全文获取类型
收费全文 | 37996篇 |
免费 | 6686篇 |
国内免费 | 9207篇 |
专业分类
测绘学 | 3429篇 |
大气科学 | 5172篇 |
地球物理 | 6862篇 |
地质学 | 22269篇 |
海洋学 | 4634篇 |
天文学 | 3421篇 |
综合类 | 2458篇 |
自然地理 | 5644篇 |
出版年
2024年 | 159篇 |
2023年 | 484篇 |
2022年 | 1265篇 |
2021年 | 1421篇 |
2020年 | 1372篇 |
2019年 | 1784篇 |
2018年 | 1274篇 |
2017年 | 1464篇 |
2016年 | 1515篇 |
2015年 | 1723篇 |
2014年 | 2187篇 |
2013年 | 2191篇 |
2012年 | 2316篇 |
2011年 | 2495篇 |
2010年 | 2126篇 |
2009年 | 2695篇 |
2008年 | 2621篇 |
2007年 | 2711篇 |
2006年 | 2714篇 |
2005年 | 2522篇 |
2004年 | 2234篇 |
2003年 | 2103篇 |
2002年 | 1797篇 |
2001年 | 1594篇 |
2000年 | 1601篇 |
1999年 | 1415篇 |
1998年 | 1224篇 |
1997年 | 883篇 |
1996年 | 757篇 |
1995年 | 653篇 |
1994年 | 596篇 |
1993年 | 523篇 |
1992年 | 344篇 |
1991年 | 310篇 |
1990年 | 214篇 |
1989年 | 163篇 |
1988年 | 134篇 |
1987年 | 78篇 |
1986年 | 45篇 |
1985年 | 39篇 |
1984年 | 28篇 |
1983年 | 18篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1978年 | 14篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
Larisa A. Yakovina Yakiv V. Pavlenko Carlos Abia 《Astrophysics and Space Science》2003,288(3):279-286
Lithium abundances in the atmospheres of the super Li-rich C-giants WZ Cas and WX Cyg are derived by the spectral synthesis
technique using the Li I resonance line at λ670.8 nm and three subordinate lines at λλ 812.6, 610.4 and 497.2 nm. The differences
between the Li abundances derived from the λ670.8 nm line and the λλ 497.2, 812.6 nm lines do not exceed ±0.5 dex. The lithium
line at λ610.4 nm provides typically lower abundances than the resonance line (by ≈ 1 dex). The mean LTE and NLTE Li abundances
from three Li I lines (excluding λ610.4 nm) are 4.7, 4.9 for WZ Cas, and 4.6, 4.8 for WX Cyg, respectively.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
43.
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
44.
45.
46.
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
47.
48.
49.
A short summary of recent progress in measuring and understanding turbulence during magnetic reconnection in laboratory plasmas
is given. Magnetic reconnection is considered as a primary process to dissipate magnetic energy in laboratory and astrophysical
plasmas. A central question concerns why the observed reconnection rates are much faster than predictions made by classical
theories, such as the Sweet–Parker model based on MHD with classical Spitzer resistivity. Often, the local resistivity is
conjectured to be enhanced by turbulence to accelerate reconnection rates either in the context of the Sweet–Parker model
or by facilitating setup of the Pestchek model. Measurements at a dedicated laboratory experiment, called MRX or Magnetic
Reconnection Experiment, have indicated existence of strong electromagnetic turbulence in current sheets undergoing fast reconnection.
The origin of the turbulence has been identified as right-hand polarized whistler waves, propagating obliquely to the reconnecting
field, with a phase velocity comparable to the relative drift velocity. These waves are consistent with an obliquely propagating
electromagnetic lower-hybrid drift instability driven by drift speeds large compared to the Alfven speed in high-beta plasmas.
Interestingly, this instability may explain electromagnetic turbulence also observed in collisionless shocks, which are common
in energetic astrophysical phenomena. 相似文献
50.
滇西动态重力网的分形特征及空间分辨力 总被引:1,自引:1,他引:0
贾民育 《大地测量与地球动力学》1996,(4)
介绍了用分形学描述地球物理观测网非均匀分布和联合应用分形特征与Shannon定理确定最佳网格距的方法。研究了滇西动态重力网的分形特征,它的分形维Df=1.27,最佳网格距r0=28km。讨论了1986年至1994年间网区发生的8次Ms>5.0级地震前重力场变化的可信性,指出这些变化的波长均大于100km,至少2倍于网的最小空间分辨力,因而是可信的 相似文献