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221.
222.
Majid Ehteshami Richard C. Peralta Hubert Eisele Howard Deer Terry Tindall 《Ground water》1991,29(6):862-868
223.
Richard K. Olsson 《Sedimentary Geology》1991,70(2-4):195-208
The New Jersey margin contains an extensive record of Cretaceous to Eocene sea-level fluctuations. These events have been documented on the basis of sedimentology, benthic foraminiferal paleobathymetry (paleoslope), biostratigraphic recognition of unconformities and their associated hiatuses, and on seismic reflection records. The record of sea-level change for the New Jersey margin shows a long-term (second-order) rise beginning in the upper Albian that is punctuated by numerous third-order cycles of change in the Upper Cretaceous, Paleocene, and Eocene. The sequences deposited during these cycles that are most readily recognizable, are separated by type 1 unconformities. Sequences bracketed by one or two type 2 unconformities are more difficult to resolve, although many have been identified. Sequences shown on the cycle chart of Haq et al. (1987) of less than 1 Ma duration are the most difficult to recognize and many have not been identified in the New Jersey section.
Benthic foraminiferal paleoslope studies indicate that relative sea-level rise on the New Jersey margin varied on the order of 10–120 m above present sea level. Much of the preserved record in the coastal plain consists of sediments deposited during rising sea level. This has led to a stacked record of sea-level rise events separated by unconformities. 相似文献
224.
The rate of compositional and isotopic exchange between minerals may be enhanced significantly if the rock is deformed simultaneously.
The enhanced exchange rate may result from a reduction in grain size (shorter distance for volume diffusion), dissolution
and growth of grains by diffusion creep (pressure solution), or the movement of high-angle grain boundaries through strained
grains during recrystallization in the dislocation creep regime. The migration of high-angle grain boundaries provides high
diffusivity paths for the rapid exchange of components during recrystallization. The operation of the latter process has been
demonstrated by deforming aggregates consisting of two plagioclases (An1 and An79) at 900°C, 1 GPa confining pressure, and a strain rate of ∼2x10-6s-1. The polygonal, recrystallized grains were analyzed using an analytical transmission electron microscope and have a variable
but often intermediate composition. At the conditions of these experiments, the volume interdiffusion rate of NaSi/CaAl is
too slow to produce any observable chemical change, and microstructural-chemical relations indicate that the contribution
from diffusion creep was insignificant except for initially fine-grained (2–10 μm) aggregates. These results indicate that
strain-induced recrystallization can be an effective mechanism for enhancing the kinetics of metamorphic reactions and for
resetting the isotope systematics of minerals such as feldspars, pyroxenes, and amphiboles. 相似文献
225.
In 1991, a deep seismic reflection line, MPNI-9101, was acquired in the southern North Sea from the Mesozoic Broad Fourteens Basin, across the West Netherlands Basin onto the London-Brabant Massif (LBM). The resultant section shows a strongly reflective lower crust beneath the area of Mesozoic basin development. This lower crustal reflectivity continues to be strong beneath the LBM. The travel time to the base of the reflective zone increases from approximately 11.0 s beneath the Mesozoic basins to 12.5 s beneath the LBM, suggesting a southward thickening of the crust (Rijkers et al., 1993). Based on these travel times and information from deep wells and refraction surveys. Moho depth is estimated to increase from about 31 km beneath the Mesozoic basins to about 38 km beneath the LBM. This difference in depth to the Moho can partly be explained by coaxial stretching of the crust beneath the Mesozoic basins. In comparison with the Mesozoic basins, the crust beneath the LBM was thickened during the Caledonian and Variscan orogenies. 相似文献
226.
