全文获取类型
| 收费全文 | 29039篇 |
| 免费 | 6356篇 |
| 国内免费 | 6606篇 |
专业分类
| 测绘学 | 1462篇 |
| 大气科学 | 1732篇 |
| 地球物理 | 4962篇 |
| 地质学 | 21056篇 |
| 海洋学 | 3029篇 |
| 天文学 | 5250篇 |
| 综合类 | 1786篇 |
| 自然地理 | 2724篇 |
出版年
| 2024年 | 135篇 |
| 2023年 | 434篇 |
| 2022年 | 965篇 |
| 2021年 | 1243篇 |
| 2020年 | 1178篇 |
| 2019年 | 1356篇 |
| 2018年 | 1192篇 |
| 2017年 | 1280篇 |
| 2016年 | 1402篇 |
| 2015年 | 1407篇 |
| 2014年 | 1909篇 |
| 2013年 | 1976篇 |
| 2012年 | 2076篇 |
| 2011年 | 2269篇 |
| 2010年 | 1993篇 |
| 2009年 | 2404篇 |
| 2008年 | 2272篇 |
| 2007年 | 2319篇 |
| 2006年 | 2054篇 |
| 2005年 | 1780篇 |
| 2004年 | 1563篇 |
| 2003年 | 1318篇 |
| 2002年 | 1111篇 |
| 2001年 | 1100篇 |
| 2000年 | 1013篇 |
| 1999年 | 862篇 |
| 1998年 | 720篇 |
| 1997年 | 468篇 |
| 1996年 | 428篇 |
| 1995年 | 334篇 |
| 1994年 | 291篇 |
| 1993年 | 256篇 |
| 1992年 | 213篇 |
| 1991年 | 131篇 |
| 1990年 | 107篇 |
| 1989年 | 84篇 |
| 1988年 | 79篇 |
| 1987年 | 37篇 |
| 1986年 | 44篇 |
| 1985年 | 48篇 |
| 1984年 | 39篇 |
| 1983年 | 22篇 |
| 1982年 | 20篇 |
| 1981年 | 8篇 |
| 1980年 | 14篇 |
| 1979年 | 7篇 |
| 1978年 | 7篇 |
| 1977年 | 21篇 |
| 1954年 | 4篇 |
| 1875年 | 1篇 |
排序方式： 共有10000条查询结果，搜索用时 188 毫秒
101.
102.
103.
We present a new Very Large Array (VLA) image of Saturn, made from data taken in October 1998 at a wavelength of λ3.6 cm. The moderate ring opening angle (B≈15°) allows us to explore direct transmission of microwave photons through the A and C rings. We find a strong asymmetry of photons transmitted through the A ring, but not in the C ring, a new diagnostic of wake structure in the ring particles. We also find a weak asymmetry between east and west for the far side of the ansae. To facilitate quantitative comparison between dynamic models of the A ring and radio observations, we extend our Monte Carlo radiative transfer code (described in Dunn et al., 2002, Icarus 160, 132-160) to include idealized wakes. We show the idealized model can reproduce the properties of dynamic simulations in directly transmitted light. We examine the model behavior in directly transmitted and scattered light over a range of physical and geometric wake parameters. Finally, we present a wake model with a plausible set of physical parameters that quantitatively reproduces the observed intensity and asymmetry of the A ring both across the planet and in the ansae. 相似文献
104.
This paper is aimed towards investigating the filtration law of an incompressible viscous Newtonian fluid through a rigid non-inertial porous medium (e.g. a porous medium placed in a centrifuge basket). The filtration law is obtained by upscaling the flow equations at the pore scale. The upscaling technique is the homogenization method of multiple scale expansions which rigorously gives the macroscopic behaviour and the effective properties without any prerequisite on the form of the macroscopic equations. The derived filtration law is similar to Darcy's law, but the tensor of permeability presents the following remarkable properties: it depends upon the angular velocity of the porous matrix, it verifies Hall–Onsager's relationship and it is a non-symmetric tensor. We thus deduce that, under rotation, an isotropic porous medium leads to a non-isotropic effective permeability. In this paper, we present the results of numerical simulations of the flow through rotating porous media. This allows us to highlight the deviations of the flow due to Coriolis effects at both the microscopic scale (i.e. the pore scale), and the macroscopic scale (i.e. the sample scale). The above results confirm that for an isotropic medium, phenomenological laws already proposed in the literature fails at reproducing three-dimensional Coriolis effects in all types of pores geometry. We show that Coriolis effects may lead to significant variations of the permeability measured during centrifuge tests when the inverse Ekman number Ek−1 is 𝒪(1). These variations are estimated to be less than 5% if Ek−1<0.2, which is the case of classical geotechnical centrifuge tests. We finally conclude by showing that available experimental data from tests carried out in centrifuges are not sufficient to determining the effective tensor of permeability of rotating porous media. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
105.
WANG Li-ping LI Chuang TANG Bing-yong 《东北亚地学研究》2005,8(1):78-93
The Donghetang Formation （Upper Devonian） in central Tarim Basin has been thought an important oil and gas reservoir since the abundant oil and gas resources were found in the wells W16, W20, W34, and other fields. However, the sedimentary environment of the Donghetang Formation has been disputed because it suffered from both tidal and fluvial actions and there were not rich fossils in the sandstone. After the authors analyzed sedimentary features by means of drill cores, well logging data, paleosols, and with SEM obseruations, three kinds of sedimentary environments were distinguished： alluvial fan, tide-dominated estuary, and shelf. Particularly, the sedimentary features of tide-dominated estuary were studied in detail. Besides, the authors discussed sedimentary characteristics of the Donghetang Formation which was divided into two fourth-order sequences and five system tracts. At the same time, according to the forming process of five system tracts, the whole vertical evolution and lateral transition of tide-dominated estuary were illustrated clearly. Finally, the reservoir quality was evaluated based on porosity and permeability. 相似文献
106.
107.
108.
109.
110.
本文在Ｔｈｏｒｎｅ工作的基础上讨论了吸积盘中黑洞的有关参量的演化，以及由Ｓｃｈｗａｒｚｓｃｈｉｌｄ黑洞吸积盘向Ｋｅｒｒ黑洞吸积盘演化过程中对吸积盘辐射通量的影响，最后针对几个典型的辐射过程，分别讨论了黑洞吸积盘在牛顿框架中的温度分布方程与广义相对论的温度分布方程的热不稳定性，并给出此类问题的热不稳定性的判据。 相似文献