全文获取类型
收费全文 | 995篇 |
免费 | 137篇 |
国内免费 | 190篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 8篇 |
地球物理 | 239篇 |
地质学 | 348篇 |
海洋学 | 437篇 |
天文学 | 139篇 |
综合类 | 25篇 |
自然地理 | 112篇 |
出版年
2024年 | 1篇 |
2023年 | 10篇 |
2022年 | 19篇 |
2021年 | 18篇 |
2020年 | 20篇 |
2019年 | 52篇 |
2018年 | 35篇 |
2017年 | 26篇 |
2016年 | 24篇 |
2015年 | 38篇 |
2014年 | 55篇 |
2013年 | 56篇 |
2012年 | 43篇 |
2011年 | 36篇 |
2010年 | 27篇 |
2009年 | 73篇 |
2008年 | 66篇 |
2007年 | 90篇 |
2006年 | 85篇 |
2005年 | 65篇 |
2004年 | 64篇 |
2003年 | 60篇 |
2002年 | 38篇 |
2001年 | 44篇 |
2000年 | 25篇 |
1999年 | 27篇 |
1998年 | 31篇 |
1997年 | 25篇 |
1996年 | 41篇 |
1995年 | 21篇 |
1994年 | 17篇 |
1993年 | 17篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1322条查询结果,搜索用时 15 毫秒
1.
Average velocity in streams is a key variable for the analysis and modelling of hydrological and hydraulic processes underpinning water resources science and practice. The present study evaluates the impact of the sampling duration on the quality of average velocity measurements acquired with contemporary instruments such as Acoustic Doppler Velocimeters (ADV) an Acoustic Doppler Current Profilers (ADCP). The evaluation combines considerations on turbulent flows and principles and configurations of acoustic instruments with practical experience in conducting customized analysis for uncertainty analysis purposes. The study sheds new insights on the spatial and temporal variability of the uncertainty in the measurement of average velocities due to variable sampling durations acting in isolation from other sources of uncertainties. Sampling durations of 90 and 150 s are found sufficient for ADV and ADCP, respectively, to obtain reliable average velocities in a flow affected only by natural turbulence and instrument noise. Larger sampling durations are needed for measurements in most of the natural streams exposed to additional sources of data variability. 相似文献
2.
R. F. Griffin 《Journal of Astrophysics and Astronomy》1990,11(4):533-540
Photoelectric radial-velocity measurements show that HD 118670 is a double-lined spectroscopic binary in an orbit which is
not quite circular and whose period is about 48 days. Spectral types of K0 V and K7 V would satisfy the photometry and the
mass ratio; the mass function would then suggest the possibility of eclipses. However, actual spectral classification indicates
a luminosity somewhat above the main sequence 相似文献
3.
Jorge Luis De Souza 《Pure and Applied Geophysics》1991,136(2-3):245-264
The Rayleigh wave phase and group velocities in the period range of 24–39 sec, obtained from two earthquakes which occurred in northeastern brazil and which were recorded by the Brazilian seismological station RDJ (Rio de Janeiro), have been used to study crustal and upper mantle structures of the Brazilian coastal region. Three crustal and upper mantle models have been tried out to explain crustal and upper mantle structures of the region. The upper crust has not been resolved, due basically to the narrow period range of the phase and group velocities data. The phase velocity inversions have exhibited good resolutions for both lower crust and upper mantle, with shear wave velocities characteristic of these regions. The group velocity data inversions for these models have showed good results only for the lower crust. The shear wave velocities of the lower crust (3.86 and 3.89 km/sec), obtained with phase velocity inversions, are similar to that (=3.89 km/sec) found byHwang (1985) to the eastern South American region, while group velocity inversions have presented shear velocity (=3.75 km/sec) similar to that (=3.78 km/sec) found byLazcano (1972) to the Brazilian shield. It was not possible to define sharply the crust-mantle transition, but an analysis of the phase and group velocity inversions results has indicated that the total thickness of the crust should be between 30 and 39 km. The crustal and upper mantle model, obtained with phase velocity inversion, can be used as a preliminary model for the Brazilian coast. 相似文献
4.
5.
6.
7.
8.
9.
10.
从射线声学和简正波声学的角度,概述了海洋声层析的基本理论,包括射线走时反演、简正波走时反演、简正波相位反演和简正波水平折射层析。海洋声层析以反演海水温度和流速为基础。还总结了声层析在海洋学研究中的应用。 相似文献