全文获取类型
收费全文 | 53411篇 |
免费 | 8233篇 |
国内免费 | 11359篇 |
专业分类
测绘学 | 4222篇 |
大气科学 | 5257篇 |
地球物理 | 9689篇 |
地质学 | 29751篇 |
海洋学 | 5338篇 |
天文学 | 7895篇 |
综合类 | 3426篇 |
自然地理 | 7425篇 |
出版年
2024年 | 180篇 |
2023年 | 440篇 |
2022年 | 1228篇 |
2021年 | 1420篇 |
2020年 | 1515篇 |
2019年 | 1886篇 |
2018年 | 1466篇 |
2017年 | 1690篇 |
2016年 | 1832篇 |
2015年 | 2050篇 |
2014年 | 2516篇 |
2013年 | 2557篇 |
2012年 | 2856篇 |
2011年 | 3138篇 |
2010年 | 2737篇 |
2009年 | 3568篇 |
2008年 | 3461篇 |
2007年 | 3969篇 |
2006年 | 3894篇 |
2005年 | 3579篇 |
2004年 | 3281篇 |
2003年 | 3185篇 |
2002年 | 2809篇 |
2001年 | 2415篇 |
2000年 | 2219篇 |
1999年 | 2060篇 |
1998年 | 1889篇 |
1997年 | 1423篇 |
1996年 | 1303篇 |
1995年 | 1167篇 |
1994年 | 1163篇 |
1993年 | 957篇 |
1992年 | 745篇 |
1991年 | 537篇 |
1990年 | 484篇 |
1989年 | 378篇 |
1988年 | 294篇 |
1987年 | 194篇 |
1986年 | 128篇 |
1985年 | 92篇 |
1984年 | 39篇 |
1983年 | 38篇 |
1982年 | 42篇 |
1981年 | 31篇 |
1980年 | 27篇 |
1979年 | 28篇 |
1978年 | 37篇 |
1977年 | 24篇 |
1975年 | 4篇 |
1954年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 781 毫秒
21.
Xue-Fei Chen Zhan-Wen HanNational Astronomical Observatories Yunnan Observatory Chinese Academy of Sciences. Kunming Graduate School of the Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2005,5(1):65-76
We have studied the influence of different choices of core-envelope transition point on the final merger of contact binaries with two main-sequence components. A binary of 1.00 + 0.90M⊙ with an initial orbital period of 0.35d is examined. The mass fraction of the primary mixed with the matter of the secondary, qmix, determined by the chosen core-envelope transition point, ranges from 0.04 to 1.00 in our analysis. If as qmix< 0.8, none of the 相似文献
22.
23.
24.
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
25.
26.
中国1∶100万景观生态制图设计 总被引:5,自引:0,他引:5
中国1∶100万景观生态图系借鉴国内外传统景观制图方法和制图规范,在遥感、地理信息系统先进技术的支持下,设计研制其制图方法、制图内容、样图和技术流程,同时提出初步的景观分类系统,为今后编制中国1∶100万景观生态图奠定基础。 相似文献
27.
ENVIRONMENTAL SUSTAINABILITY AND SCENARIOS OF URBANIZATION IN ARID AREA——A Case Study in Wuwei City of Gansu Province 总被引:1,自引:0,他引:1
YOUFei LIYu DONGSuo-cheng 《中国地理科学(英文版)》2005,15(2):120-130
1IN T R O D U C T IO N The western China isfacinggrowing problems of eco- logicaland economic development. The disparitiebse- tween the socio-economy of the western and eastern China were enlarging, and the major ecologicalprob- lems stilelvolve as past(H… 相似文献
28.
中国古生教授学会微体古生物学分会举行代表大会和学术年会中国古竽物学会微体古物学分会第五次会员代表大分暨第六次不术年会于1996年1月24日到30日在福州市召开。来自全国地质、石油、煤炭的和产、科研和大学的100多位代表参加了这次大会和学术研讨。大会共... 相似文献
29.
V2213 Cyg was discovered as a variable star by Pavlenko (1999) in 1998. We present our photometry of V2213 Cyg from 1998–2003
based on CCD observations with the K-380 Cassegrain telescope of CrAO and the 60 cm Zeiss telescope of SAI. Observations have
been carried out mostly in R and sometimes in B and V Johnson system. The total amount of data is 2270 points, covering ∼50 nights. We classify this binary as a W UMa-type contact
system. Using all data we determined the orbital period to be 0.350079 ± 0.000007 day. The mean brightness varies between
R = 14.35 and 14.05. The mean 1999–2003 orbital light curve has two humps and a primary minimum (I), which is 0.04 mag brighter
than the deeper secondary one (II). The mean humps have slightly different height. The difference between two individual maxima
varies within 0.1 mag, which may indicate an activity of the components. The highest hump is an asymmetrical one: it has sort
of a shoulder at phases 0.75–0.80, before entering the less deep primary minimum (phase 0.0). The system is rather reddened,
its colour indices are: B−V ∼ 0.8 and V−R ∼ 0.7, and give a spectral class of V2213 Cyg earlier than K. 相似文献
30.
We consider the evolution of certain low-mass binaries, incorporating models of (a) internal evolution, (b) tidal friction,
(c) dynamo activity driven by an elementary α,Ω dynamo, (d) stellar wind driven by the activity, and (e) magnetic braking
as a consequence of wind and poloidal dynamo-generated magnetic field. In some circumstances the stellar wind is found to
remove mass on a nuclear timescale, as is necessary to explain some observed systems.
We can hope that various uncertainties in the model may be clarified by a careful comparison of the models with such observed
quantities as rotation periods. These are modified by processes (a), (b) and (e). Assuming that stellar evolution is slow,
rotation rate should in some circumstances represent a balance between magnetic braking trying to slow the star down and tidal
friction trying to spin it up. Preliminary attempts are promising, but indicate that some fine tuning is necessary.
When there is a third body present, in an orbit which is inclined but not necessarily of short period, the eccentricity of
a close binary can be strongly modified by ‘Kozai cycles’. We show that this may complicate attempts to account for spin rates
of stars in close binaries. 相似文献