全文获取类型
收费全文 | 1390篇 |
免费 | 65篇 |
国内免费 | 114篇 |
专业分类
测绘学 | 63篇 |
大气科学 | 54篇 |
地球物理 | 100篇 |
地质学 | 140篇 |
海洋学 | 146篇 |
天文学 | 958篇 |
综合类 | 45篇 |
自然地理 | 63篇 |
出版年
2024年 | 3篇 |
2023年 | 8篇 |
2022年 | 16篇 |
2021年 | 19篇 |
2020年 | 23篇 |
2019年 | 28篇 |
2018年 | 20篇 |
2017年 | 23篇 |
2016年 | 21篇 |
2015年 | 43篇 |
2014年 | 41篇 |
2013年 | 61篇 |
2012年 | 37篇 |
2011年 | 30篇 |
2010年 | 41篇 |
2009年 | 84篇 |
2008年 | 56篇 |
2007年 | 97篇 |
2006年 | 91篇 |
2005年 | 110篇 |
2004年 | 102篇 |
2003年 | 94篇 |
2002年 | 89篇 |
2001年 | 70篇 |
2000年 | 68篇 |
1999年 | 70篇 |
1998年 | 93篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 21篇 |
1994年 | 15篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1976年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1569条查询结果,搜索用时 31 毫秒
151.
S. Hubrig A. F. Kholtygin M. Schller R. I. Anderson S. Saesen J. F. Gonzlez I. Ilyin M. Briquet 《Astronomische Nachrichten》2015,336(2):168-177
Our recent search for the presence of a magnetic field in the bright early A‐type supergiant HD 92207 using FORS 2 in spectropolarimetric mode revealed the presence of a longitudinal magnetic field of the order of a few hundred Gauss. However, the definite confirmation of the magnetic nature of this object remained pending due to the detection of shortterm spectral variability probably affecting the position of line profiles in left‐ and right‐hand polarized spectra. We present new magnetic field measurements of HD 92207 obtained on three different epochs in 2013 and 2014 using FORS 2 in spectropolarimetric mode. A 3σ detection of the mean longitudinal magnetic field using the entire spectrum, 〈Bz〉all = 104 ± 34 G, was achieved in observations obtained in 2014 January. At this epoch, the position of the spectral lines appeared stable. Our analysis of spectral line shapes recorded in opposite circularly polarized light, i.e. in light with opposite sense of rotation, reveals that line profiles in the light polarized in a certain direction appear slightly split. The mechanism causing such a behaviour in the circularly polarized light is currently unknown. Trying to settle the issue of short‐term variability, we searched for changes in the spectral line profiles on a time scale of 8–10 min using HARPS polarimetric spectra and on a time scale of 3–4 min using time series obtained with the CORALIE spectrograph. No significant variability was detected on these time scales during the epochs studied. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
152.
L. Kaderhandt A. Barr Domínguez R. Chini M. Hackstein M. Haas F. Pozo Nuez M. Murphy 《Astronomische Nachrichten》2015,336(7):677-681
We present a first overview of variable stars in the Bochum Galactic Disk Survey (GDS) with emphasis on eclipsing binaries (EBs). This ongoing survey is performed by a robotic twin refractor at the Universitätssternwarte Bochum located near Cerro Armazones in Chile. It comprises a mosaic of 268 fields in a stripe of Δb = ±3° along the Galactic plane observed once per month simultaneously in the Sloan r and i filters with a detection limit of rs ∼ 16 mag and is ∼ 15 mag. The data from the first three years until the end of February 2014 yields a total of 41718 variable stars with variability amplitudes between 0.1–6 mag. A cross‐match with SIMBAD identified 11 465 of these variables unambiguously, while 2184 had multiple matches; most of the remaining stars could be matched with 2MASS objects. Among the SIMBAD‐listed objects with single matches, only 1982 turned out as known variables while a further 256 are suspected of variability. That leaves a total of 39480 potentially new variables. The group of known variables comprises 419 stars (21 %) that are classified as EBs while 443 (22%) are of other types; for the remaining 1120 catalogued variables (57 %) the type is unknown. Investigating variability as a function of spectral type, we find that SIMBAD provides spectral types for 2811 (25 %) of the identified stars. Spectral classes B (26 %), A (20 %), and M (25%) contain the most numerous variables, while all other classes contribute less than 10% each. More than half of the B (55 %) and A (56%) stars are designated as EBs, suggesting that hundreds of new B‐ and A‐type EBs may be contained in the GDS archive. In contrast, among the numerous M stars no EBs are known. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
153.
Based on a search for multi‐periodic variability among the semi‐regular red variable stars in the database of the All Sky Automated Survey (ASAS), a sample of 72 typical examples is presented. Their period analysis was performed using the Discrete Fourier Transform. In 41 stars we identified two significant periods each, simultaneously present, while the remaining 31 cases revealed even three such periods per star. They occur in a range roughly between 50 and 3000 days. Inter‐relationships between these periods were analyzed using the “double period diagram” which compares adjacent periods, and the so‐called “Petersen diagram”, the period ratio vs. the shorter period. In both diagrams we could identify six sequences of accumulation of the period values. For five of these sequences (containing 97 % of all data points) we found an almost perfect coincidence with those of previous studies which were based on very different samples of semiregular red variables. Therefore, existence and locations of these sequences in the diagrams seem to be universal features, which appear in any data set of semi‐regularly variable red giants of the AGB; we conclude that they are caused by different pulsation modes as the typical and consistent properties of similar stellar AGB configurations. Stellar pulsations can be considered as the principal cause of the observed periodic variability of these stars, and not binary, rotation of a spotted surface or other possible reasons suggested in the literature. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
154.
155.
利用一种非定常的恒星非局部对流理论,对球状星团中低光度的红巨星进行了线性非绝热脉动理论计算.结果表明,对所有温度高于约5400 K模型的基音到4阶泛音都是脉动稳定的.随着恒星光度的增大,低阶泛音也变得脉动不稳定.对中低光度的红巨星,脉动稳定性非常低,接近中性稳定.因此他们将是不变星或非常小振幅的短周期变星(P<2天). 相似文献
156.
157.
158.
The results of 27 h of time series photometry of SDSS 121209.31+013627.7 are presented. The binary period established from spectroscopy is confirmed and refined to 0.061 412 d (88.43 min). The photometric variations are dominated by a brightening of about 16 mmag, lasting a little less than half a binary cycle. The amplitude is approximately the same in V , R and white light. A secondary small brightness increase during each cycle may also be present. We speculate that SDSS 121209.31+013627.7 may be a polar in a low state. 相似文献
159.
Results are presented from an analysis of observations in a sample of 53 long-period pulsating stars (44 of which are Mira-type
and 9 are semiregular variables). A catalog of the characteristics of the individual pulsation cycles of the light curves
is obtained for these stars. A correlation analysis of the characteristics of the individual pulsation cycles is carried out
for each star. A number if diagrams relating the variability of the characteristics of the individual cycles to the average
parameters of the variability of the stars and to their spectral classes. New criteria for classifying long-period variables
are proposed on the basis of these diagrams.
__________
Translated from Astrofizika, Vol. 49, No. 4, pp. 595–612 (November 2006). 相似文献
160.