全文获取类型
收费全文 | 258871篇 |
免费 | 4360篇 |
国内免费 | 3388篇 |
专业分类
测绘学 | 7006篇 |
大气科学 | 19149篇 |
地球物理 | 54415篇 |
地质学 | 89363篇 |
海洋学 | 21402篇 |
天文学 | 56194篇 |
综合类 | 1020篇 |
自然地理 | 18070篇 |
出版年
2021年 | 2284篇 |
2020年 | 2640篇 |
2019年 | 2877篇 |
2018年 | 3336篇 |
2017年 | 3024篇 |
2016年 | 5647篇 |
2015年 | 4258篇 |
2014年 | 6983篇 |
2013年 | 14296篇 |
2012年 | 6478篇 |
2011年 | 7815篇 |
2010年 | 6737篇 |
2009年 | 9446篇 |
2008年 | 8359篇 |
2007年 | 7726篇 |
2006年 | 9729篇 |
2005年 | 7747篇 |
2004年 | 7675篇 |
2003年 | 7184篇 |
2002年 | 6794篇 |
2001年 | 6056篇 |
2000年 | 5984篇 |
1999年 | 5218篇 |
1998年 | 5239篇 |
1997年 | 5063篇 |
1996年 | 4702篇 |
1995年 | 4448篇 |
1994年 | 4125篇 |
1993年 | 3873篇 |
1992年 | 3667篇 |
1991年 | 3605篇 |
1990年 | 3783篇 |
1989年 | 3525篇 |
1988年 | 3311篇 |
1987年 | 3863篇 |
1986年 | 3408篇 |
1985年 | 4246篇 |
1984年 | 4755篇 |
1983年 | 4425篇 |
1982年 | 4334篇 |
1981年 | 3943篇 |
1980年 | 3649篇 |
1979年 | 3516篇 |
1978年 | 3486篇 |
1977年 | 3284篇 |
1976年 | 3051篇 |
1975年 | 2963篇 |
1974年 | 2927篇 |
1973年 | 3079篇 |
1972年 | 2029篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
861.
862.
Up-temperature flow of surface-derived fluids in the mid-crust: the role of pre-orogenic burial of hydrated fault rocks 总被引:1,自引:0,他引:1
The Walter‐Outalpa shear zone in the southern Curnamona Province of NE South Australia is an example of a shear zone that has undergone intensely focused fluid flow and alteration at mid‐crustal depths. Results from this study have demonstrated that the intense deformation and ductile shear zone reactivation, at amphibolite facies conditions of 534 ± 20 °C and 500 ± 82 MPa, that overprint the Proterozoic Willyama Supergroup occurred during the Delamerian Orogeny (c. 500 Ma) (EPMA monazite ages of 501 ± 16 and 491 ± 19 Ma). This is in contrast to the general belief that the majority of basement deformation and alteration in the southern Curnamona Province occurred during the waning stages of the Olarian Orogeny (c. 1610–1580 Ma). These shear zones contain hydrous mineral assemblages that cut wall rocks that have experienced amphibolite facies metamorphism during the Olarian Orogeny. The shear zone rock volumes have much lower δ18O values (as low as 1‰) than their unsheared counterparts (7–9‰), and calculated fluid δ18O values (5–8‰) consistent with a surface‐derived fluid source. Hydrous minerals show a decrease in δD(H2O) from ?14 to ?22‰, for minerals outside the shear zones, to ?28 to ?40‰, for minerals within the shear zones consistent with a contribution from a meteoric source. It is unclear how near‐surface fluids initially under hydrostatic pressure penetrate into the middle crust where fluid pressures approach lithostatic, and where fluid flow is expected to be dominantly upward because of pressure gradients. We propose a mechanism whereby faulting during basin formation associated with the Adelaidean Rift Complex (c. 700 Ma) created broad hydrous zones containing mineral assemblages in equilibrium with surface waters. These panels of fault rock were subsequently buried to depths where the onset of metamorphism begins to dehydrate the fault rock volumes evolving a low δ18O fluid that is channelled through shear zones related to Delamerian Orogenic activity. 相似文献
863.
864.
865.
866.
I. R. Plimer 《Mineralogy and Petrology》2006,88(3-4):443-478
Summary The Palaeoproterozoic Broken Hill Pb–Zn–Ag stratiform orebody is intimately associated with manganoan garnet-bearing rocks.
On stratigraphic and chemical grounds it is argued that garnet-rich metasediments below, equivalent to and above massive sulphide
were hydrothermal precipitates. Other manganoan garnet rocks formed during pre-metamorphic hydrothermal alteration, syn-metamorphic
dehydration and reaction of manganese with prograde pelitic rocks, reaction between cataclastic manganese-bearing sulphide
rocks injected along axial planes, shears and faults and pelitic wall rocks and reaction between dolerite dykes and sulphide
rocks. 相似文献
867.
868.
The U.S. and U.K. literatures have discussed “food deserts,” reflecting populated, typically urban, low‐income areas with limited access to full‐service supermarkets. Less is known about supermarket accessibility within Canadian cities. This article uses the minimum distance and coverage methods to determine supermarket accessibility within the city of Edmonton, Canada, with a focus on high‐need and inner‐city neighborhoods. The results show that for 1999 both of these areas generally had higher accessibility than the remainder of the city, but six high‐need neighborhoods had poor supermarket accessibility. We conclude by examining potential reasons for differences in supermarket accessibility between Canadian, U.S., and U.K. cities. 相似文献
869.
870.
Károly Posgay Tamás Bodoky Zoltán Hajnal Tivadar M. Tóth Tamás Fancsik Endre Hegeds Attila Cs. Kovács Ern Takács 《Geophysical Journal International》2006,167(1):187-203
The geologic origin of subhorizontal reflections, often observed in crustal seismic sections, was investigated by establishing metamorphic facies and strength of rocks in depth, and correlating these properties to seismic reflection sections from eastern Hungary. Estimation of the depths of metamorphic mineral stability zones utilized the principles developed by Fyfe et al. and known geothermal data of the area. The strength versus depth profile was derived by relating local seismic P -wave interval velocities to Meissner et al. 's activation energy. The results show that the series of subhorizontal reflections, observed in the Pannonian Basin, are a consequence of combined metamorphic and rheologic changes in depths. The synthesis of the integrated data set suggests that the retrograde alteration of the pre-Tertiary basement above the percolation threshold was made possible by the softening effect of shear zones and their water-conducting capacity. The subhorizontal reflections of highest energy, of the consolidated crust below the percolation threshold, originate in the depths of greenschist, amphibolite and granulite metamorphic mineral facies, which were formed in geothermal and pressure conditions similar to those existing today. These results imply the overprint of earlier (Variscan) metamorphic sequences of the crust by more recent retrograde metamorphic processes. 相似文献