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41.
This paper presents a comparison of a granular material studied experimentally and numerically. Simple shear tests were performed inside the magnetic core of magnetic resonance imaging (MRI) equipment. Spherical pharmaceutical pills were used as the granular material, with each pill's centre location determined by MRI. These centre locations in the initial assembly were then used as the initial configuration in the numerical simulation using the discrete element method. The contact properties between pharmaceutical pills used in the numerical simulation were obtained experimentally. The numerical predication was compared with experimental data at both macroscopic and microscopic levels. Good agreement was found at both levels. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
42.
We compare the initial behavior of Fe/O and He/H abundance ratios and their relationship to the evolution of the proton energy spectra in "small" and "large" gradual solar energetic particle (SEP) events. The results are qualitatively consistent with the behavior predicted by the theory of Ng et al. published in 1999. He/H ratios that initially rise with time are a signature of scattering by non-Kolmogorov Alfvén wave spectra generated by intense beams of shock-accelerated protons streaming outward in large gradual SEP events. 相似文献
43.
D. N. Mungai C. J. Stigter C. L. Coulson J. K. Ng’ang’a 《Theoretical and Applied Climatology》2000,65(1-2):63-78
Summary Global radiation, soil temperature and soil moisture data were obtained from a 4–6 year old Cassia siamea/maize (CM) alley cropping (or hedgerow intercropping) system, at a semi-arid site at Machakos, Kenya, in the late eighties.
With the growing need to explore and manage variations in agro-ecosystems these results deserve new attention. They quantify,
in a simple but detailed manner, the influence of hedgerows on the microclimate of their intercrop and for comparison provide
a sole maize (SM) control. Due to inhomogeneity of Cassia and maize, as well as limited budgets, the sampling methodology
and the choice of appropriate equipment, including the sensors, demanded special attention. The diurnal patterns of soil temperatures
at 7.5 cm depth represented well the shading patterns of the hedgerows. This can be developed into an operational auxiliary
methodology of integrated shade quantification. With proper precautions, the developed sampling methodologies showed appropriately
the time integrated values of the three microclimatic parameters with enough detail to understand yield differences between
treatments and between rows. This approach may therefore be recommended for on-farm quantification of even greater spatial
variability of parameters. The limitations of the selected methods are highlighted. Experiences with some alternative methods
are also discussed.
Received September 2, 1998/Revised June 28, 1999 相似文献
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This paper describes a benchmark problem for a floating stone columns supported embankment. In the 3D model, a thick soft subsoil deposit represented by Singapore marine clay was treated by floating stone columns to support a 2.0 m high embankment. The 3D numerical results were compared among different constitutive models such as the hardening soil model, soft soil model, modified Cam-clay model and Mohr-Coulomb model, highlighting the effect of non-linearity in the overall performance of the ground structure. The advanced constitutive soil models allow more realistic soil response to be investigated. From the numerical results, the Mohr-Coulomb model with elastic-perfectly plastic stress-strain response was able to give comparable total settlements but failed to demonstrate some intrinsic behaviours obtained with advanced soil models. These intrinsic behaviours include the mode of failure, displacements profile, stress transfer mechanism and rate of consolidation. This benchmark example has given us an improved understanding of the performance of floating stone columns when a more realistic soil behaviour is modelled. 相似文献
49.
Ng. Ibohal Singh 《Astrophysics and Space Science》1988,148(2):199-205
A slow rotation perturbation of Robertson-Walker universes filled with perfect fluid has been investigated. It is found that the unit-four vector of perfect fluid hasno angular velocity in the perturbed cosmological models. The slow rotation which is related to the dragging of the local inertial frames, is compatible only with the cases of positive and negative curvatures of the cosmological universe. The intrinsic velocity vector field of the Universe isexpanding as well asshearing. 相似文献
50.
A new computer program (CONBAL-2) is developed for 2D numerical simulations of granular soil by random arrays of spheres. CONBAL-2 uses the discrete-element method and is based on 3D program TRUBAL, previously presented by Cundall. As in TRUBAL, the new program models a random array of elastic spheres in a periodic space. The main modification of TRUBAL is the implementation by the authors of a rigorous solution for the force–displacement relation at the interparticle contacts. This force-displacement relation is a function of the elastic constants, friction coefficient and sizes of the spheres, with the properties of quartz used to simulate sand. Other specific features of CONBAL-2 include its 2D character, the lack of particle rotation and its capability to simulate shear loading on any plane. Simulated laboratory test results are presented using CONBAL-2 and several random arrays of 531 spheres having two particle sizes. These simulations include monotonic loading drained and undrained (constant volume) ‘triaxial’ experiments, as well as a cyclic-loading, constant-volume ‘torsional shear’ test. The stress–strain curves, effective stress paths, volume changes, as well as the ‘pore water pressure’ build-up behaviour obtained in the simulations compare favourably—qualitatively and in some aspects quantitatively—with similar laboratory results on sands. However, the simulated soil is somewhat stiffer and stronger due to the perfectly rounded particles, limited range of grain sizes, lack of particle rotation and 2D character of the model. 相似文献