全文获取类型
收费全文 | 81827篇 |
免费 | 1213篇 |
国内免费 | 1366篇 |
专业分类
测绘学 | 2766篇 |
大气科学 | 5892篇 |
地球物理 | 16431篇 |
地质学 | 32008篇 |
海洋学 | 6026篇 |
天文学 | 14937篇 |
综合类 | 2342篇 |
自然地理 | 4004篇 |
出版年
2022年 | 384篇 |
2021年 | 645篇 |
2020年 | 697篇 |
2019年 | 704篇 |
2018年 | 6087篇 |
2017年 | 5299篇 |
2016年 | 4258篇 |
2015年 | 1261篇 |
2014年 | 1875篇 |
2013年 | 3034篇 |
2012年 | 2837篇 |
2011年 | 4965篇 |
2010年 | 4124篇 |
2009年 | 5126篇 |
2008年 | 4285篇 |
2007年 | 4623篇 |
2006年 | 2328篇 |
2005年 | 1913篇 |
2004年 | 2048篇 |
2003年 | 1942篇 |
2002年 | 1697篇 |
2001年 | 1343篇 |
2000年 | 1317篇 |
1999年 | 1080篇 |
1998年 | 1144篇 |
1997年 | 1042篇 |
1996年 | 859篇 |
1995年 | 859篇 |
1994年 | 803篇 |
1993年 | 663篇 |
1992年 | 605篇 |
1991年 | 621篇 |
1990年 | 697篇 |
1989年 | 588篇 |
1988年 | 553篇 |
1987年 | 705篇 |
1986年 | 582篇 |
1985年 | 745篇 |
1984年 | 811篇 |
1983年 | 806篇 |
1982年 | 685篇 |
1981年 | 715篇 |
1980年 | 634篇 |
1979年 | 586篇 |
1978年 | 586篇 |
1977年 | 527篇 |
1976年 | 500篇 |
1975年 | 509篇 |
1974年 | 494篇 |
1973年 | 521篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Michael S. Dinniman John M. Klinck Walker O. Smith Jr. 《Deep Sea Research Part II: Topical Studies in Oceanography》2003,50(22-26):3103
Transport of warm, nutrient-rich Circumpolar Deep Water (CDW) onto Antarctic continental shelves and coastal seas has important effects on physical and biological processes. The present study investigates the locations of this transport and its dynamics in the Ross Sea with a high-resolution three-dimensional numerical model. The model circulation is forced by daily wind stress along with heat and salt fluxes calculated from atmospheric climatologies by bulk formulae. All surface fluxes are modified by an imposed climatological ice cover. Waters under the Ross Ice Shelf are not included explicitly, but their effect on temperature and salinity is imposed in a buffer zone at the southern end of the model domain. A simple nutrient uptake is calculated based on the climatological chlorophyll distribution and Monod uptake kinetics.Model circulation is strongly affected by bottom topography, due to weak stratification, and agrees with schematics of the general flow and long-term current measurements except near the southern boundary. The sea-surface temperature is similar to satellite estimates except that the warmest simulated temperatures are slightly higher than observations. There is a significant correlation between the curvature of the shelf break and the transport across the shelf break. A momentum term balance shows that momentum advection helps to force flow across the shelf break in specific locations due to the curvature of the bathymetry (that is, the isobaths curve in front of the flow). For the model to create a strong intrusion of CDW onto the shelf, it appears two mechanisms are necessary. First, CDW is driven onto the shelf at least partially due to momentum advection and the curvature of the shelf break; then, the general circulation on the shelf takes the CDW into the interior. 相似文献
992.
993.
