全文获取类型
收费全文 | 386篇 |
免费 | 6篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 68篇 |
地球物理 | 53篇 |
地质学 | 112篇 |
海洋学 | 21篇 |
天文学 | 75篇 |
综合类 | 4篇 |
自然地理 | 58篇 |
出版年
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2018年 | 9篇 |
2017年 | 8篇 |
2016年 | 5篇 |
2015年 | 4篇 |
2014年 | 9篇 |
2013年 | 17篇 |
2012年 | 8篇 |
2011年 | 17篇 |
2010年 | 10篇 |
2009年 | 15篇 |
2008年 | 7篇 |
2007年 | 14篇 |
2006年 | 12篇 |
2005年 | 10篇 |
2004年 | 17篇 |
2003年 | 10篇 |
2002年 | 9篇 |
2001年 | 14篇 |
2000年 | 13篇 |
1999年 | 9篇 |
1998年 | 8篇 |
1997年 | 9篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 15篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1972年 | 2篇 |
1971年 | 9篇 |
排序方式: 共有397条查询结果,搜索用时 15 毫秒
91.
We examine the shape of a “rubble pile” asteroid as it slowly gains angular momentum by YORP torque, to the point where “landsliding” occurs. We find that it evolves to a “top” shape with constant angle of repose from the equator up to mid-latitude, closely resembling the shapes of several nearly critically spinning asteroids imaged by radar, most notably (66391) 1999 KW4 [Ostro, S.J., Margot, J.-L., Benner, L.A.M., Giorgini, J.D., Scheeres, D.J., Fahnestock, E.G., Broschart, S.B., Bellerose, J., Nolan, M.C., Magri, C., Pravec, P., Scheirich, P., Rose, R., Jurgens, R.F., De Jong, E.M., Suzuki, S., 2006. Science 314, 1276-1280]. Similar calculations for non-spinning extremely prolate or oblate “rubble piles” show that even loose rubble can sustain shapes far from fluid equilibrium, thus inferences based on fluid equilibrium are generally useless for inferring bulk properties such as density of small bodies. We also investigate the tidal effects of a binary system with a “top shape” primary spinning at near the critical limit for stability. We find that very close to the stability limit, the tide from the secondary can actually levitate loose debris from the surface and re-deposit it, in a process we call “tidal saltation.” In the process, angular momentum is transferred from the primary spin to the satellite orbit, thus maintaining the equilibrium of near-critical spin as YORP continues to add angular momentum to the system. We note that this process is in fact dynamically related to the process of “shepherding” of narrow rings by neighboring satellites. 相似文献
92.
Dmitry P. Gladkochub Sergei A. Pisarevsky Tatiana V. Donskaya Richard E. Ernst Michael T.D. Wingate Ulf Söderlund Anatoliy M. Mazukabzov Eugene V. Sklyarov Michael A. Hamilton John A. Hanes 《Precambrian Research》2010
We present a summary of late Paleoproterozoic to Neoproterozoic mafic magmatism in the Siberian craton, including recently published U–Pb and 40Ar–39Ar dates. These new precise ages suggest that at least some of the previously published K–Ar ages of Siberian mafic bodies should be ignored. The time–space geochronological chart, or the ‘barcode’ of mafic magmatic events shows significant differences between northern and southern Siberia. Both are characterized by ∼1900–1700 Ma magmatic events, but then there was an almost 1 Ga mafic magmatic ‘pause’ in south Siberia until ∼800 Ma. Meanwhile there are indications of multiple mafic magmatic events in North Siberia (Anabar shield and Olenek uplift) between ∼1600 and 1000 Ma. A series of magmatic events probably related to the breakup of Rodinia occurred in southern Siberia after ∼800 Ma. So far, there are no indications of late Neoproterozoic mafic magmatism in North Siberia. Ca. 1000–950 Ma mafic sills were reported from Meso- to Neo-Proterozoic sedimentary successions in the Sette-Daban area on the east side of the Siberian craton, but their tectonic setting is debated. Recent Ar–Ar dates of ∼1750 Ma for NW-trending dykes in the Aldan and Anabar shields, together with similar-age NNE-trending Baikal uplift dykes in south-eastern Siberia suggest the existence of a giant radial dyke swarm possibly related to a mantle plume centred in the Vilyui River area. 相似文献
93.
