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101.
Neil F. Glasser Philip D. Hughes Cassandra Fenton Christoph Schnabel Henrik Rother 《第四纪科学杂志》2012,27(1):97-104
This paper presents results of the analysis of paired cosmogenic isotopes (10Be and 26Al) from eight quartz‐rich samples collected from ice‐moulded bedrock on the Aran ridge, the highest land in the British Isles south of Snowdon. On the Aran ridge, comprising the summits of Aran Fawddwy (905 m a.s.l.) and Aran Benllyn (885 m a.s.l.), 26Al and 10Be ages indicate complete ice coverage and glacial erosion at the global Last Glacial Maximum (LGM). Six samples from the summit ridge above 750–800 m a.s.l. yielded paired 10Be and 26Al ages ranging from 17.2 to 34.4 ka, respectively. Four of these samples are very close in age (10Be ages of 17.5 ± 0.6, 17.5 ± 0.7, 19.7 ± 0.8 and 20.0 ± 0.7 ka) and are interpreted as representing the exposure age of the summit ridge. Two other summit samples are much older (10Be ages of 27.5 ± 1.0 and 33.9 ± 1.2 ka) and these results may indicate nuclide inheritance. The 26Al/10Be ratios for all samples are indistinguishable within one‐sigma uncertainty from the production rate ratio line, indicating that there is no evidence for a complex exposure history. These results indicate that the last Welsh Ice Cap was thick enough to completely cover the Aran ridge and achieve glacial erosion at the LGM. However, between c. 20 and 17 ka ridge summits were exposed as nunataks at a time when glacial erosion at lower elevations (below 750–800 m a.s.l.) was achieved by large outlet glaciers in the valleys surrounding the mountains. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
102.
Elizabeth A. Bagshaw Stephen Burrow Jemma L. Wadham James Bowden Ben Lishman Mike Salter Richard Barnes Peter Nienow 《水文研究》2012,26(20):3157-3160
This briefing describes the first deployment of a new electronic tracer (E‐tracer) for obtaining along‐flowpath measurements in subsurface hydrological systems. These low‐cost, wireless sensor platforms were deployed into moulins on the Greenland Ice Sheet. After descending into the moulin, the tracers travelled through the subglacial drainage system before emerging at the glacier portal. They are capable of collecting along‐flowpath data from the point of injection until detection. The E‐tracers emit a radio frequency signal, which enables sensor identification, location and recovery from the proglacial plain. The second generation of prototype E‐tracers recorded water pressure, but the robust sensor design provides a versatile platform for measuring a range of parameters, including temperature and electrical conductivity, in hydrological environments that are challenging to monitor using tethered sensors. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
103.
Neil F. Glasser Samuel Clemmens Christoph Schnabel Cassandra R. Fenton Lanny McHargue 《Quaternary Science Reviews》2009,28(27-28):3448-3458
We report cosmogenic surface exposure 10Be ages of 21 boulders on moraines in the Jeullesh and Tuco Valleys, Cordillera Blanca, Peru (~10°S at altitudes above 4200 m). Ages are based on the sea-level at high-latitude reference production rate and scaling system of Lifton et al. (2005. Addressing solar modulation and long-term uncertainties in scaling secondary cosmic rays for in situ cosmogenic nuclide applications. Earth and Planetary Science Letters 239, 140–161) in the CRONUS-Earth online calculator of Balco et al. (2008. A complete and easily accessible means of calculating surface exposure ages or erosion rates from 10Be and 26Al measurements. Quaternary Geochronology 3, 174–195). Using the Lifton system, large outer lateral moraines in the Jeullesh Valley have a 10Be exposure age of 12.4 ka, inside of which are smaller moraine systems dated to 10.8, 9.7 and 7.6 ka. Large outer lateral moraines in the Tuco Valley have a 10Be exposure age of 12.5 ka, with inner moraines dated to 11.3 and 10.7 ka. Collectively, these data indicate that glacier recession from the Last Glacial Maximum (LGM) in the Cordillera Blanca was punctuated by three to four stillstands or minor advances during the period 12.5–7.6 ka, spanning the Younger Dryas Chronozone (YDC; ~12.9–11.6 ka) and the cold event identified in Greenland ice cores and many other parts of the world at 8.2 ka. The inferred fluctuations of tropical glaciers at these times, well after their withdrawal from the LGM, indicate an increase in precipitation or a decrease in temperature in this region. Although palaeoenvironmental records show regional and temporal variability, comparison with proxy records (lacustrine sediments and ice cores) indicate that regionally this was a cold, dry period so we ascribe these glacier advances to reduced atmospheric temperature rather than increased precipitation. 相似文献
104.
