全文获取类型
收费全文 | 4005篇 |
免费 | 368篇 |
国内免费 | 473篇 |
专业分类
测绘学 | 21篇 |
大气科学 | 292篇 |
地球物理 | 1412篇 |
地质学 | 379篇 |
海洋学 | 1275篇 |
天文学 | 705篇 |
综合类 | 68篇 |
自然地理 | 694篇 |
出版年
2024年 | 15篇 |
2023年 | 42篇 |
2022年 | 47篇 |
2021年 | 45篇 |
2020年 | 64篇 |
2019年 | 106篇 |
2018年 | 69篇 |
2017年 | 89篇 |
2016年 | 80篇 |
2015年 | 91篇 |
2014年 | 119篇 |
2013年 | 209篇 |
2012年 | 61篇 |
2011年 | 147篇 |
2010年 | 149篇 |
2009年 | 248篇 |
2008年 | 292篇 |
2007年 | 358篇 |
2006年 | 250篇 |
2005年 | 198篇 |
2004年 | 215篇 |
2003年 | 232篇 |
2002年 | 206篇 |
2001年 | 140篇 |
2000年 | 159篇 |
1999年 | 177篇 |
1998年 | 174篇 |
1997年 | 84篇 |
1996年 | 118篇 |
1995年 | 97篇 |
1994年 | 91篇 |
1993年 | 81篇 |
1992年 | 75篇 |
1991年 | 62篇 |
1990年 | 57篇 |
1989年 | 45篇 |
1988年 | 30篇 |
1987年 | 27篇 |
1986年 | 19篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 19篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1954年 | 4篇 |
排序方式: 共有4846条查询结果,搜索用时 15 毫秒
51.
If convection in the Earth's liquid outer core is disrupted, degrades to turbulence and begins to behave in a chaotic manner, it will destabilize the Earth's magnetic field and provide the seeds for kimberlite melts via turbulent jets of silicate rich core material which invade the lower mantle. These (proto-) melts may then be captured by extreme amplitude solitary nonlinear waves generated through interaction of the outer core surface with the base of the mantle. A pressure differential behind the wave front then provides a mechanism for the captured melt to ascend to the upper mantle and crust so quickly that emplacement may indirectly promote a type of impact fracture cone within the relatively brittle crust. These waves are very rare but of finite probability. The assumption of turbulence transmission between layers is justified using a simple three-layer liquid model. The core derived melts eventually become frozen in place as localised topographic highs in the Mohorovicic discontinuity (Moho), or as deep rooted intrusive events. The intrusion's final composition is a function of melt contamination by two separate sources: the core contaminated mantle base and subducted Archean crust. The mega-wave hypothesis offers a plausible vehicle for early stage emplacement of kimberlite pipes and explains the age association of diamondiferous kimberlites with magnetic reversals and tectonic plate rearrangements. 相似文献
52.
P. Pato M. Otero M. Válega C.B. Lopes M.E. Pereira A.C. Duarte 《Marine pollution bulletin》2010,60(10):1658-1666
After having estimated the patterns of flow to the ocean and found some seasonal and tidal differences, mainly with regard to the relative importance of dissolved and particulate fractions, mercury partitioning at the interface between a contaminated lagoon and the Atlantic Ocean was investigated during four tidal cycles in contrasting season and tidal regimes. Mercury was found to be located predominantely in the particulate fraction throughout the year, contributing to its retention within the system. Seasonal conditions, variations in marine and fluvial signals and processes affecting bed sediment resuspension influenced the character and concentration of suspended particulate matter in the water column. Variation in the nature, levels and partitioning of organic carbon in the particulate fraction affected levels of particulate mercury as well as mercury partitioning. These results highlight the dominant role of suspended particulate matter in the distribution of anthropogenic mercury and reinforce the importance of competitive behavior related to organic carbon in mercury scavenging. 相似文献
53.
S. Jane Arthur 《Astrophysics and Space Science》2002,281(1-2):267-270
The radiation produced by the gas cooling behind a fast supernova remnant shock in the interstellar medium is capable of ionizing
the undisturbed medium ahead of the shock wave. In this work I investigate the nonequilibrium evolution of these photoionized
precursor regions by means of radiation-hydrodynamic simulations of supernova remnant evolution.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
54.
面波频散反演是揭示地下速度结构的一项重要手段.传统面波勘探技术侧重于多台站阵列数据频散分析.旋转地震学理论框架下六分量地震观测时,仅利用单台站记录的平动与旋转分量就可以获得面波频散曲线.本文从频率域谐振分析出发,利用模态叠加正演方法,讨论了不同模型下平动与旋转联合估算Rayleigh波相速度的可靠性.结果表明:单台站多分量地震数据估算的频散曲线受多种因素影响,估计过程存在一定的系统误差;典型浅层地质模型下,单点估算与多道面波分析方法(MASW)提取的Rayleigh波频散曲线在低频段吻合性好;若要降低单点多分量地震估算的系统误差,仍需研发配套的波场分离与不同阶频散谱的高精度提取技术.
相似文献55.
