全文获取类型
收费全文 | 1151篇 |
免费 | 190篇 |
国内免费 | 236篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 372篇 |
地球物理 | 280篇 |
地质学 | 248篇 |
海洋学 | 224篇 |
天文学 | 306篇 |
综合类 | 34篇 |
自然地理 | 100篇 |
出版年
2024年 | 8篇 |
2023年 | 13篇 |
2022年 | 18篇 |
2021年 | 26篇 |
2020年 | 32篇 |
2019年 | 52篇 |
2018年 | 30篇 |
2017年 | 32篇 |
2016年 | 31篇 |
2015年 | 38篇 |
2014年 | 43篇 |
2013年 | 77篇 |
2012年 | 42篇 |
2011年 | 52篇 |
2010年 | 38篇 |
2009年 | 87篇 |
2008年 | 83篇 |
2007年 | 90篇 |
2006年 | 84篇 |
2005年 | 66篇 |
2004年 | 76篇 |
2003年 | 67篇 |
2002年 | 55篇 |
2001年 | 58篇 |
2000年 | 53篇 |
1999年 | 59篇 |
1998年 | 52篇 |
1997年 | 33篇 |
1996年 | 28篇 |
1995年 | 23篇 |
1994年 | 39篇 |
1993年 | 19篇 |
1992年 | 22篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 14篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1577条查询结果,搜索用时 15 毫秒
261.
262.
The turbulence field of airflow in the lee of a dune has significant impacts on dune dynamics and related processes. We used particle image velocimetry in a wind tunnel simulation to obtain detailed velocity measurements in the lee of two‐dimensional transverse dune models, then used the results to analyse their turbulence fields. The dune models used in this study had a single lee angle of 30°, and a total of six stoss angles: 3°, 5°, 10°, 15°, 20° and 25°. We used vorticity, turbulence intensity, Reynolds stress and turbulent kinetic energy to characterize the turbulence fields. These parameters were functions of stoss angle, wind velocity, distance from the dune crest and height above the ground surface. The stoss angles could generally be divided into two groups based on the profiles of mean velocity, turbulence and Reynolds stress. Stoss angles of 3° and 5° usually had similar profiles, and angles of 15°, 20° and 25° formed a second group with similar profiles. The profiles for the stoss angle of 10° were usually transitional and were intermediate between the two groups. Vorticity, Reynolds stress and turbulent kinetic energy increased monotonically with increasing free‐stream wind velocity, but their variations with respect to the stoss angle were complex. The stoss angles of 15° and 20° had the maximum values of these three parameters, thus these angles may have special significance in dune development given the characteristics of the mean velocity fields and turbulence fields they produce within the lee airflow. It is the streamwise velocity component and its turbulence that determine the surface shear stress. Copyright © 2008 John Wiley and Sons, Ltd. 相似文献
263.
树轮资料(1511~1954)太阳活动的多尺度分析——EMD方法的应用 总被引:1,自引:0,他引:1
用EMD对Stu iver等提供的树轮14C资料进行分析,结果为:①得到太阳活动的准3、6、11、22、44、110、200、300 a的周期;从趋势项中可以得到准600 a甚至更长的周期波动;②可以判断太阳活动经典的极小期,与公认的极小期有一定的滞后性。从树轮14C含量的变化趋势中可以判断从1954~2100年的太阳活动变化逐渐变强,从2100~2350年太阳活动逐渐开始变弱;③从每个尺度周期波动的时变特征中可以得到,即使在太阳活动的极小期,太阳活动依然存在频率和强度不同的周期波动。 相似文献
264.
库水位升降联合降雨作用下库岸边坡中的浸润线研究 总被引:6,自引:1,他引:5
库岸边坡中的地下水对其稳定性有重大影响,目前还没有统一的公式用来计算岸坡中的浸润线。为此,建立隔水底板呈缓倾角的均质岸坡模型,采用稳定渗流情况下的浸润线作为非稳定渗流的初始值,推导出库水位升降联合降雨作用下该模型中浸润线的近似解析解。利用Geo-Slope中的SEEP/W程序,对浸润线的近似解析解进行验证分析,结果表明,在不同库水位升降和降雨的组合条件下,由近似解析解确定的浸润线与数值模拟结果基本一致。对库水位升降联合降雨作用下赵树岭滑坡中的浸润线进行研究,利用实测浸润线验证了近似解析解的正确性,并预测了赵树岭滑坡在快速蓄水、快速蓄水+暴雨、快速泄水及快速泄水+暴雨4种工况下(库水位波动范围为145~175 m)浸润线的变化情况。最后,从解析解的适用条件出发剖析了近似解析解误差产生的原因,为应用浸润线解析解解决实际问题提供依据。 相似文献
265.
S. Mathis T. Decressin A. Palacios P. Eggenberger L. Siess S. Talon C. Charbonnel S. Turck-Chièze J.-P. Zahn 《Astronomische Nachrichten》2007,328(10):1062-1065
Stellar radiation zones are the seat of meridional currents. This circulation has a strong impact on the transport of angular momentum and the mixing of chemicals that modify the evolution of stars. First, we recall in details the dynamical processes that are taking place in differentially rotating stellar radiation zones and the assumptions which are adopted for their modelling in stellar evolution. Then, we present our new results of numerical simulations which allow us to follow in 2D the secular hydrodynamics of rotating stars, assuming that anisotropic turbulence enforces a shellular rotation law and taking into account the transport of angular momentum by internal gravity waves. The different behaviors of the meridional circulation in function of the type of stars which is studied are discussed with their physical origin and their consequences on the transport of angular momentum and of chemicals. Finally, we show how this work is leading to a dynamical vision of the evolution of rotating stars from their birth to their death. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
266.
267.
The angular momentum transport in rotating turbulent convection is simulated with the NIRVANA code for Taylor numbers up to 106. The box consists of an unstable layer embedded in two stable overshoot layers. We find the expected anisotropies in the rotating anisotropic turbulence field: 〈u′2r〉 exceeds 〈u′2ϕ〉, and 〈u′2ϕ〉 exceeds 〈u′2θ〉. The resulting radial angular momentum transport is directed inwards and peaks in the middle of the convective layer. The resulting latitudinal angular momentum transport is equatorwards, peaks at the surface and is highly concentrated to the equatorial region. Apart from a factor of 2–3 the total amplitudes of the cross‐correlations are of the same order of magnitude. In the lower overshoot region (‘tachocline’) the cross‐correlations are negative. It is argued that the concentration of the latitudinal angular momentum transport towards the surface and towards the equator does not too strongly reduce its potential to produce rotation laws with accelerated equators. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
268.
269.
邓永光 《华东地质学院学报》2000,23(3):214-221
人类生存环境的变化是人类共同关心的环境问题之一,最直接影响环境变化的自然因素有气候变化、海平面和陆地的升降等,通过对有关广西沿海海平面和地壳运动资料的研究,初步分析了地壳运动对沿海地区产生的不良环境变化。 相似文献
270.
Osvaldo L. L. Moraes 《Boundary-Layer Meteorology》2000,96(3):317-335
This paper presents results of turbulence measurementsmade in the south of Brazil in the Pampa region.Data collected at 1Hz are used to calculatestandard deviations of temperature and velocities. Onthe other hand data collected at 10Hz areused to study the behaviour of spectra and cospectraof turbulence in the surface layer. Dimensionless dissipation rates of turbulent kinetic energy and temperature variance are also presented. The frameworkof Monin–Obukhov Similarity theory is used and allresults are compared with other experimentalstudies. 相似文献