全文获取类型
收费全文 | 68132篇 |
免费 | 993篇 |
国内免费 | 438篇 |
专业分类
测绘学 | 1432篇 |
大气科学 | 3938篇 |
地球物理 | 13422篇 |
地质学 | 25215篇 |
海洋学 | 6218篇 |
天文学 | 15889篇 |
综合类 | 174篇 |
自然地理 | 3275篇 |
出版年
2022年 | 599篇 |
2021年 | 923篇 |
2020年 | 1037篇 |
2019年 | 1163篇 |
2018年 | 2247篇 |
2017年 | 2122篇 |
2016年 | 2324篇 |
2015年 | 1084篇 |
2014年 | 2163篇 |
2013年 | 3476篇 |
2012年 | 2439篇 |
2011年 | 3098篇 |
2010年 | 2805篇 |
2009年 | 3328篇 |
2008年 | 2993篇 |
2007年 | 3171篇 |
2006年 | 2874篇 |
2005年 | 1801篇 |
2004年 | 1725篇 |
2003年 | 1779篇 |
2002年 | 1603篇 |
2001年 | 1507篇 |
2000年 | 1318篇 |
1999年 | 1060篇 |
1998年 | 1082篇 |
1997年 | 1121篇 |
1996年 | 879篇 |
1995年 | 874篇 |
1994年 | 789篇 |
1993年 | 698篇 |
1992年 | 653篇 |
1991年 | 687篇 |
1990年 | 731篇 |
1989年 | 634篇 |
1988年 | 601篇 |
1987年 | 640篇 |
1986年 | 579篇 |
1985年 | 776篇 |
1984年 | 813篇 |
1983年 | 802篇 |
1982年 | 741篇 |
1981年 | 680篇 |
1980年 | 655篇 |
1979年 | 590篇 |
1978年 | 597篇 |
1977年 | 574篇 |
1976年 | 503篇 |
1975年 | 514篇 |
1974年 | 495篇 |
1973年 | 554篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
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
23.
24.
V. Delouille J. De Patoul J. F. Hochedez L. Jacques J. P. Antoine 《Solar physics》2005,228(1-2):301-321
The extreme ultraviolet imaging telescope (EIT) of SOHO offers a unique record of the solar atmosphere for its sampling in
temperature, field of view, resolution, duration, and cadence. To investigate globally and locally its topology and evolution
during the solar cycle, we consider a multi-scale approach, and more precisely we use the wavelet spectrum.
We present three results among the applications of such a procedure. First, we estimate the typical dimension of the supergranules
as seen in the 30.4 nm passband, and we show that the evolution of the characteristic network scale is almost in phase with
the solar cycle. Second, we build pertinent time series that give the evolution of the signal energy present in the corona
at different scales. We propose a method that detects eruptions and post-flaring activity in EUV image sequences. Third, we
introduce a new way to extract active regions in EIT images, with perspectives in, e.g., long-term irradiance analysis. 相似文献
25.
26.
27.
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
28.
29.
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
30.
We discuss long-time changes of polar activity of the Sun using the new observational data sets in the optical range during
1872–2001. A study of the secular and cycle variations of the magnetic activity at the high-latitude regions is the main goal
that includes polar magnetic field reversals during 1872–2001 and secular changes of the duration of polar activity cycles.
The secular increase of the area of polar zones during the minimum activity in the last 120 years and as consequence a decrease
of coronal temperature of the Sun in the high-latitude zones during the last 50 years. Correlation between the polar cycles
of Caii-K bright points with the Wolf sunspot numbers cycles, W(t), and the 22-year polar magnetic cycles of Caii-K bright points at the high latitudes during 1905–1995 is discussed. 相似文献