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101.
Chris Koen Ruby Van Rooyen Francois Van Wyk Freddy Marang 《Monthly notices of the Royal Astronomical Society》1999,309(4):1051-1062
HD 23194, a member of the Pleiades, was found to pulsate with a period of about 30 min. The literature on the star is reviewed, and it is concluded that it may be a marginal Am star in a binary system. HD 95321 is an evolved Am ( ρ Puppis) star with a 5.1-h periodicity. Mode identification of its pulsation, based on multicolour photometry, suggests that the oscillation is probably non-radial with ℓ=2. We also report on the discovery of six other new δ Scuti stars, some of which may be pulsating in gravity modes. 相似文献
102.
Particulate organic carbon (POC) is vertically transported to the oceanic interior by aggregates and their ballasts, mainly CaCO3 and biogenic opal, with a smaller role for lithogenic aerosols through the mesopelagic zone. Diel migrating zooplankton communities effect vertical transport and remineralization of POC in the upper layers of the ocean. Below 1.5 km, the presence of zooplankton is reduced and thus the aggregates travel mainly by gravitational transport. We normalized the fluxes of POC, CaCO3, and biogenic opal from data published on samples collected at 134 globally distributed, bottom-tethered, time-series sediment trap (TS-trap) stations to annual mole fluxes at the mesopelagic/bathypelagic boundary (m/b) at 2 km and defined them as Fm/bCorg, Fm/bCinorg, and Fm/bSibio. Using this global data set, we investigated (1) the geographic contrasts of POC export at m/b and (2) the supply rate of ∑CO2 to the world mesopelagic water column. Fm/bCorg varies from 25 (Pacific Warm Pool) to 605 (divergent Arabian Sea) mmolC m−2 yr−1; Fm/bCinorg varies from >8 (high latitude Polar Oceans) or 15 (Pacific Warm Pool) to 459 (divergent Arabian Sea) mmolC m−2 yr−1; and Fm/bSibio, the most spatially/temporally variable flux, ranges from 6 (North Atlantic Drift) to 1118 (Pacific Subarctic Gyre) mmolSi m−2 yr−1. The oceanic region exhibiting the highest POC flux over a significantly large region is the area of the North Pacific Boreal Gyres where the average Fm/bCorg = 213, Fm/bCinorg = 126, and Fm/bSibio = 578 mmol m−2 yr−1. Fm/bCorg and Fm/bCinorg are particularly high in large upwelling margins, including the divergent Arabian Sea and off Cape Verde. One of the data sets showing the lowest flux over a significant region/basin is Fm/bCorg = 39, Fm/bCinorg = 69, and Fm/bSibio = 22 mmol m−2 yr−1 in the North Pacific subtropical/tropical gyres; Pan-Atlantic average fluxes are similar except Fm/bSibio fluxes are even lower. Where Corg/Cinorg and Sibio/Cinorg are <1 defines the “Carbonate Ocean”, and where these ratios are ?1 defines the “Silica Ocean”. The Carbonate Ocean occupies about 80% of the present world pelagic ocean between the two major oceanographic fronts, the North Pacific Polar Front and the Antarctic Polar Front, and the Silica Ocean is found on the polar sides of these fronts. The total global annual fluxes of Fm/bCorg, Fm/bCinorg, and Fm/bSibio at m/b calculated by parameterizations of the export flux data from 134 stations are surprisingly similar; 36.2, 33.8, and 34.6 teramol yr−1 (120, 112, and 114 mmol m−2 yr−1), respectively, resulting in a near uniform binary ratio between the above three elements of about one. The global ternary % ratios estimated from 152 TS-trap samples of the three elements are 35:32:33. From our global Fm/bCorg and a published model estimate of the global export production, we estimate the regeneration rate of CO2 through the mesopelagic zone by the biological pump is 441 teramolC yr−1. Based on our global Fm/bCinorg and recently estimated global primary production of PIC, 36-86 teramolC yr−1 of PIC is assumed to be dissolved within the upper 2 km of the water column. 相似文献
103.
