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51.
Abstract To assess the predictive significance of meteorological parameters for forecasting discharge from the Dokriani Glacier basin in the Himalayan region, discharge autocorrelation and correlations between discharge and meteorological factors were investigated on a monthly and a seasonal basis. Changes in correlations between discharge and meteorological variables, lagged by 0–3 days, were determined. Discharge autocorrelation was found to be very high for each individual summer month and for the melt season as a whole. This suggests that a substantial meltwater storage in the glacier, which results in a delayed response of runoff, and therefore discharge, from the highly glacierized basins is very much dependent on the previous day's discharge. A comparison of correlations between discharge and temperature, and discharge and precipitation shows that temperature has a better correlation with discharge during June and September, while precipitation has good correlation with discharge in July and August. Variations in the physical features of the glacier, weather conditions, and precipitation and its distribution with time over the basin account for changes in correlations. To forecast the runoff from the Dokriani Glacier basin, multiple linear regression equations were developed separately for each month and for the whole melt season. A better forecast was obtained using the seasonal regression equation. A comparison of correlations for the Dokriani Glacier with those for the Z'mutt Glacier basin, Switzerland, illustrates that, for both basins, the previous day's discharge (Qi-1) shows maximum autocorrelation throughout the melt period. Whereas a good correlation between discharge and temperature was observed for the Z'mutt Glacier basin for the whole melt period, for the Dokriani Glacier basin it was strong at the beginning and end of the ablation season. Runoff delaying behaviour in the Dokriani Glacier basin is found more prominent than in the Z'mutt Glacier basin early in the melt season. Water storage appears to be less significant in the Dokriani Glacier than in the Z'mutt Glacier towards the end of the ablation season. The strength of correlation between discharge and precipitation is higher for the Dokriani Glacier basin than for the Z'mutt Glacier basin. This is due to higher rainfall in the Dokriani Glacier basin. In general, for both glacier basins, maximum correlation is found between discharge and precipitation on the same day. 相似文献
52.
H. MIZUOCHI M. SATISH‐KUMAR Y. MOTOYOSHI K. MICHIBAYASHI 《Journal of Metamorphic Geology》2010,28(5):509-526
Calcite–dolomite solvus geothermometry is a versatile method for the estimation of metamorphic temperature because of its simplicity. However, in medium‐ to high‐grade metamorphic rocks the accuracy of estimating temperature by the integration of unmixed dolomite and calcite is hampered by the heterogeneous distribution of unmixed dolomite, difficulties in distinguishing between preexisting and exsolved dolomite and demarcating grain boundaries. In this study, it is shown that calcite–dolomite solvus thermometry can be applied to calcite inclusions in forsterite and spinel for the estimation of peak metamorphic temperature in granulite facies marbles from Skallevikshalsen, East Antarctica. The marbles are comprised of a granoblastic mineral assemblage of calcite + dolomite + forsterite + diopside + spinel + phlogopite ± apatite, characteristic of granulite facies metamorphic conditions. Forsterite, spinel and apatite frequently contain ‘negative crystal’ inclusions of carbonates that display homogeneously distributed dolomite lamellae. On the basis of narrow ranges of temperature (850–870 °C) recorded from carbonate inclusions compared with the range from matrix carbonate it is regarded that the inclusion carbonates represent a closed system. Furthermore, this estimate is consistent with dolomite–graphite carbon isotope geothermometry, and is considered to be the best estimate of peak metamorphic temperature for this region. Matrix calcite records different stages of retrograde metamorphism and re‐equilibration of calcite that continued until Mg diffusion ceased at ~460 °C. Electron backscattered diffraction (EBSD) results together with morphological features of unmixed coarse tabular dolomite suggest anisotropic diffusion and mineral growth are influenced by crystallographic orientation. Identification of sub‐grain boundaries and formation of fine‐grained unmixing in calcite rims suggest the presence of grain boundary fluids in the late retrograde stages of metamorphic evolution. These results, thus, demonstrate the usefulness of carbonate inclusion geothermometry in estimating the peak metamorphic temperatures of high‐grade terranes and the application of EBSD in understanding the unmixing behaviour of minerals with solid solutions. 相似文献
53.
The fine silt deposits of Jammu (J & K State, India) stretch all along the Siwalik foothills from Jammu to the Potwar Plateau
in Pakistan. The post-Siwalik deposits, first discussed by de Terra and Paterson (1939), are attributed to wind action. The
deposits termed as ‘Potwar loessic silt’ comprising sandy silt are essentially of late Quaternary age (75–18 ka) and are re-looked
herein from the point of view of genesis and climatic significance. The sorting, skewness and kurtosis parameters of fine
silts of Jammu suggest fluvial environment of the deposits wherein the water budget fluctuated. The weak pedogenesis of fine
silts at certain intervals corroborate to periods of less or no sedimentation. The bivariant plot studies further suggest
fluvial environment of deposition for the fine silt at Jammu, with regular fluctuations in the budget of river water that
was perhaps in consonance with oscillations in the climate of the region. 相似文献
54.
FABIEN DURAND FABRICE PAPA ATIQUR RAHMAN SUJIT KUMAR BALA 《Journal of Earth System Science》2011,120(5):859-872
This study investigates the impact of monthly Ganges–Brahmaputra river discharge variations on Bay of Bengal salinity and
temperature during the period 1992–1999. The Ganges–Brahmaputra river discharge is characterized by a well-defined seasonal
cycle with strong interannual variations. The highest/lowest yearly peak discharge occurs in summer 1998/summer 1992, with
1998 value amounting to twice that of 1992. This river discharge is then used to force an ocean general circulation model.
