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111.
112.
Environmental changes in the northern Altai during the last millennium documented in Lake Teletskoye pollen record 总被引:1,自引:0,他引:1
Andrei A. Andreev Roberto Pierau Ivan A. Kalugin Andrei V. Daryin Lyubov G. Smolyaninova Bernhard Diekmann 《Quaternary Research》2007,67(3):394-399
A high-resolution pollen record from Lake Teletskoye documents the climate-related vegetation history of the northern Altai Mountain region during the last millennium. Siberian pine taiga with Scots pine, fir, spruce, and birch dominated the vegetation between ca. AD 1050 and 1100. The climate was similar to modern. In the beginning of the 12th century, birch and shrub alder increased. Lowered pollen concentrations and simultaneous peaks in herbs (especially Artemisia and Poaceae), ferns, and charcoal fragments point to colder and more arid climate conditions than before, with frequent fire events. Around AD 1200, regional climate became warmer and more humid than present, as revealed by an increase of Siberian pine and decreases of dry herb taxa and charcoal contents. Climatic conditions were rather stable until ca. AD 1410. An increase of Artemisia pollen may reflect slightly drier climate conditions between AD 1410 and 1560. Increases in Alnus, Betula, Artemisia, and Chenopodiaceae pollen and in charcoal particle contents may reflect further deterioration of climate conditions between AD 1560 and 1810, consistent with the Little Ice Age. After AD 1850 the vegetation gradually approached the modern one, in conjunction with ongoing climate warming. 相似文献
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Byoung‐Young Choi Seong‐Taek Yun Bernhard Mayer Gi‐Tak Chae Kyoung‐Ho Kim Kangjoo Kim Yong‐Kwon Koh 《水文研究》2010,24(3):317-330
We evaluated sources and pathways of groundwater recharge for a heterogeneous alluvial aquifer beneath an agricultural field, based on multi‐level monitoring of hydrochemistry and environmental isotopes of a riverside groundwater system at Buyeo, Korea. Two distinct groundwater zones were identified with depth: (1) a shallow oxic groundwater zone, characterized by elevated concentrations of NO3? and (2) a deeper (>10–14 m from the ground surface) sub‐oxic groundwater zone with high concentrations of dissolved Fe, silica, and HCO3?, but little nitrate. The change of redox zones occurred at a depth where the aquifer sediments change from an upper sandy stratum to a silty stratum with mud caps. The δ18O and δ2H values of groundwater were also different between the two zones. Hydrochemical and δ18O? δ2H data of oxic groundwater are similar to those of soil water. This illustrates that recharge of oxic groundwater mainly occurs through direct infiltration of rain and irrigation water in the sandy soil area where vegetable cropping with abundant fertilizer use is predominant. Oxic groundwater is therefore severely contaminated by agrochemical pollutants such as nitrate. In contrast, deeper sub‐oxic groundwater contains only small amounts of dissolved oxygen (DO) and NO3?. The 3H contents and elevated silica concentrations in sub‐oxic groundwater indicate a somewhat longer mean residence time of groundwater within this part of the aquifer. Sub‐oxic groundwater was also characterized by higher δ18O and δ2H values and lower d‐excess values, indicating significant evaporation during recharge. We suggest that recharge of sub‐oxic groundwater occurs in the areas of paddy rice fields where standing irrigation and rain water are affected by strong evaporation, and that reducing conditions develop during subsequent sub‐surface infiltration. This study illustrates the existence of two groundwater bodies with different recharge processes within an alluvial aquifer. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Bernhard Chapligin Melanie J. Leng Anne Alexandre Akira Ijiri Aldo Shemesh Ulrike Herzschuh Hanno Meyer Yusuke Okazaki Zachary D. Sharp Corinne Sonzogni Florence Sylvestre Ruth Yam 《Geochimica et cosmochimica acta》2011,75(22):7242-7256
Several techniques have been introduced in the last decades for the dehydration and release of O2 from biogenic silica (opal-A) for oxygen-isotope analysis. However, only one silica standard is universally available: a quartz standard (NBS28) distributed by the IAEA, Vienna. Hence, there is a need for biogenic silica working standards. This paper compares the existing methods of oxygen-isotope analyses of opal-A and aims to characterize additional possible working standards to calibrate the δ18O values of biogenic silica. For this purpose, an inter-laboratory comparison was organized. Six potential working standard materials were analysed repeatedly against NBS28 by eight participating laboratories using their specific analytical methods. The materials cover a wide range of δ18O values (+23 to +43‰) and include diatoms (marine, lacustrine), phytoliths and synthetically-produced hydrous silica. To characterize the proposed standards, chemical analyses and imaging by scanning electron microscopy (SEM) were also performed. Despite procedural differences at each laboratory, all methods are in reasonable agreement with a standard deviation (SD) for δ18O values between 0.3‰ and 0.9‰ (1σ). Based on the results, we propose four additional biogenic silica working standards (PS1772-8: 42.8‰; BFC: 29.0‰; MSG60: 37.0‰; G95-25-CL leaves: 36.6‰) for δ18O analyses, available on request through the relevant laboratories. 相似文献
119.
