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991.
Temperature variations recovered from tree-rings in the middle Qilian Mountain over the last millennium 总被引:21,自引:5,他引:16
LIU Xiaohong QIN Dahe SHAO Xuemei CHEN Tuo & REN Jiawen . Cold Arid Regions Environmental Engineering Research Institute Chinese Academy of Sciences Lanzhou China . Institute of Geographical Sciences Natural Resources Research Chinese Academy of Sciences Beijing China 《中国科学D辑(英文版)》2005,48(4):521-529
During the past 1000 years, there had been sev-eral widespread climate events on the earth, such asthe ‘Medieval Warm Period’, the ‘Little Ice Age’ andthe recent warming from the later part of the nine-teenth century onward[1,2]. To better understand thedetails of climatic history on a regional scale, morehigh-resolution, millennia-length climate reconstruc-tions are needed by intensive, multiproxy investigationof ice cores, sediments of loess and lakes, corals andtree-rings. Since … 相似文献
992.
Jaan-Mati?PunningEmail author Tiiu?Koff Ene?Kadastik Annika?Mikom?gi 《Journal of Paleolimnology》2005,34(3):377-390
The main aim of this study was to reconstruct the history of water level fluctuations of a small dimictic lake during the Holocene based on the lithological and geochemical composition of sediments. We studied lithological and geochemical parameters in sediment cores extracted along a transect through Lake Juusa in southeastern Estonia. Analysis revealed that LOI550 and CaCO3 content in the accumulated sediment are dependent on water depth. At depths greater than 3 m, the relationship between organic carbon and CaCO3 is inverse, whereas no relationship exists at shallower depths. Lake-level changes are well depicted on the grain-size distribution profiles and macrofossil composition. An increase in the >315μm fraction appeared during the initial phases of water level fluctuations, followed by an increase in the 100–315μm fraction. The >36μm fraction dominated the silt fraction. Higher OC/N ratios in shallow water sediments reflect the dominance of macrophytes vegetation. 相似文献
993.
994.
995.
Geoffrey D. Corner Vasili V. Kolka Vladimir Y. Yevzerov Jakob J. Mller 《Global and Planetary Change》2001,31(1-4)
A relative sea-level curve for the Holocene is constructed for Polyarny on the Kola Peninsula, northwest Russia. The curve is based on 18 radiocarbon dates of isolation contacts, identified from lithological and diatomological criteria, in nine lake basins situated between 12 and 57 m a.s.l. Most of the lakes show a conformable, regressive I–II–III (marine–transitional–freshwater) facies succession, indicating a postglacial history comprising an early (10,000–9000 radiocarbon years BP) phase of rapid, glacio-isostatically induced emergence (5 cm year−1) and a later phase (after 7000 years BP,) having a moderate rate of emergence (<0.5 cm year−1). Three lakes together record a phase of very low rate of emergence or slight sea-level rise at a level of 27 m a.s.l., between 8500 and 7000 years BP, which correlates with the regional Tapes transgression. Pollen stratigraphy in the highest lake shows that the area was deglaciated before the Younger Dryas and that previously reconstructed Younger Dryas glacier margins along the north Kola coast lie too far north. 相似文献
996.
This paper discusses the dating of stratigraphically important Quaternary sequences from a site near Fenit, Co. Kerry, which have been the subject of debate since they were first described by Mitchell in 1970. The overall stratigraphy of the Quaternary deposits have been investigated and detailed analyses of the organic material carried out. Pollen from biogenic sediments have been analysed and samples of peat dated using the uranium-thorium disequilibrium method. The pollen assemblages match no others previously recorded in Ireland and appear to represent a cool temperate phase following the last interglacial. The uranium-thorium dates of between 114000 and 123 000 yr BP indicate that the deposit dates from Oxygen Isotope Stage 5, possibly post-dating the last temperate stage (the Eemian Stage interglacial; Oxygen Isotope Substage 5e). The dating of this deposit and the realisation that it is not penultimate temperate stage (Gortian) in age invalidates much recent speculation on the age of the Gortian interglacial. 相似文献
997.
John A. Williams 《Estuarine, Coastal and Shelf Science》1983,16(3):291-298
The diurnal burrow depth distribution of Talitrus saltator, a sand-beach talitrid amphipod was examined in relation to moisture content and temperature profiles of the substrate. Individuals burrow to depths maintaining a moisture content of between 2·0 and 4·0% irrespective of the temperature profile, and therefore burrow depth is suggested to be regulated primarily by the requirements of the amphipods for an optimal humidity environment. 相似文献
998.
Times of minimum derived from photometry obtained in 1963, 1967, 1978, and 1979 are presented. With these and previously published
times, the period is studied. A constant period increase (quadratic ephemeris) represents most of the times but there was
a period decrease in 1934 and possibly in 1984. A 50-year magnetic cycle is discussed
On leave from Dyer Observatory, Vanderbilt University, Nashville, Tennessee. 相似文献
999.
Bruce E. Frey G.Fritz Riedel Ann E. Bass Lawrence F. Small 《Estuarine, Coastal and Shelf Science》1983,17(2):181-187
Experiments were conducted in which we tested the effects of hexavalent chromium on both natural assemblages of phytoplankton and cultures of Thalassiosira pseudonana clone 3H. Water was collected from various locations in Yaquina Bay, Oregon, with salinities ranging from 32·5‰ to 0·03‰. A variety of nutrient regimes were tested by adding major nutrients and micro-nutrients, and/or stripping micro-nutrients with activated carbon. In one high salinity experiment, chromium was stimulatory, as were micro-nutrient additions. In other high and medium salinity experiments, chromium was neither stimulatory nor inhibitory, at levels up to 1·9 μ mole l?1 Cr. There was, however, slight inhibition of growth at 19·0 μ mole l?1 Cr, due specifically to inhibition of Skeletonema costatum. In our freshwater experiments, chromium was very inhibitory at 1·9 μ mole l?1 Cr, and slightly inhibitory at 0·19 μ mole l?1 Cr. Species inhibited by chromium were Surirella ovata, Detonula confervacea, and Cyclotella sp. Experiments were conducted with T. pseudonana grown over a wide range of salinities. Chromium was found to be very inhibitory in freshwater and became progressively less toxic as the salinity increased. Most inhibition was neutralized by a salinity of 2·1‰. 相似文献
1000.
The Coriolis forces/accelerations due to the tidal deformations (shifts) have been estimated at points on the physical Earth’s
surface. The maximum tidal accelerations occur in the direction of the prime vertical, i.e. in the prime vertical component
of the deflection of the vertical. They amount to about 0.05 μGal (50 nGal). This is just about the accuracy level achieved
recently by the best superconducting gravimeters (SG) exhibiting 0.1 μGal accuracy (nanoGal level). The main goal of the paper
is to determine the necessity of Coriolis forces be taken into account in next future. 相似文献