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71.
甚低频电磁法在河南省竹园铜矿的应用 总被引:9,自引:0,他引:9
简要叙述了甚低频电磁法的方法技术,并以河南省西峡县竹园铜矿为例,介绍了甚低频法寻找铜多金属硫化物矿床的显著效果。结合工作效果,对甚低频法的不足之处提出了3点看法。 相似文献
72.
M. Poddar 《Pure and Applied Geophysics》1981,119(5):1024-1036
FollowingDmitriev (1960) a rigorous theoretical solution for the problem of scattering by a perfectly conducting inclined half-plane buried in a uniform conductive half-space has been obtained for plane wave excitation. The resultant integral equation for the Laplace transform of scattering current in the half-plane is solved numerically by the method of successive approximation. The scattered fields at the surface of the half-space are found by integrating the half-space Green's function over the transform of the scattering current.The effects of depth of burial and inclination, of the half-plane on the scattered fields are studied in detail. An increase in the depth of burial leads to attenuation of the fields. Inclination introduces asymmetry in the field profiles beside affecting its magnitude. Depth of exploration is greater for quadrature component. An interpretation scheme based on a phasor diagram is presented for the VLF-EM method of exploration for rich vein deposits in a conductive terrain.List of symbols
x, y, z
Space co-ordinates
-
Half-space conductivity
- 0
Free-space permeability
-
Excitation frequency (angular)
-
T
Time
-
h
Depth of the half-plane
-
a
Inclination of the half-plane
-
E
x
x-Directed total electric field
-
E
x
p
x-Directed primary electric field
-
E
xo
p
x-Directed primary electric field atz=0 directly over the half-plane
-
H
y
y-Component of total magnetic field
-
H
y
p
y-Component of primary magnetic field
-
H
y0
p
y-Component of primary magnetic field atz=0 directly over the half-plane
-
H
z
z-Component of total magnetic field
-
H
z
p
z-Component of primary magnetic field
-
J
x
Surface density ofx-directed scattering current
-
G
Green's function
-
k
0,K
Wave numbers
-
u,u
0,u
1,u
2
Functions
-
Space co-ordinate
-
s
Variable in transform domain
-
Variable of integration
-
Normalized scattering current
-
Laplace transform of
-
N
Normalized
- , 0, 1, 2
Functions
-
t
Variable of integration
-
Skin depth
-
H
Total magnetic field
-
H
p
Primary magnetic field
-
H
0
p
Primary magnetic field atz=0 directly over the half-plane
-
M,Q,R,S,U,V
Functions
-
N
1,N
2
Functions 相似文献
73.
In the paper, the mathematical tools, used for the modelling of the electromagnetic field of the harmonic plane wave in the two-dimensional inhomogeneous medium (the case ofE-polarization), are presented. Further, the resolving power of some parameters, that are measured in the VLF and VLF-R methods, is compared in the case of two vertical conductive dykes. To this aim, all the usual parameters of the VLF method and the most important parameter of the VLF-R method () have been chosen. Two groups of models that differ in resistivities have been considered. In each of the groups the distance of the dykes is variable. The parameters |H
y|, which has shown most promising in this respect, is examined also from the point of view of the sensibility to geological noise. The results of the modelling are illustrated by two examples of the results of field measurements. 相似文献
74.
Integrated geophysical surveys using vertical electrical sounding (VES), very low frequency (VLF) EM, radiation counting,
total magnetic field and self-potential (SP) measurements are carried out to characterize the geothermal area around a hot
spring in the Nayagarh district, Orissa, India that lies in the East Indian geothermal province. The study was performed to
delineate the fracture pattern, contaminated groundwater movement and possible heating source. VES interpretations suggest
a three- to four-layer structure in the area. Resistivity survey near the hot spring suggests that weathered and fractured
formations constitute the main aquifer system and extend to 60 m depth. Current flow measured at various electrode separations
normalized by the applied voltage suggests that fractures extend to a greater depth. Detailed VLF study shows that fractures
extend beyond 70 m depth. VLF anomaly has also very good correlation with the total magnetic field measured along the same
profiles. Study results suggest that a gridded pattern of VLF survey could map the underground conductive fracture zones that
can identify the movement of contaminated groundwater flow. Therefore, precautionary measures can be taken to check further
contamination by delineating subsurface conducting structures. Self potential (SP) measured over the hot spring does not show
a large anomaly in favor of the presence of a sulphide mineral body. A small positive (5–15mV) SP anomaly is measured which
may be streaming potential due to subsurface fluid flow. A high radiation is measured about four kilometers from the hot spring,
suggesting possible radiogenic heating. However, the exact nature of the heating source and its depth is not known in the
area. Deep resistivity followed by a magneto-telluric survey could reveal the deeper structures. 相似文献
75.
