全文获取类型
收费全文 | 756篇 |
免费 | 19篇 |
国内免费 | 15篇 |
专业分类
测绘学 | 22篇 |
大气科学 | 60篇 |
地球物理 | 166篇 |
地质学 | 349篇 |
海洋学 | 38篇 |
天文学 | 115篇 |
综合类 | 2篇 |
自然地理 | 38篇 |
出版年
2022年 | 5篇 |
2021年 | 6篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 11篇 |
2016年 | 18篇 |
2015年 | 12篇 |
2014年 | 24篇 |
2013年 | 37篇 |
2012年 | 27篇 |
2011年 | 24篇 |
2010年 | 31篇 |
2009年 | 34篇 |
2008年 | 23篇 |
2007年 | 38篇 |
2006年 | 28篇 |
2005年 | 23篇 |
2004年 | 26篇 |
2003年 | 25篇 |
2002年 | 29篇 |
2001年 | 25篇 |
2000年 | 16篇 |
1999年 | 17篇 |
1998年 | 15篇 |
1997年 | 14篇 |
1996年 | 23篇 |
1995年 | 15篇 |
1994年 | 9篇 |
1993年 | 10篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 14篇 |
1989年 | 19篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1975年 | 7篇 |
1973年 | 5篇 |
1971年 | 4篇 |
1966年 | 5篇 |
1958年 | 5篇 |
排序方式: 共有790条查询结果,搜索用时 344 毫秒
141.
142.
For the period September 1978 to December 1982 we have identified 55 solar flare particle events for which our instruments on board the ISEE-3 (ICE) spacecraft detected electrons above 10 MeV. Combining our data with those from the ULEWAT spectrometer (MPI Garching and University of Maryland) electron spectra in the range from 0.1 to 100 MeV were obtained. The observed spectral shapes can be divided into two classes. The spectra of the one class can be fit by a single power law in rigidity over the entire observed range. The spectra of the other class deviate from a power law, instead exhibiting a steepening at low rigidities and a flattening at high rigidities. Events with power-law spectra are associated with impulsive (<1 hr duration) soft X-ray emission, whereas events with hardening spectra are associated with long-duration (<1 hr) soft X-ray emission. The characteristics of long-duration events are consistent with diffusive shock acceleration taking place high in the corona. Electron spectra of short-duration flares are well reproduced by the distribution functions derived from a model assuming simultaneous second-order Fermi acceleration and Coulomb losses operating in closed flare loops. 相似文献
143.
Wolfgang Kuhnt Florian Luderer Sandra Nederbragt Jürgen Thurow Thomas Wagner 《International Journal of Earth Sciences》2005,94(1):147-159
High sedimentation rates (up to 12 cm/kyear) of laminated organic carbon-rich biogenic limestones in the Tarfaya Basin provide an unusually high (millennial) resolution record of the late Cenomanian oceanic anoxic event (OAE-2). The global positive carbon-isotope excursion across the Cenomanian–Turonian corresponds to 11 light/dark sedimentary cycles. We interpret these cycles as a response to orbital obliquity variation and estimate the duration of the complete excursion as 440 kyear or one long eccentricity cycle. On this timescale, the main increase in 13C values occurred over a short time interval of less than 20 kyear in the late Cenomanian and reached a first maximum approximately 15 kyear prior to the bulk (mainly coccoliths) 18O-derived sea surface maximum temperature that occurs coeval to the extinction of Rotalipora cushmani. Organic carbon-accumulation rates follow obliquity cycles, reaching a maximum approximately 10 kyear after the last occurrence of R. cushmani, then slowly decreasing during the early Turonian. Thus, the maximum temperature and the maximum organic carbon accumulation in the Tarfaya Basin lagged by at least 15 kyear behind the global carbon-isotope shift and a proposed reduction of atmospheric CO2 content. The climate change across the Cenomanian/Turonian boundary probably occurred independent of CO2 levels and may have been controlled by different greenhouse gases (water vapour and methane) and changes in ocean circulation (i.e., opening of the Equatorial Atlantic gateway) 相似文献
144.
U-Pb zircon ages for the Luzhenguan Complex in northern part of the eastern Dabie orogen 总被引:4,自引:0,他引:4
Wolfgang Siebe 《中国科学D辑(英文版)》2005,48(9):1357-1367
The Dabie Mountain is the collisional orogenic belt between the North China Block and the Yangtze Block. As the eastern segment of the central-China orogenic belt, its tectonic framework is corresponding to the Qinling orogenic belt as a whole[1]. The NHB in northern part of Dabie Orogen is regarded as the joint belt between the Yangtze Block and the North China Block, and roughly corresponds to the north Qinling belt of the Qinling orogenic belt, which separated the Tongbai-Dabie hig… 相似文献
145.
W. Kundt 《Journal of Astrophysics and Astronomy》1984,5(3):277-283
Constraints are derived on the acceleration of charges in shocks to highly relativistic energies. When applied to the extended
extragalactic radio sources and to the cosmic rays, they cast doubt on the mechanism of ‘in-situ acceleration’, both for energy,
entropy and statistical mechanics reasons. 相似文献
146.
Żelaźniewicz Andrzej Dörr Wolfgang Bylina Paweł Franke Wolfgang Haack Udo Heinisch Helmut Schastok Janina Grandmontagne Klaus Kulicki Cyprian 《International Journal of Earth Sciences》2004,93(5):773-781
We report U–Pb single zircon ages from three pre-Variscan granitoids in the NE part of the Bohemian Massif. The Platerówka granodiorite from the Lausitz-Izera Unit, the Polish Sudetes, has been dated at 533±9 Ma. The Bitouchov granite form the SW part of the South Krkonoe Unit, the Czech Sudetes, gave an age of 540+11/–10 Ma, and the Wdroe granodiorite in the Fore-Sudetic Block yielded 548±9 Ma. All these latest Vendian/Early Cambrian granitoids represent the post-tectonic expression of a late Proterozoic Cadomian orogenic cycle and demonstrate the eastward extent of the Cadomian basement into the Variscan orogen. Granodiorites of similar age have so far been reported from Brittany and especially from the Saxo-Thuringian Terrane to the NE and SW of the Elbe Fault Zone. We conclude that the Saxo-Thuringian Terrane extends across the Elbe and Sudetic Marginal Fault Zones into the Fore-Sudetic Block. 相似文献
147.
