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411.
Summary The present paper contains some lead isotope analyses on galena specimens occuring in the central part of the Eastern Desert of Egypt. Thermal emission mass spectrometric technique is applied to these analyses. Recent methods of calculations for galena dating are used in determining the geochronological significance of the data. The lead isotopic composition of the samples has revealed the possible existence of two orogenic events accompanied with metallization that took place about 1000 m.y. and 600 m.y. ago. 相似文献
412.
S. A. El Wakil A. El Sheikh M. T. Attia A. El Shahat 《Astrophysics and Space Science》1988,140(1):65-72
In this work we connect the problem of anisotropic radiation transfer in a sphere with diffuse reflectivity and containing an energy source with the problem of source free amisotropic radiation transfer with isotropic boundary condition. Exact equation for radiation heat flux for the first problem is obtained in terms of the source, the flux and the albedo of the second problem. Modeled kernel is used to represent the anisotropy of the phase function. Numerical results are given. 相似文献
413.
In this paper, a new base isolation system, namely the sliding concave foundation (SCF), is introduced and the behaviour of the buildings using such a system is theoretically investigated. A building supported on the new system behaves like a compound pendulum during seismic excitation. The pendulum behaviour accompanied by the large radius of foundation curvature shifts the fundamental period of the system to a high value (e.g. more than 8sec), in a frequency range where none of the previously recorded earthquakes had considerable energy. This results in a large decrease in the structural responses. Since small friction forces are essential on the contact surfaces, PTFE sheets can be used as sliding surfaces. Although the pure frictional sliding systems have the same efficiency as the SCF, in reducing the responses of the superstructure, the main advantage of the new system is a significant decrease in sliding displacement. The performance of the SCF subjected to a number of harmonic and non‐harmonic base excitations is studied and its ability to reduce the structural responses is examined. Some numerical examples are solved for a single‐degree‐of‐freedom (SDOF) structure and the responses are compared with the responses of the same SDOF structure on a fixed base or a pure frictional sliding support system. The comparisons confirm the effectiveness of the new system. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
414.
A monitoring program was undertaken to evaluate the adverse impacts of the El Arish power plant on the northeastern Sinai coast of Egypt. This program spanned 28 months and includes intensive hydrographic surveying, measurements of waves, longshore current, littoral drift, currents behind the breaker zone, offshore currents, sea-level variation and water quality. The shoreline dynamics of the region have been substantially disrupted due to the high-intensity longshore transport and the interruption of longshore transport by the shore-perpendicular intake breakwaters. Maximum erosion of 5.5 m/year has been documented east of the breakwater. This erosion has been continuing eastwards, threatening the resort centers on the downcoast beaches. On the other hand, accretion (11.7 m/year) is recorded along the western side of the breakwater, accumulating great volumes of sand which is transported to the east by littoral currents. Part of this sand enters the intake basin, causing sedimentation problems by the easterly and westerly littoral drifts and cross-shore currents. In other respect, an unprotected offshore channel dredged in front of the water discharger, east of the intake, acts as an effective trap for the predominantly easterly sand drift, subsequently interrupting sediments moving from the east, accelerating processes of erosion to the east. The cooling and wastewater discharging from the discharger to the sea are insignificantly warmer than the upcoast water and not contaminated with chemical wastes. The thermal and chemical plume has no significant effect on the quality of the coastal water in the region. 相似文献
415.
The Sidi Flah and Ougnat inliers are located in the eastern Anti-Atlas antiform between the Anti-Atlas Major Fault (AAMF) and South Atlas Fault (SAF). They consist of many granitoid intrusions emplaced into Neoproterozoic metasedimentary rocks and surmounted by upper Neoproterozoic A-type granites. The Sidi Flah (Saghro) and Ougnat granitoids are part of the Neoproterozoic magmatic activity related to northwards subduction of an oceanic plate beneath the Saghro continental margin. They are post-orogenic I- and S-type granitoids related to the ending of the compressional deformation in this Pan-African belt. A petrographic, geochemical and zircon typology study leads us to subdivide these rocks into three magmatic groups: (1) a medium- to high-K calc-alkaline group formed by quartz diorites and amphibole granodiorites is found in both Sidi Flah and Ougnat inliers; (2) a high-K calc-alkaline group is present in Sidi Flah. These two groups have a (deeper and) hybrid mantle-crust origin; (3) a peraluminous group in Ougnat is linked to the post-collisional setting and has a shallow crustal source. On a primitive mantle-normalized trace-element diagram, almost all of these rocks show a significant Nb depletion relative to K and La, which is typical of the calc-alkaline magmatism from the subduction-zone environment. Absence of structural marks of thrusting upon the West African craton (WAC) of this arc system and the ophiolitic suite in Bou-Azzer, and the presence of Imiter muscovite-bearing granite as part of Pan-African belt do not support the localization of northern limit of WAC at the level of SAF. 相似文献
416.
Discrimination between primary magmatic biotites, reequilibrated biotites and neoformed biotites 总被引:11,自引:0,他引:11
Hassane Nachit Abderrahmane Ibhi El Hassan Abia Mohcine Ben Ohoud 《Comptes Rendus Geoscience》2005,337(16):367
The ternary diagram TiO2–FeO*–MgO (FeO* = FeO + MnO) is proposed as a quantitative objective tool for distinguishing between primary magmatic biotites and those that are more or less reequilibrated, or possibly neoformed, by or within a hydrothermal fluid. The limit of the domains of the primary magmatic biotites, the reequilibrated biotites and the neoformed biotites were determined on the basis of optical, paragenetic and chemical criteria. To cite this article: H. Nachit et al., C. R. Geoscience 337 (2005). 相似文献
417.
The use of statistical techniques in studying the causes of geochemical variations in aquifers can provide important results
which cannot be derived in other ways. In this study, data from the Wadi Shueib catchment area in Jordan is evaluated, using
principle component factor and multivariate factor analysis in order to better understand the variablility in groundwater
chemistry and evaluate the sources of pollution and the susceptibility of these aquifers to the different sources of pollution.
This study clearly demonstrates that these statistical techniques can help determine the various mechanisms causing chemical
variation in the aquifers and the relative susceptibility of each aquifer to different types of pollution.
Received: 13 March 1996 · Accepted: 18 June 1996 相似文献
418.
El Nour AH 《GeoJournal》1989,18(4):369-377
The study of urbanization has, in recent years, assumed increasing importance in developing countries not only because these countries are in the process of facing rapid urbanization, but also because the process of urbanization has been recognized as a part of a larger process of economic and social change which is affecting the rural areas. 相似文献
419.
420.
This paper deals with the mineralogy of the continental shelf sediments of Abu-Quir Bay, N Coast of Egypt. The three dimentional distributions (normal to the shore line, in the breaker and offshore zones and along profiles E-W0 of different material individuals for twelve profiles were discussed. The patternal distribution of the recorded minerals along the bay was controlled by selective transport of the sediments by the E-W littoral current. A general trend for the decrease of the heaviest minerals from the source area (Rosetta Mouth) was observed. The opaques, garnet, zircon and epidote are concentrated in the breaker zone sediments, while the other (pyroxens and mica) are concentrated in the offshore zone sediments. Considerable amounts of opaques, amphiboles, monazite, garnet, staurolite and tourmaline were concentrated near Maadia Outlet, this is most probably attributed to the subsurface old sediments of Canopic Branch. Correlation between the present work (1978–1979) and other mineralogical work during (1971–1973), Rashed 1978) was attemptted. 相似文献