全文获取类型
收费全文 | 475篇 |
免费 | 27篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 88篇 |
地球物理 | 133篇 |
地质学 | 152篇 |
海洋学 | 31篇 |
天文学 | 72篇 |
综合类 | 3篇 |
自然地理 | 21篇 |
出版年
2024年 | 2篇 |
2023年 | 3篇 |
2022年 | 8篇 |
2021年 | 11篇 |
2020年 | 13篇 |
2019年 | 8篇 |
2018年 | 15篇 |
2017年 | 20篇 |
2016年 | 35篇 |
2015年 | 30篇 |
2014年 | 19篇 |
2013年 | 30篇 |
2012年 | 29篇 |
2011年 | 24篇 |
2010年 | 21篇 |
2009年 | 33篇 |
2008年 | 31篇 |
2007年 | 10篇 |
2006年 | 20篇 |
2005年 | 21篇 |
2004年 | 13篇 |
2003年 | 8篇 |
2002年 | 8篇 |
2001年 | 3篇 |
2000年 | 7篇 |
1999年 | 9篇 |
1998年 | 3篇 |
1997年 | 14篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有507条查询结果,搜索用时 0 毫秒
51.
Precipitation variability and trends in Ghana: An intercomparison of observational and reanalysis products 总被引:2,自引:0,他引:2
Inter-annual variability and trends of annual/seasonal precipitation totals in Ghana are analyzed considering different gridded observational (gauge- and/or satellite-based) and reanalysis products. A quality-controlled dataset formed by fourteen gauges from the Ghana Meteorological Agency (GMet) is used as reference for the period 1961–2010. Firstly, a good agreement is found between GMet and all the observational products in terms of variability, with better results for the gauge-based products—correlations in the range of 0.7–1.0 and nearly null biases—than for the satellite-gauge merged and satellite-derived products. In contrast, reanalyses exhibit a very poor performance, with correlations below 0.4 and large biases in most of the cases. Secondly, a Mann-Kendall trend analysis is carried out. In most cases, GMet data reveal the existence of predominant decreasing (increasing) trends for the first (second) half of the period of study, 1961–1985 (1986–2010). Again, observational products are shown to reproduce well the observed trends—with worst results for purely satellite-derived data—whereas reanalyses lead in general to unrealistic stronger than observed trends, with contradictory results (opposite signs for different reanalyses) in some cases. Similar inconsistencies are also found when analyzing trends of extreme precipitation indicators. Therefore, this study provides a warning concerning the use of reanalysis data as pseudo-observations in Ghana. 相似文献
52.
53.
Dante Minniti Marina Rejkuba Doug Geisler Jose Gabriel Funes 《Astrophysics and Space Science》2004,290(3-4):363-377
VLT images in BVI are used to identify globular clusters in the central region of NGC5128. Based on the sizes, optical magnitudes and colors, a hundred candidate globular clusters are identified with projected galactocentric distances 1 kpc < R G < 5 kpc. These clusters have magnitudes 18 < V < 20.5 or ?10.3 < M V < ?7.8 at the distance of this galaxy, and colors 0.8 < V?I < 1.5 and 0.5 < B?V < 1.5. These identifications allow us to compare the properties of the X-ray globular cluster population discovered recently in this galaxy. 相似文献
54.
In the present study we address the issue of discerning between deterministic and stochastic paradigms in order to understand the behavior of the solar cycle. To this end we show the degree of correlation between the instantaneous amplitude and frequency in the sunspot number time series by the use of the Gabor analytic signal. We compare this correlation with those arising from two theoretical models: (a) the Barnes model of widespread use in the literature and (b) a spatial truncation of the MHD equations. We show that comparisons between the correlation observed in the sunspot time series with those arising from theoretical models can be used to refute one of the models. 相似文献
55.
Gabriel Lipshitz 《The Professional geographer》1991,43(4):445-456
Studies of migration patterns in national peripheries of countries do not distinguish between different population groups in these regions. The present study examines spatial patterns of Arab and Jewish populations in Israel's national periphery. The migration trends of Arabs and Jews in the northern national periphery (the Galilee) are compared with those of the southern national periphery (the Negev). The Arab and Jewish populations within these areas show different spatial patterns of migration: in both the northern and the southern peripheries, Jews tend to migrate from the periphery to the core, while Arabs tend to migrate within the periphery. These differences increase the ratio of Arabs to Jews in both regions. The findings suggest that researchers should examine subregions and subgroups when studying migration patterns. 相似文献
56.
