全文获取类型
收费全文 | 42946篇 |
免费 | 2320篇 |
国内免费 | 3112篇 |
专业分类
测绘学 | 1691篇 |
大气科学 | 4682篇 |
地球物理 | 8407篇 |
地质学 | 20304篇 |
海洋学 | 3730篇 |
天文学 | 6122篇 |
综合类 | 1271篇 |
自然地理 | 2171篇 |
出版年
2024年 | 74篇 |
2023年 | 296篇 |
2022年 | 536篇 |
2021年 | 645篇 |
2020年 | 552篇 |
2019年 | 594篇 |
2018年 | 3995篇 |
2017年 | 3736篇 |
2016年 | 2589篇 |
2015年 | 771篇 |
2014年 | 956篇 |
2013年 | 1029篇 |
2012年 | 1943篇 |
2011年 | 3879篇 |
2010年 | 3649篇 |
2009年 | 3815篇 |
2008年 | 3040篇 |
2007年 | 3713篇 |
2006年 | 791篇 |
2005年 | 1244篇 |
2004年 | 980篇 |
2003年 | 1055篇 |
2002年 | 850篇 |
2001年 | 592篇 |
2000年 | 594篇 |
1999年 | 688篇 |
1998年 | 614篇 |
1997年 | 590篇 |
1996年 | 574篇 |
1995年 | 460篇 |
1994年 | 434篇 |
1993年 | 378篇 |
1992年 | 329篇 |
1991年 | 291篇 |
1990年 | 244篇 |
1989年 | 220篇 |
1988年 | 175篇 |
1987年 | 158篇 |
1986年 | 132篇 |
1985年 | 109篇 |
1984年 | 106篇 |
1983年 | 92篇 |
1982年 | 110篇 |
1981年 | 93篇 |
1980年 | 96篇 |
1979年 | 64篇 |
1977年 | 54篇 |
1976年 | 56篇 |
1975年 | 36篇 |
1973年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
We present our spectroscopic observations of the novae V1425, V1493, and V1494 Aql carried out with the 125-cm telescope at the Crimean Station of the Sternberg Astronomical Institute in the wavelength range 4000–11000 Å. We measured the emission-line intensities, determined the nova shell expansion velocities from the line profile FWHMs and components, and estimated the interstellar reddening from the first members of the Balmer series. The chemical composition of the nova shells is analyzed. Nitrogen and oxygen were found to be overabundant in V1425 and V1494 Aql; the helium abundance turned out to be normal in the two stars. 相似文献
3.
The magnetic-field distribution outside a flat, infinitely conductive unbounded disk in the field of a point magnetic dipole is determined. A relationship is established between the problem of magnetic-field determination and the problem of the flow of an ideal incompressible fluid around an infinitely thin disk. 相似文献
4.
5.
A wide-field time-series CCD photometric survey of variable stars in the field of the open cluster NGC 2168 was carried out using the BATC Schmidt telescope. In total 13 new variable stars are discovered with three W UMa systems, one EA type and two EB type eclipsing binaries (one of them could be a W UMa system), and seven pulsating stars including three candidates of δScuti stars. 相似文献
6.
Zhi Xu Cheng Fang Wei-Qun Can Astronomy Department of Nanjing University Nanjing Purple Mountain Observatory Chinese Academy of Sciences Nanjing 《中国天文和天体物理学报》2005,5(5):519-530
Chromospheric lines, including Ha, Lyα, Lyβand CaⅡK, CaⅡ8542, are systemically and quantitatively investigated with respect to the non-thermal excitation and ionization due to particle beam bombardment for a series of solar semi-empirical atmospheric models. As a result we propose to use the contrast in the integrated intensity of hydrogen lines to estimate the total energy flux of the bombarding beam during the solar flare impulsive phase. Partial frequency redistribution is considered in the Lyαline calculation and a smaller intensity enhancement in the Ha line-centers is found than in the previous results of Fang et al. 相似文献
7.
E. C. Hopewell M. J. Barlow J. E. Drew Y. C. Unruh Q. A. Parker M. J. Pierce P. A. Crowther C. Knigge S. Phillipps A. A. Zijlstra 《Monthly notices of the Royal Astronomical Society》2005,363(3):857-866
We report the discovery of five massive Wolf–Rayet (WR) stars resulting from a programme of follow-up spectroscopy of candidate emission-line stars in the Anglo-Australian Observatory United Kingdom Schmidt Telescope (AAO/UKST) Southern Galactic Plane Hα survey. The 6195–6775 Å spectra of the stars are presented and discussed. A WC9 class is assigned to all five stars through comparison of their spectra with those of known late-type WC stars, bringing the known total number of Galactic WC9 stars to 44. Whilst three of the five WC9 stars exhibit near-infrared (NIR) excesses characteristic of hot dust emission (as seen in the great majority of known WC9 stars), we find that two of the stars show no discernible evidence of such excesses. This increases the number of known WC9 stars without NIR excesses to seven. Reddenings and distances for all five stars are estimated. 相似文献
8.
B. A. Ivanov 《Solar System Research》2005,39(5):381-409
Multi-ring impact basins have been found on the surfaces of almost all planetary bodies in the Solar system with solid crusts. The details of their formation mechanism are still unclear. We present results of our numerical modeling of the formation of the largest known terrestrial impact craters. The geological and geophysical data on these structures accumulated over many decades are used to place constraints on the parameters of available numerical models with a dual purpose: (i) to choose parameters in available mechanical models for the crustal response of planetary bodies to a large impact and (ii) to use numerical modeling to refine the possible range of original diameters and the morphology of partially eroded terrestrial craters. We present numerical modeling results for the Vredefort, Sudbury, Chicxulub, and Popigai impact craters and compare these results with available geological and geophysical information. 相似文献
9.
We consider the particular solutions of the evolutionary system of equations in elements that correspond to planar and spatial circular orbits of the singly averaged Hill problem. We analyze the stability of planar and spatial circular orbits to inclination and eccentricity, respectively. We construct the instability regions of both particular solutions in the plane of parameters of the problem. 相似文献
10.