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排序方式: 共有105条查询结果,搜索用时 62 毫秒
81.
岩石力学试验中试样选择和抗压强度预测方法研究 总被引:6,自引:0,他引:6
岩石力学试验是岩石力学的基础,是研究岩石力学与工程的重要手段之一,但岩石力学试验的结果往往要受到很多因素的影响,试验结果的离散是普遍存在的,有时可能会得到完全相反的结论。以超声波传播速度、回弹值与岩石强度之间相互关系为基础,综合两种方法的优点,把超声-回弹综合法应用到岩石试样选择中,在正式试验之前,挑出那些可能会使试验结果很离散的试样,可以提高室内试验的测试准确程度。实践表明,这种综合选样方法具有较好的适用性,对有缺陷的试样有较好的识辨能力,而且方便、快速、对试样没有损伤,同时,超声-回弹综合法可以较好地预测岩石的抗压强度。因此,这种综合方法在岩石试样选择和强度预测中值得借鉴。 相似文献
82.
Bianchi Type I magnetized string cosmological model following the techniques used by Letelier and Stachel, is investigated.
To get a determinate model, we assume a condition ∊ = λ (geometric string) where ∊ is the rest energy density, λ the string
tension density and expansion (θ) is proportional to eigen value σ1
1 of shear tensor (σ
j
i
), which leads to A = ℓ (BC)
n
where A, B, C are metric potentials and ℓ and n are constants. The behaviour of the model in presence and absence of magnetic field is discussed. The physical and geometrical
aspects of the model are also discussed. 相似文献
83.
S. Nesslinger H. Drechsel R. Lorenz P. Harmanec P. Mayer M. Wolf 《Astrophysics and Space Science》2006,301(1-4):47-49
A Cosmological model with a viscous fluid in Kaluza-Klein metric is obtained assuming a time-dependent equation of state.
The solution is in fact a generalization of an earlier work by Hajj and Boutros for a perfect fluid. It is also found that
dimensional reduction of the extra space takes place such that the five-dimensional universe naturally evolves into an effective
four-dimensional one. The dynamical behavior of the model is examined and it is also found that with a decrease in extra space
the observable 3D space entropy increases thus accounting for the large value of entropy observable at present. 相似文献
84.
Corrado Massa 《Astrophysics and Space Science》2007,310(3-4):209-210
The generalized Buchdahl inequality in the presence of a positive cosmological constant gives rise to a constraint on the
mass density of celestial bodies. We find that such a constraint implies an upper bound on the mass and radius of spherical
celestial bodies born from macroscopic superstrings. We obtain a maximal mass of about 1015 solar masses and a maximal radius of about 80 million light years, not far from the observed mass and size of the largest
structures in the universe, viz. the superclusters of galaxies. 相似文献
85.
Marcelo Samuel Berman 《Astrophysics and Space Science》2007,310(3-4):205-207
We find a solution for exponential inflation in Brans–Dicke cosmology endowed with a cosmological term, which includes time-varying
shear and vorticity. We find that the scalar field and the scale factor increase exponentialy while shear, vorticity, energy
density, cosmic pressure and the cosmological term decay exponentialy for negative beta, where beta is defined in the text. 相似文献
86.
An axially symmetric Bianchi type-I space-time is considered in the presence of perfect fluid source in the scale-covariant
theory of gravitation formulated by Canuto et al. [1977a, Phys. Rev. Lett. 39, 429]. With the help of special law of variation for Hubble’s parameter proposed by Bermann [1983, Nuovo Cimento 74B, 182] a cosmological model with a negative constant declaration parameter is obtained in this theory. Some physical properties
of the model are also discussed. 相似文献
87.
This study presents the first unequivocal identification of natural radiation-induced defects in illites. Middle Proterozoic
illites related to unconformity-type uranium deposits of Canada and Australia were studied using electron paramagnetic resonance
(EPR) spectroscopy at X- and Q-band frequencies. The saturation behaviour of EPR spectra as a function of power demonstrates
that native defects of illites are different from those known in other clays as kaolinite, dickite or smectite. Q-band spectra
indicate the presence of several––at least two––native defects. The EPR signal is dominated by an axially distorted spectrum
with apparent principal components as follows: g
∥ = 2.032 and g
⊥ = 1.993. The corresponding defect is named as Ai center. The study of oriented specimen confirms the strong anisotropy, and shows that the main defect has its g
∥ component perpendicular to the (ab) plane of illite. These defects in illite correspond to electron holes located on oxygen
atoms of the structure and likely associated to Si, according to the lack of hyperfine structure. The Ai center in illite has similar EPR parameters to the A center in kaolinite and dickite. The isochronal annealing data suggest
that illite can be used as a dosimeter in the geosphere. However, the determination of half-life and activation energy of
the Ai center requires additional work. 相似文献
88.
Bianchi Type I string dust cosmological models in presence and absence of magnetic field following the techniques used by
Letelier and Stachel, are investigated. To get the deterministic solution, we have assumed that σ
11 is proportional to the expansion (θ) where σ
11 is the eigen value of shear tensor (σ
i
j
) and which leads to A=N(BC)−n
, n>0 where A,B,C are metric potentials and
, N and ℓ are constants. The behaviour of the models in presence and absence of magnetic field are discussed. The other physical and
geometrical aspects of the model are also discussed. 相似文献
89.
C. P. Singh 《Astrophysics and Space Science》2009,323(2):197-203
In this paper we consider a locally-rotationally-symmetric (LRS) Bianchi type-V perfect fluid model with variable cosmological
‘constant’ representing the energy density of vacuum. The field equations are solved with and without heat conduction by using
a variation law for the mean Hubble parameter, which is related to the average scale factor of the metric and yields a constant
value of the deceleration parameter. A constant value of deceleration parameter generates power-law form of average scale
factor which is used to find the exact solutions with and without heat conduction with decaying vacuum density. The solutions
presented here satisfy all the necessary conditions for the physically acceptability. The thermodynamical relations in decaying
vacuum fluid model are also studied in detail. 相似文献
90.
Mathieu Duttine Gérard Villeneuve Françoise Bechtel Gérard Demazeau 《Comptes Rendus Geoscience》2002,334(13):949-955
Natural quartz crystals coming from Madagascar, Angola, Brazil, and Spain were studied by EPR after β irradiation in order to characterise the paramagnetic centres due to impurities, and examine in which way their relative proportion could constitute a useful criterion for origin researches. In all our samples, EPR experiments revealed germanium centres [GeO4/M+]° with M = Li or Na, aluminium ones [AlO4/h]° and two titanium centres ([TiO4/H+]° and [TiO4/M+]°) also appeared, except for samples coming from Spain. The comparison of the relative concentrations of paramagnetic species led us on to draw diagrams that allowed distinguishing the origins of the studied samples using only EPR spectra. To cite this article: M. Duttine et al., C. R. Geoscience 334 (2002) 949–955. 相似文献