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101.
Summary The evolution of geophysical parameters over Indian Ocean during two contrasting monsoon years 2002 (drought) and 2003 (normal)
were studied using TRMM/TMI satellite data. Analysis indicates that there was a lack of total water vapour (TWV) build up
over Western Indian Ocean (WIO) during May 2002 (drought) when compared to 2003 (normal). Negative (positive) TWV anomalies
were found over the WIO in May 2002 (2003). In 2002, negative SST anomaly of ∼1.5 °C is found over entire WIO when compared
to 2003. Anomalously high sea surface wind speed (SWS) anomaly over the South West Indian Ocean (SWIO) and WIO would have
resulted in cooling of the sea surface in May 2002 in comparison to 2003. In 2003 the wind speed anomaly over entire WIO and
Arabian Sea (AS) was negative, whereas sea surface temperature (SST) anomaly was positive over the same region, which would
have resulted in higher moisture availability over these regions. A negative (positive) TWV anomaly over Eastern Arabian Sea
(EAS) and positive (negative) anomaly over WIO forms a dipole structure. In the month of June no major difference is seen
in all these parameters over the Indian Ocean. In July 2002 the entire WIO and AS was drier by 10–15 mm as compared to 2003.
The pentad (5 day) average TWV values shows high (>55 mm) TWV convergence over EAS and Bay of Bengal (BoB) during active periods
of 2003, which gives high rainfall over these regions. However, during 2002 although TWV over BoB was >55 mm but it was ∼45–55 mm
over EAS during entire July and hence less rainfall.
The evaporation has been calculated from the bulk aerodynamic formula using TRMM/TMI geophysical products. It has been seen
that the major portion of evaporative moisture flux is coming from southern Indian Ocean (SIO) between 15 and 25° S. Evaporation
in June was more over AS and SIO in 2003 when compared to 2002 which may lead to reduce moisture supply in July 2002 and hence
less rainfall compared to July 2003. 相似文献
102.
103.
104.
M. A. Rahman P. N. Bhat B. S. Acharya V. R. Chitnis P. Majumdar P. R. Vishwanath 《Experimental Astronomy》2001,11(2):113-131
We study the propagation of erenkov photons generated by Very HighEnergy -rays and hadrons in the atmosphere. The photon productionheight distributions are estimated from semi-empirical methods andcompared with those derived by standard simulation techniques. Incidentspectra at various observation altitudes are then derived after applyingwavelength dependent corrections due to photon attenuation in theatmosphere during the propagation of photons from the height of productionto the height of observation. These are generated both for -ray and hadron primaries of various energies. The derivedproduction height distributions agree very well with those generated bythe simulation package `CORSIKA' at all energies and for both -ray and proton primaries. The incident photon spectra are found to beboth altitude and primary energy dependent. The peak ofthe incident spectrum shifts towards the shorter wavelength withincreasing altitude of observation for a given primary. Also the peak ofthe photon spectrum shifts towards the shorter wavelength withincreasing energy of the primary at a given altitude. The fraction of the UVcomponent in the incident erenkov spectrum is estimated both for-ray and hadronic primaries at various observation altitudes andenergies. Hadron generated erenkov spectra are marginally richer in UVlight and the difference increases slightly at higher altitudes. The fraction of the UV to the visible light in the erenkov spectrum could be a usefulparameter to separate -rays from cosmic ray background only if onecan measure this fraction very accurately. 相似文献
105.
Summary Changes in the frequency of tropical cyclones developing over the Arabian Sea and the Bay of Bengal have been studied utilizing
122 year (1877–1998) data of tropical cyclone frequency. There have been significant increasing trends in the cyclone frequency
over the Bay of Bengal during November and May which are main cyclone months. During transitional monsoon months; June and
September however, the frequency has decreased. The results have been presented for five months, i.e., May-November which
are relevant as far as tropical cyclone frequency over the Arabian Sea and the Bay of Bengal are concerned. The tropical cyclone
frequency in the Arabian Sea has not shown any significant trend, probably due to small normal frequency.
The frequency time series has been subjected to the spectral analysis to obtain the significant periods. The cyclone frequency
over the Bay of Bengal during May has shown a 29 year cycle. A significant 44 year cycle has been found during November. Over
the Arabian Sea significant cycles of 13 and 10 years have been observed during May-June and November, respectively. The tropical
cyclone frequency in the North Indian Ocean has a prominent El Ni?o-Southern Oscillation (ENSO) scale cycle (2–5 years) during
all above five months. The annual cyclone frequency exhibits 29 year and ENSO scale (2–4 years) oscillations. There is a reduction
in tropical cyclone activity over the Bay of Bengal in severe cyclone months May and November during warm phases of ENSO.
Examination of the frequencies of severe cyclones with maximum sustained winds ≥ 48 knots has revealed that these cyclones
have become more frequent in the North Indian Ocean during intense cyclone period of the year. The rate of intensification
of tropical disturbances to severe cyclone stage has registered an upward trend.
Received June 7, 1999/Revised March 20, 2000 相似文献
106.
