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排序方式: 共有470条查询结果,搜索用时 15 毫秒
61.
62.
Claude J. Allegre Dalila Ben Othman Mireille Polve Pierre Richard 《Physics of the Earth and Planetary Interiors》1979,19(4):293-306
The neodymium-strontium isotopic correlation observed in most of the Earth mantle materials is evaluated by means of direct modelling. Several geochemical models are quantitatively developed to explain the observations. The main results of this modelling are that such a correlation is not geochemically trivial and that it corresponds to specific conditions in chemical fractionation. These specific conditions seem to be satisfied by solid-liquid partitioning in magmatic conditions. The discussion of the experimental data supports a continuous convecting-magmatic fractionation model for a large proportion of the mantle. 相似文献
63.
Neodymium isotopic analyses have been measured on nine ophiolites and four orogenic lherzolites. εNd varies from +12 to +3 in the ophiolites and from +18 to +2 in the orogenic lherzolites. The majority of the analyses plot on a εNd-εSr correlation line as defined by Nd and Sr isotopic analyses of oceanic basalts. However, certain ophiolitic and lherzolitic samples exhibit high87Sr/86Sr ratios and as such lie to the right of the correlation line towards seawater compositions.From these data one can postulate several origins for ophiolites including that of mid-ocean ridges and ocean islands. If the orogenic lherzolites are interpreted as representative of the mantle occurring below active ridges a more complex model is required involving mantle heterogeneity and multi-episodic chemical fractionation starting prior to 2 Ga ago. 相似文献
64.
65.
Claude T. Herzberg 《Contributions to Mineralogy and Petrology》1978,66(4):375-382
The temperatures and pressures of subsolidus equilibration of garnet-websterites (garnet+clinopyroxene+orthopyroxene) can be determined to within 3 kilobars from alumina solubility properties of clinopyroxene (Herzberg, 1978) and orthopyroxene (Wood, 1974, 1975). These calculations require knowledge of the oxidation state of iron and the effect of alumina on the mutual solubility of the two pyroxenes. The conditions of total dissolution of exsolved garnet and orthopyroxene required to yield single-phase subcalcic clinopyroxenites from Salt Lake Crater and the French Pyrenees have been determined. Many of these clinopyroxenites were transported 20 to 60 km up the mantle column before exsolution was terminated. Such transport was probably accomplished by convective upwelling of hot mantle peridotite and its contained anatectic products, rather than by precipitation from ascending magmas. 相似文献
66.
Dr Claude Lang 《Aquatic Sciences - Research Across Boundaries》1974,36(2):301-350
In Lake Geneva (Switzerland), the macrofauna of the stony lake bottom was studied in seven stations from 1969 to 1971. The
modifications in animal communities since the beginning of the century can be attributed partly to the increasing eutrophication
of the lake and partly to the introduction of new species. The stations are classified according to the structure of their
animal communities, which enables us to deduce the degree of eutrophication of each station. The analysis of factors which
influence the animals' microdistribution on lakebottom stones reveals many complicated interactions. As a result of this complexity,
further research projects were concentrated on leeches (Hirudinea) which colonize artificial substrates in imitation of the
underface of stones.Helobdella stagnalis, Erpobdella octoculata andGlossiphonia complanata form the major part of collected fauna. Density fluctuations, population structures (age groups) and quantitative relations
between these three species as well as their vertical and horizontal distribution patterns were examined in great detail.
相似文献
67.
The facies development of the Spanish Triassic corresponds to the typical three-fold subdivision of the Germanic Facies: Buntsandstein, Muschelkalk and Keuper. Two intervals interpreted as epeiric carbonate platforms: lower Muschelkalk (Anisian) and upper Muschelkalk (Ladinian) are recognized during the Middle Triassic of northeastern Spain. These carbonate intervals are separated by one siliciclastic/evaporitic interval interpreted as sabbkha and saline deposits: middle Muschelkalk facies (Lower Ladinian). In northeastern Spain (Catalonian Coastal Ranges), two Middle Triassic sections comprising lower Muschelkalk facies have yielded the following conodont taxa: Paragondolella bulgarica, P. hanbulogi, P. bifurcata, Neogondolella constricta, N. cornuta, N. excentrica and N. basisymmetrica . The conodont sequence allows recognition of the P. bulgarica and N. constricta zones. These results indicate a middle–upper Pelsonian to upper Illyrian age (middle–upper Anisian), and represent the first conodont-chronostratigraphic approximation for the lower Muschelkalk facies of the western part of the Sephardic Province of the Triassic Tethys Realm. 相似文献
68.
