightly stronger, there is a tendency for magnetic flux to become concentrated into 'ribbon-like' structures which are comparable to those observed in solar plages. The dependence of these simulations upon the strength of the imposed magnetic field is analysed in detail, and the concept of the fractal dimension is used to make a further, more quantitative comparison between these simulations and photospheric observations. 相似文献
143.
国家重大科学工程项目LAMOST总控系统的程序设计是一个庞大的软件工程．其总控系统下共包括8个既相互独立又互有关联的子系统．如何通过良好的软件设计方法来处理好这8个子系统之间的关系使其协调运转，以及如何确保软件开发的可维护性、可持续性是研究重点． 相似文献
144.
145.
146.
提要 本文详细讨论了一种三维重力位场快速正反演方法。作者在前人工作的基础上,对算法作了行之有效的改进,通过对反演中的不稳定因素进行各种理论模型试算,得出保证迭代反演稳定收敛的准则,编制出可在微型机IBM—PC上运行的人机对话式自动正反演程序。本文还对各种不均质模型进行了模似计算并将该方法应用于某含油气沉积盆地的双层界面构造研究,揭示出了储油有利地段。 相似文献
147.
The process of non-linear ambipolar diffusion in the region overlying the solar surface can be an effective mechanism for producing sharp magnetic structures and current sheets. These may be the sites responsible for the occurrence of connectivity of magnetic field lines, and the subsequent explosive input of energy for heating of some of the features in the atmosphere of the Sun.. 相似文献
148.
149.
V. Castellani S. Degl'Innocenti P. G. Prada Moroni 《Monthly notices of the Royal Astronomical Society》2001,320(1):66-72
We compare theoretical stellar models for main sequence (MS) stars with the Hipparcos data base for the Hyades cluster to give a warning against the uncritical use of available theoretical scenarios and to show how formal MS fittings can be fortuitous if not fictitious. Moreover, we find that none of the current theoretical scenarios appears able to account for an observed mismatch between theoretical predictions and observations of the coolest Hyades MS stars. Finally, we show that current theoretical models probably give too faint He burning luminosities unlike the case of less massive He burning models, with degenerate progenitors, which have been suggested to suffer the opposite discrepancy. 相似文献
150.