全文获取类型
| 收费全文 | 13608篇 |
| 免费 | 1421篇 |
| 国内免费 | 2280篇 |
专业分类
| 测绘学 | 294篇 |
| 大气科学 | 583篇 |
| 地球物理 | 2298篇 |
| 地质学 | 5230篇 |
| 海洋学 | 1529篇 |
| 天文学 | 5675篇 |
| 综合类 | 666篇 |
| 自然地理 | 1034篇 |
出版年
| 2024年 | 42篇 |
| 2023年 | 106篇 |
| 2022年 | 301篇 |
| 2021年 | 345篇 |
| 2020年 | 346篇 |
| 2019年 | 450篇 |
| 2018年 | 356篇 |
| 2017年 | 342篇 |
| 2016年 | 387篇 |
| 2015年 | 391篇 |
| 2014年 | 668篇 |
| 2013年 | 725篇 |
| 2012年 | 739篇 |
| 2011年 | 821篇 |
| 2010年 | 925篇 |
| 2009年 | 1271篇 |
| 2008年 | 1183篇 |
| 2007年 | 1105篇 |
| 2006年 | 1002篇 |
| 2005年 | 887篇 |
| 2004年 | 761篇 |
| 2003年 | 673篇 |
| 2002年 | 517篇 |
| 2001年 | 474篇 |
| 2000年 | 474篇 |
| 1999年 | 439篇 |
| 1998年 | 328篇 |
| 1997年 | 189篇 |
| 1996年 | 168篇 |
| 1995年 | 150篇 |
| 1994年 | 136篇 |
| 1993年 | 126篇 |
| 1992年 | 85篇 |
| 1991年 | 71篇 |
| 1990年 | 48篇 |
| 1989年 | 47篇 |
| 1988年 | 37篇 |
| 1987年 | 20篇 |
| 1986年 | 24篇 |
| 1985年 | 32篇 |
| 1984年 | 23篇 |
| 1983年 | 18篇 |
| 1982年 | 21篇 |
| 1981年 | 7篇 |
| 1980年 | 11篇 |
| 1979年 | 9篇 |
| 1978年 | 7篇 |
| 1977年 | 15篇 |
| 1954年 | 2篇 |
| 1875年 | 1篇 |
排序方式： 共有10000条查询结果，搜索用时 31 毫秒
81.
The absolute magnitudeM
v
of the hydrogen deficient binary υ Sgr has been estimated as -4.8 ± 1.0 from the distribution of the interstellar reddening,
polarization and interstellar lines of the surrounding stars. From the ANS observations obtained at the time of the secondary
eclipse, it appears that the hotter secondary is surrounded by a disc with colours of a B8-B9 star. The λ 1550 CIv absorption
line arising in the stellar wind does not show any change in strength during the secondary minimum. The upper limit to the
mass-loss rate from the high temperature wind is estimated as ≤ 5 × 10-7 M⊙ yr-1 from the 2 cm and 6 cm radio observations.
Based on observations obtained with the Astronomical Netherlands Satellite and VLA. The National Radio Astronomy Observatory’s
Very Large Array at Socorro, New Mexico is operated by Associated Universities Inc. under contract with the National Science
Foundation. 相似文献
82.
83.
84.
We present a new Very Large Array (VLA) image of Saturn, made from data taken in October 1998 at a wavelength of λ3.6 cm. The moderate ring opening angle (B≈15°) allows us to explore direct transmission of microwave photons through the A and C rings. We find a strong asymmetry of photons transmitted through the A ring, but not in the C ring, a new diagnostic of wake structure in the ring particles. We also find a weak asymmetry between east and west for the far side of the ansae. To facilitate quantitative comparison between dynamic models of the A ring and radio observations, we extend our Monte Carlo radiative transfer code (described in Dunn et al., 2002, Icarus 160, 132-160) to include idealized wakes. We show the idealized model can reproduce the properties of dynamic simulations in directly transmitted light. We examine the model behavior in directly transmitted and scattered light over a range of physical and geometric wake parameters. Finally, we present a wake model with a plausible set of physical parameters that quantitatively reproduces the observed intensity and asymmetry of the A ring both across the planet and in the ansae. 相似文献
85.
86.
87.
本文对第２２太阳周（１９８７年１月至１９９２年１２月）中发生过Ｍ级以上的Ｘ射线耀斑（Ｈα耀斑级别≥Ｍ级，并伴有Ｘ射线的耀斑）对应的３９５个活动区资料进行了耀斑指数的统计，得到的结果：１．２２太阳周Ｍ级以上Ｘ射线耀斑级别综合指数表，２．２２太阳周Ｍ级以上Ｘ射线耀斑总指数表，３．第２２太阳周Ｍ级以上Ｘ射线耀斑总指数随时间的变化曲线，４．第２２太阳周Ｍ级以上Ｘ射线濯斑总指数直方图，该图表明第２２太阳周活动的极大年分别是１９８９和１９９１年，为第２３周太阳活动预报提供了可用参数。 相似文献
88.
89.
R. F. Griffin 《Journal of Astrophysics and Astronomy》1990,11(4):533-540
Photoelectric radial-velocity measurements show that HD 118670 is a double-lined spectroscopic binary in an orbit which is
not quite circular and whose period is about 48 days. Spectral types of K0 V and K7 V would satisfy the photometry and the
mass ratio; the mass function would then suggest the possibility of eclipses. However, actual spectral classification indicates
a luminosity somewhat above the main sequence 相似文献
90.
The sand–loess transition zone in north China is sensitive to climate change, and is an ideal place to investigate past environmental changes. However, past climate change at millennial–centennial timescales in this region has not been well reconstructed because of limited numerical dating. Alternations of sandy loam soils with aeolian sand layers in the Mu Us and Otindag sand fields, which lie along the sand–loess transition zone, indicate multiple intervals of dune activity and stability. This change is probably a response to variations of the East Asian monsoon climate during the late Quaternary. The single aliquot regeneration (SAR) optically stimulated luminescence (OSL) dating protocol, which has been successfully applied to aeolian deposits worldwide, is applied to these two sand fields in this study. The OSL ages provide reliable constraints for reconstruction of past climate changes at suborbital timescale. Sections in both sand fields contain aeolian sand beds recording millennial‐scale episodes of dry climate and widespread dune activation, including episodes at about the same time as Heinrich Event 5 and the Younger Dryas in the North Atlantic region. These results demonstrate the potential of aeolian sediments in semi‐arid north China to record millennial‐scale climatic events, and also suggest that dry–wet climate variation at the desert margin in China may be linked to climatic change elsewhere in the Northern Hemisphere, through atmospheric circulation. This article was published online on 27 November 2008. An error was subsequently identified. This notice is included in the online and print versions to indicate that both have been corrected (16 December 2008). Copyright © 2008 John Wiley & Sons, Ltd. 相似文献