高灵敏度GPS技术的研究进展 总被引:10,自引:1,他引:10
介绍了高灵敏度GPS(High—Sensitivity GPS)技术的研究进展及高灵敏度GPS技术的应用前景和研究意义。分析了GPS信号在室内、森林、城市等一般GPS接收机无法应用环境的特性,综述了高灵敏度GPS关键技术的基本原理。高灵敏度GPS技术的核心就是室内环境微弱GPS信号的捕获技术,重点介绍了捕获室内环境弱GPS信号的基本方法,总结了各种捕获算法的特点。 相似文献
76.
Ikeya Motoji 《中国地震研究》1998,(3)
We present an electromagnetic model of a fault using the piezoelectric effect and the elastic dislocation theory to investigate theoretically the spatial distribution of the stress-induced charges associated with faulting. The relevant seismic electric field associated with these induced charges can be estimated quantitatively. Therefore, this simple model would provide a solid framework for additional theoretical developments on the explanations of the anomalous seismoelectric signals. The spatial distribution of the stress-induced charges around a vertical rectangular fault showed complicated characteristics. The estimation of the electric field associated with the stress-induced charges during the 1995 Kobe earthquake was consistent with the previous investigation from some reported anomalous seismic phenomena. 相似文献
77.
78.
On May 2, 1993 more than 200 seismic events from an underground mine in Tyrol/Austria were recorded with short-period seismometers of a local seismic network which was introduced in the late 1980s to monitor the tectonic seismicity in Tyrol in greater detail. The cause of this series of mining-associated events has become the subject of intensive investigations — as it was associated with a subsidence affecting an area of 10.000 m2. Underground observations revealed a number of discontinuities along which the rock mass was able to move. Seismic recordings of the close-by seismic stations revealed two types of mechanisms: One mechanism seems to be associated with pure block-sliding along several discontinuities, while other signals indicate additional collapse. The consideration and combination of several seismological principles made possible the construction of a model of the mine collapse. 相似文献
79.
Airborne very low frequency (VLF) data are routinely collected by national agencies and commercial companies together with
other passive geophysical measurements of the static magnetic field and radiometric data. The purpose of this paper is to
demonstrate that both standard three-component VLF and tensor VLF (TVLF) data contain a lot of useful quantitative and qualitative
information about the electrical conductivity distribution in the upper few hundred meters of the crystalline basement. We
first give a new derivation of the fundamental transfer functions (the tipper) used in the TVLF technique. We then show that
the tipper can be estimated from simultaneous measurements of the wave magnetic fields from at least two transmitters with
somewhat different frequencies, and present a simple model by which the maximum error introduced by the difference in frequencies
can be found. Single transmitter scalar VLF maps emphasise those conductive structures that have dominant strikes in the direction
of the transmitter. Multiple transmitter transfer functions are dependent only upon the underlying conductivity structure.
Two dimensional structures can be quantitatively modelled by modern inversion methods developed originally for deep electromagnetic
magnetotelluric (MT) soundings. In such cases three-component VLF measurements can be modelled easily upon appropriate rotation
of the co-ordinate system to “strike” co-ordinates. Single frequency transfer functions (tippers) have real and imaginary
parts that carry information on not only lateral contrasts in conductivity, as usually stated in text books, but, taken together,
they provide a robust tool for determining the background conductivity level away from distinct conductors, and they can also
be used to discriminate between deep and shallow conductors. Based upon simulations using multi-frequency data, it can be
concluded that such a new development would dramatically increase the resolving power of airborne VLF measurements. 相似文献
80.