56.
Mathijs van Ledden Geoffrey Vaughn Joost Lansen Frank Wiersma Mewburn Amsterdam 《Continental Shelf Research》2009
The objective of the research is to analyze in detail the causes and consequences of the unusual event at the coast of Guyana (South America) during October 16–19, 2005. Several sea defense structures were damaged and flooding of low-lying areas occurred. A data analysis of offshore wave and water level characteristics shows an abrupt change in wave direction from east to almost north on October 16, 2005 and a sudden increase in the offshore peak period up to extreme values. The offshore significant wave height was also relatively high, and these wave characteristics coincided with springtide conditions. The long-wave periods and the sharp transition in wave direction indicate that this event is associated with swell waves generated by a depression far away. An analysis of hurricanes and depressions reveals that a severe depression in the Northern Atlantic Ocean during October 11–15 was the origin of this swell event. Numerical computations with SWAN have been carried out to investigate the propagation of the offshore wave characteristics towards the shoreline. The SWAN model includes wave damping due to the presence of soft mud deposits. A calibration of the parameters has been carried out using joint offshore and onshore wave data from November 2006. The numerical simulations of the event in October 2005 clearly demonstrate that the mud banks damp the wave heights, but have almost no effect on the peak period. The resulting waves at the steep sea walls can be classified as surging waves causing severe runup and overtopping. The obtained insights are translated into practical recommendations for the Guyana Sea and River Defence Division in Guyana to build a sustainable management and maintenance of the sea defenses in the future. 相似文献
57.
This paper presents a new perturbation solution of the non-linear Boussinesq equation for one-dimensional tidal groundwater flow in a coastal unconfined aquifer. Built upon the work of Parlange et al. [Parlange, J.-Y., Stagnitti, F., Starr, J.L., Braddock, R.D., 1984. Free-surface flow in porous media and periodic solution of the shallow-flow approximation, J. Hydrol., 70, 251–263], the solution adopts a new perturbation parameter that is by definition less than unit, and thus is applicable to a wider range of physical conditions within the constraint of the Boussinesq approximation. This approach avoids a secular term in the third-order perturbation equation of Parlange et al. (1984), enabling the derivation of the third- and higher-order solutions. In comparison with a numerical (“exact”) solution, the new perturbation solution is shown to be slightly more accurate than that of Parlange et al. (1984) with the second-order approximation. The obtained third-order solution exhibits considerable improvement in accuracy. In relatively simple analytical forms, the present perturbation solution will help to understand better the non-linear characteristics of tidal water table fluctuations in as modeled by the non-linear Boussinesq equation coastal unconfined aquifers. 相似文献
58.
Joanna Staneva Emil V. Stanev Jörg-Olaf Wolff Thomas H. Badewien Rainer Reuter Burghard Flemming Alexander Bartholomä Karsten Bolding 《Continental Shelf Research》2009
This work deals with analysis of hydrographic observations and results of numerical simulations. The data base includes acoustic Doppler current profilers (ADCP) observations, continuous measurements on data stations and satellite data originating from the medium resolution imaging spectrometer (MERIS) onboard the European Space Agency (ESA) satellite ENVISAT with a spatial resolution of 300 m. Numerical simulations use nested models with horizontal resolutions ranging from 1 km in the German Bight to 200 m in the East Frisian Wadden Sea coupled with a suspended matter transport model. Modern satellite observations have now a comparable horizontal resolution with high-resolution numerical model of the entire area of the East Frisian Wadden Sea allowing to describe and validate new and so far unknown patterns of sediment distribution. The two data sets are consistent and reveal an oscillatory behaviour of sediment pools to the north of the back-barrier basins and clear propagation patterns of tidally driven suspended particulate matter outflow into the North Sea. The good agreement between observations and simulations is convincing evidence that the model simulates the basic dynamics and sediment transport processes, which motivates its further use in hindcasting, as well as in the initial steps towards forecasting circulation and sediment dynamics in the coastal zone. 相似文献
59.
Numerical simulation of sloshing waves in a 3D tank based on a finite element method 总被引:8,自引:0,他引:8
The sloshing waves in a three dimensional (3D) tank are analysed using a finite element method based on the fully non-linear wave potential theory. When the tank is undergoing two dimensional (2D) motion, the calculated results are found to be in very good agreement with other published data. Extensive calculation has been made for the tank in 3D motion. As in 2D motion, in addition to normal standing waves, travelling waves and bores are also observed. It is found that high pressures occur in various circumstances, which could have important implications for many engineering designs. 相似文献
60.
北大西洋涛动位相转换的数值研究 总被引:1,自引:0,他引:1
借助一个非线性准地转正压模型,模拟了基本西风气流的强弱、不同空间分布的天气尺度扰动涡对北大西洋涛动(NAO)位相转换的作用,以及大尺度双波地形对其的影响.通过一系列的对比试验发现,适当弱的基本西风气流有利于下游系统西退使NAO由正(负)位相转换为负(正)位相;振幅强、活动范围大的天气尺度扰动波是NAO由负位相转换为正位... 相似文献