全文获取类型
收费全文 | 12028篇 |
免费 | 2154篇 |
国内免费 | 1887篇 |
专业分类
测绘学 | 890篇 |
大气科学 | 1138篇 |
地球物理 | 3315篇 |
地质学 | 4637篇 |
海洋学 | 956篇 |
天文学 | 3246篇 |
综合类 | 758篇 |
自然地理 | 1129篇 |
出版年
2024年 | 57篇 |
2023年 | 117篇 |
2022年 | 262篇 |
2021年 | 331篇 |
2020年 | 336篇 |
2019年 | 467篇 |
2018年 | 311篇 |
2017年 | 347篇 |
2016年 | 380篇 |
2015年 | 456篇 |
2014年 | 537篇 |
2013年 | 618篇 |
2012年 | 631篇 |
2011年 | 695篇 |
2010年 | 507篇 |
2009年 | 918篇 |
2008年 | 787篇 |
2007年 | 1002篇 |
2006年 | 926篇 |
2005年 | 749篇 |
2004年 | 699篇 |
2003年 | 687篇 |
2002年 | 539篇 |
2001年 | 486篇 |
2000年 | 456篇 |
1999年 | 456篇 |
1998年 | 442篇 |
1997年 | 315篇 |
1996年 | 297篇 |
1995年 | 222篇 |
1994年 | 213篇 |
1993年 | 197篇 |
1992年 | 147篇 |
1991年 | 96篇 |
1990年 | 99篇 |
1989年 | 83篇 |
1988年 | 60篇 |
1987年 | 42篇 |
1986年 | 24篇 |
1985年 | 17篇 |
1984年 | 11篇 |
1983年 | 1篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1971年 | 2篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
81.
82.
83.
84.
Belinda Kalomeni E. Rennan PekÜnlÜ Kadri Yakut 《Astrophysics and Space Science》2005,296(1-4):477-480
In this study, we present a photometric study of AM Her, a prototype of a class of magnetic CVs. Optical photometry of AM
Her was obtained using the Russian–Turkish 1.5 m telescope at TüBİTAK National Observatory (TUG) in August 2003. The R band light curve of the system shows two maxima and two minima during one orbital cycle. In both observing nights the star
showed flickering at a significant level. The measured flickering time scale is about 5 min. 相似文献
85.
86.
Hari Om Vats 《Journal of Astrophysics and Astronomy》2006,27(2-3):227-235
Examples of extreme events of solar wind and their effect on geomagnetic conditions are discussed here. It is found that there
are two regimes of high speed solar wind streams with a threshold of ∼ 850 km s-1. Geomagnetic activity enhancement rate (GAER) is defined as an average increase in Ap value per unit average increase in
the peak solar wind velocity (Vp) during the stream. GAER was found to be different in the two regimes of high speed streams
with +ve and-ve IMF. GAER is 0.73 and 0.53 for solar wind streams with +ve and -ve IMF respectively for the extremely high
speed streams (< 850 km s-1). This indicates that streams above the threshold speed with +ve IMF are 1.4 times more effective in enhancing geomagnetic
activity than those with -ve IMF. However, the high speed streams below the threshold with -ve IMF are 1.1 times more effective
in enhancing geomagnetic activity than those with +ve IMF. The violent solar activity period (October–November 2003) of cycle
23 presents a very special case during which many severe and strong effects were seen in the environment of the Earth and
other planets; however, the z-component of IMF (Bz) is mostly positive during this period. The most severe geomagnetic storm
of this cycle occurred when Bz was positive. 相似文献
87.
88.
89.
90.
Dong-Mei Qin Ping Guo Zhan-Yi Hu Yong-Heng ZhaoNational Laboratory of Pattern Recognition Laboratory Institute of Automation Chinese Academy of Sciences Beijing dmqin@nlpr.ia.ac.cnDepartment of Computer Sciences Beijing Normal University Beijing National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2003,3(3)
For LAMOST, the largest sky survey program in China, the solution of the problem of automatic discrimination of stars from galaxies by spectra has shown that the results of the PSF test can be significantly refined. However, the problem is made worse when the redshifts of galaxies are not available. We present a new automatic method of star/(normal) galaxy separation, which is based on Statistical Mixture Modeling with Radial Basis Function Neural Networks (SMM-RBFNN). This work is a continuation of our previous one, where active and non-active celestial objects were successfully segregated. By combining the method in this paper and the previous one, stars can now be effectively separated from galaxies and AGNs by their spectra-a major goal of LAMOST, and an indispensable step in any automatic spectrum classification system. In our work, the training set includes standard stellar spectra from Jacoby's spectrum library and simulated galaxy spectra of EO, SO, Sa, Sb types with redshift ranging from 0 to 1 相似文献