全文获取类型
| 收费全文 | 1049篇 |
| 免费 | 295篇 |
| 国内免费 | 457篇 |
专业分类
| 测绘学 | 86篇 |
| 大气科学 | 549篇 |
| 地球物理 | 374篇 |
| 地质学 | 439篇 |
| 海洋学 | 191篇 |
| 天文学 | 8篇 |
| 综合类 | 68篇 |
| 自然地理 | 86篇 |
出版年
| 2024年 | 4篇 |
| 2023年 | 17篇 |
| 2022年 | 34篇 |
| 2021年 | 45篇 |
| 2020年 | 63篇 |
| 2019年 | 81篇 |
| 2018年 | 46篇 |
| 2017年 | 55篇 |
| 2016年 | 61篇 |
| 2015年 | 59篇 |
| 2014年 | 78篇 |
| 2013年 | 93篇 |
| 2012年 | 81篇 |
| 2011年 | 95篇 |
| 2010年 | 82篇 |
| 2009年 | 67篇 |
| 2008年 | 94篇 |
| 2007年 | 91篇 |
| 2006年 | 93篇 |
| 2005年 | 63篇 |
| 2004年 | 77篇 |
| 2003年 | 52篇 |
| 2002年 | 54篇 |
| 2001年 | 45篇 |
| 2000年 | 28篇 |
| 1999年 | 46篇 |
| 1998年 | 46篇 |
| 1997年 | 19篇 |
| 1996年 | 31篇 |
| 1995年 | 30篇 |
| 1994年 | 25篇 |
| 1993年 | 14篇 |
| 1992年 | 12篇 |
| 1991年 | 5篇 |
| 1990年 | 4篇 |
| 1989年 | 6篇 |
| 1988年 | 2篇 |
| 1987年 | 2篇 |
| 1985年 | 1篇 |
排序方式： 共有1801条查询结果，搜索用时 187 毫秒
1.
1 INTRODUCTIONGlobal change research involves much geo-objectsand geo-process, such as climate and environmentalchange, substance and energy cycling, land-use/land-cover change (LUCC), interactivity between human and nature, etc.. So it need cooperation frommany research communities including international research programs groups such as IGBP (InternationalGeosphere-Biosphere Programme IPCC (Intergovemmental Panel on Climate Change), IHDP (InternationalHuman Dimension Program o… 相似文献
2.
Univariate and multivariate stress release models are fitted to historical earthquake data from North China. It is shown that a better fit is obtained by treating separately the Eastern part of the region, including the North China Plain and Bohai Sea, and the Western part of the region, including the Ordos Plateau and its Eastern boundary. Further improvement is obtained by fitting the large events (M7.6) and smaller events in the Western region by different stress release models. The comparisons are made by computing the likelihoods of the fitted models and discounting the number of parameters used by Akaike's AIC criterion. The models are used to develop long-term risk scenarios for the East and West regions. 相似文献
3.
Stefan Wessling Claudia Kuenzer Winfried Kessels Manfred W. Wuttke 《International Journal of Coal Geology》2008,74(3-4):175-184
Coal seams burning underneath the surface are recognized all over the world and have drawn increasing public attention in the past years. Frequently, such fires are analyzed by detecting anomalies like increased exhaust gas concentrations and soil temperatures at the surface. A proper analysis presumes the understanding of involved processes, which determine the spatial distribution and dynamic behavior of the anomalies.In this paper, we explain the relevance of mechanical and energy transport processes with respect to the occurrence of temperature anomalies at the surface. Two approaches are presented, aiming to obtain insight into the underground coal fire situation: In-situ temperature mapping and numerical simulation. In 2000 to 2005, annual temperature mapping in the Wuda (Inner Mongolia, PR China) coal fire area showed that most thermal anomalies on the surface are closely related to fractures, where hot exhaust gases from the coal fire are released. Those fractures develop due to rock mechanical failure after volume reduction in the seams. The measured signals at the surface are therefore strongly affected by mechanical processes.More insight into causes and effects of involved energy transport processes is obtained by numerical simulation of the dynamic behavior of coal fires. Simulations show the inter-relation between release and transport of thermal energy in and around underground coal fires. Our simulation results show a time delay between the coal fire propagation and the observed appearance of the surface temperature signal. Additionally, the overall energy flux away from the burning coal seam into the surrounding bedrock is about 30-times higher than the flux through the surface. This is of particular importance for an estimation of the energy released based on surface temperature measurements. Finally, the simulation results also prove that a fire propagation rate estimated from the interpretation of surface anomalies can differ from the actual rate in the seam. 相似文献
4.
