全文获取类型
收费全文 | 3246篇 |
免费 | 436篇 |
国内免费 | 470篇 |
专业分类
测绘学 | 154篇 |
大气科学 | 186篇 |
地球物理 | 772篇 |
地质学 | 732篇 |
海洋学 | 1474篇 |
天文学 | 177篇 |
综合类 | 195篇 |
自然地理 | 462篇 |
出版年
2024年 | 10篇 |
2023年 | 19篇 |
2022年 | 91篇 |
2021年 | 97篇 |
2020年 | 114篇 |
2019年 | 146篇 |
2018年 | 101篇 |
2017年 | 138篇 |
2016年 | 130篇 |
2015年 | 133篇 |
2014年 | 163篇 |
2013年 | 204篇 |
2012年 | 158篇 |
2011年 | 157篇 |
2010年 | 161篇 |
2009年 | 197篇 |
2008年 | 205篇 |
2007年 | 209篇 |
2006年 | 190篇 |
2005年 | 177篇 |
2004年 | 176篇 |
2003年 | 144篇 |
2002年 | 120篇 |
2001年 | 105篇 |
2000年 | 118篇 |
1999年 | 88篇 |
1998年 | 79篇 |
1997年 | 73篇 |
1996年 | 59篇 |
1995年 | 53篇 |
1994年 | 70篇 |
1993年 | 43篇 |
1992年 | 44篇 |
1991年 | 32篇 |
1990年 | 21篇 |
1989年 | 24篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1983年 | 14篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 1篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有4152条查询结果,搜索用时 234 毫秒
51.
Eric Wolanski David Williams Simon Spagnol Hubert Chanson 《Estuarine, Coastal and Shelf Science》2004,60(4):629-636
Measurements in the macro-tidal Daly Estuary show that the presence of an undular tidal bore contributed negligibly to the dissipation of tidal energy. No recirculation bubble was observed between a trough and the following wave crest in the lee waves following the undular bore. This differs to stationary undular bores in laboratory experiments at larger Froude numbers where a recirculation bubble exists. Secondary motions and the turbulence generated by the undular bore had no measurable influence on the sediment transport. This situation contrasts with the intense sediment resuspension observed in breaking tidal bores. The tidally averaged sediment budget in the Daly Estuary was controlled by the asymmetry of tidal currents. The undular bore may widen the river by breaking along the banks that it undercuts, leading to bank slippage. A patch of river-wide macro-turbulence of 3-min duration occurred about 20 min after the passage of the bore during accelerating tidal currents. 相似文献
52.
This paper describes the extension of a fluid-flow simulations method to capture the free surface evolution around a full-scale Tension Leg Platform (TLP). The focus is on the prediction of the resulting hydrodynamic loading on the various elements of the TLP in turbulent flow conditions and, in particular, on quantifying the effects of the free surface distortion on this loading. The basic method uses finite-volume techniques to discretize the differential equations governing conservation of mass and momentum in three dimensions. The time-averaged forms of the equations are used, and the effects of turbulence are accounted for by using a two-equation, eddy-viscosity closure. The method is extended here via the incorporation of surface-tracking algorithm on a moving grid to predict the free-surface shape. The algorithm was checked against experimental measurements from two benchmark flows: the flow over a submerged semi-circular cylinder and the flow around a floating parabolic hull. Predictions of forces on a model TLP were then obtained both with and without allowing for the deformation of the free surface. The results suggest that the free surface effects on the hydrodynamic loads are small for the values of Froude number typically encountered in offshore engineering practice. 相似文献
53.
54.
55.
