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161.
Three‐dimensional time‐harmonic fundamental solutions for a fluid‐saturated poroelastic half‐space with partially permeable free surface
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By virtue of a pair of scalar potentials for the displacement of the solid skeleton and the pore fluid pressure field of a saturated poroelastic medium, an alternative solution method to the Helmholtz decomposition is developed for the wave propagation problems in the framework of Biot's theory. As an application, a comprehensive solution for three‐dimensional response of an isotropic poroelastic half‐space with a partially permeable hydraulic free surface under an arbitrarily distributed time‐harmonic internal force field and fluid sources is developed. The Green's functions for the poroelastic fields, corresponding to point, ring, and disk loads, are reduced to semi‐infinite complex‐valued integrals that can be evaluated numerically by an appropriate quadrature scheme. Analytical and numerical comparisons are made with existing elastic and poroelastic solutions to illustrate the quality and features of the solution. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
162.
Two-dimensional hydraulic fracturing simulations using the cohesive zone model (CZM) can be readily found in the literature; however, to our knowledge, verified 3D cohesive zone modeling is not available. We present the development of a 3D fully coupled hydro-mechanical finite element method (FEM) model (with parallel computation framework) and its application to hydraulic fracturing. A special zero-thickness interface element based on the CZM is developed for modeling fracture propagation and fluid flow. A local traction-separation law with strain softening is used to capture tensile cracking. The model is verified by considering penny-shaped hydraulic fracture and plain strain Kristianovich‑Geertsma‑de Klerk hydraulic fracture (in 3D) in the viscosity- and toughness-dominated regimes. Good agreement between numerical results and analytical solutions has been achieved. The model is used to investigate the influence of rock and fluid properties on hydraulic fracturing. Lower stiffness tip cohesive elements tend to yield a larger elastic deformation around the fracture tips before the tensile strength is reached, generating a larger fracture length and lower fracture pressure compared with higher stiffness elements. It is found that the energy release rate has almost no influence on hydraulic fracturing in the viscosity-dominated regime because the energy spent in creating new fractures is too small when compared with the total input energy. For the toughness-dominated regime, the released energy during fracturing should be accurately captured; relatively large tensile strength should be used in order to match numerical results to the asymptotic analytical solutions. It requires smaller elements when compared with those used in the viscosity-dominated regime. 相似文献
163.
Ahmad Norazhar Mohd YATIM Mohd Talib LATIF Fatimah AHAMAD Md Firoz KHAN Mohd Shahrul Mohd NADZIR Liew JUNENG 《大气科学进展》2019,36(12):1355-1370
This study investigates the recent extreme temperature trends across 19 stations in the Klang Valley, Malaysia, over the period 2006-16. Fourteen extreme index trends were analyzed using the Mann-Kendall non-parametric test, with Sen’s slope as a magnitude estimator. Generally, the annual daily mean temperature, daily mean maximum temperature, and daily mean minimum temperature in the Klang Valley increased significantly, by 0.07°C yr~(-1), 0.07°C yr~(-1)and 0.08°C yr~(-1),respectively. For the warm temperature indices, the results indicated a significant upward trend for the annual maximum of maximum temperature, by 0.09°C yr~(-1), and the annual maximum of minimum temperature, by 0.11°C yr~(-1). The results for the total number of warm days and warm nights showed significant increasing trends of 5.02 d yr~(-1)and 6.92 d yr~(-1),respectively. For the cold temperature indices, there were upward trends for the annual minimum of maximum temperature,by 0.09°C yr~(-1), and the annual minimum of minimum temperature, by 0.03°C yr~(-1), concurrent with the decreases in the total number cold days (TX10P), with-3.80 d yr~(-1), and cold nights (TN10P), with-4.33 d yr~(-1). The 34°C and 37°C summer days results showed significant upward trends of 4.10 d yr~(-1) and 0.25 d yr~(-1), respectively. Overall, these findings showed upward warming trends in the Klang Valley, with the minimum temperature rate increasing more than that of the maximum temperature, especially in urban areas. 相似文献
164.
