全文获取类型
收费全文 | 137篇 |
免费 | 0篇 |
专业分类
地球物理 | 2篇 |
地质学 | 99篇 |
海洋学 | 2篇 |
天文学 | 32篇 |
自然地理 | 2篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 9篇 |
2016年 | 6篇 |
2015年 | 1篇 |
2014年 | 6篇 |
2013年 | 7篇 |
2012年 | 11篇 |
2011年 | 9篇 |
2010年 | 10篇 |
2009年 | 9篇 |
2008年 | 8篇 |
2007年 | 22篇 |
2006年 | 7篇 |
2005年 | 1篇 |
2004年 | 1篇 |
2003年 | 2篇 |
2002年 | 1篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1983年 | 2篇 |
排序方式: 共有137条查询结果,搜索用时 21 毫秒
1.
We have mapped three star-forming regions (G265.14+1.45, G269.16?1.14, G291.27?0.71) in the CS(3–2) and C34S(2–1) lines using the 15 m SEST telescope (Chile), and analyzed the relative positions of methanol and H2O masers, IRAS sources, and emission maxima in the CS lines. In most cases, the maser positions are close to those of the IRAS sources. We compared the radial velocities of the maser sources and high-density CS cores, and estimated the CS column densities assuming LTE. The sizes, densities, and masses of the dense core are estimated; the masses obtained in the LTE approximation agree with the virial masses. 相似文献
2.
3.
The Biscayarhalvøya-Holtedahlfonna zone (BHZ) in north-western Spitsbergen is a north-south trending, narrow horst, with crystalline basement rocks exposed under a Devonian unconformity. Previous K-Ar, 40 Ar/39 Ar and Rb-Sr analyses have confirmed the occurrence of Caledonian thermal events, and Grenvillian ages have been obtained by conventional zircon U-Pb and single-zircon Pb evaporation methods. A total of 55 zircon grains from three samples (an augen metagranite, a micaceous schist and a granitic neosome of migmatite) have been analysed by the single-zircon Pb evaporation method. The grains with the age range of ca. 950-1100 My (million years) are the major component in all three samples, suggesting tectono-thermal activity in that period. The detrital versus resorption orgin of the rounded shapes of these grains from the granitic neosome is not clear yet. Therefore, the ages of the migmatization and of the sedimentary protoliths are not concluded. The youngest presumed detrital grain from the granitic neosome is 1060 My old. The metagranite, cutting the Richarddalen unit, yielded grains with an age of ca. 950 Mya. A granite dyke with an age range of 955-968 My cuts the Biscayarhuken unit in the northern Liefdefjorden area. These indicate the sedimentary protoliths of the Richarddalen and Biscayarhuken units are pre-Neoproterozoic. The youngest detrital zircon ages of ca. 940 My indicate Neoproterozoic sedimentary protoliths of the Solanderfjellet micaceous schists. A significant population of zircon grains with an age range of 1600-1900 My in all three samples suggests a wide exposure of these rocks in the source areas during Meso- and Neoproterozoic times. Several Archean ages have also been obtained. The results are generally conformable with those obtained from north-western Spitsbergen. 相似文献
4.
Astronomy Letters - We have investigated the methanol CH3OH lines at frequencies of 19.967 GHz [21-30 E(vt = 0) transition] and 20.971 GHz [101-112 E+(vt = 1) transition] toward the massive region... 相似文献
5.
A complete sample of 104 bright active galactic nuclei (AGNs) from the “Planck” catalog (early results) were observed at 36.8 GHz with the 22-m radio telescope of the Crimean Astrophysical Observatory (CrAO).Variability indices of the sources at this frequency were determined based on data from theWMAP space observatory, theMetsa¨ hovi RadioObservatory (Finland), and the CrimeanAstrophysical Observatory. New observational results confirm that the variability of these AGNs is stronger in the millimeter than at other radio wavelengths. The variability indices probably change as a result of the systematic decrease in the AGN flux densities in the transition to the infrared. Some radio sources demonstrate significant flux-density variations, including decreases, which sometimes cause them to fall out of the analysed sample. The change of the variability index in the millimeter is consistent with the suggestion that this variability is due to intrinsic processes in binary supermassive black holes at an evolutionary stage close to coalescence. All 104 of the sources studied are well known objects that are included in various radio catalogs and have flux densities exceeding 1 Jy at 36.8 GHz. 相似文献
6.