Castro-Miguel Rutilio Legorreta-Paulín Gabriel Bonifaz-Alfonzo Roberto Aceves-Quesada José Fernando Castillo-Santiago Miguel Ángel 《Natural Hazards》2022,113(1):767-788
Natural Hazards - Little study has been done on the effect of the pixel neighborhood information when modeling landslide susceptibility using multiple logistic regression (MLR). The present... 相似文献
57.
58.
59.
The aim of this paper is to investigate different aspects of the seasonal-to-interannual temperature variability in Eastern Patagonia, the southernmost area of South America, east of the Andes Cordillera. Homogenous regions of seasonal variability and the atmospheric circulation patterns associated with warm and cold conditions in each of them are described in this study. Relationships between temperature in Eastern Patagonia and that registered in other areas of southern South America are also addressed. Results show that the northern and southern areas of Eastern Patagonia have different temperature variability in summer and autumn whereas the temperature variability tends to be more homogeneous within the region during winter and spring. Warm (cold) conditions in the northern areas are associated with reinforced (weakened) westerlies in summer, winter and spring whereas northerly (southerly) advections of warm (cold) air toward the region produce such conditions in autumn. Temperature in the southern portion of Eastern Patagonia is affected by anticyclonic (cyclonic) anomalies that enhance (reduce) the incoming solar radiation and induce reinforced (weakened) westerlies promoting warm (cold) conditions in the region. Furthermore, cyclonic (anticyclonic) anomalies at subpolar latitudes hinder (favor) outbreaks of cold air increasing (decreasing) the temperature over areas of Eastern Patagonia. The circulation anomalies associated with warm (cold) conditions in Eastern Patagonia also promote cold (warm) conditions over areas of northern Argentina, Paraguay and southern Brazil. Consequently, a dipole of temperature is detected in southern South America with centers of opposite sign over these regions. 相似文献
60.
To investigate how velocity variances and spectra are modified by the simultaneous action of topography and canopy, two flume
experiments were carried out on a train of gentle cosine hills differing in surface cover. The first experiment was conducted
above a bare surface while the second experiment was conducted within and above a densely arrayed rod canopy. The velocity
variances and spectra from these two experiments were compared in the middle, inner, and near-surface layers. In the middle
layer, and for the canopy surface, longitudinal and vertical velocity variances () were in phase with the hill-induced spatial mean velocity perturbation (Δu) around the so-called background state (taken here as the longitudinal mean at a given height) as predicted by rapid distortion
theory (RDT). However, for the bare surface case, and remained out of phase with Δu by about L/2, where L is the hill half-length. In the canopy layer, wake production was a significant source of turbulent energy for , and its action was to re-align velocity variances with Δu in those layers, a mechanism completely absent for the bare surface case. Such a lower ‘boundary condition’ resulted in longitudinal
variations of to be nearly in phase with Δu above the canopy surface. In the inner and middle layers, the spectral distortions by the hill remained significant for the
background state of the bare surface case but not for the canopy surface case. In particular, in the inner and middle layers
of the bare surface case, the effective exponents derived from the locally measured power spectra diverged from their expected
− 5/3 value for inertial subrange scales. These departures spatially correlated with the hill surface. However, for the canopy
surface case, the spectral exponents were near − 5/3 above the canopy though the minor differences from − 5/3 were also
correlated with the hill surface. Inside the canopy, wake production and energy short-circuiting resulted in significant departures
from − 5/3. These departures from − 5/3 also appeared correlated with the hill surface through the wake production contribution
and its alignment with Δu. Moreover, scales commensurate with Von Karman street vorticies well described wake production scales inside the canopy,
confirming the important role of the mean flow in producing wakes. The spectra inside the canopy on the lee side of the hill,
where a negative mean flow delineated a recirculation zone, suggested that the wake production scales there were ‘broader’
when compared to their counterpart outside the recirculation zone. Inside the recirculation zone, there was significantly
more energy at higher frequencies when compared to regions outside the recirculation zone. 相似文献