全文获取类型
收费全文 | 283篇 |
免费 | 5篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 16篇 |
地球物理 | 56篇 |
地质学 | 112篇 |
海洋学 | 50篇 |
天文学 | 29篇 |
自然地理 | 26篇 |
出版年
2022年 | 2篇 |
2020年 | 2篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 11篇 |
2016年 | 4篇 |
2015年 | 2篇 |
2014年 | 2篇 |
2013年 | 22篇 |
2012年 | 7篇 |
2011年 | 10篇 |
2010年 | 8篇 |
2009年 | 20篇 |
2008年 | 13篇 |
2007年 | 5篇 |
2006年 | 5篇 |
2005年 | 7篇 |
2004年 | 8篇 |
2003年 | 5篇 |
2002年 | 11篇 |
2001年 | 4篇 |
2000年 | 12篇 |
1999年 | 10篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1991年 | 2篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1988年 | 4篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1970年 | 2篇 |
1940年 | 1篇 |
1928年 | 1篇 |
1912年 | 1篇 |
1910年 | 1篇 |
1892年 | 1篇 |
1889年 | 1篇 |
排序方式: 共有293条查询结果,搜索用时 0 毫秒
261.
Ambient and dynamic pore pressures in fine-grained submarine sediments: Mississippi Delta 总被引:2,自引:0,他引:2
A multisensor piezometer probe has measured pore pressures in fine-grained submarine sediments of the Mississippi Delta over a period of approximately eight months. Data presented here cover the initial 2650 hours of the experiment. Dynamic and ambient pore pressures were recorded. Analogue data collected from the time of probe insertion include decay characteristics, steady-state (ambient) excess pore pressures, and the response of pore pressures to surface wave activity. The probe was installed in 43–44 ft of water near an offshore platform in the East Bay area of the Delta. Sensors were located at 21, 41 and 51 ft below the mudline. Ambient excess pore pressures were determined to be 0.7, 2.8 and 6.6 psi (lb/in2) at the respective depths. The relatively high excess pressures and the measured laboratory wet unit weights of the soil result in a significantly low effective stress. Pressure fluctuations due to tidal and surface wave activity were observed to produce significant pore pressure response in these soils. Preliminary data obtained using high-airentry and corundum stones indicate that considerably more research is necessary in order to fully understand the peculiarities observed in the data and to assess the role of dissolved and free gas on the pore pressures in submarine sediments. 相似文献
262.
A.F. Bennett 《Progress in Oceanography》1985,15(2):129-156
The generalized inverse method of Bennett and McIntosh (1982) is used to assess the efficiency of instrument arrays with observe deterministic fields. The arrays considered are combinations of points at which bottom pressures are observed (Cartwright, 1978), plus paths along which averaged barotropic velocities are observed, by the acoustic tomography technique of reciprocal shooting (Munk and Wunsch, 1982a,b). The barotropic M2 tide is used as an example of a field which is being observed by the array, and for which an interpolation or smoothing is required. The treatment of observations of individual inter-annual events would be similar.It is shown that the generalized inverse method for the objective analysis of deterministic fields is formally identical to the Gandin (1965) method for the objective analysis of random fields.Construction of the generalized inverse requires the inversion of an Hermitian positive definite matrix. Array efficiency is characterized by the number of significant eigenvalues of the matrix.The admission of errors in the observations and dynamics necessitates the choice of weights in a variational principle. The choice is made by prior estimation of the relative error variances. It is also necessary to choose locally singular weighting functions for the dynamics, in order to ensure non-singular interpolating or smoothing fields. The dominant array modes are defined and constructed. These are the interpolating fields which make the most stable contribution to the generalized inverse.An example of inversion is carried out using simulated data. 相似文献
263.
The paper discusses electron intensities observed on two rocket flights over auroral arcs. On both occasions there was an order-of-magnitude increase in the electron phase-space density as the rocket moved northwards across the arc from a southern region of relatively hard precipitation to an adjacent northern region of softer (but still intense) precipitation. These two distinct regions formed northern and southern ‘curtains’ to the arcs. Electrons observed to the south of one of the arcs had the same phase-space density as those in the southern curtain of the arc. It is concluded that the electrons producing the auroral arcs were accelerated at the boundary between two source plasmas in the magnetosphere. The possible identity of the source plasmas is discussed. From the various types of election energy spectra encountered it is suggested that time-varying magnetic fields played an important part in the acceleration of the electrons that produced the auroral arcs. 相似文献
264.
265.
266.
267.
Mobile, location‐aware computing technology is widely available. In this article we sketch out a manifesto on mobile computing in geographic education (MoGeo) for consideration and debate within the geographic community. At the core of our argument is the idea that emerging mobile computing technologies will allow teachers to bring the classroom and pedagogic materials into the field, and that the resulting in situ educational experience will enhance learning by contextualizing the complex and abstract concepts that we teach. We provide a set of key principles that can guide the development of field experiences for students using these new technologies. 相似文献
268.
Eclogite of recycled slab origin has often been invoked in the source region of mid-ocean ridge and ocean-island basalts. Melts of this eclogitic material are expected to be enriched in incompatible elements including major elements such as Na and Ti. In order to investigate the controls on trace element chemistry of a melt from such a recycled component we have performed trace element partitioning experiments in the simple systems CMAS (CaO-MgO-Al2O3-SiO2), NCMAS (Na2O-CMAS) and Ti-CMAS (TiO2-CMAS) at 3 GPa and 1298-1500°C using analogue eclogitic compositions.We show that sodium has a profound effect on clinopyroxene-melt partition coefficients. NCMAS is characterized by elevated partition coefficients, relative to CMAS for all elements except Li. The increase is more pronounced for more highly charged cations, resulting in negative partitioning anomalies for Li, Sr, Ba and Pb. In contrast to sodium, titanium has very little effect on trace element partitioning for all elements except Nb and Ta, which are retained by the rutile that is saturated in this run. 相似文献
269.
270.