全文获取类型
收费全文 | 4000篇 |
免费 | 147篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 169篇 |
大气科学 | 577篇 |
地球物理 | 940篇 |
地质学 | 1660篇 |
海洋学 | 160篇 |
天文学 | 500篇 |
综合类 | 15篇 |
自然地理 | 136篇 |
出版年
2021年 | 62篇 |
2020年 | 56篇 |
2019年 | 37篇 |
2018年 | 123篇 |
2017年 | 140篇 |
2016年 | 211篇 |
2015年 | 125篇 |
2014年 | 189篇 |
2013年 | 239篇 |
2012年 | 92篇 |
2011年 | 150篇 |
2010年 | 160篇 |
2009年 | 199篇 |
2008年 | 137篇 |
2007年 | 106篇 |
2006年 | 98篇 |
2005年 | 77篇 |
2004年 | 51篇 |
2003年 | 59篇 |
2002年 | 81篇 |
2001年 | 76篇 |
2000年 | 65篇 |
1999年 | 66篇 |
1998年 | 68篇 |
1997年 | 61篇 |
1996年 | 52篇 |
1995年 | 62篇 |
1994年 | 70篇 |
1993年 | 32篇 |
1992年 | 34篇 |
1991年 | 31篇 |
1990年 | 41篇 |
1989年 | 36篇 |
1988年 | 29篇 |
1987年 | 32篇 |
1985年 | 45篇 |
1984年 | 44篇 |
1983年 | 53篇 |
1982年 | 41篇 |
1981年 | 42篇 |
1980年 | 38篇 |
1979年 | 32篇 |
1978年 | 55篇 |
1977年 | 31篇 |
1976年 | 33篇 |
1975年 | 44篇 |
1974年 | 51篇 |
1973年 | 48篇 |
1969年 | 25篇 |
1968年 | 25篇 |
排序方式: 共有4157条查询结果,搜索用时 178 毫秒
951.
952.
G. F. Chörny 《Celestial Mechanics and Dynamical Astronomy》2007,97(4):229-248
A restricted three-body problem for a dust particle, in presence of a spherical cometary nucleus in an eccentric (elliptic,
parabolic or hyperbolic) orbit about the Sun, is considered. The force of radiation pressure and the Poynting– Robertson effect
are taken into account. The differential equations of the particle’s non-inertial spatial motion are investigated both analytically
and numerically. With the help of a complex representation, a new single equation of the motion is obtained. Conversion of
the equations of motion system into a single equation allows the derivation of simple expressions similar to the integral
of energy and integrals of areas. The derived expressions are named quasiintegrals. Relative values of terms of the energy
quasiintegral for a smallest, largest, and a mean comet are calculated. We have found that in a number of cases the quasiintegrals
are related to the regular integrals of motion, and discuss how the quasiintegrals may be applied to find some significant
constraints on the motion of a body of infinitesimal mass. 相似文献
953.
Mike Walker Sigfus Johnsen Sune Olander Rasmussen Trevor Popp Jørgen‐Peder Steffensen Phil Gibbard Wim Hoek John Lowe John Andrews Svante Björck Les C. Cwynar Konrad Hughen Peter Kershaw Bernd Kromer Thomas Litt David J. Lowe Takeshi Nakagawa Rewi Newnham Jakob Schwander 《第四纪科学杂志》2009,24(1):3-17
The Greenland ice core from NorthGRIP (NGRIP) contains a proxy climate record across the Pleistocene–Holocene boundary of unprecedented clarity and resolution. Analysis of an array of physical and chemical parameters within the ice enables the base of the Holocene, as reflected in the first signs of climatic warming at the end of the Younger Dryas/Greenland Stadial 1 cold phase, to be located with a high degree of precision. This climatic event is most clearly reflected in an abrupt shift in deuterium excess values, accompanied by more gradual changes in δ18O, dust concentration, a range of chemical species, and annual layer thickness. A timescale based on multi‐parameter annual layer counting provides an age of 11 700 calendar yr b2 k (before AD 2000) for the base of the Holocene, with a maximum counting error of 99 yr. A proposal that an archived core from this unique sequence should constitute the Global Stratotype Section and Point (GSSP) for the base of the Holocene Series/Epoch (Quaternary System/Period) has been ratified by the International Union of Geological Sciences. Five auxiliary stratotypes for the Pleistocene–Holocene boundary have also been recognised. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
954.
