全文获取类型
收费全文 | 4087篇 |
免费 | 561篇 |
国内免费 | 1033篇 |
专业分类
测绘学 | 33篇 |
大气科学 | 1239篇 |
地球物理 | 1106篇 |
地质学 | 337篇 |
海洋学 | 1471篇 |
天文学 | 692篇 |
综合类 | 96篇 |
自然地理 | 707篇 |
出版年
2024年 | 16篇 |
2023年 | 53篇 |
2022年 | 99篇 |
2021年 | 95篇 |
2020年 | 140篇 |
2019年 | 188篇 |
2018年 | 107篇 |
2017年 | 124篇 |
2016年 | 101篇 |
2015年 | 137篇 |
2014年 | 172篇 |
2013年 | 256篇 |
2012年 | 119篇 |
2011年 | 190篇 |
2010年 | 168篇 |
2009年 | 294篇 |
2008年 | 321篇 |
2007年 | 384篇 |
2006年 | 295篇 |
2005年 | 227篇 |
2004年 | 235篇 |
2003年 | 244篇 |
2002年 | 204篇 |
2001年 | 154篇 |
2000年 | 155篇 |
1999年 | 180篇 |
1998年 | 174篇 |
1997年 | 97篇 |
1996年 | 123篇 |
1995年 | 104篇 |
1994年 | 92篇 |
1993年 | 78篇 |
1992年 | 64篇 |
1991年 | 59篇 |
1990年 | 48篇 |
1989年 | 42篇 |
1988年 | 26篇 |
1987年 | 25篇 |
1986年 | 18篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 19篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1954年 | 4篇 |
排序方式: 共有5681条查询结果,搜索用时 31 毫秒
21.
22.
23.
24.
25.
26.
The effect of particle-particle interaction on the adiabatic index γ for an electron-positron plasma is considered. An improved method for numerically calculating the Hartree-Fock exchange integral is presented and its relativistic asymptotics is determined. An approximation formula is derived for the correlation part of the interaction in the low-density limit. This formula includes degeneracy and the positron component. 相似文献
27.
S. A. Petrova 《Monthly notices of the Royal Astronomical Society》2006,368(4):1764-1772
Pulsar radio emission is modelled as a sum of two completely polarized non-orthogonal modes with the randomly varying Stokes parameters and intensity ratio. The modes are the result of polarization evolution of the original natural waves in the hot, magnetized, weakly inhomogeneous plasma of the pulsar magnetosphere. In the course of the wavemode coupling, the linearly polarized natural waves acquire purely orthogonal elliptical polarizations. Further on, as the waves pass through the cyclotron resonance, they become non-orthogonal. The pulse-to-pulse fluctuations of the final polarization characteristics and the intensity ratio of the modes are attributed to the temporal fluctuations in the plasma flow.
The model suggested allows one to reproduce the basic features of the one-dimensional distributions of the individual-pulse polarization characteristics. Besides that, the propagation origin of the pulsar polarization implies a certain correlation between the mode ellipticity and position angle. On a qualitative level, for different sets of parameters, the expected correlations appear compatible with the observed ones. Further theoretical studies are necessary to establish the quantitative correspondence of the model to the observational results and to develop a technique of diagnostics of the pulsar plasma on this basis. 相似文献
The model suggested allows one to reproduce the basic features of the one-dimensional distributions of the individual-pulse polarization characteristics. Besides that, the propagation origin of the pulsar polarization implies a certain correlation between the mode ellipticity and position angle. On a qualitative level, for different sets of parameters, the expected correlations appear compatible with the observed ones. Further theoretical studies are necessary to establish the quantitative correspondence of the model to the observational results and to develop a technique of diagnostics of the pulsar plasma on this basis. 相似文献
28.
The spatial extent of ion cyclotron waves at Io has been interpreted as requiring a multistep acceleration and transport process: exospheric ions are accelerated outward (relative to Jupiter) due to the corotation electric field, neutralized due to charge exchange in the surrounding exosphere, and then reionized after traveling far across magnetic field lines, at which point they generate the waves. The trajectories of the particles away from Io are sensitive to the location of their initial ionization. This paper examines the spatial distributions of fast neutrals produced under varying conditions in order to provide constraints on the possible structure and nature of the Io exosphere. While a rapid onset of cyclotron waves at a specific location around Io can be modeled with a single, point-source region of ions, such as might occur over a volcano, the regional extent of the waves suggests multiple or distributed sources. 相似文献
29.
30.
Jorge Luis De Souza 《Pure and Applied Geophysics》1991,136(2-3):245-264
The Rayleigh wave phase and group velocities in the period range of 24–39 sec, obtained from two earthquakes which occurred in northeastern brazil and which were recorded by the Brazilian seismological station RDJ (Rio de Janeiro), have been used to study crustal and upper mantle structures of the Brazilian coastal region. Three crustal and upper mantle models have been tried out to explain crustal and upper mantle structures of the region. The upper crust has not been resolved, due basically to the narrow period range of the phase and group velocities data. The phase velocity inversions have exhibited good resolutions for both lower crust and upper mantle, with shear wave velocities characteristic of these regions. The group velocity data inversions for these models have showed good results only for the lower crust. The shear wave velocities of the lower crust (3.86 and 3.89 km/sec), obtained with phase velocity inversions, are similar to that (=3.89 km/sec) found byHwang (1985) to the eastern South American region, while group velocity inversions have presented shear velocity (=3.75 km/sec) similar to that (=3.78 km/sec) found byLazcano (1972) to the Brazilian shield. It was not possible to define sharply the crust-mantle transition, but an analysis of the phase and group velocity inversions results has indicated that the total thickness of the crust should be between 30 and 39 km. The crustal and upper mantle model, obtained with phase velocity inversion, can be used as a preliminary model for the Brazilian coast. 相似文献