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61.
A technique to detect man-made interference in the visibility data of the Mauritius Radio Telescope (MRT) has been developed.
This technique is based on the understanding that the interference is generally ‘spiky’ in nature and has Fourier components
beyond the maximum frequency which can arise from the radio sky and can therefore be identified. We take the sum of magnitudes
of visibilities on all the baselines measured at a given time to improve detectability. This is then high-pass filtered to
get a time series from which the contribution of the sky is removed. Interference is detected in the high-pass data using
an iterative scheme. In each iteration, interference with amplitudes beyond a certain threshold is detected. These points
are then removed from the original time series and the resulting data are high-pass filtered and the process repeated. We
have also studied the statistics of the strength, numbers, time of occurrence and duration of the interference at the MRT.
The statistics indicate that most often the interference excision can be carried out while post-integrating the visibilities
by giving a zero weight to the interference points. 相似文献
62.
海安地震台新场地的地电阻率观测于2004年12月初步建成,在试观测期间发现地电阻率东西测向观测数据严重受农村广播干扰,这种干扰国内未见报道,本文初步分析和总结了这种干扰的特征、产生机理及干扰排除措施,对其他台站建设地电阻率观测台站有一定的指导意义。 相似文献
63.
Ce(Ⅳ)-As(Ⅲ)体系测定铱的关键问题是解决干扰。讨论了利用此体系测定复杂地质样品中痕量铱的干扰问题。通过加入活化剂等方法,有效消除了Ce(Ⅳ)-As(Ⅲ)体系中铂、钯元素对测定铱的严重干扰。用此拟定的方法一人测定一批50个样品,仅需3天,标样的测定值与标准值符合较好。 相似文献
64.
Guo Yahong 《中国地震研究》2007,21(2):204-209
Along with intense rock strain and rock bursting processes at the late stage of earthquake preparation, mechanical-electrical energy conversion appears in the seismogenic region and its nearby rock formations, which correspondingly stimulate certain electromagnetic effects. The paper mainly analyzes the pre-seismic electromagnetic effect of the ionosphere and proposes a method of monitoring VLF radio waves over the additional ionized region and so on. It is deemed that the method is of significance for short and imminent term prediction of strong earthquakes. 相似文献
65.
66.
Surface oscillations — A possible source of fracture induced electromagnetic radiation 总被引:1,自引:0,他引:1
Radio frequency electromagnetic radiation (EMR) registered hundreds of kilometres away from an earthquake epicentre is detected hours before earthquakes. Yet, accurate earthquakes prediction by their self-induced EMR still remains in its infancy due in part to the lack of understanding of EMR's origin. Here we present a viable model of this origin, according to which EMR is emitted by an oscillating dipole created by ions moving collectively as a surface wave on both sides of the crack; when the crack halts, the EMR pulse amplitude decays by interaction with bulk phonons. The model is shown to be able to provide crack dimensions and velocities, to explain some general similarities of different fracturing processes and indicate the existence of a general failure mechanism. Results raise the hope of developing an EMR based genuine earthquake prediction system. 相似文献
67.
68.
J. Vassal M. Menvielle Y. Cohen M. Dukhan V. Doumouya K. Boka O. Fambitakoye 《Annales Geophysicae》1998,16(6):677-697
In the framework of the French-Ivorian participation to the IEEY, a network of 10 electromagnetic stations were installed at African longitudes. The aim of this experiment was twofold: firstly, to study the magnetic signature of the equatorial electrojet on the one hand, and secondly, to characterize the induced electric field variations on the other hand. The first results of the magnetic field investigations were presented by Doumouya and coworkers. Those of the electric field experiment will be discussed in this study. The electromagnetic experiment will be described. The analysis of the electromagnetic transient variations was conducted in accordance with the classical distinction between quiet and disturbed magnetic situations. A morphological analysis of the recordings is given, taking into consideration successively quiet and disturbed magnetic situations, with the results interpreted in terms of the characterization of external and internal sources. Particular attention was paid to the effects of the source characteristics on the induced field of internal origin, and to the bias they may consequently cause to the results of electromagnetic probing of the Earth; the source effect in electromagnetic induction studies. During quiet magnetic situations, our results demonstrated the existence of two different sources. One of these, the SRE source, was responsible for most of the magnetic diurnal variation and corresponded to the well-known magnetic signature of the equatorial electrojet. The other source (the SR*E source) was responsible for most of the electric diurnal variation, and was also likely to be an ionospheric source. Electric and magnetic diurnal variations are therefore related to different ionospheric sources, and interpreting the electric diurnal variation as induced by the magnetic field diurnal variation is not relevant. Furthermore, the magnetotelluric probing of the upper mantle at dip equator latitudes with the electromagnetic diurnal variation is consequently impossible to perform. In the case of irregular variations, the source effect related to the equatorial electrojet is also discussed. A Gaussian model of equatorial electrojet was considered, and apparent resistivities were computed for two models of stratified Earth corresponding to the average resistive structure of the two tectonic provinces crossed by the profile: a sedimentary basin and a cratonic shield. The apparent resistivity curves were found to depend significantly on both the model used and the distance to the center of the electrojet. These numerical results confirm the existence of a daytime source effect related to the equatorial electrojet. Furthermore, we show that the results account for the observed differences between daytime and night-time apparent resistivity curves. In particular, it was shown that electromagnetic probing of the Earth using the classical Cagniard-Tikhonov magnetotelluric method is impossible with daytime recordings made at dip latitude stations. 相似文献
69.
地震前电磁辐射信息特征研究 总被引:2,自引:0,他引:2
反映电磁辐射信息的地震前异常变化很多,但都有一个震前平静-加强-平静然后发震的特征,为了更好地体现这种特征,根据十几年来河北廊坊电磁台网的观测资料,通过给不同强度段的各台日信息量赋予不同的权值,并把当日各台权值累加来反映当日内多台信息量集中的强弱,然后把上述权累加和用一种不连续积分的方法反映异常的持续时间,通过对监测范围内4次Ms≥5.0地震震例分析,发现该方法反映震前异常特征明显,短临效果很好, 相似文献
70.
Cylindrically symmetric inhomogeneous string cosmological model in presence of electromagnetic field is investigated. We have
assumed that F
23 is the only non-vanishing component of F
ij
. To get the deterministic solution, it has been assumed that the expansion (θ) in the model is proportional to the eigen value σ
1
1 of the shear tensor σ
i
j
. The physical and geometric aspects of the model are also discussed.
相似文献