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61.
Catherine S. E. Bale Trevor Ingham Roisin Commane Dwayne E. Heard William J. Bloss 《Journal of Atmospheric Chemistry》2008,60(1):51-70
A field instrument has been developed for the purpose of measuring gas-phase atmospheric iodine species in the marine boundary
layer. Vacuum UV resonance-fluorescence (RF), generated using a microwave discharge lamp, is employed to detect atomic iodine
via the (5p46s)–(5p5) transitions around 178–184 nm. The system can be operated in two modes; either to directly measure ambient iodine atoms,
or to measure the total photolabile iodine loading of ambient air, through broadband visible photolysis of photolabile iodine-containing
species, with subsequent RF detection of the iodine atoms released. In both cases the instrument allows for the in situ measurement
of the species detected, which is advantageous for gathering information concerning their local sources and distribution.
The instrument is calibrated through generation of a known concentration of iodine atoms from the photolysis of I2 using a mercury pen-ray lamp. The instrument was deployed for the first time in August 2007 at Mace Head on the west coast
of Ireland; initial results from this field trial are presented. Ambient iodine atoms were measured at levels up to 22 ± 4.8 ppt
during the day, coinciding with the lowest tides, when Laminaria seaweed beds were exposed. The total photolabile iodine loading was also measured during several night-time and day-time
periods and was found to correlate inversely with tidal height. Inferred I2 concentrations based on these measurements indicate levels of several hundred ppt at the Mace Head site. These measurements
represent the first direct observations of ambient iodine atoms and measurement of total photolabile iodine in the atmosphere. 相似文献
62.
63.
Germination inhibition of the marine macrophyte Phyllospora comosa was utilized as a sub-lethal end-point to assess and compare the effects of four oil dispersants and dispersed diesel fuel and crude oil combinations. Inhibition of germination by the water-soluble fraction of diesel fuel increased following the addition of each of the dispersants; the nominal 48-h EC50 concentration of diesel fuel declined from 6800 to approximately 400 μl l−1 nominal for each dispersed combination. This contrasted with crude oil, where the addition of two dispersants resulted in an enhanced germination rate and an increase in nominal EC50 concentrations from 130 μl l−1 for the undispersed crude to 4000 and 2500 μl l−1. The results indicate that, while germination inhibition of P. comosa may be enhanced by the chemical dispersal of oil, the response varies with type of both oil and oil dispersant. 相似文献
64.
We combined a surface irradiance model with a non-spectral photosynthesisirradiance model to estimate the daily, average rate
of mixed-layer primary production in the Arabian Sea for the 15th day of months at the end of the northeast monsoon, the southwest
monsoon, and the fall and spring inter-monsoons. Our model experiment uses climatologies of cloud cover, mixed-layer thickness,
and satellite ocean-color observations of phytoplankton biomass.
Modelled surface radiation is at an annual maximum in May beneath nearly cloud-free skies just prior to the summer solstice.
The model estimate of surface radiation diminishes through the southwest monsoon over most of the northern Arabian Sea to
an annual minimum in August due to intense cloudiness.
In agreement with previous ship-based measurements, the photosynthesis-irradiance model predicts that the mixed-layer primary
production in the Arabian Sea is extremely seasonal, and peaks annually during the southwest monsoon to the north-west of
the atmospheric Findlater Jet and along the coast of Somalia. Northern Arabian Sea maxima predicted for both the summer and
winter monsoons are separated by periods of low mixed-layer primary production, the fall and spring inter-monsoons. The annual
cycles of modelled mixed-layer primary production differ by region in the Arabian Sea due to varying monsoon influence and
circulation dynamics. 相似文献
65.
We treat the ocean carbon cycle as a coupled physical-biogeochemical process. The interactions between mixed-layer dynamics
and growth of phytoplankton in the layer are discussed, and the formal relationship between phytoplankton accumulation and
new production is examined. A coupled biological-physical model is presented for studying the classical spring bloom in the
N. Atlantic, and possible differences in the mechanisms that drive the seasonal phytoplankton blooms in the N. Atlantic and
the Arabian Sea are discussed. Finally, recommendations are made for observational programs to improve our understanding of
the biologically-mediated carbon cycle in the Arabian Sea. 相似文献
66.
