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131.
Lavas and intrusives from Ayios Mamas, at the western end of the Limassol Forest Complex, south of the Arakapas Fault Belt, Troodos, comprise three groups: (A) a basal sequence of pillow lavas (intruded by dikes and sills) with the phenocryst assemblage PLAG+CPX+MT±OL; (B) a middle sequence of pillows and massive flows [CPX+PLAG±OL]; and (C) an upper sequence mostly of pillows and breccia [OL+OPX+CPX+SP]. The lower group is tholeiitic, and the upper two groups boninitic. Group C whole-rock and glass Mg-numbers exceed 72 and range up to 78, with corresponding olivine compositions of Fo92. They are strongly depleted in high-field strength elements, and on the basis of Cr-Y variation and major element mass balances, are interpreted to reflect partial melting of a basalt-depleted (CPX-) harzburgite source. Group A tholeiites, in contrast, are interpreted to derive from a more fertile lherzolite source. Magmaphile and compatible trace element variation is best modelled after an open magma system, involving periodic replenishment, tapping, and fractionation, although neither tholeiites nor boninites represent steady-state compositions. The boninites belong to a CaO-rich, SiO2-poor variant, resembling those from Guam, but contrasting with those from Bonin and Cape Vogel. MORB-normalized enrichment of low-field strength elements K, Sr, Ba, and Rb in all groups indicates subduction-derived source contamination. It is proposed that the Ayios Mamas section reflects splitting of a volcanic arc, prior to back-arc spreading in an environment analogous to that of the present-day Andaman Sea. 相似文献
132.
H. A. Bridgman R. C. Schnell G. A. Herbert B. A. Bodhaine S. J. Oltmans 《Journal of Atmospheric Chemistry》1989,9(1-3):49-70
In April 1986, a well-instrumented NOAA WP-3D research aircraft conducted three flights in the Canadian Arctic tied to the Canadian Atmospheric Environment Service baseline station in Alert, Northwest Territories. Two of the flights were coordinated with the National Aeronautical Establishment of Canada Twin Otter and the University of Washington C-131 research aircraft. The haze observed in the Canadian Arctic was well-aged and mixed throughout the troposphere in concentrations well below those observed during the previous weeks in the Alaskan Arctic. Over the ice, beneath the surface temperature inversion, ozone was generally depleted to near zero. Over the coast at Alert, there is evidence that topography and downslope winds reduce the strength of the inversion, thus allowing lower tropospheric gases and aerosols to mix down to the surface. At the top of the troposphere, an aerosol-depleted region was observed. In the lower stratosphere, aerosol concentrations were elevated above those observed in the troposphere. 相似文献
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Dr. Herbert Von Löffler 《Aquatic Sciences - Research Across Boundaries》1984,46(1):147-162
The reactions of the bream,Abramis brama, to the ecological changes due to man-made eutrophication of Lake Constance were investigated.
It could be demonstrated that the bream adapted only to a negligible amount. Likely due to its largeness, structure of the
body and population composition the bream is more conservative than perch, roach and whitefish. The only reactions to the
changed environment are modificated vertical and horizontal distribution and partly plancton feeding in summer.
相似文献
135.
