全文获取类型
收费全文 | 1439篇 |
免费 | 188篇 |
国内免费 | 420篇 |
专业分类
测绘学 | 90篇 |
大气科学 | 130篇 |
地球物理 | 355篇 |
地质学 | 908篇 |
海洋学 | 219篇 |
天文学 | 84篇 |
综合类 | 78篇 |
自然地理 | 183篇 |
出版年
2024年 | 7篇 |
2023年 | 28篇 |
2022年 | 33篇 |
2021年 | 48篇 |
2020年 | 57篇 |
2019年 | 65篇 |
2018年 | 54篇 |
2017年 | 57篇 |
2016年 | 73篇 |
2015年 | 67篇 |
2014年 | 72篇 |
2013年 | 87篇 |
2012年 | 90篇 |
2011年 | 76篇 |
2010年 | 81篇 |
2009年 | 81篇 |
2008年 | 94篇 |
2007年 | 105篇 |
2006年 | 98篇 |
2005年 | 91篇 |
2004年 | 79篇 |
2003年 | 59篇 |
2002年 | 76篇 |
2001年 | 42篇 |
2000年 | 68篇 |
1999年 | 75篇 |
1998年 | 43篇 |
1997年 | 39篇 |
1996年 | 36篇 |
1995年 | 31篇 |
1994年 | 19篇 |
1993年 | 30篇 |
1992年 | 17篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有2047条查询结果,搜索用时 218 毫秒
451.
Zhi-Fu Gao Ci-Xing Chen Na Wang Xin-Jun Zhao Zhao-Jun Wang 《Astronomische Nachrichten》2024,345(2-3):e240012
There are many rotating spheroids in the universe, and many astronomers and physicists have used theoretical methods to study the characteristics of stellar gravity since Newton's time. This paper derives the solutions of eight scattering states , , and for the Dirac equation with positive-energy , and establishes the relationship between the differential scattering cross section and the stellar density . It is found that: (1) For the eight scattering states, their average scattering cross-sections are proportional to , and depend on the star's radius, and the higher the stellar density , the greater the sensitivity of to the change of ; (2) For the four scattering states , their average scattering amplitudes and depend on the mass of the particles; while for the other four scattering states , , then and are independent of . This study links the gravitational characteristics of stars with the scattering cross section, creating a new method for studying the gravitational characteristics, which helps to reveal the mystery of the gravity of rotating ellipsoidal stars. 相似文献
452.
This paper presents a comparison of two variational formats for fully saturated porous media subjected to dynamic loading, whereby the general situation of relative fluid acceleration is considered: (1) the classical three‐field ( u , p, w )‐format and (2) a novel two‐field ( u , p)‐format, where the seepage velocity w is a spatially ‘local’ field whose treatment resembles that of internal variables in material models. The limited numerical comparison shows that the ( u , p)‐format competes well with the ( u , p, w )‐format. Indeed, it is consistent with the general acceleration modeling in the full range of permeabilities. Moreover, in the low permeability regime (where the magnitude of w is insignificant), the new format reflects the situation pertinent to ‘added‐mass’ and is more efficient than the classical ( u , p, w )‐format. Finally, the ( u , p)‐formatcan conveniently be implemented in existing FE‐codes based on the ‘added mass’ formulation. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
453.
454.
我国东部夏季降水百年雨型的多时间尺度变化特征研究 总被引:8,自引:4,他引:8
本文用1900-1950年的我国实测的与内插的降水、气温资料,结合近代先进的统计方法对立了1900-1950年我国东部夏季降水雨型序列,并将其与已有的近48年(1951-1998年)的夏季雨型序列相衔接,进而研究了近百年我国夏季雨带的演变规律及其与ENSO的关系,此外,还研究了百年夏季雨型与大气活动中心在基本态时间尺度上的关系,研究了北太平洋涛动和我国夏季降水的关系。 相似文献
455.
456.
The one-dimensional pressure head profile above a fixed water-table was studied for different steady infiltration rates. As shown in previous studies, when the infiltration rate (qin) is less than the soil saturated hydraulic conductivity (Ks), this profile can be divided into two parts: (1) from the water-table surface (z0) to an elevation zγ, the pressure head varies from 0 to a value hγ such as K(hγ)=−qin; (2) above the elevation zγ the pressure head is constant and equal to hγ. Above the water-table the zone where the pressure head is variable has been called ‘transition zone’. Its height is shown to be highly variable and to depend on soil properties as well as on the infiltration rate. This transition zone is not the ‘capillary fringe’ as defined by Gillham (Gillham R.W., 1984. The capillary fringe and its effect on water-table response. J. Hydrol. 67, 307–324). Numerical experiments performed with HYDRUS-2D® for the case of a water-table drained by parallel ditches have shown that the height of the transition zone is similar in the one-dimensional profile and in the two-dimensional system as long as the local slope of the water-table is small. This result is important since in a two-dimensional system, the transition zone is the place where all the horizontal component of the unsaturated flow occurs. The ratio of the horizontal component of the unsaturated flow vs the total horizontal flow in both the unsaturated and saturated zones has been computed. For a given soil, this ratio decreases as the infiltration rate increases; for a given infiltration rate, the soil with the thinnest transition zone transfers the largest amount of water above the water-table. 相似文献
457.
用大量弹簧滑块组成的模型可以模拟地震的复杂性,本文以细胞自动机(CA)为数学工具,结合地震学和岩石力学的结果,考虑了能量的输入和损耗,进行了地震事件的数字模拟。对模型中输出的“地震”事件进行了时间和空间的多分形分析,并对自组织临界(SOC)状态进行了讨论,进而得到事件至少在时间域里的分布呈现出层次结构,符合自相似特征。本文的CA模型属于确定性的混沌系统,而对于处在SOC状态下的大量事件的频度和大小的统计与G-R指数律很好地吻合。结果表明,虽然自组织(SO)可能是更准确的地震表征,但SOC仍然是研究地震现象的很好的模式。 相似文献
458.
459.
460.
Analysis of State and Provincial Atlas Reviews* 总被引:1,自引:0,他引:1
Ninety-eight reviews of state and provincial atlases are examined in order to address several questions. Reviews are subjected to content analysis to identify the judgement criteria that experts use in evaluating a provincial or state atlas, and the aspects of each criterion that reviewers praise or condemn. An attempt is made to search for expert consensus and to identify a provincial or state atlas review recipe. The research reported here is part of a larger study undertaken to assist those in the process of planning a new provincial or state atlas initiative. This paper also assists individuals who are searching for rules and guidelines when undertaking an atlas review. 相似文献