全文获取类型
收费全文 | 100篇 |
免费 | 2篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 3篇 |
地球物理 | 29篇 |
地质学 | 46篇 |
海洋学 | 8篇 |
天文学 | 10篇 |
自然地理 | 5篇 |
出版年
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 3篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 5篇 |
2013年 | 4篇 |
2012年 | 1篇 |
2011年 | 3篇 |
2009年 | 4篇 |
2008年 | 5篇 |
2007年 | 3篇 |
2006年 | 4篇 |
2005年 | 3篇 |
2004年 | 7篇 |
2003年 | 2篇 |
2002年 | 2篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1996年 | 2篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 3篇 |
1970年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有102条查询结果,搜索用时 31 毫秒
81.
Noble P. Abraham Sijo Sebastian G. Sreekala Savithri E. Devi G. Renuka Venugopal Chandu 《Astrophysics and Space Science》2014,349(1):49-55
A popular model of a cometary plasma is hydrogen (H+) with positively charged oxygen (O+) as a heavier ion component. However, the discovery of negatively charged oxygen (O?) ions enables one to model a cometary plasma as a pair-ion plasma (of O+ and O?) with hydrogen as a third ion constituent. We have, therefore, studied the stability of the ion-acoustic wave in such a pair-ion plasma with hydrogen and electrons streaming with velocities $V_{d\mathrm{H}^{+}}$ and V de , respectively, relative to the oxygen ions. We find the calculated frequency of the ion-acoustic wave with this model to be in good agreement with the observed frequencies. The ion-acoustic wave can also be driven unstable by the streaming velocity of the hydrogen ions. The growth rate increases with increasing hydrogen density $n_{\mathrm{H}^{+}}$ , and streaming velocities $V_{d\mathrm{H}^{+}}$ and V de . It, however, decreases with increasing oxygen ion densities $n_{\mathrm{O}^{+}}$ and $n_{\mathrm{O}^{-}}$ . 相似文献
82.
Alan J. Lewitus David L. White Raphael G. Tymowski Mark E. Geesey Sabrina N. Hymel Peter A. Noble 《Estuaries and Coasts》2005,28(1):160-172
CHEMTAX is a matrix factorization program used to derive taxonomic structure of phytoplankton from photosynthetic pigment
vitios. The program was originally developed from and applied to the analysis of oceanic phytoplankton assemblages. We found
that application of the original CHEMTAX reference matrix to southeastern United States estuarine systems produced inaccurate
results, as verified by microscopy. Modification of the matrix, based primarily on the pigment ratios of 33 estuarine isolates,
improved the predictive capabilities of CHEMTAX for our samples. Limitations of the method included an overstimation of diatom
biomass (due to the inability to differentiate diatoms from taxa with chloroplasts derived from diatom endosymbionts, notably
some dinoflagellates) and a tendency to exclude some raphidophyte species. In complement with microscopic verification, the
method was shown to improve assessment of phytoplankton taxonomic composition. 相似文献
83.
The mean residence time (MRT) of karst groundwater in three mountainous catchments of the Western Himalaya was estimated using multiple approaches: the tritium method, the sine wave model and tracer tests. Water samples were collected from precipitation, glacier melt, streams and karst springs for δ2H and tritium analysis during 2012 and 2013. High tritium values were observed in winter precipitation and low values in summer precipitation. The variation of tritium in karst springs was similar to that of the streams, whereas glacier melt showed lower tritium values. The MRT of cold karst springs was shorter than that of warm karst springs. The tracer breakthrough curves (TBC) retrieved for different springs suggested a short travel time for groundwater and possibly conduit flow. Deterioration of water quality and variation in flux magnitude are the two main practical consequences of the short travel time of karst groundwater in the region.
EDITOR D. KoutsoyiannisASSOCIATE EDITOR K. Heal 相似文献
84.
85.
86.
