全文获取类型
收费全文 | 1091篇 |
免费 | 37篇 |
国内免费 | 33篇 |
专业分类
测绘学 | 94篇 |
大气科学 | 25篇 |
地球物理 | 59篇 |
地质学 | 52篇 |
海洋学 | 52篇 |
天文学 | 829篇 |
综合类 | 24篇 |
自然地理 | 26篇 |
出版年
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 12篇 |
2020年 | 12篇 |
2019年 | 15篇 |
2018年 | 6篇 |
2017年 | 19篇 |
2016年 | 13篇 |
2015年 | 11篇 |
2014年 | 20篇 |
2013年 | 22篇 |
2012年 | 19篇 |
2011年 | 17篇 |
2010年 | 16篇 |
2009年 | 83篇 |
2008年 | 63篇 |
2007年 | 86篇 |
2006年 | 91篇 |
2005年 | 89篇 |
2004年 | 96篇 |
2003年 | 86篇 |
2002年 | 42篇 |
2001年 | 66篇 |
2000年 | 52篇 |
1999年 | 50篇 |
1998年 | 69篇 |
1997年 | 9篇 |
1996年 | 7篇 |
1995年 | 14篇 |
1994年 | 11篇 |
1993年 | 11篇 |
1992年 | 9篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 2篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1161条查询结果,搜索用时 359 毫秒
131.
132.
133.
134.
We discuss the propagation of spectral line and continuum radiation in a clumpy medium and give general expressions for the observed absorption or emission from a cloud population. We show that the affect of the medium clumpiness can usually be characterised by a single number multiplying the mean column opacity. Our result provides a simpler proof and generalization of the result of Martin et al. (1984). The formalism provides a simple way to understand the effects of clumping on molecular line profiles and ratios; for example, how clumping effects the interpretation of 13CO(1–0) to 12CO(1–0) line ratios. It also can be used as a propagation operator in physical models of clumpy media where the incident radiation effects the spectral line emissivity. We are working to extend the formalism to the propagation of masers in a clumpy medium, but in this case, there are special difficulties because formal expectation values are not characteristic of observations because they are biased by rare events. 相似文献
135.
Srikumar M. Menon D. Anish Roshi T. Rajendra Prasad 《Monthly notices of the Royal Astronomical Society》2005,356(3):958-962
We present the results of a search for the ground-state hyperfine transition of the OH radical near 53 MHz using the National Mesosphere–Stratosphere–Troposphere (MST) Radar Facility at Gadanki, India. The observed position was G48.4−1.4 near the Galactic plane. The OH line is not detected. We place a 3σ upper limit for the line flux density at 39 Jy from our observations. We also did not detect recombination lines (RLs) of carbon, which were within the frequency range of our observations. The 3σ upper limit of 20 Jy obtained for the flux density of carbon RLs, along with observations at 34.5 and 327 MHz, are used to constrain the physical properties of the line-forming region. Our upper limit is consistent with the line emission expected from a partially ionized region with electron temperature, density and path lengths in the range 20–300 K, 0.03–0.3 cm−3 and 0.1–170 pc, respectively. 相似文献
136.
137.
Patrick Petitjean 《Astrophysics and Space Science》2002,281(1-2):467-470
I describe briefly the status of an ongoing mini-survey for molecular hydrogen in high-redshift Damped Lyman-α systems using
UVES at the VLT. H2 is detected in about 30% of the cases. When H2 is not detected the molecular fraction f = 2N(H2)/(2N(H2)+N(HI) is smaller than 10-5. Therefore, most of the DLA systems arise in warm (T > 3000 K) and diffuse neutral gas embedded in a strong UV flux. The very recent detection of HD molecules in a Damped Lyman-α
system at z
abs = 2.337 demonstrates the possibility to discuss the high redshift chemistry.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
138.
139.
140.