全文获取类型
收费全文 | 1631篇 |
免费 | 184篇 |
国内免费 | 202篇 |
专业分类
测绘学 | 426篇 |
大气科学 | 164篇 |
地球物理 | 500篇 |
地质学 | 345篇 |
海洋学 | 215篇 |
天文学 | 87篇 |
综合类 | 111篇 |
自然地理 | 169篇 |
出版年
2024年 | 8篇 |
2023年 | 9篇 |
2022年 | 38篇 |
2021年 | 55篇 |
2020年 | 48篇 |
2019年 | 76篇 |
2018年 | 46篇 |
2017年 | 70篇 |
2016年 | 75篇 |
2015年 | 84篇 |
2014年 | 88篇 |
2013年 | 107篇 |
2012年 | 97篇 |
2011年 | 65篇 |
2010年 | 65篇 |
2009年 | 82篇 |
2008年 | 89篇 |
2007年 | 114篇 |
2006年 | 90篇 |
2005年 | 72篇 |
2004年 | 83篇 |
2003年 | 80篇 |
2002年 | 46篇 |
2001年 | 41篇 |
2000年 | 54篇 |
1999年 | 50篇 |
1998年 | 46篇 |
1997年 | 30篇 |
1996年 | 39篇 |
1995年 | 27篇 |
1994年 | 25篇 |
1993年 | 22篇 |
1992年 | 19篇 |
1991年 | 14篇 |
1990年 | 18篇 |
1989年 | 8篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有2017条查询结果,搜索用时 15 毫秒
131.
TheQvaluevariationsinthepreparingpro┐cesofrockruptureBINWANG1)(王彬),ZHAO-YONGXU1)(许昭永),JIN-MINGZHAO1)(赵晋明)YI-LIHU2)(胡毅力)1)Sei... 相似文献
132.
Studyonthecharacteristicsofcrust┐mantletransitionzoneinWesternYunnanProvinceHONG-XIANGHU(胡鸿翔)ZHONG-YANGLIN(林中洋)YIN-JUBIAN(边银... 相似文献
133.
Claudio Chiaruttini Stefano Grimaz Enrico Priolo 《Soil Dynamics and Earthquake Engineering》1996,15(2):75
A two-dimensional elastic Chebyshev spectral element method (SPEM) is used to model the seismic wavefield within a massive structure and in its vicinity. We consider 2-D models where a linear elastic structure, with quadrangular cross-section, resting on an elastic homogeneous half-space, is impinged upon by the waves generated by a surface impulse at some distance. The scattering of Rayleigh waves and the response of the structure are extensively analysed in a parametric way, varying size, mechanical parameters and shape of the load. Some of the models considered are representative of embankments and earth dams. The simulation shows that some models resonate, storing part of the incoming energy. With realistic parameters, the lowest resonance frequency is due to pure shear deformation and is controlled by the shear velocity and height of the load. Flexural modes are excited only at higher frequencies. The acceleration at the top of the structure may be five/seven times higher than at the base, depending on the mass of the structure. The gradual release of trapped energy produces a ground roll lasting several seconds after the wave front has passed. The ground-roll amplitude depends on the sturcture's mass and can be as large as 30% of the peak acceleration. Outside resonance conditions, the ground motion is almost unaffected by the presence of the artefact; the horizontal motion on top of it is nearly twice the motion at ground level. Similar results should be expected when the incident field is an upcoming shear wave. A qualitative discussion shows that the presence of anelastic attenuation in the embankment does not significantly alter the preceding conclusions, unless it is of very low values (e.g. Q < 15).The modelling results that we discuss indicate that the soil-structure interaction may substantially alter the ‘free-field’ ground motion. From a practical point of view, the main conclusions are: (1) careful analysis is necessary when interpreting seismic records collected in the vicinity of large artefacts; (2) seismic hazard at a site may depend on the presence of man-made structures such as embankments, dams, tall and massive buildings. 相似文献
134.
135.
