全文获取类型
收费全文 | 111篇 |
免费 | 45篇 |
国内免费 | 38篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 62篇 |
地球物理 | 66篇 |
地质学 | 31篇 |
海洋学 | 6篇 |
天文学 | 12篇 |
综合类 | 5篇 |
自然地理 | 5篇 |
出版年
2023年 | 3篇 |
2022年 | 1篇 |
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 9篇 |
2018年 | 3篇 |
2017年 | 11篇 |
2016年 | 11篇 |
2015年 | 8篇 |
2014年 | 5篇 |
2013年 | 13篇 |
2012年 | 11篇 |
2011年 | 15篇 |
2010年 | 7篇 |
2009年 | 7篇 |
2008年 | 12篇 |
2007年 | 10篇 |
2006年 | 11篇 |
2005年 | 2篇 |
2004年 | 8篇 |
2003年 | 2篇 |
2002年 | 5篇 |
2001年 | 5篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有194条查询结果,搜索用时 31 毫秒
41.
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
42.
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
43.
44.
Ground-based SAR interferometry for monitoring mass movements 总被引:11,自引:3,他引:8
G.?Antonello N.?CasagliEmail author P.?Farina D.?Leva G.?Nico A.?J.?Sieber D.?Tarchi 《Landslides》2004,1(1):21-28
An innovative technique for the remote assessment of ground displacements, based on radar interferometry and implemented using ground-based instrumentation (GB-InSAR), has been tested in recent years on a number of selected case sites. The system, known as LISA, developed by the Joint Research Centre (JRC) of the European Commission, is a ground-based radar interferometer specifically designed for field use. It is composed of two radar antennas mounted on a linear rail which horizontally slides to form a synthetic aperture. Coherent SAR processing converts the raw data into an image containing, for each pixel, information on the wave phase, which depends on the target-sensor distance. Consecutive couples of SAR images can be cross-correlated to form interferograms representing phase variations which can be directly related to ground displacement along the sight-line of the radar system, since they are acquired from exactly the same position. Several applications of the system have been conducted on a number of mass movements located in Italy, in order to validate the technique for the monitoring of landslides. GB-InSAR has proved its potential for the measurement of the superficial ground displacements of different landslide types, in terms of failure mechanism, materials involved, kinematics, water content and deformation rates. In particular conditions, such as fast-moving phenomena and inaccessible areas, the technique can be employed directly as a monitoring tool, providing multi-temporal displacement maps of the observed area. Additionally, some applications of the GB-InSAR have provided a fundamental support to decision makers during landslide emergencies, allowing the civil protection authorities to assess the risk and to manage an effective emergency response. 相似文献
45.
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
46.
上海市气象局于1997年从美国引进了一部多普勒天气雷达WSR-88D,该雷达采用24 h连续工作的方式投入日常的业务运行,在天气探测和气象服务中发挥了重要作用。在多年的运行过程中,该雷达也出现了各种不同类型的故障,有些重要故障直接导致了雷达的停机,给气象服务带来了一定影响。文章介绍和总结了该雷达出现的一些主要故障,这些故障集中在雷达发射机部分的射频驱动器、聚焦线圈电源、触发放大器、调制器、后充电调整器等部件上。通过对这些部件的功能和工作原理的分析,详细介绍了分析和排除这些故障的关键技术。 相似文献
47.
Judith L. Pipher 《Experimental Astronomy》1994,3(1-4):1-8
Ten years ago, Forrest presented the first astronomical images with an SBRC 32×32 InSb array camera at the first NASA-Ames Infrared Detector Technology Workshop. Soon after, SBRC began development of 58×62 InSb arrays, both for ground-based astronomy and for SIRTF. By the time of the 1987 Hilo workshop Ground-based Astronomical Observations with Infrared Array Detectors astronomical results from cameras based on SBRC 32×32 and 58×62 InSb arrays, a CE linear InSb array, and a French 32×32 InSb CID array were presented. And at the Tucson 1990 meeting Astrophysics with Infrared Arrays, it was clear that this new technology was no longer the province of IR pundits, but provided a tool for all astronomers. At this meeting, the first astronomical observations with SBRC's new, gateless passivation 256×256 InSb arrays will be presented: they perform spectacularly!In this review, I can only broadly brush on the interesting science completed with InSb array cameras. Because of the broad wavelength coverage (1–5.5 m) of InSb, and the extremely high performance levels throughout the band, InSb cameras are used not only in the near IR, but also from 3–5.5 m, where unique science is achieved. For example, the point-like central engines of AGNs are delineated at L and M, and Br and 3.29 m dust emission images of galactic and extragalactic objects yield excitation conditions. Examples of imaging spectroscopy, high spatial resolution imaging, as well as deep, broad-band imaging with InSb cameras at this meeting illustrate the power of InSb array cameras. 相似文献
48.
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
49.
50.
During the analysis of archived VLF data from Indian low latitude ground stations, some discrete VLF emissions recorded at
the low latitude ground station Gulmarg (geomagnetic latitude 24°26′N; geomagnetic longitude 147°09′E, L = 1.28) during moderate
magnetic storm activity (Σ K
P
− = 32, K
P
index varies from 4 to 6 during the observation period) on 6/7 March, 1986 are presented in this paper. The dynamic spectra
of these discrete VLF emissions were observed along with tweeks and its harmonics, which is interesting and complex to explain.
In most of the events the harmonic frequency of tweeks correlates with the starting frequency of harmonics of discrete emissions.
In order to explain the observed features of discrete VLF emissions, we propose cyclotron resonance interaction between whistler
mode wave and energetic electrons of inner radiation belt as possible generation mechanism. An attempt is also made to determine
parallel energy, anisotropy and wave growth relevant to the generation process of VLF emissions. 相似文献