An experimental study examined the 96-h net influx from seawater of the anthropogenic radionuclides (241)Am, (60)Co and (134)Cs through the egg-case of the spotted dogfish Scyliorhinus canicula. Net influx directly through the wall of the egg-case was greatest for (134)Cs, then (241)Am and lastly (60)Co. Within the egg-case wall itself the measured concentration factors (CFs) and their gradients in the external, median and internal layers showed that for both (241)Am and (60)Co they were >10(3) in the external layer and declined by an order of magnitude in the interior layer. In contrast (134)Cs had a CF of only about three in the external layer which declined by a factor of 2 towards the two more internal layers of the egg-case. The egg-case apertures, that open within the prehatching stage of embryological development, significantly (P<0.05) increased the net influx of (241)Am and (60)Co to the interior of the egg-case, although their water concentrations were still lower than those in the labelled seawater bath. In contrast, the aperture did not increase the net influx of (134)Cs whose water concentrations equilibrated with those in seawater. Together these results indicate that the egg-case wall is very permeable to (134)Cs, representing little barrier to its movement, and hence consistent with the lack of importance of the aperture in determining its internal water concentrations in the egg-case. In contrast, (241)Am and (60)Co show much higher rates of accumulation by the egg-case, consistent with the measured reduced permeability of its wall, and therefore giving greater prominence to its aperture in the net transfer of these two radionuclides to the egg case's interior. The presence of the embryo within its egg-case did not significantly (P>0.05) affect the rates of influx of radioisotopes, with the exception of an interactive effect for (60)Co with the egg-case aperture (P<0.05). The CF of only (241)Am in the embryo itself relative to the external seawater concentration was significantly (P<0.05) enhanced by the presence of the aperture. 相似文献
104.
Frédéric Schmidt Bernard Schmitt Francois Forget Patrick Martin Jean-Pierre Bibring the OMEGA Team 《Planetary and Space Science》2010,58(10):1129-1138
The polar condensation/sublimation of CO2, that involve about one fourth of the atmosphere mass, is the major Martian climatic cycle. Early observations in visible and thermal infrared have shown that the sublimation of the Seasonal South Polar Cap (SSPC) is not symmetric around the geographic South Pole.Here we use observations by OMEGA/Mars Express in the near-infrared to detect unambiguously the presence of CO2 at the surface, and to estimate albedo. Second, we estimate the sublimation of CO2 released in the atmosphere and show that there is a two-step process. From Ls=180° to 220°, the sublimation is nearly symmetric with a slight advantage for the cryptic region. After Ls=220° the anti-cryptic region sublimation is stronger. Those two phases are not balanced such that there is 22% ± 9 more mass the anti-cryptic region, arguing for more snow precipitation. We compare those results with the MOLA height measurements. Finally we discuss implications for the Martian atmosphere about general circulation and gas tracers, e.g. Ar. 相似文献
105.
当数值预报模式的分辨率得到提高时,模式中扩散系数的数值大小必然随之改变。通常情况下,一方面,扩散系数的数值应足够大(即有下限值),以便过滤掉模式中不想要的小尺度噪音;另一方面,扩散系数的数值应尽量小(即有上限值),以免出现计算不稳定。本文提出一种确定高分辨率模式中扩散系数数值大小的客观方法,即"双试验"(twin experiment)同化方法(初始低分辨率模式的预报结果作为"观测资料",新的高分辨率模式作为同化模式),从而通过伴随变分同化方法来确定控制变量(即扩散系数)的数值大小。本文采用一维浅水模式测试和描述上述试验方案。通过低分辨率模式预报结果和高分辨率模式预报结果的比较(高、低分辨率模式预报结果的比较在低分辨率模式格点上进行),采用最小二乘法可客观求得适用于高分辨率模式的扩散系数的"最优"值。数值试验结果表明,采用这种方法得到的高分辨率模式的扩散系数,不仅能过滤掉模式中不想要的小尺度噪音,而且能够避免出现计算不稳定。研究还指出,当扩散系数的大小略微超过其上限值时(这种情况在极小化迭代中有可能会出现),计算不稳定的出现将使目标函数的数值迅速增加,并导致极小化程序收敛的失败;时间步长的减小(约20%)可以显著地改进目标函数的条件数,从而可避免极小化程序收敛的失败。 相似文献
106.