The Eifelian sedimentary record in the epeiric Baltic Basin contains an extensive brecciated interval known as the Narva Breccia. During recent decades, the origin of this breccia has been attributed to (1) palaeoseismicity, (2) extraterrestrial impact event or (3) diagenetic collapse. Our studies show the presence of two different breccia types that form 11 stratigraphic horizons and contain several laterally and stratigraphically unrelated breccias. The occurrence of Type‐1 and Type‐2 breccias, together with carbonate sabkha and carbonate inter‐ to supratidal tidal flat deposits on the basin margins, indicates synsedimentary brecciation formed in a sabkha environment. Type‐2 breccia could also originate from wave‐cycling loading. 相似文献
955.
This paper examines Earth System Science as a novel approach to global environmental change research. Drawing upon Michel Foucault's governmentality concept, the paper opens up the Earth System metaphor to political analysis and asks what it does to our understanding of nature and society as a governable domain. We trace the scientific practices that have produced the Earth System as a thinkable analytical category back to the International Geophysical Year in 1957. We also identify ‘the Anthropocene’ as a central and yet ambiguous system of thought for Earth System Science that harbours different strategies for sustainability in terms of (1) the persons over whom government is to be exercised; (2) the distribution of tasks and actions between authorities; and (3) contrasting ideals or principles for how government should be directed. 相似文献
956.
L. Kölbl 《International Journal of Earth Sciences》1927,18(5):321-349
Ohne Zusammenfassung 相似文献
957.
For the case of Tycho’s supernova remnant (SNR) we present the relation between the blast wave and contact discontinuity radii
calculated within the nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs. It is demonstrated that these radii
are confirmed by recently published Chandra measurements which show that the observed contact discontinuity radius is so close
to the shock radius that it can only be explained by efficient CR acceleration which in turn makes the medium more compressible.
Together with the recently determined new value E
sn=1.2×1051 erg of the SN explosion energy this also confirms our previous conclusion that a TeV γ-ray flux of (2–5)×10−13 erg/(cm2 s) is to be expected from Tycho’s SNR. Chandra measurements and the HEGRA upper limit of the TeV γ-ray flux together limit the source distance d to 3.3≤d≤4 kpc. 相似文献
958.
Jens Böcher 《Boreas: An International Journal of Quaternary Research》2012,41(4):644-659
Sediments from the last interglacial (Eemian) in Jameson Land, East Greenland, and the Thule area, NW Greenland, have revealed a number of insect fragments of both arctic and more or less warmth‐demanding species. Altogether, the interglacial fauna of Coleoptera (beetles) indicates boreal conditions. Undoubtedly, a large fraction of the insect fauna succumbed when the mild Eemian climate cooled drastically during the last glacial stage. However, a group of hardy species now found far north into the High Arctic might be glacial survivors. It is, however, still puzzling why well‐adapted arctic beetle species such as Amara alpina and Isochnus arcticus did not survive the last glacial stage in Greenland. Two factors that have not been sufficiently considered when discussing survival contra extinction are the importance of microclimate and the number of sun‐hours during the Arctic summer. Even among the Coleoptera, which as a group fares quite badly in the Arctic, there might be survivors, at least among those found both during the interglacial and as fossils during the early Holocene. First of all, glacial survival applies to the seed bug Nysius groenlandicus, which was widespread during the Eemian, was found soon after the last deglaciation, and is now almost omnipresent in Greenland. 相似文献
959.
960.
Fred Saunders Salim M. Mohammed Narriman Jiddawi Karolina Nordin Bengt Lundèn Sara Sjöling 《Ocean & Coastal Management》2010,53(4):150-160
Coastal areas in East Africa are experiencing rapid economic, resource management, demographic and technological shifts. In response diverse Community-based Natural Resource Management (CBNRM) applications have been embraced to provide mutual conservation and use benefits. These initiatives have met with mixed success in practice. Reflecting on the limitations of past research using common pool resources theory theory to study CBNRM we use insights from actor oriented theory combined with satellite image analysis to describe and discuss the forces dynamically influencing institutional and mangrove forest cover change at Kisakasaka, Zanzibar focussing on the formal CBNRM project period between 1996 and 2001, but also considering the period before and after this. We examine the shifting social relations that affected the performance and viability of the formal CBNRM arrangements. An integrated approach was taken to the presentation and discussion of results where it was possible to enrich and expand explanations of socio-environmental change, which was driven by a lack of government support, the undermining effects of party political divisions, and the lack of institutional adaptive capacity. We conclude that this was a useful approach to explain CBNRM intervention events at Kisakasaka. 相似文献