全文获取类型
收费全文 | 7151篇 |
免费 | 661篇 |
国内免费 | 758篇 |
专业分类
测绘学 | 173篇 |
大气科学 | 1500篇 |
地球物理 | 1403篇 |
地质学 | 1178篇 |
海洋学 | 455篇 |
天文学 | 3563篇 |
综合类 | 38篇 |
自然地理 | 260篇 |
出版年
2024年 | 17篇 |
2023年 | 78篇 |
2022年 | 143篇 |
2021年 | 208篇 |
2020年 | 153篇 |
2019年 | 169篇 |
2018年 | 177篇 |
2017年 | 276篇 |
2016年 | 298篇 |
2015年 | 346篇 |
2014年 | 393篇 |
2013年 | 483篇 |
2012年 | 345篇 |
2011年 | 371篇 |
2010年 | 415篇 |
2009年 | 616篇 |
2008年 | 429篇 |
2007年 | 540篇 |
2006年 | 502篇 |
2005年 | 410篇 |
2004年 | 334篇 |
2003年 | 295篇 |
2002年 | 262篇 |
2001年 | 151篇 |
2000年 | 225篇 |
1999年 | 221篇 |
1998年 | 112篇 |
1997年 | 35篇 |
1996年 | 36篇 |
1995年 | 38篇 |
1994年 | 32篇 |
1993年 | 21篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1987年 | 20篇 |
1986年 | 18篇 |
1985年 | 19篇 |
1983年 | 13篇 |
1982年 | 30篇 |
1981年 | 15篇 |
1980年 | 18篇 |
1979年 | 19篇 |
1978年 | 20篇 |
1977年 | 20篇 |
1976年 | 17篇 |
1975年 | 19篇 |
1974年 | 22篇 |
1973年 | 12篇 |
1972年 | 13篇 |
1970年 | 11篇 |
排序方式: 共有8570条查询结果,搜索用时 15 毫秒
21.
22.
23.
We present a new general scheme for calculating the structure and dynamics of radiation-pressure-driven photoionized flows. The new method goes one step beyond the Sobolev approximation. It involves a numerical solution of the radiative transfer in absorption lines, including the effects of differential expansion and line interactions such as line locking and blanketing. We also present a new scheme for calculating the radiation pressure due to trapped line photons in finite, differentially expanding flows. We compare our results for the radiation pressure force with those obtained using the Sobolev approximation and show the limitations of the latter. In particular, we demonstrate that the Sobolev method gives a poor approximation near discontinuity surfaces and its neglect of line blanketing can lead to erroneous results in high-velocity flows. We combine the newly calculated radiation pressure force with self-consistent photoionization and thermal calculations to study the dynamics and spectral features of broad absorption-line flows and highly ionized gas flows in active galactic nuclei (AGN). A comparison with Sobolev-type calculations shows that the latter overestimates the terminal velocity of the flow and, conversely, underestimates its opacity. We also show that line locking on broad emission lines can have a significant effect on the dynamics and spectral features of AGN flows. 相似文献
24.
25.
26.
The Electron Energy Spectrum from Large Solar Flares 总被引:2,自引:0,他引:2
G. M. Simnett 《Solar physics》2006,237(2):383-395
We report on the differential electron spectrum for intense transient events seen at one AU by the EPAM instrument on the
Advanced Composition Explorer (ACE) spacecraft. Over an observing period from September 1997 to September 2005, there were 45 major events that could be
reliably identified with a source flare on the Sun. In the ∼40 – 300 keV energy range, the electron spectral index was between
one and three for all but two of the events. Twenty-five of the events were associated with Geostationary Operational Environmental
Satellites (GOES) X-ray class X flares. We compare this result with the spectral index measured from electron pulse events,
lasting approx. one hour or less, where the spectral index is typically much softer than three. This suggests that the measured
spectral index of near-relativistic electrons at one AU may be a reliable indicator of the source. We also examine the likelihood
that fast coronal mass ejections (CMEs) are responsible in themselves for accelerating near-relativistic electrons and conclude
that they do not. 相似文献
27.
J. C. A. Miller-Jones R. P. Fender E. Nakar 《Monthly notices of the Royal Astronomical Society》2006,367(4):1432-1440
We present a collation of the available data on the opening angles of jets in X-ray binaries, which in most cases are small (≲10°). Under the assumption of no confinement, we calculate the Lorentz factors required to produce such small opening angles via the transverse relativistic Doppler effect. The derived Lorentz factors, which are in most cases lower limits, are found to be large, with a mean >10, comparable to those estimated for active galactic nuclei (AGN) and much higher than the commonly assumed values for X-ray binaries of 2–5. Jet power constraints do not, in most cases, rule out such high Lorentz factors. The upper limits on the opening angles show no evidence for smaller Lorentz factors in the steady jets of Cygnus X-1 and GRS 1915+105. In those sources in which deceleration has been observed (notably XTE J1550−564 and Cygnus X-3), some confinement of the jets must be occurring, and we briefly discuss possible confinement mechanisms. It is however possible that all the jets could be confined, in which case the requirement for high bulk Lorentz factors can be relaxed. 相似文献
28.
29.
We examine possible locations for the primordial disk of the Edgeworth-Kuiper Belt (EKB), using several subsets of the known objects as markers of the total mass distribution. Using a secular perturbation theory, we find that the primordial plane of the EKB could have remained thin enough to escape detection only if it is clustered very closely about the invariable plane of the Solar System. 相似文献
30.