全文获取类型
收费全文 | 1332篇 |
免费 | 45篇 |
国内免费 | 15篇 |
专业分类
测绘学 | 33篇 |
大气科学 | 99篇 |
地球物理 | 328篇 |
地质学 | 584篇 |
海洋学 | 109篇 |
天文学 | 140篇 |
综合类 | 5篇 |
自然地理 | 94篇 |
出版年
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 9篇 |
2018年 | 27篇 |
2017年 | 29篇 |
2016年 | 46篇 |
2015年 | 29篇 |
2014年 | 33篇 |
2013年 | 79篇 |
2012年 | 48篇 |
2011年 | 73篇 |
2010年 | 78篇 |
2009年 | 80篇 |
2008年 | 61篇 |
2007年 | 63篇 |
2006年 | 56篇 |
2005年 | 81篇 |
2004年 | 60篇 |
2003年 | 45篇 |
2002年 | 43篇 |
2001年 | 36篇 |
2000年 | 22篇 |
1999年 | 30篇 |
1998年 | 23篇 |
1997年 | 11篇 |
1996年 | 20篇 |
1995年 | 15篇 |
1994年 | 16篇 |
1993年 | 9篇 |
1992年 | 18篇 |
1991年 | 11篇 |
1990年 | 15篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 16篇 |
1985年 | 16篇 |
1984年 | 16篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 16篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1975年 | 4篇 |
1974年 | 13篇 |
1973年 | 5篇 |
1953年 | 2篇 |
排序方式: 共有1392条查询结果,搜索用时 0 毫秒
991.
A detailed climatic study of the Antarctic Peninsula from 1850 to 1980 has been carried out through the analysis of deuterium content in the snow layers of Dalinger Dome (James Ross Island, Antarctic Peninsula). It is based on the high correlation found between mean deuterium contents at this site and temperature data from stations within this region going back as far as April 1903 for the Argentine Orcadas station.The strong correlation between isotopes and temperatures first reveals a 1956 isotope reference for the region considered. Secondly, the isotope-temperature gradient is estimated at 4.5%. °C–1 for deuterium.After checking that the major temperature anomalies on the Antarctic Peninsula recorded since 1904 (according to available data) correspond to annual mean stable isotope peaks at Dalinger Dome, the amplitude of four prior anomalies are estimated in °C. Finally, a cooling of about 2 °C since 1850 is suggested for the region. 相似文献
992.
993.
994.
François Guichard Thomas M. Church Michel Treuil Henri Jaffrezic 《Geochimica et cosmochimica acta》1979,43(7):983-997
A large variety of barites collected from marine and continental environments was analyzed by neutron activation for the rare-earth elements (REE) La, Ce, Sm, Eu and Dy. Relative to chondrites, all barites show a decrease of the lighter REE from La toward Eu. The abundance and distribution of rare earths in barites show a distinction of barite types. Deep-sea barites have large REE concentrations as do other authigenic deep-sea minerals and display the chondrite normalized Eu minimum, but not the negative Ce anomaly, of sea water. Other barites, mostly on land, some hydrothermal, and others of shallow marine origin, display lower total Ree concentrations. Chondrite normalized positive Eu anomalies are displayed by those varieties of reducing sedimentary and metamorphic origin.Distribution of REE in barite can be attributed both to crystallographic constraints of substitution, and to solution complexing of REE in the precipitating medium. Plots of rare earth partitioning versus effective ion size suggest that the decreasing enrichment toward Eu for all barite types is caused by crystallographic constraints due to contraction of the substituting REE ion sizes relative to the size of the host Ba ion. Solution effects on REE substitution in barite can be evaluated by writing solid solution distribution equations based on mass action of REE and Ba sulfates and the lanthanide (Ln) solution species Ln (CO3)?54), LnSO+4, LnCl+2 and LnF+2. Under normal sea water conditions, solution complexing plays a minor role. However, increased alkalinities of reducing sediments and increased brine chlorinities could cause significant complexing and deplete REE heavier than Eu. Besides Dy in barites, this could be true for aqueous precipitation of REE in general. 相似文献
995.
Jacques Dorel Sylvain Eschenbrenner Michel Feuillard 《Pure and Applied Geophysics》1979,117(5):1050-1069
Summary In 1976 and 1977, seismic profiles were carried out in Guadeloupe. Two profiles were established in the area of La Soufriére volcano and one profile through the northern part of Guadeloupe and southern part of Grande Terre. The two first profiles were occupied from 1 to 30 km and the third profile between 5 and 50 km.The interpretation shows that the superficial structures are characterized by a three-layers model: the compressional velocity is about 2.7 to 3.0 km/s down to a depth from 1 to 3 km. Below this, the velocity is between 4.0 and 4.5 km/s in a layer whose thickness varies from 1 to 2.5 km. Under this layer we find a 6.0–6.1 km/s layer which is one of the two known crustal layer under Lesser Antilles. The boundary between the old and new are which form the Lesser Antilles arc, is marked by a thicker layer of sediments on the eastern flank of recent volcanic chain. 相似文献
996.