A strain of thermophilic fungus Aspergillus fumigatus was cultured with K-bearing minerals to determine if microbe-mineral interactions enhance the release of mineralic potassium. Experiments were carried out in two settings, one with the mineral grains and the fungal cells in direct contact, and the other employing a membrane (pore size 0.22 μm) to separate the two. Measurements over a period of 30 days showed that, irrespective of the experimental setup, the concentration of free K in the culture was drastically higher than those in any of the control experiments where no living organism was present. Moreover, the occurrence of mineral-cell physical contact enhanced potassium release by an additional factor of 3 to 4 in comparison to the separation experiments. For contact experiments, Electron Probe Microanalysis revealed the formation of mycelium-mineral aggregates, and Atomic Force Microscopy imaging further indicated the possible ingestion of mineral particles by the fungus cells. Contrasting to what was observed and expected in control experiments, the potassium solubilization rate showed a positive dependence upon pH when fungi and minerals were mixed directly, and exhibited no correlations with solution acidity if cell-rock contact was restrained. These results appear to suggest that A. fumigatus promoted potassium release by means of at least three likely routes, one through the complexation of soluble organic ligands, another appealing to the immobile biopolymers such as the insoluble components of secretion, and the third related to the mechanical forces in association with the direct physical contact between cells and mineral particles. 相似文献
5.
作者研究三维变系数抛物方程 Douglas交替方向隐格式的稳定性和收敛性。采用 H1能量估计方法 ,证明格式按离散 H1范数是绝对稳定的 ,并且收敛阶为 O(Δ t2 + h2 ) 相似文献
6.
7.
Presented here is a compact explicit difference scheme of high accuracy for solving the extended Boussinesq equations.For time discretization,a three-stage explicit Runge-Kutta method with TVD property is used at predicting stage,a cubic spline function is adopted at correcting stage,which made the time discretization accuracy up to fourth order;For spatial discretization,a three-point explicit compact difference scheme with arbitrary order accuracy is employed.The extended Boussinesq equations derived by Beji and Nadaoka are solved by the proposed scheme.The numerical results agree well with the experimental data.At the same time,the comparisons of the two numerical results between the present scheme and low accuracy difference method are made,which further show the necessity of using high accuracy scheme to solve the extended Boussinesq equations.As a valid sample,the wave propagation on the rectangular step is formulated by the present scheme,the modelled results are in better agreement with the experimental data than those of Kittitanasuan. 相似文献
8.
The Princeton Ocean Model with realistic bottom topography has been used to investigate the summer temperature decrease in
the past 25 years in Fukuoka Bay. The vertical mixing of the model is expressed by a scheme that effectively includes the
influences of interannual variations of tidal currents and wind. The results show that the historical temperature decrease
in summer has been caused by tidal currents and wind weakening in the past 25 years in Fukuoka Bay. The weakening of tidal
currents and wind gives rise to weakening of the vertical mixing, and to enhancement of the estuarine circulation in the bay.
The enhancement of the estuarine circulation activates the inflow of open-ocean water toward Fukuoka Bay. Coastal water in
summer has therefore tended to be colder and more saline in the past 25 years. This interannual variation in coastal waters
is called “open-oceanization” in this study. On the basis of the numerical model, it is anticipated that the temperature will
decrease by 0.2°C in the next 25 years in Fukuoka Bay if the tide and wind weaken persistently as in the present bay. 相似文献
9.
10.