全文获取类型
收费全文 | 317篇 |
免费 | 8篇 |
专业分类
测绘学 | 31篇 |
大气科学 | 14篇 |
地球物理 | 52篇 |
地质学 | 160篇 |
海洋学 | 8篇 |
天文学 | 50篇 |
自然地理 | 10篇 |
出版年
2022年 | 3篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2018年 | 8篇 |
2017年 | 16篇 |
2016年 | 8篇 |
2015年 | 6篇 |
2014年 | 22篇 |
2013年 | 15篇 |
2012年 | 16篇 |
2011年 | 18篇 |
2010年 | 12篇 |
2009年 | 20篇 |
2008年 | 9篇 |
2007年 | 15篇 |
2006年 | 6篇 |
2005年 | 10篇 |
2004年 | 4篇 |
2003年 | 7篇 |
2002年 | 8篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1997年 | 9篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1972年 | 1篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1967年 | 1篇 |
1964年 | 1篇 |
1963年 | 3篇 |
1962年 | 1篇 |
排序方式: 共有325条查询结果,搜索用时 15 毫秒
51.
One interesting method of constraining the dense matter Equations of State is to measure the advancement of the periastron of the orbit of a binary radio pulsar (when it belongs to a double neutron star system). There is a great deal of interest on applicability of this procedure to the double pulsar system PSR J0737-3039 (A/B). Although the above method can be applied to PSR A in future within some limitations, for PSR B this method cannot be applied. On the other hand, the study of genesis of PSR B might be useful in this connection and its low mass might be an indication that it could be a strange star. 相似文献
52.
In high-Mg, Al metapelites, monophase sapphirine corona occur around spinel–corundum aggregates in monomineralic cordierite
layers, and bi-phase orthopyroxene–sillimanite aggregates replace locally warped sapphirine in polygonized cordierite aggregates.
P–T phase topologies computed (Perple_X software) using compositions of cordierite-rich layers that host the reaction textures
did not match the assemblages for the discontinuous reactions spinel + corundum + cordierite → sapphirine and sapphirine + cordierite → orthopyroxene + sillimanite.
Instead, the reaction assemblages were reproduced using P–T pseudosection analysis for micro-domain reaction volumes estimated from compositions of product phases in the volume proportion
they occur. The results are consistent with known phase relations deduced using Schreinmakers P–T grids. Apparently, the compositions of cordierite-rich layers that hosted the reaction textures were inadequate chemical
proxies for determining P–T–X relations of phase-boundary controlled reactions influenced by compositions of the nearest-neighbor minerals in the proportion
they react (effective composition), and not in the proportion they existed in the layer/bulk rock. In other words, P–T–X phase topologies and reconstructed P–T paths in dry and aluminous rocks may be best understood by thermodynamic modeling of reactions using effective reaction volume
compositions rather than the bulk composition of the rock or the mineralogical layer that host the reaction textures. 相似文献
53.
Natural and man-made disasters like earthquakes, landslides, avalanches, unplanned mining are some of the most serious factors responsible for earth surface displacement. These incidences can be harmful for the society due to loss of life and also threatful for future urban development. Therefore, continuous monitoring of disasters in terms of displacements is of fundamental importance in a modern well-organized society to understand its effects on the social and economic fabric. Availability of SAR data has been proved to be an excellent source for estimation of surface displacements with high accuracies. However, in India, SAR interferometry-related displacement measurement has still not gained appreciable momentum. More rigorous research needs to be carried out for the efficient use of this new generation technique. This review article is an attempt to discuss the issues related to SAR-based displacement studies so far conducted on Indian Himalayan region and possible advanced alternatives. 相似文献
54.
The Frewens sandstone is composed of two elongate tide-influenced sandstone bodies that are positioned directly above and slightly landward of a more wave-influenced lobate sandstone. The 20-km-long, 3-km-wide Frewens sandstone bodies coarsen upwards and fine away from their axes, have gradational bases and margins and have eroded tops abruptly overlain by marine shales. These sandstones are superbly exposed in large cliffs on the banks of the South Fork of the Powder River in central Wyoming, USA. The deposits change upwards from thinly interbedded sandstones and mudstones to metre-thick heterolithic cross-strata and, finally, to metres-thick sandstone-dominated cross-strata. There is abundant evidence for tidal modulation of depositional flows; however, palaeocurrents were strongly ebb-dominated and nearly parallel the trend of sandstone-body elongation. Detailed mapping of stratal geometry and facies across these exposures shows a complex internal architecture. Large-scale bedding units within sandstone bodies are defined by alternations in facies, bed thickness and the abundance of shales. Such bedsets are inclined (5°–15°) in walls oriented parallel to palaeoflow and gradually decrease in dip over hundreds of metres as they extend from the sandstone-dominated deposits higher in a sandstone body to muddier deposits lower in the body. Where viewed perpendicular to palaeoflow, bedsets are 100-metre-wide lenses that shingle off the sandstone-body axis towards its margins. The sandstone bodies are interpreted as sand ridge deposits formed on the shoreface of a tide-influenced river delta. Metres-thick cross-strata in the upper parts of sandstone bodies resemble deposits of bars (sandwaves) formed where tidal currents moved across shallows and the tops of tidal ridges. Heterolithic deposits lower in sandstone bodies record fluctuating currents caused by ebb and flood tides and varying river discharge. Erosion surfaces capping sandstone bodies record tidal ravinement. The tidal ridges were abandoned following transgression and covered with marine mud as waters deepened. 相似文献
55.