James F. Allan Rodey Batiza Richard O. Sack 《Contributions to Mineralogy and Petrology》1994,116(1-2):47-61
A wide compositional continuum of basalts has been erupted from near-ridge seamounts constructed on the Cocos Plate between the Clipperton and Orozco Francture Zones. They range from highly evolved to moderately primitive (3.0–7.8% MgO), LREE-enriched alkali basalts, to moderately evolved to near-primary (5.2–9.5% MgO) tholeiites indistinguishable from N-type MORB. The data set of 159 quench glass analyses exhibits a remarkably consistent variation in both major and trace element composition that is keyed to variations in (La/Sm). Modeling of potential liquid lines of descent at pressures ranging from 1 bar to 8 kbar shows that this covariation is partially due to systematic differences in liquid lines of descent, where the alkaline lavas have undergone substantially more high pressure clinopyroxene fractionation and substantially less low pressure plagioclase fractionation than the tholeiites. In addition, systematic variation in the composition of the more primitive glasses indicates that they were derived from mixing of discrete enriched and depleted melts in the heterogenous seamount mantle source at pressures of 8–10 kbar and greater, and that clinopyroxene may be a residual phase during partial melting. These results show that porous media flow in the seamount mantle source is minor and that melt transport is accomplished primarily through cracking and diking. This study supports suggestions that the general homogeneity of basalt along the EPR is due to mixing in sub-axial magma chambers and mush zones, with additional mixing during partial mantle melting and melt segregation. 相似文献
227.
Richard B. Rood 《Pure and Applied Geophysics》1985,123(5):733-755
The concept of planetary wave breaking (McIntyre andPalmer, 1983; 1984) is critically reviewed. It is concluded that the wave breaking signature is not unique to any particular dynamic event in the stratosphere. Therefore, the classification of stratospheric transport events, such as wave breaking, groups fundamentally different events together. Better qualification of the wave breaking signature and a more solid theoretical basis of planetary wave breaking must be presented if the concept is to be of significant utility in describing stratospheric tracer transport. 相似文献
228.
Prior to the recent discovery of high-temperature vanadium sublimates at the fumaroles of Izalco volcano, El Salvador, the only vanadium minerals known were those formed at low-temperature surface conditions. Six new vanadium compounds have already been discovered at Izalco volcano, and five of these have been elevated to mineral status. Two of the minerals are among the most vanadium-rich compounds known in nature.Field studies and studies of the crystal chemistry of the sublimate phases have allowed delineation of the conditions of exsolution of vanadium-bearing gases from the magma and conditions of sublimation of the vanadium compounds. A vanadium halogen or oxyhalogen gas phase was exsolved from a basaltic magma when the magma was 550 m below the summit crater. As the gas rose to the fumaroles and mixed with the atmosphere, the oxygen fugacity rose from that of the magma to at least 10−3,5 bar. At the fumaroles, the vanadium compounds sublimated at various temperatures, but a minimum temperature of 760° can be determined for one of the phases based on geothermometry determined from phase relations in the system CuO-V2O5. The studies have demonstrated that a vanadium-bearing gas can segregate from a magma with normal basaltic concentrations of vanadium. 相似文献
229.
The analytical data received in an inter-laboratory study of four Canadian reference samples were treated by two different methods in order to arrive at "usable values" for the concentration of each constituent. The first method ("Select Laboratories"), proposed by S. Abbey (S.A.), is based on the fact that some laboratories consistently produce better results than others. S.A. suggests an approach which permits isolation of results from such laboratories, calculation of a mean or a median of such results and use of one or the other as the concentration of a constituent. That approach involves a degree of subjectivity and S.A. attempts to demonstrate the validity of his approach by means of several tests applied to the results obtained for the four samples. 相似文献
230.
Exposure of specimens of Mytilus edulis to dissolved copper leads to a fall in the filtration rate measured in whole animals. The copper concentration leading to a 50% reduction in the filtration rate was found to be 0.094 mg I−1. This effect was abolished on depletion of the monoamine content of the animal using reserpine. It is suggested that there may be a chemosensory mechanism present in the animals which responds to increased levels of metals in the seawater leading to a reduction in the rate of ciliary beating and mediated via the branchial nerve. 相似文献