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191.
192.
Nineteen species of Diptera (16 in each zone) from seven families were found in monthly collections (June 1979 through May 1980) in two Mississippi marsh plant zones dominated byJuncus roemerianus Scheele andSpartina cynosuroides (L.) Roth, respectively. TheJuncus zone was dominated by a species ofPalpomyia-Bezzia complex, two species ofBezzia (Ceratopogonidae),Paratendipes sp.,Limnophyes sp. (Chironomidae) andThinophilus frontalis (Dolichopodidae).Palpomyia-Bezzia sp.,Culicoides hollensis, Ormosia sp. (Tipulidae) andPelastoneurus abbreviatus (Dolichopodidae) dominated theSpartina zone. Total inset density and species richness were lowest in June and July in both zones, corresponding to a pulse of adult emergence. Overall, total density was significantly higher in theSpartina zone with mean values of 165 and 245 insects m?2 for the {Juncus} and {Spartina} zones, respectively. In addition to total density, differences in abundance were apparent for a number of species between marsh zones. Patterns could be attributed to species-specific habitat preference., predation by aquatic predators, and/or by interactions of the infauna themselves. 相似文献
193.
R.Dale Guthrie 《Quaternary Research》1984,22(2):231-241
Broken large mammal fossil bones in eastern Beringia have been used to argue for a middle-Wisconsin, or earlier, time of human entry into North America, It has been inferred that these controversial Pleistocene bones are artifacts because (1) they are similar to those found in archaeological sites and (2) they can be reproduced in the laboratory by replication. However, fractured, flaked, polished, faceted, cut, and scratched bones similar to the purportedly human artifacts described from Beringia are known to be produced by natural processes. New experimental data demonstrate that identifications of Pleistocene bone artifacts on the basis of differential staining and fresh breakage are suspect. Physical processes, such as the violent forces of river ice breakups in the north, and bone crushing by mammalian scavengers produce similar pseudo-artifacts. Additionally, the middle-Wisconsin dates associated with some of the finished tools, and human and dog bones from Beringia are open to question. The lack of credible dates on these artifacts raises doubt about the model of human colonization of Beringia, developed in the 1960s, which proposed an interstadial colonization of the New World. 相似文献
194.
195.
Following the catastrophic “Great Sumatra–Andaman” earthquake- tsunami in the Indian Ocean on the 26th December 2004, questions
have been asked about the frequency and magnitude of tsunami within the region. We present a summary of the previously published
lists of Indian Ocean Tsunami (IOT) and the results of a preliminary search of archival materials held at the India Records
Office, at the British Library in London. We demonstrate that in some cases, normal tidal movements and floods associated
with tropical cyclones have been erroneously listed as tsunami. We summarise archival material for tsunami that occurred in
1945, 1941, 1881, 1819, 1762 and a little known tsunami in 1843. We present the results of modelling of the 2004, 1861 and
1833 tsunami generated by earthquakes off Sumatra and the 1945 Makran earthquake and tsunami, and examine how these results
help to explain some of the historical observations. The highly directional component to tsunami propagation illustrated by
the numerical models may explain why we are unable to locate archival records of the 1861 and 1833 tsunami at important locations
like Rangoon, Kolkata (formally Calcutta) and Chennai (formally Madras), despite reports that these events created large tsunami
that inundated western Sumatra. The numerical models identify other areas (particularly the central and southern Indian Ocean
islands) where the 1833 tsunami may have had a large enough effect to produce a historic record. We recommend further archival
research, coastal geological investigations of tsunami impacts and detailed modelling of tsunami propagation to better understand
the record and effects of tsunami in the Indian Ocean and to estimate their likelihood of occurring in the future. 相似文献
196.
In early January 1888, James E. Keeler was one of the first astronomers to work with the very new Lick Observatory 36-in. refractor. On January 7 while observing Saturn visually on a night of very fine seeing, he discovered a narrow, dark “division” in the outer part of the A ring. Despite repeated attempts, neither Keeler nor any of the other Lick observers saw this gap again until over a year later, on March 2, 1889, another night of extremely good seeing. On that occasion not only Keeler, but also E. S. Holden, J. M. Schaeberle, and E. E. Barnard all observed “Mr. Keeler's division,” as Barnard called it. It could only be seen using very high magnification with this large telescope, at a site known to be excellent, on the nights of very best definition. This gap is not the same as the feature which J. F. Encke had earlier discovered and described as a low-contrast division nearly in the middle of the A ring, and had drawn as nearly the same width as Cassini's division. Later visual observations by B. Lyot and A. Dollfus, again on nights of fine seeing with large telescopes, showed that the Encke division is complex. To them, with the best resolution, it appeared as three wide minima of light, fuzzy, and of low contrast, with a narrow, well-marked minimum of light at its outer edge. The outer edge is just where Keeler placed his gap, although he did not see the low-contrast structure in the Encke division. The images, with much superior resolution obtained from the Pioneer and Voyager space probes, show that the Encke division is even more complex than Lyot and Dollfus realized, but confirm the narrow Keeler feature as a true gap in the outer part of the A ring. 相似文献
197.
N. I. Fisher J. F. Huntington D. R. Jackett M. E. Willcox J. W. Creasey 《Mathematical Geology》1985,17(2):177-194
A frequently encountered problem in structural geology is the analysis and interpretation of directional data with a geographical distribution. Such data may arise, for example, as samples of fracture strikes collected at a number of locations (rocky outcrops, road cuttings, etc.), trends of geological structures mapped in underground mines where they are exposed in the tunnel roof, or as lineaments annotated on aerial or satellite photographs. From such data, it is of interest to determine the structural domains in the area, that is, to partition the area into subareas of homogeneous structural pattern. This paper presents a method for performing such an analysis, and applies it to a data set collected from an underground coal mine. 相似文献
198.
Hydrographic and atmospheric analysis of an autumnal upwelling event in the Ria of Vigo (NW Iberian Peninsula) 总被引:2,自引:0,他引:2
M. deCastro A.W. Dale M. Gmez-Gesteira R. Prego I. Alvarez 《Estuarine, Coastal and Shelf Science》2006,68(3-4):529
An autumnal upwelling event was observed in the Ria of Vigo (NW Iberian Peninsula) on 15th November 2001. This event was analyzed by means of thermohaline variables measured at CTD stations located in the study area, satellite sea surface temperature and wind data provided by QuikSCAT. Salinity and temperature distributions revealed that the upwelled water mass was Eastern North Atlantic Central Water (ENACW), typically observed during summer upwelling events. However, previous to the upwelling event, the characteristic autumnal body of water was recorded on 31st October 2001. Subsequent sea surface temperature and upwelling index corroborated the presence of an autumnal upwelling event of approximately 15 days duration. The probability of upwelling-favorable winds (from 1999 to 2004) was lower during autumn–winter than during spring–summer, although they may occur at any time of the year. Probabilities of 45% were calculated for February and November, with the highest probability (65%) corresponding to July. 相似文献
199.
Eric P. Chassignet Hernan Arango David Dietrich Tal Ezer Michael Ghil Dale B. Haidvogel C. -C. Ma Avichal Mehra Afonso M. Paiva Ziv Sirkes 《Dynamics of Atmospheres and Oceans》2000,32(3-4)
The results of an intercomparison experiment performed with five numerical ocean models of different architecture are presented. While all models are able to simulate the large-scale characteristics of the North Atlantic circulation with a fair degree of realism, they also exhibit differences that can be attributed to the choices made in vertical coordinates, domain size, and boundary conditions. 相似文献
200.