全文获取类型
收费全文 | 6956篇 |
免费 | 1472篇 |
国内免费 | 2660篇 |
专业分类
测绘学 | 397篇 |
大气科学 | 1944篇 |
地球物理 | 1388篇 |
地质学 | 3594篇 |
海洋学 | 1641篇 |
天文学 | 1111篇 |
综合类 | 431篇 |
自然地理 | 582篇 |
出版年
2024年 | 40篇 |
2023年 | 106篇 |
2022年 | 242篇 |
2021年 | 250篇 |
2020年 | 291篇 |
2019年 | 392篇 |
2018年 | 317篇 |
2017年 | 286篇 |
2016年 | 311篇 |
2015年 | 352篇 |
2014年 | 499篇 |
2013年 | 492篇 |
2012年 | 461篇 |
2011年 | 531篇 |
2010年 | 459篇 |
2009年 | 593篇 |
2008年 | 527篇 |
2007年 | 681篇 |
2006年 | 630篇 |
2005年 | 500篇 |
2004年 | 496篇 |
2003年 | 422篇 |
2002年 | 336篇 |
2001年 | 281篇 |
2000年 | 278篇 |
1999年 | 246篇 |
1998年 | 231篇 |
1997年 | 157篇 |
1996年 | 154篇 |
1995年 | 128篇 |
1994年 | 115篇 |
1993年 | 59篇 |
1992年 | 53篇 |
1991年 | 45篇 |
1990年 | 31篇 |
1989年 | 23篇 |
1988年 | 11篇 |
1987年 | 11篇 |
1986年 | 6篇 |
1985年 | 11篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1977年 | 2篇 |
1976年 | 7篇 |
1974年 | 1篇 |
1973年 | 4篇 |
1971年 | 2篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
301.
302.
垂荡式波浪能装置在海洋可再生能源开发中被广泛应用,通过浮子与摇杆在垂荡方向的相对运动吸收波浪能。在以往相关的运动预报数值分析中,通常基于微幅波假设,仅考虑浮子与摇杆在垂荡方向的运动,忽略摇杆其他自由度运动。建立并求解了垂荡式波浪能装置的非线性联合运动方程组,分析垂荡式波浪能装置的波浪载荷、浮子与平台连接处的受力情况。数值计算系统的运动响应,并将计算结果与已有的试验数据进行比较验证,结果表明数值模拟的垂荡式波能装置的运动响应与试验结果相符合。最后,应用本计算方法分析PTO(power take-off)参数对波能装置发电性能的影响。 相似文献
303.
Ran Wei Alan T. Murray 《International journal of geographical information science》2016,30(3):432-450
Location siting is an important part of service provision, with much potential to impact operational efficiency, safety, security, system reliability, etc. A class of location models seeks to optimize coverage of demand for service that is continuously distributed across space. Decision-making and planning contexts include police/fire resource allocation for a community, siting cellular towers to support cell phone signal transmission, locating emergency warning sirens to alert the public of severe weather and other related dangers, and many others as well. When facilities can be sited anywhere in continuous space to provide coverage to an entire region, this is a very computationally challenging problem to solve because potential demand for service is everywhere and there are an infinite number of potential facility sites to consider. This article develops a new parallel solution approach for this location coverage optimization problem through an iterative bounding scheme on multi-core architectures. The developed approach is applied to site emergency warning sirens in Dublin, Ohio, and fire stations in Elk Grove, California. Results demonstrate the effectiveness and efficiency of the proposed approach, enabling real-time analysis and planning. This work illustrates that the integration of cyberinfrastructure can significantly improve computational efficiency in solving challenging spatial optimization problems, fitting the themes of this special issue: cyberinfrastructure, GIS, and spatial optimization. 相似文献
304.
Richard L. Church 《International journal of geographical information science》2016,30(3):535-553
ABSTRACTThe efficiency of public investments and services has been of interest to geographic researchers for several decades. While in the private sector inefficiency often leads to higher prices, loss of competitiveness, and loss of business, in the public sector inefficiency in service provision does not necessarily lead to immediate changes. In many cases, it is not an entirely easy task to analyze a particular service as appropriate data may be difficult to obtain and hidden in detailed budgets. In this paper, we develop an integrative approach that uses cyber search, Geographic Information System (GIS), and spatial optimization to estimate the spatial efficiency of fire protection services in Los Angeles (LA) County. We develop a cyber-search process to identify current deployment patterns of fire stations across the major urban region of LA County. We compare the results of our search to existing databases. Using spatial optimization, we estimate the level of deployment that is needed to meet desired coverage levels based upon the location of an ideal fire station pattern, and then compare this ideal level of deployment to the existing system as a means of estimating spatial efficiency. GIS is adopted throughout the paper to simulate the demand locations, to conduct location-based spatial analysis, to visualize fire station data, and to map model simulation results. Finally, we show that the existing system in LA County has considerable room for improvement. The methodology presented in this paper is both novel and groundbreaking, and the automated assessments are readily transferable to other counties and jurisdictions. 相似文献
305.
