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881.
Seismotectonic parameters including the Gutenberg-Richter b-value and multifractal dimensions D2 and D15 of seismicity patterns (both spatial and temporal) were compared to GPS-derived maximum shear and dilatation strains measured in the Marmara Sea region of western Turkey along the Northern Anatolian Fault Zone (NAFZ). Comparisons of seismotectonic parameters and GPS-derived maximum shear and dilatation strain along the NAFZ in the vicinity of the 1999 M7.4 Izmit earthquake reveal a positive correlation (r = 0.5, p = 0.05) between average dilatation and the Gutenberg-Richter b-value. Significant negative correlation (r = − 0.56, p = 0.03 and r = − 0.56, p = 0.02) was also observed between the spatial fractal dimension D2 and GPS-derived maximum geodetic and shear strain. This relationship suggests that, as maximum geodetic and shear strains increase, seismicity becomes increasingly clustered.Anomalous interrelationships are observed in the Marmara Sea region prior to the Izmit event along a bend in the NAFZ near the eastern end of the Marmara Sea known as the Northern Boundary Fault (NBF). An asperity is located near the northwest end of the NBF. Along the 50-km length of the NBF, GPS strains become slightly compressive. The correlation between b-value and GPS-derived dilatation suggests that regions in compression have increased probability of larger magnitude rupture. The NBF appears to serve as an impediment to the transfer of strain from east to west along the NAFZ. Recurrence times for large earthquakes along the NBF are larger than in surrounding areas. Temporal clustering of seismicity in the vicinity of the NBF may represent foreshocks of an impending rupture. 相似文献
882.
Water infiltration characteristics of unsaturated soil slope and its effect on suction and stability 总被引:3,自引:1,他引:3
Bujang B. K. Huat Faisal HJ. Ali T. H. Low 《Geotechnical and Geological Engineering》2006,24(5):1293-1306
Rainfall has been considered the cause of the majority of slope failures and landslides that happened in regions experiencing
high seasonal rainfalls. The mechanism of the failures was mainly due to the lost of matric suction of soils by rainwater.
This paper presents the results of a laboratory model study on the effect of slope angle and surface cover on water infiltration
into soil and soil matric suction. A field infiltration test is carried out for comparison. A parametric study is also done
to examine the effect of permeability ratio, development of perched water table and rainfall intensity on the factor of safety
against instability of a soil slope. Results of the model study show that different surface covers on slopes have an effect
on the water infiltration. Generally the covered surface (grass or geosynthetic net) has a lower infiltration rate compared
with the bare (no cover) surface. On the effect of slope angle, it was observed that water infiltration decrease with increase
in the slope steepness. With regards to the movement of the wetting front, it appears that water infiltration is more at the
toe compared with the top of the model slope. Based on the parametric study, it is found factor of safety of the slope against
instability drops for slope with higher ratio of permeability for the permeable and impermeable stratum. As the perched water
table is formed, the factor of safety decreased. The rainfall intensity also has a marked effect on the slope factor of safety.
The higher the intensity of the rainfall, the higher is the infiltration rate into the soil, hence the lower is the factor
of safety against slope instability. 相似文献
883.
Ali A. Gharib 《Acta Geophysica》2006,54(4):361-377
The crustal structure of North Abu-Simbel area was studied using spectral ratios of short-period P waves. Three-component short period seismograms from the Masmas seismic station of the Egyptian National Seismic Network
Stations were used. The Thomson-Haskell matrix formulation was applied for linearly elastic, homogeneous crustal layers. The
obtained model suggests that the crust under the study region consists of a thin (0.8 km) superficial top layer with a P-wave velocity of 3.8±0.7 km/s and three distinct layers with a mean P-wave velocity of 6.6 km/s, overlaying the upper mantle
with a P-wave velocity of 8.3 km/s (fixed).
The results were obtained for 14 different earthquakes. The P-wave velocities of the three layers are: 5.8±0.6 km/s, 6.5±0.4 km/s and 7.2±0.3 km/s. The total depth to the Moho interface
is 32±2 km. The crustal velocity model estimated using observations is relatively simple, being characterized by smooth velocity
variations through the middle and lower crust and normal crustal thickness. The resultant crustal model is consistent with
the model obtained from previous deep seismic soundings along the northern part of Aswan lake zone. 相似文献
884.
Estimation of frequency dependent coda wave attenuation structure at the vicinity of Cairo Metropolitan Area 总被引:1,自引:0,他引:1
Salah El-Hadidy M. E. Mohamed Adel Ahmed Deif Ahmed Sayed Abu El-Ata S. R. Moustafa Sayed 《Acta Geophysica》2006,54(2):177-186
Estimation of seismic wave attenuation in the shallow crust in terms of coda wave Q structure previously investigated in the vicinity of Cairo Metropolitan Area was improved using seismograms of local earthquakes
recorded by the Egyptian National Seismic Network. The seismic wave attenuation was measured from the time decay of coda wave
amplitudes on narrow bandpass filtered seismograms based on the single scattering theory. The frequency bands of interest
are from 1.5 to 18 Hz. In general, the values obtained for various events recorded at El-Fayoum and Wadi Hagul stations are
very similar for all frequency bands. A regional attenuation law Q
c
= 85.66 f
0.79 was obtained. 相似文献
885.
