全文获取类型
收费全文 | 3035篇 |
免费 | 172篇 |
国内免费 | 34篇 |
专业分类
测绘学 | 117篇 |
大气科学 | 255篇 |
地球物理 | 663篇 |
地质学 | 1124篇 |
海洋学 | 258篇 |
天文学 | 520篇 |
综合类 | 14篇 |
自然地理 | 290篇 |
出版年
2023年 | 19篇 |
2022年 | 23篇 |
2021年 | 69篇 |
2020年 | 94篇 |
2019年 | 83篇 |
2018年 | 98篇 |
2017年 | 114篇 |
2016年 | 142篇 |
2015年 | 99篇 |
2014年 | 127篇 |
2013年 | 186篇 |
2012年 | 136篇 |
2011年 | 184篇 |
2010年 | 163篇 |
2009年 | 164篇 |
2008年 | 145篇 |
2007年 | 114篇 |
2006年 | 105篇 |
2005年 | 109篇 |
2004年 | 94篇 |
2003年 | 93篇 |
2002年 | 84篇 |
2001年 | 62篇 |
2000年 | 62篇 |
1999年 | 46篇 |
1998年 | 45篇 |
1997年 | 39篇 |
1996年 | 36篇 |
1995年 | 35篇 |
1994年 | 20篇 |
1993年 | 20篇 |
1992年 | 28篇 |
1991年 | 20篇 |
1990年 | 26篇 |
1989年 | 13篇 |
1988年 | 18篇 |
1987年 | 21篇 |
1985年 | 25篇 |
1984年 | 28篇 |
1983年 | 22篇 |
1982年 | 27篇 |
1981年 | 25篇 |
1980年 | 17篇 |
1979年 | 17篇 |
1978年 | 18篇 |
1977年 | 19篇 |
1976年 | 13篇 |
1975年 | 16篇 |
1974年 | 18篇 |
1973年 | 9篇 |
排序方式: 共有3241条查询结果,搜索用时 62 毫秒
991.
Age constraints on the evolution of the Austroalpine basement to the south of the Tauern Window 总被引:1,自引:0,他引:1
Siegfried Siegesmund Till Heinrichs Rolf L. Romer Daniel Doman 《International Journal of Earth Sciences》2007,96(3):415-432
The Austroalpine basement to the south of the Tauern Window once was part of the northern margin of Gondwana. It includes
the “Altkristallin” and the phyllitic Thurntaler Complex. In the Altkristallin (AMU, MPU), suites of arc-related metamafic
sequences occur together with calc-alkaline metagranite. SHRIMP U–Pb dating of zircon from calc-alkaline metagranite associated
with an eclogitic amphibolite give an age of 470 ± 3 Ma interpreted as the age of protolith emplacement. In the Thurntaler
Complex, metaporphyroids occur together with tholeiitic as well as alkaline within-plate basalt-type metabasite. The metaryholites
of this association give a crystallization SHRIMP age of 477 ± 4 Ma, which suggests contemporaneity of arc-related and extensional
settings in the Austroalpine basement units. The age data demonstrate widespread magmatic activity associated with the Early-Ordovician
amalgamation at the end of the 550–470 Ma subduction–accretion–collision cycle. The Pb–Pb and U–Pb systematics of step-wise
leached staurolite and kyanite from the peak-metamorphic assemblage of the Altkristallin indicate that (1) step-wise leaching
of staurolite and kyanite yields the age of inclusions rather than the host; (2) zircon inclusions in staurolite suggest an
Ordovician or older age for the precursor of the staurolite-schists; (3) the weighted average of the 206Pb/238U data of the various leaching steps yields a Variscan age for the inclusions (ilmenite, biotite, and andesine). Since these
inclusions are part of the metamorphic mineral assemblage, this age provides a minimum estimate for staurolite growth, i.e.,
metamorphism. Thus, the Pb–Pb and U–Pb systematics of staurolite provide evidence for a Variscan metamorphism of the Austroalpine
basement, e.g., MPU, AMU and Thurntaler Complex, to the south of the Tauern Window. 相似文献
992.
