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841.
Experimental studies of the elastohydrodynamics of towed flexible cylinders aided by video image processing are reported. A scale model of a prototype hydrophone array has been designed, fabricated, and tested in a speed range of 1.0 to 4.5 m/sec. The experiments were conducted in a 67-m long towing tank. The instrumented flexible member, 12.7 mm in diameter and 13.55 m long, was fixed at the one end and free at the other and was slightly lighter than neutrally bouyant. Three tail drogue configurations were employed. An integral part of the physical model tests was the development and utilization of a microcomputer based video image processing system for model configuration reconstitution. Instability characteristics, tail acceleration spectral densities, lift force due to curvature, and drag coefficients are quantified and discussed. 相似文献
842.
843.
The distribution and biomass of macroalgae, principally Enteromorpha spp., have been estimated in Langstone Harbour, a 19 km2 tidal basin in southenrn England. Comprehensive mapping was carried out annually at the time of maximum biomass and monthly mapping of selected areas allowed seasonal changes to be studied. Aerial false-colour photography and ground-level mapping were used for assessing the area and density of cover of macroalgae, but have identified no continuous trends between 1973 and 1982. In nine years, some 48% of the intertidal mudflat has supported >75% macroalgal cover at some stage, but generally only one-third of this potential has been achieved annually. The average peak biomass was determined by a stratified sampling method and varied about a mean of 38.5 g dry weight per square metre and showed significant annual differences. The processes controlling macroalgal growth and distribution reviewed, but, in general, factors other than nutrient availability are effective in determining areas supporting high macroalgal cover in any particular year. 相似文献
844.
A method for the prediction of ocean waves was developed on the basis of the single-parameter growth equation of wind waves, proposed byToba (1978) on the basis of similarity in growing wind waves. The applicability of the method to actual problems was tested by hindcasting the wave characteristics with the method, for two cases with differing time and space scales, one in Kii Channel Approach, Japan, and the other in the North Atlantic Ocean. The results showed that the present method can predict waves within an error of 1.3 m in wave heights, which ranged from 3 to 12 m. 相似文献
845.
846.
The solubility of iron, aluminium, manganese and phosphorus has been determined in aerosol samples collected between 49°N and 52°S during three cruises conducted in the Atlantic Ocean as part of the European Union funded IRONAGES programme. Solubilities (defined at pH 4.7) determined for Fe and Al in samples of Saharan dust were significantly lower (medians 1.7% and 3.0%, respectively) than the solubilities of these metals in aerosols from other source regions (whole dataset medians 5.2% and 9.0%, respectively). Mn solubility also varied with aerosol source, but the median solubility of Mn in Saharan dust was very similar to the median for the dataset as a whole (55% and 56%, respectively). The observed solubility of aerosol P was ∼ 32%, with P solubility in Saharan aerosol perhaps as low as 10%. Laboratory studies have indicated that aerosol Fe solubility is enhanced by acid processing. No relationship could be found between Fe solubility and the concentrations of acid species (non-seasalt SO42−, NO3−) nor the net acidity of the aerosol, so we are unable to confirm that this process is significant in the atmosphere. In terms of the supply of soluble Fe to oceanic ecosystems on a global scale, the observed higher solubility for Fe in non-Saharan aerosols is probably not significant because the Sahara is easily the dominant source of Fe to the Atlantic. On a smaller scale however, higher solubility for aerosol Fe may alter our understanding of Fe cycling in regions such as the remote Southern Ocean. 相似文献
847.
848.
D. Nof 《Progress in Oceanography》2003,56(2):223-247
A ‘quasi-island’ approach for examining the meridional flux of warm and intermediate water from the Southern Ocean into the South Atlantic, the South Pacific and the Indian Ocean has recently been proposed (
[Nof, 2000a] and [Nof, 2002]). This approach considers the continents to be ‘pseudo islands’ in the sense that they are entirely surrounded by water, but have no circulation around them. The method employs an integration of the linearized momentum equations along a closed contour containing the continents. This allows the meridional transport into these oceans to be computed without having to find the detailed solution to the complete wind-thermohaline problem.The solution gives two results; one expected, the other unexpected. It shows that, as expected, about 9±5 Sv of upper and intermediate water enter the South Atlantic from the Southern Ocean. The unexpected result is that the Pacific-Indian Ocean system should contain a ‘shallow’ meridional overturning cell carrying 18±5 Sv. What is meant by shallow here is that the cell does not extend all the way to the bottom (as it does in the Atlantic) but is terminated at mid-depth. (This reflects the fact that there is no bottom water formation in the Pacific.) Both of these calculations rely on the observation that there is almost no flow through the Bering Strait and on the assumption that there is a negligible pressure torque on the Bering Strait’s sill.Here, we present a new and different approach, which does not rely on either of the above two conditions regarding the Bering Strait and yet gives essentially the same result. The approach does not involve any quasi-island calculation but rather employs an integration of the linearized zonal momentum equation along a closed open-water latitudinal belt connecting the tips of South Africa and South America. The integration relies on the existence of a belt (corridor) where the linearized general circulation equations are valid. It allows for a net northward mass flux through either the Sverdrup interior or the western boundary currents. It is found that the belt-corridor approach gives 29±5 Sv for the total meridional flux of surface and intermediate water from the Southern Ocean. This agrees very well with the quasi-island calculations, which give a total northward flux of 27±5 Sv. Given the spacing between the continents and the small variability of the southern winds with longitude, one may assume that 9 Sv of the total 29 Sv enters the Atlantic and the other 20 Sv enters the combined Pacific-Indian Ocean system, which is also in agreement with the quasi-island calculation. These agreements indicate that the assumptions made in the earlier studies regarding the Bering Strait are probably valid. 相似文献
849.
Regeneration of sand waves after dredging 总被引:2,自引:0,他引:2
Sand waves are large bed waves on the seabed, being a few metres high and lying hundreds of metres apart. In some cases, these sand waves occur in navigation channels. If these sand waves reduce the water depth to an unacceptable level and hinder navigation, they need to be dredged. It has been observed in the Bisanseto Channel in Japan that the sand waves tend to regain their shape after dredging. In this paper, we address modelling of this regeneration of sand waves, aiming to predict this process. For this purpose, we combine a very simple, yet effective, amplitude-evolution model based on the Landau equation, with measurements in the Bisanseto Channel. The model parameters are tuned to the measured data using a genetic algorithm, a stochastic optimization routine. The results are good. The tuned model accurately reproduces the measured growth of the sand waves. The differences between the measured weave heights and the model results are smaller than the measurement noise. Furthermore, the resulting parameters are surprisingly consistent, given the large variations in the sediment characteristics, the water depth and the flow field. This approach was tested on its predictive capacity using a synthetic test case. The model was tuned based on constructed predredging data and the amplitude evolution as measured for over 2 years. After tuning, the predictions were accurate for about 10 years. Thus, it is shown that the approach could be a useful tool in the optimization of dredging strategies in case of dredging of sand waves. 相似文献
850.
This paper discusses a theoretical model of the electromagnetic field induced by internal waves of baric origin. Comparison
of thein situ data on the differences between the horizontal electrical field potentials conditioned by internal waves in some Black Sea
and tropical Atlantic areas and of the results of calculations of the model electrical field's intensity in those areas shows
their good agreement. The dependences of the electromagnetic field component amplitudes on the internal waves parameters and
sea-bed rock conductivity are considered.
Translated by Vladimir A. Puchkin. 相似文献