全文获取类型
收费全文 | 29433篇 |
免费 | 5086篇 |
国内免费 | 8006篇 |
专业分类
测绘学 | 1734篇 |
大气科学 | 6650篇 |
地球物理 | 5229篇 |
地质学 | 14055篇 |
海洋学 | 3814篇 |
天文学 | 5250篇 |
综合类 | 1791篇 |
自然地理 | 4002篇 |
出版年
2024年 | 114篇 |
2023年 | 441篇 |
2022年 | 1029篇 |
2021年 | 1126篇 |
2020年 | 1151篇 |
2019年 | 1368篇 |
2018年 | 1155篇 |
2017年 | 1095篇 |
2016年 | 1203篇 |
2015年 | 1359篇 |
2014年 | 1883篇 |
2013年 | 1832篇 |
2012年 | 2023篇 |
2011年 | 2102篇 |
2010年 | 2057篇 |
2009年 | 2463篇 |
2008年 | 2296篇 |
2007年 | 2339篇 |
2006年 | 2345篇 |
2005年 | 1961篇 |
2004年 | 1786篇 |
2003年 | 1463篇 |
2002年 | 1240篇 |
2001年 | 1176篇 |
2000年 | 983篇 |
1999年 | 907篇 |
1998年 | 721篇 |
1997年 | 550篇 |
1996年 | 437篇 |
1995年 | 351篇 |
1994年 | 336篇 |
1993年 | 328篇 |
1992年 | 220篇 |
1991年 | 154篇 |
1990年 | 98篇 |
1989年 | 96篇 |
1988年 | 66篇 |
1987年 | 33篇 |
1986年 | 38篇 |
1985年 | 41篇 |
1984年 | 34篇 |
1983年 | 29篇 |
1982年 | 22篇 |
1981年 | 11篇 |
1980年 | 15篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1977年 | 16篇 |
1954年 | 7篇 |
1875年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Titan has been observed with UVES, the UV-Visual Echelle Spectrograph at the Very Large Telescope, with the aim of characterizing the zonal wind flow. We use a retrieval scheme originally developed for absolute stellar accelerometry [Connes, P., 1985. Astrophys. Space Sci., 110, 211-255] to extract the velocity signal by simultaneously taking into account all the lines present in the spectrum. The method allows to measure the Doppler shift induced at a given point by the zonal wind flow, with high precision. The short-wavelength channel (4200-5200 Å) probes one scale height higher than the long-wavelength one (5200-6200 Å), and we observe statistically significant evidence for stronger winds at higher altitudes. The results show a high dispersion. Globally, we detect prograde zonal winds, with lower limits of 62 and 50 m s−1 at the regions centered at 200 and 170 km altitude, but approximately a quarter of the measurements indicates null or retrograde winds. 相似文献
102.
103.
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
104.
105.
106.
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
107.
吴泽忠 《成都信息工程学院学报》2004,19(2):258-262
在序线性拓扑空间里研究了含有集约束向量极值问题的最优性条件,并建立了充分性和必要性条件. 相似文献
108.
基于Windows消息机制的人机交互的研究与应用 总被引:1,自引:0,他引:1
结合实例着重介绍了如何通过串行通讯利用Windows的消息机制来解决目前工业设备控制中人机交互的模拟问题,并对这两种技术进行了详细的论述. 相似文献
109.
110.