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981.
982.
在缺乏其他资料的情况下,地脉动常常用做确定地震动对地表介质产生影响效应的简便手段。本文以银川市区为研究对象,根据地震勘探资料有目的的选取5条测线在银川市区进行地脉动观测,观测点共141个。用Nakamura提出的HV谱比法解析观测数据,在给定地下构造剪切波速度(VS)的基础上,由H/V比值曲线中的基本频率推测盆地深层地下构造。通过理论计算进一步验证了解析结果。结合前人地震勘探资料推测了银川市区脉动基本频率分布特征,并给出2D和3D银川市基底构造变化情况,对比分析表明,HV谱比法得到的脉动基本频率值可以反映银川盆地基底变化情况。 相似文献
983.
Anisotropic reverse-time migration for tilted TI media 总被引:1,自引:0,他引:1
Seismic anisotropy in dipping shales results in imaging and positioning problems for underlying structures. We develop an anisotropic reverse‐time depth migration approach for P‐wave and SV‐wave seismic data in transversely isotropic (TI) media with a tilted axis of symmetry normal to bedding. Based on an accurate phase velocity formula and dispersion relationships for weak anisotropy, we derive the wave equation for P‐wave and SV‐wave propagation in tilted transversely isotropic (TTI) media. The accuracy of the P‐wave equation and the SV‐wave equation is analyzed and compared with other acoustic wave equations for TTI media. Using this analysis and the pseudo‐spectral method, we apply reverse‐time migration to numerical and physical‐model data. According to the comparison between the isotropic and anisotropic migration results, the anisotropic reverse‐time depth migration offers significant improvements in positioning and reflector continuity over those obtained using isotropic algorithms. 相似文献
984.
985.
J. Du W.E. Ward J. Oberheide T. Nakamura T. Tsuda 《Journal of Atmospheric and Solar》2007,69(17-18):2159
The extended Canadian Middle Atmosphere Model (extended CMAM) is a general circulation model, which extends from the surface to about 210 km. Spatial complex spectral analysis is applied to horizontal winds simulated by the extended CMAM to obtain semidiurnal tidal amplitudes and phases (from e5 to w5) in the mesosphere and lower thermosphere (MLT) region. The dominant w2 migrating component and the presence of eight nonmigrating tides (w3, w4, w5, e1, e2, e3, e4 and e5) in the mid-latitudes are identified. Components w1 and s0, which tend to maximize at high latitudes, will be discussed separately in a later paper. The migrating semidiurnal tide (w2) has amplitudes reaching over 20 m s−1 for both zonal and meridional winds in the mid-latitude region. Its form compares well to the published results. The amplitudes of nonmigrating semidiurnal tides are non-negligible compared with the migrating semidiurnal tides. The amplitudes for w3 and e2 exceed 12 and 8 m s−1, respectively.Comparisons are made with four nonmigrating semidiurnal components (w3, w4, e1 and e2) derived from the TIMED Doppler interferometer (TIDI) wind measurements between 85 and 105 km altitude and between 45°S and 45°N latitude. Overall, the basic CMAM and TIDI latitudinal structures of the amplitudes agree well and the agreement between the annual mean amplitudes varies with component. Relative to the TIDI results, the CMAM seasonal variations of w4 are in good agreement, of e2 are in reasonable agreement, of w3 are in partial agreement and of e1 are in poor agreement.The 11 semidiurnal components from the model are superimposed to generate the total semidiurnal winds at Jakarta (6°S, 106°E) and Kototabang (0°, 100°E) and are compared with measurements from two equatorial meteor radar stations at these sites. The relative contributions of components to the reconstructed amplitude vary from month to month. The CMAM reconstructions are generally larger than the radar results by a factor varying between one and two. The phases in the radar data are typically stationary with respect to height, whereas they generally decrease with height in the CMAM reconstruction. 相似文献
986.
987.
Nonlinear seismic response analysis of arch dam-foundation systems- part I dam-foundation rock interaction 总被引:1,自引:0,他引:1
The arch dam–foundation rock dynamic interaction and the nonlinear opening and closing effects of contact joints on arch dam
are important to the seismic response analysis of arch dams. Up to date, there is not yet a reasonable and rigorous procedure
including the two factors in seismic response analysis. The methods for the analysis of arch dam–foundation rock dynamic interaction
in frequency domain are not suitable to the problem with nonlinear behaviors, in this paper, so an analysis method in time
domain is proposed by combining the explicit finite element method and the transmitting boundary, and the dynamic relaxation
technique is adopted to obtain the initial static response for dynamic analysis. Moreover, the influence of arch dam–foundation
dynamic interaction with energy dispersion on seismic response of designed Xiaowan arch dam in China is studied by comparing
the results of the proposed method and the conventional method with the massless foundation, and the local material nonlinear
and nonhomogeneous behaviors of foundation rock are also considered. The reservoir water effect is assumed as Westergaard
added mass model in calculation. The influence of the closing–opening effects of contact joints of arch dam on the seismic
response will be studied in another paper. 相似文献
988.
989.
Land cover changes based on plant successions: Deforestation,rehabilitation and degeneration of forest in the upper Dadu River watershed 总被引:2,自引:0,他引:2
Jianzhong?Yan Yili?ZhangEmail author Wanqi?Bai Yanhua?Liu Weikai?Bao Linshan?Liu Du?Zheng 《中国科学D辑(英文版)》2005,48(12):2214-2230
The land use/cover classification system is the foundation for land use/cover change study. Remote sensing data were firstly used for land use and land cover classification in the United States in 1971 and the Anderson Classification System was proposed in 1976[1], which was put into use in mapping 1:250000 land use and land cover of the United States. A series of new land cover classification systems have been established in recent years through research projects such as FAO LCCS and Bi… 相似文献
990.
Dušan Němec 《Mineralogy and Petrology》1964,9(1-2):42-85
Ohne ZusammenfassungMit 18 Textabbildungen 相似文献