Our main result is that the impact of these rivers on the variability of Bay of Bengal sea surface salinity is strong in the
northern part, with excess run-off forcing fresh anomalies, and vice versa. Most of the years, the influence of the interannual variability of river discharge on the Bay salinity does not extend south
of ~10°N. This stands in contrast with the available observations and is probably linked to the relatively coarse resolution
of our model. However, the extreme discharge anomaly of 1998 is exported through the southern boundary of the Bay and penetrates
the south-eastern Arabian Sea a few months after the discharge peak. In response to the discharge anomalies, the model simulates
significant mixed-layer temperature anomalies in the northern Bay of Bengal. This has the potential to influence the climate
of the area. From our conclusions, it appears necessary to use a numerical model with higher resolution (both on the horizontal
and vertical) to quantitatively investigate the upper Bay of Bengal salinity structure. 相似文献
55.
Meso-scale atmospheric events promote phytoplankton blooms in the coastal Bay of Bengal 总被引:1,自引:0,他引:1
K MANEESHA V V S S SARMA N P C REDDY Y SADHURAM T V RAMANA MURTY V V SARMA M DILEEP KUMAR 《Journal of Earth System Science》2011,120(4):773-782
The Bay of Bengal is considered to be a low productive region compared to the Arabian Sea based on conventional seasonal observations.
Such seasonal observations are not representative of a calendar year since the conventional approach might miss episodic high
productive events associated with extreme atmospheric processes. We examined here the influence of extreme atmospheric events,
such as heavy rainfall and cyclone Sidr, on phytoplankton biomass in the western Bay of Bengal using both in situ time-series observations and satellite derived Chlorophyll a (Chl a) and sea surface temperature (SST). Supply of nutrients through the runoff driven by episodic heavy rainfall (234 mm) on
4–5 October 2007 caused an increase in Chl a concentration by four times than the previous in the coastal Bay was observed within two weeks. Similar increase in Chl a, by 3 to 10 times, was observed on the right side of the cyclone Sidr track in the central Bay of Bengal after the cyclone Sidr. These two episodic events caused phytoplankton blooms in the western Bay of Bengal which enhanced ~40% of fishery production
during October–December 2007 compared to that in the same period in 2006. 相似文献
56.
NAVEEN GANDHI SANJEEV KUMAR S PRAKASH R RAMESH M S SHESHSHAYEE 《Journal of Earth System Science》2011,120(1):99-111
Various experiments involving the measurement of new, regenerated and total productivity using 15N and 13C tracers were carried out in the Bay of Bengal (BOB) and in the Arabian Sea. Results from 15N tracer experiments indicate that nitrate uptake can be underestimated by experiments with incubation time <4 hours. Indirect
evidence suggests pico- and nano-phytoplankton, on their dominance over microphytoplankton, can also influence the f-ratios.
Difference in energy requirement for assimilation of different nitrogen compounds decides the preferred nitrogen source during
the early hours of incubation. Variation in light intensity during incubation also plays a significant role in the assimilation
of nitrogen. Results from time course experiments with both 15N and 13C tracers suggest that photoinhibition appears significant in BOB and the Arabian Sea during noon. A significant correlation
has been found in the productivity values obtained using 15N and 13C tracers. 相似文献
57.
58.
59.
N. BHANDARI S. V. S. MURTY P. N. SHUKLA R. R. MAHAJAN A. D. SHUKLA G. LASHKARI M. S. SISODIA R. P. TRIPATHI G. PARTHASARATHY H. C. VERMA I. A. FRANCHI 《Meteoritics & planetary science》2008,43(4):761-770
Abstract— We report here a chance find of a meteorite in the sand dunes of Ararki village of Hanumangarh district in the Rajasthan desert of northwest India. Chemical and petrological evidence in conjunction with isotopic composition of oxygen indicate that it is an L5 chondrite. The fayalite content of olivines is 26.3 mol%. The meteorite has some serpentinized olivines and 0.3% carbon having a terrestrial isotopic composition, indicating that it is moderately weathered. The absence of 22Na indicate that the meteorite fell to Earth more than a decade ago. The cosmic‐ray exposure age based on cosmogenic 21Ne is 7.2 Ma. Low density of cosmic‐ray heavy nuclei tracks, low 26A1 activity, the shielding parameter [(22Ne/21Ne)C = 1.094] and absence of neutron capture effects indicate cosmic‐ray shielding in a meteoroid having radius of about 16 cm, implying a meteoroid mass of about 60 kg and ablation of about 93%. The gas retention ages, based on U/Th‐4He and K‐40Ar are 1.1 and 0.58 Ga, respectively, suggesting a heating and degassing event late in the history of this meteorite. 相似文献
60.
R.K. VERMA 《Geophysical Prospecting》1980,28(5):776-791
An analysis of the equivalence phenomenon, analogous to that encountered in resistivity sounding, has been made for electromagnetic (frequency) sounding with the following systems: horizontal coplanar coils, perpendicular coils, vertical coplanar coils, and vertical coaxial coils. Cases analyzed are three-layer H and K type resistivity distributions. The theoretical responses for the EM sounding systems have been computed by the digital linear filter method using short filters. An analysis has been made of the resolution by the four EM systems considered f the equivalence effect. It is concluded that from the equivalence point of view electromagnetic (frequency) sounding has relatively better resolution compared to resistivity sounding for the H type three-layer cases. For the K type three-layer cases electromagnetic (frequency) sounding provides a serious problem in resolution similar to that encountered in resistivity sounding. Empirical relationships have been established for the H and K type cases respectively in order to numerically quantify the equivalence involved in electromagnetic (frequency) sounding. 相似文献