全文获取类型
收费全文 | 66548篇 |
免费 | 1041篇 |
国内免费 | 595篇 |
专业分类
测绘学 | 1572篇 |
大气科学 | 4324篇 |
地球物理 | 12951篇 |
地质学 | 23953篇 |
海洋学 | 6103篇 |
天文学 | 15932篇 |
综合类 | 150篇 |
自然地理 | 3199篇 |
出版年
2022年 | 458篇 |
2021年 | 735篇 |
2020年 | 846篇 |
2019年 | 871篇 |
2018年 | 1875篇 |
2017年 | 1741篇 |
2016年 | 2052篇 |
2015年 | 1077篇 |
2014年 | 1946篇 |
2013年 | 3507篇 |
2012年 | 2128篇 |
2011年 | 2813篇 |
2010年 | 2504篇 |
2009年 | 3306篇 |
2008年 | 2782篇 |
2007年 | 2839篇 |
2006年 | 2646篇 |
2005年 | 1835篇 |
2004年 | 1808篇 |
2003年 | 1700篇 |
2002年 | 1661篇 |
2001年 | 1505篇 |
2000年 | 1416篇 |
1999年 | 1190篇 |
1998年 | 1227篇 |
1997年 | 1172篇 |
1996年 | 1016篇 |
1995年 | 986篇 |
1994年 | 937篇 |
1993年 | 781篇 |
1992年 | 747篇 |
1991年 | 747篇 |
1990年 | 845篇 |
1989年 | 674篇 |
1988年 | 654篇 |
1987年 | 812篇 |
1986年 | 666篇 |
1985年 | 883篇 |
1984年 | 916篇 |
1983年 | 874篇 |
1982年 | 814篇 |
1981年 | 766篇 |
1980年 | 702篇 |
1979年 | 641篇 |
1978年 | 655篇 |
1977年 | 564篇 |
1976年 | 565篇 |
1975年 | 565篇 |
1974年 | 536篇 |
1973年 | 564篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
311.
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
312.
313.
314.
S. TACHIBANA H. NAGAHARA S. MOSTEFAOUI N. T. KITA 《Meteoritics & planetary science》2003,38(6):939-962
Abstract— We have studied the relationship between bulk chemical compositions and relative formation ages inferred from the initial 26Al/27Al ratios for sixteen ferromagnesian chondrules in least equilibrated ordinary chondrites, Semarkona (LL3.0) and Bishunpur (LL3.1). The initial 26Al/27Al ratios of these chondrules were obtained by Kita et al. (2000) and Mostefaoui et al. (2002), corresponding to relative ages from 0.7 ± 0.2 to 2.4 ?0.4/+0.7 Myr after calcium‐aluminum‐rich inclusions (CAIs), by assuming a homogeneous distribution of 26Al in the early solar system. The measured bulk compositions of the chondrules cover the compositional range of ferromagnesian chondrules reported in the literature and, thus, the chondrules in this study are regarded as representatives of ferromagnesian chondrules. The relative ages of the chondrules appear to correlate with bulk abundances of Si and the volatile elements (Na, K, Mn, and Cr), but there seems to exist no correlation of relative ages neither with Fe nor with refractory elements. Younger chondrules tend to be richer in Si and volatile elements. Our result supports the result of Mostefaoui et al. (2002) who suggested that pyroxene‐rich chondrules are younger than olivine‐rich ones. The correlation provides an important constraint on chondrule formation in the early solar system. It is explained by chondrule formation in an open system, where silicon and volatile elements evaporated from chondrule melts during chondrule formation and recondensed as chondrule precursors of the next generation. 相似文献
315.
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
316.
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
317.
318.
319.
Ohne Zusammenfassung 相似文献
320.