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71.
Praveena Krishnan P. K. Kunhikrishnan S. Muraleedharan Nair Sudha Ravindran Radhika Ramachandran D. B. Subrahamanyam M. Venkata Ramana 《Journal of Earth System Science》2004,113(3):353-363
This paper discusses the observations of the Atmospheric Surface Layer (ASL) parameters during the solar eclipse of August
11th, 1999. Intensive surface layer experiments were conducted at Ahmedabad (23‡21′N, 72‡36′E), the western part of India,
which was close to the totality path. This rare event provided by nature is utilised to document the surface layer effects
during the eclipse period using measurements of high frequency fluctuations of temperature, tri-axial wind components as well
as mean parameters such as temperature, humidity, wind speed and subsoil temperature. Analysis showed that during the eclipse
period, the turbulence parameters were affected leading to the suppression of the turbulence process, the main dynamic process
in the atmospheric boundary layer, while the mean parameters showed variations within the natural variability of the observational
period. The spectra of the wind components and temperature indicated decrease in spectral power by one order in magnitude
during the eclipse period. The rate of dissipation of turbulent kinetic energy is found to decrease by more than one order
during the eclipse period. The stability parameter showed a change from unstable to stable condition during the period of
eclipse and back to unstable condition by the end of eclipse 相似文献
72.
The urban land cover mapping and automated extraction of building boundaries is a crucial step in generating three-dimensional city models. This study proposes an object-based point cloud labelling technique to semantically label light detection and ranging (LiDAR) data captured over an urban scene. Spectral data from multispectral images are also used to complement the geometrical information from LiDAR data. Initial object primitives are created using a modified colour-based region growing technique. Multiple classifier system is then applied on the features extracted from the segments for classification and also for reducing the subjectivity involved in the selection of classifier and improving the precision of the results. The proposed methodology produces two outputs: (i) urban land cover classes and (ii) buildings masks which are further reconstructed and vectorized into three-dimensional buildings footprints. Experiments carried out on three airborne LiDAR datasets show that the proposed technique successfully discriminates urban land covers and detect urban buildings. 相似文献
73.
Classification of remotely sensed images is a rich research field wherein techniques from conventional statistics to recent developments such as Artificial Neural Network, Fuzzy logic etc. has wide applications. Conventionally remotely sensed image classification referred to pixel classification based on broad categories such as vegetation and water bodies. With the availability of high-resolution imageries, shape analysis of macro structures contained in images becomes an important and difficult task. Although conventional statistical pattern recognition techniques give a reasonable result, Artificial neural network methods seem to be giving better results. In this paper, we give a survey of feed-forward neural network used for shape classification and a Hopfield model with an improved learning rule, for a typical shape analysis problem. 相似文献
74.
Antibiotic resistant pathogens versus human impacts: a study from three eco-regions of the Chennai coast, southern India 总被引:1,自引:0,他引:1
We assessed the occurrence of pollution indicators and antibiotic resistant bacterial isolates from water and sediment samples of three different eco-regions of the Chennai coast between March - May of 2010. Total of 960 bacterial strains belonging to four genera were isolated which show the highest frequencies of resistance to vancomycin (53.6%) and penicillin (52.6%) (except Enterococcus sp., which is highly resistant to erythromycin) and lowest frequencies of resistance to chloramphenicol (3.43%), ciprofloxacin (3.95%), gentamicin (4.68%), and tetracycline (6.97%). The E. coli, Vibrio sp., Salmonella sp. and Enterococcus sp. show high frequency of resistance to 2-5 antibacterials of 60.4%, 45.83%, 69.16% and 46.6%, respectively. High pollution indices (PI - 6.66-14.06) and antibiotic resistance indices (ARI - 0.29-0.343) indicate that the coastal environment is highly exposed to antibiotic sources that suggesting to avoid direct contact. 相似文献
75.