Savko K. A. Samsonov A. V. Larionov A. N. Korish E. Kh. Bazikov N. S. 《Doklady Earth Sciences》2018,478(1):115-119
Doklady Earth Sciences - Framing of the Archaean greenstone belts of the Kursk Block (KB) of the East Sarmatia preserves rocks of the TTG association: those do not form massifs with distinct... 相似文献
7.
A. E. Volvach L. N. Volvach M. G. Larionov H. D. Aller M. F. Aller 《Astronomy Reports》2007,51(6):450-459
Variations in the radio flux of 3C 454.3 on various time scales from decades to a year are analyzed using long-term monitoring data at five frequencies from 4.8 to 36.8 GHz obtained at the University of Michigan Radio Astronomy Observatory and the Crimean Astrophysical Observatory. A spectral analysis of the light curves at the various frequencies reveals the presence of five periodic components. The long-and short-period components of the variability are compared using models for the precessional and orbital periods for motion in the system. The parameters for the supposed binary black-hole system are determined: the dimensions of the orbit and masses of the central black holes. The dynamics of the powerful flare in 2005–2006 are examined, and the time delays for its development from the optical to the radio and between radio frequencies are determined. The different frequency spectra of different individual flares can be explained in a model with a moving, expanding cloud that is first optically thick, then becomes optically thin at successively lower frequencies as it expands. 相似文献
8.
Vendian tectono-magmatic events in mantle ophiolitic complexes of the polar Urals: U-Pb dating of zircon from chromitite 总被引:1,自引:0,他引:1
Geological and isotopic evidence of Late Vendian magmatic events in restitic ultramafic mantle rocks of the Voikar-Syn’ya ophiolitic massif are considered and correlated with events at the eastern margin of the East European Platform. The geological and isotopic data show that the ophiolitic complexes of the Polar Urals were formed during several stages. The percolation of melts through peridotites was recorded in the newly formed mineral assemblages, for example, olivine + chromite ± zircon. Zircon crystallized from the residual fraction of the evolved basic melt that impregnated peridotite. The active interaction of hot restitic harzburgite with the migrating melt resumed repeatedly and could have led to the formation of several generations of chromite-bearing dunite. An important geological inference can be made from this suggestion: There is a high probability that isotopic markers of different age have been retained in restitic mantle complexes of ophiolites. The U-Pb dating of zircons with a SHRIMP-2 ion microprobe has shown that the isotopic age of seven grains is 585.3 ± 6 Ma (MSWD is 0.036 and the probability of concordance is 0.85). The obtained age of zircon from chromitite marks a Vendian tectonomagmatic event that occurred in the upper mantle of the transitional zone between the East European Plate and the oceanic basin. The island-arc complexes of the Polar Urals developed on the tectonically juxtaposed fragments of the Early Paleozoic and pre-Paleozoic oceanic crust. These crustal rocks were reworked during younger magmatic events related to the origin of the Middle Paleozoic island arcs. As a result, the rocks that formed in different geological epochs were locally retained in the restitic mantle complexes of a spatially indivisible ophiolitic association. 相似文献
9.
A molecular cloud and high-velocity outflow associated with the star-forming region L379 IRS3 have been mapped in the 6?1-50E methanol and CS (3-2) lines using the 12-meter Kitt Peak telescope. The estimated CS column density and abundance in the molecular cloud are 8×1014 cm?2 and 4×10?9, respectively. LVG modeling of the methanol emission constrains the gas density in the cloud to (1–4)×105 cm?3 and the gas kinetic temperature to 20–45 K. The upper limit on the density of the high-velocity gas is 105 cm?3. 相似文献
10.