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141.
Chris Harris Brian R Watters P Bruce Groenewald 《Contributions to Mineralogy and Petrology》1991,107(1):100-111
Regional dolerite dykes of Mesozoic age in western Dronning Maud Land are variable in both major and trace element composition
and include picritic types (MgO>18 wt%). The range in incompatible element concentrations is considerable (e.g. Zr 40–478
ppm) and shows little correlation with MgO content. Both high-and low-Ti, Zr (HTZ and LTZ) magma types are present and there
is a spread of compositions between these types. Major element oxide variations in dykes having MgO>10 wt% indicate that olivine
and orthoyproxene fractionation occurred, presumably at an early high-pressure stage of magma evolution. Major element oxide
variations in dykes having MgO<10 wt% indicate control by olivine and clinopyroxene. A minority of the more evolved dykes
are compositionally similar to the nearby Kirwan basalts, but the majority cannot be related to the Kirwan basalts by any
simple petrogenetic process as they contain higher concentrations of incompatible elements and have higher Mg-numbers. The
HTZ Dronning Maud Land dolerites have incompatible trace element concentrations which are very similar to the HTZ basalt magma
types of the Karoo of southern Africa with the exception of lower K and Rb in DML dolerites. The HTZ dolerites occur in the
part of Dronning Maud Land which appears to have been tectonically stable since the Archaean and are not found to intrude
the surrounding high-grade (about 1000 Ma) metamorphic rocks of the Sverdrup Group. These data provide qualified support for
models which seek to relate spatially the HTZ Mesozoic basalt types of Gondwana to sources beneath stable Archaean cratons. 相似文献
142.
Carbonic fluid inclusions in South Indian granulites: evidence for entrapment during charnockite formation 总被引:1,自引:0,他引:1
M. Santosh D. H. Jackson N. B. W. Harris D. P. Mattey 《Contributions to Mineralogy and Petrology》1991,108(3):318-330
Field evidence and fluid inclusion studies on South Indian incipient charnockites suggest that charnockite formation occurred
during a decompressional brittle regime following the ‘peak’ of metamorphism and regional deformation. The most abundant type
of inclusions in quartz and garnet grains in these charnockites contain high-density carbonic fluids, although lower-density
fluids occur in younger arrays of inclusions. Discrete fluid inclusion generations optically are observed to decrepitate over
well-defined temperature intervals, and quantitative measurements of CO2 abundance released from these inclusions by stepped thermal decrepitation show up to a four-fold increase (by volume) in
the incipient charnockites relative to the adjacent gneisses from which they are derived. Studies based on optical thermometry,
visual decrepitation and stepped-heating inclusion release together indicate that entrapment of carbonic fluids coincided
with charnockite formation. We confirm that an influx of carbon dioxide-rich fluids is associated with the amphibolite-granulite
transition, as recorded by the incipient charnockites, the remnants of which are commonly preserved as the earliest generation
of high-density fluid inclusions. 相似文献
143.
A new multidimensional scaling (MS) technique, referred to as the Pijk model, is formulated on the basis of associations among triple objects (samples or variables), instead of pairs of objects as used in the usual MS methods, such as factor analysis. The computational scheme provided for this method is the reduction of an original problem to a standard eigenvalue-eigenvector problem. The major goal of the technique is simplification and reduction of data structures and the rescaling of original objects into a new and reduced space, so that patterns and relations of the original objects can be conventiently examined in two-dimensional “factor” plots. The Pïjk method is illustrated and tested by using a set of geochemical data related to the epithermal gold and silver vein deposits in the Walker Lake quadrangle of Nevada and California. The characteristics of element associations suggested in the Pijk analysis are consistent with field observations. A preliminary comparison between the new method and the ordinary factor analysis also is made on the basis of the same data set. Results are encouraging in that analysis by the Pijk model captures triple-object associations that might be missed by the ordinary factor analysis which considers only pair-variable correlations 相似文献
144.
