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1.
Holocene climate variability 总被引:17,自引:0,他引:17
2.
3.
The edge-on presentation of Saturn's rings and satellites system has provided a rare opportunity to observe total eclipses of Titan. During its emersion from the Saturnian shadow (1980, June 28), Titan has been observed simultaneously in the visible and the infrared ranges (6000–9000 Å, 11.8 μm and 20 μm). No change has been recorded in these three spectral ranges. Our observations tend to support the thick-atmosphere model, which has been shown to be valid by Voyager a few months later. 相似文献
4.
Stellar occultations by comets can be used for studying the dust opacity of the coma in the vicinity of the cometary nucleus. This method provides high spatial resolution. If faint stars (V ≤ 15) are used in the densest regions of the sky, the event probability is typically one every 2 hr. This probability can be enhanced by a factor of 40 if the Space Telescope is used. 相似文献
5.
In any matter-antimatter symmetric cosmology the primeval nucleosynthesis imposes a typical size of a region of matter (antimatter) much larger than the diffusion length of neutrons. Observational results on the abundances of cosmic deuterium and helium are used to evaluate how large it has to be. As a result we find that a minimal sizeL 1~1.5×108 cm at the temperatureT=1 MeV is compatible with the standard abundances of primeval helium and deuterium. 相似文献
6.
Synthetic spectra of Comet Halley between 2.5 and 15 μm are calculated on the basis of current cometary models. This study shows that molecules which are most likely detectable in the infrared range include H2O, CO, CO2, CH4, NH3, N2H4, and H2CO. The flux emitted by these molecules, mostly due to resonant scattering, should be sufficient for detection by a flyby mission. 相似文献
7.
We reduced ultraviolet spectra of Saturn from the IUE satellite to produce a geometric albedo of the planet from 1500 to 3000 Å. By matching computer models to the albedo we determined a chemical composition consistent with the data. This model includes C2H2 and C2H6 with mixing ratios and distributions of (9 ± 3) × 10?8 in the top 20 mbar of the atmosphere with none below for C2H2 and (6 ± 1) × 10?6 also in the top 20 mbar with none below for C2H6. The C2H2 and C2H6 distributions and the C2H6 mixing ratio are taken directly from the Voyager IRIS model [R. Courtin et al., Bull. Amer. Astron. Soc.13, 722 (1981), and private communication]. The Voyager IRIS model also includes PH3, which is not consistent with the uv albedo from 1800 to 2400 Å. Our model requires a previously unidentified absorber to explain the albedo near 1600 Å. After considering several candidates, we find that the best fit to the data is obtained with H2O, having a column density of (6 ± 1) × 10?3 cm-am. 相似文献
8.
M. Guélin N. Brouillet J. Cernicharo F. Combes A. Wooten 《Astrophysics and Space Science》2008,313(1-3):45-51
High angular resolution mm-wave observations of the Orion-KL region, made with the IRAM Plateau de Bure interferometer (PdBI),
reveal the presence of several cores of size 103 AU, which have distinct spectral signatures. Complex molecules such as ethanol, vinyl cyanide and dimethyl ether show different
distributions and their relative abundance varies from core to core by orders of magnitude. The molecular column densities
derived in the cores also differ widely from the beam-averaged column densities observed with large single-dish telescopes.
Obviously, the predictions of hot core chemistry models must be checked against high resolution observations. ALMA, which
allies sensitivity and high angular resolution, will be a key instrument for this type of studies.
The PdBI observations were part of a search for interstellar glycine, also carried out with the IRAM 30-m telescope and the
Green Bank Telescope. We derive a 3σ upper limit on the column density of glycine of 1×1015 cm−2 per 2″×3″ beam in the Orion Hot Core and Compact Ridge.
Based on observations made with the IRAM PdB Interferometer, the IRAM 30-m telescope and the NRAO Green-Bank telescope. IRAM
is supported by CNRS, MPG and IGN. 相似文献
9.
A late Pleistocene and Holocene mineral magnetic record from sediments of Lake Aibi,Dzungarian Basin,NW China 总被引:1,自引:0,他引:1
Alina Tudryn Piotr Tucholka Elisabeth Gibert Francoise Gasse Keiquin Wei 《Journal of Paleolimnology》2010,44(1):109-121
We studied mineral magnetic properties of a 6-m-long, late Pleistocene through Holocene sediment sequence from Lake Aibi in
Dzungaria (Zunggary, Junggar), northern Xinjiang, China. Results were used to infer environmental changes and are compared
with previously studied cores from Lake Manas. Both water bodies occupy the deepest parts of the Dzungarian Basin and are
remnants of large Holocene lakes. During the Late Pleistocene, the magnetic mineralogy in both lakes was dominated by detrital,
iron oxide minerals. Oxic conditions, which dominated during sedimentation and early diagenesis, persisted over the Pleistocene–Holocene
transition. Later, during the middle Holocene, lake bottom conditions enabled authigenic formation of iron sulphide minerals
such as pyrite (FeS2) in Lake Aibi, and pyrite and greigite (Fe3S4) in Lake Manas. This iron sulphide mineralogy suggests increased biological activity in stagnant, anoxic bottom waters. Anoxic
bottom conditions started about 9.8 cal kyr BP in Lake Manas and at about 7.2 cal kyr BP in Lake Aibi. A short dry event recorded
in Lake Manas between 6.8 and 5.2 cal kyr BP is not clearly observed in Lake Aibi. In the late Holocene, i.e. the last 2.8 cal
kyr, sediments of both lakes are again characterised by iron oxides, suggesting well-mixed, shallow water bodies. For this
recent period, it seems that the detrital material in the two lakes had a common origin. Magnetic properties of sediments
in Lakes Aibi and Manas show broadly similar environmental evolution during the late Pleistocene and Holocene. Nevertheless,
despite the close proximity of the two lakes (~200 km) in the same basin, they display some different magnetic properties
and record environmental changes at different times. 相似文献
10.
暴露岩石中宇生核素的浓度与暴露年代、侵蚀速率相关,暴露年代和侵蚀速率可相互求证,但两者均为未知数时,可求算出最大侵蚀速率和最小暴露年代。据此得出张八岭地区的最大侵蚀速率为7 12m/Ma,最小暴露年代为(85700±1500)a,这一年代远小于统一夷平面的形成年代(7~3 6Ma),造成这种差距的主要原因是:①张八岭地区侵蚀速率大,岩石中宇生核素的浓度较早达到平衡,即达到该地区的测年上限;②采样地区曾被土壤覆盖,造成计算年代值过于年轻。 相似文献