Inversion of SASW dispersion curves based on maximum flexibility coefficients in the wave number domain 总被引:3,自引:0,他引:3
Spectral analysis of surface waves (SASW) is a nondestructive in-situ testing method that is used to determine stiffness profiles of soil and pavement sites based on dispersion characteristics of Rayleigh-type surface waves.Inversion of the Rayleigh wave dispersion curve of a site provides information on the variation of shear-wave velocity with depth. In the inversion procedures currently used for SASW tests, the field dispersion curve is matched with a theoretical dispersion curve obtained for the fundamental mode of surface wave propagation.In order to overcome difficulties associated with the presence of multi-modes in SASW signals, a new inversion method based on the maximum vertical flexibility coefficient is introduced in this paper. Unlike root-searching methods, the new method easily identifies the predominant propagation modes. In this new approach, the simplex method is used to match field and theoretical dispersion curves automatically. The purpose of this paper is to present the details of the new method and to demonstrate its advantages. 相似文献
886.
Xian-Feng Liu Jeroen Tromp Adam M Dziewonski 《Earth and Planetary Science Letters》1998,160(3-4):343-351
In 1983, Lay and Helmberger [Geophys. J. R. Astron. Soc. 75 (1983) 799–837] reported the detection of a precursor to the seismic phase ScS. They attributed this precursor to a sharp seismic discontinuity located several hundred kilometers above the core–mantle boundary. Such a lowermost mantle discontinuity implies the existence of a sharp phase change or a chemical boundary. Precursors to ScS and, less frequently, PcP have since been observed in numerous locations, but are not a global phenomenon. Frequently, PcP precursors are weak or absent when ScS precursors are observed in the same location, and vice versa. There can be significant variations in the amplitude and arrival time of the precursor relative to the main phase. The presence or absence of these precursors has led to speculations about the nature of the lowermost mantle. Here we demonstrate that ScS or PcP precursors may be produced by gradients in seismic wave speed associated with large-scale lowermost mantle heterogeneity. Rather than a phase or chemical boundary with substantial topography, such gradients require lateral variations in temperature and, close to the core–mantle boundary, composition. 相似文献
887.
888.
Hüseyin Yaln M.Niyazi Gündodu Alain Gourgaud Philippe Vidal Ali Uurum 《Journal of Volcanology and Geothermal Research》1998,85(1-4)
Neogene Yamadağı volcanic rocks consist of basaltic trachyandesite, trachyandesite, andesite, and dacite. The major- and trace-element chemistry indicates that the lavas are dominantly calc-alkaline and mildly alkaline in character, sodic in nature, and intermediate to acidic in composition. REE and trace-element patterns of volcanic rocks are similar to those typical of within plate magmatics. Volcanic rocks have low 87Sr/86Sr (0.70389–0.70633) and high 143Nd/144Nd ratios (0.51267–0.51276) and mostly plot within the mantle array of the isotope ratio diagram. The linear correlations among 87Sr/86Sr−143Nd/144Nd, SiO2−87Sr/86Sr and SiO2−143Nd/144Nd isotope ratios in the volcanics suggest that fractional crystallization combined with minor assimilation was an important process within the collision zone. 相似文献
889.
Ali A. Karimi Jeremy A. Redman Roberto F. Ruiz 《Ground Water Monitoring & Remediation》1998,18(2):150-158
A two-year pilot study involving the recharge of a ground water basin with reclaimed water was completed in the city of Los Angeles. The city's Department of Water and Power is planning to initiate several ground water recharge projects using reclaimed water in the near future. One such project is the Headworks Recharge Project, the focus of this paper, Approximately 1 cfs of the Los Angeles (LA) River water comprised of 70% tertiary treated reclaimed water was recharged on a two-day wet and five-day dry cycle. The recharge water was then extracted from the basin approximately 1000 feet downgradient. Results showed greater than 4-log removal of coliform bacteria, up to 87% reduction in TOC, and compliance of the product water with federal and state drinking water standards. Model simulation showed after 15 years of recharging 3000 acre-feet per year of the LA River water and extracting about 10,000 acre-feet from the basin, the product water would contain from 5% to 15% reclaimed water. This is well below the maximum allowable limit of 20% stipulated by the California regulation. 相似文献
890.
An analytical solution for the joint effects of the Earth oblateness and the direct solar radiation pressure on the motion
of an Artificial Earth Satellite of complex shape is constructed. The equations of motion are derived in the previous paper
(hereafter refered to as paper I). The solution is effected through two canonical transformations retaining secular and periodic
terms up to orders 3 and 2 respectively. The developments stressed on the effects of the radiation pressure and its coupling
with the earth's gravity. A procedure for the computation of position and velocity is outlined. The conditions of the resonance
are determined and the procedure for the transformations in the case of resonance is outlined. The solution revealed as expected
that radiation pressure produced secular effects at the third order resulting from the coupling between periodic terms at
lower orders. These affect both the main satellite body and the antenna.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献