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91.
Relative abundances of carbon and aluminium with respect to silicon have been calculated in the QSOs PHL957, PKS0237-23, 1331+170, 3C191 and M132. Relative abundance of Fe with respect to Mg has been also calculated in the QSOs 1331+170 and PHL938. The ratiosN(C)/N(Si),N(Al)/N(Si) andN(Fe)/N(Mg) in QSOs considered as a class are (5.5±1.6), (0.13±0.03) and (2.6±1.2), respectively.The ratioN(C)/N(Si) shows a mild trend of increase with decreasing emission redshift. This suggests the possibility that the QSOs might be evolving chemically. 相似文献
92.
Parijat Thakur D.K. Chakraborty † 《Monthly notices of the Royal Astronomical Society》2001,328(1):330-338
The projected properties of some triaxial mass models are studied. The models are flattened versions of a set of spherical models. They are constructed by addition of two spherical harmonic terms to a spherical model. The projected properties exhibit strong correlations, when a model with a given set of intrinsic parameters is viewed in all possible orientations. The correlation plots appear to carry signatures of the intrinsic shape of the mass model. Rigorous shape estimates, using Bayesian statistics, yield satisfactory results for the test cases. 相似文献
93.
River bank erosion hazard study of river Ganga,upstream of Farakka barrage using remote sensing and GIS 总被引:1,自引:0,他引:1
This study has been carried out to analyze and report the river bank erosion hazard due to morphometric change of the Ganga
River (also called Ganges in English) in the upstream of Farakka Barrage up to Rajmahal. Morphometric parameters, such as,
Sinuosity, Braidedness Index, and percentage of the island area to the total river reach area were measured for the year of
1955, 1977, 1990, 2001, 2003, and 2005 from LANDSAT and IRS satellite images. The analysis shows that there is a drastic increase
in all of those parameters over the period of time. This study has found that bank failure is because of certain factors like
soil stratification of the river bank, presence of hard rocky area (Rajmahal), high load of sediment and difficulty of dredging
and construction of Farakka Barrage as an obstruction to the natural river flow. For the increasing sinuosity, the river has
been engulfing the large areas of left bank every year. The victims are mostly Manikchak and Kaliachak-II blocks of Malda
district, with a loss of around 1,670 ha agricultural land since 1977. Temporal shift measurements for the river reach between
Farakka and Rajmahal has been done with help of 22 cross-sections in this reach. Erosion impact area has also been estimated
to emphasize the devastating nature of the hazard. 相似文献
94.
The 20 October 1991 Uttarkashi earthquake killed over a thousand people and caused extensive damage to property in the Garhwal Himalaya region. The body wave magnitude of the earthquake was 6.6, and the fault plane solution indicates reverse faulting. The hypocenrre was located at a focal depth of about 12 km between the Chail and Jutogh Thrusts, but movement propagated southward along the Jamak–Gangori Fault (JGF) and Dunda fault (DF) which are developed as blind faults related to the growing Uttarkashi antiform. 相似文献
95.
The integral balance method has been used to obtain an approximate analytical solution of a nonlinear boundary value problem which arises in the theory of diffusion with a concentration-dependent coefficient. It is the purpose of this paper to give an interpretation of the supposition of interface reactions which obey the law of kinetic mass action.Nomenclature
C(Z,t)
concentration
-
C
0
concentration at initial time
-
D
diffusivity
-
D
0
diffusivity at initial time
-
F(t)
a function of time
-
K
0
half-order reaction rate constant
-
k
1
first-order reaction rate constant
-
k
2
second-order reaction rate constante
-
L
characteristic length
-
n
parameter
-
t
time
-
Z
space variable
Dimensionless variables and similarity criteria
nondimensional half-order reaction rate constant
-
nondimensional first-order reaction rate constant
-
nondimensional second-order reaction rate constant
-
x=Z/L
dimensionless space variable
-
F
0=D
0
t/L
2
Fourier number
-
g(F
0)=[F(t)–C
0]/C
0
a function of generalized time
- (x, F
0)=[C(x,t)–C
0]/C
0
dimensionless concentration
- <(F
0)>
dimensionless average concentration 相似文献
96.