Estimation of catchment yield and associated uncertainties due to climate change in a mountainous catchment in Australia
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This paper examines the impacts of climate change on future water yield with associated uncertainties in a mountainous catchment in Australia using a multi‐model approach based on four global climate models (GCMs), 200 realisations (50 realisations from each GCM) of downscaled rainfalls, 2 hydrological models and 6 sets of model parameters. The ensemble projections by the GCMs showed that the mean annual rainfall is likely to reduce in the future decades by 2–5% in comparison with the current climate (1987–2012). The results of ensemble runoff projections indicated that the mean annual runoff would reduce in future decades by 35%. However, considerable uncertainty in the runoff estimates was found as the ensemble results project changes of the 5th (dry scenario) and 95th (wet scenario) percentiles by ?73% to +27%, ?73% to +12%, ?77% to +21% and ?80% to +24% in the decades of 2021–2030, 2031–2040, 2061–2070 and 2071–2080, respectively. Results of uncertainty estimation demonstrated that the choice of GCMs dominates overall uncertainty. Realisation uncertainty (arising from repetitive simulations for a given time step during downscaling of the GCM data to catchment scale) of the downscaled rainfall data was also found to be remarkably high. Uncertainty linked to the choice of hydrological models was found to be quite small in comparison with the GCM and realisation uncertainty. The hydrological model parameter uncertainty was found to be lowest among the sources of uncertainties considered in this study. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
107.
In this study, a quantitative assessment of uncertainty was made in connection with the calibration of Australian Water Balance Model (AWBM) for both gauged and ungauged catchment cases. For the gauged catchment, five different rainfall data sets, 23 different calibration data lengths and eight different optimization techniques were adopted. For the ungauged catchment case, the optimum parameter sets obtained from the nearest gauged catchment were transposed to the ungauged catchments, and two regional prediction equations were used to estimate runoff. Uncertainties were ascertained by comparing the observed and modelled runoffs by the AWBM on the basis of different combinations of methods, model parameters and input data. The main finding from this study was that the uncertainties in the AWBM modelling outputs could vary from ?1.3% to 70% owing to different input rainfall data, ?5.7% to 11% owing to different calibration data lengths and ?6% to 0.2% owing to different optimization techniques adopted in the calibration of the AWBM. The performance of the AWBM model was found to be dominated mainly by the selection of appropriate rainfall data followed by the selection of an appropriate calibration data length and optimization algorithm. Use of relatively short data length (e.g. 3 to 6 years) in the calibration was found to generate relatively poor results. Effects of different optimization techniques on the calibration were found to be minimal. The uncertainties reported here in relation to the calibration and runoff estimation by the AWBM model are relevant to the selected study catchments, which are likely to differ for other catchments. The methodology presented in this paper can be applied to other catchments in Australia and other countries using AWBM and similar rainfall–runoff models. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
108.
Md. Mahabubur Rahman Tasnim Ara Mohiuddin Ibn Shafique Md. Abdur Rahman Mohammad Lutfor Rahman 《Singapore journal of tropical geography》2023,44(3):499-518
Considering the adverse outcomes of thunderstorm-mediated lightning in recent years, this study aimed to identify the most thunderstorm-and-casualty prone regions and seasons in Bangladesh, via geospatial mapping. We attempted to forecast the number of yearly thunderstorm (TS) days for each meteorological station and district-level lightning casualties by using TS days as a proxy variable. Data on TS days and lightning casualties were collected from Bangladesh Meteorological Department and Network for Information, Response And Preparedness Activities on Disaster respectively. This study analysed 629 fatalities and 232 injuries. The Integrated Nested Laplace Approximation with Matern covariance function was employed to assess the spatial pattern of TS days. Polynomial regressions were used to forecast the number of TS days and the single clustered Generalized Estimating Equations method was employed to explore the relationship between the number of TS days and lightning casualties. The results indicated that the mean number of TS days per station increased in recent years, particularly in February, March, April, and September. We found the months of April, May, June, and September to be the most threatening months due to TS events and related casualties. The northeast region was identified as the most TS-prone region with the highest number of casualties in Bangladesh. Our analysis suggests that it might remain the most hazardous region in coming years. 相似文献
109.
After the landfall of Cyclone Sidr along the southwestern coast of Bangladesh on November 15, 2007, emergency and public health
personnel within and beyond Bangladesh anticipated a massive outbreak of water-borne and other diseases in most affected areas.
Fortunately, such an outbreak did not occur. The objectives of this paper are to examine the extent and pattern of illnesses
experienced by Cyclone Sidr survivors in the aftermath of its landfall and to investigate household and individual-level factors
associated with such illnesses. Based on face-to-face interviews conducted among 277 randomly selected Sidr survivors living
in the four most severely impacted coastal districts, this study found that the post-cyclone incidence of water-borne, respiratory,
and other diseases was not unusually high. Only 52 persons suffered Sidr-related illnesses, and their illnesses were significantly
associated with household income, and gender and age of the Sidr survivors. A major outbreak of such diseases was largely
avoided because of the proper distribution of food and safe drinking water, as well as the timely implementation of health
care intervention measures. This important finding will aid relevant authorities in successfully responding to outbreaks of
diseases following a future extreme event in Bangladesh and perhaps elsewhere. 相似文献
110.
Passive earth pressure on embedded anchor plates constitutes a viable resisting force for the design of underground structures. In the current practice, these forces are empirically calculated, ignoring the effects of the depth of embedment and the level of consolidation of the surrounding soil, which takes place during plate installation on the in situ stress levels. Accordingly, wide discrepancies between predicted and measured pullout capacities of these plates were reported in the literature. Numerical model was developed using finite-element technique and the constitutive law of Mohr?CCoulomb to simulate the case of a retaining wall partially supported by an embedded anchor plate in sand. The results produced in this investigation showed that the passive earth pressure acting on anchor plates increases due to the increase of angle of shearing resistance and the overconsolidation ratio of sand, and it decreases due to an increase of the embedment depth of anchor. Design theories were developed for the case of embedded anchor plate in overconsolidated sand. The theories developed will satisfy the design needed in terms of allowable pullout load and/or displacement. 相似文献