全文获取类型
收费全文 | 321篇 |
免费 | 8篇 |
专业分类
测绘学 | 31篇 |
大气科学 | 15篇 |
地球物理 | 51篇 |
地质学 | 161篇 |
海洋学 | 9篇 |
天文学 | 52篇 |
自然地理 | 10篇 |
出版年
2022年 | 5篇 |
2021年 | 2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 | 21篇 |
2008年 | 10篇 |
2007年 | 15篇 |
2006年 | 7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329条查询结果,搜索用时 15 毫秒
1.
We investigate the evolution of rotation period and spindown age of a pulsar whose surface magnetic field undergoes a phase
of growth. Application of these results to the Crab pulsar strongly indicates that its parameters cannot be accounted for
by the field growth theories. 相似文献
2.
B. K. Bhattacharya V. K. Dadhwal 《Journal of the Indian Society of Remote Sensing》2005,33(2):331-338
The retrieval of land (soil-vegetation complex) surface temperature (LST) was carried out over semi-arid mixed agriculture
landscape of Gujarat using thermal bands (channel 4 and 5) and ground emissivity from atmospherically corrected NDVI of NOAA
AVHRR LAC images. The atmospheric correction of Visible and NIR band reflectance was done using SMAC model. The LST computed
from split-window method and subsequently corrected with fractional vegetation cover were then compared with near synchronous
ground observations of soil and air temperatures made during 13–17 January and April, 1997 at five Land Surface Processes
Experiment (LASPEX) sites of Anand, Sanand, Derol, Arnej and Khandha covering 100 km x 100 km. The fractional vegetation cover
corrected LST at noon hrs. varied from 301.6 – 311.9K in January and from 315.8 – 325.6K in April. The LSTcorr were found to lie in the mid way between AT and ST during January. But in April, LST were found to be more close to ST which
may be due to relatively poor vegetation growth as indicated by lower NDVI values in April indicating more contribution to
LST from exposed soil surface. 相似文献
3.
ABSTRACT A process‐based facies model for asymmetric wave‐influenced deltas predicts significant river‐borne muds with potentially lower quality reservoir facies in prodelta and downdrift areas, and better quality sand in updrift areas. Many ancient barrier‐lagoon systems and ‘offshore bars’ may be better reinterpreted as components of large‐scale asymmetric wave‐influenced deltaic systems. The proposed model is based on a re‐evaluation of several modern examples. An asymmetry index A is defined as the ratio between the net longshore transport rate at the mouth (in m3 year?1) and river discharge (in 106 m3 month?1). Symmetry is favoured in deltas with an index below ≈ 200 (e.g. Tiber, lobes of the Godavari delta, Rosetta lobe of the Nile, Ebro), whereas deltas with a higher index are asymmetric (e.g. Danube – Sf. Gheorghe lobe, Brazos, Damietta lobe of the Nile). Periodic deflection of the river mouth for significant distances in the downdrift direction occurs in extreme cases of littoral drift dominance (e.g. Mahanadi), resulting in a series of randomly distributed, quasi‐parallel series of sand spits and channel fills. Asymmetric deltas show variable proportions of river‐, wave‐ and tide‐dominated facies both among and within their lobes. Bayhead deltas, lagoons and barrier islands form naturally in prograding asymmetric deltas and are not necessarily associated with transgressive systems. This complexity underlines the necessity of interpreting ancient depositional systems in a larger palaeogeographic context. 相似文献
4.
Prosenjit Ghosh S. K. Bhattacharya Ashok Sahni R. K. Kar D. M. Mohabey K. Ambwani 《Cretaceous Research》2003,24(6):743-750
A single locality of the Late Cretaceous (Maastrichtian) Lameta Formation at Pisdura in Central India has yielded a large number of coprolites attributed to titanosaurian dinosaurs. Internally the coprolites are dark grey and contain abundant plant tissues and other organic materials. The plant tissues are mostly of gymnospermous origin. In addition, remains of bacterial colonies, fungal spores and algae are seen in the macerated fraction under scanning electron microscope. The dark grey appearance is probably attributable to fine-grained organic matter within voids in tracheids or xylem. The average 13C/12C ratio of the organic matter in the coprolites is -24‰ (relative to PDB) suggesting that plants of C3type were the main diet of their producers. A comparison of δ15N value (about 4‰ w.r.t. air) of the coprolites with that of faecal matter of modern herbivores and carnivores suggests that gut fermentation may not have been an active mechanism in the digestion process of titanosaurs. 相似文献
5.
