全文获取类型
收费全文 | 250篇 |
免费 | 3篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 4篇 |
地球物理 | 42篇 |
地质学 | 123篇 |
海洋学 | 37篇 |
天文学 | 25篇 |
自然地理 | 20篇 |
出版年
2020年 | 5篇 |
2019年 | 1篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 2篇 |
2014年 | 4篇 |
2013年 | 15篇 |
2012年 | 7篇 |
2011年 | 13篇 |
2010年 | 7篇 |
2009年 | 14篇 |
2008年 | 12篇 |
2007年 | 6篇 |
2006年 | 11篇 |
2005年 | 9篇 |
2004年 | 10篇 |
2003年 | 13篇 |
2002年 | 3篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 5篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有254条查询结果,搜索用时 46 毫秒
251.
Viscous effects are expected to significantly contribute to reconnective energy release mechanisms in solar flares. While simple scaling arguments based on head-on reconnection suggest that viscous dissipation may dominate resistive dissipation, it is not clear whether these findings can be applied in more general merging situations. Here we perform side-by-side planar reconnection simulations driven by the Orszag–Tang vortex, for both classical and Braginskii forms of the viscosity. This formulation has the advantage of providing an autonomous MHD system that develops strong current layers, sustained by large-scale vortical shearing flows. The dissipation rates are shown to follow analytically based scaling laws, which suggest that viscous losses generated from large-scale non-uniform velocity fields are likely to dominate resistive losses in current-sheet reconnection solutions. 相似文献
252.
We measured tissue phosphorus content of high and low intertidal Hormosira banksii to test the hypothesis that tissue phosphorus content would be greater in individuals from the low intertidal because of greater total uptake associated with longer immersion in seawater. Moreover, we predicted that tissue phosphorus would be greater at sites where the seawater contained higher phosphate concentrations. There was a positive, linear relationship between local seawater phosphate concentrations and tissue phosphorus content of H. banksii from high and low intertidal zones at six different sites in winter. However, there were no comparable relationships in summer, even though the range of seawater phosphate concentration was similar in both seasons. The phosphorus contents of low intertidal H. banksii were significantly greater than high intertidal H. banksii in winter, but not in summer. Reasons for these differences may be related to greater access to seawater phosphate in low intertidal algae (than those in the high intertidal) in winter, followed by greater utilisation of the internal phosphorus between winter and summer, due to faster growth rates in the low intertidal. 相似文献
253.
Trace elements and cathodoluminescence of quartz in stockwork veins of Mongolian porphyry-style deposits 总被引:1,自引:0,他引:1
Axel Müller Richard Herrington Robin Armstrong Reimar Seltmann Douglas J. Kirwin Nina G. Stenina Andreas Kronz 《Mineralium Deposita》2010,45(7):707-727
The combination of scanning electron microscope–cathodoluminescence (CL), fluid inclusion analysis and high-resolution electron
probe microanalysis of Al, Ti, K and Fe in vein quartz has yielded results permitting a greater understanding of the complex
mineralisation of the Central Oyu Tolgoi and Zesen Uul porphyry-style deposits, southern Mongolia. These data demonstrate
the relationship between quartz precipitation, dissolution and ore deposition as the mineralising fluid chemistry changed
through time. Four major quartz generations are identified in the A-type veins from the stockworks of both the Central Oyu
Tolgoi (OTi to OTiv) and Zesen Uul deposits (ZUi to ZUiv). Despite differences in the associated alteration and mineralisation
style, the observed CL textures and trace element signatures of the quartz generations are comparable between deposits. The
OTi and ZUi stage formed both the primary network of A-type veins and pervasive silicification of the host rock. Using the
Ti-in-quartz geothermometer, crystallisation temperatures for OTi and ZUi of between 598°C and 880°C are indicated. The main
stage of sulphide mineralisation was accompanied by the dissolution of pre-existing quartz (OTi and ZUi) and precipitation
of a weakly luminescent generation of quartz (OTii and ZUii) with a low Ti content, reflected in a calculated temperature
drop from approximately 700°C to 340°C in Central Oyu Tolgoi and 445°C in Zesen Uul. OTii and ZUii stage quartzes show high
and variable Al concentrations. The next stage of quartz in both deposits (OTiii and ZUiii) forms a fine network of veins
in cracks formed in pre-existing quartz. OTiii and ZUiii quartz contain measurable fluid inclusions of moderate salinity (3–17.1 wt.%
NaCl eq.), entrapped in the temperature range 256°C to 385°C. OTiii and ZUiii are not related to any sulphide mineralisation.
The final OTiv and ZUiv stages are characterised by quartz–calcite micro-breccias that penetrate the A-type veins. Based on
the calculated entrapment temperatures, the OTiv/ZUiv stage crystallised between 212°C and 335°C, and the quartz is characterised
by elevated but variable Al and Fe contents. The CL and trace element signatures of the OTi to OTiii and ZUi to ZUiii stages
of the two Mongolian porphyries show similar features to those observed in porphyry-style deposits from other regions. This
suggests that a common sequence of quartz crystallisation occurs during the formation of early veins in many porphyry copper
systems. 相似文献
254.
Galina P. Bulanova Michael J. Walter Chris B. Smith Simon C. Kohn Lora S. Armstrong Jon Blundy Luiz Gobbo 《Contributions to Mineralogy and Petrology》2010,160(4):489-510
We report on a suite of diamonds from the Cretaceous Collier 4 kimberlite pipe, Juina, Brazil, that are predominantly nitrogen-free
type II crystals showing complex internal growth structures. Syngenetic mineral inclusions comprise calcium- and titanium-rich
phases with perovskite stoichiometry, Ca-rich majoritic-garnet, clinopyroxene, olivine, TAPP phase, minerals with stoichiometries
of CAS and K-hollandite phases, SiO2, FeO, native iron, low-Ni sulfides, and Ca–Mg-carbonate. We divide the diamonds into three groups on the basis of the carbon
isotope compositions (δ13C) of diamond core zones. Group 1 diamonds have heavy, mantle-like δ13C (−5 to −10‰) with mineral inclusions indicating a transition zone origin from mafic protoliths. Group 2 diamonds have intermediate
δ13C (−12 to −15‰), with inclusion compositions indicating crystallization from near-primary and differentiated carbonated melts
derived from oceanic crust in the deep upper mantle or transition zone. A 206Pb/238U age of 101 ± 7 Ma on a CaTiSi-perovskite inclusion (Group 2) is close to the kimberlite emplacement time (93.1 ± 1.5 Ma).
Group 3 diamonds have extremely light δ13C (−25‰), and host inclusions have compositions akin to high-pressure–temperature phases expected to be stable in pelagic
sediments subducted to transition zone depths. Collectively, the Collier 4 diamonds and their inclusions indicate multi-stage,
polybaric growth histories in dynamically changing chemical environments. The young inclusion age, the ubiquitous chemical
and isotopic characteristics indicative of subducted materials, and the regional tectonic history, suggest a model in which
generation of sublithospheric diamonds and their inclusions, and the proto-kimberlite magmas, are related genetically, temporally
and geographically to the interaction of subducted lithosphere and a Cretaceous plume. 相似文献