Mudimu George T. Zuo Ting Shah Ashfaq Ahmad Nalwimba Nkumbu Ado Abdou Matsalabi 《GeoJournal》2021,86(6):2927-2943
GeoJournal - Despite the Zimbabwean State’s narrative and discourse that in fast track land reform areas ‘land leasing is illegal’, there is a surge in land leasing. This article... 相似文献
165.
Shah Ashfaq Ahmad Wu Wenya Gong Zaiwu Pal Indrajit Khan Jahangir 《Natural Hazards》2021,105(2):1977-2005
Natural Hazards - Children spend more than two-thirds of their total daytime in schools and becoming more persuasive in shielding them from potential hazards. Schools have a responsibility to... 相似文献
166.
Khanday Suhail Ahmad Hussain Monowar Das Amit Kumar 《Geotechnical and Geological Engineering》2021,39(8):5429-5443
Geotechnical and Geological Engineering - Peat is a problematic or weak soil derived from fossilized organic material. The characteristics of peat like low shear strength (3–16 kPa),... 相似文献
167.
Ahmad Neyamadpour W. A. T. Wan Abdullah Samsudin Taib 《Journal of Earth System Science》2010,119(1):27-40
The objective of this paper is to investigate the applicability of artificial neural networks in inverting quasi-3D DC resistivity
imaging data. An electrical resistivity imaging survey was carried out along seven parallel lines using a dipole-dipole array
to confirm the validation of the results of an inversion using an artificial neural network technique. The model used to produce
synthetic data to train the artificial neural network was a homogeneous medium of 100Ωm resistivity with an embedded anomalous
body of 1000Ωm resistivity. The network was trained using 21 datasets (comprising 12159 data points) and tested on another
11 synthetic datasets (comprising 6369 data points) and on real field data. Another 24 test datasets (comprising 13896 data
points) consisting of different resistivities for the background and the anomalous bodies were used in order to test the interpolation
and extrapolation of network properties. Different learning paradigms were tried in the training process of the neural network,
with the resilient propagation paradigm being the most efficient. The number of nodes, hidden layers, and efficient values
for learning rate and momentum coefficient have been studied. Although a significant correlation between results of the neural
network and the conventional robust inversion technique was found, the ANN results show more details of the subsurface structure,
and the RMS misfits for the results of the neural network are less than seen with conventional methods. The interpreted results
show that the trained network was able to invert quasi-3D electrical resistivity imaging data obtained by dipole-dipole configuration
both rapidly and accurately. 相似文献
168.
We derive the cosmic energy equation for the non-point mass system of galaxies (galaxies with halos) by using the adiabatic
approximation for the growth of gravitational clustering of galaxies in the expanding Universe. The cosmic energy equation
so derived represents the general form of conservation of energy for the expanding volume. Using the derived form of cosmic
energy equation we try to study the evolution of correlation potential energy of the system. We also try to explore the condition
under which the approximation of extensivity may be applied to the infinite gravitating non-point mass system of galaxies. 相似文献
169.
Ahmad Rami El-Nabulsi 《Astrophysics and Space Science》2010,325(2):149-152
We investigate the cosmological dynamics of a four-dimensional Friedmann–Robertson–Walker homogenous and isotropic universe from Gauss–Bonnet higher-order curvature corrections, together with nonminimal coupling and with an infrared effective action of gravity based on a second-order gauge formulation for the Lorentz group. We study the evolution of the universe in such a model, identifying its key properties. Many new interesting features are revealed and discussed in some detail. 相似文献
170.
The Reshian-Lamnian area within the Hazara-Kashmir syntaxis in Pakistan is composed mainly of the rocks of the Salkhala, Panjal
and Murree formations. Base metal sulfide mineralization in the form of sphalerite and galena with lesser amounts of chalcopyrite
and pyrite is present within the Salkhala Formation of the study area. Chemically all these ore phases are homogeneous in
composition. The Pb isotopic composition of galena from the area suggests that there is very little or negligible variation
in the ratios of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb. Modal ages ranging from 509 to 562 Ma and the μ values of 10.71 to 10.93 have been calculated for the studied Pb-Zn mineralization.
On the basis of field features, mineralogy and Pb-isotope signatures, it is concluded that the Pb-Zn sulfide mineralization
in the Reshian-Lamnia area is pre-Himalayan in age and can be correlated with the Cambro-Ordovician (Pan-African) orogenic
event. 相似文献