全文获取类型
收费全文 | 45082篇 |
免费 | 749篇 |
国内免费 | 450篇 |
专业分类
测绘学 | 1149篇 |
大气科学 | 2948篇 |
地球物理 | 9098篇 |
地质学 | 15722篇 |
海洋学 | 3969篇 |
天文学 | 10943篇 |
综合类 | 158篇 |
自然地理 | 2294篇 |
出版年
2022年 | 278篇 |
2021年 | 465篇 |
2020年 | 505篇 |
2019年 | 512篇 |
2018年 | 1118篇 |
2017年 | 1007篇 |
2016年 | 1250篇 |
2015年 | 704篇 |
2014年 | 1200篇 |
2013年 | 2238篇 |
2012年 | 1359篇 |
2011年 | 1812篇 |
2010年 | 1637篇 |
2009年 | 2228篇 |
2008年 | 1854篇 |
2007年 | 1843篇 |
2006年 | 1732篇 |
2005年 | 1281篇 |
2004年 | 1301篇 |
2003年 | 1200篇 |
2002年 | 1164篇 |
2001年 | 1032篇 |
2000年 | 983篇 |
1999年 | 845篇 |
1998年 | 866篇 |
1997年 | 832篇 |
1996年 | 710篇 |
1995年 | 718篇 |
1994年 | 638篇 |
1993年 | 544篇 |
1992年 | 514篇 |
1991年 | 514篇 |
1990年 | 590篇 |
1989年 | 504篇 |
1988年 | 460篇 |
1987年 | 603篇 |
1986年 | 490篇 |
1985年 | 614篇 |
1984年 | 694篇 |
1983年 | 663篇 |
1982年 | 592篇 |
1981年 | 617篇 |
1980年 | 515篇 |
1979年 | 477篇 |
1978年 | 481篇 |
1977年 | 437篇 |
1976年 | 428篇 |
1975年 | 419篇 |
1974年 | 399篇 |
1973年 | 432篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
221.
R.H. Brown K.H. Baines J.-P. Bibring F. Capaccioni R.N. Clark D.P. Cruikshank V. Formisano Y. Langevin T.B. McCord V. Mennella P.D. Nicholson C. Sotin M.A. Chamberlain G. Hansen M. Showalter 《Icarus》2003,164(2):461-470
The Cassini Visual and Infrared Mapping Spectrometer (VIMS) is an imaging spectrometer covering the wavelength range 0.3-5.2 μm in 352 spectral channels, with a nominal instantaneous field of view of 0.5 mrad. The Cassini flyby of Jupiter represented a unique opportunity to accomplish two important goals: scientific observations of the jovian system and functional tests of the VIMS instrument under conditions similar to those expected to obtain during Cassini's 4-year tour of the saturnian system. Results acquired over a complete range of visual to near-infrared wavelengths from 0.3 to 5.2 μm are presented. First detections include methane fluorescence on Jupiter, a surprisingly high opposition surge on Europa, the first visual-near-IR spectra of Himalia and Jupiter's optically-thin ring system, and the first near-infrared observations of the rings over an extensive range of phase angles (0-120°). Similarities in the center-to-limb profiles of H+3 and CH4 emissions indicate that the H+3 ionospheric density is solar-controlled outside of the auroral regions. The existence of jovian NH3 absorption at 0.93 μm is confirmed. Himalia has a slightly reddish spectrum, an apparent absorption near 3 μm, and a geometric albedo of 0.06±0.01 at 2.2 μm (assuming an 85-km radius). If the 3-μm feature in Himalia's spectrum is eventually confirmed, it would be suggestive of the presence of water in some form, either free, bound, or incorporated in layer-lattice silicates. Finally, a mean ring-particle radius of 10 μm is found to be consistent with Mie-scattering models fit to VIMS near-infrared observations acquired over 0-120° phase angle. 相似文献
222.
223.
224.
The magnitude and spatial distribution of snow on sea ice are both integral components of the ocean–sea‐ice–atmosphere system. Although there exists a number of algorithms to estimate the snow water equivalent (SWE) on terrestrial surfaces, to date there is no precise method to estimate SWE on sea ice. Physical snow properties and in situ microwave radiometry at 19, 37 and 85 GHz, V and H polarization were collected for a 10‐day period over 20 first‐year sea ice sites. We present and compare the in situ physical, electrical and microwave emission properties of snow over smooth Arctic first‐year sea ice for 19 of the 20 sites sampled. Physical processes creating the observed vertical patterns in the physical and electrical properties are discussed. An algorithm is then developed from the relationship between the SWE and the brightness temperature measured at 37 GHz (55°) H polarization and the air temperature. The multiple regression between these variables is able to account for over 90% of the variability in the measured SWE. This algorithm is validated with a small in situ data set collected during the 1999 field experiment. We then compare our data against the NASA snow thickness algorithm, designed as part of the NASA Earth Enterprise Program. The results indicated a lack of agreement between the NASA algorithm and the algorithm developed here. This lack of agreement is attributed to differences in scale between the Special Sensor Microwave/Imager and surface radiometers and to differences in the Antarctic versus Arctic snow physical and electrical properties. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
225.
Gérard Daigne Patrick Charlot Christine Ducourant Jean-François Lestrade 《Astrophysics and Space Science》2003,286(1-2):255-260
The question of positioning the optical counterparts of the ICRF quasars is outlined in the perspective of future space astrometry
missions, which ultimately will bring a new realization of the ICRS in the optical range. Ground-based interferometry with
a dual-field observing mode (PRIMA/VLTI),together with the missions DIVA and FAME, will have a key role in building an extragalactic
reference frame in the optical/near-IR range with about the same accuracy as that of the present (VLBI) primary frame.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
226.
227.
228.
229.
Abstract— In this study, we have performed pulse‐heating experiments at different temperatures for three organic molecules (a polycyclic aromatic hydrocarbon [PAH], a ketone, and an amino acid) absorbed into microporous aluminum oxide (Al2O3) in order to imitate the heating of the organic molecules in interplanetary dust particles (IDPs) and micrometeorites (MMs) during atmospheric entry and to investigate their survival. We have shown that modest amounts (a few percent) of these organic molecules survive pulse‐heating at temperatures in the 700 to 900 °C range. This suggests that the porosity in IDPs and MMs, combined with a sublimable phase (organic material, water), produces an ablative cooling effect, which permits the survival of organic molecules that would otherwise be lost either by thermal degradation or evaporation during atmospheric entry. 相似文献
230.