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811.
John Lovell Stuart Crampin Russ Evans S. Balamir Üçer 《Geophysical Journal International》1987,91(2):313-330
Summary. The third occupation (experiment TDP3) of recording sites above a persistent swarm of microearthquakes near the North Anatolian Fault, with a larger seismic network and over a longer period of time, confirms and refines previous observations with greater resolution. The greater resolution in earthquake locations has revealed marked clustering in time and space. Many, perhaps most, of the earthquakes belong to clusters, where successive earthquakes originate in a very small volume and have similar fault mechanisms. Such studies allow the progression of seismic activity of small earthquakes to be followed in some detail, and may reveal features which are hidden in larger and more complex earthquake sequences. 相似文献
812.
During the last sunspot maximum, major auroras occurred over Boston, MA (L = 3.1) on 23/24 March 1969 and 8/9 March 1970, during which optical and incoherent scatter radar measurements were made simultaneously from the Blue Hill Observatory and Millstone Field Station, respectively. The paper presents the results of these measurements and attempts a self-consistent interpretation of them. It is found that a major increase (5–10 times) in the abundance of molecular species (O2 and N2) at F-region heights must have occurred; this was not accompanied by any appreciable increase in the major neutral species, atomic oxygen. From the radar data, the energy input to the F-region can be separated into direct heating by secondary electrons, downward heat flow from the magnetosphere and a low-energy non-ionizing electron flux. The total observed intensity of the predominant optical emission from atomic oxygen at 6300 Å can then be predicted satisfactorily by summing the contributions to this emission from impact excitation by ambient electrons, from the low-energy precipitating electrons and from dissociative recombination. 相似文献
813.
The effects of Gaussian random and linear phase change on the response of the matched azimuth processor of a synthetic aperture imaging radar is analyzed numerically. 相似文献
814.
The relationship between sedimentary diatom assemblages and lakewater pH in 35 Quebec lakes,Canada 总被引:1,自引:0,他引:1
Surface sediment diatoms from 35 soft-water lakes in southern Quebec were studied to examine the relationship with lakewater pH. The lakes ranged in pH from 5.25 to 7.66. The species composition and the relative abundance of diatoms in the study lakes was found to be closely related to pH and/or factors closely associated with pH. Predictive models were developed to infer lakewater pH using simple linear regression equations of index alpha, index B, and multiple regressions using pH preference categories. Among the predictive models examined here, the multiple regression technique provided the highest correlation coefficient (r2=0.88) and the lowest standard error (±0.26 of a pH unit) in computing diatom-inferred pH. This model appears to be the most appropriate to reconstruct lake pH histories in Quebec region. 相似文献
815.
The binding capacities of surface waters for Cd, Cu, and Pb were determined for eight water samples representing four rivers and two swamps from Florida and Georgia in the southeastern United States The binding capacity ranges were CdBC=0 04 to 0 79 μg atm/L, CuBC=1 0 to 5 4 μg atm/L, and PbBC=5 0 to 17 8 μg atm/L Binding capacity values from the southeastern United States are shown to be in good agreement with values reported from the northeastern part of the country and northern Europe The CdBC was due primarily to inorganic ligand binding, while PbBC was predominantly a result of organic matter The CuBC was due to a complex function of both organic and inorganic binding Significant portions of the CuBC and PbBC could be removed from the waters by ultrafiltration of particles between 0·45 μm and 52 Å in diameter Ultrafiltration, even to removing particles > 13 Å diameter, did not affect the CdBC Distributional studies of the dissolved organic carbon in these systems reveal that significant fractions of the DOC are present in the ultrafilterable fraction which contains significant portions of the CuBC and PbBC 相似文献
816.
Epidote phenocrysts in dacitic dikes,Boulder County,Colorado 总被引:1,自引:0,他引:1
Epidote (Ps21%) crystallized early as elongate phenocrysts in Late Cretaceous rhyodacitic dikes in the vicinity of Ward, Boulder County, Colorado. Other unusual phenocryst phases are garnet (Gr17–24%) and muscovite. In a xenolith containing kyanite, corundum, biotite, and plagioclase, magmatic garnet grew as a rim around xenocrystic pyrope-rich (Py37%) garnet. The xenolith was derived from a granulite-facies zone, not represented at the present-day erosion surface which is composed of upper amphibolite-facies cordierite and sillimanite-bearing gneisses. The dike magmas were fed not from an immediately underlying batholith but from a magma chamber at a depth corresponding to a pressure of 8–13 kilobars. Phenocrysts cystallized in the temperature range 800 to 700° C, under H2O and O2 activities greater than normal for silicic magmas. This occurrence shows convincingly not only that epidote can be magmatic but that it is a possible early-crystallization phase in silicic magmas. 相似文献
817.
