全文获取类型
收费全文 | 4188篇 |
免费 | 687篇 |
国内免费 | 695篇 |
专业分类
测绘学 | 1710篇 |
大气科学 | 159篇 |
地球物理 | 991篇 |
地质学 | 1880篇 |
海洋学 | 297篇 |
天文学 | 26篇 |
综合类 | 292篇 |
自然地理 | 215篇 |
出版年
2024年 | 9篇 |
2023年 | 40篇 |
2022年 | 172篇 |
2021年 | 200篇 |
2020年 | 232篇 |
2019年 | 188篇 |
2018年 | 171篇 |
2017年 | 266篇 |
2016年 | 260篇 |
2015年 | 231篇 |
2014年 | 319篇 |
2013年 | 356篇 |
2012年 | 336篇 |
2011年 | 331篇 |
2010年 | 211篇 |
2009年 | 264篇 |
2008年 | 294篇 |
2007年 | 270篇 |
2006年 | 264篇 |
2005年 | 240篇 |
2004年 | 195篇 |
2003年 | 115篇 |
2002年 | 116篇 |
2001年 | 82篇 |
2000年 | 82篇 |
1999年 | 64篇 |
1998年 | 56篇 |
1997年 | 52篇 |
1996年 | 30篇 |
1995年 | 28篇 |
1994年 | 20篇 |
1993年 | 20篇 |
1992年 | 13篇 |
1991年 | 10篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1971年 | 1篇 |
1954年 | 2篇 |
1900年 | 3篇 |
1897年 | 1篇 |
1880年 | 1篇 |
排序方式: 共有5570条查询结果,搜索用时 31 毫秒
11.
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
12.
AbstractThe ground vibrations during pile driving operation have a drastic potential to undermine the surrounding structures both in land and reclaimed land. Particularly, reclaimed land necessitates ample application of pile driving due to the weak land condition. To prevent the structural damage, attenuation of the ground vibrations to an allowable level through active isolation of circular open trench is the scope of this study. In this research, finite element simulations of continuous impact pile driving process from the ground surface was executed with particular attention to the pile-soil interaction, and thereby, the efficiency of open trench application in attenuation of the unsafe distance of different structures was surveyed using the vibration sensitivity degree. Regarding the crucial parameters of an open trench (depth, width, and location), it was concluded that a sufficient high depth can attenuate the unsafe distance up to 68%, the trench width variations are less effective, and an average pile-trench distance is the most efficient option. The excavation volume was also concluded as another crucial parameter in open trench design which takes all three parameters into account. The trench depth equal to the pile’s maximum critical depth of vibration was inferred for an optimum design. 相似文献
13.
14.
Nowadays there are some chronic serious environmental problems, such as eutrophication, blue tide and so on, in a complicated coastal zone or a semi-enclosed bay, because the water exchanges between an inner bay and an outer sea is weak compared with the supply of contaminant. Under this situation, a method to improve the water quality by 3-dimensional small unsymmetrical structures has been proposed by Komatsu et al. In this paper, several numerical simulations of the tidal current and concentration for various arrangements of bottom roughness in a semi-enclosed model bay are carfled out with a depth-averaged 2-D numerical model. The model is solved by the hybrid finite analytic method with nonstaggered grid. And the SIMPLES algorithm with Rhie and Chow' s momentum interpolation technique is used for the simulation. The effect of Komatsu' s method for water purification is examined by numerical simulation. The result of numerical experiment indicates that it is possible to generate a new tidal residual current and to activate a tidal exchange by bottom roughness arrangement only. 相似文献
15.
Modelling nitrogen and phosphorus cycles and dissolved oxygen in the Zhujiang Estuary Ⅰ. Model development 总被引:1,自引:0,他引:1
wrmcrloxHuman activities related to the population growth and developrnent of industry and rnwhci-pality have led to the incrouing hadings of various POllutants into estudries during the past fewdecades. These increasing edlutant lOadings have caused declined estuallne hedth which can bemereured by a vdriety of indices. In order to obtain solutions to environrnent problerns, re-sources manageTnnt apencies are supporting a holistic approach to envirorirnental management.An effcient strategy t… 相似文献
16.
The mixing characteristics of particles such as dredged sediment of variable size discharged into cross flow are studied by a 3D numerical model, which is developed to model the particle-fluid two-phase flow. The Eulerian method with the modified k-ε parameterization of turbulence for the fluid phase is used to solve fluid phase, while a Lagrangian method for the solid phase (particles), both the processes are coupled through the momentum sources. In the model the wake turbulence induced by particles has been included as additional source term in the k-ε model; and the variable drift velocities of the particles are treated efficiently by the Lagrangian method in which the particles are tracked explicitly and the diffusion process is approximated by a random walk model. The hydrodynamic behavior of dumping a cloud of particles is governed by the total buoyancy of the cloud, the drag force on each particle and the velocity of cross-flow. The computed results show a roughly linear relationship between the displacement of the frontal position and the longitudinal width of the particle cloud. The particle size in the cloud and the velocity of cross flow dominate the flow behavior. The computed results are compared with the results of laboratory experiments and satisfactory agreement is obtained. 相似文献
17.
18.
东营城区高精度三维地震采集方法研究 总被引:3,自引:0,他引:3
根据东营城区内建筑物较多,环境干扰较大,地下构造复杂,断裂非常发育,目的层埋藏深,资料信噪比较低的特点,以地震老资料和钻井资料为基础,建立地震地质模型,利用射线追踪技术选取合适的观测系统参数。充分利用卫星数字地图,没计了灵活多变的观测系统,采用可控震源与炸药震源配合使用方法,及时对城区内地下面元的覆盖次数、方位角和炮检距的分布进行质量监控,利用现场处理系统对资料进行及时分析,提高了地震资料品质。所获得的东营城区高精度三维地震采集资料显示,其浅中层分辨率和中深层信噪比都有了明显改善,取得了良好的地质效果。 相似文献
19.
20.