全文获取类型
收费全文 | 10027篇 |
免费 | 737篇 |
国内免费 | 203篇 |
专业分类
测绘学 | 333篇 |
大气科学 | 982篇 |
地球物理 | 3167篇 |
地质学 | 3727篇 |
海洋学 | 724篇 |
天文学 | 1088篇 |
综合类 | 205篇 |
自然地理 | 741篇 |
出版年
2022年 | 31篇 |
2021年 | 80篇 |
2020年 | 66篇 |
2019年 | 79篇 |
2018年 | 528篇 |
2017年 | 452篇 |
2016年 | 378篇 |
2015年 | 282篇 |
2014年 | 242篇 |
2013年 | 345篇 |
2012年 | 796篇 |
2011年 | 656篇 |
2010年 | 288篇 |
2009年 | 378篇 |
2008年 | 328篇 |
2007年 | 308篇 |
2006年 | 331篇 |
2005年 | 997篇 |
2004年 | 1022篇 |
2003年 | 783篇 |
2002年 | 321篇 |
2001年 | 146篇 |
2000年 | 142篇 |
1999年 | 96篇 |
1998年 | 89篇 |
1997年 | 81篇 |
1996年 | 73篇 |
1995年 | 87篇 |
1994年 | 82篇 |
1993年 | 62篇 |
1992年 | 66篇 |
1991年 | 60篇 |
1990年 | 78篇 |
1989年 | 66篇 |
1988年 | 61篇 |
1987年 | 68篇 |
1986年 | 59篇 |
1985年 | 70篇 |
1984年 | 91篇 |
1983年 | 71篇 |
1982年 | 70篇 |
1981年 | 59篇 |
1980年 | 71篇 |
1979年 | 55篇 |
1978年 | 57篇 |
1977年 | 41篇 |
1976年 | 53篇 |
1975年 | 55篇 |
1974年 | 39篇 |
1973年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Patrick F. Roche Christopher Packham Charles M. Telesco James T. Radomski Almudena Alonso-Herrero David K. Aitken Luis Colina Eric Perlman 《Monthly notices of the Royal Astronomical Society》2006,367(4):1689-1698
High spatial resolution spectroscopy at 8–13 μm with T-ReCS on Gemini-S has revealed striking variations in the mid-infrared emission and absorption in the nucleus of the Circinus galaxy (hereafter Circinus) on subarcsecond scales. The core of Circinus is compact and obscured by a substantial column of cool silicate dust. Weak extended emission to the east and west coincides with the coronal line region and arises from featureless dust grains which are probably heated by line emission in the coronal emission zone. The extended emission on the east side of the nucleus displays a much deeper silicate absorption than that on the west, indicating significant columns of cool material along the line of sight and corresponding to an additional extinction of AV ∼ 25 mag . Emission bands from aromatic hydrocarbons are not subject to this additional extinction, are relatively weak in the core and in the coronal line region, and are much more spatially extended than the continuum dust emission; they presumably arise in the circumnuclear star-forming regions. These data are interpreted in terms of an inclined disc-like structure around the nucleus extending over tens of parsecs and possibly related to the inner disc found from observations of water masers by Greenhill et al.. 相似文献
962.
963.
James B. Garvin 《Earth, Moon, and Planets》2004,94(3-4):221-232
The Vision for U.S. Space Exploration offers new opportunities for aggressively increasing the pace of scientific discoveries across the Solar System by empowering an on-site partnership between humans and robotics, enhanced by new technology-enabled capabilities. In particular, the early emphasis of this new Vision will be on development of new scientific activities on the Moon, and later on Mars. Integration of in situ traditional science activities with creative new types of applied scientific research on the Moon and Mars is a key ingredient in the US Vision. The Apollo era record of achievement involving human exploration is particularly informative, as it demonstrates the accelerated pace of scientific discovery and understanding that resulted from human “on site” activities, however briefly, on planetary surfaces. An example of how integrated human and robotic exploration can enable breakthrough science on the planet Mars is provided in order to illustrate these points. The scientific opportunities associated with the Vision for US Space Exploration are many, and with the incorporation of human-based capabilities on the Moon and Mars, an accelerated pace of discovery and understanding will be possible. 相似文献
964.
D. Heath Jones Will Saunders Matthew Colless Mike A. Read Quentin A. Parker Fred G. Watson Lachlan A. Campbell Daniel Burkey Thomas Mauch Lesa Moore Malcolm Hartley Paul Cass Dionne James Ken Russell Kristin Fiegert John Dawe John Huchra Tom Jarrett Ofer Lahav John Lucey Gary A. Mamon Dominique Proust Elaine M. Sadler Ken-ichi Wakamatsu 《Monthly notices of the Royal Astronomical Society》2004,355(3):747-763
965.
James Hamilton 《Applied Ocean Research》1993,15(6):373-380
An extension is proposed to the standard peak value distribution for time histories possessing wide banded spectra, which allows the distribution of an associated variable to be calculated at the instant that the peak value occurs, the theory is applicable to a wide range of practical circumstances, where it is desired to specify the value of associated response variables at the instant that the dominant response is a maximum. An example is given of the specification of coincident heave and roll of a barge for input to a structural load case analysis. 相似文献
966.
James E. H.Turner JeremyAllington-Smith † ScottChapman ‡ RobertContent ChristineDone RogerHaynes § DavidLee ¶ SimonMorris 《Monthly notices of the Royal Astronomical Society》2002,331(2):284-292
The centre of NGC 4151 has been observed in the J band with the SMIRFS integral field unit (IFU) on the UK Infrared Telescope. A map of [Fe ii ] emission is derived, and compared with the distributions of the optical narrow-line region and radio jet. We conclude that, because the [Fe ii ] emission is associated more closely with the visible narrow-line region than with the radio jet, it arises mainly through photoionization of gas by collimated X-rays from the Seyfert nucleus. The velocity field and strength with respect to Pa β are found to be consistent with this argument. The performance of the IFU is considered briefly, and techniques for observation and data analysis are discussed. 相似文献
967.
968.
969.
Witold Maciejewski James Binney 《Monthly notices of the Royal Astronomical Society》2001,323(4):831-838
We consider long-slit emission-line spectra of galactic nuclei when the slit is wider than the instrumental point spread function, and the target has large velocity gradients. The finite width of the slit generates complex distributions of brightness at a given spatial point in the measured spectrum, which can be misinterpreted as coming from additional physically distinct nuclear components. We illustrate this phenomenon for the case of a thin disc in circular motion around a nuclear black hole (BH). We develop a new method for estimating the mass of the BH that exploits a feature in the spectrum at the outer edge of the BH's sphere of influence, and therefore gives higher sensitivity to BH detection than traditional methods. Moreover, with this method we can determine the BH mass and the inclination of the surrounding disc separately, whereas the traditional approach to BH estimation requires two long-slit spectra to be taken. We show that, with a given spectrograph, the detectability of a BH depends on the sense of rotation of the nuclear disc. We apply our method to estimate the BH mass in M84 from a publicly available spectrum, and recover a value four times lower than that published previously from the same data. 相似文献
970.
W. James Shuttleworth 《水文研究》2002,16(10):2037-2039