A. W. Harris 《Earth, Moon, and Planets》1995,71(3):113-117
I derive an approximate criterion for the tidal disruption of a rubble pile body as it passes close to a planet (or the sun): % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeqyWdi3aaS% baaSqaaiaacogaaeqaaOGaeyisIS7aamWaaeaacaaIYaGaeqyWdihd% caWGWbGccaGGDbWaaeWaaeaadaWcaaqaaiaadkfamiaadchaaOqaai% aadkhaaaaacaGLOaGaayzkaaWaaWbaaSqabeaacaaIZaaaaOGaey4k% aSYaaeWaaeaadaWcaaqaaiabeM8a3bqaaiabeM8a3XGaaGimaaaaaO% GaayjkaiaawMcaamaaCaaaleqabaGaaGOmaaaaaOGaay5waiaaw2fa% amaabmaabaWaaSaaaeaacaWGHbaabaGaamOyaaaaaiaawIcacaGLPa% aacaGGSaaaaa!5229!\[\rho _c \approx \left[ {2\rho p]\left( {\frac{{Rp}}{r}} \right)^3 + \left( {\frac{\omega }{{\omega 0}}} \right)^2 } \right]\left( {\frac{a}{b}} \right),\] where
c
is the critical density below which the body will be disrupted,
p
is the density of the planet (or sun), R
p
is the radius of the planet, r is the periapse distance, is the rotation frequency of the body, 0 is the surface orbit frequency about a body of unit density, and a/b is the axis ratio of the body, considered as a prolate ellipsoid. For P/Shoemaker Levy 9, in its passage close to Jupiter in 1992, this expression suggests that the critical density is ~1.2 for a spherical, non-spinning nucleus, but could be >2.5 for a 2:1 elongate body with a typical rotation period of ~10 hours. 相似文献
145.
HuiJun Jin XiaoLi Chang DongLiang Luo RuiXia He LanZhi L SiZhong Yang DongXin Guo XueMei Chen Stuart A. Harris 《寒旱区科学》2016,8(4):269-296
In Northeast China, permafrost advanced and retreated several times under the influences of fluctuating paleo-climates and paleo-environments since the Late Pleistocene. During the last 60 years, many new data were obtained and studies were conducted on the evolution of permafrost in Northeast China, but so far no systematic summary and review have been made. Based on sedimentary sequences, remains of past permafrost, paleo-flora and-fauna records, and dating data, permafrost evolution since the Late Pleistocene has been analyzed and reconstructed in this paper. Paleo-temperatures reconstructed from the remains of past permafrost and those from paleo-flora and-fauna are compared, and thus the southern limit of permafrost(SLP) in each climate period is inferred by the relationship of the permafrost distribution and the mean annual air/ground temperatures(MAAT/MAGT). Thus, the evolutionary history of permafrost is here divided into five stages:(1) the Late Pleistocene(Last Glaciation, or LG)(65 to 10–8.5 ka), the Last Glaciation Maximum(LGM, 21–13 ka) in particular, the coldest period in the latest history with a cooling of about 6~10 ?C, characterized by extensive occurrences of glaciation, flourishing Mammathas-Coelodonta Faunal Complex(MCFC), widespread aeolian deposits, and significant sea level lowering, and permafrost greatly expanded southwards almost to the coastal plains(37?N–41?N);(2) the Holocene Megathermal Period(HMP, 8.5–7.0 to 4.0–3.0 ka), 3~5 ?C warmer than today, permafrost retreated to about 52°N;(3) the Late Holocene Cold Period(Neoglaciation)(4.0–3.0 to 1.0–0.5 ka), a cooling of 1~3 ?C, some earlier thawed permafrost was refrozen or attached, and the SLP invaded southwards to 46?N;(4) the Little Ice Age(LIA, 500 to 100–150 a), the latest cold period with significant permafrost expansion; and(5) climate warming since the last century, during which Northeast China has undergone extensive permafrost degradation. The frequent and substantial expansions and retreats of permafrost have greatly impacted cold-region environments in Northeast China. North of the SLP during the HMP, or in the present continuous permafrost zone, the existing permafrost was largely formed during the LG and was later overlapped by the permafrost formed in the Neoglaciation. To the south, it was formed in the Neoglaciation. However, many aspects of permafrost evolution still await further investigations, such as data integration, numerical reconstruction, and merging of Chinese permafrost history with those of bordering regions as well as collaboration with related disciplines. Of these, studieson the evolution and degradation of permafrost during the past 150 years and its hydrological, ecological, and environmental impacts should be prioritized. 相似文献
146.
147.
148.
149.
150.
Data from the GEOS 3 and SEASAT Satellites have provided a very accurate geoid map over the oceans. Broad bathymetric features
in the oceans such as oceanic swells and plateaus are fully compensated. For these features it can be shown that the geoid
anomalies due to the density structure of the lithosphere are proportional to the first moment of the density distribution.
Deepening of the ocean basins is attributed to thermal isostasy. The thickness of the oceanic lithosphere increases with age
due to the loss of heat to the sea floor. Bathymetry and the geoid provide constraints on the extent of this heat loss. Offsets
in the geoid across major fracture zones can also be used to constrain this problem. Geoid-bathymetry correlations show that
the Hawaiian and Bermuda swells and the Cape Verde Rise are probably due to lithospheric thinning. A similar correlation for
the Walvis Ridge and Agulhas Plateau indicates that these features are probably due to an anomalously light mantle lithosphere. 相似文献