Richard J. Squire Walter Herrmann Daniel Pape D. Ian Chalmers 《Mineralium Deposita》2007,42(5):489-503
The early Palaeozoic Macquarie Arc, southeastern Australia, hosts a variety of major late Ordovician to earliest Silurian
subduction-related deposits (e.g., Cadia East, Ridgeway, Cadia Hill, Cowal and Northparkes). However, there is uncertainty
about whether coeval high-sulfidation epithermal deposits, which occur in intra-oceanic metallogenic belts elsewhere in the
West Pacific, (e.g., Lepanto and Chinkuashih), are also present in the Macquarie Arc. This has led to suggestions that their
absence may be due to the poor preservation potential of deposits that form at relatively shallow crustal levels in ancient
rocks. We present here an interpretation for evolution of the Peak Hill Au–Cu deposit based on the distribution of alteration
facies, sulfur isotope data from several textural forms of pyrite and barite, and an assessment of the regional volcanic and
sedimentary facies architecture. These data show that the Peak Hill deposit displays a distinct sub-vertical zoning with a
pyrophyllite and vuggy-quartz core, that today extends about 350 m east–west and at least 550 m north–south, which grades
out through paragonite+muscovite, kaolinite to a chlorite+epidote alteration zone at the margin. The alteration zoning reflects
both lower temperatures and neutralisation of acid fluids with increasing distance from the core, which represents the conduit
along which hot acidic hydrothermal fluids were channelled. Several temporally overlapping events of silicification, bladed-quartz-pyrite
veining, brecciation and pyrite veining occurred during the last stages of hydrothermal alteration, although most appear to
predate mineralisation. Au–Cu mineralisation was associated with late quartz-pyrite-barite veins, and the highest gold grades
occur mainly in microcrystalline-quartz-altered rocks in the paragonite+muscovite alteration zone, generally within 50 m outward
from the boundary of the pyrophyllite and vuggy-quartz core. Sulfur- and lead-isotope data, and the characteristic zoning
of ore minerals and alteration assemblages support a magmatic source for the hydrothermal fluids. Similarities in many of
the isotopic signatures between Peak Hill and deposits such as Northparkes support generation of the high-sulfidation mineralisation
during the Late Ordovician to earliest Silurian (possibly ca. 440 Ma) metallogenic event. The Late Ordovician to Early Silurian
volcanic and sedimentary facies associations at Peak Hill are consistent with alteration and mineralisation occurring in rocks
deposited in a submarine setting. 相似文献
993.
Daniel G. Strawn Patrick Hickey Andrew Knudsen Leslie Baker 《Environmental Geology》2007,52(1):109-122
To remediate Pb contaminated soils it is proposed that phosphorus can be amended to the soils to transform the Pb into poorly
soluble Pb-phosphate mineral phases. However, remediation strategies must account for variable Pb speciation and site-specific
factors. In this study soil mineralogy and Pb speciation in soils from P-amended field trials at sites within the Coeur d’Alene
River Basin in Idaho, USA were investigated. The soils are contaminated from mining activities and are enriched with Fe and
Mn. Selective extraction of the soils indicated that the Fe oxides are poorly crystalline. XRD of the soil clay size fractions
identified quartz, muscovite, kaolinite, siderite, lepidocrocite, and chlorite minerals. Amendment with P fertilizer dissolved
the siderite. No Pb–phosphate minerals were detected by XRD. Electron microprobe analysis showed direct correlations between
Pb, Fe, and Mn in the unamended soils, and negative correlations between Pb and Si. Lead and Mn were strongly correlated.
In the amended soils Fe and P were strongly correlated. Results indicate that the Pb is associated with poorly crystalline
Fe and Mn oxides, and that added P is primarily associated with Fe oxide phases. Comparisons of pore water Pb concentrations
with chloropyromorphite and plumbogummite solubility suggest that in the phosphate-amended soils the pore waters are undersaturated
in these phases, whereas several of the control soil pore waters were oversaturated, indicating the added phosphate suppressed
the Pb solubility. Results from this research provide insight into the geochemistry occurring in the P-remediated soils that
will help in making management and remediation decisions. 相似文献
994.
The burrowing crab,Chasmagnathus granulatus, is the dominant benthic macroinvertebrate of southwest Atlantic salt marshes and tidal flats, having strong ecosystem engineering
effects by direct and indirect effects on soil, vegetation, invertebrates, fishes, and birds. Vegetation structure is a main
component for bird habitat selection, since greater habitat complexity generates higher niche diversity. This environmental
complexity can be modified by species interactions or disturbance events (i.e., by crabs), in turn modifying the associated
community. The bird species of salt marshes of the southwest Atlantic are highly dependent on these ecosystems. We assessed
the effects of the burrowing crab on the structure of the cordgrass,Spartina densiflora, marshes, and how these changes affected the composition and diversity of birds. This study was conducted at the Mar Chiquita
Coastal Lagoon, Argentina (37°40′S, 57°23′W).S. densiflora marshes were classified within three categories: marshes without burrowing crabs, marshes with low burrow densities, and
marshes with high burrow densities. We made vegetation and bird surveys during spring beforeS. densiflora produce seeds and in summer when seeds are abundant. We also manipulated inflorescence (i.e., spike) density (a variable
affected by crabs) to assess the effect on bird habitat use. The highest inflorescence density ofS. densiflora and highest bird diversity were recorded at low burrow densities. Cover and height ofS. densiflora were negatively correlated with burrow density. The number of bird species and the number of red-capped wren-spinetail,Spartonoica maluroides, were negatively related with cover and height ofS. densiflora. Experiments confirmed that granivorous species used areas with higher spike densities, a variable related to crab burrow
density. Burrowing crabs directly and indirectly affect the cover, height, spike density, and morphologic characteristic of
seeds ofS. densiflora marshes. These effects indirectly affect the bird community that uses these marshes, being negatively related toS. maluroides and total bird abundance, and positively related to bird diversity. 相似文献
995.
