全文获取类型
收费全文 | 9624篇 |
免费 | 1580篇 |
国内免费 | 1980篇 |
专业分类
测绘学 | 442篇 |
大气科学 | 2156篇 |
地球物理 | 3870篇 |
地质学 | 2898篇 |
海洋学 | 1603篇 |
天文学 | 758篇 |
综合类 | 459篇 |
自然地理 | 998篇 |
出版年
2024年 | 49篇 |
2023年 | 119篇 |
2022年 | 216篇 |
2021年 | 276篇 |
2020年 | 273篇 |
2019年 | 362篇 |
2018年 | 260篇 |
2017年 | 292篇 |
2016年 | 324篇 |
2015年 | 347篇 |
2014年 | 411篇 |
2013年 | 525篇 |
2012年 | 416篇 |
2011年 | 468篇 |
2010年 | 431篇 |
2009年 | 586篇 |
2008年 | 600篇 |
2007年 | 722篇 |
2006年 | 646篇 |
2005年 | 562篇 |
2004年 | 512篇 |
2003年 | 510篇 |
2002年 | 458篇 |
2001年 | 390篇 |
2000年 | 392篇 |
1999年 | 436篇 |
1998年 | 432篇 |
1997年 | 319篇 |
1996年 | 360篇 |
1995年 | 351篇 |
1994年 | 268篇 |
1993年 | 186篇 |
1992年 | 138篇 |
1991年 | 122篇 |
1990年 | 98篇 |
1989年 | 73篇 |
1988年 | 72篇 |
1987年 | 37篇 |
1986年 | 26篇 |
1985年 | 15篇 |
1984年 | 24篇 |
1983年 | 7篇 |
1982年 | 11篇 |
1981年 | 3篇 |
1980年 | 20篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 11篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
21.
G. Machabeli D. Khechinashvili G. Melikidze D. Shapakidze 《Monthly notices of the Royal Astronomical Society》2001,327(3):984-988
We present a model for microstructure in pulsar radio emission. We propose that micropulses result from alteration of the radio wave generation region by nearly transverse drift waves propagating across the pulsar magnetic field and encircling the bundle of the open magnetic field lines. It is demonstrated that such waves can modify the curvature of the field lines significantly. This, in turn, affects strongly fulfilment of the resonance conditions necessary for the excitation of radio waves. The time-scale of micropulses is therefore determined by the wavelength of the drift waves. The main features of the microstructure are naturally explained within the framework of this model. 相似文献
22.
Prediction of Stellar Atmospheric Parameters using Instance-Based Machine Learning and Genetic Algorithms 总被引:1,自引:0,他引:1
In this article we present a method for the automated prediction of stellar atmospheric parameters from spectral indices.
This method uses a genetic algorithm (GA) for the selection of relevant spectral indices and prototypical stars and predicts
their properties, using the k-nearest neighbors method (KNN). We have applied the method to predict the effective temperature,
surface gravity, metallicity, luminosity class and spectral class of stars from spectral indices. Our experimental results
show that the feature selection performed by the genetic algorithm reduces the running time of KNN up to 92%, and the predictive
accuracy error up to 35%.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
23.
V. Maupin 《Geophysical Journal International》1985,83(2):379-398
Summary. Surface wave behaviour in flat anisotropic structures is first illustrated by performing an exact computation on a simple two-layer model. The variational procedure of Smith & Dahlen is then used to compute the partial derivatives of surface wave phase velocities with respect to the elastic parameters in more realistic earth models. Linear relationships between the partial derivatives for a general anisotropic structure and those for a transversely isotropic structure are derived. When considering waves propagating in a fixed direction, there are only four independent derivatives for Rayleigh waves, and two for Love waves. To avoid the lack of resolution in an inverse method, we propose to use physically constrained models. These results are illustrated by using a model with hexagonal symmetry and a symmetry axis oriented either vertically or horizontally. Quasi-Love- and quasi-Rayleigh-wave partial derivatives are computed for both axis orientations. Modes up to the second overtone and periods ranging between 45 and 130 s have been considered. Finally, anomalies of phase velocity are computed in an oceanic model made of 1/6 oriented olivine crystals with horizontal or vertical preferred orientations of the a -axis. 相似文献
24.
Yehuda Ben-Zion 《Geophysical Journal International》1990,101(3):507-528
25.
This paper presents two and three dimensional simulations of the interaction of shocks with media with large numbers of dense
inclusions. An approximate model of the interaction of a starburst wind with the surrounding galactic ISM illustrates issues
which must be addressed in global models of ISM dynamics. As a step towards developing the sub-grid model of multiphase turbulence,
we define and study a form of ‘multiphase Riemann problem’. This allows us to develop macroscopic characteristics of the flows
which may be compared to such subgrid models. 相似文献
26.
27.
28.
29.
30.