The kinetics of oxygen exchange between the GeO4Al12(OH)24(OH2)12(aq) molecule and aqueous solutions
Alasdair P. LeeBrian L. Phillips William H. Casey 《Geochimica et cosmochimica acta》2002,66(4):577-587
We report rates of oxygen exchange with bulk solution for an aqueous complex, IVGeO4Al12(OH)24(OH2)128+(aq) (GeAl12), that is similar in structure to both the IVAlO4Al12(OH)24(OH2)127+(aq) (Al13) and IVGaO4Al12(OH)24(OH2)127+(aq) (GaAl12) molecules studied previously. All of these molecules have ε-Keggin-like structures, but in the GeAl12 molecule, occupancy of the central tetrahedral metal site by Ge(IV) results in a molecular charge of +8, rather than +7, as in the Al13 and GaAl12. Rates of exchange between oxygen sites in this molecule and bulk solution were measured over a temperature range of 274.5 to 289.5 K and 2.95 < pH < 4.58 using 17O-NMR.Apparent rate parameters for exchange of the bound water molecules (η-OH2) are kex298 = 200 (±100) s−1, ΔH‡ = 46 (±8) kJ · mol−1, and ΔS‡ = −46 (±24) J · mol−1 K−1 and are similar to those we measured previously for the GaAl12 and Al13 complexes. In contrast to the Al13 and GaAl12 molecules, we observe a small but significant pH dependence on rates of solvolysis that is not yet fully constrained and that indicates a contribution from the partly deprotonated GeAl12 species.The two topologically distinct μ2-OH sites in the GeAl12 molecule exchange at greatly differing rates. The more labile set of μ2-OH sites in the GeAl12 molecule exchange at a rate that is faster than can be measured by the 17O-NMR isotopic-equilibration technique. The second set of μ2-OH sites have rate parameters of kex298 = 6.6 (±0.2) · 10−4 s−1, ΔH‡ = 82 (±2) kJ · mol−1, and ΔS‡ = −29 (±7) J · mol−1 · K−1, corresponding to exchanges ≈40 and ≈1550 times, respectively, more rapid than the less labile μ2-OH sites in the Al13 and GaAl12 molecules. We find evidence of nearly first-order pH dependence on the rate of exchange of this μ2-OH site with bulk solution for the GeAl12 molecule, which contrasts with Al13 and GaAl12 molecules. 相似文献
87.
Alasdair D. L. Skelton 《Contributions to Mineralogy and Petrology》1996,125(1):75-84
A suite of metabasite dykes, emplaced within the Albee Formation, east-central Vermont, preserves evidence of interaction with a CO2-bearing hydrous fluid during Acadian metamorphism. Coupled advective and diffusive cross-layer fluxes of CO2 are recorded by forwards progress of the hydration-carbonation reaction: 3 amphibole + 2 epidote + 8 H2O + 10 CO2 = 3 chlorite + 10 calcite + 21 quartz Advection, diffusion and mineral reaction rates are modelled from reaction progress data through application of an analytical solution to the 1-D mass conservation equation for linear reaction kinetics (Lichtner 1988; Lasaga and Rye 1993; Skelton et al. in press). Dimensionless Peclet (Pe) and Damköhler (ND) numbers which describe the ratios of advection to diffusion and reaction rate to advection are thus resolved, from which time-integrated fluid fluxes are calculated. Small Pe (<10), large ND (>10) and small time-integrated fluid fluxes (<5 m3/m2) are obtained, predicting that cross-layer fluxes of CO2 are largely diffusive. It follows that, within the Albee schists, fluid flow must have been layer parallel. Where fluid flow is layer parallel, it is both interesting and informative to consider the geometry of fluid flow at a fold hinge. For layer-parallel fluid flow to be maintained, the flow direction must reverse which is difficult to justify with regards to the driving force. It is perhaps more reasonable that fluid should “escape” through the fold hinge (cf. Skelton et al. 1995), either via close-spaced microveins (cf. Cole and Graham 1994) or macro-scale axial-planar quartz veins (Ferry 1992, 1994). At present, the Albee schists are ~ vertical and strike ~ N–S. This reflects: (1) E–W recumbent folding of strata (early Acadian “nappe-stage” deformation; D1); (2) N–S arching of strata (late Acadian “dome-stage” deformation; D2). In the Strafford Quadrangle, east-central Vermont, curious “Coarse Garnet Schists” occur in the axial regions of D1 fold closures. On the basis of this spatial association, crystal morphologies, reaction textures and chemical zoning profiles, it is postulated that the Coarse Garnet Schists developed in response to structurally focused fluid escape. That fluid flow was syn-D1 is implicit to this argument. As such, layer-parallel fluid flow must have been ~ horizontal. Although this conclusion is in close agreement with that of Ferry (1994), up-temperature fluid flow is not implicated. 相似文献
88.
