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961.
962.
Summary. ?Cyclone track predictions in the Indian seas (Bay of Bengal and Arabian Sea) with a quasi-Lagrangian model (QLM) have been
attempted. QLM has a horizontal resolution of 40 km and 16 sigma levels in the vertical. It is integrated in a domain of about
4400 × 4400 km2. A new initialization procedure to provide initial fields for running the model has been designed. The initialization procedure
consists of updating the global model forecasts, used as first guess, provided by the National Center for Medium Range Weather
Forecasting (NCMRWF), New Delhi. A new version of IMD’s operational optimum interpolation scheme has been created to suit
the QLM grid structure. Lateral boundary conditions are computed from the extended forecasts of NCMRWF. The track forecasts
in each case show a reasonable skill of the forecast model in predicting the direction of movement within acceptable limits
of forecast errors, which are comparable to some of the best models operated by advanced NWP centers of the world. Even the
recurving storms are well predicted. Evolution of the vertical motion fields are also studied which reveal some interesting
features, which are described in detail in the text. The composited vertical motion fields are projected against observed
rainfall distribution, which show a good spatial correspondence.
Received August 9, 2001; revised March 12, 2002; accepted June 17, 2002
Published online: May 8, 2003 相似文献
963.
P. L. S. Rao 《Meteorology and Atmospheric Physics》2003,83(1-2):19-33
Summary ?During winter season, atmospheric systems, which traverse from west to east interact with the Himalayan massif and produce
widespread rainfall over North India. In this study, we made an endeavor to examine the mean circulation features and large-scale
budgets of kinetic energy, heat and moisture over Himalayas and the adjoining domain for winter season. The time-mean circulation
is bifurcated into stable mean and transient eddy parts and examined the mean component of the circulation. The uninitialized
daily analyses of European Centre for Medium range Weather Forecasts (ECMWF) for five winter seasons (1986–90) comprising
December, January and February (DJF) have been used for the purpose.
We noticed certain zones of strong activity over Iran, Afghanistan, and West China regions during winter season. These are
characterized by intense vertical motions, cyclonic vorticity and adiabatic generation of kinetic energy. The features noticed
over these zones include strong horizontal convergence of heat and moisture. These zones are further characterized by massive
adiabatic conversion of available potential energy to kinetic energy. These features are conducive for the growth of atmospheric
systems, which traverse over the zones and produce precipitation subsequently.
Received November 16, 2000; revised February 5, 2002 相似文献
964.
965.
P. Chittibabu S. K. Dube J. B. Macnabb T. S. Murty A. D. Rao U. C. Mohanty P. C. Sinha 《Natural Hazards》2004,31(2):455-485
Storm surges generated by the strong tangential wind stressesand normal atmospheric pressure gradients at the sea surface due to tropical cyclones (TC'S)have been studied with the goal of detecting any significant and systematic changes due to climatechange. Cyclone and storm surge data for the 19th and 20th centuries for the Bay of Bengalcoast of the state of Orissa in India are available to varying degrees of quality and detail,the data being more scientific since the advent of the India Meteorological Department in 1875.Based on more precise data for the period 1971 to 2000, statistical projections have been madeon the probable intensities of tropical cyclones for various return periods. The super cyclone ofOctober 29, 1999 (SC1999) appears to have a return period of about 50 years. The cyclones of1831, 1885 and possibly the one in 1895 could have been super cyclones. During the 19th century,there were 72 flooding events associated with cyclones, whereas in the 20th century therewere only 56 events. There was no observational evidence to suggest that there was an increaseeither in the frequency or intensity of cyclones or storm surges on the coast of Orissa. However,the impact of cyclones and surges is on the increase due to increase of population and coastalinfrastructure. 相似文献
966.
D. S. V. V. D. Prasad P. V. S. Rama Rao G. Uma S. Gopi Krishna K. Venkateswarlu 《Journal of Earth System Science》2005,114(4):437-441
Using the data of amplitude scintillations recorded at 244 MHz from the geostationary satellite, FLEETSAT (73‡E) at a low
latitude station, Waltair (17.7‡N, 83.3‡E, 20‡N dip), during the increasing sunspot activity period of 1997–2000, the effect
of the geomagnetic storms on the occurrence of ionospheric scintillations has been studied. A total of 60 SC storms studied
during this period, following the Aarons’ criterion, reveals that the local time of onset of the recovery phase of the geomagnetic
storms play an important role in the generation or inhibition of the ionospheric irregularities. Out of the 60 storms studied,
nearly 60 to 70% satisfied the categories I, II and III of Aarons’ criteria. However, in the remaining 30 to 40% of the cases,
no consistent results were observed. Thus, there is a necessity for further investigation of the effect of geomagnetic storms
on ionospheric irregularities, particularly with reference to the altitude variations of the F-layer (h’F) relating to the
changes in the local electric fields. 相似文献
967.
Over-exploitation of groundwater results in decline of water levels, leading to intrusion of salt water along the coastal
region, which is a natural phenomenon. A groundwater quality survey has been carried out to assess such phenomena along the
coast of Visakhapatnam, Andhra Pradesh, India. Brackish groundwaters are observed in most of the wells. The rest of the wells
show a fresh water environment. The factors responsible for the brackish groundwater quality with respect to the influence
of seawater are assessed, using the standard ionic ratios, such as Ca2+:Mg2+, TA:TH and Cl−:HCO−
3. Results suggest that the brackish nature in most of the groundwaters is not due to the seawater influence, but is caused
by the hydrogeochemical process. Some influence of seawater on the groundwater quality is observed along the rock fractures.
The combined effect of seawater and urban wastewaters is due to the inferior quality of groundwater in a few wells, where
they are at topographic lows close to the coast. 相似文献
968.
The Mahanadi River is one of the largest river systems in the east coast of Indiaand the estuary drains and communicates with the Bay of Bengal. The seasonallyvarying fresh water river discharge and the intrusion of salt water from the baydepend on the flow associated with the semi-diurnal component of the astronomicaltide (dominated by M2 component). A numerical model has been developed tosimulate and study the salinity structure, velocity profile, flow and circulation patternand have been compared with the observed data. A reasonably good agreement isnoticed between the model simulations and the observations. The model result hasbeen utilised to compute sediment load transport to the estuary channel over a tidalcycle as well as on a monthly time scale. The sediment load transport owing to monthlyclimatological rainfall is discussed and it is inferred that a dynamic equilibrium existson a long-term over good/bad monsoons. 相似文献
969.
970.