全文获取类型
收费全文 | 247篇 |
免费 | 4篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 24篇 |
地球物理 | 20篇 |
地质学 | 153篇 |
海洋学 | 15篇 |
天文学 | 3篇 |
综合类 | 1篇 |
自然地理 | 34篇 |
出版年
2021年 | 1篇 |
2020年 | 1篇 |
2016年 | 2篇 |
2015年 | 1篇 |
2014年 | 1篇 |
2013年 | 15篇 |
2012年 | 3篇 |
2011年 | 7篇 |
2010年 | 4篇 |
2009年 | 6篇 |
2008年 | 7篇 |
2007年 | 7篇 |
2006年 | 12篇 |
2005年 | 2篇 |
2004年 | 11篇 |
2003年 | 5篇 |
2002年 | 11篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 10篇 |
1998年 | 5篇 |
1997年 | 10篇 |
1996年 | 12篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 17篇 |
1990年 | 11篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1969年 | 2篇 |
1966年 | 1篇 |
1964年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有251条查询结果,搜索用时 92 毫秒
81.
82.
83.
Water-deficient Calc-alkaline Plutonic Rocks of Northeastern Superior Province, Canada: Significance of Charnockitic Magmatism 总被引:5,自引:0,他引:5
Calc-alkaline batholiths of the Archaean Minto block, northeasternSuperior Province, Canada, have pyroxene- and hornblende-bearingmineral assemblages inferred to have crystallized from hot,water-undersaturated magmas at 2·7292·724Ga. A regional amphibolite- to granulite-facies tectonothermalevent at 2·70 Ga resulted in mild to negligible metamorphiceffects on the dominantly granodioritic units. Geochemical,textural and thermobarometric studies define the crystallizationhistory in compositions ranging from cumulate pyroxenite throughquartz diorite, granodiorite, granite, and syn-magmatic gabbroicdykes. Early magmatic assemblages include orthopyroxene, clinopyroxene,plagioclase, biotite, FeTi oxides and ternary feldspar,indicating crystallization from magmas containing <2 wt %H2O at 1100900°C. Water enrichment in the residualmelt induced hornblende crystallization at 5 ± 1 kbar,800600°C. Characterized by a continuum of large ionlithophile element (LILE)-enriched, high field strength element(HFSE)-depleted compositions, the I-type suite resembles moderncontinental arc batholiths in composition and size but not primarymineralogy. Magmatic arcs produced between 2·75 and 1·85Ga commonly have charnockitic components, possibly because slab-derivedfluids interacted with mantle wedges at ambient temperatureshigher by 100°C than at present, producing large volumesof water-deficient magma. KEY WORDS: granitoid rocks; igneous pyroxenes; water-undersaturated magma; charnockite 相似文献
84.
85.
Application and evaluation of universal kriging for optimal contouring of groundwater levels 总被引:4,自引:0,他引:4
B V N P KAMBHAMMETTU PRAVEENA ALLENA JAMES P KING 《Journal of Earth System Science》2011,120(3):413-422
This paper deals with the application of universal kriging to interpolate water table elevations from their measurements at
random locations. Geographic information system tools were used to generate the continuous surface of water table elevations
for the Carlsbad area alluvial aquifer located to the southeast of New Mexico, USA. Water table elevations in the 38 monitoring
wells that are common to 1996 and 2003 irrigation years follows normal distribution. A generalized MATLAB? code was developed to generate omni-directional and directional semi-variograms (at 22.5° intervals). Low-order polynomials
were used to model the trend as the water table profile exhibits a south-east gradient. Different theoretical semi-variogram
models were tried to select the base semi-variogram for performing geostatistical interpolation. The contour maps of water
table elevations exhibit significant decrease in the water table from 1996 to 2003. Statistical analysis performed on the
estimated contours revealed that the decrease in water table is between 0.6 and 4.5 m at 90% confidence. The estimation variance
contours show that the error in estimation was more than 8 m2 in the west and south-west portions of the aquifer due to the absence of monitoring wells. 相似文献
86.
87.
88.
89.
Abstract Daily flow records, rainfall data and tropical cyclone maps during 1970–1998 are used to document the impact of tropical cyclones (TCs) on floods in the Rewa River system, Viti Levu, Fiji. Floods are large, brief, isolated events caused by TCs and non-TC tropical rainstorms. More floods are caused by tropical rainstorms than by TCs, but TC floods are larger. The log Pearson Type III distribution consistently provided the best fit to partial duration flood series and the widely-recommended generalized Pareto distribution performed very poorly, underscoring the need to test a variety of distributions for a particular geographic location. Tropical cyclones occur more often in Fiji during negative values of the Southern Oscillation Index (SOI) and all TCs that occurred during El Niño conditions caused floods. Peak flood discharges caused by TCs are inversely correlated with the SOI, reflecting possible links with tropical cyclone frequency and precipitation intensity. 相似文献
90.
Diagenesis of late Cenozoic diatomaceous deposits and formation of the bottom simulating reflector in the southern Bering Sea* 总被引:1,自引:0,他引:1
JAMES R. HEIN DAVID W. SCHOLL JOHN A. BARRON MARJORIE G. JONES JACQUELYN MILLER 《Sedimentology》1978,25(2):155-181
Diatom ooze and diatomaceous mudstone overlie terrigenous mudstone beds at Leg 19 Deep Sea Drilling Project sites. The diatomaceous units are 300-725 m thick but most commonly are about 600 m. Diagenesis of diatom frustules follows a predictable series of physical and chemical changes that are related primarily to temperature (depth of burial and local geothermal gradient). During the first 300-400 m of burial frustules are fragmented and undergo mild dissolution. By 600 m dissolution of opal-A (biogenic silica) is widespread. Silica reprecipitates abundantly as inorganic opal-A between 600 and 700 m sub-bottom depth. Inorganic opal-A is rapidly transformed by crystal growth to opal-CT. The result is formation of silica cemented mudstone and porcelanite beds. A regional acoustic reflector (called the bottom-simulating reflector, or BSR) occurs near 600 m depth in the sections. This acoustic event marks the upper surface where silicification (cementation) is active. In Bering Sea deposits, opal-A is transformed to opal-CT at temperatures between 35° and 50°C. This temperature range corresponds to a sub-bottom depth of about 600 m and is the area where silicification is most active. Thus, the BSR represents an isothermal surface; the temperature it records is that required to transform opal-A to opal-CT. Deposition of at least 500 m of diatomaceous sediment was required before the temperature at the base of the diatomaceous section was appropriate (35°-50°C) for silica diagenesis to occur. Accordingly, silica diagenesis did not begin until Pleistocene time. Once silicification began, in response to sediment accumulation during the Quaternary, the diagenetic front (the BSR) moved upsection in pace with the upward migrating thermal boundary. X-ray diffractograms and SEM photographs show three silica phases, biogenic opal-A, inorganic opal-A’, and opal-CT. These have crystallite sizes of 11-16 A, 20-27 A, and 40-81 A, respectively, normal to 101. The d(101) reflection of opal-CT decreases with depth of burial at DSDP Site 192. This occurs by solid-state ordering and requires at least 700 m of burial. Most clinoptilolite in Leg 19 cores forms from the diagenesis of siliceous debris rather than from the alteration of volcanic debris as is commonly reported. 相似文献