Abhijit Mukherjee Prosun Bhattacharya Fei Shi Alan E. Fryar Arun B. Mukherjee Zheng M. Xie Gunnar Jacks Jochen Bundschuh 《Applied Geochemistry》2009
Elevated As concentrations in groundwater of the Huhhot basin (HB), Inner Mongolia, China, and the western Bengal basin (WBB), India, have been known for decades. However, few studies have been performed to comprehend the processes controlling overall groundwater chemistry in the HB. In this study, the controls on solute chemistry in the HB have been interpreted and compared with the well-studied WBB, which has a very different climate, physiography, lithology, and aquifer characteristics than the HB. In general, there are marked differences in solute chemistry between HB and WBB groundwaters. Stable isotopic signatures indicate meteoric recharge in the HB in a colder climate, distant from the source of moisture, in comparison to the warm, humid WBB. The major-ion composition of the moderately reducing HB groundwater is dominated by a mixed-ion (Ca–Na–HCO3–Cl) hydrochemical facies with an evolutionary trend along the regional hydraulic gradient. Molar ratios and thermodynamic calculations show that HB groundwater has not been affected by cation exchange, but is dominated by weathering of feldspars (allitization) and equilibrium with gibbsite and anorthite. Mineral weathering and mobilization of As could occur as recharging water flows through fractured, argillaceous, metamorphic or volcanic rocks in the adjoining mountain-front areas, and deposits solutes near the center of the basin. In contrast, WBB groundwater is Ca–HCO3-dominated, indicative of calcite weathering, with some cation exchange and silicate weathering (monosiallitization). 相似文献
56.
Biswajit Ghosh Tapan Pal Anindya Bhattacharya Dipankar Das 《Mineralogy and Petrology》2009,96(1-2):59-70
Chromites occurring in different modes have been characterized from ophiolites of Rutland Island, a part of Burma-Andaman-Java subduction complex in the Bay of Bengal. Chromite mainly occurs as massive chromitite pods in mantle ultramafic tectonite and as thin massive chromitite bands together with minor disseminations in crustal ultramafic cumulate. Other than pods chromite also appears as: (a) anhedral restitic grains, (b) strings occurring as exsolved phases and as (c) symplectitic intergrowth with orthopyroxene in mantle tectonite. The chromites occurring as massive chromitite pods and bands contain high Cr (Cr#—73 to 80). Restitic chromite grains in mantle ultramafics are high-Mg (Mg#—58), high-Al (Al2O3—34 wt.%) and intermediate-Cr (Cr#—37) chromites. The bivariant plots of TiO2 wt.% vs 100Cr#, Mg# vs Cr# and Cr-Al-Fe3+ ternary discrimination diagram show that the massive and disseminated chromites fall in the boninitic field. The (Al2O3)melt and (FeO/MgO)melt values for the massive chromitites are estimated as 10 wt.% to 11 wt.% and 0.67–1.78 respectively, corroborating a boninitic parentage. Massive chromitite on Fe2+/Fe3+ vs Al2O3 wt.% and TiO2 wt.% vs Al2O3 wt.% plots occupy mainly the field of supra-subduction zone peridotites. High-Mg olivine (Fo91?93), high-Mg orthopyroxene (En~90) and high-Cr chromites of Rutland ophiolite are all supportive of boninitic source at supra-subduction zone setting. 57Fe Mössbauer study of chromite of beach placer shows that chromites occur in partly inverse spinel structure with iron distribution as Fe3+(A)Fe2+(A)Fe2+(B) which might be a result of oxidation. The olivine-spinel geothermometry shows 650–700°C re-equilibration temperature which is much lower than near crystallization temperature (950–1,050°C) derived from orthopyroxene-clinopyroxene assemblage. At supra-subduction setting an oxidizing hydrous fluid derived from subducting slab might have a major influence during the formation of Rutland ophiolite in this part of Burma-Java subduction complex. 相似文献
57.
M. Chatterjee J. Canário S. K. Sarkar V. Branco A. K. Bhattacharya K. K. Satpathy 《Environmental Geology》2009,57(5):1125-1134
Mercury concentrations (HgT) in fine-grained fraction (<63 μm) of core sediments of the Hugli–Matla–Bidyadhari estuarine complex, India were analyzed.
Results revealed a wide range of spatial variations (<4–93 ng g−1 dry weight) with a definite enhancement level at the lower stretch of the estuarine complex infested with mangrove plants,
which might act as a sink to HgT. An elevated concentration of Hg was encountered in surface/subsurface layer of the core in majority of the cases resulting
from physical, biogenic and postdepositional diagenetic processes that remobilized and resuspended the metal from deeper sediments.
