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591.
The development of the phytoplankton was observed from 1984 to 1986 in the Warnow-River (GDR, Mecklenburg). The dominant algae throughout the year were the Bacillariophyceae with their maximum in spring (1984: 36.1 mm3/1, 1986: 32.3 mm3/1) or in autumn (1985: 48.3 mm3/1). There is not any limitation of phytoplankton by inorganic nutritation (N, P) throughout the year. The phytoplankton production was most influenced by the turbulance of water. Classification of banked-up rivers with the help of the plankton-quotients of Thunmark and Nygaard is impossible.  相似文献   
592.
The paper presents results from a laboratory investigation into the dynamic properties of natural intact and model organic soils by means of resonant-column tests. The natural intact organic soils were sands, cohesive soils and peats with varying content of calcium carbonate. The model organic soils were formed in laboratory by mixing kaolinite and paper pulp. The influence of various soil parameters, such as strain level, confining stress, void ratio, plasticity index, organic content and secondary consolidation time on shear modulus, G, and damping ratio, DT, is presented and discussed. The test results on natural organic soils show that only high organic contents (OC ≥ 25%) have significant influence on G and DT at both small and high shear strains. For the model organic soils, however, a significant influence of even lower values of organic content (5% ≤ OC ≤ 20%) on G at small strains and DT at both small and high strains is observed.  相似文献   
593.
Anhydrous spinel peridotite xenoliths in Quaternary nepheline-basanite and melilite- or sodalite-bearing lavas of the Wau-en-Namus volcano in S Libya range from lherzolites to harzburgites recording melt extraction in a shallow setting (≤ 2 GPa). Primary clinopyroxenes have distinct trace element characteristics documenting LILE (large ion lithophile element) depletion or enrichment events predating the formation of glass pockets and veins in the xenoliths. These glasses are aluminous and alkali-rich, range in composition from ultrabasic to silicic (43–67 wt.% SiO2) and may contain empty vugs and micro-phenocrysts of olivine, clinopyroxene, spinel, plagioclase, sodalite, apatite that are similar in composition to phenocrysts in the host lavas. Reactions of infiltrating melt and xenolith minerals are documented by diffuse Fe–Ca-rich rims of olivine in contact with glass, and by spongy-textured reaction domains caused by incongruent dissolution of primary pyroxenes and spinel. Some glasses have trace element characteristics similar to that of the host Ne-basanite, suggesting they were derived from the same source during entrainment and transport to the surface. Incompatible element enrichment and Sr–Nd isotopic compositions of the analyzed host lava are similar to HIMU (high μ; μ = 238Pb/204Pb)-type magmas, but the Pb isotopic composition is less radiogenic compared to other intra-plate Neogene magmatic rocks from N Africa.  相似文献   
594.
Mudstone experience periodic swell and shrink behavior due to alternate wetting and drying cycles at arid and semi-arid regions with distinctive seasonal changes. This paper examines the influence of cyclic wetting and drying on swelling strain and swelling pressure to simulate the behavior of such rocks under heavy structures (such as building foundations) and behind the stiff support systems (such as concrete linings). Mudstone samples from Bakhtiari formation of Masjed-Soleiman region in south west of Iran were chosen to perform the laboratory tests. The swelling strain under different dead pressures and also swelling pressure under oedometeric condition were measured over time. The maximum swelling strain and pressure increased with each cycle but it had a bound. Increasing the number of wetting and drying cycles reduces the time required to reach ultimate swelling of mudstone. This is a very important conclusion which helps to determine ultimate swelling behavior in a faster way as opposed to performing standard swelling tests for very long periods. The laboratory’s results are also in good correspondence with field measurements.  相似文献   
595.
By means of the RUBIKON multi-channel detector system with integrated grism spectrograph, attached to the Bochum 61cm telescope, five primary standars stars have been intercompared and an additional secondary standard star (HD 37027 in the center field of the LMC) has been set up in the wavelength range of 326–777 nm.  相似文献   
596.
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598.
We carry out 2.5D MHD simulations to study the interaction between a dipolar magnetic field of a T Tauri Star, a circumstellar accretion disk, and the halo above the disk. The initial disk is the result of 1D radiation hydrodynamics computations with opacities appropriate for low temperatures. The gas is assumed resistive, and inside the disk accretion is driven by a Shakura–Sunyaev-type eddy viscosity. Magnetocentrifugal forces due to the rotational shear between the star and the Keplerian disk cause the magnetic field to be stretched outwards and part of the field lines are opened. For a solar-mass central star and an accretion rate of 10?8 solar masses per year a field strength of 100 G (measured on the surface of the star) launches a substantial outflow from the inner parts of the disk. For a field strength of 1 kG the inner parts of disk is disrupted. The truncation of the disk turns out to be temporary, but the magnetic field structure remains changed after the disk is rebuilt.  相似文献   
599.
During the combatting of oil spills, the handling of the stable sea water in crude oil emulsions called ‘chocolate mousses’, either at sea or on the beach, is often a major problem.

A recent laboratory study of the formation and properties of such emulsions revealed the key roles played by asphaltenes and crystallized wax in their stability.

Viscosity measurements showed that mousses with 70% vol. sea water are thixotropic and may solidify after having been pumped into the hold of a salvage vessel or into a storage tank. During a search for novel chemicals for combatting oil spills we found a type of chemical additive that is effective in preventing the formation of mousses, in greatly improving the pumpability of mousses once formed and in decreasing their water content after recovery or during storage. The additive, designated LA 1834, has been tested successfully in the laboratory, on a semi-technical scale in cooperation with the Netherlands State Waterways Board and in the large-scale clean-up operation after a recent oil spill in Greece. The compound keeps oil from dispersing vertically into the water column, when applied to spilled oil or mousse on a sea water surface and holds promise of environmental acceptability.  相似文献   

600.
A model representing the profile of the silicate absorption band at 9.8 μm in the spectra of BECKLIN -NEUGEBAUER objects has been developed, solving the equation of radiative transfer. The model based on the condition of radiative equilibrium, on an analytical temperature distribution and on the assumption of constant density in the circumstellar shell allows the evaluation of the optical depth in the band's centre and the investigation of the effect of the temperature variation at the inner boundary of the envelope. The optical depth in the band's centre ist calculated for the BN point source.  相似文献   
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