全文获取类型
收费全文 | 796篇 |
免费 | 47篇 |
国内免费 | 13篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 45篇 |
地球物理 | 237篇 |
地质学 | 177篇 |
海洋学 | 61篇 |
天文学 | 140篇 |
自然地理 | 182篇 |
出版年
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 15篇 |
2018年 | 15篇 |
2017年 | 13篇 |
2016年 | 27篇 |
2015年 | 19篇 |
2014年 | 17篇 |
2013年 | 44篇 |
2012年 | 23篇 |
2011年 | 31篇 |
2010年 | 19篇 |
2009年 | 48篇 |
2008年 | 41篇 |
2007年 | 33篇 |
2006年 | 31篇 |
2005年 | 32篇 |
2004年 | 43篇 |
2003年 | 26篇 |
2002年 | 39篇 |
2001年 | 28篇 |
2000年 | 18篇 |
1999年 | 13篇 |
1998年 | 21篇 |
1997年 | 21篇 |
1996年 | 16篇 |
1995年 | 8篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 23篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 9篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1970年 | 4篇 |
1965年 | 2篇 |
1924年 | 2篇 |
排序方式: 共有856条查询结果,搜索用时 15 毫秒
101.
102.
Summary. We examine the way in which measurements of velocity anisotropy can add to our understanding of upper mantle structure. Measurements of P -wave velocity anisotropy in a single plane contain very little direct information about the anisotropic structure. A promising technique is to fit the observed velocity variation with a mixture of an assumed anisotropic constituent and a proportion of isotropic material. Using this technique, mixtures of orthorhombic and transversely isotropic olivine are obtained, which are in excellent agreement with observed velocity variations in the Pacific. 相似文献
103.
104.
Summary. Observations of surface waves crossing ocean basins indicate that, at least in some cases, a better interpretation of what was previously considered to be the simultaneous arrival of fundamental Love and second Rayleigh modes, with similar group velocities, is the coupled motion of the second-generalized mode surface wave propagating in an anisotropic upper-mantle. This mode displays the polarization anomalies expected from anisotropic alignments caused by syntectonic recrystallization of olivine in a zone of horizontal shear. The polarity of the pattern of anomalies, found in waves crossing the Pacific Basin, suggests that the lithosphere is dragging the asthenosphere. 相似文献
105.
106.
Distinctive Particle Motion of Surface Waves as a Diagnostic of Anisotropic Layering 总被引:3,自引:0,他引:3
Stuart Crampin 《Geophysical Journal International》1975,40(2):177-186
107.
Stuart Bradley Yvette Perrott Paul Behrens Andy Oldroyd 《Boundary-Layer Meteorology》2012,143(1):37-48
The quality of lidar and sodar wind estimates is generally judged through comparisons with mast-mounted instruments, and the
resulting regressions. Evaluation of the relative merits of lidars versus sodars is complicated by the fact that lidars are
generally placed close to a mast whereas sodars are generally placed some distance from a mast so that acoustic reflections
off the mast are reduced. This leads to the two technologies, lidar and sodar, not being compared in similar situations. Differences
arising from the two geometries can be expected to be larger in complex terrain, where the wind regime can vary significantly
spatially. The current work explores these differences in moderately complex terrain. Lidar–mast comparisons are performed
with the lidar close to an 80 m mast, and sodar–mast comparisons performed with the sodar 300 m from the mast. Systematic
variations in estimated wind speed are found to occur with height, consistent with predictions from a simple flow model. When
the lidar was moved to the sodar location, further from the mast, there were significant changes in the estimated wind speeds
and a reduction in correlation with the mast-based wind speeds, as expected. However, the correlation between collocated lidar and sodar winds was high. This finding emphasizes that any comparison of two remote sensing instruments needs to be
through similar experiments, and that differences in accuracy often reported for the lidar and sodar technologies are likely
to be contaminated due to poor comparison configurations. A method was devised to simulate the sodar being collocated with
the mast, by using the lidar–sodar measurements and the lidar–mast measurements. It was found that there was then no statistically
detectable difference between lidar–mast regressions and sodar–mast regressions for the particular lidar and sodar tested.
Both remote sensing instruments were also found to be good estimators of Weibull parameters, as compared with those derived
from mast data. The conclusion is that the sodar measured the winds above the sodar with a similar accuracy to the lidar measuring
winds above the lidar. 相似文献
108.
Kirsty J. Rhook Paul M. Geil J. Stuart B. Wyithe 《Monthly notices of the Royal Astronomical Society》2009,392(4):1388-1396
It has recently been suggested that the power spectrum of redshifted 21 cm fluctuations could be used to measure the scale of baryonic acoustic oscillations (BAOs) during the reionization era. The resulting measurements are potentially as precise as those offered by the next generation of galaxy redshift surveys at lower redshift. However, unlike galaxy redshift surveys, which in the linear regime are subject to a scale-independent galaxy bias, the growth of ionized regions during reionization is thought to introduce a strongly scale-dependent relationship between the 21 cm and mass power spectra. We use a seminumerical model for reionization to assess the impact of ionized regions on the precision and accuracy with which the BAO scale could be measured using redshifted 21 cm observations. For a model in which reionization is completed at z ∼ 6 , we find that the constraints on the BAO scale are not systematically biased at z ≳ 6.5 . In this scenario, and assuming the sensitivity attainable with a low-frequency array comprising 10 times the collecting area of the Murchison Widefield Array, the BAO scale could be measured to within 1.5 per cent in the range 6.5 ≲ z ≲ 7.5 . 相似文献
109.
110.