Xu Ruisong Guangzhou New Technology Institute of Geology Academia Sinica Jiang Minxi 《《地质学报》英文版》1992,66(4)
The vegetation has been poisoned by gold in the western Guangdong-Hainan region. The gold content ofthe leaves there is as high as 10-1961 times the abundance, the chlorophyll content is 10%-30% lower thanthat of the vegetation in metamorphic terrains and 10%-20% higher than that in granite terrains, and thecarotenoid content is 10%-44% lower than the background value. The water content of leaves is 10% to 20%lower than the background value. The cells of leaves are deformed and broken. The leaf surface shows colourspots and becomes yellow or dark green. The spectral reflectance of the leaf surface is 5%-30% higher than thebackground value: the spectral shape has shifted 5-15 nm to the short wavelength. The gray scales of eanopyon images of Landsat TM and airborne imaging scanner (AIS) are 10%-100% higher than the backgroundvalues. On Landsat TM and AIS false colour images, plants poisoned by gold display a yellow color, whichdisinguishes them from background plants. According to the spectral and image features of goldbiogeochemical effects, the author has constructed a gold information system and expert prediction system,and thus two gold target areas and two gold prospect areas have been identified rapidly, economically andaccurately in the western Guangdong-Hainan region which is extensively covered by vegetation. 相似文献
136.
Periodicites in hydrologic data are frequently estimated and studied. In some cases the periodic components are subtracted from the data to obtain the stochastic components. In other cases the physical reasons for the occurrence of these periodicities are investigated. Apart from the annual cycle in the hydrologic data, periods corresponding to the 11 year sunspot cycle, the Hale cycle and others have been detected.The conclusions from most of these studies depend on the reliability and robustness of the methods used to detect these periodicities. Several spectral analysis methods have been proposed to investigate periodicities in time series data. Several of these have been compared to each other. The methods by Siddiqui and Wang and by Damsleth and Spjotvoll, which are stepwise procedures of spectrum estimation, have not been evaluated. 相似文献
137.
Sediment shear Q from airgun OBS data 总被引:2,自引:0,他引:2
P. D. Bromirski L. N. Frazer F. K. Duennebier 《Geophysical Journal International》1992,110(3):465-485
138.
The time series BT profiles and surface winds and atmospheric pressure, collected in the deep waters off Ratnagiri and Karwar
during summer monsoon were utilized to document the characteristics of internal waves (IW). Low-frequency (≤2, cycle per day
(cpd)) IW off Ratnagiri are found to propagate at 83 cm/s with wavelengths of 45 km and wave heights upto 40 m. These parameters
for high-frequency (>2 cpd) IW off Karwar correspond to 99 cm/s, 3 km and 23 m. The IW off Karwar appear to leave the station
at 70° (±10°) (measured from the horizontal). The data sets were further analysed to address the harmonic composition of the
IW and identify the possible sources for the observed IW fields. Power spectra of the IW indicated energy peaks at inertial
(0·6 cpd) and tidal (1 and 2 cpd) frequencies off Ratnagiri and in the high-frequency band of 0·5–2·0 cycles per hour off
Karwar. The coherence between the IW and wind/tide is found to be good at several frequencies within the IW spectrum. This
feature probably suggests tides as a source for the IW of tidal frequencies and winds and tides as a joint source for the
IW at the remaining frequencies. 相似文献
139.
We have employed 10 digital records and computed the spectral magnitude and the seismic radiated energy for 18 large earthquakes
(M
s≥6) occurred in Eur-asian belt during 1986–1989. The nine digital stations (CD-SN) distribute all over China and one in Germany.
The spectral magnitudes of various period have different stability among stations. The stability is better for maximum spectral
magnitudemi and seismic radiated energyE, their differences among stations are smaller, especially for the stations where the ray path main penetrates the low mantle.
But the stability of corner period is usually not good. The relation between seismic radiated energy and seismic moment magnitudeM
w is lg (E)=1.5Mw+c, wherec is a constant. The maximum spectral magnitudemi=M
w+0.1, it is consistant with theoretical prediction.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 418–426, 1993.
This work supported by the Deutsche Forschungsgemeinschaft, Bonn, F. R. Germany. The support is grateful acknowledge. 相似文献
140.
Stefano Casotto 《Celestial Mechanics and Dynamical Astronomy》1995,62(1):1-22
A new method for calculating the perturbation spectrum in the framework of Kaula's linear satellite theory (LST) is introduced. The novelty of this approach consists in using recent results on the spectral decomposition of the perturbation frequencies in LST to provide a closed formulation for the amplitude and the phase of each line in the perturbation spectrum. The theory presented here can be applied to perturbations in the elements or in the radial and transverse directions due to the geopotential or to the tides. Separate algorithms are developed for application to orbits with circulating or frozen perigee. 相似文献