全文获取类型
收费全文 | 1258篇 |
免费 | 116篇 |
国内免费 | 117篇 |
专业分类
测绘学 | 30篇 |
大气科学 | 92篇 |
地球物理 | 143篇 |
地质学 | 455篇 |
海洋学 | 34篇 |
天文学 | 337篇 |
综合类 | 47篇 |
自然地理 | 353篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 33篇 |
2021年 | 26篇 |
2020年 | 25篇 |
2019年 | 37篇 |
2018年 | 34篇 |
2017年 | 34篇 |
2016年 | 45篇 |
2015年 | 51篇 |
2014年 | 49篇 |
2013年 | 74篇 |
2012年 | 38篇 |
2011年 | 54篇 |
2010年 | 43篇 |
2009年 | 81篇 |
2008年 | 66篇 |
2007年 | 80篇 |
2006年 | 80篇 |
2005年 | 81篇 |
2004年 | 73篇 |
2003年 | 59篇 |
2002年 | 65篇 |
2001年 | 53篇 |
2000年 | 42篇 |
1999年 | 42篇 |
1998年 | 39篇 |
1997年 | 20篇 |
1996年 | 23篇 |
1995年 | 15篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1992年 | 15篇 |
1991年 | 13篇 |
1990年 | 15篇 |
1989年 | 18篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 10篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有1491条查询结果,搜索用时 203 毫秒
131.
Kirsty J. Rhook Martin G. Haehnelt 《Monthly notices of the Royal Astronomical Society》2006,373(2):623-631
H ii regions surrounding supermassive black holes (SMBHs) in an otherwise still neutral intergalactic medium (IGM) are likely to be the most easily detectable sources by future 21-cm experiments like LOFAR. We have made predictions for the size distribution of such H ii regions for several physically motivated models for BH growth at high redshift and compared this to the expected LOFAR sensitivity to these sources. The number of potentially detectable H ii regions does not only depend on the ionization state of the IGM and the decoupling of the spin temperature of the neutral hydrogen from the cosmic microwave background temperature, but is also strongly sensitive to the rate of growth of BHs at high redshift. If the SMBHs at redshift 6 were built up via continuous Eddington-limited accretion from low mass seed BHs at high redshift, then LOFAR is not expected to detect isolated QSO H ii regions at redshifts much larger than 6, and only if the IGM is still significantly neutral. If the high-redshift growth of BHs starts with massive seed BHs and is driven by short-lived accretion events following the merging of BH hosting galaxies then the detection of H ii regions surrounding SMBHs may extend to redshifts as large as 8–9 but is still very sensitive to the redshift to which the IGM remains significantly neutral. The most optimistic predictions are for a model where the SMBHs at z > 6 have grown slowly. H ii regions around SMBHs may then be detected to significantly larger redshifts. 相似文献
132.
河南省电子政务空间信息服务系统建设与典型应用 总被引:2,自引:0,他引:2
介绍了河南省电子政务空间信息服务系统的项目背景、系统总体设计,论述了数据处理与集成建库所涉及的一些关键技术,并以中原城市群空间信息服务系统为典型应用,作了进一步的探讨。 相似文献
133.
134.
V. Firpo G. Bosch † N. Morrell †‡ 《Monthly notices of the Royal Astronomical Society》2005,356(4):1357-1361
We present results of a search for giant H ii regions in southern galaxies. Using high-resolution spectra, obtained with the Magellan Inamori Kyocera Echelle (MIKE) at the Las Campanas Magellan II telescope, we were able to resolve the emission-line profiles and determine the intrinsic velocity dispersion of the ionized gas. Out of four observed regions, selected from previous CCD narrow-band photometry, we detected three H ii regions showing supersonic velocity dispersion, characteristic of giant H ii regions, and their location in diagnostic diagrams suggests that a powerful starburst is the source of ionization energy. 相似文献
135.
136.
O. Ragos K. E. Papadakis C. G. Zagouras 《Celestial Mechanics and Dynamical Astronomy》1997,67(4):251-274
The regions of quasi-periodic motion around non-symmetric periodic orbits in the vicinity of the triangular equilibrium points
are studied numerically. First, for a value of the mass parameter less than Routh's critical value, the stability regions
determined by quasi-periodic motion are examined around the existing families of short (Ls
4) and long (Ll
4) period solutions. Then, for two values of μ greater than the Routh value, the unified family Lsl
4, to which, in these cases, Ls
4 and Ll
4 merge, is considered. It is found that such regions surround in general the linearly stable segments of the corresponding
families and become smaller as the mass ratio increases.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
137.
138.
139.
K. V. Krasnobaev 《Astronomy Letters》2002,28(9):594-600
The effect of a time-varying radiation flux incident on an ionization front on the generation of ionization-shock front oscillations in the interstellar medium is analyzed analytically and numerically. We take into account both variations in the flux of ionizing radiation directly from the source that produces the ionization front and the absorption of energetic photons by the post-front plasma. Based on our calculations, we show that the time dependence of the radiation flux can be an additional factor (apart from small inhomogeneities in the interstellar medium) that contributes to the amplification of oscillations and to the kinetic energy input to the observed turbulent motions in H II regions. 相似文献
140.
D. D. Ryutov J. O. Kane A. Mizuta M. W. Pound B. A. Remington 《Astrophysics and Space Science》2007,307(1-3):173-177
The dynamics of photoevaporated molecular clouds is determined by the ablative pressure acting on the ionization front. An
important step in the understanding of the ensuing motion is to develop the linear stability theory for an initially flat
front. Despite the simplifications introduced by linearization, the problem remains quite complex and still draws a lot of
attention. The complexity is related to the large number of effects that have to be included in the analysis: acceleration
of the front, possible temporal variation of the intensity of the ionizing radiation, the tilt of the radiation flux with
respect to the normal to the surface, and partial absorption of the incident radiation in the ablated material. In this paper,
we describe a model where all these effects can be taken into account simultaneously, and a relatively simple and universal
dispersion relation can be obtained. The proposed phenomenological model may prove to be a helpful tool in assessing the feasibility
of the laboratory experiments directed towards scaled modeling of astrophysical phenomena.
PACS Numbers: 98.38.Dq, 98.38.Hv, 52.38.Mf, 5257.FG, 52.72.+v 相似文献