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991.
Introduction During and before the construction of the Three Gorges Project, the annual observation was continuously undertaken by the Three Gorges gravity observation network established around the head area of the reservoir (the section between Sandouping and Badong). This network has pro-vided substantial high precise data related to seismic activity. However, the annual gravity survey together monitoring of the existed observation stations can hardly effective monitor some potential sei… 相似文献
992.
The depth determination from the gravity data in frequency domain is carried out using the classical fast Fourier transform
(FFT) method utilizing scaling properties of ensemble of anomalous source. The problem of calculating power spectrum from
the FFT is well described in the literature. Here, the application of other high-resolution methods of power spectrum calculation,
such as maximum entropy method (MEM) and multi-taper method (MTM) are explored to estimate depth to anomalous sources. At
the outset, the FFT, the MEM and the MTM are tested on synthetic gravity data, generated for different types of synthetic
models and then all these methods are applied to the field gravity data of the Bengal basin. The MTM with scaling is found
to be superior for providing the detailed subsurface information rather than the MEM and the FFT methods in the case of synthetic
as well as field examples. 相似文献
993.
First, we present three different definitions of the vertical which relate to (i) astronomical longitude and astronomical
latitude as spherical coordinates in gravity space, (ii) Gauss surface normal coordinates (also called geodetic coordinates)
of type ellipsoidal longitude and ellipsoidal latitude and (iii) Jacobi ellipsoidal coordinates of type spheroidal longitude
and spheroidal latitude in geometry space. Up to terms of second order those vertical deflections agree to each other. Vertical
deflections and gravity disturbances relate to a reference gravity potential. In order to refer the horizontal and vertical
components of the disturbing gravity field to a reference gravity field, which is physically meaningful, we have chosen the
Somigliana-Pizzetti gravity potential as well as its gradient. Second, we give a new closed-form representation of Somigliana-Pizzetti
gravity, accurate to the sub Nano Gal level. Third, we represent the gravitational disturbing potential in terms of Jacobi
ellipsoidal harmonics. As soon as we take reference to a normal potential of Somigliana-Pizzetti type, the ellipsoidal harmonics
of degree/order (0,0), (1,0), (1, − 1), (1,1) and (2,0) are eliminated from the gravitational disturbing potential. Fourth,
we compute in all detail the gradient of the gravitational disturbing potential, in particular in orthonormal ellipsoidal
vector harmonics. Proper weighting functions for orthonormality on the International Reference Ellipsoid are constructed and
tabulated. In this way, we finally arrive at an ellipsoidal harmonic representation of vertical deflections and gravity disturbances.
Fifth, for an ellipsoidal harmonic Gravity Earth Model (SEGEN: http://www.uni-stuttgart.de/gi/research/paper/coefficients/coefficients.zip)
up to degree/order 360/360 we compute the global maps of ellipsoidal vertical deflections and ellipsoidal gravity disturbances
which transfer a great amount of geophysical information in a properly chosen equiareal ellipsoidal map projection. 相似文献
994.
Hydraulic fills used in Australian mines have similar grain size distributions whilst having quite different specific gravity
values, typically in the range of 2.7–4.4. When produced and distributed in slurry at 65–75% by solid content, they settle
to produce fills with similar geotechnical characteristics. The fills under investigation have been found to settle, in the
laboratory, to a dry density of about 0.56 × specific gravity, a saturation water content of about 17–34%, and a porosity
of 37–49%. A quick estimate of the optimum water content that gives the minimum porosity may be obtained by locating the intersection
of the saturation curve and minimum porosity line, which may simply be done on a water content vs. porosity plot. However,
transportability of the slurry requires it to be mixed at water content substantially greater than the optimum water content.
As the tailings settle out of suspension, they settle to relative density of 50–80%. This paper shows that the current empirical
relationships relating relative density and N-value to friction angle for sands will significantly underestimate the friction angle of the hydraulic fills. Based on limited
experimental data, a unique relationship between relative density and friction angle is proposed for hydraulic fills placed
in some Australian mines. 相似文献
995.
