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91.
92.
Two three-dimensional split-film anemometers were used to measure turbulence statistics within and above a corn canopy. Normalised profiles of mean windspeed, root-mean-square velocity, momentum flux, and heat flux were constructed from half-hourly averages by dividing within-canopy measurements by the simultaneous canopy-top measurement. With the exception of the heat flux, these profiles showed consistent shape from day to day. Time series of the three velocity components were recorded on magnetic tape and subsequently analysed to obtain Eulerian time and length scales and the power spectrum of each component at several heights. The timescale was found to have a local minimum value at the top of the canopy. However the length scale L
wformed from the timescale and the root-mean-square vertical velocity varied with height as L
w 0.1 z. The power-spectra were non-dimensionalised to facilitate comparison of spectra at different heights and times. All spectra had -5/3 regions spanning at least two decades in frequency. 相似文献
93.
Albert Eggers Jeffery Krausse Harold Rush James Ward 《Journal of Volcanology and Geothermal Research》1976,1(3):229-236
Gravity changes of up to 1.2 ± 0.1 mgal (1 standard deviation) were measured at three points within 400 m of an active vent on Pacaya volcano, Guatemala during eleven days of January, 1975. For five continuous days gravity varied inversely with the average muzzle velocity of ejecta, the frequency of volcanic explosions, and the frequency of volcanic earthquakes. The gravity changes are most reasonably interpreted as the product of intravolcanic movements of magma with masses one to two orders of magnitude larger than any flow ever erupted from the volcano. However, elevation changes and/or combination of elevation and mass distribution changes could also have been an important factor in effecting the observed gravity variations. Because we lack elevation control on the gravity stations, we are unable to unequivocally conclude which factor or which combination of factors produced the gravity changes. The study indicates the possibility of gravity monitoring of hazardous volcanoes as a predictive tool, and as an added means for investigating the internal mechanism of volcanic eruptions. 相似文献
94.
95.
Peter M. Ward 《Geoforum》1976,7(5-6)
The paper describes spatially the zonal movements of residents to three squatter settlements established at different time periods in Mexico City. In addition, moves are related to the dynamics of the low income housing system and previous theories of intra-city squatter migration behaviour are evaluated. The data corroborate the concept that the traditionally accepted pattern of centre to periphery, tenement to squatter settlement movements has altered. Direct movement into the periphery on the part of incoming migrants is increasingly important, and older established squatter areas are the most important suppliers of population in recent invasions. The implications for the distribution and structure of housing opportunities for future low-income populations in Mexico City are discussed. 相似文献
96.
Embryos and juveniles of the sheepshead minnow (Cyprinodon variegatus), a saltwater fish, were exposed to ammonium jarosite, a waste product of the processing of zinc ore, during a 28-day posthatch, flow-through toxicity test. Exposure to measured ammonium jarosite concentrations ≤ 290 ppm had no significant effect on the hatching success of embryos. However, slight delays in hatching were observed in test concentrations ≥ 140 ppm. Although exposure to test concentrations ≥ 140 ppm significantly decreased the ability of juvenile fish to uncurl after hatching, juvenile mortality was significantly increased only in test concentrations ≥ 230 ppm. There was no effect on growth of juvenile fish in jarosite concentrations ≤ 230 ppm. The estimated maximum acceptable toxicant concentration (MATC), based on measured concentrations, was > 140< 230 ppm. 相似文献
97.
