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91.
This paper focuses on the influence of the initial void ratio on the evolution of the passive earth pressure and the formation
of shear zones in a dry sand body behind a retaining wall. For the numerical simulation a rigid and very rough retaining wall
undergoing a horizontal translation against the backfill is considered. The essential mechanical properties of cohesionless
granular soil are described with a micro-polar hypoplastic model which takes into account stresses and couple stresses, pressure
dependent limit void ratios and the mean grain size as a characteristic length. Numerical investigations are carried out with
an initially medium dense and initially loose sand using a homogeneous and random distribution of the initial void ratio.
The geometry of calculated shear zones is discussed and compared with a corresponding laboratory model test. 相似文献
92.
地球磁场极性在地质历史中发生过相当频繁的倒转。作者将地球内部划分为岩石圈-软流圈-中圈-液圈-固核等5个动力学圈层,认为中圈与固核间可异步旋转;地球偶极磁场由中圈与固核异步旋转时所驱动的液圈中的封闭涡流与系磁场作用产生;该偶极子场极性由地球所通过的银道面上侧或下侧磁场方向及液圈涡流的方向共同决定,二者之一反向,极性发生倒转。 相似文献
93.
J. Höpfner 《Journal of Geodesy》2001,75(2-3):137-150
The annual and semiannual residuals derived in the axial angular momentum budget of the solid Earth–atmosphere system reflect
significant signals. They must be caused by further excitation sources. Since, in particular, the contribution for the wind
term from the atmospheric layer between the 10 and 0.3 hPa levels to the seasonal variations in length of day (LOD) is still
missing, it is necessary to extend the top level into the upper stratosphere up to 0.3 hPa. Under the conservation of the
total angular momentum of the entire Earth, variations in the oceanic angular momentum (OAM) and the hydrological angular
momentum (HAM) are further significant excitation sources at seasonal time scales. Focusing on other contributions to the
Earth's axial angular momentum budget, the following data are used in this study: axial atmospheric angular momentum (AAM)
data derived for the 10–0.3 hPa layer from 1991 to 1997 for computing the missing wind effects; axial OAM functions as generated
by oceanic general circulation models (GCMs), namely for the ECHAM3 and the MICOM models, available from 1975 to 1994 and
from 1992 to 1994, respectively, for computing the oceanic contributions to LOD changes, and, concerning the HAM variations,
the seasonal estimates of the hydrological contribution as derived by Chao and O'Connor [(1988) Geophys J 94: 263–270]. Using
vector representation, it is shown that the vectors achieve a close balance in the global axial angular momentum budget within
the estimated uncertainties of the momentum quantities on seasonal time scales.
Received: 6 April 2000 / Accepted: 13 December 2000 相似文献
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97.
Lunar Laser Ranging: Glorious Past And A Bright Future 总被引:1,自引:0,他引:1
Peter J. Shelus 《Surveys in Geophysics》2001,22(5-6):517-535
Lunar Laser Ranging (LLR), a part of the NASA Apollo program, has beenon-going for more than 30 years. It provides the grist for a multi-disciplinarydata analysis mill. Results exist for solid Earth sciences, geodesy and geodynamics,solar system ephemerides, terrestrial and celestial reference frames, lunar physics,general relativity and gravitational theory. Combined with other data, it treatsprecession of the Earth's spin axis, lunar induced nutation, polar motion/Earthrotation, Earth orbit obliquity to the ecliptic, intersection of the celestial equatorwith the ecliptic, luni-solar solid body tides, lunar tidal deceleration, lunar physicaland free librations, structure of the moon and energy dissipation in the lunar interior.LLR provides input to lunar surface cartography and surveying, Earth station and lunar retroreflector location and motion, mass of the Earth-moon system, lunar and terrestrial gravity harmonics and Love numbers, relativistic geodesic precession, and the equivalence principle of general relativity. With the passive nature of the reflectors and steady improvement in observing equipment and data analysis, LLR continues to provide state-of-the-art results. Gains are steady as the data-base expands. After more than 30 years, LLR remains the only active Apollo experiment. It is important to recognize examples of efficient and cost effective progress of research. LLR is just such an example. 相似文献
98.
The polar motion prediction is computed as a least-squares extrapolation of the polar motion data. The least-squares model consists of a Chandler circle with constant or variable amplitude, annual and semiannual ellipses, and a bias. The model with constant amplitude of the Chandler oscillation is fit to the last three years of polar motion data and the model with variable amplitude of the Chandler oscillation is fit to the whole time series ranging from 1973.0 to 2001.1. The variable amplitude of the Chandler oscillation is modeled from the envelope of the Chandler oscillation filtered by the Fourier transform band pass filter from the long-term IERS EOPC01 polar motion series. The accuracy of the polar motion prediction depends mostly on the phase variation of the annual oscillation, which is treated as a constant in the least-squares adjustment. There were two significant changes of the annual oscillation phase of the order of 30° before the two El Niño events in 1982/83 and 1997/98. 相似文献
99.
General characteristics of the recent horizontal crustal movement in Chinese mainland 总被引:5,自引:0,他引:5
1 Introduction of GPS observation dataThe Crustal Movement Observation Network of China (CMONOC) is a major scientific project in China organized by China Seismological Bureau and paticipated by the Bureau of Surveying and Mapping of the General Staff, the Chinese Academy of Sciences and the National Bureau of Surveying and Mapping. Based on the observation data of 25 fiducial stations and 56 basic stations in CMONOC (Figure 1 and Table 1), collected from August 26 to September… 相似文献
100.
潮汐沉积物记录着一系列的潮汐周期。本文简要介绍了几种主要的现代潮汐周期,在此基础上回顾了最近十余年来国外对周期性潮汐沉积物,特别是潮汐韵律层的研究进展,系统介绍了几种从古代沉积物中识别出来的潮汐周期,包括基本潮汐(半日潮、全日潮和混合潮),大-小潮周期以及一些长期周波动等。最后对潮汐韵律层在推测地史时期地-月系的演化历史中的意义作了评述。 相似文献