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RICHARD M. TIPPING 《Boreas: An International Journal of Quaternary Research》1989,18(4):333-341
Peaks of Pinus pollen inseveraldetailed early postglacial (Flandrian) pollen diagrams from western Scotland are interpreted as the result of a change in the prevailing wind direction and intensity during climatic amelioration following the Loch Lomond Stadial (Younger Dryas). This origin implies a degree of syn-chroneity in this palynological feature, which if proven would be valuable in the poorly dated early postglacial. The absence of this palynological feature at many sites may be the result of poor sampling or stratigraphic resolution. 相似文献
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Diagenesis refers to those changes which take place in sediments after sedimentation but before lithification (the conversion to solid rock), while metamorphism is defined as the process whereby alterations to the composition, texture or mineralogy take place in consolidated rocks. However, the boundary between diagenesis and metamorphism is gradual/transitional and somewhat arbitrary; it cannot be sharply defined. A consequence of this is that studies of rocks affected by alteration at low temperatures and pressures have been neglected. Within the last decade, however, more attention has been focused on this type of alteration and significant advances have been made in the field of low-grade metamorphism, particularly over the last five years or so. The Caledonide rocks of Wales have been at the forefront of such investigations. 相似文献
146.
The prospects for establishing synchroneity in the early postglacial pollen peak of Juniperus in the British Isles 总被引:2,自引:0,他引:2
RICHARD M. TIPPING 《Boreas: An International Journal of Quaternary Research》1987,16(2):155-163
Tipping, Richard M. 1987 06 01: The prospects for establishing synchroneity in the early postglacial pollen peak of Juniperus in the British Isles. Boreas , Vol. 16, pp. 155–163. Oslo. ISSN 0300–9483.
Seventy radiocarbon assays on the early postglacial Juniperus pollen peak in the British Isles are collated in order to test the hypothesis that the expansion of Juniperus was synchronous in the British Isles. The necessity of screening this data base is discussed, as are the screening procedures adopted. A number of problems concerned with screening are highlighted, which are related to the paucity of information available from which to assess the reliability of a date. The accepted radiocarbon dates are analysed by computer-generated histograms. No clear pattern of synchroneity is found. The possibility of a diachronous distribution across the British Isles is examined. The methods employed in this study illustrate the problems of using large samples of radiocarbon dates, and exemplify the stringent procedures required in handling such data. 相似文献
Seventy radiocarbon assays on the early postglacial Juniperus pollen peak in the British Isles are collated in order to test the hypothesis that the expansion of Juniperus was synchronous in the British Isles. The necessity of screening this data base is discussed, as are the screening procedures adopted. A number of problems concerned with screening are highlighted, which are related to the paucity of information available from which to assess the reliability of a date. The accepted radiocarbon dates are analysed by computer-generated histograms. No clear pattern of synchroneity is found. The possibility of a diachronous distribution across the British Isles is examined. The methods employed in this study illustrate the problems of using large samples of radiocarbon dates, and exemplify the stringent procedures required in handling such data. 相似文献
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GRAHAME J. LARSON DANIEL E. LAWSON EDWARD B. EVENSON ÓSKAR KNUDSEN RICHARD B. ALLEY MANTHA S. PHANIKUMAR 《Boreas: An International Journal of Quaternary Research》2010,39(3):457-470
Larson, G.J., Lawson, D.E., Evenson, E.B., Knudsen, Ó., Alley, R.B. & Phanikumar, M.S. 2010: Origin of stratified basal ice in outlet glaciers of Vatnajökull and Öræfajökull, Iceland. Boreas, Vol. 39, pp. 457–470. 10.1111/j.1502‐3885.2009.00134.x. ISSN 0300‐9483. During the period 2000–2005, we collected samples of englacial ice, vent water, frazil/anchor ice and stratified basal ice from warm‐based outlet glaciers of Vatnajökull and Öræfajökull, Iceland, and analysed them for 3H, 18O and D. Results of 3H analyses show that the stratified basal ice contains 3H from atmospheric thermonuclear testing and is younger than the englacial ice. Results of the 18O and D analyses show that frazil/anchor and stratified basal ice are both enriched by an average of 2.4‰ in 18O and 11‰ in D relative to vent water. These values are consistent with fractionation during partial freezing of supercooled subglacial water in an open system, one in which the remaining water is continuously removed and replenished by water of similar composition. The isotopic data and field observations do not support either a regelation or a thermal ad‐freeze‐on origin for the stratified basal ice. 相似文献
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KARL CHARVIN GARY J. HAMPSON KERRY L. GALLAGHER RICHARD LABOURDETTE 《Sedimentology》2010,57(3):760-785
Although modern wave‐dominated shorelines exhibit complex geomorphologies, their ancient counterparts are typically described in terms of shoreface‐shelf parasequences with a simple internal architecture. This discrepancy can lead to poor discrimination between, and incorrect identification of, different types of wave‐dominated shoreline in the stratigraphic record. Documented in this paper are the variability in facies characteristics, high‐resolution stratigraphic architecture and interpreted palaeo‐geomorphology within a single parasequence that is interpreted to record the advance of an ancient asymmetrical wave‐dominated delta. The Standardville (Ab1) parasequence of the Aberdeen Member, Blackhawk Formation is exposed in the Book Cliffs of central Utah, USA. This parasequence, and four others in the Aberdeen Member, record the eastward progradation of north/south‐trending, wave‐dominated shorelines. Within the Standardville (Ab1) parasequence, distal wave‐dominated shoreface‐shelf deposits in the eastern part of the study area are overlain across a downlap surface by southward prograding fluvial‐dominated delta‐front deposits, which have previously been assigned to a separate ‘stranded lowstand parasequence’ formed by a significant, allogenic change in relative sea‐level. High‐resolution stratigraphic analysis of these deposits reveals that they are instead more likely to record a single episode of shoreline progradation characterized by alternating periods of normal regressive and forced regressive shoreline trajectory because of minor cyclical fluctuations in relative sea‐level. Interpreted normal regressive shoreline trajectories within the wave‐dominated shoreface‐shelf deposits are marked by aggradational stacking of bedsets bounded by non‐depositional discontinuity surfaces. Interpreted forced regressive shoreline trajectories in the same deposits are characterized by shallow incision of fluvial distributary channels and strongly progradational stacking of bedsets bounded by erosional discontinuity surfaces that record enhanced wave‐base scour. Fluvial‐dominated delta‐front deposits most probably record the regression of a lobate delta parallel to the regional shoreline into an embayment that was sheltered from wave influence. Wave‐dominated shoreface‐shelf and fluvial‐dominated delta‐front deposits occur within the same parasequence, and their interpretation as the respective updrift and downdrift flanks of a single asymmetrical wave‐dominated delta that periodically shifted its position provides the most straightforward explanation of the distribution and relative orientation of these two deposit types. 相似文献