C. K. Paull W. Ussler H. G. Greene R. Keaten P. Mitts J. Barry 《Geo-Marine Letters》2002,22(4):227-232
A sediment gravity flow descended through the axis of Monterey Canyon on 20 December 2001 at 13:35 Pacific standard time. The timing of this event is documented by a current-meter package which recorded an 11.9-dbar pressure increase in less than 10 min and was found 550 m down-canyon from its deployment site, buried completely within a >70-cm-thick gravity flow deposit. This event is believed to have started in less than 290 m of water because an instrument at this location was also lost at the same time. A 178-cm core collected after the event from the axis of the canyon at 1,297-m water depth contained fresh, greenish, chlorophyll-rich organic material at 32-cm sub-bottom depth, suggesting the event extended to this water depth. The only trigger identified for this mass movement event appears to be moderate sea and surf conditions. Thus, gravity flow events of this magnitude do not require an exceptional triggering event. 相似文献
994.
995.
The aim of this paper is to present an analytical expression for the vertical distribution of the correlation between the horizontal (
) and vertical (
) wave velocity components. This quantity,
, which appears explicitly in the time-averaged momentum balance equations, has been shown to play an important role in the vertical distribution of wave-induced currents.The proposed formulation for
is based on an identity that relates the effective (wave) shear stress
to the effective (wave) normal stresses (
2 and
2) and to the vorticity of the oscillatory flow
gw. This general expression has been applied to simplified situations and has been shown to degenerate into other existing formulations with comparable simplifying assumptions, viz. irrotational waves in shallow water over an arbitrary bottom topography and breaking waves over a horizontal bottom.The model has also been applied to the case of waves interacting with a depth-varying current over a horizontal bottom, in which preliminary results have been obtained for a simplified situation invoking linear (small-amplitude) wave theory. 相似文献
996.
V. A. Dulov S. I. Klyushnikov V. N. Kudryavtsev O. V. Shulgin O. G. Shcherbak 《Physical Oceanography》1991,2(4):269-282
An overview of experiments is given on the observation of the dependence of the intensity of wind wave breaking on large-scale
currents' inhomogeneities and atmospheric boundary layer stratification. The data were interpreted using a model in which
the variance of the wind wave breaking intensity reflects fluctuations in the influx of energy to wind waves due to various
factors.
Translated by V. Puchkin. 相似文献
997.
Large deposits of marine clays are encountered all along the Indian coastal belt. These clays are pleistocene to recent in origin, are considered to be young, and were deposited in a salt or brackish environment. These clays are very soft in consistency with low in-situ strength and high compressibility. The properties of these soil deposits depend mainly on the clay minerals present. In the present investigation, the mineralogical studies of some Cochin marine clays were carried out using XRD technique. The physical and chemical properties of these deposits were also reported. The test results were compared with some earlier reported works on marine clays. 相似文献
998.
The effects of varying intensities of off-road vehicle and pedestrian traffic on vegetation height and percent-cover were investigated at two sites representing pioneer and climax dune shrubland communities in South African dune systems. In all cases, a decreasing trend in vegetation height and percentage cover subsequent to application of the treatments was evident, although this was more clear in the shrub than in the pioneer community. The impact on vegetation variables increased with increasing intensity of vehicle and pedestrian treatments. Vehicles driven along a curved path resulted in greater vegetation destruction than those driven along a straight path. High intensity (single application) treatments resulted in an initial decrease in vegetation height and cover immediately after the impact, which was followed by a further decline over the next 3 months. This two-step response was attributed to the subsequent gradual death of the vegetation which was not evident immediately following the impact. Due to their faster growth rate, pioneer dune communities appear to have the capacity to recover following impacts, while dune shrub communities tend to be more vulnerable, exhibiting signs of damage for longer periods. The results of this study have value for managers of coastal dune systems, particularly those impacted by human recreational activities. 相似文献
999.
S. G. Buynov 《Physical Oceanography》1992,3(6):471-473
The possibilities of measuring the temperature of seawater as a continuous medium are analysed. It is shown that contemporary thin-film platinum resistance thermometers are inadequate for seawater temperature measurements because of their lag and resolution. The following shortcomings of these thermometers are indicated: heat dissipation by the terminals and the need for them to be hermetically sealed. A prospective improved design is suggested for a thermomagnetic temperature transducer, which provides for the minimal possible lag for the required resolution.Translated by V. Puchkin. 相似文献
1000.