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71.
72.
Matthew R. Patrick Tim Orr David Wilson David Dow Richard Freeman 《Bulletin of Volcanology》2011,73(6):639-653
In late 2007, a perched lava channel, built up to 45 m above the preexisting surface, developed during the ongoing eruption
near Pu‘u ‘Ō‘ō cone on Kīlauea Volcano’s east rift zone. The lava channel was segmented into four pools extending over a total
of 1.4 km. From late October to mid-December, a cyclic behavior, consisting of steady lava level rise terminated by vigorous
spattering and an abrupt drop in lava level, was commonly observed in pool 1. We use geologic observations, video, time-lapse
camera images, and seismicity to characterize and understand this cyclic behavior. Spattering episodes occurred at intervals
of 40–100 min during peak activity and involved small (5–10-m-high) fountains limited to the margins of the pool. Most spattering
episodes had fountains which migrated downchannel. Each spattering episode was associated with a rapid lava level drop of
about 1 m, which was concurrent with a conspicuous cigar-shaped tremor burst with peak frequencies of 4–5 Hz. We interpret
this cyclic behavior to be gas pistoning, and this is the first documented instance of gas pistoning in lava well away from
the deeper conduit. Our observations and data indicate that the gas pistoning was driven by gas accumulation beneath the visco-elastic
component of the surface crust, contrary to other studies which attribute similar behavior to the periodic rise of gas slugs.
The gas piston events typically had a gas mass of about 2,500 kg (similar to the explosions at Stromboli), with gas accumulation
and release rates of about 1.1 and 5.7 kg s−1, respectively. The time-averaged gas output rate of the gas pistoning events accounted for about 1–2% of the total gas output
rate of the east rift zone eruption. 相似文献
73.
Production of n-alkyl lipids in living plants and implications for the geologic past 总被引:2,自引:0,他引:2
Aaron F. Diefendorf Katherine H. Freeman Heather V. Graham 《Geochimica et cosmochimica acta》2011,75(23):7472-7485
Leaf waxes (i.e., n-alkyl lipids or n-alkanes) are land-plant biomarkers widely used to reconstruct changes in climate and the carbon isotopic composition of the atmosphere. There is little information available, however, on how the production of leaf waxes by different kinds of plants might influence the abundance and isotopic composition of n-alkanes in sedimentary archives. This lack of information increases uncertainty in interpreting n-alkyl lipid abundance and δ13C signals in ancient settings. We provide here n-alkyl abundance distributions and carbon isotope fractionation data for deciduous and evergreen angiosperm and gymnosperm leaves from 46 tree species, representing 24 families. n-Alkane abundances are significantly higher in angiosperms than gymnosperms; many of the gymnosperm species investigated did not produce any n-alkanes. On average, deciduous angiosperms produce 200 times more n-alkanes than deciduous gymnosperms. Although differences between angiosperms and gymnosperms dominate the variance in n-alkane abundance, leaf life-span is also important, with higher n-alkane abundances in longer-lived leaves. n-Alkanol abundances covary with n-alkanes, but n-alkanoic acids have similar abundances across all plant groups. Isotopic fractionation between leaf tissue and individual alkanes (εlipid) varies by as much as 10‰ among different chain lengths. Overall, εlipid values are slightly lower (−4.5‰) for angiosperm than for gymnosperm (−2.5‰) n-alkanes. Angiosperms commonly express slightly higher Δleaf (photosynthetic discrimination) relative to gymnosperms under similar growth conditions. As a result, angiosperm n-alkanes are expected to be generally 3-5‰ more depleted in 13C relative to gymnosperm alkanes for the same locality. Differences in n-alkane production indicate the biomarker record will largely (but not exclusively) reflect angiosperms if both groups were present, and also that evergreen plants will likely be overrepresented compared with deciduous ones. We apply our modern lipid abundance patterns and εlipid results to constrain the magnitude of the carbon isotope excursion (CIE) at the onset of the Paleocene-Eocene Thermal Maximum (55.8 Ma). When Bighorn Basin (WY) sediment n-alkanes are interpreted in context of floral changes and modern n-alkane production estimates for angiosperms and gymnosperms, the CIE is greater in magnitude (−5.6‰) by ∼1‰ compared to previous estimates that do not take into account n-alkane production. 相似文献
74.