In an attempt to evaulate the hypothesis that petroleum formation can be simulated using high temperatures, Green River Shale from Colorado, U.S.A., was subjected to closed-system pyrolysis for 16 hr at temperatures ranging from 300 to 500°C. Variations in the pyrolysis products (gases, volatile liquids, and organics extracts) over this temperature range duplicate the variations observed in many in situ studies of petroleum maturation.The sequence of products formed over this temperature range was used to define five different zones of maturation reactions: (1) a heterobond cracking zone; (2) a labile carbon bond cracking zone; (3) a free radical synthesis zone; (4) a wet gas formation zone; and (5) a dry gas formation zone. This high temperature simulation of maturation can be used to test other factors in petroleum formation such as mineral catalysis. 相似文献
818.
819.
High-temperature oxide-melt calorimetry and Rietveld refinement of powder X-ray diffraction patterns were used to investigate the energetics and structure of the hematite–corundum solid solution and ternary phase FeAlO3 (with FeGaO3 structure). The mixing enthalpies in the solid solution can be described by a polynomial ΔHmix=WX hem(1?X hem) with W=116 ± 10 kJ mol?1. The excess mixing enthalpies are too positive to reproduce the experimental phase diagram, and excess entropies in the solid solution should be considered. The hematite–corundum solvus can be approximately reproduced by a symmetric, regular-like solution model with ΔG excess=(W H ?TW S )X hem X cor, where W H= 116 ± 10 kJ mol?1 and W S =32 ± 4 J mol?1 K?1. In this model, short-range order (SRO) of Fe/Al is neglected because SRO probably becomes important only at intermediate compositions close to Fe:Al=1:1 but these compositions cannot be synthesized. The volume of mixing is positive for Al-hematite but almost ideal for Fe-corundum. Moreover, the degree of deviation from Vegard's law for Al-hematite depends on the history of the samples. Introduction of Al into the hematite structure causes varying distortion of the hexagonal network of oxygen ions while the position of the metal ions remains intact. Distortion of the hexagonal network of oxygen ions attains a minimum at the composition (Fe0.95Al0.05)2O3. The enthalpy of formation of FeAlO3 from oxides at 298 K is 27.9 ± 1.8 kJ mol?1. Its estimated standard entropy (including configurational entropy due to disorder of Fe/Al) is 98.9 J mol?1 K?1, giving the standard free energy of formation at 298 K from oxides and elements as +19.1 ± 1.8 and ?1144.2 ± 2.0 kJ mol?1, respectively. The heat capacity of FeAlO3 is approximated as C p (T in K)= 175.8 ? 0.002472T ? (1.958 × 106)/T 2? 917.3/T 0.5+(7.546 × 10?6) T 2 between 298 and 1550 K, based on differential scanning calorimetric measurements. No ferrous iron was detected in FeAlO3 by Mössbauer spectroscopy. The ternary phase is entropy stabilized and is predicted to be stable above about 1730 ± 70 K, in good agreement with the experiment. Static lattice calculations show that the LiNbO3-, FeGaO3-, FeTiO3-, and disordered corundum-like FeAlO3 structures are less stable (in the order in which they are listed) than a mechanical mixture of corundum and hematite. At high temperatures, the FeGaO3-like structure is favored by its entropy, and its stability field appears on the phase diagram. 相似文献
820.
Although geological comparisons between Australia and North America have provided a basis for various Neoproterozoic Rodinia reconstructions, quantitative support from precisely dated palaeomagnetic poles has so far been lacking. We report U–Pb ages and palaeomagnetic results for two suites of mafic sills within the intracratonic Bangemall Basin of Western Australia, one of which is dated at 1070 ± 6 Ma and carries a high‐stability palaeomagnetic remanence. Comparison of the Bangemall palaeopole with Laurentian data suggests that previous reconstructions of eastern Australia against either western Canada (SWEAT) or the western United States (AUSWUS) are not viable at 1070 Ma. This implies that the Pacific Ocean did not form by separation of Australia–Antarctica from Laurentia, and that up to 10 000 km of late Neoproterozoic passive margins need to be matched with other continental blocks within any proposed Rodinia supercontinent. Our results permit a reconstruction (AUSMEX) that closely aligns late Mesoproterozoic orogenic belts in north‐east Australia and southernmost Laurentia. 相似文献