全文获取类型
收费全文 | 2894篇 |
免费 | 75篇 |
国内免费 | 56篇 |
专业分类
测绘学 | 294篇 |
大气科学 | 266篇 |
地球物理 | 509篇 |
地质学 | 1343篇 |
海洋学 | 140篇 |
天文学 | 360篇 |
综合类 | 51篇 |
自然地理 | 62篇 |
出版年
2023年 | 16篇 |
2022年 | 55篇 |
2021年 | 62篇 |
2020年 | 66篇 |
2019年 | 70篇 |
2018年 | 262篇 |
2017年 | 244篇 |
2016年 | 226篇 |
2015年 | 140篇 |
2014年 | 220篇 |
2013年 | 264篇 |
2012年 | 162篇 |
2011年 | 165篇 |
2010年 | 137篇 |
2009年 | 138篇 |
2008年 | 122篇 |
2007年 | 81篇 |
2006年 | 73篇 |
2005年 | 45篇 |
2004年 | 38篇 |
2003年 | 33篇 |
2002年 | 26篇 |
2001年 | 17篇 |
2000年 | 28篇 |
1999年 | 19篇 |
1998年 | 16篇 |
1997年 | 17篇 |
1996年 | 10篇 |
1995年 | 11篇 |
1994年 | 19篇 |
1993年 | 14篇 |
1992年 | 6篇 |
1991年 | 24篇 |
1990年 | 19篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 17篇 |
1986年 | 14篇 |
1985年 | 15篇 |
1984年 | 12篇 |
1982年 | 6篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1975年 | 8篇 |
1974年 | 11篇 |
1973年 | 6篇 |
1972年 | 8篇 |
1971年 | 5篇 |
1969年 | 5篇 |
排序方式: 共有3025条查询结果,搜索用时 15 毫秒
51.
Santanu Kumar Bhowmik 《Journal of Earth System Science》1997,106(3):131-146
A suite of rocks from Borra Carbonate Granulite Complex (BCGC) in the Eastern Ghats granulite belt displays superposed structures
and overprinted mineral assemblages that reveal multiple episodes of tectonothermal reworking of the complex under granulite
facies condition. Five distinct episodes of deformation (D1, D2, D3, D4 and D5) and four phases of metamorphism (M1, M2, M3 and M4) are recorded. The signature of the earliest tectonothermal event, D1 is a gneissic foliation (S1) denned by segregation of peak granulite facies mineral assemblages corresponding to prograde M1 metamorphism. M2 metamorphic overprint represents an episode of near-isobaric cooling of the complex under a static condition. D2 represents an episode of ductile deformation manifested by isoclinal folding (F2) and associated extensional structures, within a broad framework of coaxial bulk deformation. The present study reveals that
D2 took place subsequent to M2 - Subsequent deformation, D3, produced F3 folds and also deformations of boudins formed during D2. M3, which is synchronous with F3, represents a near isothermal decompression of the BCGC. This was followed by a weak structural readjustment (D4), producing E-W cross folds. The latter was not, however, associated with any recognizable petrological reworking. In the
terminal events, deformation (D5) and mineral reactions (M4) were localized along narrow intersecting shear zones. The latter acted as channelways for carbonic and still later hydrous
fluid infiltration. The available thermobarometric data from BCGC and other areas of the Eastern Ghats belt reveal that reworking
during M2 and M3 ensued in a thermally perturbed regime. The high thermal regime might also have persisted during carbonic fluid infiltration
related to terminal reworking (M4). 相似文献
52.
53.
The electron cyclotron waves that originate at low altitudes (<0.5 RE) and observed by ground facilities have been studied in the presence of a weak parallel electric field in auroral magnetoplasma consisting of trapped energetic auroral electrons and cold background electrons of ionospheric origin. The model distribution for auroral trapped electrons is taken as Maxwellian ring distribution. An expression for the growth rate has been obtained in the presence of parallel electric field assuming that the real frequency in the whistler mode is not affected by the presence of the electric field. The results show that waves grow (or damp) in amplitude for a parallel (or antiparallel) electric field. The influence of the electric field is more pronounced at a shorter wavelength spectrum. An increase in population of energetic electrons increases the growth rate and thus, plays a significant role in the wave excitation process in the auroral regions. 相似文献
54.
The concept of the equivalent free surface has been extended to determine the seismic horizontal pullout capacity of shallow
vertical strip plate anchors buried in sand. The analysis has been done rigorously by using the method of stress characteristics.
The results have been expressed in the form of non-dimensional charts. The pullout resistance has been found to reduce quite
extensively with increase in the magnitude of horizontal earthquake acceleration. The results were compared with the previously
published data, and it was seen that the computed pullout resistance with the proposed method was found to be lowest.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
55.
Mechanism of arrested charnockite formation at Nemmara, Palghat region, southern India 总被引:3,自引:0,他引:3
The formation of arrested charnockite is an excellent example of structurally controlled channellised fluid flow along specific sites accompanied by selective elemental mobility and mineralogical changes. The present paper recognises and focuses study on three types of arrested charnockite formation from Palghat region, namely, shear-controlled, foliation parallel and boudin-neck types, and address their spatio-temporal relations to regional-scale charnoenderbite. The shear-controlled and foliation parallel types post-date deformation and migmatisation. The boudin-neck type, on the contrary, is coeval with partial melting and followed the path of cooling and decreasing water activity in the gneiss. K-feldspar veining around plagioclase and quartz, symplectitic intergrowth of biotite+quartz after orthopyroxene and K-feldspar, and fluid inclusion data suggests the presence of alkalic supercritical brine and low-density CO2-rich fluid during charnockite formation. Charnockite domains developed following the breakdown of hornblende, biotite and quartz are characterised by a more or less pronounced depletion of Fe, Ca, Mg and Ti and trace elements Y and Zr, compared to their counterpart gneiss. REE spectra indicate a subtle depletion in the HREE near the centre of the charnockite domain. Although close-pair samples of gneiss–charnockite are isochemical, on a scale of a few millimetres, bi-directional element movement, related to the formation of new mineral was noted. It is postulated that arrested charnockite formation developed in situ on local scale within the granitic domains of the hornblende-biotite gneiss, in the presence of CO2-rich fluids and alkalic supercritical saline brine. This process post-dated the time of regional granulite (charnoenderbite) and large regional scale retrogression and migmatisation. 相似文献
56.
D. Shankar S. S. C. Shenoi R. K. Nayak P. N. Vinayachandran G. Nampoothiri A. M. Almeida G. S. Michael M. R. Ramesh Kumar D. Sundar O. P. Sreejith 《Journal of Earth System Science》2005,114(5):459-474
Hydrographic observations in the eastern Arabian Sea (EAS) during summer monsoon 2002 (during the first phase of the Arabian
Sea Monsoon Experiment (ARMEX)) include two approximately fortnight-long CTD time series. A barrier layer was observed occasionally
during the two time series. These ephemeral barrier layers were caused byin situ rainfall, and by advection of low-salinity (high-salinity) waters at the surface (below the surface mixed layer). These barrier
layers were advected away from the source region by the West India Coastal Current and had no discernible effect on the sea
surface temperature. The three high-salinity water masses, the Arabian Sea High Salinity Water (ASHSW), Persian Gulf Water
(PGW), and Red Sea Water (RSW), and the Arabian Sea Salinity Minimum also exhibited intermittency: they appeared and disappeared
during the time series. The concentration of the ASHSW, PGW, and RSW decreased equatorward, and that of the RSW also decreased
offshore. The observations suggest that the RSW is advected equatorward along the continental slope off the Indian west coast. 相似文献
57.
58.
59.
60.