Sea level fluctuations in central California at subtidal to decadal and longer time scales with implications for San Francisco Bay, California 总被引:1,自引:0,他引:1
Sea level elevations from near the mouth of San Francisco Bay are used to describe the low-frequency variability of forcing of the coastal ocean on the Bay at a variety of temporal scales. About 90% of subtidal fluctuations in sea level in San Francisco Bay are driven by the sea level variations in the coastal ocean that propagate into the Bay at the estuary mouth. We use the 100-year sea level record available at San Francisco to document a 1.9 mm/yr mean sea level rise, and to determine fluctuations related to El Nino-Southern Oscillation (ENSO) and other climatic events. At time scales greater than 1 year, ENSO dominates the sea level signal and can result in fluctuations in sea level of 10–15 cm. Alongshore wind stress data from central California are also analyzed to determine the impact of changes in coastal elevation at the mouth of San Francisco Bay within the synoptic wind band of 2–30 days. At least 40% of the subtidal fluctuations in sea level of the Bay are tied to the large-scale regional wind field affecting sea level variations in the coastal ocean, with little local, direct wind forcing of the Bay itself. The majority of the subtidal sea level fluctuations within the Bay that are not related to the coastal ocean sea level signal are forced by an east–west sea level gradient resulting from tidally induced variations in sea level at specific beat frequencies that are enhanced in the northern reach of the Bay. River discharge into the Bay through the Sacramento and San Joaquin River Delta also contributes to the east–west gradient, but to a lesser degree. 相似文献
89.
The mussel digestive gland epithelial cells provide a key interface between the organism and pollutants such as aromatic hydrocarbons. The simulation of their uptake and export mechanisms as well as an internal protein degradation pathway, and any subsequent disruption to any of them, has been undertaken. A computational model is described, which simulates the flow of carbon and nitrogen through a mussel's digestive cell. The model uses a compartmentalised view of the cell with inviolate 'pipelines' connecting each of the volume-variable partitions. Only the major physiological pathways relevant to the flow of either carbon or nitrogen or volume are modelled. Simulated response to hydrocarbon exposure is examined. 相似文献
90.
Long-term monthly sea level and sea surface temperature (SST) anomalies from central California show that during winter months, positive anomalies are associated with El Niño events and the negative ones with La Niña events. There is no significant impact on monthly mean anomalies associated with Pacific decadal oscillations, although there is a tendency for more extreme events and greater variance during positive decadal oscillations. The very strong 1997–1998 El Niño was analyzed with respect to the long-term historic record to assess the forcing mechanisms for sea level and SST. Beginning in the spring of 1997, we observed several long-period (>30 days) fluctuations in daily sea level with amplitudes of over 10 cm at San Francisco, California. Fluctuations of poleward long-period alongshore wind stress anomalies (AWSA) are coherent with the sea level anomalies. However, the wind stress cannot entirely account for the observed sea level signals. The sea level fluctuations are also correlated with sea level fluctuations observed further south at Los Angeles and Tumaco, Columbia, which showed a poleward phase propagation of the sea level signal. We suggest that the sea level fluctuations were, to a greater degree, forced by the passage of remotely generated and coastally trapped waves that were generated along the equator and propagated to the north along the west coast of North America. However, both local and remote AWSA can significantly modulate the sea level signals. The arrival of coastally trapped waves began in the spring of 1997, which is earlier than previous strong El Niño events such as the 1982–1983 event. 相似文献