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91.
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
92.
We perform a strong ground motion simulation using a modified semi-empirical technique (Midorikawa in Tectonophysics 218:287–295, 1993), with frequency-dependent radiation pattern model. Joshi et al. (Nat Hazards 71:587–609, 2014) have modified the semi-empirical technique to incorporate the modeling of strong motion generation areas (SMGAs). A frequency-dependent radiation pattern model is applied to simulate high-frequency ground motion more precisely. Identified SMGAs (Kurahashi and Irikura in Earth Planets Space 63:571–576, 2011) of the 2011 off the Pacific coast of Tohoku earthquake (M w = 9.0) were modeled using this modified technique. We analyzed the effect of changing seismic moment values of SMGAs on the simulated acceleration time series. Final selection of the moment values of SMGAs is based on the root-mean-square error (RMSE) of waveform comparison. Records are simulated for both frequency-dependent and constant radiation pattern function. Simulated records for both cases are compared with observed records in terms of peak ground acceleration, peak ground velocity and pseudo-acceleration response spectra at different stations. Comparison of simulated and observed records in terms of RMSE suggests that the method is capable of simulating record, which matches in a wide frequency range for this earthquake and bears realistic appearance in terms of shape and strong motion parameters. The results confirm the efficacy and suitability of rupture model defined by five SMGAs for the developed modified technique. 相似文献
93.
The semiempirical approach based on envelope summation method given by Midorikawa (Tectonophysics 218:287–295, 1993) has been modified in this paper for modeling of strong motion generation areas (SMGAs). Horizontal components of strong ground motion have been simulated using modifications in the semiempirical approach given by Joshi et al. (Nat Hazard 71:587–609, 2014). Various modifications in the technique account for finite rupture source, layering of earth, componentwise division of energy and frequency-dependent radiation pattern. In this paper, SMGAs of the Uttarkashi earthquake have been modeled. Two different isolated wave packets in the recorded accelerogram have been identified from recorded ground motion, which accounts for two different SMGAs in the entire rupture plane. The approximate locations of SMGAs within the rupture plane were estimated using spatio-temporal variation of 77 aftershocks. Source parameters of each SMGA were calculated from theoretical and observed source displacement spectra computed from two different wave packets in the record. The final model of rupture plane responsible for the Uttarkashi earthquake consists of two SMGAs, and the same has been used to simulate horizontal components of acceleration records at different station using modified semiempirical technique. Comparison of the observed and simulated acceleration records in terms of root mean square error confirms the suitability of the final source model for the Uttarkashi earthquake. 相似文献
94.
Climate Dynamics - The Tropical Indian Ocean (TIO) is seen to exhibit robust warming after the 1950s. Most of the previous studies on the Indian Ocean (IO) surface and subsurface temperature... 相似文献
95.
Open-cast mining generates sediment in river systems at globally significant scales. One of the challenges in attributing
measured sediment loads to upstream mining activities is establishing the source of sediments that are a mixture of natural
and mining-based materials. The environmental magnetic data (mass-specific magnetic susceptibility, anhysteretic remanent
magnetisation, isothermal remanent magnetisation and inter-parametric ratios) on 57 samples of suspended sediment from the
Bhadra River in the Sahyadri (the Western Ghat) of India have been used in this study. Samples were collected upstream, adjacent to and downstream of
Kudremukh, a mountainous and high rainfall site where the largest mechanised open-cast mine in south Asia was located. Graphical
and multivariate analyses and modelling of the data show that on average ~29% of the river suspended load downstream of the
mine is derived from mining and allied activities at Kudremukh although the mine occupies less than 5% of the catchment. The
contribution of primary ore is the maximum (18%), followed by transitional hard weathered ore (7%) and weathered ore (4%).
The model has done a fairly good job of unmixing; the sum of errors is <1 for 40 samples, 1–4,254 for five samples and >71,000
for four samples. Modelling of samples with small mass seems to produce large errors. This investigation demonstrates the
utility of environmental magnetic data, which can be obtained in a simple and rapid manner, and the unmixing of such data
in identifying the contribution of mining activities to the total suspended sediment load. 相似文献
96.
Sandeep Tambe M. L. Arrawatia Narpati Sharma 《Journal of the Indian Society of Remote Sensing》2011,39(4):555-564
Sikkim is a small, mountainous, Indian state (7,096 km2) located in the eastern Himalayan region. Though a global biodiversity hotspot, it has been relatively less studied. A detailed
forest type, density and change dynamics study was undertaken, using SATELLITE remote sensing data and intensive field verification.
The landscape was found to be dominated by alpine and nival ecosystems, with a large portion above the tree line, considerable
snow cover, and a sizeable area under forest cover (72%, 5,094 km2). A total of 18 landscape components including 14 vegetation classes were delineated, with the major ones being oak forest,
alpine meadow, alpine scrub, conifer forest and alder-cardamom agro-forestry. Of the 3,154 km2 of forests below the tree line, 40% were found to be dense (>40% tree canopy cover). A sizeable portion of the non dense
forests below the tree line was contributed by the degradation of oak forests, which was confirmed by change detection analysis.
However on a positive front over the past decade, ban on grazing and felling of trees in forests has been implemented. In
order to expand the extent of dense forests, further efforts are needed for the restoration of oak forests such as fire protection,
providing alternatives to firewood use, promotion of alder-cardamom agro-forestry in the private lands and protection of the
small-sized, fragmented forest patches in the subtropical belt. 相似文献
97.
This paper describes the effects of time step on the simulation of tropical climate in the NCAR-Community Atmosphere Model version 3 (CAM3). A set of multi-year integrations are carried out in a real-planet framework using actual land?Cocean distribution and observed sea surface temperature. Over the tropics there is an increase in total rainfall with a decrease in time step size. Using a lower time step, there is a decrease in the convective component of rainfall, however, the stratiform component increases, and more than compensates the decrease in the former, thus leading to a higher total rainfall. A decrease in time step leads to an increase in the frequencies of moderate, and heavy rainfall categories, which is responsible for the increase in time mean total rainfall over the tropics. Also, the spatial distribution of rainfall becomes more realistic during both summer and winter seasons. In regard to the simulation of equatorial waves, it is found that a lower time step leads to a reduction in the speed of Kelvin waves. The latent heating profile becomes more bottom-heavy with a reduction in time step size, which potentially leads to slower Kelvin waves. Finally, additional experiments conducted in an aqua-planet framework show a consistent and systematic change in the analyzed variables with change in time step, and hence confirm the robustness of the results across modeling frameworks. 相似文献
98.
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
99.
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
100.
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