全文获取类型
收费全文 | 205篇 |
免费 | 3篇 |
专业分类
测绘学 | 22篇 |
大气科学 | 14篇 |
地球物理 | 33篇 |
地质学 | 89篇 |
海洋学 | 3篇 |
天文学 | 40篇 |
自然地理 | 7篇 |
出版年
2022年 | 2篇 |
2021年 | 6篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 17篇 |
2017年 | 16篇 |
2016年 | 20篇 |
2015年 | 12篇 |
2014年 | 17篇 |
2013年 | 14篇 |
2012年 | 5篇 |
2011年 | 15篇 |
2010年 | 8篇 |
2009年 | 12篇 |
2008年 | 9篇 |
2007年 | 3篇 |
2006年 | 6篇 |
2005年 | 4篇 |
2004年 | 5篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1996年 | 2篇 |
1993年 | 3篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1984年 | 5篇 |
1981年 | 1篇 |
1974年 | 1篇 |
1973年 | 4篇 |
1971年 | 3篇 |
排序方式: 共有208条查询结果,搜索用时 62 毫秒
1.
The kinetic Alfven waves in the presence of homogeneous magnetic field plasma with multi-ions effect are investigated. The dispersion relation and normalised damping rate are derived for low-\(\beta\) plasma using kinetic theory. The effect of density variation of \(\text{H}^{+}\), \(\text{He}^{+}\) and \(\text{O}^{+}\) ions is observed on frequency and damping rate of the wave. The variation of frequency (\(\omega\)) and normalised damping rate (\(\gamma / \varOmega_{H^{ +}} \)) of the wave are studied with respect to \(k_{ \bot} \rho_{j}\), where \(k_{ \bot} \) is the perpendicular wave number, \(\rho_{j}\) is the ion gyroradius and \(j \) denotes \(\text{H}^{+}\), \(\text{He}^{+}\) and \(\text{O}^{+}\) ions. The variation with \(k_{ \bot} \rho_{j}\) is considered over wide range. The parameters appropriate to cusp region are used for the explanation of results. It is found that with hydrogen and helium ions gyration, the frequency of wave is influenced by the density variation of \(\text{H}^{+}\) and \(\text{He}^{+}\) ions but remains insensitive to the change in density of \(\text{O}^{+}\) ions. For oxygen ion gyration, the frequency of wave varies over a short range only for \(\text{O}^{+}\) ion density variation. The wave shows damping at lower altitude due to variation in density of lighter \(\text{H}^{+}\) and \(\text{He}^{+}\) ions whereas at higher altitude only heavy \(\text{O}^{+}\) ions contribute in wave damping. The damping of wave may be due to landau damping or energy transfer from wave to particles. The present study signifies that the both lighter and heavier ions dominate differently to change the characteristics of kinetic Alfven wave and density variation is also an important parameter to understand wave phenomena in cusp region. 相似文献
2.
Shamik Ghosh Pankaj Jain Gopal Kashyap Rahul Kothari Sharvari Nadkarni-Ghosh Prabhakar Tiwari 《Journal of Astrophysics and Astronomy》2016,37(4):25
There currently exist many observations which are not consistent with the cosmological principle. We review these observations with a particular emphasis on those relevant for the Square Kilometre Array (SKA). In particular, several different data sets indicate a preferred direction pointing approximately towards the Virgo cluster. We also observe a hemispherical anisotropy in the Cosmic Microwave Background radiation (CMB) temperature fluctuations. Although these inconsistencies may be attributed to systematic effects, there remains the possibility that they indicate new physics and various theories have been proposed to explain them. One possibility, which we discuss in this review, is the generation of perturbation modes during the early pre-inflationary epoch, when the Universe may not obey the cosmological principle. Better measurements will provide better constraints on these theories. In particular, we propose measurement of the dipole in number counts, sky brightness, polarized flux and polarization orientations of radio sources. We also suggest test of alignment of linear polarizations of sources as a function of their relative separation. Finally we propose measurement of hemispherical anisotropy or equivalently dipole modulation in radio sources. 相似文献
3.
Doklady Earth Sciences - Kaladgi rocks are very well exposed in Belgaum district of Karnatak state, with adjacent to Maharashtra state. The rocks exposed in the study area comprises mainly of... 相似文献
4.
5.
