全文获取类型
收费全文 | 38947篇 |
免费 | 752篇 |
国内免费 | 243篇 |
专业分类
测绘学 | 760篇 |
大气科学 | 2590篇 |
地球物理 | 7674篇 |
地质学 | 14127篇 |
海洋学 | 3578篇 |
天文学 | 8763篇 |
综合类 | 89篇 |
自然地理 | 2361篇 |
出版年
2022年 | 257篇 |
2021年 | 442篇 |
2020年 | 503篇 |
2019年 | 581篇 |
2018年 | 1016篇 |
2017年 | 1016篇 |
2016年 | 1085篇 |
2015年 | 587篇 |
2014年 | 1041篇 |
2013年 | 1858篇 |
2012年 | 1201篇 |
2011年 | 1640篇 |
2010年 | 1449篇 |
2009年 | 1816篇 |
2008年 | 1642篇 |
2007年 | 1701篇 |
2006年 | 1567篇 |
2005年 | 1076篇 |
2004年 | 1085篇 |
2003年 | 1115篇 |
2002年 | 1004篇 |
2001年 | 872篇 |
2000年 | 800篇 |
1999年 | 726篇 |
1998年 | 718篇 |
1997年 | 724篇 |
1996年 | 591篇 |
1995年 | 575篇 |
1994年 | 504篇 |
1993年 | 455篇 |
1992年 | 410篇 |
1991年 | 428篇 |
1990年 | 438篇 |
1989年 | 392篇 |
1988年 | 370篇 |
1987年 | 402篇 |
1986年 | 415篇 |
1985年 | 509篇 |
1984年 | 546篇 |
1983年 | 544篇 |
1982年 | 496篇 |
1981年 | 456篇 |
1980年 | 430篇 |
1979年 | 409篇 |
1978年 | 376篇 |
1977年 | 384篇 |
1976年 | 345篇 |
1975年 | 356篇 |
1974年 | 340篇 |
1973年 | 371篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Mallory S. E. Roberts Crystal L. Brogan Bryan M. Gaensler Jason W. T. Hessels C.-Y. Ng Roger W. Romani 《Astrophysics and Space Science》2005,297(1-4):93-100
A remarkable number of pulsar wind nebulae (PWN) are coincident with EGRET γ-ray sources. X-ray and radio imaging studies of unidentified EGRET sources have resulted in the discovery of at least six new pulsar wind nebulae (PWN). Stationary PWN (SPWN) appear to be
associated with steady EGRET sources with hard spectra, typical for γ-ray pulsars. Their toroidal morphologies can help determine the geometry of the
pulsar which is useful for constraining models of pulsed γ-ray emission. Rapidly moving PWN (RPWN) with more cometary morphologies
seem to be associated with variable EGRET sources in regions where the ambient medium is dense compared to what is typical for the ISM. 相似文献
12.
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
13.
14.
15.
The main properties of the first- and second-order moments of polarized hydrogen lines, forming in the presence of stationary electric and magnetic fields, are reviewed. The analytical results presented here apply directly to the case of optically-thin emission lines in the LTE regime. Some applications of such results to electric- and magnetic-field diagnostics in (solar) plasmas are then briefly considered.On leave from the Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, Largo E. Fermi 5, I-50125 Firenze, Italy 相似文献
16.
17.
18.
The elm decline of 5000 14C yr ago has been the most widely discussed phenomenon in post‐glacial vegetation history. This pan‐European reduction of elm populations, echoed in the decimation of elmwoods in Europe during the twentieth century, has attracted a series of interrelated hypotheses involving climate change, human activity, disease and soil deterioration. The elm bark beetle (Scolytus scolytus L.) is an essential component of disease explanations. We present evidence for the presence of the beetle over a prolonged period (ca. 7950–4910 yr BP [8800–5660 cal. yr BP]) from a lowland raised mire deposit in northeast Scotland, with its final appearance at this site, and the first and only appearance in another mire of a single scolytid find, around the time of the elm decline. The subfossil S. scolytus finds are not only the first from Scotland, but they also represent the most comprehensive sequence of finds anywhere. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
19.
20.
The growth of Glasgow from a small town into a heavily industrialised conurbation depended greatly on its local geological riches. Extensive mining and quarrying of a range of minerals took place from the 18th century onwards. The early underground stoop and room (pillar and stall) workings, and the backfilled quarries, together with variably consolidated natural superficial deposits, have bequeathed to the city a heritage of unwanted engineering problems which cannot easily be quantified. Recent work by the British Geological Survey (BGS) illustrates the scale of both geological and man-made problems. 相似文献