全文获取类型
收费全文 | 101964篇 |
免费 | 1499篇 |
国内免费 | 898篇 |
专业分类
测绘学 | 2472篇 |
大气科学 | 7016篇 |
地球物理 | 20458篇 |
地质学 | 36189篇 |
海洋学 | 8790篇 |
天文学 | 23418篇 |
综合类 | 271篇 |
自然地理 | 5747篇 |
出版年
2022年 | 549篇 |
2021年 | 967篇 |
2020年 | 1060篇 |
2019年 | 1114篇 |
2018年 | 2565篇 |
2017年 | 2379篇 |
2016年 | 2956篇 |
2015年 | 1748篇 |
2014年 | 2919篇 |
2013年 | 5296篇 |
2012年 | 3104篇 |
2011年 | 4228篇 |
2010年 | 3655篇 |
2009年 | 4925篇 |
2008年 | 4414篇 |
2007年 | 4227篇 |
2006年 | 3987篇 |
2005年 | 3141篇 |
2004年 | 3081篇 |
2003年 | 2872篇 |
2002年 | 2678篇 |
2001年 | 2466篇 |
2000年 | 2340篇 |
1999年 | 1936篇 |
1998年 | 2031篇 |
1997年 | 1941篇 |
1996年 | 1596篇 |
1995年 | 1631篇 |
1994年 | 1389篇 |
1993年 | 1279篇 |
1992年 | 1241篇 |
1991年 | 1154篇 |
1990年 | 1300篇 |
1989年 | 1104篇 |
1988年 | 1016篇 |
1987年 | 1270篇 |
1986年 | 1039篇 |
1985年 | 1332篇 |
1984年 | 1456篇 |
1983年 | 1406篇 |
1982年 | 1272篇 |
1981年 | 1199篇 |
1980年 | 1058篇 |
1979年 | 986篇 |
1978年 | 1005篇 |
1977年 | 904篇 |
1976年 | 885篇 |
1975年 | 835篇 |
1974年 | 822篇 |
1973年 | 834篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Based on CCD spectra obtained with the PFES echelle spectrometer of the 6-m telescope, we have determined for the first time the effective temperature T eff=5900 K, surface gravity logg=0.0, and detailed chemical composition of the faint star identified with the infrared source IRAS 23304+6147 by the model-atmosphere method. Its metallicity indicates that the object belongs to the old Galactic disk (the mean abundance of the iron-group elements V, Cr, and Fe for IRAS 23304+6147 is [X/H]=?0.61 dex). The stellar atmosphere exhibits an enhancement of carbon and nitrogen, [C/Fe]=+0.98, [N/Fe]=+1.36, and C/O>1. Significant overabundances of lanthanides were detected: the mean [X/Fe]=+1.04 for La, Ce, Pr, Nd, and Eu. The elemental abundances suggest that the atmospheric chemical composition of IRAS 23304+6147 was modified mainly by nucleosynthesis followed by mixing. By modeling the object's spectrum, we revealed absorption features at the positions of well-known absorption diffuse interstellar bands (DIBs). An analysis of radial-velocity and intensity measurements for these DIBs leads us to conclude that, for IRAS 23304+6147, the DIBs originate mostly in its circumstellar dust envelope expanding at a velocity of about 20 km s?1. Molecular C2 Swan emission bands were detected in the object's spectrum, which also originate in the circumstellar envelope. There is a close match between the object's atmospheric effective temperatures determined independently by the model-atmosphere method and by modeling its optical and infrared energy distribution, within the accuracy of the methods. 相似文献
992.
993.
994.
995.
996.
997.
998.
999.
The mean width and distribution of penumbral filaments of a sunspot have been estimated, using white light photographs obtained with a vacuum, Newtonian type, telescope. Three areas corresponding to the penumbra of a sunspot have been analysed. Data were collected during the solar eclipse of June 1973. The photometric profiles of the Moon limb over the photosphere have been analysed to obtain useful information on both, atmospheric and instrumental perturbation on each exposure. The mean value of the width of penumbral filaments is 0.37 arc sec.Now at INTA-Villafranca, S.T.S., P.O. Box 54065, Madrid, Spain. 相似文献
1000.
Continuous measurements of the geomagnetic field variations at ground stations are important to investigate several aspects of magnetospheric dynamics related to variations in the solar wind conditions which, ultimately, originate from the Sun. We present a comparative analysis of geomagnetic field measurements at several ground stations with simultaneous magnetospheric and interplanetary observations in order to understand the origin and characteristics of the observed fluctuations. The results suggest that long period geomagnetic field fluctuations can be directly driven by solar wind density fluctuations at the same frequencies via the modulation of the magnetopause current. We also discuss the possible occurrence of additional contributions related with cavity/waveguide resonances of the entire magnetosphere as well as those of resonance processes of the geomagnetic field lines. 相似文献