全文获取类型
收费全文 | 297篇 |
免费 | 6篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 24篇 |
大气科学 | 14篇 |
地球物理 | 56篇 |
地质学 | 146篇 |
海洋学 | 13篇 |
天文学 | 49篇 |
自然地理 | 5篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 22篇 |
2017年 | 24篇 |
2016年 | 13篇 |
2015年 | 9篇 |
2014年 | 18篇 |
2013年 | 30篇 |
2012年 | 11篇 |
2011年 | 18篇 |
2010年 | 15篇 |
2009年 | 15篇 |
2008年 | 7篇 |
2007年 | 7篇 |
2006年 | 9篇 |
2005年 | 6篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 6篇 |
2001年 | 4篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1967年 | 2篇 |
排序方式: 共有307条查询结果,搜索用时 828 毫秒
91.
P. K. Mukherjee 《Bulletin of Volcanology》1971,35(4):887-906
Nine basaltic lava-flows, which vary in thickness between 60 feet and 300 feet, were established in the NW Rajmahals. The flows were, at places, laid down one above the other and, at others, were found to contain intervening intertrappean horizons. All the flows are essentially of basaltic composition and are made up of labradoritie plagioclase, pigeonitic and augitic pyroxene, opaque ore, primary glass and secondary minerals (palagonite, secondary silica, calcite and zeolite). The phenocrystic plagioclase ranges in composition between An72 and An62, while the constituents of the groundmass range between An50 and An17. The microphenocrysts of pyroxene are mainly augitic and occasionally pigeonitic while the constituents of the groundmass are essentially pigeonitic. The opaque minerals are magnetite and ilmenite. Petrographically, the lava-flows are more or less similar to one another. The first three flows are, however, more remarkably porphyritic and a little coarser in grain size than the six overlying flows. The eighth flow is devoid of palagonite. Calcite occurs only in certain portions of the second flow. There is a gradual increase in the percentage of primary glass from the first to the ninth flow with a corresponding fall in the total percentage of plagioclase and pyroxene. Statistical analysis of the grain size variation in the plagioclases was carried out and the results were found to be directly related to the prevailing rates of cooling in the different flows and also in the different horizons of the same flow. Modal analysis of the nine flows (in all, 98 samples) was carried out and this brought out some interesting results. Samples from three of the flows were analysed chemically and the corresponding norms were calculated. The order of crystallisation of the primary constituents was established from petrographic and petrological studies. The basaltic magma, which gave rise to the lava-flows of this region, does not appear to have undergone any significant differentiation during the course of its cooling and consolidation. The only discernible effect of crystallisati on differentiation was an enrichment of silica (and, perhaps, alkalis) in the residual liquids and no noteworthy enrichment of iron appears to have occurred at any stage. 相似文献
92.
Sunita Mukherjee 《Pure and Applied Geophysics》1969,72(1):45-50
Summary Stresses produced due to a moving load over the plane surface (supposed to be rough) of a semi-infinite transversely isotropic medium have been calculated in this paper. 相似文献
93.
Sunita Mukherjee 《Pure and Applied Geophysics》1968,70(1):39-46
Summary By using the Laplace transform method, solution has been obtained for the elastodynamic problem due to blast pulse on the inner surface of a spherical cavity in an infinite spherically aeolotropic elastic solid. Both types of blast producing radial and rotational waves have been considered. 相似文献
94.
Sulphide ore mineralization developed in proximity to iron formations in a cyclic volcano-sedimentary sequence that forms
the offshore part of the late Archaean intracratonic basin of the Chitradurga greenstone belt, south India. The chemistry
of volcanic suite attests to an extensive rock-water interaction resulting in exchange of Si and Na for divalent cations,
including Cu, Pb and Zn. The exchange took place during hydrothermal alteration of basalt prior to its involvement in regional
deformation and metamorphism. A hydrothermal convection system extracted Cu, Zn and Pb from sea-floor basalts during a static
phase of evolution of the Chitradurga basin and developed the stratabound ore deposit within the pyroclastics and the stringer
ores below. 相似文献
95.
