全文获取类型
收费全文 | 9284篇 |
免费 | 250篇 |
国内免费 | 336篇 |
专业分类
测绘学 | 265篇 |
大气科学 | 763篇 |
地球物理 | 1887篇 |
地质学 | 3493篇 |
海洋学 | 760篇 |
天文学 | 2119篇 |
综合类 | 40篇 |
自然地理 | 543篇 |
出版年
2023年 | 53篇 |
2022年 | 58篇 |
2021年 | 74篇 |
2020年 | 83篇 |
2019年 | 97篇 |
2018年 | 267篇 |
2017年 | 218篇 |
2016年 | 314篇 |
2015年 | 186篇 |
2014年 | 305篇 |
2013年 | 482篇 |
2012年 | 291篇 |
2011年 | 478篇 |
2010年 | 360篇 |
2009年 | 572篇 |
2008年 | 435篇 |
2007年 | 418篇 |
2006年 | 409篇 |
2005年 | 385篇 |
2004年 | 340篇 |
2003年 | 318篇 |
2002年 | 302篇 |
2001年 | 259篇 |
2000年 | 245篇 |
1999年 | 207篇 |
1998年 | 194篇 |
1997年 | 182篇 |
1996年 | 174篇 |
1995年 | 155篇 |
1994年 | 135篇 |
1993年 | 108篇 |
1992年 | 93篇 |
1991年 | 101篇 |
1990年 | 92篇 |
1989年 | 90篇 |
1988年 | 71篇 |
1987年 | 109篇 |
1986年 | 75篇 |
1985年 | 79篇 |
1984年 | 81篇 |
1983年 | 93篇 |
1982年 | 88篇 |
1981年 | 82篇 |
1980年 | 66篇 |
1979年 | 60篇 |
1977年 | 56篇 |
1976年 | 62篇 |
1975年 | 43篇 |
1973年 | 55篇 |
1972年 | 41篇 |
排序方式: 共有9870条查询结果,搜索用时 31 毫秒
41.
Yu. G. Shkuratov K. Muinonen E. Bowell K. Lumme J. I. Peltoniemi M. A. Kreslavsky D. G. Stankevich V. P. Tishkovetz N. V. Opanasenko L. Y. Melkumova 《Earth, Moon, and Planets》1994,65(3):201-246
About a dozen physical mechanisms and models aspire to explain the negative polarization of light scattered by atmosphereless celestial bodies. This is too large a number for the reliable interpretation of observational data. Through a comparative analysis of the models, our main goal is to answer the question: Does any one model have an advantage over the others? Our analysis is based on new laboratory polarimetric and photometric data as well as on theoretical results. We show that the widely used models due to Hopfield and Wolff cannot realistically explain the phase-angle dependence of the degree of polarization observed at small phase angles. The so-called interference or coherent backscattering mechanism is the most promising model. Models based on that mechanism use well-defined physical parameters to explain both negative polarization and the opposition effect. They are supported by laboratory experiments, particularly those showing enhancement of negative polarization with decreasing particle size down to the wavelength of light. According to the interference mechanism, pronounced negative branches of polarization, like those of C-class asteroids, may indicate a high degree of optical inhomogeneity of light-scattering surfaces at small scales. The mechanism also seems appropriate for treating the negative polarization and opposition effects of cometary dust comae, planetary rings, and the zodiacal light. 相似文献
42.
43.
44.
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
45.
46.
Gamma-ray burst remnants become trans-relativistic typically in days to tens of days, and they enter the deep Newtonian phase in tens of days to months, during which the majority of shock-accelerated electrons will no longer be highly relativistic. However, a small portion of electrons are still accelerated to ultra-relativistic speeds and are capable of emitting synchrotron radiation. The distribution function for electrons is re-derived here so that synchrotron emission from these relativistic electrons can be calculated. Based on the revised model, optical afterglows from both isotropic fireballs and highly collimated jets are studied numerically, and compared to analytical results. In the beamed cases, it is found that, in addition to the steepening due to the edge effect and the lateral expansion effect, the light curves are universally characterized by a flattening during the deep Newtonian phase. 相似文献
47.
The IRAS and 2MASS associations for 193 T Tauri stars are identified in this paper. From the color–color diagrams and spectral index, it is found that the IR excesses for most samples are due to thermal emission from the circumstellar material, as suggested previously. It is also found that the IR excesses at IRAS region for few T Tauri stars and the near-IR excesses for some T Tauri stars are likely attributed to free-free emission or free-bound emission from the circumstellar ionized gas. Moreover, It is found in deredened J–H versus H–K color–color diagram that there is a slight separation in different spectral groups. The T Tauri stars locus equation in J–H versus H–K color–color diagram for our sample is also presented. 相似文献
48.
49.
50.