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961.
962.
Xinling Qin L. B. Pedersen Yulin Zhao Ping Zhang Fuye Qian Wei Qian Zhengnan Li Jingxian Du 《地震学报(英文版)》1992,5(2):355-365
It is shown by the result of digital magnetotelluric soundings in the Tangshan seismic area and its surrounding regions that
the crust under the surface conductive sediments is divided into two layers,i. e., the resistive upper crust and the conductive
lower crust. The upper crust wherein the Tangshan main shock and most of the aftershocks occurred is a convex lens-like body
which is cut by faults at the east, south and west sides. The focus of the mainshock was located at the position of maximum
thickness of the resistive upper crust while the spatial variation of Curie point isothermal surface and the deepest limit
of the depths of aftershocks coincide with the downward depression of the bottom of the resistive upper crust. Thus, the Tangshan
main shock and most of its aftershocks were related closely to the resistive upper crust from the view points of either vertical
layering or lateral variations. And there were only a very few aftershocks in the conductive lower crust. The mechanical property
of the rocks transforms from being brittle in the upper crust into ductile in the lower crust mainly due to the combination
of different factors, e.g., increase of confining pressure, change in minerals, rise in temperature as well as stabilization
of slips by high pore—pressure. A small amount of water and a rise in temperature may lead to a decrease of the electric resistivity
within the rock while a change in the static pressure and mineral content within the rock causes very little change in the
electric resistivity. Thus it is deduced that a resistive upper crust and a more conductive lower crust from the view points
of either vertical or lateral variations are related to the brittle and ductile properties respectively. Hence it is possible
that there is a relationship between the electric structure of the crust and zones of potential seismic hazard.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 354–363, 1991.
The project is supported by the Chinese Joint Seismological Science Foundation, and the Swedish International Development
Authority. 相似文献
963.
The method of complex demodulation has been used here to compute the amplitude and phase of a signal present in a geomagnetic
series using, Banks’ method. It is found that the results are quite accurate when four or more continuous cycles of the signal
of interest are present. The same limitations have also been observed when band-pass filters are used to isolate a signal.
The information on phase is always correct. It is concluded that complex demodulation will give correct results for periodic
variations like 11-year, 27-day, Sq or pulsations; but will give small values of amplitude for signals like sudden impulses
or bays. The latter is not a limitation in conductivity studies where ratios likeZ/H, Z/D orH/D are mostly used in calculations. It has been shown that even with the records of one magnetic storm the cause of anomalies
can be accurately identified which otherwise would need a large number of events. 相似文献
964.
The paper presents a computational algorithm designed for efficient modelling of apparent resistivity over complex geological
structures, using finite element method. The algorithm can be used to study variations of apparent resistivities using any
electrode configuration at any point on the earth’s surface, not necessarily regular. A Schlumberger apparent resistivity
sounding curve over a buried anticline, is presented here as an example and compared with the corresponding analytical curve,
to demonstrate the correctness of the FEM algorithm.
The various potential derivatives required for the computation of apparent resistivities evaluated through different electrode
configurations have been obtained by calculating the ‘influence coefficients’ using reciprocal theorems, an approach successfully
applied in structural engineering. In essence, a set of self balancing nodal currents, obtained from the appropriate derivative(s)
of the shape functions of the elements contributing to the point of observation, is applied as the load vector.
The resulting quantities corresponding to the potential distribution in traditional finite element method, then, turn out
to be the potential derivatives at the point of observation for different positions of the current electrodes. These are known
as influence coefficients.
The continuum nature of the domain beyond the region of interest has been modelled by using ‘infinite elements’ across which
the potential is assumed to decay exponentially. 相似文献
965.
966.
DZSS-1型深层数字地震仪由三分量检波器CDJ-6B、数据采集单元、磁带机、编码钟和回放装置组成。它采用循环浮点放大-A/D转换技术、低噪音运算放大器、CMOS器件,使仪器噪音小于0.3μV(折合到前级放大器输入端,均值),动态范围大于96dB,采用调相制、串码、单轨盒式数字磁带记录。仪器频带范围1-30Hz,浮点72dB。有钟差显示(±1ms)、噪音和误操作显示。仪器主要技术指标(道间一致性、漂移、噪音、串音、误码率、主放台阶精度)可用微机进行检测,能满足地震测深和其它低频数字测量之用。 相似文献
967.
968.
969.
The structure of atmospheric boundary layer determines the ability of atmospheric dispersion and has an essential impact on airborne aerosols. In this paper, the data of a radio sounding experiment held in Dongguan National Meteorological Observation Station, which is in a coastal city in Pearl River Delta, as well as the data of atmospheric aerosols, were utilized in order to analyze the characteristics of atmospheric boundary layer and its effects on surface aerosol concentrations. The results are showed at follows: the local circulations, associated with dominant winds, made complex structures of atmospheric layers, as the cold air and systematic winds weakened in the end of a cold air event. Weakened wind shears and inversion layers, especially a strong near-surface inversion layer, remarkably diminished the atmospheric diffusion abilities and facilitated an especially high concentration of surface aerosols. The convergence line or weak shear line of sea breeze in the ground level helps weaken the atmospheric diffusion abilities and results in atmospheric aerosols accumulation. 相似文献
970.
本文回顾了在青藏高原东北缘(32°-40°N,100°-108°E)地区深地震测深研究的主要成果,给出了这一地区地壳中地震波速度结构的特征和莫霍面的形态。 相似文献