全文获取类型
收费全文 | 5406篇 |
免费 | 1047篇 |
国内免费 | 1289篇 |
专业分类
测绘学 | 132篇 |
大气科学 | 462篇 |
地球物理 | 1522篇 |
地质学 | 3702篇 |
海洋学 | 433篇 |
天文学 | 573篇 |
综合类 | 302篇 |
自然地理 | 616篇 |
出版年
2024年 | 39篇 |
2023年 | 104篇 |
2022年 | 227篇 |
2021年 | 230篇 |
2020年 | 214篇 |
2019年 | 273篇 |
2018年 | 223篇 |
2017年 | 212篇 |
2016年 | 222篇 |
2015年 | 261篇 |
2014年 | 305篇 |
2013年 | 300篇 |
2012年 | 350篇 |
2011年 | 335篇 |
2010年 | 265篇 |
2009年 | 363篇 |
2008年 | 376篇 |
2007年 | 412篇 |
2006年 | 378篇 |
2005年 | 307篇 |
2004年 | 300篇 |
2003年 | 255篇 |
2002年 | 215篇 |
2001年 | 178篇 |
2000年 | 187篇 |
1999年 | 143篇 |
1998年 | 177篇 |
1997年 | 172篇 |
1996年 | 132篇 |
1995年 | 104篇 |
1994年 | 99篇 |
1993年 | 76篇 |
1992年 | 79篇 |
1991年 | 43篇 |
1990年 | 52篇 |
1989年 | 43篇 |
1988年 | 34篇 |
1987年 | 9篇 |
1986年 | 22篇 |
1985年 | 7篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1973年 | 1篇 |
1954年 | 4篇 |
排序方式: 共有7742条查询结果,搜索用时 46 毫秒
1.
2.
中国古生教授学会微体古生物学分会举行代表大会和学术年会中国古竽物学会微体古物学分会第五次会员代表大分暨第六次不术年会于1996年1月24日到30日在福州市召开。来自全国地质、石油、煤炭的和产、科研和大学的100多位代表参加了这次大会和学术研讨。大会共... 相似文献
3.
4.
本文利用宽波段能谱结构讨论了四个PG类星体的红外辐射机制.结果表明,在产生红外连续辐射的可能机制中,非热的、具有幂律特征的辐射和被核光度加热的“核尘埃”的热再辐射是红外辐射的主要来源.对于高光度的活动星系核,它的主星系的红外辐射及恒星形成区的红外辐射是可以忽略的. 相似文献
5.
6.
C. Dickinson R. D. Davies R. J. Davis 《Monthly notices of the Royal Astronomical Society》2003,341(2):369-384
A full-sky template map of the Galactic free–free foreground emission component is increasingly important for high-sensitivity cosmic microwave background (CMB) experiments. We use the recently published Hα data of both the northern and southern skies as the basis for such a template.
The first step is to correct the Hα maps for dust absorption using the 100-μm dust maps of Schlegel, Finkbeiner & Davis. We show that for a range of longitudes, the Galactic latitude distribution of absorption suggests that it is 33 per cent of the full extragalactic absorption. A reliable absorption-corrected Hα map can be produced for ∼95 per cent of the sky; the area for which a template cannot be recovered is the Galactic plane area | b | < 5°, l = 260°–0°–160° and some isolated dense dust clouds at intermediate latitudes.
The second step is to convert the dust-corrected Hα data into a predicted radio surface brightness. The free–free emission formula is revised to give an accurate expression (1 per cent) for the radio emission covering the frequency range 100 MHz–100 GHz and the electron temperature range 3000–20 000 K. The main uncertainty when applying this expression is the variation of electron temperature across the sky. The emission formula is verified in several extended H ii regions using data in the range 408–2326 MHz.
A full-sky free–free template map is presented at 30 GHz; the scaling to other frequencies is given. The Haslam et al. all-sky 408-MHz map of the sky can be corrected for this free–free component, which amounts to a ≈6 per cent correction at intermediate and high latitudes, to provide a pure synchrotron all-sky template. The implications for CMB experiments are discussed. 相似文献
The first step is to correct the Hα maps for dust absorption using the 100-μm dust maps of Schlegel, Finkbeiner & Davis. We show that for a range of longitudes, the Galactic latitude distribution of absorption suggests that it is 33 per cent of the full extragalactic absorption. A reliable absorption-corrected Hα map can be produced for ∼95 per cent of the sky; the area for which a template cannot be recovered is the Galactic plane area | b | < 5°, l = 260°–0°–160° and some isolated dense dust clouds at intermediate latitudes.
The second step is to convert the dust-corrected Hα data into a predicted radio surface brightness. The free–free emission formula is revised to give an accurate expression (1 per cent) for the radio emission covering the frequency range 100 MHz–100 GHz and the electron temperature range 3000–20 000 K. The main uncertainty when applying this expression is the variation of electron temperature across the sky. The emission formula is verified in several extended H ii regions using data in the range 408–2326 MHz.
A full-sky free–free template map is presented at 30 GHz; the scaling to other frequencies is given. The Haslam et al. all-sky 408-MHz map of the sky can be corrected for this free–free component, which amounts to a ≈6 per cent correction at intermediate and high latitudes, to provide a pure synchrotron all-sky template. The implications for CMB experiments are discussed. 相似文献
7.
8.
The results of a photometric monitoring of the quasar 4C 38.41, performed at the optical R and B bands in 2002 February–March, are presented. With a 60/90 cm Schmidt telescope at the Xinglong station of the National Astronomical Observatories of China, we observed the source exhibiting amplitude variations of up to 0.78 mag in both bands during the whole campaign. Intraday and even intranight variations are detected as well. A typical variability time-scale of about 36 d is derived from our 2-month observations at the optical bands, which is identical to that found at a radio wavelength of 92 cm, suggesting a common origin for the variations in 4C 38.41 from optical to radio bands. 相似文献
9.
10.