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151.
Owing to increased winter balances especially since AD 1988/89, almost all valley outlet glaciers of Jostedalsbreen in western Norway are experiencing the largest advance since that of the early 18th century, the regional "Little Ice Age" maximum. Brigsdalsbreen advanced 441 m between 1987 and 1997. By the end of this period, the glacier had reached the outlet of the proglacial lake Brigsdalsvatnet, ploughing into unfrozen, fine-grained, water-soaked glaciolimnic sediments from the lake bottom and forming frontal moraines. These moraines are characterised by a lack of internal structures and preferred fabric. Owing to the strong advance, the moraine morphology is constantly changing, leaving only temporary moraine ridges.
Observations made along the glacier front suggest that the formation of these moraines can best be described as "bulldozed moraines", since the term push moraine, commonly associated with advancing glaciers, should be restricted to permafront environments. Different processes involved in moraine formation at frontal and lateral glacier margins result from variations in proglacial sediment properties, microrelief and glacier dynamics. Among these processes, large boulders left in the proglacial areas are pushed forward, forming pressure ridges on the distal side. Some of the largest boulders ( c . 80–120 m3 ) are overturned or rotated by the glacier. 相似文献
Observations made along the glacier front suggest that the formation of these moraines can best be described as "bulldozed moraines", since the term push moraine, commonly associated with advancing glaciers, should be restricted to permafront environments. Different processes involved in moraine formation at frontal and lateral glacier margins result from variations in proglacial sediment properties, microrelief and glacier dynamics. Among these processes, large boulders left in the proglacial areas are pushed forward, forming pressure ridges on the distal side. Some of the largest boulders ( c . 80–120 m
152.
Cloud-to-ground (CG) lightning observations for the warm seasons (May-September) of 1989 and 1990 were analyzed for the Great Lakes region in order to assess the diurnal variations in the lightning characteristics. Several parameters, including flash rate, the spatial extent of lightning activity, first stroke peak current, and the percentage of positive flashes, varied markedly over the course of the day. In contrast, other parameters, such as the frequency of lightning periods and the multiplicity of both negative and positive CG flashes, displayed little diurnal variation. A large degree of intraseasonal (i.e., month-to-month) variation was observed in the diurnal patterns for several of the lightning parameters. 相似文献
153.
P. Herzsprung K. Friese G. Packroff M. Schimmele K. Wendt-Potthoff M. Winkler 《洁净——土壤、空气、水》1998,26(5):253-262
The investigated coal mining lakes (ML 111, ML 117, and ML 107) in the Lusatian lignite mining district are extremely acidic. The concentrations of iron in these geogenic acidified lakes are orders of magnitude higher than in acidic bog lakes and softwater lakes acidified by atmospheric deposition. For the most part ferric iron was the predominant species by a Fe(III) to Fe(II) ratio of more than 10. Density stratification of the water column leads to vertical concentration gradients of ferrous iron. Extremely high concentrations of ferrous iron were found in the anoxic layers above the sediment of ML 111 and ML 107. High concentrations of Fe(II) were correlated with high concentrations of carbon dioxide. A microbial potential to reduce ferric iron was found in the sediments. In ML 111 and ML 117 the concentrations of Fe(II) in the epilimnion were markedly higher than in the oxic hypolimnetic layers. It can be suggested that the occurence of ferrous iron in the epilimnion is of photochemical origin, as described for softwater lakes. Minimum concentrations of dissolved organic carbon in the epilimnion could be correlated to the increase of ferrous iron concentrations. Especially in springtime and summer the concentrations of Fe(II) in the epilimnion were higher than in the oxic hypolimnetic layer below. 相似文献
154.
Rebecca Winkler Robert Luther Michael H. Poelchau Kai Wünnemann Thomas Kenkmann 《Meteoritics & planetary science》2018,53(8):1733-1755
Two impact cratering experiments on nonporous rock targets were carried out to determine the influence of target composition on the structural mechanisms of subsurface deformation. Projectiles of 2.5 mm diameter were accelerated to ~5 km s−1 and impacted onto blocks of marble or quartzite. Subsurface deformation was mapped and analyzed on the microscale using thin sections of the bisected craters. Additionally, both experiments were modeled and the calculated strain zones underneath the craters were compared to experimental deformation features. Microanalysis shows that the formation of radial, tensile, and intragranular cracks is a common response of both nonporous materials to impact cratering. In the quartzite target, the subsurface damage is additionally characterized by highly localized deformation along shear bands with intense grain comminution, surrounded by damage zones. In contrast, the marble target shows closely spaced calcite twinning and cleavage activation. Crater diameter and depth as well as the damage lens underneath the crater are unexpectedly smaller in the marble target compared to the quartzite target, which is in contradiction to the marble's much weaker compressive and tensile strengths. However, numerical models result in craters that are similar in size as well as in strain accumulation at the end of transient crater formation, indicating that current models should still be viewed cautiously when compared to experimental details. 相似文献
155.