Christopher K. Junium Brendan J. KeelyKatherine H. Freeman Michael A. Arthur 《Organic Geochemistry》2011,42(7):856-859
Liquid chromatography, multi-stage mass spectrometry (LC-MSn) of acetone extracts confirms the presence of mesochlorophyllone in the mid-Cretaceous black shales of Demerara Rise. This finding represents molecular confirmation of the oldest primary chlorins in the geologic record and is evidence for a chlorophyll a source for bicycloalkanoporphyrins in the Demerara Rise black shales. 相似文献
75.
吉林南部辉南-靖宇地区岩石圈地幔氧化-还原状态及研究意义 总被引:3,自引:2,他引:1
吉林省南部辉南-靖宇地区第四纪碱性玄武岩中的地幔包体主要为尖晶石相二辉橄榄岩和方辉橄榄岩。二辉橄榄岩和方辉橄榄岩的平衡温度分别为770~1000℃和850~1025℃,对应的氧逸度 (fO2)值分别为FMQ -0.70至+0.34 (均值为FMQ -0.06) 和FMQ -0.46至+0.05 (均值为FMQ -0.15),它们与深海橄榄岩(abyssal peridotites)以及软流圈地幔的fO2相似。橄榄岩的fO2值,连同其全岩化学成分(如Mg#、Al2O3、CaO、Ni、Co和Cr)和矿物化学成分(如橄榄石的Fo、尖晶石的Cr#和Mg#,以及辉石的Mg#)特征,表明辉南-靖宇地区龙岗火山群下面的岩石圈地幔很可能是在晚中生代以来,伴随着华北克拉通和扬子板块的碰撞以及来自东侧太平洋板块和北侧蒙古-额霍次克(Mongolo-Okhotsk)板块分别向西和向南的俯冲叠加,原来的古老岩石圈失衡、塌陷(拆沉?),取而代之的深部软流圈底辟、上涌,又经历了低度部分熔融的产物。 相似文献
76.
Meryl Waugh M. J. Drinkwater R. L. Webster L. Staveley-Smith V. A. Kilborn D. G. Barnes R. Bhathal W. J. G. de Blok P. J. Boyce M. J. Disney R. D. Ekers K. C. Freeman B. K. Gibson P. A. Henning H. Jerjen P. M. Knezek B. Koribalski M. Marquarding R. F. Minchin R. M. Price M. E. Putman † S. D. Ryder E. M. Sadler F. Stootman M. A. Zwaan 《Monthly notices of the Royal Astronomical Society》2002,337(2):641-656
77.
V.S. Tsypin D.KH. Morozov J.J.E. Herrera J.J. Martinell M. Tendler I.F. Potapenko A.S. de Assis C.A. de Azevedo 《Astrophysics and Space Science》1997,256(1-2):431-436
The transport processes in edge (collisional) plasmas of tokamaks with smooth profiles of macroscopic plasma parameters and induced poloidal and toroidal plasma flows, are considered. The toroidal and poloidal velocities of particles, the radial electric field and the ion heat flux are derived. It is shown that forces, induced by radio frequency waves, plasma turbulence or neutral beam injection, can be used to control the poloidal and toroidal plasma velocities, as well as ion heat conductivity, in a wide range of these values. 相似文献
78.
J.G. Farmer M.C. Graham C. Yafa J.M. Cloy A.J. Freeman A.B. MacKenzie 《Global and Planetary Change》2006,53(4):240
The well characterised temporal trend in the 206Pb/207Pb atom ratio of atmospheric lead deposition in Scotland during the 20th century was used to investigate the surface integrity of several cores collected by different methods from Flanders Moss ombrotrophic peat bog, central Scotland, during 1996–2001. Based on 206Pb/207Pb profile comparisons, in conjunction with identified 210Pb radionuclide inventory deficits for two of the cores, it was deduced that 25 ± 7 yrs worth of material was missing from the more seriously affected core. After allowing for an appropriate vertical offset based on 206Pb/207Pb profile matching, the subsequent matching of profiles of titanium, lead, sulfur, arsenic, iron, phosphorus and manganese in three cores for which total concentration data were available was excellent. Without such offset correction, erroneous conclusions could have been drawn concerning the recent historical record of anthropogenic lead and arsenic deposition, the position of the redox boundary, which controls geochemical cycling and enrichment of iron, and the nutrient recycling status of manganese and phosphorus in the near-surface vegetation. Topographic, vegetative and coring (both device and operator) influences may have been responsible, thus endorsing the use of reliable, multiple core sampling and the use of lead isotope ratio profiles, supplemented by appropriate radionuclide data, in both assessing and ensuring the surface integrity of peat cores. 相似文献
79.
80.