全文获取类型
收费全文 | 1048篇 |
免费 | 195篇 |
国内免费 | 267篇 |
专业分类
测绘学 | 37篇 |
大气科学 | 154篇 |
地球物理 | 194篇 |
地质学 | 668篇 |
海洋学 | 106篇 |
天文学 | 219篇 |
综合类 | 72篇 |
自然地理 | 60篇 |
出版年
2024年 | 14篇 |
2023年 | 19篇 |
2022年 | 45篇 |
2021年 | 55篇 |
2020年 | 47篇 |
2019年 | 50篇 |
2018年 | 46篇 |
2017年 | 43篇 |
2016年 | 52篇 |
2015年 | 49篇 |
2014年 | 67篇 |
2013年 | 61篇 |
2012年 | 68篇 |
2011年 | 68篇 |
2010年 | 63篇 |
2009年 | 79篇 |
2008年 | 60篇 |
2007年 | 71篇 |
2006年 | 94篇 |
2005年 | 72篇 |
2004年 | 50篇 |
2003年 | 49篇 |
2002年 | 51篇 |
2001年 | 31篇 |
2000年 | 30篇 |
1999年 | 35篇 |
1998年 | 34篇 |
1997年 | 19篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 23篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
排序方式: 共有1510条查询结果,搜索用时 15 毫秒
141.
142.
143.
Thierry Montmerle Jean-Charles Augereau Marc Chaussidon Mathieu Gounelle Bernard Marty Alessandro Morbidelli 《Earth, Moon, and Planets》2006,98(1-4):39-95
The solar system, as we know it today, is about 4.5 billion years old. It is widely believed that it was essentially completed 100 million years after the formation of the Sun, which itself took less than 1 million years, although the exact chronology remains highly uncertain. For instance: which, of the giant planets or the terrestrial planets, formed first, and how? How did they acquire their mass? What was the early evolution of the “primitive solar nebula” (solar nebula for short)? What is its relation with the circumstellar disks that are ubiquitous around young low-mass stars today? Is it possible to define a “time zero” (t 0), the epoch of the formation of the solar system? Is the solar system exceptional or common? This astronomical chapter focuses on the early stages, which determine in large part the subsequent evolution of the proto-solar system. This evolution is logarithmic, being very fast initially, then gradually slowing down. The chapter is thus divided in three parts: (1) The first million years: the stellar era. The dominant phase is the formation of the Sun in a stellar cluster, via accretion of material from a circumstellar disk, itself fed by a progressively vanishing circumstellar envelope. (2) The first 10 million years: the disk era. The dominant phase is the evolution and progressive disappearance of circumstellar disks around evolved young stars; planets will start to form at this stage. Important constraints on the solar nebula and on planet formation are drawn from the most primitive objects in the solar system, i.e., meteorites. (3) The first 100 million years: the “telluric” era. This phase is dominated by terrestrial (rocky) planet formation and differentiation, and the appearance of oceans and atmospheres. 相似文献
144.
Elena B Volynets Svetlana A Schorokhova Ge Sun 《东北亚地学研究》2006,9(1):1-12
IntroductionThe Late Triassic strata andflora developed andwell outcropped in southern Pri morye,Russia.Thestrata are marine and non-marine alternate for eachother and yield abundant mollusk and plant fossilsinwhich the Late Triassic Mongugai flora is well-known in the world.Kryshtofovich(1910,1921,1924)and Kryshtofovich&Prynada(1932)studiedthis florainthe earlier ti me,and consequently,Sre-brodolyskaja(1958,1961,1968),Schorokhova(1975,1977,1997,2004)and Krassilov&Schorokhova(1970,1975)ma… 相似文献
145.
146.
M.S. Oey 《Astrophysics and Space Science》2002,281(1-2):483-486
Two fundamental constraints on the earliest star formation conditions in the Galaxy are an apparent empirical low-metallicity threshold of-4 ? [Fe/H], an and upper limit to the fraction of Population III halo stars of F III < 4 × 10-4. How do these observed constraints compare with predictions of simple models? This is investigated within the framework of element dispersal from clustered core-collapse SNe. Simple arguments considering turbulent mixing within multi-phase ISM suggest that the observed low-metallicity threshold is consistent with rough expected values. However, the observed limit on F III is two orders of magnitude larger than predictions from this simple, one-zone inhomogeneous chemical evolution. 相似文献
147.
Richard M. Tipping 《第四纪科学杂志》1988,3(2):171-182
Recent publications have presented palynological data from the early postglacial period in the British Isles, which have been interpreted as reflecting sequential glacial retreat following the Loch Lomond Stadial, The methodologies and results of these studies were examined and were concluded to be insufficient to demonstrate glacial retreat. A more cautious methodology was adopted and tested at several pollen sites in the Awe valley, Scotland. The results differed from previous studies in not demonstrating the sequence of palynological changes predicted from the hypothesis. These results need to be replicated at other localities, however, before the deglacial chronology hypothesis can be dismissed. Proposals to test the hypothesis further are suggested. 相似文献
148.
149.
Diagenetic signatures of stratal surfaces in the Upper Jurassic Fulmar Formation, Central North Sea, UKCS 总被引:2,自引:0,他引:2
FIONA E. BURNS STUART D. BURLEY ROB L. GAWTHORPE JOHN E. POLLARD 《Sedimentology》2005,52(6):1155-1185
Sedimentation rate and changes in relative sea level affect early diagenetic cementation along key stratal surfaces within the deeply buried Upper Jurassic Fulmar Formation, South Central Graben, UKCS. As a result of the bioturbated nature of the shallow marine strata, variations in ichnofabrics and cross-cutting relationships between trace fossils are important in identifying and correlating stratal surfaces. Two transgressive and two regressive surfaces/sequence boundaries were studied, using petrographical, mineralogical and geochemical techniques. Cements, including early diagenetic pyrite framboids, grain-rimming apatite, microcrystalline dolomite and ankerite, occur at, above and immediately below both transgressive and forced regressive surfaces/sequence boundaries. Breaks or subdued rates of sedimentation associated with both types of surfaces meant that the sediment package resided within early diagenetic zones for prolonged periods of time, enhancing diagenetic reactions at and below the surfaces. The distribution of ankerite, despite being a deep-burial cement, was primarily controlled by concentrations of bioclasts that are particularly abundant at transgressive surfaces. The diagenetic character of the forced regressive surfaces/sequence boundaries is more complex than that of the transgressive surfaces, both in terms of mineralogy and paragenesis. This is attributed to the superimposition of diagenetic assemblages as a result of erosion, re-sedimentation and sediment by-passing. Although the diagenetic signature of the surfaces has been modified by dissolution/replacement reactions during deep burial, early diagenetic signatures can still be distinguished. 相似文献
150.
The features of the CLEAN algorithm for Fourier analysis of time series with data separated by long pauses are analyzed in detail. Estimates are obtained for the limits of variability of the parameters of harmonic components that can be determined on a specified time grid. This analysis are used to search for harmonic components in the spectral line profile variations of the star Ori A (O8III) obtained in 2001 with the 1 m telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences.Translated from Astrofizika, Vol. 48, No. 1, pp. 87–100 (February 2005). 相似文献