156.
Roberto E. San Juan-Farfán Lkhamsuren Bayarjargal Björn Winkler Eiken Haussühl Miguel Avalos-Borja Keith Refson Victor Milman 《Physics and Chemistry of Minerals》2011,38(9):693-700
We have measured the pressure-induced change in the lattice dynamics of diaspore, α-AlO(OH), by in situ Raman spectroscopy
up to 25 GPa. The spectra are evaluated by density functional perturbation theory-based atomistic model calculations. The
assignment of calculated to experimentally observed Raman bands is based on the calculation of Raman intensities. We discuss
the accuracy of the approach employed for these calculations and explain the relative magnitudes of mode Grüneisen parameters. 相似文献
157.
158.
Julie A. Winkler 《自然地理学》2013,34(3):210-224
This study was prompted by the apparent confusion in the meteorological and climatological literature on the time of day very heavy precipitation is most likely to occur. Harmonic analysis and cluster analysis were used to investigate the large-scale spatial variations in the diurnal cycle of very heavy precipitation in the United States east of the Rocky Mountains. Significant spatial variations in the diurnal cycle of very heavy precipitation were found to exist, and seven largely contiguous regions with unique diurnal characteristics of very heavy precipitation were identified. 相似文献
159.
Moraine sequences in front of seven relatively low‐altitude glaciers in the Breheimen region of central southern Norway are described and dated using a ‘multi‐proxy’ approach to moraine stratigraphy. Lichenometric dating, based on the Rhizocarpon subgenus, is used to construct a composite moraine chronology, which indicates eight phases of synchronous moraine formation: AD 1793–1799, 1807–1813, 1845–1852, 1859–1862, 1879–1885, 1897–1898, 1906–1908 and 1931–1933. Although the existence of a few cases of older moraines, possibly dating from earlier in the eighteenth or late in the seventeenth centuries cannot be ruled out by lichenometry, Schmidt hammer R‐values from boulders on outermost moraine ridges suggest an absence of Holocene moraines older than the Little Ice Age. Twenty‐three radiocarbon dates from buried soils and peat associated with outermost moraines at three glaciers—Tverreggibreen, Storegrovbreen and Greinbreen—also indicate that the ‘Little Ice Age’ glacier maximum was the Neoglacial maximum at most if not all glaciers. Several maximum age estimates for the Little Ice Age glacier maximum range between the fifteenth and seventeenth centuries, with the youngest from a buried soil being AD 1693. A pre‐Little Ice Age maximum cannot be ruled out at Greinbreen, however, where the age of buried peat suggests the outermost moraine dates from AD 981–1399 (at variance with the lichenometric evidence). Glaciofluvial stratigraphy at Tverreggibreen provides evidence for minor glacier advances about AD 655–963 and AD 1277–1396, respectively. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
160.
RW Jabado SM Al Ghais W Hamza DP Robinson AC Henderson 《African Journal of Marine Science》2016,38(2):217-232
Landing site and market surveys of sharks landed along the Arabian Gulf coast of the United Arab Emirates were undertaken between October 2010 and September 2012 to obtain biological data from this artisanal fishery. Data were collected on the size and sex of 12 482 individuals representing 30 species. Maximum sizes of Carcharhinus sorrah, C. amblyrhynchoides and Hemipristis elongata were extended by at least 300?mm total length (TL) compared with published global maxima. The size at 50% maturity was determined for males of five species and this indicated that the males of smaller shark species (<1 000 mm maximum TL) in the fishery were largely mature. For many species, including Loxodon macrorhinus and Mustelus mosis, overall sex ratios were male-biased, indicating that sexual segregation is likely in those species. Furthermore, sex ratios for several species, such as Rhizoprionodon acutus, showed differences across seasons. Overall, the landings contained a high proportion of juveniles, causing concerns about the sustainability of this fishery. Biological parameters of a number of species differed from those recorded earlier for the region, demonstrating a need for additional local data collection to support the development of management measures. 相似文献