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21.
Subhash Lele 《Mathematical Geology》1993,25(5):573-602
Euclidean Distance Matrix Analysis (EDMA) of form is a coordinate free approach to the analysis of form using landmark data. In this paper, the problem of estimation of mean form, variance-covariance matrix, and mean form difference under the Gaussian perturbation model is considered using EDMA. The suggested estimators are based on the method of moments. They are shown to be consistent, that is as the sample size increases these estimators approach the true parameters. They are also shown to be computationally very simple. A method to improve their efficiency is suggested. Estimation in the presence of missing data is studied. In addition, it is shown that the superimposition method of estimation leads to incorrect mean form and variance-covariance structure. 相似文献
22.
We analyze the 26 November 2005 solar radio event observed interferometrically at frequencies of 244 and 611 MHz by the Giant Metrewave Radio Telescope (GMRT) in Pune, India. These observations are used to make interferometric maps of the event at both frequencies with the time cadence of 1 s from 06:50 to 07:12 UT. These maps reveal several radio sources. The light curves of these sources show that only two sources at 244 MHz and 611 MHz are well correlated in time. The EUV flare is more localized with flare loops located rather away from the radio sources. Using SoHO/MDI observations and potential magnetic field extrapolation we demonstrate that both the correlated sources are located in the fan structure of magnetic field lines starting from a coronal magnetic null point. Wavelet analysis of the light curves of the radio sources detects tadpoles with periods in the range P=10?–?83 s. These wavelet tadpoles indicate the presence of fast magnetoacoustic waves that propagate in the fan structure of the coronal magnetic null point. We estimate the plasma parameters in the studied radio sources and find them consistent with the presented scenario involving the coronal magnetic null point. 相似文献
23.
Here we report the statistical analysis of 160 isolated decimetric type III bursts, a majority of them (74%) having central frequency above 1000 MHz, observed in 8 flares by the spectrometer Phoenix. The most important finding of the detailed analysis is: 67% of all the bursts are reverse slope, 38% normal and 5% bi-directional. Also, we obtained the following results: (a) the best fits for the average half power duration and for the average drift rate as a function of frequency are given by t1/2=1.7×104f–0.60and /df/dt|=(0.09±0.03)f(1.35 ± 0.10), respectively; (b) the frequency range of most of the type III bursts is less than 250 MHz; (c) the number of bursts decreases with increasing starting frequency and flux; (d) peak flux decreases with increasing frequency. The relations obtained fit well for higher frequency observations. Assuming an improved density model and type III emission at 2ndharmonic, the beam parameters of type III bursts are determined. 相似文献
24.
A wide-band digital decimetric spectroscope is in the process of development at INPE (Brazil), in conjunction with a 9-m diameter polar mounted antenna. Initially, this spectroscope was operating over a narrow-band 1.6 ± 0.05 MHz in an analogue mode. Here we report a slow drifting 5.0 MHz s-1, narrow-band 1630-1580 MHz, split frequency solar burst lasting for about 15 s, observed on 15 June, 1991. The separation between the split components is 30 MHz, and the upper split frequency component is more intense than the lower split frequency component. These observed characteristics favour the hypothesis of conversion of plasma waves by combinational scattering on upgoing ion-sound waves in a magnetic loop. Existing strong electron density gradients across the magnetic field in the source region will reduce the free-free absorption of radiation at the fundamental frequency. In order to explain the observed temporal characteristics of the upper and lower split frequency components, the radiation has to propagate at some angle to the electron density gradient in the source region. Estimated physical parameters of the source and exciters are as follows: (i) maximum source size (height) 2 × 107 cm; (ii) velocity and length of ion-sound pulse 3.1 × 106 cm s-1 and 5 × 107 cm, respectively, and (iii) velocity of the exciter of plasma waves (electron or proton beam) 5 × 108 cm s-1.On leave from the Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia. 相似文献
25.
In previous attempts to show one-to-one correlation between type III bursts and X-ray spikes, there have been ambiguities as to which of several X-ray spikes are correlated with any given type III burst. Here, we present observations that show clear associations of X-ray bursts with RS type III bursts between 16:46 UT and 16:52 UT on July 9, 1985. The hard X-ray observations were made at energies above 25 keV with HXRBS on SMM and the radio observations were made at 1.63 GHz using the 13.7m Itapetinga antenna in R and L polarization with a time resolution of 3 ms. Detailed comparison between the hard X-ray and radio observations shows:
- In at least 13 cases we can identify the associated hard X-ray and decimetric RS bursts.
- On average, the X-ray peaks were delayed from the peak of the RS bursts at 1.6 GHz by ~ 400 ms although a delay as long as 1 s was observed in one case.
26.
Subhash Lele 《Mathematical Geology》1995,27(5):673-692
Two important problems in the practical implementation of kriging are: (1) estimation of the variogram, and (2) estimation of the prediction error. In this paper, a nonparametric estimator of the variogram to circumvent the problem of the precise choice of a variogram model is proposed. Using orthogonal decomposition of the kriging predictor and the prediction error, a method for selecting, what may be considered, a statistical neighborhood is suggested. The prediction error estimates based on this scheme, in fact, reflects the true prediction error, thus leading to proper coverage for the corresponding prediction interval. By simulations and a reanalysis of published data, it is shown that the proposals made in this paper are useful in practice. 相似文献
27.