XIAO Feng MENG Ling-shun College of GeoExploration Science Technology Jilin University Changchun China 《吉林大学学报(地球科学版)》2006,(Z2)
有限元插值法利用区域边界上的少量数据可计算区域重力异常。由于只有区域数据参与插值计算,其结果更准确。通过教学模型实验得出结论:在区域场近似二次或三次曲面的条件下,有限元插值法比最小二乘法计算的区域场更接近真实值。在某盆地的重力资料处理中,用有限元插值法分离出该区的局部重力异常. 相似文献
996.
A finite element model of incremental displacement constraint equations (IDCE), based on an existing node‐to‐surface concept, is implemented to deal with dynamic contact surfaces in the seismic behaviour analysis of cracked concrete gravity dams. After verification for sliding, rocking and impact, the IDCE model is applied to study the seismic responses of concrete gravity dams with different profiles and crack locations for a variety of parameters, such as coefficient of friction, water level and type of earthquake, as well as impact damping based on the concept of coefficient of restitution. It is revealed that cracked concrete gravity dams can experience not only sliding and rocking modes, but also the drifting mode in some cases of crack either at the base or at a height. Downstream sliding is normally accompanied by rocking, especially for the cases of crack at a height. Due to rocking and drifting, a cracked dam may still acquire a certain amount of residual sliding even if the effective coefficient of friction is relatively high. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
997.
998.
Comparative studies of short-term ionospheric variability in the F region ionosphere during rapid sequence sounding campaign
“HIRAC/SolarMax” (23–29 April 2001) are presented. The ionospheric short-term fluctuations have been studied in detail using
measurements from vertical sounding at Ebro (40.8 °N, 0.5 ° E) and Průhonice (49.9 °N, 14.5 °E) in the period range from 15
minutes to 2 hours. The electron density measurements contain variations that indicate the possible presence of propagating
gravity waves. Regular wave-like bursts were found during quiet days at both stations in electron concentration in F region,
with an increase of the oscillation activity after sunrise and then during late afternoon, and at sunset and after sunset.
Solar Terminator is assumed to be one of the sources of the regular wave bursts detected in the ionosphere during campaign
HIRAC. As expected, substantial intensification in longer period gravity waves was found to occur during the disturbed period
on April 28. Particular enhancement of the wave-like activity during disturbed day is discussed, being significant evidences
of a change of the wave-like activity pattern at a height around 200 km. 相似文献
999.
Former geophysical surveys performed in the region of the volcanic centre of the České Stř edohoří Mts. in North Bohemia (the
Ohře Rift zone) showed that anomalous volcanic bodies and features can be effectively identified within sedimentary environment.
For this reason we carried out new geophysical measurements in the area of the main mafic intrusion of essexitic character.
The target was the exact location and geometry of the intrusion and its relation to other components of the volcanic centre.
We used gravity, magnetic, shallow seismic and electromagnetic techniques. The new gravity and magnetic data were tied to
the old databases so that we could investigate the area as a whole complex. Electromagnetic measurements were applied in the
area of the expected extent of the intrusion, and the seismic measurements in the central part of the intrusion.
Based on all the data, mainly on gravity modelling, we delineated not only the surface and subsurface extent of the intrusion,
but we also defined the hidden relief of the intrusion. It was found that the intrusion is formed by a single body that has
a few protrusions, and not by a set of separate individual intrusions, as indicated by surface outcrops. However, the body
of the intrusion is affected by a major fault that caused lithological differences on both sides (essexite/monzodiorite).
In detail we show the depth of the debris cover and the thickness of the weathered zone in the central part of the essexite
body. We also derived indications of tectonic elements in the area of the intrusion in the main structural/tectonic direction
in the region. The results will be utilized to establish a 3D geological model of the whole volcanic centre.
This investigation may serve as an example of non-seismic geophysical exploration applied to the study of volcanic centres
surrounded by sedimentary rocks. 相似文献
1000.