Christian A. Miller Bernhard Peucker-Ehrenbrink Franco Marcantonio 《Geochimica et cosmochimica acta》2011,75(22):7146-7179
We re-evaluate the cycling of molybdenum (Mo) and rhenium (Re) in the near-surface environment. World river average Mo and Re concentrations, initially based on a handful of rivers, are calculated using 38 rivers representing five continents, and 11 of 19 large-scale drainage regions. Our new river concentration estimates are 8.0 nmol kg−1 (Mo), and 16.5 pmol kg−1 (Re, natural + anthropogenic). The linear relationship of dissolved Re and in global rivers (R2 = 0.76) indicates labile continental Re is predominantly hosted within sulfide minerals and reduced sediments; it also provides a means of correcting for the anthropogenic contribution of Re to world rivers using independent estimates of anthropogenic sulfate. Approximately 30% of Re in global rivers is anthropogenic, yielding a pre-anthropogenic world river average of 11.2 pmol Re kg−1. The potential for anthropogenic contribution is also seen in the non-negligible Re concentrations in precipitation (0.03-5.9 pmol kg−1), and the nmol kg−1 level Re concentrations of mine waters. The linear Mo- relationship (R2 = 0.69) indicates that the predominant source of Mo to rivers is the weathering of pyrite. An anthropogenic Mo correction was not done as anthropogenically-influenced samples do not display the unambiguous metal enrichment observed for Re. Metal concentrations in high temperature hydrothermal fluids from the Manus Basin indicate that calculated end-member fluids (i.e. Mg-free) yield negative Mo and Re concentrations, showing that Mo and Re can be removed more quickly than Mg during recharge. High temperature hydrothermal fluids are unimportant sinks relative to their river sources 0.4% (Mo), and 0.1% (pre-anthropogenic Re). We calculate new seawater response times of 4.4 × 105 yr (τMo) and 1.3 × 105 yr (τRe, pre-anthropogenic). 相似文献
120.
Hannah Pomella Urs Klötzli Robert Scholger Michael Stipp Bernhard Fügenschuh 《International Journal of Earth Sciences》2011,100(8):1827-1850
This study concentrates on small intrusions along two important faults of the Giudicarie fault system, the Northern Giudicarie
and the Meran-Mauls fault, summarised under the term tonalitic lamellae. Magnetic fabric analyses in combination with structural
field data indicate dextral strike slip deformation along the NE–SW striking northern part of the Giudicarie fault system,
the Meran-Mauls fault, overprinted by younger thrusting. The regional stressfield was oriented approximately NNW–SSE during
Tertiary times. The distinctive change in deformation along the Meran-Mauls fault from dextral strike slip to top-SE thrusting
may be caused by a rotation or bending of the fault after the intrusion of the tonalites and the formation of their horizontal
magnetic foliation. Based on the assumption of a preliminary straight Periadriatic lineament bent by the NNW-wards advancement
of the Southalpine indenter, the tonalitic lamellae may be interpreted as lenses sheared off from the Adamello batholith during
indentation. New U/Pb data on zircon show that some of the lamellae are of Oligocene (Rupelian), others of Late Eocene (Priabonian)
age. An amphibole-gabbro lens occurring on the Meran-Mauls fault provides a Middle Eocene (Bartonian) age. Among the major
Periadriatic plutons, only the southern units of the Adamello batholith also intruded in the Eocene that suggests a strong
correlation between the tonalitic lamellae and the Adamello batholith. The analyses of the remanent magnetisation and the
Curie point determinations argue for magnetite as the main carrier of a viscous magnetisation blocked at relatively low temperatures.
This indicates slow cooling of the investigated intrusions along the Giudicarie fault system down to approximately 300°C,
which is in contrast to the fast cooling determined for the Adamello intrusion units currently at the surface. The new zircon
fission track data also show later cooling of the tonalites along the Giudicarie fault system when compared with the Adamello
batholith in the south and the Mauls lamellae in the north, indicating that this area contains magmatic bodies exhumed from
a deeper structural level than in the Adamello and the Mauls region. This may be due to important top-SE thrusting and transpressive
faulting in the footwall of the Northern Giudicarie fault and the Meran-Mauls fault. 相似文献