Eugene Yee R. Chan P. R. Kosteniuk G. M. Chandler C. A. Biltoft J. F. Bowers 《Boundary-Layer Meteorology》1995,76(1-2):41-67
This paper describes a study of the vertical structure of concentration fluctuations in a neutrally buoyant plume from an elevated point source in slightly convective to moderately stable meteorological conditions at ranges of between 12.5 and 100 m for a range of source heights between 1 and 5 m. Observations were made of concentration fluctuations in a dispersing plume using a vertical array of sixteen very fast-response photoionization detectors placed at heights between 0.5 and 16 m. Vertical profiles of a number of concentration statistics were extracted, namely, mean concentration, fluctuation intensity, intermittency factor, peak-to-mean concentration ratio, mean dissipation rate of concentration variance, and various concentration time and length scales of dominant motions in the plume (e.g., integral macro-scale, in-plume mid-scale and Taylor micro-scale). The profiles revealed a similarity to corresponding crosswind profiles for a fully elevated plume, but showed greater and greater departure from the latter shapes once the plume had grown in the vertical so that its lower dege began to interact progressively more strongly with the ground. The evolution of the concentration probability density function at a fixed range, but with decreasing height from the ground, is similar to that obtained at a fixed height but with increasing distance from the source. Concentration power spectra obtained at different heights all had an extensive inertial-convective subrange spanning at least two decades in frequency, but spectra measured near the ground had a greater proportion of the total concentration variance in the lower frequencies (energetic subrange), with a correspondingly smaller proportion in the higher frequencies (inertial-convective subrange). It is believed that these effects result from the increased mean shear near the surface, and blocking by the surface. The effect of enhanced shear-induced molecular diffusion on concentration fluctuations is examined. 相似文献
94.
Ohne Zusammenfassung 相似文献
95.
Charles W. Neal Robert T. Dodd Eugene Jarosewich Michael E. Lipschutz 《Geochimica et cosmochimica acta》1981,45(6):891-898
Radiochemical neutron activation analysis of Ag, As, Au, Bi, Co, Cs, Ga, In, Rb, Sb, Te, Tl and Zn and major element data in 14 L4-6 and 3 LL5 chondrites indicates that the L-group is unusually variable and may represent at least 2 sub-groups differing in formation history. Chemical trends in the S/Fe-rich sub-group support textural evidence indicating late loss of a shock-formed Fe-Ni-S melt; the S/Fe-poor sub-group seemingly reflects nebular fractionation only. Highly mobile In and Zn apparently reflect shock-induced loss from L-chondrites. Data for L5 chondrites suggest higher formation temperatures and/or degrees of shock than for LL5 chondrites. 相似文献
96.
Chu-Fa Tsai Justine Welch Kwei-Yang Chang John Shaeffer L. Eugene Cronin 《Estuaries and Coasts》1979,2(3):141-153
Baltimore Harbor, a tributary area of the northern Chesapeake Bay, has recelved and is receiving large quantities of chemical pollutants. As part of a cooperative study to explore possible corrective treatment for existing pollution burdens, gross bioassay analyses were performed for sediments from nine representative stations, employing two species of fish, mummichogs (Fundulus heteroclitus) and spot (Leiostomus xanthurus), and one mollusc, the soft-shell clam (Mya arenaria). Acclimated organisms were exposed in static systems to a series of concentrations of suspended sediment from each station, to fuller's earth in suspension, and in control tanks for 48 hours. Parallel analysis of the sediment was performed for the metals, Pb, Cr, Zn, Ca, As, for PCB's and for hexane extracts. The sediments were all substantially polluted with low correlations among components. Twenty-four hour TLm and 48-hour TLm increased proportionately with sediment concentration but display species specificity. The relationships observed permit use of mummichog data to index gross toxicity of sediments throughout the harbor. Further comparison of mummichog 24-hour TLm value with benthie species diversity determined in a previous study permitted zoning of the entire harbor into highly toxic, moderately toxic, low toxic and slightly toxic zones. Gross toxicity of sediments determined by bioassay can therefore be used as an index of the suitability of the sediments for benthic macroinvertebrate communities. 相似文献
97.
98.
99.
Steve P. Schilling Paul E. Carrara Ren A. Thompson Eugene Y. Iwatsubo 《Quaternary Research》2004,61(3):325-329
The cataclysmic eruption of Mount St. Helens on May 18, 1980, resulted in a large, north-facing amphitheater, with a steep headwall rising 700 m above the crater floor. In this deeply shaded niche a glacier, here named the Amphitheater glacier, has formed. Tongues of ice-containing crevasses extend from the main ice mass around both the east and the west sides of the lava dome that occupies the center of the crater floor. Aerial photographs taken in September 1996 reveal a small glacier in the southwest portion of the amphitheater containing several crevasses and a bergschrund-like feature at its head. The extent of the glacier at this time is probably about 0.1 km2. By September 2001, the debris-laden glacier had grown to about 1 km2 in area, with a maximum thickness of about 200 m, and contained an estimated 120,000,000 m3 of ice and rock debris. Approximately one-third of the volume of the glacier is thought to be rock debris derived mainly from rock avalanches from the surrounding amphitheater walls. The newly formed Amphitheater glacier is not only the largest glacier on Mount St. Helens but its aerial extent exceeds that of all other remaining glaciers combined. 相似文献
100.