R. Paul Philp Trevor D. Gilbert Jane Friedrich 《Geochimica et cosmochimica acta》1981,45(7):1173-1180
Bicyclanes previously reported only in heavily biodegraded Texas Gulf Coast crudes have been found to be ubiquitous in Australian crude oils of non-marine origin from four different basins. The compounds are present in oils, thought to be derived from the same or similar sources, that have undergone varying degrees of biodegradation. They are also found to be present in oils of different geological age. In addition a series of tricyclic diterpenoid hydrocarbons was common to four oils from the Gippsland Basin. Four of these compounds had the molecular formula C20H34 and mass spectral fragmentation patterns suggested they were mono-unsaturated diterpenoids. The presence of unsaturated diterpenoids in crude oils appears to be a unique observation. It is proposed that the diterpenoids may be the source of the bicyclanes also observed in these oils. 相似文献
67.
Sixteen sets of apatite/liquid partition coefficients (Dap/liq) for the rare earth elements (REE; La, Sm, Dy, Lu) and six values for Sr were experimentally determined in natural systems ranging from basanite to granite. The apatite + melt (glass) assemblages were obtained from starting glasses artificially enriched in REE, Sr and fluorapatite components; these were run under dry and hydrous conditions of 7.5–20 kbar and 950–1120°C in a solid-media, piston-cylinder apparatus. An SEM-equipped electron microprobe was used for subsequent measurement of REE and Sr concentrations in coexisting apatites and quenched glasses. The resulting partition coefficient patterns resemble previously determined apatite phenocryst/groundmass concentration ratios in the following respects: (1) the rare earth patterns are uniformly concave downward (i.e., the middle REE are more compatible in apatite than the light and heavy REE); (2) DREEap/liq is much higher for silicic melts than for basic ones; and (3) strontium (and therefore Eu2+) is less concentrated by apatite than are the trivalent REE. The effects of both temperature and melt composition on DREEap/liq are systematic and pronounced. At 950°C, for example, a change in melt SiO2 content from 50 to 68 wt.% causes the average REE partition coefficient to increase from ~7 to ~30. A 130°C increase in temperature, on the other hand, results in a two-fold decrease in DREEap/liq. Partitioning of Sr is insenstitive to changes in melt composition and temperature, and neither the Sr nor the REE partition coefficients appear to be affected by variations in pressure or H2O content of the melt.The experimentally determined partition coefficients can be used not only in trace element modelling, but also to distinguish apatite phenocrysts from xenocrysts in rocks. Reported apatite megacryst/host basalt REE concentration ratios [12], for example, are considerably higher than the equilibrium partition coefficients, which suggest that in this particular case the apatite is actually xenocrystic.A reversal experiment incorporated in our study yielded diffusion profiles of REE in apatite, from which we extracted a REEαCa interdiffusion coefficient of 2–4×10?14 cm2/s at 1120°C. Extrapolated downward to crustal temperatures, this low value suggests that complete REE equilibrium between felsic partial melts and residual apatite is rarely established. 相似文献
68.
69.
The role of sphene as an accessory phase in the high-pressure partial melting of hydrous mafic compositions 总被引:1,自引:0,他引:1
In a high-pressure experimental study of reactions and possible melt products occurring in the deep continental crust or in subducted oceanic crust, sphene has been identified over a pressure range of 10–18 kbar and to temperatures of 1020°C. Sphene may be a refractory phase with up to 60% partial melting for hydrous mafic compositions. Sphene breaks down at lower pressure than the maximum pressure stability of amphibole in hydrous mafic compositions, and rutile rather than sphene is the important Ti-bearing accessory phase at pressures greater than 16–18 kbar. Sphene and rutile coexist to pressures as low as 14 kbar. This implies that amphibole eclogites containing primary sphene and no rutile have most likely formed at depths less than 45 km.The presence of minor sphene as a residual phase in equilibrium with low-Ti silicic liquids may have a marked effect on the REE distribution in derivative liquids. Thus melts in equilibrium with a garnet and sphene-bearing residuum may have less light-REE-enriched patterns than those predicted when garnet is a residual phase without coexisting sphene. This effect is modelled using REE patterns for sphenes from high-grade metamorphic terrains of western Norway.Both the new REE data and the experimental study have important implications for the genesis of low-Ti magmas formed in continental margins and island arcs. 相似文献
70.
The experimental crystallization of staurolite in two mafic compositions at high pressures (24–26 kb) and temperatures (740 °–760 ° C) is reported. This, together with a recent report of staurolite from metamorphosed basic igneous rocks from Fiordland, New Zealand, leads to the conclusion that Staurolite may be an important subordinate phase in the subducted lithosphere. The synthesized staurolites are more magnesian than those occuring in natural metapelitic assemblages and are characterized by relatively high Si, Ti, Mg, Ca, and low Al, Fe. 相似文献