The apparent molal volume, φV of boric acid, B(OH)3 and sodium borate, NaB(OH)4, have been determined in 35%. salinity seawater and 0·725 molal NaCl solutions at 0 and 25°C from precise density measurements. Similar to the behavior of nonelectrolytes and electrolytes in pure water, the φV of B(OH)3 is a linear function of added molality and the φV of NaB(OH)4 is a linear function of the square root of added molarity in seawater and NaCl solutions. The partial molal volumes, , of B(OH)3 and NaB(OH)4 in seawater and NaCl were determined from the φV's by extrapolating to infinite dilution in the medium. The of B(OH)3 is larger in NaCl and seawater than pure water apparently due to the ability of electrolytes to dehydrate the nonelectrolyte B(OH)3. The of NaB(OH)4 in itself, NaCl and seawater is larger than the expected value at 0·725 molal ionic strength due to ion pair formation [Na+ + B(OH)4? → NaB(OH)40]. The volume change for the formation of NaB(OH)40 in itself and NaCl was found to be equal to 29·4 ml mol?1 at 25°C and 0·725 molal ionic strength. These large 's indicate that at least one water molecule is released when the ion pair is formed [Na+ + B(OH)4? → H2O + NaOB(OH)20]. The observed in seawater and the (NaB0) in water and NaCl were used to estimate for the formation of MgB+ and CaB+. The volume change for the ionization of B(OH)3 in NaCl and seawater was determined from the molal volume data. Values of were found in seawater and in NaCl, respectively, at 0 and 25°C. The effect of pressure on the ionization of B(OH)3 in NaCl and seawater at 0 and 25°C determined from the volume change is in excellent agreement with direct measurements in artificial seawater (culberson and Pytkowicz, 1968; Disteche and Disteche, 1967) and natural seawater (Culberson and Pytkowicz, 1968). 相似文献
98.
A method for the dynamic analysis of staggered wall-beam frames is developed using consistent mass terms which are derived and given in simple terms. The method uses effective stiffnesses for wall-beam elements developed in an earlier paper. Experiments using a nine storey 1 : 15 scale perspex model are described. The first three natural frequencies of the model were obtained using two methods: sinusoidal external excitation of the structure with the base fixed and white noise excitation employing a single degree-of-freedom shake table, in the latter method with and without the addition of mass throughout the model. Agreement between analytical predictions of the first three natural frequencies and mode shapes and experimentally determined values is considered satisfactory, particularly for the first two modes. The lumped mass assumption gave reasonable results for these two cases, whereas the consistent mass theory gave reasonable results for the first three natural frequencies. 相似文献
99.
Elevated nutrients have the potential to disrupt reproduction in scleractinian corals, with consequent impacts on population dynamics. Reproduction in broadcast spawning (Montipora capitata) and brooding (Pocillopora damicornis) species was assessed following exposure to elevated ammonium in a microcosm experiment. Planulation in P. damicornis ceased following 4 months of ammonium exposure and did not recover until 3 months after termination of nutrient enrichment. Larval settlement and survivorship were not affected by ammonium enrichment. Few significant changes were found for reproductive parameters of M. capitata. There was a significant but small decrease in egg size (430 microm in control eggs to 408 microm in eggs from ammonium enrichment treatments), but no differences in total fecundity or fertilization success. This may be related to the presence of zooxanthellae in the eggs of M. capitata, in contrast to changes in reproduction previously reported in Acropora species, whose eggs do not contain zooxanthellae. 相似文献
100.
Richard I. Davies Hajime Sugai & Martin J. Ward 《Monthly notices of the Royal Astronomical Society》1998,300(2):388-396
We present near-infrared emission-line images of the circumnuclear ring in NGC 1068. We have measured the Brγ fluxes in a number of star-forming complexes and derived the extinction for each of these by comparison with Hα. We investigate the star-forming histories of these regions and find that a short burst of star formation occurred coevally throughout the ring within the last 30–40 Myr, and perhaps as recently as 4–7 Myr ago. The 1–0 S(1) flux and S(1)/Brγ ratios indicate that as well as fluorescence, shock-excited H2 emission contributes to the total flux. There is excess H2 flux to the north-west where the ionization cone crosses the ring, and we show that it is possible that the non-stellar continuum from the Seyfert nucleus which produces the high-excitation lines could also be causing fluorescence at the edges of molecular clouds in the ring. The nuclear 1–0 S(1) is more extended than previously realized but only along the bar's major axis, and we consider mechanisms for its excitation. 相似文献