Using earthquakes relocated in north‐east Taiwan, we estimated b‐value distribution along a cross‐section located near the Ryukyu slab edge, and four b‐value anomalous areas are evidenced: (1) a high b‐value body lying on top of a low Vp, low Vs and high Vp/Vs sausage‐like body was considered as a region of enhanced partial melt or water supply above which seismicity occurs; (2) beneath the Ilan Plain, an anomalous area characterized by b‐values slightly higher than 1.1 might give evidence to the magma conduits to the Kueishantao Island; (3) above the Ryukyu Wadati‐Benioff zone, at depths ranging from 90 to 110 km, a high b‐value anomaly might correspond to the depth where dehydration occurs in the subducting oceanic plate; and (4) a low b‐value area located within the Ryukyu slab, at depths ranging from 70 to 90 km, might be linked to the compressive mechanisms shown by focal mechanisms and the bending of the subducting plate. 相似文献
69.
Pierre‐Yves Pascal Claude Bellemare Wolfgang Sterrer Henricus T. S. Boschker Silvina Gonzalez‐Rizzo Olivier Gros 《Marine Ecology》2015,36(2):246-257
Haplognathia ruberrima is a cosmopolitan gnathostomulid species found in sulfur bacterial mats in mangroves in Guadeloupe (French West Indies). Haplognathia ruberrima presents a δ13C value lower than all measured meiofaunal grazers and lower than the available measured food sources of this environment. This low δ13C value can not be due to specific ingestion of 13C‐depleted methanogenic bacteria because abundances of those bacteria are reduced in surficial and deep sediments as revealed by δ13C of bacterial fatty acid. According to scanning electron microscope observations, no bacterial ectosymbionts were observed at the surface of the gnathostomulids, and transmission electron microscope views revealed the absence of bacterial endosymbionts. Energy‐dispersive X‐ray spectroscopy analysis detected low levels of sulfur (0.32%±0.8) in biological tissues of H. ruberrima, confirming the absence of thioautotrophic bacterial symbionts in these animals. Consequently, the low δ13C value of H. ruberrima can not be due to the presence of sulfur‐oxidizing symbionts but more probably to the selective and exclusive consumption of free‐living, sulfur‐oxidizing bacteria. 相似文献
70.
Jutta ZIPFEL Bradley L. JOLLIFF Ralf GELLERT Kenneth E. HERKENHOFF Rudolf RIEDER Robert ANDERSON James F. BELL III Johannes BRÜCKNER Joy A. CRISP Philip R. CHRISTENSEN Benton C. CLARK Paulo A.
De SOUZA Jr. Gerlind DREIBUS Claude
D’USTON Thanasis ECONOMOU Steven P. GOREVAN Brian C. HAHN Göstar KLINGELHÖFER Timothy J. McCOY Harry Y. McSWEEN Jr. Douglas W. MING Richard V. MORRIS Daniel S. RODIONOV Steven W. SQUYRES Heinrich WÄNKE Shawn P. WRIGHT Michael B. WYATT Albert S. YEN 《Meteoritics & planetary science》2011,46(1):1-20
Abstract– The Opportunity rover of the Mars Exploration Rover mission encountered an isolated rock fragment with textural, mineralogical, and chemical properties similar to basaltic shergottites. This finding was confirmed by all rover instruments, and a comprehensive study of these results is reported here. Spectra from the miniature thermal emission spectrometer and the Panoramic Camera reveal a pyroxene‐rich mineralogy, which is also evident in Mössbauer spectra and in normative mineralogy derived from bulk chemistry measured by the alpha particle X‐ray spectrometer. The correspondence of Bounce Rock’s chemical composition with the composition of certain basaltic shergottites, especially Elephant Moraine (EET) 79001 lithology B and Queen Alexandra Range (QUE) 94201, is very close, with only Cl, Fe, and Ti exhibiting deviations. Chemical analyses further demonstrate characteristics typical of Mars such as the Fe/Mn ratio and P concentrations. Possible shock features support the idea that Bounce Rock was ejected from an impact crater, most likely in the Meridiani Planum region. Bopolu crater, 19.3 km in diameter, located 75 km to the southwest could be the source crater. To date, no other rocks of this composition have been encountered by any of the rovers on Mars. The finding of Bounce Rock by the Opportunity rover provides further direct evidence for an origin of basaltic shergottite meteorites from Mars. 相似文献