Claire Workman Love Dalen Sergey Vartanyan Beth Shapiro Pavel Kosintsev Andrei Sher Anders Gotherstrom Ian Barnes 《Quaternary Science Reviews》2011,30(17-18):2304-2308
Patterns in the spatial or temporal distribution of genotypes may be indicative of natural selection. Previous work on the woolly mammoth melanocortin-1 receptor (Mc1r) gene identified three polymorphic positions that suggest Pleistocene populations may have harboured both light- and dark-haired mammoths (Rompler et al., 2006, 313: 62). Here, we extend this work and present the first population-level analysis of a functional gene in an extinct species. We genotyped the Mc1r gene in 47 woolly mammoth samples excavated from sites across the central portion of the woolly mammoths’ former range to examine the extent of variation of this polymorphism through time and across space. Only one individual was found to be heterozygous, indicating that the frequency of the ‘light’ mutant allele was very low. We conclude that light-coloured woolly mammoths would have been very rare, and may even have been non-existent if the ‘light’ mutant allele was strongly selected against in its homozygotic form. With the increasing availability of large-scale sequencing technologies, population-level datasets capable of identifying local adaptation will become increasingly attainable. 相似文献
105.
All carbonates associated with the ultramafic rocks and serpentinites of the western United States are shown by their stable isotope ratios to be of near-surface, low-temperature origin. These include vein materials that have been previously classified as hydrothermal. New laboratory and natural data were obtained on the equilibrium isotope relations between hydromagnesite and water. The origins of travertines in the ultramafic area are easily distinguished on the basis of their stable isotope ratios. The extremely heavy isotope ratios of nesquehonites suggest an intricate evaporating-film mechanism of formation. 相似文献
106.
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108.
Abstract A nearly complete skeleton of a fossil sperm whale from the Middle Miocene age Bessho Formation at Shiga-mura, Nagano Prefecture, the most complete fossil physeterid skeleton found in Japan, is here named Scaldicetus shigensis, new species. Its abruptly tapered rostrum, deep supracranial basin, and high occipital crest are typical of physeterids. Large teeth with crenulate enamel on conical crowns, present in both the palate and mandible, are consistent with the genus Scaldicetus du Bus, 1867, a genus originally based on fossils discovered in the Antwerp Basin, Belgium. Scaldicetus shigensis is relatively primitive, having a relatively long, slender rostrum, large zygomatic arches, large tympanic bullae, prominent occipital condyles, low tooth count and a sloping occipital shield that is deeply emarginated laterally by large temporal fossae. The probable mandibular tooth count is 12, only one more than the primitive eutherian mammalian dentition. Despite its abundant primitive characters, Scaldicetus shigensis has very asymmetrical external nares, comparable to the living sperm whale, Physeter catodon, and is in this way more derived than most of the contemporaneous fossil physeterids. At a time when other sperm whales were more highly evolved, Scaldicetus shigensis retained a primitive occipital shield, large tympanic bullae, and low tooth count, as in primitive Oligocene odontocetes such as Agorophiidae. It was a relict form in Middle Miocene time, and provides an indication of a primitive stage of sperm whale evolution heretofore undocumented. Fossils from elsewhere previously referred to as Scaldicetus, largely on the basis of tooth characters, range in age from Early Miocene to Plio-Pleistocene time. Cranial material that would clarify relationships is lacking for most of these, and this time range seems too long for a cetacean genus. Because of this simplistic approach to identifications, Scaldicetus is probably a grade taxon, not a natural biological grouping. However, the tooth morphology of Scaldicetus shigensis is correct for the genus Scaldicetus, so we provisionally assign it to this genus. Redefinition of the genus Scaldicetus and revision of the Physeteridae are beyond the scope of the present study. 相似文献
109.
Quantitative determinations of helium and other noble gas concentrations in pore waters of marine sediments permit the calculation of helium fluxes out of the sedimentary column. Values of 1.1 and 6.4 × 104 atoms/cm2 sec were found for two locations in the northeast Pacific. These fluxes are one to two orders of magnitude less than those based on theoretical degassing models of the earth or on measurements of excess helium in the deep ocean water. 相似文献
110.