Benthic photosynthesis in submerged Wadden Sea intertidal flats 总被引:3,自引:1,他引:3
Markus Billerbeck Hans Ry Katja Bosselmann Markus Huettel 《Estuarine, Coastal and Shelf Science》2007,71(3-4):704-716
In this study we compare benthic photosynthesis during inundation in coarse sand, fine sand, and mixed sediment (sand/mud) intertidal flats in the German Wadden Sea. In situ determinations of oxygen-, DIC- and nutrient fluxes in stirred benthic chamber incubations were combined with measurements of sedimentary chlorophyll, incident light intensity at the sediment surface and scalar irradiance within the sediment. During submergence, microphytobenthos was light limited at all study sites as indicated by rapid response of gross photosynthesis to increasing incident light at the sea floor. However, depth integrated scalar irradiance was 2 to 3 times higher in the sands than in the mud. Consequently, gross photosynthesis in the net autotrophic fine sand and coarse sand flats during inundation was on average 4 and 11 times higher than in the net heterotrophic mud flat, despite higher total chlorophyll concentration in mud. Benthic photosynthesis may be enhanced in intertidal sands during inundation due to: (1) higher light availability to the microphytobenthos in the sands compared to muds, (2) more efficient transport of photosynthesis-limiting solutes to the microalgae with pore water flows in the permeable sands, and (3) more active metabolic state and different life strategies of microphytobenthos inhabiting sands. 相似文献
56.
57.
In this study, the impact of oceanic processes on the sensitivity of transient climate change is investigated using two sets of coupled experiments with and without tidal forcing, which are termed Exp_Tide and Exp_Control,respectively. After introducing tidal forcing, the transient climate response(TCR) decreases from 2.32 K to 1.90 K,and the surface air temperature warming at high latitudes decreases by 29%. Large ocean heat uptake efficiency and heat storage can explain the low TCR in Exp_Tide. Approximately 21% more heat is stored in the ocean in Exp_Tide(1.10×10~(24) J) than in Exp_Control(0.91×10~(24) J). Most of the large ocean warming occurs in the upper 1 000 m between 60°S and 60°N, primarily in the Atlantic and Southern Oceans. This ocean warming is closely related to the Atlantic Meridional Overturning Circulation(AMOC). The initial transport at mid-and high latitudes and the decline in the AMOC observed in Exp_Tide are both larger than those observed in Exp_Control. The spatial structures of AMOC are also different with and without tidal forcing in present experiments. The AMOC in Exp_Tide has a large northward extension. We also investigated the relationship between AMOC and TCR suggested by previous studies using the present experiments. 相似文献
58.
59.
60.
Beginning June of 1993 suites of 13 water samples have been collected at Oyster Landing, North Inlet (SC), every 20 days covering two consecutive tidal cycles at 2.07 h intervals. In order to ascertain whether this large (and still growing) water chemistry data set can be used to determine tidal fluxes of nutrients and sediments, we coupled measured concentrations to estimates of instantaneous tidal discharge based on a basin water storage curve and hindcast tides. The mean advective fluxes of all constituents, including salt, showed statistically significant exports. This result, however, is largely due to an ebb bias in the sampling protocol, which resulted in 52% of the samples being collected on ebb tide versus a theoretical percentage of 48%. When this bias was corrected by reducing the mean discharge (−610 l s−1) to a value (−125 l s−1) that produced a balance between the mean advective and dispersive salt fluxes, the advective fluxes of the other constituents were reduced to values that are not significantly different from zero. In addition to a statistically significant dispersive influx of salt, significant dispersive exports were found for DON, NH4, DOP, PO4 and DOC. All particulate constituents (PN, PP, ISS and OSS) yielded dispersive fluxes that were not significantly different from zero. Annual material budgets for the Oyster Landing basin based on the dispersive fluxes of all constituents (except salt) are generally similar in magnitude and direction to those measured by [Dame, R.F., Spurrier, J.D., Williams, T.M., Kjerfve, B., Zingmark, R.G., Wolaver, T.G., Chrzanowski, T.H., McKeller, H.N., Vernberg, F.J., 1991. Annual material processing by a salt marsh-estuarine basin in South Carolina, USA. Marine Ecology Progress Series 72, 153–166.] in the nearby and ecologically similar Bly Creek basin, indicating that the dispersive fluxes determined in this study are realistic. We offer suggestions for improving the reliability and usefulness of future Oyster Landing water quality data. 相似文献