At Malanjkhand, Central India, lode-type copper (-molybdenum) mineralization occurs within calcalkaline tonalite-granodiorite
plutonic rocks of early Proterozoic age. The bulk of the mineralization occurs in sheeted quartz-sulfide veins, and K-silicate
alteration assemblages, defined by alkali feldspar (K-feldspar ≫ albite) + dusty hematite in feldspar ± biotite ± muscovite,
are prominent within the ore zone and the adjacent host rock. Weak propylitic alteration, defined by albite + biotite + epidote/zoisite,
surrounds the K-silicate alteration zone. The mineralized zone is approximately 2 km in strike length, has a maximum thickness
of 200 m and dips 65°–75°, along which low-grade mineralization has been traced up to a depth of about 1 km. The ore reserve
has been conservatively estimated to be 92 million tonnes with an average Cu-content of 1.30%. Supergene oxidation, accompanied
by limited copper enrichment, is observed down to a depth of 100m or more from the surface. Primary ores consist essentially
of chalcopyrite and pyrite with minor magnetite and molybdenite. δ34S (‰) values in pyrite and chalcopyrite (−0.38 to +2.90) fall within the range characteristic of granitoid-hosted copper deposits.
δ18O (‰) values for vein quartz (+ 6.99 to +8.80) suggest exclusive involvement of juvenile water. Annealed fabrics are common
in the ore. The sequence of events that led to the present state of hypogene mineralization is suggested to be as follows:
fracturing of the host rock, emplacement of barren vein quartz, pronounced wall-rock alteration accompanied by disseminated
mineralization and the ultimate stage of intense silicification accompanied by copper mineralization. Fragments of vein quartz
and altered wall rocks and striae in the ore suggest post-mineralization deformation. The recrystallization fabric, particularly
in chalcopyrite and sphalerite, is a product of dynamic recrystallization associated with the post-mineralization shearing.
The petrology of the host rocks, hydrothermal alteration assemblages, ore mineral associations, fluid inclusions and the sulfur
and oxygen isotopes of ores are comparable to those in Phanerozoic (and reported Precambrian) porphyry-copper systems, and
the Malanjkhand deposit has important implications for both metallogenic models for, and mineral exploration in, Precambrian
terrains. 相似文献
6.
H. N. Bhattacharya Abhijit Chakraborty Biplab Bhattacharya 《Journal of Earth System Science》2005,114(3):275-286
Basal part of the Gondwana Supergroup represented by Talchir and Karharbari Formations (Permo-Carboniferous) records an abrupt
change-over from glacio-marine to terrestrial fluviolacustrine depositional environment. The contact between the two is an
unconformity. Facies analysis of the glacio-marine Talchir Formation reveals that basal glaciogenic and reworked glaciogenic
sediments are buried under storm influenced inner and outer shelf sediments. Facies associations of the Karharbari Formation
suggest deposition as fluvio-lacustrine deposits in fault-controlled troughs. An attempt has been made in this paper to explain
the sedimentation pattern in Talchir and Karharbari basins, and the abrupt change-over from glacio-marine to terrestrial fluviolacustrine
depositional environment in terms of glacio-isostacy. 相似文献
7.
AK Mishra D. Bhattacharya 《Fragblast: International Journal for Blasting and Fragmentation》2005,9(1):47-59
The mineral industry is leading towards a technology driven optimization process. Drilling and blasting are such unit operations in a mine, which can alter the balance sheet of the mine if not planned properly. The development, improvement and utilization of innovative technologies in terms of blast monitoring instruments and explosives technology are important for cost effectiveness and safety of mineral industries.
The ever-growing demand for minerals has compelled the industry to adopt large opencast projects using heavy equipment. This has necessitated use of a few hundred tonnes of explosives in each blast. The bulk delivered fourth generation explosives have solved the problem of explosive loading to a large extent as it provides improved safety in manufacturing, transportation and handling. Bulk delivered emulsion is non-explosive until gasification is complete and a large quantity of explosive can be transported and loaded into blast holes efficiently and with safety. The priming of bulk delivered explosives in Indian mines uses the conventional PETN/TNT-based boosters. The conventional booster possesses safety problems in terms of handling and use, so Indian Explosives Ltd has developed an emulsion-based booster (Powergel Boost).
