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951.
Summary The gravitational potential energy of the Sun and its corresponding internal energy have been estimated on the basis of the
standard model of the Sun's internal structure. It is demonstrated that the principal moment of inertia of the Sun, computed
from the model, does not fit the hydrostatic equilibrium limit. 相似文献
952.
Johana Brokešová 《Pure and Applied Geophysics》1996,148(3-4):503-538
The seismic wave field, in its high-frequency asymptotic approximation, can be interpolated from a low- to a high-resolution spatial grid of receivers and, possibly, point sources by interpolating the eikonal (travel time) and the amplitude. These quantities can be considered as functions of position only. The travel time and the amplitude are assumed to vary in space only slowly, otherwise the validity conditions of the theory behind would be violated. Relatively coarse spatial sampling is then usually sufficient to obtain their reasonable interpolation. The interpolation is performed in 2-D models of different complexity. The interpolation geometry is either 1-D, 2-D, or 3-D according to the source-receiver distribution. Several interpolation methods are applied: the Fourier interpolation based on the sampling theorem, the linear interpolation, and the interpolation by means of the paraxial approximation. These techniques, based on completely different concepts, are tested by comparing their results with a reference ray-theory solution computed for gathers and grids with fine sampling. The paraxial method holds up as the most efficient and accurate in evaluating travel times from all investigated techniques. However, it is not suitable for approximation of amplitudes, for which the linear interpolation has proved to be universal and accurate enough to provide results acceptable for many seismological applications. 相似文献
953.
The prediction of critical frequency foF2 is of great importance in the area of short-wave telecommunication and ionospheric modelling. The test study of foF2 data should enable the validity of data used in
PRIME
map generating and testing to be checked. The preliminary results show that some data should not be used because they could affect the latest results of
PRIME
map generating, testing and improving. 相似文献
954.
Summary A computer-assisted weather categorization was applied to meteorological time series measured at the Mileovka Observatory (a mountain station) and Prague-Klementinum (an inner city site). Groups of winter days (December, January and February) with extreme mean temperatures were examined with respect to their frequency of occurrence and presence of any trends in the period 1941–1988. In general, frequencies of cold categories exhibited a decreasing trend, and frequencies of warm categories tended to increase. In both series a prominent negative trend in temperature amplitude was detected within warm clusters, related to a statistically insignificant decline in the maximum temperature and an increase in the minimum temperature. Additional analysis indicates that changes in circulation patterns occurred over the region during the period investigated, namely strengthening of zonal circulation in winter.With 6 Figures 相似文献
955.
Estimation of the accuracy of geopotential models 总被引:1,自引:0,他引:1
Summary The new Geopotential Model Testing (GMT) method has been theoretically developed and practically applied. It is free of any hypothesis, the limiting factors are the accuracy of the geocentric position of the GMT sites and of their normal heights, as well as the accuracy of the geopotential value W0 on the geoid used as the testing value given a-priori. The GMT procedure occurs on the physical Earth's surface, no reductions are applied. No limits as regards the magnitude of the heights above sea level of the GMT sites are required. The rms error at discrete points of the most recent geopotential model JGM-3 comes out at about ± 1·5 m. 相似文献
956.
Summary The aim of this study is the evaluation of the sea breeze speed on the basis of its energy. Energetics of the sea breeze can
be studied by means of the available potential energy (APE). Part of this energy is transformed into the kinetic energy of
the sea breeze. Some similarity exists between the large scale processes of the circulation and the small coastal air circulation
due to the fact that both circulations are triggered by the same physics, i.e., solenoidal activity of the baroclinic atmosphere.
To evaluate the sea breeze speed, APE was calculated by use of the Lorenz’s equation (1955), and which is possible if the
coastal circulation is considered to be a closed system in a hydrostatic equilibrium. For calculations and verifications hourly
sea-surface temperatures, near-ground air temperatures and wind speed measurements, as well as the radio-sounding measurements
at 12 UTC were used at the Zadar station (ϕ = 44° 08′ N, λ = 15° 13′ E), which is situated in the central part of the eastern
Adriatic coast. Two days with an undisturbed sea breeze circulation were extracted using the methods for minimizing other
atmospheric influences. Calculated hourly near ground sea breeze speeds obtained in this way were higher than the measured
ones. With the assumption that some of the APE is transformed into the kinetic energy it is possible to obtain characteristic
speed of the developed sea breeze with small discrepancies to the near-ground measurements. If 6.6% of the mean daily near
ground APE was taken to be transformed to the mean daily kinetic sea breeze energy on the 29th and 4.2% on the 30th September
2002, the best agreement was obtained with the mean daily measured near ground sea breeze speed. This range of values can
be attributed to inability to extract precise values for the lapse-rate needed in the APE sea breeze calculations. Results
show similarities to the general circulation of the atmosphere, since about 10% of the APE is transformed to the kinetic energy
of the sea breeze. On the other hand calculated wind speed at the lower branch of the borderline coastal circulation was not
dependent on the integral value of the APE over the land, but on its value at the near-ground level. 相似文献
957.
Summary Using temperature and pressure records from Czech meteorological stations and NCEP/NCAR reanalysis series, we tested for the
presence of detectable nonlinearity in univariate and multivariate climatic time series. The method of surrogate data was
utilized for nonlinearity detection – results of nonlinear prediction for the original series were compared to the results
for series whose nonlinear structure was randomized. The prediction was done by means of local linear models in the reconstructed
phase space. None or very weak nonlinearity was found in the single (univariate) series, and pressure series generally exhibited
stronger nonlinearity than series of temperature (daily mean, minimum or maximum). Distinct nonlinearity was found in all
tested multivariate systems, especially when both temperatures and pressures were used simultaneously to form the phase space.
Nonlinearity tests were carried out for 30-year and 10-year-long datasets and nonlinear behavior was generally more apparent
in the longer versions. In addition, the tested systems showed more substantial nonlinearity when the success of short-range
prediction was used as the discriminating statistic; with an increase of the prediction time, detectable nonlinearity became
weaker and it disappeared completely for long-term prediction. 相似文献
958.
On the detection of weak strain parallel to the bedding by magnetic anisotropy: A mathematical model study 总被引:2,自引:0,他引:2
Summary Five mathematical models of the superposition of deformational magnetic fabric on sedimentary magnetic fabric are presented.
These models are represented by various combinations of pure shear and simple shear. The diagrams of the variations in the
main magnetic anisotropy parameters with strain can help in recognizing weak ductile deformation in sedimentary rocks.
Реэюме Пруво?rt;umся nяmь мamемamuческuх мо?rt;елеŭ суnерnозuцuu ?rt;еформaцuонноŭ мa?rt;нumноŭ mексmуры на осa?rt;очноŭ мa?rt;нumноŭ mексmуре. Мо?rt;елu ире?rt;сmвaлены в рaзных комбuнaцuях чuсmо?rt;о с?rt;вu?rt;а ц иросmо?rt;о с?rt;вu?rt;а. Дua?rt;раaммы вaрuaцuŭ в ?rt;лaвных naрaмеmрaх мa?rt;нumноŭ aнuзоmроnuu с ?rt;еформaцuеŭ мо?rt;уm nомочь nрu рaсnознaвaнuu слaбых nлaсmuчных ?rt;еформaцŭŭ в осa?rt;очных nоро?rt;aх.相似文献
959.
Summary The long-termed stability of the NTA 1024 Gamma spectrometer was investigated. In order to reduce the influence of the instability of the linear amplifier, a method of mathematical transformation of the spectrum was introduced. 相似文献
960.