全文获取类型
收费全文 | 52101篇 |
免费 | 8866篇 |
国内免费 | 10886篇 |
专业分类
测绘学 | 6000篇 |
大气科学 | 7092篇 |
地球物理 | 8536篇 |
地质学 | 26112篇 |
海洋学 | 5878篇 |
天文学 | 3437篇 |
综合类 | 3936篇 |
自然地理 | 10862篇 |
出版年
2024年 | 216篇 |
2023年 | 715篇 |
2022年 | 1981篇 |
2021年 | 2298篇 |
2020年 | 2199篇 |
2019年 | 2519篇 |
2018年 | 1999篇 |
2017年 | 2344篇 |
2016年 | 2381篇 |
2015年 | 2614篇 |
2014年 | 3228篇 |
2013年 | 3321篇 |
2012年 | 3348篇 |
2011年 | 3436篇 |
2010年 | 2843篇 |
2009年 | 3404篇 |
2008年 | 3342篇 |
2007年 | 3515篇 |
2006年 | 3422篇 |
2005年 | 3147篇 |
2004年 | 2774篇 |
2003年 | 2496篇 |
2002年 | 2143篇 |
2001年 | 1842篇 |
2000年 | 1830篇 |
1999年 | 1576篇 |
1998年 | 1366篇 |
1997年 | 1012篇 |
1996年 | 827篇 |
1995年 | 718篇 |
1994年 | 687篇 |
1993年 | 572篇 |
1992年 | 444篇 |
1991年 | 347篇 |
1990年 | 249篇 |
1989年 | 180篇 |
1988年 | 147篇 |
1987年 | 96篇 |
1986年 | 58篇 |
1985年 | 51篇 |
1984年 | 28篇 |
1983年 | 20篇 |
1982年 | 16篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1978年 | 17篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1954年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
韩玲 《地球科学与环境学报》2003,25(1):74-75
提出了一种基于格网DEM的粗差检测及剔除方法,其基本思想是对每个表面上的点,在坡度上,高程或突变量引起的形状不连续,可能被怀疑有误差,通过坡度上每个点,应用坡度逼近或改变量来计算,考虑坡度变化的相对值,并以这些相对值计算一个统计值为判断该点合法性的阈值,使计算结果更为可靠。 相似文献
102.
应用GPS观测青藏高原东北缘应力场变化 总被引:2,自引:0,他引:2
采用各向同性弹性地球模型推导了地面位移场速率与地壳内任意点应力场变化的边界积分关系,同时利用青藏高原东北缘1999~2001年观测的GPS资料对观测区地壳深度为5 km和25 km的主应力和最大剪应力进行了计算分析.结果表明,青藏高原东北缘的主应力变化主要集中在祁连山断裂、海原断裂等,在1920~1954年间历史上发生过多次震级为7.0~8.5级强震的断裂附近,并具有主应力变化沿断层走向分布、最大剪应力沿断层走向交替变化等特征. 相似文献
103.
104.
105.
We consider the effects of projection, internal absorption, and gas-or stellar-velocity dispersion on the measured rotation curves of galaxies with edge-on disks. Axisymmetric disk models clearly show that the rotational velocity in the inner galaxy is highly underestimated. As a result, an extended portion that imitates nearly rigid rotation appears. At galactocentric distances where the absorption is low (i.e., it does not exceed 0.3–0.5m kpc?1), the line profiles can have two peaks, and a rotation curve with minimum distortions can be obtained by estimating the position of the peak that corresponds to a higher rotational velocity. However, the high-velocity peak disappears in high-absorption regions and the actual shape of the rotation curve cannot be reproduced from line-of-sight velocity estimates. In general, the optical rotation curves for edge-on galaxies are of little use in reconstructing the mass distribution in the inner regions, particularly for galaxies with a steep velocity gradient in the central region. In this case, estimating the rotation velocities for outer (transparent) disk regions yields correct results. 相似文献
106.
107.
108.
REGIONAL DEMOGRAPHIC STRUCTURE OF THE UNITED STATES 总被引:1,自引:0,他引:1
Richard L. Morrill 《The Professional geographer》1990,42(1):38-53
This paper analyzes the surprisingly great variation in demographic character across the states, utilizing data on fertility, mortality, age, sex, mobility, household character, abortion, race and ethnicity. A fairly simple regional pattern is revealed that is less related to levels of economic development than to long-standing historical cultural differences. 相似文献
109.
DEVELOPMENTSTRATEGIESOFWATERANDLANDRESOURCESINTHEHEXIREGION,CHINA肖洪浪,高前兆,李福兴DEVELOPMENTSTRATEGIESOFWATERANDLANDRESOURCESINTHE... 相似文献
110.
J. I. Read M. I. Wilkinson N. W. Evans G. Gilmore Jan T. Kleyna 《Monthly notices of the Royal Astronomical Society》2006,366(2):429-437
We present an improved analytic calculation for the tidal radius of satellites and test our results against N -body simulations.
The tidal radius in general depends upon four factors: the potential of the host galaxy, the potential of the satellite, the orbit of the satellite and the orbit of the star within the satellite . We demonstrate that this last point is critical and suggest using three tidal radii to cover the range of orbits of stars within the satellite. In this way we show explicitly that prograde star orbits will be more easily stripped than radial orbits; while radial orbits are more easily stripped than retrograde ones. This result has previously been established by several authors numerically, but can now be understood analytically. For point mass, power-law (which includes the isothermal sphere), and a restricted class of split power-law potentials our solution is fully analytic. For more general potentials, we provide an equation which may be rapidly solved numerically.
Over short times (≲1–2 Gyr ∼1 satellite orbit), we find excellent agreement between our analytic and numerical models. Over longer times, star orbits within the satellite are transformed by the tidal field of the host galaxy. In a Hubble time, this causes a convergence of the three limiting tidal radii towards the prograde stripping radius. Beyond the prograde stripping radius, the velocity dispersion will be tangentially anisotropic. 相似文献
The tidal radius in general depends upon four factors: the potential of the host galaxy, the potential of the satellite, the orbit of the satellite and the orbit of the star within the satellite . We demonstrate that this last point is critical and suggest using three tidal radii to cover the range of orbits of stars within the satellite. In this way we show explicitly that prograde star orbits will be more easily stripped than radial orbits; while radial orbits are more easily stripped than retrograde ones. This result has previously been established by several authors numerically, but can now be understood analytically. For point mass, power-law (which includes the isothermal sphere), and a restricted class of split power-law potentials our solution is fully analytic. For more general potentials, we provide an equation which may be rapidly solved numerically.
Over short times (≲1–2 Gyr ∼1 satellite orbit), we find excellent agreement between our analytic and numerical models. Over longer times, star orbits within the satellite are transformed by the tidal field of the host galaxy. In a Hubble time, this causes a convergence of the three limiting tidal radii towards the prograde stripping radius. Beyond the prograde stripping radius, the velocity dispersion will be tangentially anisotropic. 相似文献