R. Krishnan Suchithra Sundaram P. Swapna Vinay Kumar D. C. Ayantika M. Mujumdar 《Climate Dynamics》2011,37(1-2):1-17
This paper examines an issue concerning the simulation of anomalously wet Indian summer monsoons like 1994 which co-occurred with strong positive Indian Ocean Dipole (IOD) conditions in the tropical Indian Ocean. Contrary to observations it has been noticed that standalone atmospheric general circulation models (AGCM) forced with observed SST boundary condition, consistently depicted a decrease of the summer monsoon rainfall during 1994 over the Indian region. Given the ocean?Catmosphere coupling during IOD events, we have examined whether the failure of standalone AGCM simulations in capturing wet Indian monsoons like 1994 can be remedied by including a simple form of coupling that allows the monsoon circulation to dynamically interact with the IOD anomalies. With this view, we have performed a suite of simulations by coupling an AGCM to a slab-ocean model with spatially varying mixed-layer-depth (MLD) specified from observations for the 1994 IOD; as well as four other cases (1983, 1997, 2006, 2007). The specification of spatially varying MLD from observations allows us to constrain the model to observed IOD conditions. It is seen that the inclusion of coupling significantly improves the large-scale circulation response by strengthening the monsoon cross-equatorial flow; leading to precipitation enhancement over the subcontinent and rainfall decrease over south-eastern tropical Indian Ocean??in a manner broadly consistent with observations. A plausible physical mechanism is suggested to explain the monsoonal response in the coupled frame-work. These results warrant the need for improved monsoon simulations with fully coupled models to be able to better capture the observed monsoon interannual variability. 相似文献
76.
77.
Smith P Krishnan P 《Population geography : a journal of the Association of Population Geographers of India》1994,16(1-2):23-32
"Data from the 1981 Census of Canada are used to develop a typology of migrants on the basis of their personal characteristics. Migrants are defined as those individuals who have changed their residence since the 1976 Census, crossing at least a municipal boundary. Socio-economic and demographic characteristics are perceived to differentiate stayers from movers, and to distinguish each migrant type [that is to say] intraprovincial, interprovincial and international. Discriminant analysis is applied to classify people into migrant types based on their personal characteristics and the typology developed." 相似文献
78.
Spatial Connectivity: From Variograms to Multiple-Point Measures 总被引:3,自引:0,他引:3
Anisotropy and curvilinearity are common characteristics of geological structures. Traditional measures of connectivity such as the variogram are rectilinear in that they do not take into account the curvilinearity of these structures. Recent developments in geostatistics have demonstrated and simulated the effect of curvilinearity and multiple-point (mp) connectivity on the output of transfer functions such as flow simulators. A set of curvilinear channels and set of elliptical lenses may share the same variogram and rectilinear connectivity but would yield different flow responses because of their different curvilinearity. A measure of curvilinearity generalizing the variogram measure is therefore proposed. The proposed measure is directional with a tolerance cone and depends on distance with a tolerance, as with an experimental variogram. 相似文献
79.
Muvva Venkata Ramana Praveena Krishnan P. K. Kunhikrishnan 《Boundary-Layer Meteorology》2004,111(1):153-157
Some characteristic features of the atmospheric surfacelayer over an inland tropical station, Lucknow (27°N, 81°E)in India, are investigated for different seasons using micrometeorological data collected at the 10-m levelof an instrumented tower. Seasonal monsoonal variations in wind circulation (north-easterliesand south-westerlies) dominate the flow over this part of the region. This study utilizesthe wind, temperature and humidity data obtained for a period of one year from February 1996 to January 1997. The diurnal variation of mean parameterssuch as temperature, relative humidity, and wind speed are studied for different seasonsnamely pre-, south-west, post- and north-east monsoon periods. Turbulent statistics are computedusing the eddy correlation technique, and are studied under the framework of Monin–Obukhov similarity theory with results compared with otherexperimental studies reported in the literature. It is found that the turbulence statistics arenearly independent of season and the near-neutral values of the normalized standard deviations ofthe three wind components, temperature and specific humidityare found to be 1.00 ± 0.04 (vertical), 2.63 ± 0.36(longitudinal), 2.19 ± 0.06 (lateral), 6.56 ± 0.33and 6.45 ± 0.33 respectively. 相似文献
80.
Preferred orientations of phyllosilicate grains in the shaley rocks of the Labrador Trough were studied using a pole-figure goniometer. Transmitted X-rays permit determination of the basal planes of chlorite and muscovite. From their preferred orientation, strain is calculated according to March's theory. By choosing samples in successively more strongly deformed domains, a strain history can be recognized which started with compaction by loss of pore volume under an overburden and was later followed by an early homogeneous tectonic shortening parallel to bedding and at a right angle to the fold axis. Buckling occurred next, with strain in the limbs becoming different from that in the hinges; the limbs were lengthened parallel to bedding and nearly normal to the fold axis. Continuing appression, finally, led to pervasive shortening normal to the axial plane with concurrent stretching both updip along the axial plane and along the fold axis. This latter stretching may have occurred when variable-plunge basin and dome structures of the Labrador Trough were formed. 相似文献