全文获取类型
收费全文 | 13672篇 |
免费 | 2874篇 |
国内免费 | 3599篇 |
专业分类
测绘学 | 2793篇 |
大气科学 | 2816篇 |
地球物理 | 3412篇 |
地质学 | 6610篇 |
海洋学 | 1918篇 |
天文学 | 473篇 |
综合类 | 933篇 |
自然地理 | 1190篇 |
出版年
2024年 | 48篇 |
2023年 | 155篇 |
2022年 | 482篇 |
2021年 | 567篇 |
2020年 | 610篇 |
2019年 | 726篇 |
2018年 | 593篇 |
2017年 | 720篇 |
2016年 | 702篇 |
2015年 | 757篇 |
2014年 | 1013篇 |
2013年 | 1078篇 |
2012年 | 1032篇 |
2011年 | 1038篇 |
2010年 | 802篇 |
2009年 | 1018篇 |
2008年 | 1025篇 |
2007年 | 1073篇 |
2006年 | 1014篇 |
2005年 | 835篇 |
2004年 | 784篇 |
2003年 | 599篇 |
2002年 | 596篇 |
2001年 | 438篇 |
2000年 | 413篇 |
1999年 | 355篇 |
1998年 | 318篇 |
1997年 | 272篇 |
1996年 | 219篇 |
1995年 | 174篇 |
1994年 | 181篇 |
1993年 | 118篇 |
1992年 | 94篇 |
1991年 | 68篇 |
1990年 | 54篇 |
1989年 | 25篇 |
1988年 | 38篇 |
1987年 | 26篇 |
1986年 | 15篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 9篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1971年 | 4篇 |
1954年 | 5篇 |
1900年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
海拉尔盆地乌尔逊凹陷古流体动力场数值模拟 总被引:5,自引:0,他引:5
杨金侠 《地球科学与环境学报》2003,25(3):41-47
首先对地下水动力场进行数学描述,以水动力为主线,建立适合该地区的数学模型,选择正确的地质模型参数,主要采用数值计算和模拟等手段,在恢复出乌尔逊凹陷主要目的层在不同地质历史时期古水动力的基础上又恢复出古流体势的演化历史。整体上,在乌尔逊凹陷,各主要地质时期的油势演化特征为西部地区大于东部地区,乌南大于乌北,且低势区的发育有较好的继承性。最后,依据油气聚集理论,进行油气运移聚集系统的划分、油气运移方向的分析,从而得出有关研究区油气运移聚集条件的认识,主要从流体动力的角度考虑,指出有利聚集区,认为在乌尔逊凹陷苏4~苏18井区、苏132~苏17~铜2井区及巴1~巴2~巴4井区为有利油气运移聚集区。 相似文献
32.
33.
Stable oxygen isotope analysis and measurement of several dissolved cations and anions of bulk meltwater samples have provided information about the hydrochemical environment of the glacial hydrological system at Imersuaq Glacier, an outlet tongue from the Greenland ice‐sheet, West Greenland. The samples were collected at frequent intervals during the period 20–28 July 2000 in a small (<20 L s?1) englacial meltwater outlet at the glacier margin. The results document the following findings: (i) a marked diurnal variation of δ18O is related to the composition of oxygen isotope provenances, mainly near‐marginal local superimposed ice and basal up‐sheared ice further up‐glacier; (ii) a relationship is seen between all base cations (Na+, K+, Ca2+, Mg2+), SO42? and δ18O, indicating that solute acquisition is provided by solid–solution contact with the up‐sheared ice—as the relationship with Cl? is weak the influence of seasalt‐derived solutes is small in the area; (iii) when the melt rate is high, two diurnal maxima of δ18O values and solute concentrations are measured, and it is suggested that a snow meltwater component is responsible for the second maximum of δ18O—a short residence time leads to a delayed decrease in ion concentrations. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
34.
35.
以首都圈地区现今活动断层上近20年的位移测量资料为依据,用二维线弹性有限元对该区断层的活动特征进行了拟合,并结合有关资料讨论了该区的地震危险性。结果表明:1977-1986年间该区主压应力优势方位与华北较一致,约为N45°-80°E;1986-1990年其主压应力方向向北偏转,约为N5°-60°E;1990年至现在其主压应力又向东偏转,角度大于第一阶段,约为N80°-95°E。该区的张家口-延庆一带近期有发生中强震的可能;丰镇-阳高-大同地区和凉城-古营盘地区应力较高,也应引起注意。 相似文献
36.
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
37.
A theoretical model for wind‐sand flow is developed by considering the coupling between wind flow and sand particle motion, the latter subject to the Magnus effect, under different atmospheric stability conditions. Using this model, the characteristics of the wind‐sand flow are discussed in detail. The results show that the atmospheric stability and the Magnus effect both have a strong influence on wind profiles and on the trajectories of sand particles. This approach produces results with characteristics that differ from those previously reported; the latter only applying to atmospheric conditions of neutral stability. The saltating sand reaches a greater height under non‐neutral stability than under neutral stability, while the maximum horizontal distance is greater under unstable conditions and is smaller under stable conditions than under conditions of neutral stability. 相似文献
38.
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
39.
Delineation of groundwater protection zones by the backward particle tracking method: theoretical background and GIS-based stochastic analysis 总被引:1,自引:0,他引:1
Konstadinos N. Moutsopoulos Alexandra Gemitzi Vassilios A. Tsihrintzis 《Environmental Geology》2008,54(5):1081-1090
The backward particle tracking method, an effective and powerful tool that can be used to delineate groundwater protection
zones, is presented. The theoretical background and insights on the applicability of this method are provided. Moreover, the
present work enriches the backward particle tracking method with an uncertainty analysis concerning the porosity values, applying
a Monte Carlo (MC) approach, coupled with the use of geographical information systems (GIS). As an application example, a
wellfield in the Komotini area, Greece, is investigated. The present study may serve as a potential guideline for wellfield
delineation, particularly in areas like Greece where lack of data related to the hydrogeological system is often a problem. 相似文献
40.
Development of a 3D GIS and its application to karst areas 总被引:1,自引:0,他引:1
There is a growing interest in modeling and analyzing karst phenomena in three dimensions. This paper integrates geology,
groundwater hydrology, geographic information system (GIS), database management system (DBMS), visualization and data mining
to study karst features in Huaibei, China. The 3D geo-objects retrieved from the karst area are analyzed and mapped into different
abstract levels. The spatial relationships among the objects are constructed by a dual-linker. The shapes of the 3D objects
and the topological models with attributes are stored and maintained in the DBMS. Spatial analysis was then used to integrate
the data in the DBMS and the 3D model to form a virtual reality (VR) to provide analytical functions such as distribution
analysis, correlation query, and probability assessment. The research successfully implements 3D modeling and analyses in
the karst area, and meanwhile provides an efficient tool for government policy-makers to set out restrictions on water resource
development in the area. 相似文献