Triaxial shear testing of polished slickensided surfaces 总被引:1,自引:1,他引:0
Christopher L. Meehan Binod Tiwari Thomas L. Brandon J. Michael Duncan 《Landslides》2011,8(4):449-458
A series of consolidated-drained triaxial tests were performed on precut and polished clay specimens to measure their drained
residual strength. Two soils were tested during this research program: Rancho Solano Clay and San Francisco Bay Mud. Specimens
were tested using a specially modified triaxial compression device which was developed to minimize the effects of end-platen
restraint on the measured strengths. Special attention was paid to the influence of changing specimen area and membrane effects
during the test. Triaxial test results were compared with baseline measurements of drained residual shear strength that were
made for each of the clay soils using Bromhead ring shear tests and polished-specimen direct shear tests. Residual strength
values measured in the triaxial device were higher than the drained residual strengths measured in the Bromhead ring shear
apparatus and the direct shear device, indicating that this test approach is more challenging than the use of direct shear
tests conducted on polished slickensided surfaces. Comparison of single stage and multistage triaxial test data indicates
that multistage triaxial testing may work well for specimens that fail along a well-defined plane, provided that careful attention
is given to the effects of end platen restraint, membrane restraint, and changes in specimen area during shear. 相似文献
6.
Complexity in the earthquake mechanism is manifested in different forms such as fractal distribution, clustering of seismicity, etc., and characterized as critical phenomenon. Occurrences of earthquakes generally represent the state of metastable equilibrium. The Andaman–Sumatra subduction zone is one of the most seismically active corridors (possibly in metastable state) in the world. Recently, the region faced three major earthquakes of magnitude more than 8.5 (M ~ 9.1 on December 26, 2004; M ~ 8.6 on March 28, 2005; M ~ 8.6 on April 11, 2012). Researchers have suggested multiple causes of earthquake generation in this region including the one with possible correlation of tidal stresses with earthquake occurrences. The latter issue, however, has been hotly debated in view of the fact that a small stress generated due to tidal forcing cannot cause such a bigger magnitude earthquake. We study here the impact of tidal forcing on critically generated earthquake phenomena. We examined the statistical behavior of recurrence time interval of earthquakes using the available data for period of about 40 years from 1973 to 2013. We constrain the simple empirical toy model using the concept of catastrophe theory to evaluate the impact of small tidal forcing on the critical state of earthquakes occurrences. In addition to the major role of Helmholtz free energy during the plate motion, our analysis suggests that the stability and critical behavior of the earthquake in Sumatra region could be associated with tidal forcing, however, only for triggering of some of the “Catastrophic–Chaotic” earthquake phenomenon. 相似文献
7.
8.
We applied fast Fourier transform techniques and Morlet wavelet transform on the time series data of coronal index, solar flare index, and galactic cosmic ray, for the period 1986–2008, in order to investigate the long- and mid-term periodicities including the Rieger (\({\sim }130\) to \({\sim }190\) days), quasi-period (\({\sim }200\) to \({\sim }374\) days), and quasi-biennial periodicities (\({\sim }1.20\) to \({\sim }3.27\) years) during the combined solar cycles 22–23. We emphasize the fact that a lesser number of periodicities are found in the range of low frequencies, while the higher frequencies show a greater number of periodicities. The rotation rates at the base of convection zone have periods for coronal index of \({\sim }1.43\) years and for solar flare index of \({\sim }1.41\) year, and galactic cosmic ray, \({\sim }1.35\) year, during combined solar cycles 22–23. In relation to these two solar parameters (coronal index and solar flare index), for the solar cycles 22–23, we found that galactic cosmic ray modulation at mid cut-off rigidity (\(\hbox {Rc} = 2.43\hbox {GV}\)) is anti-correlated with time-lag of few months. 相似文献
9.
A spatially homogeneous and anisotropic locally rotationally symmetric Bianchi type-I spacetime with cosmological term \(\varLambda \) in \(f(R,T) \) theory has been studied. The exact solution of the field equations is obtained under a variation law of the Hubble parameter \((H) \) which yields a time dependent deceleration parameter (Banerjee and Das in Gen. Relativ. Gravit. 37:10, 2005). The model presents a cosmological scenario which describes early deceleration and late time acceleration. The physical parameters of the model have been analysed. 相似文献
10.