Wolfgang?StinnesbeckEmail author Gerta?Keller Thierry?Adatte Markus?Harting Doris?Stüben Georg?Istrate Utz?Kramar 《International Journal of Earth Sciences》2004,93(6):1042-1065
CSDP core Yaxcopoil-1 was drilled to a depth of 1,511 m within the Chicxulub crater. An organic-rich marly limestone near the base of the hole (1,495 to 1,452 m) was deposited in an open marine shelf environment during the latest Cenomanian (uppermost Rotalipora cushmani zone). The overlying sequence of limestones, dolomites and anhydrites (1,495 to 894 m) indicates deposition in various carbonate platform environments (e.g., sabkhas, lagoons). A 100-m-thick suevite breccia (894–794 m) identifies the Chicxulub impact event. Above the suevite breccia is a dolomitic limestone with planktic foraminiferal assemblages indicative of Plummerita hantkeninoides zone CF1, which spans the last 300 ky of the Maastrichtian. An erosional surface 50 cm above the breccia/dolomite contact marks the K/T boundary and a hiatus. Limestones above this contact contain the first Tertiary planktic foraminifera indicative of an upper P. eugubina zone P1a(2) age. Another hiatus 7 cm upsection separates zone P1a(2) and hemipelagic limestones of planktic foraminiferal Zone P1c. Planktic foraminiferal assemblages of Zone Plc to P3b age are present from a depth of 794.04 up to 775 m. The Cretaceous carbonate sequence appears to be autochthonous, with a stratigraphic sequence comparable to late Cretaceous sediments known from outside the Chicxulub crater in northern and southern Yucatan, including the late Cenomanian organic-rich marly limestone. There is no evidence that these sediments represent crater infill due to megablocks sliding into the crater, such as major disruption of sediments, chaotic changes in lithology, overturned or deep dipping megablocks, major mechanical fragmentation, shock or thermal alteration, or ductile deformation. Breccia units that are intercalated in the carbonate platform sequence are intraformational in origin (e.g., dissolution of evaporites) and dykes are rare. Major disturbances of strata by the impact therefore appear to have been confined to within less than 60 km from the proposed impact center. Yaxcopoil-1 may be located outside the collapsed transient crater cavity, either on the upper end of an elevated and tilted horst of the terrace zone, or even outside the annular crater cavity. The Chicxulub site thus records a large impact that predates the K/T boundary impact and mass extinction. 相似文献
148.
In order to evaluate the Holocene palaeoenvironmental evolution of the Ugii Nuur basin, central Mongolia, investigations on chemical and mineralogical properties of lacustrine sediments were carried out on a 630 cm sediment core from lake Ugii Nuur. The interpretation of the record is based on a principal component analysis (PCA) of the elemental composition of the samples. The results show that lacustrine deposition started at 10.6 kyr BP. Low lake level conditions were identified during the Early Holocene (10.6-7.9 kyr BP). The Mid Holocene (7.9-4.2 kyr BP) was characterized by generally higher lake levels and thus higher moisture supply, but it experienced strong climatic fluctuations. Arid conditions prevailed from 4.2-2.8 kyr BP and were followed by a stable, more humid phase until today. 相似文献
149.
Till Kuhlbrodt Stefan Rahmstorf Kirsten Zickfeld Frode Bendiksen Vikebø Svein Sundby Matthias Hofmann Peter Michael Link Alberte Bondeau Wolfgang Cramer Carlo Jaeger 《Climatic change》2009,96(4):489-537
This paper discusses the risks of a shutdown of the thermohaline circulation (THC) for the climate system, for ecosystems
in and around the North Atlantic as well as for fisheries and agriculture by way of an Integrated Assessment. The climate
model simulations are based on greenhouse gas scenarios for the 21st century and beyond. A shutdown of the THC, complete by
2150, is triggered if increased freshwater input from inland ice melt or enhanced runoff is assumed. The shutdown retards
the greenhouse gas-induced atmospheric warming trend in the Northern Hemisphere, but does not lead to a persistent net cooling.
Due to the simulated THC shutdown the sea level at the North Atlantic shores rises by up to 80 cm by 2150, in addition to
the global sea level rise. This could potentially be a serious impact that requires expensive coastal protection measures.
A reduction of marine net primary productivity is associated with the impacts of warming rather than a THC shutdown. Regional
shifts in the currents in the Nordic Seas could strongly deteriorate survival chances for cod larvae and juveniles. This could
lead to cod fisheries becoming unprofitable by the end of the 21st century. While regional socioeconomic impacts might be
large, damages would be probably small in relation to the respective gross national products. Terrestrial ecosystem productivity
is affected much more by the fertilization from the increasing CO2 concentration than by a THC shutdown. In addition, the level of warming in the 22nd to 24th century favours crop production
in northern Europe a lot, no matter whether the THC shuts down or not. CO2 emissions corridors aimed at limiting the risk of a THC breakdown to 10% or less are narrow, requiring departure from business-as-usual
in the next few decades. The uncertainty about THC risks is still high. This is seen in model analyses as well as in the experts’
views that were elicited. The overview of results presented here is the outcome of the Integrated Assessment project INTEGRATION. 相似文献
150.