全文获取类型
收费全文 | 1029篇 |
免费 | 140篇 |
国内免费 | 120篇 |
专业分类
测绘学 | 127篇 |
大气科学 | 119篇 |
地球物理 | 315篇 |
地质学 | 294篇 |
海洋学 | 200篇 |
天文学 | 22篇 |
综合类 | 54篇 |
自然地理 | 158篇 |
出版年
2024年 | 1篇 |
2023年 | 11篇 |
2022年 | 19篇 |
2021年 | 17篇 |
2020年 | 31篇 |
2019年 | 43篇 |
2018年 | 35篇 |
2017年 | 59篇 |
2016年 | 49篇 |
2015年 | 43篇 |
2014年 | 78篇 |
2013年 | 82篇 |
2012年 | 51篇 |
2011年 | 67篇 |
2010年 | 52篇 |
2009年 | 68篇 |
2008年 | 61篇 |
2007年 | 84篇 |
2006年 | 63篇 |
2005年 | 48篇 |
2004年 | 40篇 |
2003年 | 40篇 |
2002年 | 38篇 |
2001年 | 36篇 |
2000年 | 26篇 |
1999年 | 34篇 |
1998年 | 15篇 |
1997年 | 17篇 |
1996年 | 15篇 |
1995年 | 19篇 |
1994年 | 15篇 |
1993年 | 11篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1982年 | 2篇 |
排序方式: 共有1289条查询结果,搜索用时 203 毫秒
41.
A comparison of three image-object methods for the multiscale analysis of landscape structure 总被引:4,自引:0,他引:4
Geoffrey J. Hay Thomas Blaschke Danielle J. Marceau Andr Bouchard 《ISPRS Journal of Photogrammetry and Remote Sensing》2003,57(5-6):327
Within the conceptual framework of Complex Systems, we discuss the importance and challenges in extracting and linking multiscale objects from high-resolution remote sensing imagery to improve the monitoring, modeling and management of complex landscapes. In particular, we emphasize that remote sensing data are a particular case of the modifiable areal unit problem (MAUP) and describe how image-objects provide a way to reduce this problem. We then hypothesize that multiscale analysis should be guided by the intrinsic scale of the dominant landscape objects composing a scene and describe three different multiscale image-processing techniques with the potential to achieve this. Each of these techniques, i.e., Fractal Net Evolution Approach (FNEA), Linear Scale-Space and Blob-Feature Detection (SS), and Multiscale Object-Specific Analysis (MOSA), facilitates the multiscale pattern analysis, exploration and hierarchical linking of image-objects based on methods that derive spatially explicit multiscale contextual information from a single resolution of remote sensing imagery. We then outline the weaknesses and strengths of each technique and provide strategies for their improvement. 相似文献
42.
高耸塔架结构节点损伤基于神经网络的两步诊断法 总被引:15,自引:1,他引:15
本文针对高耸钢塔架结构的损伤特点,建立了具有节点损伤的有限元模型,提出了一种分层神经网络两步诊断法:第一步,由基于区域残余力理论的第一层神经网络进行结构损伤区域的初诊;第二步,由基于应变模态理论的第二层神经网络进行损伤区域内的具体损伤节点位置和程度的诊断。对一平面塔架结构的数值仿真分析表明:本文提出的损伤诊断方法的结果是令人满意的。 相似文献
43.
隧道GPS网对横向贯通误差的影响 总被引:4,自引:0,他引:4
本文在阐述隧道工程独立坐标系和隧道GPS网数据处理方法的基础上推导出GPS网对横向贯通误差影响的通用计算公式,分析了隧道GPS网基准数据位置对横向贯通误差的影响。 相似文献
44.
45.
46.
Peter M. Atkinson 《International Journal of Applied Earth Observation and Geoinformation》2004,5(4):277-291
A simple approach for incorporating a spatial weighting into a supervised classifier for remote sensing applications is presented. The classifier modifies the feature-space distance-based metric with a spatial weighting. This is facilitated by the use of a non-parametric (k-nearest neighbour, k-NN) classifier in which the spatial location of each pixel in the training data set is known and available for analysis. A remotely sensed image was simulated using a combined Boolean and geostatistical unconditional simulation approach. This simulated image comprised four wavebands and represented three classes: Managed Grassland, Woodland and Rough Grassland. This image was then used to evaluate the spatially weighted classifier. The latter resulted in modest increase in the accuracy of classification over the original k-NN approach. Two spatial distance metrics were evaluated: the non-centred covariance and a simple inverse distance weighting. The inverse distance weighting resulted in the greatest increase in accuracy in this case. 相似文献
47.