R. K. Thakur 《Astrophysics and Space Science》1992,190(2):281-292
Within the framework of FLRW cosmology withk=+1 a singularity free model of the Universe is proposed which readily accounts for the origin of the Big-Bang and for the preponderance of matter over anti-matter. It is also free from the problems of accounting for the observed large-scale homogeneity and isotropy of the Universe as well as from the problems of horizon and flatness. It is pointed out that the collapsing universe might have acted as an ultra-high energy particle accelerator. In the collapsing phase of the Universe, when the interparticle distances10–16 cm, the electromagnetic and weak interactions might have unified into electroweak interaction and as the collapse proceeded further the entire matter in the Universe might have been converted into quark-gluon plasma permeated by leptons. The gravitational energy released during the collapse might have been locked in this plasma. Ass approached 10–28 cm, grand unification of electroweak and strong interactions might have occurred. It is also suggested that, with further collapse, whens<10–33 cm super-symmetry (SUSY)—i.e., the unification of all the four interactions (viz., electromagnetic, weak, strong, and gravitational) might have occurred. During this process gravitinos, the supersymmetric partners of graviton might have been produced. As a result of the exchange of a pair of virtual gravitinos between two particles an ultra-strong repulsive force between them might have been generated. Due to this ultra-strong repulsive interaction between particles the motion of the Universe might have been reversed, i.e., the Universe might have started expanding. During expansion, whens10–28 cm, SUSY might have broken down spontaneously toSU
5 and gravity. Ass increased from 10–28 to 10–16 cm, the gravitational energy locked in the quark-gluon plasma might have been released with a gigantic explosion, the so-called Big-Bang. It is estimated here that during this Big-Bang more than 1082 GeV of energy might have been released. Whens10–16 cm,SU
5 might have broken down spontaneously toSU
3 andU
1. Expansion beyond this stage might have occurred in the manner described by the standard cosmology. It is further suggested that in due course of time expansion will be followed by contraction and the cycle of contraction-expansion-contraction will be repeated ad infinitum. 相似文献
97.
In seismic sections, the presence of a gas hydrate stability zone (GHSZ) is often marked by a bottom-simulating reflector, which has a negative polarity with respect to the seafloor. The present study reveals the response of seismic wave characteristics and amplitude versus offset (AVO) effects of large offset compressional (P) and converted (PS) waves for a GHSZ/free-gas configuration, using a two-dimensional elastic anisotropic modelling technique. The modelling results would provide a priori information, which allows unique determination of parameters of seismic models for the design of ocean bottom seismometer experiments over continental margins for the purpose of gas hydrate exploration. The AVO analyses on long offset P and PS waves based on synthetic data yield a typical gas hydrate/free-gas response, as the reflectivity increases with incidence angle. 相似文献
98.
In order to see whether the study of redshift distribution in different classes of extragalactic objects, suspected of belonging to different phases in the evolutionary sequence of galaxies, helps in arriving at a possible picture of the evolutionary sequence of galaxies, histograms have been plotted between the number and the redshift for each of the five classes of extragalactic objects, namely, the QSOs, N-galaxies, Seyfert galaxies, radio galaxies and normal galaxies. It is found that: (i) the highest peaks in the five histograms occur at distinctly different redshifts in the order (Z
peak)QSOs>(Z
peak)N-galaxies>(Z
peak)Seyfert galaxies>(Z
peak)radio galaxies> (Z
peak)normal galaxies and (ii) sufficient overlap occurs in the redshift ranges of (a) QSOs and N-galaxies, (b) N-galaxies and Seyfert galaxies, (c) Seyfert galaxies and radio galaxies and (d) radio galaxies and normal galaxies. These facts suggest that the extragalactic objects might be evolving in the sequence: QSOsN-galaxiesSeyfert galaxiesradio galaxiesnormal galaxies. Other independent evidences in support of such an evolutionary sequence have been given. Finally, various aspects of the problem associated with the picture of the evolutionary sequence of galaxies have been critically examined. 相似文献
99.
A geometrical study is made of magnetohydrostatic equilibrium of a perfectly conducting fluid considering magnetic field vector, constant along each current line. We have discussed the geometrical behaviour of Lorentz surfaces, field lines and current lines.Former address: Department of Mathematics, Banaras Hindu University, Varanasi, India. 相似文献
100.
Naresh Kumar Thakur Pasupuleti Prasada Rao N. Vishwanath Sanjeev Rajput Bhaskarabhatla Ashalatha 《Marine Geophysical Researches》2007,28(4):373-378
Seismic tomography is an effective means of estimating velocity and structure from multichannel seismic (MCS) reflection data.
In this study we have followed a 2D approach to arrive at the probable velocity field configuration from multichannel seismic
data and infer the presence of gas hydrates/free-gas in the offshore Kerala-Konkan region, along the eastern part of a seismic
line on which a bottom simulating reflector (BSR) has previously been identified. Tomographic modeling consists of the identification
of reflection phases and picking of respective travel times for various source-receiver positions. These picks were then utilized
to arrive at a 2D velocity field following a forward and inversion approach using a ray tracing technique. The modeling for
the first time brought out the finer scale velocity structure under the region of investigation. Modeling through the 2D approach
shows lateral variation in velocity field along the studied segment of the seismic line. The results indicate a thin (∼50–60 m)
sedimentary cover with velocity ranging from 1,770 to 1,850 m/s. A sedimentary layer with high P-wave velocity 1,980–2,100 m/s
below the sea floor was interpreted as the hydrate layer. The thickness of this layer varies between 110 and 140 m. The hydrate
layer is underlain by a low-velocity layer having velocities in the range 1,660–1,720 m/s. This low velocity may represent
a free gas layer, whose thickness varies between 50 and 100 m located below the hydrated layer. The investigation suggests
the occurrence of gas hydrate underlain by free gas in some parts of the Kerala-Konkan offshore region. 相似文献