全文获取类型
收费全文 | 7097篇 |
免费 | 235篇 |
国内免费 | 87篇 |
专业分类
测绘学 | 240篇 |
大气科学 | 694篇 |
地球物理 | 1500篇 |
地质学 | 2500篇 |
海洋学 | 676篇 |
天文学 | 1300篇 |
综合类 | 15篇 |
自然地理 | 494篇 |
出版年
2023年 | 19篇 |
2022年 | 52篇 |
2021年 | 93篇 |
2020年 | 114篇 |
2019年 | 107篇 |
2018年 | 211篇 |
2017年 | 190篇 |
2016年 | 263篇 |
2015年 | 172篇 |
2014年 | 219篇 |
2013年 | 345篇 |
2012年 | 310篇 |
2011年 | 411篇 |
2010年 | 321篇 |
2009年 | 443篇 |
2008年 | 379篇 |
2007年 | 325篇 |
2006年 | 330篇 |
2005年 | 308篇 |
2004年 | 403篇 |
2003年 | 314篇 |
2002年 | 248篇 |
2001年 | 179篇 |
2000年 | 180篇 |
1999年 | 143篇 |
1998年 | 171篇 |
1997年 | 100篇 |
1996年 | 78篇 |
1995年 | 68篇 |
1994年 | 60篇 |
1993年 | 62篇 |
1992年 | 63篇 |
1991年 | 51篇 |
1990年 | 49篇 |
1989年 | 30篇 |
1988年 | 20篇 |
1987年 | 32篇 |
1986年 | 25篇 |
1985年 | 30篇 |
1984年 | 44篇 |
1983年 | 35篇 |
1982年 | 22篇 |
1981年 | 28篇 |
1978年 | 29篇 |
1977年 | 26篇 |
1976年 | 27篇 |
1975年 | 31篇 |
1974年 | 19篇 |
1973年 | 23篇 |
1971年 | 19篇 |
排序方式: 共有7419条查询结果,搜索用时 250 毫秒
31.
32.
P. G. Jonker G. Nelemans Z. Wang A. K. H. Kong D. Chakrabarty M. Garcia P. J. Groot M. van der Klis T. Kerr B. Mobasher M. Sullivan T. Augusteijn B. W. Stappers P. Challis R. P. Kirshner J. Hjorth A. Delsanti 《Monthly notices of the Royal Astronomical Society》2003,344(1):201-206
We have obtained optical and near-infrared images of the field of the accreting millisecond X-ray pulsar XTE J1751−305. There are no stars in the 0.7-arcsec error circle (0.7 arcsec is the overall uncertainty arising from tying the optical and X-ray images and from the intrinsic uncertainty in the Chandra X-ray astrometric solution). We derive limiting magnitudes for the counterpart of R > 23.1, I > 21.6, Z > 20.6, J > 19.6 and K > 19.2 . We compare these upper limits with the magnitudes one would expect for simple models for the possible donor stars and the accretion disc subject to the reddening observed in X-rays for XTE J1751−305 and when put at the distance of the Galactic Centre (8.5 kpc). We conclude that our non-detection does not constrain any of the models for the accretion disc or possible donor stars. Deep, near-infrared images obtained during quiescence will, however, constrain possible models for the donor stars in this ultracompact system. 相似文献
33.
P. G. Jonker M. van der Klis C. Kouveliotou M. Méndez W. H. G. Lewin T. Belloni 《Monthly notices of the Royal Astronomical Society》2003,346(2):684-688
We have observed the eclipsing low-mass X-ray binary MS 1603.6+2600 with Chandra for 7 ks. The X-ray spectrum is well fit with a single absorbed power law with an index of ∼2. We find a clear sinusoidal modulation in the X-ray light curve with a period of 1.7 ± 0.2 h , consistent with the period of 1.85 h found before. However, no (partial) eclipses were found. We argue that if the X-ray flare observed in earlier X-ray observations was a type I X-ray burst, then the source can only be an accretion disc corona source at a distance of ∼11–24 kpc (implying a height above the Galactic disc of ∼8–17 kpc). It has also been proposed in the literature that MS 1603.76+2600 is a dipper at ∼75 kpc. We argue that, in this dipper scenario, the observed optical properties of MS 1603.6+2600 are difficult to reconcile with the optical properties one would expect on the basis of comparisons with other high-inclination, low-mass X-ray binaries, unless the X-ray flare was not a type I X-ray burst. In that case, the source can be a nearby soft X-ray transient accreting at a quiescent rate, as was proposed by Hakala et al., or a high-inclination source at ∼15–20 kpc. 相似文献
34.
A. D. Biggs D. Rusin I. W. A. Browne A. G. de Bruyn N. J. Jackson L. V. E. Koopmans J. P. McKean S. T. Myers R. D. Blandford K.-H. Chae C. D. Fassnacht M. A. Norbury T. J. Pearson P. M. Phillips A. C. S. Readhead P. N. Wilkinson 《Monthly notices of the Royal Astronomical Society》2003,338(4):1084-1088
35.
36.
37.
38.
39.
D. Kilkenny L. A. Crause F. van Wyk 《Monthly notices of the Royal Astronomical Society》2005,361(2):559-564
A new statement of the eigenvalue problem of studying small perturbations in arbitrary integrable self-gravitating systems is presented. An example of such a system, a 2D stellar disc, is considered in detail. The theory, based on the general equation for disc eigenmodes, reveals mechanisms for the formation and growth of global galactic structures. This new point of view specifies the limits of the unified theory of bar-like and spiral modes that was based on the assumption that global galactic structures could be understood in terms of low-frequency disc modes. 相似文献
40.
J. van der Plicht B. van Geel S. J. P. Bohncke J. A. A. Bos M. Blaauw A. O. M. Speranza R. Muscheler S. Bjrck 《第四纪科学杂志》2004,19(3):263-269
Accurate chronologies are essential for linking palaeoclimate archives. Carbon‐14 wiggle‐match dating was used to produce an accurate chronology for part of an early Holocene peat sequence from the Borchert (The Netherlands). Following the Younger Dryas–Preboreal transition, two climatic shifts could be inferred. Around 11 400 cal. yr BP the expansion of birch (Betula) forest was interrupted by a dry continental phase with dominantly open grassland vegetation, coeval with the PBO (Preboreal Oscillation), as observed in the GRIP ice core. At 11 250 cal. yr BP a sudden shift to a humid climate occurred. This second change appears to be contemporaneous with: (i) a sharp increase of atmospheric 14C; (ii) a temporary decline of atmospheric CO2; and (iii) an increase in the GRIP 10Be flux. The close correspondence with excursions of cosmogenic nuclides points to a decline in solar activity, which may have forced the changes in climate and vegetation at around 11 250 cal. yr BP. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献