Oxygen isotope systematics of gem corundum deposits in Madagascar: relevance for their geological origin 总被引:1,自引:1,他引:1
Gaston Giuliani Anthony Fallick Michel Rakotondrazafy Daniel Ohnenstetter Alfred Andriamamonjy Théogène Ralantoarison Saholy Rakotosamizanany Marie Razanatseheno Yohann Offant Virginie Garnier Christian Dunaigre Dietmar Schwarz Alain Mercier Voahangy Ratrimo Bruno Ralison 《Mineralium Deposita》2007,42(3):251-270
The oxygen isotopic composition of gem corundum was measured from 22 deposits and occurrences in Madagascar to provide a gemstone
geological identification and characterization. Primary corundum deposits in Madagascar are hosted in magmatic (syenite and
alkali basalt) and metamorphic rocks (gneiss, cordieritite, mafic and ultramafic rocks, marble, and calc-silicate rocks).
In both domains the circulation of fluids, especially along shear zones for metamorphic deposits, provoked in situ transformation
of the corundum host rocks with the formation of metasomatites such as phlogopite, sakenite, and corundumite. Secondary deposits
(placers) are the most important economically and are contained in detrital basins and karsts. The oxygen isotopic ratios
(18O/16O) of ruby and sapphire from primary deposits are a good indicator of their geological origin and reveal a wide range of δ18O (Vienna Standard Mean Ocean Water) between 1.3 and 15.6‰. Metamorphic rubies are defined by two groups of δ18O values in the range of 1.7 to 2.9‰ (cordieritite) and 3.8 to 6.1‰ (amphibolite). “Magmatic” rubies from pyroxenitic xenoliths
contained in the alkali basalt of Soamiakatra have δ18O values ranging between 1.3 and 4.7‰. Sapphires are classified into two main groups with δ18O in the range of 4.7 to 9.0‰ (pyroxenite and feldspathic gneiss) and 10.7 to 15.6‰ (skarn in marble from Andranondambo).
The δ18O values for gem corundum from secondary deposits have a wide spread between −0.3 and 16.5‰. The ruby and sapphire found in
placers linked to alkali basalt environments in the northern and central regions of Madagascar have consistent δ18O values between 3.5 and 6.9‰. Ruby from the placers of Vatomandry and Andilamena has δ18O values of 5.9‰, and between 0.5 and 4.0‰, respectively. The placers of the Ilakaka area are characterized by a huge variety
of colored sapphires and rubies, with δ18O values between −0.3 and 16.5‰, and their origin is debated. A comparison with oxygen isotope data obtained on gem corundum
from Eastern Africa, India, and Sri Lanka is presented. Giant placer deposits from Sri Lanka, Madagascar, and Tanzania have
a large variety of colored sapphires and rubies with a large variation in δ18O due to mingling of corundum of different origin: mafic and ultramafic rocks for ruby, desilicated pegmatites for blue sapphire,
syenite for yellow, green, and blue sapphire, and skarn in marbles for blue sapphire. 相似文献
996.
Whole-rock, Phosphate, and Silicate Compositional Trends across an Amphibolite- to Granulite-facies Transition, Tamil Nadu, India 总被引:2,自引:0,他引:2
Chemical trends from north (amphibolite facies) to south (granulitefacies) along a 95 km traverse in Tamil Nadu, Southern India,include: whole-rock depletion of Rb, Cs, Th and U, enrichmentin Ti and F, and depletion in Fe and Mn in biotite and amphibole;increases in Al and decreases in Mn in orthopyroxene; enrichmentof fluorapatite in F. K-feldspar blebs are widespread alongquartz–plagioclase grain boundaries, and could indicateeither partial melting or metasomatism. In the northernmostportion of the traverse the principal rare earth element (REE)-bearingminerals are allanite and titanite. South of a clinopyroxeneisograd, monazite grains independent of fluorapatite are themajor REE- and Th-bearing phase. Further south independent monaziteis rare but Th-free monazite inclusions are common in fluorapatite.During prograde metamorphism, independent monazite was replacedby REE-rich fluorapatite in which the monazite inclusions laterformed. The loss of independent monazite was accompanied bya loss of whole-rock Th and possibly a small depletion in lightREE. Most mineralogical features along the traverse can be accountedfor by progressive dehydration and oxidation reactions. Trace-elementdepletion is best explained by the action of an externally derivedlow H2O activity brine migrating from a source at greater depth,possibly preceded or accompanied by partial melting. KEY WORDS: granulite facies; charnockite; metasomatism; Archean; Tamil Nadu, India; fluorapatite; monazite; allanite; titanite; biotite 相似文献
997.