This paper explores the potential of an emulsion-based booster used as a primer to initiate bulk delivered emulsion explosives used in mines. An attempt has been made at a comparative study between the conventional booster and the emulsion-based booster in terms of the initiation process developed and their capability of developing and maintaining a stable detonation process in the column explosives. The study has been conducted using a continuous velocity of detonation (VOD) measuring instrument, the VODMate two channel system manufactured by Instantel Inc. of Canada. During this study three blasts were monitored. In each blast two holes were selected for study, the first hole was initiated using a conventional booster while the other one used an emulsion-based booster. The findings of the study advocates that the emulsion-based booster is capable of the efficient priming of bulk delivered column explosive with a stable detonation process in the column. 相似文献
The ever-growing demand for minerals has compelled the industry to adopt large opencast projects using heavy equipment. This has necessitated use of a few hundred tonnes of explosives in each blast. The bulk delivered fourth generation explosives have solved the problem of explosive loading to a large extent as it provides improved safety in manufacturing, transportation and handling. Bulk delivered emulsion is non-explosive until gasification is complete and a large quantity of explosive can be transported and loaded into blast holes efficiently and with safety. The priming of bulk delivered explosives in Indian mines uses the conventional PETN/TNT-based boosters. The conventional booster possesses safety problems in terms of handling and use, so Indian Explosives Ltd has developed an emulsion-based booster (Powergel Boost).
This paper explores the potential of an emulsion-based booster used as a primer to initiate bulk delivered emulsion explosives used in mines. An attempt has been made at a comparative study between the conventional booster and the emulsion-based booster in terms of the initiation process developed and their capability of developing and maintaining a stable detonation process in the column explosives. The study has been conducted using a continuous velocity of detonation (VOD) measuring instrument, the VODMate two channel system manufactured by Instantel Inc. of Canada. During this study three blasts were monitored. In each blast two holes were selected for study, the first hole was initiated using a conventional booster while the other one used an emulsion-based booster. The findings of the study advocates that the emulsion-based booster is capable of the efficient priming of bulk delivered column explosive with a stable detonation process in the column. 相似文献
8.
9.
10.
Dhruba Mukhopadhyay Tapas Bhattacharya Tapan Chakraborty Arun Kanti Dey 《Journal of Earth System Science》1990,99(2):249-268
In the western part of the North Singhbhum fold belt near Lotapahar and Sonua the remobilized basement block of Chakradharpur
Gneiss is overlain by a metasedimentary assemblage consisting of quartz arenite, conglomerate, slate-phyllite, greywacke with
volcanogenic material, volcaniclastic rocks and chert. The rock assemblage suggests an association of volcanism, turbidite
deposition and debris flow in the basin. The grade of metamorphism is very low, the common metamorphic minerals being muscovite,
chlorite, biotite and stilpnomelane. Three phases of deformation have affected the rocks. The principal D1 structure is a
penetrative planar fabric, parallel to or at low angle to bedding. No D1 major fold is observed and the regional importance
of this deformation is uncertain. The D2 deformation has given rise to a number of northerly plunging major folds on E-W axial
planes. These have nearly reclined geometry and theL
2lineation is mostly downdip on theS
2surface, though some variation in pitch is observed. The morphology of D2 planar fabric varies from slaty cleavage/schistosity
to crenulation cleavage and solution cleavage. D3 deformation is weak and has given rise to puckers and broad warps on schistosity
and bedding. The D2 major folds south of Lotapahar are second order folds in the core of the Ongarbira syncline whose easterly
closure is exposed east of the mapped area. Photogeological study suggests that the easterly and westerly closing folds together
form a large synclinal sheath fold. There is a continuity of structures from north to south and no mylonite belt is present,
though there is attenuation and disruption along the fold limbs. Therefore, the Singhbhum shear zone cannot be extended westwards
in the present area. There is no evidence that in this area a discontinuity surface separates two orogenic belts of Archaean
and Proterozoic age. 相似文献