A strong positive correlation was observed between the Hg and clay fraction content of the sediments, while the correlations
of Hg with Al, Fe and Mn were poor. Based on the index of geoaccumulation (I
geo) and effects range-low (ER-L) value, it is considered that the sediments are less polluted and thus there is less chance
of ecotoxicological risk to organisms living in sediments. 相似文献
58.
An automated geo-hazard warning system is the need of the hour. It is integration of automation in hazard evaluation and warning communication. The primary objective of this paper is to explain a geo-hazard warning system based on Internet-resident concept and available cellular mobile infrastructure that makes use of geo-spatial data. The functionality of the system is modular in architecture having input, understanding, expert, output and warning modules. Thus, the system provides flexibility in integration between different types of hazard evaluation and communication systems leading to a generalized hazard warning system. The developed system has been validated for landslide hazard in Indian conditions. It has been realized through utilization of landslide causative factors, rainfall forecast from NASA??s TRMM (Tropical Rainfall Measuring Mission) and knowledge base of landslide hazard intensity map and invokes the warning as warranted. The system evaluated hazard commensurate with expert evaluation within 5?C6?% variability, and the warning message permeability has been found to be virtually instantaneous, with a maximum time lag recorded as 50?s, minimum of 10?s. So it could be concluded that a novel and stand-alone system for dynamic hazard warning has been developed and implemented. Such a handy system could be very useful in a densely populated country where people are unaware of the impending hazard. 相似文献
59.
Oswaldo Eduardo Ramos Ramos Luis Fernando Cáceres Mauricio Rodolfo Ormachea Muñoz Prosun Bhattacharya Israel Quino Jorge Quintanilla Ondra Sracek Roger Thunvik Jochen Bundschuh Maria Eugenia García 《Environmental Earth Sciences》2012,66(3):793-807
Water management in semiarid and arid catchments such as the Poopó Lake Basin requires improved understanding of the complex behavior of the various contaminants, which affect the drinking water quality and considered as crucial for sustainable development of the region. Mechanisms of arsenic (As) release in the surface and groundwater were studied. Hydrochemical data for surface water (4 samples) and groundwater (28 samples) were collected in a small watershed in the Poopó catchment at the highland of the Bolivian Andes (Altiplano). All of them show high electrical conductivity values and moderately oxidizing conditions. The surface water contains high concentration of sulfate and the trace elements As, Zn and Pb in the zone affected by acid mine drainage. There is a large variability of the concentration of As and of the trace elements in the groundwater in the five different regions within the Poopó catchment. The metal concentrations sensitive to changes of redox state and results of speciation modeling suggest that As (V) is a predominant aqueous species, which conforms to the prevailing oxidizing conditions in the shallow groundwater environment. Two generalized trends for As distribution were identified in groundwater: (a) high concentrations are found in the arid zone (100–250 μg/L) in the southern (region III) and in the northwestern (region V) regions, and (b) low concentrations (<50 μg/L) are found in the remaining part of the basin (region I, II and IV). However, the spatial distribution within these regions needs to be investigated further. A conclusion from the present study is that there are multiple sources of As as well as other trace elements (such as Cd, Mn and Zn) in the Poopó Lake Basin. Among the sources and the processes which led to the mobility of As and other trace metals in the region are: (a) weathering of sulfide minerals, (b) oxidation of pyrite and/or arsenopyrite in mineralized areas and (c) desorption from hydrous ferric oxide (HFO) surfaces. In non-mining areas, volcanic ash is suggested to be a significant source of As. 相似文献
60.
Mandyam B. Rajani Satadru Bhattacharya A. S. Rajawat 《Journal of the Indian Society of Remote Sensing》2011,39(4):519-527
Talakadu is a well known historic place situated on bank of the river Cauvery in Mysore district of Karnataka. The place is
close to concave side of a prominent meander where large amount of sand has accumulated. It is believed that after construction
of a reservoir upstream, sand was exposed to wind action burying the structures of Ganga dynasty and other later kingdoms.
A number of buried sites have been identified by archaeological excavations conducted so far. Presently the area forms sand
dunes with thick plantation cover. Analysis of RADAR data (fine beam RADARSAT and ENVISAT ASAR) led to identifying a hitherto
unknown buried channel through the Old Talakadu town adjoining the excavated archaeological sites. The study suggests that
RADAR penetration through the plantation canopy seems to have occurred as observed by comparing with corresponding optical
data of LISS-IV. Below the canopy, sand and shrubs on top of the channel (topographically low area) are acting as smooth surface
providing dark tone on radar imagery. During field validation GPS was extensively used to navigate through the forest canopy
and locate the buried channel, excavated archaeological sites as well as other anomalous patterns. Synergistic application
of optical (RESOURCESAT-1 LISS-IV and CARTOSAT-1 & 2) and radar (fine beam RADARSAT and ENVISAT ASAR) data led to identifying
remote sensing based guides for archaeological exploration. Integration of known archaeological sites with the identified
anomalous patterns was done in GIS environment. This study adds on to the knowledge base of the site and compliments already
known information and suggested new areas for further archaeological exploration. 相似文献