全文获取类型
收费全文 | 2174篇 |
免费 | 219篇 |
国内免费 | 352篇 |
专业分类
测绘学 | 363篇 |
大气科学 | 109篇 |
地球物理 | 216篇 |
地质学 | 831篇 |
海洋学 | 195篇 |
天文学 | 797篇 |
综合类 | 143篇 |
自然地理 | 91篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 39篇 |
2021年 | 45篇 |
2020年 | 51篇 |
2019年 | 68篇 |
2018年 | 46篇 |
2017年 | 48篇 |
2016年 | 58篇 |
2015年 | 89篇 |
2014年 | 104篇 |
2013年 | 97篇 |
2012年 | 123篇 |
2011年 | 123篇 |
2010年 | 121篇 |
2009年 | 165篇 |
2008年 | 149篇 |
2007年 | 188篇 |
2006年 | 186篇 |
2005年 | 137篇 |
2004年 | 136篇 |
2003年 | 125篇 |
2002年 | 113篇 |
2001年 | 91篇 |
2000年 | 70篇 |
1999年 | 71篇 |
1998年 | 73篇 |
1997年 | 47篇 |
1996年 | 38篇 |
1995年 | 27篇 |
1994年 | 29篇 |
1993年 | 12篇 |
1992年 | 17篇 |
1991年 | 14篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1979年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有2745条查询结果,搜索用时 31 毫秒
1.
2.
E.A. Evstigneeva R.R. de Carvalho A.L. Ribeiro H.V. Capelato 《Astrophysics and Space Science》2003,284(2):487-490
We present the preliminary results of a study of how small stellar systems merge to form larger ones. As we display the families
of galaxies in the μe - Re plane (effective surface brightness versus effective radius) we realize that different morphological types occupy different
loci, evidencing the different physical mechanisms operating in each family. As proposed by Capaccioli et al. (1992) this
diagram is the logical equivalent of the HR diagram for stars. Here we take some initial steps in understanding of how we
can establish the evolutionary tracks, solely due to dynamical processes, in the μe - Re plane, ultimately making a dwarf elliptical to turn into a normal elliptical galaxy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
4.
A. S. Oliveira J. E. Steiner D. Cieslinski 《Monthly notices of the Royal Astronomical Society》2003,346(3):963-967
The star WR 7a, also known as SPH 2, has a spectrum that resembles that of V Sagittae stars although no O vi emission has been reported. The Temporal Variance Spectrum – TVS – analysis of our data shows weak but strongly variable emission of O vi lines which is below the noise level in the intensity spectrum.
Contrary to what is seen in V Sagittae stars, optical photometric monitoring shows very little, if any, flickering. We found evidence of periodic variability. The most likely photometric period is Pphot = 0.227(±14) d , while radial velocities suggest a period of P spec = 0.204(±13) d . One-day aliases of these periods can not be ruled out. We call attention to similarities with HD 45166 and DI Cru (= WR 46), where multiple periods are present. They may be associated to the binary motion or to non-radial oscillations.
In contrast to a previous conclusion by Pereira et al., we show that WR 7a contains hydrogen. The spectrum of the primary star seems to be detectable as the N v 4604 Å absorption line is visible. If so, it means that the wind is optically thin in the continuum and that it is likely to be a helium main sequence star.
Given the similarity to HD 45166, we suggests that WR 7a may be a qWR – quasi Wolf–Rayet – star. Its classification is WN4h/CE in the Smith, Shara & Moffat three-dimensional classification system. 相似文献
Contrary to what is seen in V Sagittae stars, optical photometric monitoring shows very little, if any, flickering. We found evidence of periodic variability. The most likely photometric period is P
In contrast to a previous conclusion by Pereira et al., we show that WR 7a contains hydrogen. The spectrum of the primary star seems to be detectable as the N v 4604 Å absorption line is visible. If so, it means that the wind is optically thin in the continuum and that it is likely to be a helium main sequence star.
Given the similarity to HD 45166, we suggests that WR 7a may be a qWR – quasi Wolf–Rayet – star. Its classification is WN4h/CE in the Smith, Shara & Moffat three-dimensional classification system. 相似文献
5.
6.
J.-M. Carquillat N. Ginestet J.-L. Prieur Y. Debernardi 《Monthly notices of the Royal Astronomical Society》2003,346(2):555-564
We present the results of a radial-velocity study of eight Am stars (HD 341, 55822, 61250, 67317, 93991, 162950, 224890 and 225137) observed at Observatoire de Haute-Provence with the CORAVEL instrument. We find that these systems are single-line spectroscopic binaries whose orbital elements are determined for the first time. 相似文献
7.
8.
K. Nagamine † M. Fukugita R. Cen J.P. Ostriker 《Monthly notices of the Royal Astronomical Society》2001,327(1):L10-L14
The luminosity function of galaxies is derived from a cosmological hydrodynamic simulation of a Λ cold dark matter universe with the aid of a stellar population synthesis model. At , the resulting B -band luminosity function has a flat faint-end slope of with the characteristic luminosity and the normalization in fair agreement with observations, while the dark matter halo mass function is steep with a slope of . The colour distribution of galaxies also agrees well with local observations. We also discuss the evolution of the luminosity function, and the colour distribution of galaxies from to 5. A large evolution of the characteristic mass in the stellar mass function as a result of number evolution is compensated by luminosity evolution; the characteristic luminosity increases only by 0.8 mag from to 2, and then declines towards higher redshift, while the B -band luminosity density continues to increase from to 5 (but only slowly at . 相似文献
9.
10.