Molecular dynamics simulations are carried out to systematically address the effects of composition and pressure on melts along the MgO-SiO2 join and elucidate the role of structural modifier content on silicate melt properties. The MgO-SiO2 system shows non-ideal mixing with a negative excess volume of mixing at low pressures, but the mixing becomes closer to ideal at higher pressures. At atmospheric pressure, the viscosities and diffusivities vary by more than 3 orders of magnitude as the composition is varied along this join, with the low SiO2 melts characterized by lower viscosities and higher diffusivities; these results are in quantitative agreement with experimental results for the dependence of viscosity and diffusivity on structural modifier content in a wide range of silicate systems. The transport properties of melts in this system converge at higher pressures; at pressures greater than ∼15 GPa the viscosity and diffusivities vary by less than an order of magnitude across the entire range of compositions. The relevance of equations that relate the viscosity and diffusivity is also addressed. 相似文献
998.
Prem Chhetri Robert Stimson Jim Cooper Jonathan Corcoran Martin Bell David Pullar 《Transactions in GIS》2007,11(4):597-619
This article presents a GIS‐based methodology to integrate a measure of geographic attractiveness of localities in the process of allocating potential dwellings in the context of a large urban region. The methodology was developed for a study area in Brisbane‐South East Queensland (SEQ), known as the Sunbelt Region, a rapidly growing region and a popular tourist destination in Australia. In this article, we have used a multivariate technique to develop a set of parameterised linear equations to define underlying dimensions that drive residential location decision choices. Aesthetic and accessibility factors were identified in the factor analysis from data collected via a survey of Quality of Life. Spatial measures were based on a combination of network distance and kernel density estimation to calculate ‘aesthetic’ and ‘accessibility’ scenarios, which were then overlaid and multiplied by their subjective weights to create an ‘overall attractiveness scenario’. These development scenarios were integrated as a set of criteria to control the allocation of potential dwelling capacity over the next 25 years at a grid cell level. 相似文献
999.
1000.
Microphysical Effects of Cloud Seeding in Supercooled Stratiform Clouds Observed from NOAA Satellite
Based on the satellite retrieval methodology, the spectral characteristics and cloud microphysical properties were analyzed that included brightness temperatures of Channels 4 and 5, and their brightness temperature difference (BTD), the particle effective radius of seeded cloud track caused by an operational cloud seeding and the microphysical effects of cloud seeding were revealed by the comparisons of their differences inside and outside the seeded track. The cloud track was actually a cloud channel reaching 1.5-km deep and 14-km wide lasting for more than 80 min. The effective radius of ambient clouds was 10-15μm, while that within the cloud track ranged from 15 to 26μm. The ambient clouds were composed of supercooled droplets, and the composition of the cloud within the seeding track was ice. With respect to the rather stable reflectance of two ambient sides around the track, the visible spectral reflectance in the cloud track varied at least 10%, and reached a maximum of 35%, the reflectance of 3.7μm in the seeded track relatively decreased at least 10%. As cloud seeding advanced, the width and depth were gradually increased. Simultaneously the cloud top temperature within the track became progressively warmer with respect to the ambient clouds, and the maximum temperature differences reached 4.2 and 3.9℃at the first seeding position for Channels 4 and 5. In addition, the BTD in the track also increased steadily to a maximum of 1.4℃, compared with 0.2-0.4℃of the ambient clouds. The evidence that the seeded cloud became thinner comes from the visible image showing a channel, the warming of the cloud tops, and the increase of BTD in the seeded track. The seeded cloud became thinner mainly because the cloud top descended and it lost water to precipitation throughout its depth. For this cloud seeding case, the glaciation became apparent at cloud tops about 22 min after seeding. The formation of a cloud track in the supercooled stratiform clouds was mainly because that the seeded cloud volume glaciated into ice hydrometeors that precipitated and so lowered cloud top height. A thin line of new water clouds formed in the middle of the seeded track between 38 and 63 min after seeding, probably as a result of rising motion induced by the released latent heat of freezing. These clouds disappeared in the earlier segments of the seeded track, which suggested that the maturation of the seeding track was associated with its narrowing and eventual dissipation due to expansion of the tops of the ambient clouds from the sides inward. 相似文献