Sankar Narayan Patra Koushik Ghosh Subhash Chandra Panja 《Astrophysics and Space Science》2011,334(2):317-323
In the present paper we have analyzed the daily Forbush decrease indices from January 1, 1967 to December 31, 2003. First
filtering the time series by Simple Exponential Smoothing, we have applied Scargle Method of Periodogram on the processed
time series in order to search for its time variation. Study exhibits periodicities around 174, 245, 261, 321, 452, 510, 571,
584, 662, 703, 735, 741, 767, 774, 820, 970, 1062, 1082, 1489, 1715, 2317, 2577, 2768, 3241 and 10630 days with confidence
levels higher than 90%. Some of these periods are significantly similar to the observed periodicities of other solar activities,
like solar filament activity, solar electron flare occurrence, solar-flare rate, solar proton events, solar neutrino flux,
solar irradiance, cosmic ray intensity and flare, spectrum of the sunspot, solar wind, southern coronal hole area and solar
cycle, which may suggest that the Forbush decrease behaves similarly to these solar activities and these activities may have
a common origin. 相似文献
28.
Kopparapu Vijaya Kumar Chakradhar Chavan Sariput Sawant K. Naga Raju Prachiti Kanakdande Sangita Patode Krishna Deshpande S. K. G. Krishnamacharyulu T. Vaideswaran V. Balaram 《Contributions to Mineralogy and Petrology》2010,159(6):839-862
Spatial and temporal variations in the geochemistry of an extrusive basaltic section of Deccan traps record progressive changes
in mantle melting and crustal filtration and are relevant to understand continental flood basalt (CFB) magmatism. In the present
work we have carried out detailed field, petrographic, density and magnetic susceptibility, and geochemical investigations
on a small, semi-continuous extrusive section in the eastern Deccan Volcanic Province (DVP) to understand the role of shallow
magma chambers in CFB magmatism. Four formations, Ajanta, Chikhli, Buldhana and Karanja crop out in the Gangakhed–Ambajogai
area with increasing elevation. Our studies indicate that: (1) the Karanja Formation represents a major magma addition, as
indicated by abrupt change in texture, increases in MgO, CaO, Ni, Cr, and Sr, and drastic decreases in Al2O3, Na2O, K2O, Rb, Ba, REE, bulk-rock density and magnetic susceptibility; (2) assimilation fractional crystallization, crystal-laden
magmas, and accessory cumulus phases influence the trace element chemistry of Deccan basalts; (3) the predicted cumulate sequence
of olivine gabbro–leucogabbro–oxide-apatite gabbro is supported by the observed layered series in a shallow magma chamber
within the DVP; (4) the initial magma was saturated with olivine, plagioclase, and augite, and final the pressure of equilibration
for the Gangakhed–Ambajogai section basalts is ~2 kbar (~6 km depth); (5) petrophysical parameters act as proxies for magmatic
processes; (6) a small layer of oxide-rich basalts may represent the latest erupted pulse in a given magmatic cycle in the
DVP; (7) parental basalts to some of the red boles, considered as formation boundaries, might represent small degree partial
melts of the mantle; (8) SW Deccan basaltic-types continue into the eastern DVP; and (9) in addition to the magma chamber
processes, dynamic melting of the mantle may have controlled DVP geochemistry. The present study underscores the importance
of mapping specific stratigraphic intervals in limited areas to understand mantle and magma chamber processes relevant to
CFB magmatism. 相似文献
29.
Zebrafish (Danio rerio) genetic screens allow isolation of a wide array of problems in vertebrate biology. The effects of base analogues 5-bromouracil
and 6-aminopurine on the development of zebrafish embryos are reported for the first time in this study. The early development
of the zebrafish embryos was little affected by 5-bromouracil and 6-aminopurine, while the late development (organogenesis)
was significantly impaired. Embryos exposed to 5-bromouracil mainly showed curled tail, wavy body, golden pigmentation and
the mouth with protruding lower jaw. 6-aminopurine-treated embryos had defective anterior structures, curled tails and wavy
body. RAPD analysis showed that the majority of 5-bromouracil- and 6-aminopurine-treated larvae and fish shared banding patterns
in common with the control, suggesting that most mutagenesis induced by these agents are point mutations. However, some fish
derived from 5-bromouracil-treated embryos had golden (gol) pigmentation; and RAPD analysis revealed that their band patterns differed from those of the control. Possibly, 5-bromouracil
can occasionally cause relatively extensive changes in the fish genome. The results of this study may provide valuable help
for detailed studies of mutagenesis.
This work was supported by Ministry of Science and Technology (MOST) of China (G 1999012005). 相似文献
30.
The mechanism of the double plasma resonance has been applied to the dot-like emission structures observed in the decimetric band. In particular, the existence of dot-emissions on definite trajectories in the dynamic spectra offers a rare opportunity to delineate the details of the double resonance mechanism as well as the diagnostics of the radio source and the ambient corona. The modeling of the chains of dots points to the excitation of the electron Bernstein modes predominantly at the second cyclotron harmonic and their subsequent coalescence to produce the observed dot-emissions. The coalescence process doubles the cyclotron harmonic number and thereby reduces the cyclotron absorption significantly. The discrete nature of the emissions results from the finite extent of the resonant region due to the presence of inhomogeneities. The determination of the relative scales of spatial variation of the magnetic field and the electron density in the region of the decimetric emission is particularly desirable as it has important consequences for the energy release, acceleration processes and the configuration of the participating plasma structures. 相似文献