The activity of a silicate liquid component in a melt at an elevated liquidus temperature and pressure may be expressed analytically in terms of the 1-bar liquidus temperature activity and functions of the partial molar volume and partial molar enthalpy of mixing. Alternatively, the activity of the elevated (i.e. higherP-T) liquidus may be expressed in terms of the difference of heat content, heat capacity, entropy and volume of the component in the crystalline form and in the melt. Equating these two expressions, the partial molar enthalpy of mixing and there-from the partial molar entropy of mixing may be determined, provided the liquidus temperatures of the phase in question at both 1 bar and higher pressure and at a constant melt composition are known. Several such retrievals for CaMgSi2O6, Mg2SiO4, NaAlSi3O8, and TiO2 from experimental phase equilibrium data are presented. It is argued that as the partial molar enthalpy of mixing generally has large values, the regular solution formulation on the basis of a constant function of the activity coefficient would lead to erroneousP-T estimates for ascending magmas. 相似文献
96.
Amalbikash Mukherjee 《Contributions to Mineralogy and Petrology》1967,16(2):139-148
The role of fractional crystallization in the descent: basalt trachyte is critically examined. For each simple basalt magma type — alkaline, critically undersaturated, and oversaturated — there is a possible trachyte derived by way of fractional crystallization. Olivine removal is the main physical control that may interfere with trachytic trends at low pressure. Higher pressures widen the field of the initial basic compositions from which alkaline trachytes may fractionate. Bowen's hypothesis of trachyte formation from an undercooled basic magma is not supported by recent experimental data. Inefficiency and lack of scope of the fractional crystallization process, in the late stage of differentiation, may lead to an excess of trachytes over trachyandesites. In general, more time, taken in the basic and the salic stages of the descent, due to steeper liquidus and solidus, would result in a greater abundance of the basic and the salic rock types, compared to the intermediate varieties. 相似文献
97.
Jyotirmay Mukherjee 《Pure and Applied Geophysics》1970,82(1):11-18
Summary In this paper, the waves propagated in an infinite medium has been considered by disturbances on the surface of a burried spherical source. The disturbances are produced by two types of forces viz. i) Transient normal force, ii) Transient twist applied on the surface of the source. The solutions are obtained in a very simple form. Graphical representations of some numerical solutions has been added at the end of each problem. 相似文献
98.
Abhijit Basu 《Journal of Earth System Science》2005,114(3):375-380
Back scattered electron and transmission electron imaging of lunar soil grains reveal an abundance of submicrometer-sized
pure Fe0 globules that occur in the rinds of many soil grains and in the submillimeter sized vesicular glass-cemented grains called
agglutinates. Grain rinds are amorphous silicates that were deposited on grains exposed at the lunar surface from transient
vapors produced by hypervelocity micrometeorite impacts. Fe0 may have dissociated from Fe-compounds in a high temperature (>3000°C) vapor phase and then condensed as globules on grain
surfaces. The agglutinitic glass is a quenched product of silicate melts, also produced by micrometeorite impacts on lunar
soils. Reduction by solar wind hydrogen in agglutinitic melts may have produced immiscible droplets that solidified as globules.
The exact mechanism of formation of such Fe0 globules in lunar soils remains unresolved. 相似文献
99.
Basab Mukhopadhyay P. K. Mukherjee Debkumar Bhattacharya S. Sengupta 《Environmental Geology》2006,49(7):1009-1020
Groundwater extracted from shallow aquifers in the Bengal Delta is contaminated with arsenic. The fluviodeltaic process that
creates aquifers, ironically, extends its role to also contaminating them with arsenic. The arsenic distribution maps show
a spatial association of arsenic-contaminated wells with palaeo/cut-off/abandoned channels. Weight-on-evidences analysis indicates
that the zones of contamination occur around palaeo-channels within a corridor of 500–700 m that contains most of the contaminated
wells. These corridors are interpreted to be the zone of channel shifting. Contaminated wells represent point fractal geometry
that can be separated into isolated points and clusters. Clusters occur within the zone of channel shifting as obtained by
weight-on-evidences analysis. Isolated points occur within floodplain or back swamp areas. Clusters and isolated point fractals
are interpreted to reflect the process of arsenic release into groundwater. The migration of biomass within the permeable
sandy domain of channel deposits is proposed to be the predominant process in generating clusters. The isolated points represent
restricted biomass spreading in less permeable clay-silt dominated floodplains. 相似文献
100.
Auto-correlation analysis of wave heights in the Bay of Bengal 总被引:1,自引:0,他引:1
Time series observations of significant wave heights in the Bay of Bengal were subjected to auto-correlation analysis to determine
temporal variability scale. The analysis indicates an exponential fall of auto-correlation in the first few hours with a decorrelation
time scale of about six hours. A similar figure was found earlier for ocean surface winds. The nature of variation of auto-correlation
with time lags was also found to be similar for winds and wave heights 相似文献