全文获取类型
收费全文 | 6305篇 |
免费 | 257篇 |
国内免费 | 312篇 |
专业分类
测绘学 | 575篇 |
大气科学 | 365篇 |
地球物理 | 171篇 |
地质学 | 566篇 |
海洋学 | 252篇 |
天文学 | 3899篇 |
综合类 | 202篇 |
自然地理 | 844篇 |
出版年
2024年 | 17篇 |
2023年 | 30篇 |
2022年 | 81篇 |
2021年 | 95篇 |
2020年 | 75篇 |
2019年 | 130篇 |
2018年 | 61篇 |
2017年 | 126篇 |
2016年 | 110篇 |
2015年 | 135篇 |
2014年 | 162篇 |
2013年 | 218篇 |
2012年 | 185篇 |
2011年 | 166篇 |
2010年 | 168篇 |
2009年 | 444篇 |
2008年 | 430篇 |
2007年 | 475篇 |
2006年 | 475篇 |
2005年 | 470篇 |
2004年 | 470篇 |
2003年 | 442篇 |
2002年 | 329篇 |
2001年 | 337篇 |
2000年 | 311篇 |
1999年 | 285篇 |
1998年 | 359篇 |
1997年 | 51篇 |
1996年 | 27篇 |
1995年 | 30篇 |
1994年 | 25篇 |
1993年 | 27篇 |
1992年 | 16篇 |
1991年 | 21篇 |
1990年 | 16篇 |
1989年 | 7篇 |
1988年 | 13篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 11篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 2篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1971年 | 2篇 |
排序方式: 共有6874条查询结果,搜索用时 0 毫秒
1.
2.
3.
4.
5.
We report three new or updated techniques for probing the parameters of active galaxies based on the masses of their central
black holes MBH). First, we derived a near-IR analog of the bulge luminosity versus MBH relationship. The low scatter makes it a promising new tool to study the black hole demographics. Next, we present relations
between MBH and the10 μm and 2-10 keV nuclear luminosity. They may help to study the MBH evolution over wide redshift ranges. Finally, we measured MBH in quasars from z ∼ 3.4 to z ∼ 0.3 to search directly for MBH growth. Surprisingly, we found no evidence for growth implying that the majority of quasar host galaxies have undergone their
last major merger at z ≥ 3.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
7.
S. G. Turyshev B-G. Andersson 《Monthly notices of the Royal Astronomical Society》2003,341(2):577-582
We have studied the science rationale, goals and requirements for a mission aimed at using the gravitational lensing from the Sun as a way of achieving high angular resolution and high signal amplification. We find that such a mission concept is compromised by several practical problems. Most severe are the effects due to the plasma in the solar atmosphere which cause refraction and scattering of the propagating rays. These effects either limit the frequencies that can be observed to those above ∼1 THz, or they move the optical point outwards beyond the vacuum value of ≥550 au. (Thus for observing frequency of 300 GHz the optical point is moved outwards to ∼ 680 au.) Density fluctuations in the inner solar atmosphere will further cause random pathlength differences for different rays. The corrections for the radiation from the Sun itself will also be a major challenge at any wavelength used, but could be mitigated with coronographic techniques. Given reasonable constraints on the spacecraft (particularly in terms of size and propulsion), source selection as well as severe navigational constraints further add to the difficulties for a potential mission. Nevertheless, unbiased surveys of small-scale structure on the sky at short wavelengths might be the most promising application of such a mission. 相似文献
8.
K. A. van der Hucht 《Astronomy and Astrophysics Review》1992,4(2):123-159
Summary Recent literature on Population I Wolf-Rayet star research extending from the Milky Way to blue compact dwarf galaxies is reviewed, broken down into inventory, basic parameters and galactic distribution, atmospheres, binaries, intrinsic variability, mass loss, enrichment and evolution. Also the incidence of Wolf-Rayet stars with variable non-thermal radio emission, excess X-ray fluxes, and episodic/periodic IR excesses is reviewed. These phenomena appear to be associated with wind-wind interaction in wide long-period WR+OB binaries and with wind-compact object interaction in WR+c binaries, with orbit sizes of the order of magnitude of the WR radio photosphere sizes or larger. 相似文献
9.
M. V. Sazhin V. E. Zharov T. A. Kalinina 《Monthly notices of the Royal Astronomical Society》2001,323(4):952-964
Parallax measurements allow distances to celestial objects to be determined. Together with measurements of their position on the celestial sphere, they give a full three-dimensional picture of the location of the objects relative to the observer. The distortion of the parallax value of a distant source affected by weak microlensing is considered. This means that the weak microlensing leads to distortion of the distance scale. The gravitational deflection causes a retrograde apparent motion of the image, which is revealed as a negative parallax. It is shown that the distortions may significantly change the parallax values when they amount to several microseconds of arc. In particular, at this level many measured values of parallaxes should be negative. 相似文献
10.
Davide Lazzati Rosalba Perna Gabriele Ghisellini 《Monthly notices of the Royal Astronomical Society》2001,325(4):L19-L23
The recent detection of a transient absorption feature in the X-ray prompt emission of GRB 990705 showed the importance of such observations in the understanding of gamma-ray bursts and their progenitors. We investigate the time dependence of photoionization edges during the prompt emission of bursts in different environments. We show that their variability can be used to infer the density and geometry of the surrounding medium, giving important clues to unveil the nature of the burst progenitor. 相似文献