H. Melling R. Francois P. G. Myers W. Perrie A. Rochon R. L. Taylor 《Climatic change》2012,115(1):89-113
Canada??s IPY program funded seven marine projects spanning the North American Arctic. Work embraced oceanography, air-sea interactions, storm response, paleo-climate and trace-element chemistry. Notable findings are emerging. Conditions in the Beaufort were unusual in 2007, with very high air pressure bringing strong winds, rapid ice drift, thin winter ice, enhanced shelf-break upwelling and a maximum in freshwater retention in the Beaufort Gyre. A mapping of trace chemicals suggests that Arctic mid-depth circulation may also have reversed. Study of Canadian Arctic through-flow revealed a net annual seawater export of 44,000 cubic kilometres from the Arctic to Baffin Bay. Observations of sea ice, sustained through the IPY, affirmed that ice cover is the key attribute of Arctic seas, with wind as a potent agent in its variation. Surveys have shown that the anthropogenic decline in seawater alkalinity is aggravated in the Arctic by low temperature and low salinity resulting from ice melt. Careful experiments have revealed that Arctic phytoplankton growth is constrained by scarcity of dissolved iron where light levels are low. A manganese fingerprint in sediments has tracked changing sea level during the Ice Age. Sediment-core analysis has revealed the Arctic Oscillation as a dominant cause of long-period climate variations during the Holocene. One project has demonstrated how multi-tasked vessels can maintain a watch on Canada??s Arctic within a reliable affordable logistic framework, while a wave forecast model developed by another for the Beaufort is suitable for operational use. 相似文献
107.
Differentiation and crystallization conditions of basalts from the Kerguelen large igneous province: an experimental study 总被引:2,自引:2,他引:0
Marcus Freise Francois Holtz Marcus Nowak James S. Scoates Holger Strauss 《Contributions to Mineralogy and Petrology》2009,158(4):505-527
Phase relations of basalts from the Kerguelen large igneous province have been investigated experimentally to understand the
effect of temperature, fO2, and fugacity of volatiles (e.g., H2O and CO2) on the differentiation path of LIP basalts. The starting rock samples were a tholeiitic basalt from the Northern Kerguelen
Plateau (ODP Leg 183 Site 1140) and mildly alkalic basalt evolved from the Kerguelen Archipelago (Mt. Crozier on the Courbet
Peninsula), representing different differentiation stages of basalts related to the Kerguelen mantle plume. The influence
of temperature, water and oxygen fugacity on phase stability and composition was investigated at 500 MPa and all experiments
were fluid-saturated. Crystallization experiments were performed at temperatures between 900 and 1,160°C under oxidizing (log
fO2 ~ ΔQFM + 4) and reducing conditions (log fO2 ~ QFM) in an internally heated gas-pressure vessel equipped with a rapid quench device and a Pt-Membrane for monitoring the
fH2. In all experiments, a significant influence of the fO2 on the composition and stability of the Mg/Fe-bearing mineral phases could be observed. Under reducing conditions, the residual
melts follow a tholeiitic differentiation trend. In contrast, melts have high Mg# [Mg2+/(Mg2+ + Fe2+)] and follow a calk-alkalic differentiation trend at oxidizing conditions. The comparison of the natural phenocryst assemblages
with the experimental products allows us to constrain the differentiation and pre-eruptive conditions of these magmas. The
pre-eruptive temperature of the alkalic basalt was about 950–1,050°C. The water content of the melt was below 2.5 wt% H2O and strongly oxidizing conditions (log fO2 ~ ΔQFM + 2) were prevailing in the magma chamber prior to eruption. The temperature of the tholeiitic melt was above 1,060°C,
with a water content below 2 wt% H2O and a log fO2 ~ ΔQFM + 1. Early fractionation of clinopyroxene is a crucial step resulting in the generation of silica-poor and alkali-rich
residual melts (e.g., alkali basalt). The enrichment of alkalis in residual melts is enhanced at high fO2 and low aH2O. 相似文献
108.
109.
110.
Katrien Heirman Marc De Batist Francois Charlet Jasper Moernaut Emmanuel Chapron Robert Brümmer Mario Pino Roberto Urrutia 《第四纪科学杂志》2011,26(7):665-674
Lago Puyehue is a glacigenic lake in the Chilean Lake District (40°S) with a complex deglaciation history. A detailed seismic–stratigraphic study of its sedimentary infill indicates a much earlier retreat of the glacier from the Lago Puyehue basin than the neighbouring glacier from the Lago Rupanco basin. Because of their close proximity, Rupanco meltwater streams played an important part in the depositional processes of Lago Puyehue. A timing discrepancy between the in‐lake ages of a sediment core and the outer‐lake ages of moraine deposits (re)opens the discussion on the timing of deglaciation in the Southern Hemisphere. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献