Mario Trieloff Joachim Kunz Claude J. Allgre 《Earth and Planetary Science Letters》2002,200(3-4):297-313
New noble gas data of ultramafic xenoliths from Réunion Island, Indian Ocean, further constrain the characteristics of primordial and radiogenic noble gases in Earth’s mantle plume reservoirs. The mantle source excess of nucleogenic 21Ne is significantly higher than for the Hawaiian and Icelandic plume reservoirs, similar to excess of radiogenic 4He. 40Ar/36Ar of the Réunion mantle source can be constrained to range between 8000 and 12 000, significant 129Xe and fission Xe excess are present. Regarding the relative contribution of primordial and radiogenic rare gas nuclides, the Réunion mantle source is intermediate between Loihi- and MORB-type reservoirs. This confirms the compositional diversity of plume sources recognized in other radioisotope systematics. Another major result of this study is the identification of the same basic primordial component previously found for the Hawaiian and Icelandic mantle plumes and the MORB reservoir. It is a hybrid of solar-type He and Ne, and ‘atmosphere-like’ or ‘planetary’ Ar, Kr, Xe (Science 288 (2000) 1036). 20Ne/22Ne ratios extend to maximum values close to 12.5 (Ne-B), which is the typical signature of solar neon implanted as solar corpuscular radiation. This suggests that Earth’s solar-type noble gas inventory was acquired by small (less than km-sized) precursor planetesimals that were irradiated by an active early sun in the accretion disk after nebular gas dissipation, or, alternatively, that planetesimals incorporated constituents irradiated in transparent regions of the solar nebula. Previously, such an early irradiation scenario was suggested for carbonaceous chondrites which follow common volatile depletion trends in the sequence CI–CM–CV–Earth. In turn, CV chondrites closely match Earth’s mantle composition in 20Ne/22Ne, 36Ar/22Ne and 36Ar/38Ar. This indicates that mantle Ar could well be a planetary component inherited from precursor planetesimals. However, a corresponding conclusion for mantle Kr and Xe is less convincing yet, but this may be just due to the lack of appropriate ‘meteoritic’ building blocks matching terrestrial composition. Alternatively, heavy noble gases in Earth’s mantle could be due to admixing of severely fractionated air, but this effect must have affected all mantle sources to a very similar extent, e.g. by global subduction before the last homogenization of the mantle reservoirs. 相似文献
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139.
Climate change effects on hydrological system conditions influencing generation of storm runoff in small Alpine catchments 总被引:1,自引:0,他引:1 下载免费PDF全文
Gertraud Meißl Herbert Formayer Klaus Klebinder Florian Kerl Friedrich Schöberl Clemens Geitner Gerhard Markart David Leidinger Axel Bronstert 《水文研究》2017,31(6):1314-1330
Floods and debris flows in small Alpine torrent catchments (<10 km2) arise from a combination of critical antecedent system state conditions and mostly convective precipitation events with high precipitation intensities. Thus, climate change may influence the magnitude–frequency relationship of extreme events twofold: by a modification of the occurrence probabilities of critical hydrological system conditions and by a change of event precipitation characteristics. Three small Alpine catchments in different altitudes in Western Austria (Ruggbach, Brixenbach and Längentalbach catchment) were investigated by both field experiments and process‐based simulation. Rainfall–runoff model (HQsim) runs driven by localized climate scenarios (CNRM‐RM4.5/ARPEGE, MPI‐REMO/ECHAM5 and ICTP‐RegCM3/ECHAM5) were used in order to estimate future frequencies of stormflow triggering system state conditions. According to the differing altitudes of the study catchments, two effects of climate change on the hydrological systems can be observed. On one hand, the seasonal system state conditions of medium altitude catchments are most strongly affected by air temperature‐controlled processes such as the development of the winter snow cover as well as evapotranspiration. On the other hand, the unglaciated high‐altitude catchment is less sensitive to climate change‐induced shifts regarding days with critical antecedent soil moisture and desiccated litter layer due to its elevation‐related small proportion of sensitive areas. For the period 2071–2100, the number of days with critical antecedent soil moisture content will be significantly reduced to about 60% or even less in summer in all catchments. In contrast, the number of days with dried‐out litter layers causing hydrophobic effects will increase by up to 8%–11% of the days in the two lower altitude catchments. The intensity analyses of heavy precipitation events indicate a clear increase in rain intensities of up to 10%. 相似文献
140.
First results from wideband (electron phase energies of 5–51 eV), high-resolution (0.1 eV) spectral measurements of photoelectron–enhanced plasma lines made with the 430 MHz radar at Arecibo Observatory are presented. In the F region, photoelectrons produced by solar EUV line emissions (He II and Mg IX) give rise to plasma line spectral peaks/valleys. These and other structures occur within an enhancement zone extending from electron phase energies of 14–27 eV in both the bottomside and topside ionosphere. However, photoelectron–thermal electron Coulomb energy losses can lead to a broadened spectral structure with no resolved peaks in the topside ionosphere. The plasma line energy spectra obtained in the enhancement zone exhibit a unique relation in that phase energy is dependent on pitch angle; this relation does not exist in any other part of the energy spectrum. Moreover, large fluctuations in the difference frequency between the upshifted and downshifted plasma lines are evident in the 14–27 eV energy interval. At high phase energies near 51 eV the absolute intensities of photoelectron-excited Langmuir waves are much larger than those predicted by existing theory. The new measurements call for a revision/improvement of plasma line theory in several key areas. 相似文献