48.
The neoliberalization of ecosystem services: wetland mitigation banking and problems in environmental governance 总被引:1,自引:0,他引:1
Morgan M. Robertson 《Geoforum》2004,35(3):361-373
Wetland mitigation banking is an American neoliberal environmental policy that has created a functioning market in `ecosystem services', commodities defined using the holistic measures of ecological science. The development of this market is discussed as a project of environmental governance, defined as the nation-state's regulation of ecological relations within its territory towards stabilizing capitalist relations of power and accumulation. I argue that the wetland banking industry serves as a bellwether that presages problems that other strategies of neoliberal environmental governance will experience. Ethnographic, economic and ecological data from the Chicago-area wetland banking industry inform a discussion of two major obstacles to neoliberal strategy: the problem of relying on ecological science to define the unit of trade, and the problem of aligning the somewhat independent relations of law, politics, markets and ecosystems across an array of spatial scales. Theoretical guidance is sought from recent work on `social natures' and from the Regulationist approach to institutional political economics. 相似文献
49.
Numerical modeling of toxic nonaqueous phase liquid removal from contaminated groundwater systems: mesh effect and discretization error estimation 下载免费PDF全文
Numerical modeling has now become an indispensable tool for investigating the fundamental mechanisms of toxic nonaqueous phase liquid (NAPL) removal from contaminated groundwater systems. Because the domain of a contaminated groundwater system may involve irregular shapes in geometry, it is necessary to use general quadrilateral elements, in which two neighbor sides are no longer perpendicular to each other. This can cause numerical errors on the computational simulation results due to mesh discretization effect. After the dimensionless governing equations of NAPL dissolution problems are briefly described, the propagation theory of the mesh discretization error associated with a NAPL dissolution system is first presented for a rectangular domain and then extended to a trapezoidal domain. This leads to the establishment of the finger‐amplitude growing theory that is associated with both the corner effect that takes place just at the entrance of the flow in a trapezoidal domain and the mesh discretization effect that occurs in the whole NAPL dissolution system of the trapezoidal domain. This theory can be used to make the approximate error estimation of the corresponding computational simulation results. The related theoretical analysis and numerical results have demonstrated the following: (1) both the corner effect and the mesh discretization effect can be quantitatively viewed as a kind of small perturbation, which can grow in unstable NAPL dissolution systems, so that they can have some considerable effects on the computational results of such systems; (2) the proposed finger‐amplitude growing theory associated with the corner effect at the entrance of a trapezoidal domain is useful for correctly explaining why the finger at either the top or bottom boundary grows much faster than that within the interior of the trapezoidal domain; (3) the proposed finger‐amplitude growing theory associated with the mesh discretization error in the NAPL dissolution system of a trapezoidal domain can be used for quantitatively assessing the correctness of computational simulations of NAPL dissolution front instability problems in trapezoidal domains, so that we can ensure that the computational simulation results are controlled by the physics of the NAPL dissolution system, rather than by the numerical artifacts. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
50.
Mohammad M. Sohrabi Rohan Benjankar Daniele Tonina Seth J. Wenger Daniel J. Isaak 《水文研究》2017,31(9):1719-1733
Stream water temperature plays a significant role in aquatic ecosystems where it controls many important biological and physical processes. Reliable estimates of water temperature at the daily time step are critical in managing water resources. We developed a parsimonious piecewise Bayesian model for estimating daily stream water temperatures that account for temporal autocorrelation and both linear and nonlinear relationships with air temperature and discharge. The model was tested at 8 climatically different basins of the USA and at 34 sites within the mountainous Boise River Basin (Idaho, USA). The results show that the proposed model is robust with an average root mean square error of 1.25 °C and Nash–Sutcliffe coefficient of 0.92 over a 2‐year period. Our approach can be used to predict historic daily stream water temperatures in any location using observed daily stream temperature and regional air temperature data. 相似文献