A re-appraisal of the use of trace elements to classify and discriminate between magma series erupted in different tectonic settings 总被引:2,自引:0,他引:2
David A. Wood Jean-Louis Joron Michel Treuil 《Earth and Planetary Science Letters》1979,45(2):326-336
The hygromagmatophile element composition of basic lavas from several tectonic environments are compared with the estimated composition of the primordial mantle. The observed variations are used to subdivide mid-ocean ridge basalts (MORB) into two main types according to the tectonic character of the ridge segment from which they were erupted. Ridge segments with positive residual gravity, depth and heat flow anomalies erupt E-type MORB which are predominantly enriched in the more hygromagmatophile elements, but also include magma types which are depleted in most of these elements. Both enriched and depleted E-type MORB can be distinguished from the basalts erupted at normal ridge segments (N-type MORB) by their La/Ta ratios (in E-type MORB La/Ta ~10, in N-type MORB La/Ta is ~15) and by Hf/Ta ratios (in E-type MORB Hf/Ta> 7, in N-type MORB Hf/Ta> 7). E-type MORB can be distinguished from the basalts erupted at ocean islands by their higher Hf/Ta ratios (>2). A Th-Hf-Ta triangular diagram is used to discriminate between the different ocean floor basalts as well as those erupted at destructive plate margins, which are depleted in Ta and Nb. This diagram can also distinguish between silicic lavas from the different tectonic environments as well as identifying lavas that have been contaminated with continental crust. 相似文献
997.
Michel Prévot 《Physics of the Earth and Planetary Interiors》1977,13(4):342-345
Directional and paleointensity data for the Steens Mountain geomagnetic polarity transition do not agree with the two simplest models of reversals: rotation of undiminished dipole or gradual diminution followed by change in polarity of the dipole moment. Instead, large and rapid changes in the intensity and direction of the field occur, probably as a result of non-dipole variations. 相似文献
998.
The230Th-238U radioactive disequilibrium method was applied to the study of recent volcanic rocks from Costa Rica. Most samples are from the Irazu volcano. Some samples were dated by internal isochrons using the (230Th/232Th)-(238U/232Th) diagram, others were studied only by whole rock analyses. The evolution of the parent magma may be followed by the initial (230Th/232Th)0 ratios of the rocks. A model involving a differentiating magma chamber that existed for 140,000 years under the Irazu volcano correlates well with the observations. Other volcanoes seem to be in earlier stages of their evolution. Continuing study may help to solve the tholeiitic to andesitic volcanism relationship. 相似文献
999.
The sulphur isotope composition of 16 pyrite and chalcopyrite samples from recent sulphide deposits (“Cyana”—project RITA) and active sulphide mineralisation (“Alvin”—project RISE) associated with hydrothermal sources at 380±30°C on the East Pacific Rise at latitude 21°N have been measured. The34S/32S ratios are relatively uniform and essentially identical for both sites: δ34S=+1.4to3.0%. (CDT), mean +2.1‰. The sulphides were analysed after the majority of the very numerous micro-inclusions of anhydrite had been removed.Two independent physico-chemical analyses of the data demonstrate that about 90% of the sulphur was leached from the basaltic host rocks by the circulating seawater-hydrothermal fluids. 相似文献
1000.
Benoît Villemant Henri Jaffrezic Jean-Louis Joron Michel Treuil 《Geochimica et cosmochimica acta》1981,45(11):1997-2016
Major and seventeen trace element distribution coefficients between main phenocrysts (olivine, clinopyroxene, amphibole, mica, feldspars and Fe-Ti oxides) and groundmass have been measured in the alkali basalt suite of Chaîne des Puys (Massif Central, France). The suite appears to be a well behaved crystal fractionation series. We pinpoint key elements whose behavior is closely related to the appearance or disappearance of specific crystal phases in the fractionation process. Ta, for instance, clearly indicates the role of hydrous silicates (amphiboles and micas). Distribution coefficients are shown to vary systematically along the differentiation trend. Significantly the hygromagmaphile tendency (Treuilet al., 1979) of U, Th, Ta and La is variable along the series.The mass balance equations, where Di and Dji are the bulk and mineral/liquid distribution coefficients respectively, and xj the weight fractions of the fractionating phases, are solved by least square resolution of the overdetermined system, taking into account the analytical errors on data. The solution applied to the Chaîne des Puys suite leads to a coherent and quantitative model of the fractional crystallization process. The suite has apparently evolved in three stages. Each stage is characterized by constant bulk distribution coefficients and a specific mineral assemblage. Amphibole fractionation plays an important role in the early stages. Some intensive parameters (T, ? ?O2, PH2O) as well as f (weight fraction of residual liquid) are also estimated. 相似文献