Weijian Xue 《International journal of geographical information science》2016,30(3):554-572
ABSTRACTTo collect and dispose growing amounts of municipal solid waste (MSW) changed to be a hot topic along with the rapid urbanization in past decades. Cities are more and more dependent on the incineration instead of landfilling due to the cost-efficiency and environmental concerns. Considering the limited number of incineration plants and complicated situation of transportation in both spatial and temporal dimensions in different cities, the optimal routing for waste collection turns to be meaningful research topic. In this research, the ant colony optimization (ACO)-based multi-objective routing model coupled with min-max model and Dijkstra’s algorithm is proposed to address the question of which route to take from these waste-generating points to the target incineration plant(s) considering travel time, accident probability (black spots), and population exposure, so as to support the routing decision-making. The model is successfully implemented in Singapore and the effectiveness of the model has also been justified. Besides, few limitations of this research have also been discussed, some of which would also be the future directions of our research, especially the design and integration of a web-based routing decision-making support system. 相似文献
306.
Applying disk-based discontinuous deformation analysis (DDA) to simulate Donghekou landslide triggered by the Wenchuan earthquake 总被引:1,自引:0,他引:1
S. Amir Reza Beyabanaki Amvrossios C. Bagtzoglou Lanbo Liu 《Geomechanics and Geoengineering》2016,11(3):177-188
In this paper, for the first time, disk-based discontinuous deformation analysis (DDA) is applied to simulate a real landslide triggered by an earthquake. For this purpose, the kinematic behaviour of the Donghekou landslide triggered by the Wenchuan earthquake is simulated and the results obtained using disk-based DDA are compared with actual data. The comparisons show that there is a good agreement between the results obtained using disk-based DDA and observed data. The simulation results provided an understanding of the failure behaviour and temporal evolution of the landslide. This study shows that disk-based DDA is a practical numerical tool that can be used to simulate the post-failure behaviour of landslides triggered by an earthquake. 相似文献
307.
库车坳陷的构造变形及演化与南天山造山带的发育密切相关。库车坳陷新近纪以来的喜马拉雅晚期构造运动最为强烈,形成了天山山前大型冲断带,并造就了现今的构造格局。通过对库车坳陷北部构造样式的识别及各种应力场指示标志的测量、统计和构造解析,对野外获得的应力场指示标志划分了期次,认为喜马拉雅晚期应力场标志为近南北向挤压。结合库车坳陷区域构造要素,如地质体几何形态、边界条件、岩石力学参数等,运用弹性力学有限元数值模拟的方法获得了喜马拉雅晚期库车坳陷的区域应力场。模拟结果表明,库车坳陷喜马拉雅晚期最大主压应力方向为近南北向,与古应力场标志拟合较高,可以为库车坳陷裂缝预测和评价提供依据,对勘探开发有应用价值。 相似文献
308.
Emad Zolqadr Seyed Shahaboddin Yasrobi Mohammad Norouz Olyaei 《Geomechanics and Geoengineering》2016,11(1):1-12
This study surveys the performance of temporary soil nail walls with a maximum height of 29.3 m in the Yas project, located in Tehran. Some numerical models, with various modelling approaches, were developed using finite element software and the proper modelling approaches were specified and verified.The modelling results were analysed and compared with the in situ monitored data. The results demonstrate the model’s horizontal deformations are generally greater than the in situ monitored values. To decrease the differences between models and monitored results, the effect of variations of the soil parameters had been surveyed and the limits of needed variations were specified. 相似文献
309.
A depth-integrated model for simulating wave-induced longshore current was developed with unstructured grids. Effects of surface roller and horizontal mixing under combined waves and currents were incorporated in the numerical model. Recommended values of model coefficients were also proposed based on sensitivity analysis. Field observations and three series of laboratory measurements including two cases conducted on the plane beach and one implemented on the ideal inlet were employed to examine the predictive capability of this model. For the field case and laboratory cases conducted on the plane beach, numerical results were compared favorably with the measured data. For the case with an ideal inlet, simulated circulation pattern is supposed to be reasonable although some deviations between numerical results and measured data still can be detected. 相似文献
310.
The Eulerian?Lagrangian method (ELM) has been used by many ocean models as the solution of the advection equation, but the numerical error caused by interpolation imposes restriction on its accuracy. In the present study, hybrid N-order Lagrangian interpolation ELM (LiELM) is put forward in which the N-order Lagrangian interpolation is used at first, then the lower order Lagrangian interpolation is applied in the points where the interpolation results are abnormally higher or lower. The calculation results of a step-shaped salinity advection model are analyzed, which show that higher order (N=3?8) LiELM can reduce the mean numerical error of salinity calculation, but the numerical oscillation error is still significant. Even number order LiELM makes larger numerical oscillation error than its adjacent odd number order LiELM. Hybrid N-order LiELM can remove numerical oscillation, and it significantly reduces the mean numerical error when N is even and the current is in fixed direction, while it makes less effect on mean numerical error when N is odd or the current direction changes periodically. Hybrid odd number order LiELM makes less mean numerical error than its adjacent even number order LiELM when the current is in the fixed direction, while the mean numerical error decreases as N increases when the current direction changes periodically, so odd number of N may be better for application. Among various types of Hybrid N-order LiELM, the scheme reducing N-order directly to 1st-order may be the optimal for synthetic selection of accuracy and computational efficiency. 相似文献