全文获取类型
收费全文 | 1807篇 |
免费 | 51篇 |
专业分类
1858篇 |
出版年
2023年 | 11篇 |
2020年 | 22篇 |
2019年 | 44篇 |
2018年 | 49篇 |
2017年 | 71篇 |
2016年 | 66篇 |
2015年 | 38篇 |
2014年 | 38篇 |
2013年 | 667篇 |
2012年 | 41篇 |
2011年 | 48篇 |
2010年 | 46篇 |
2009年 | 44篇 |
2008年 | 39篇 |
2007年 | 31篇 |
2006年 | 28篇 |
2005年 | 16篇 |
2004年 | 31篇 |
2003年 | 26篇 |
2002年 | 27篇 |
2001年 | 21篇 |
2000年 | 15篇 |
1999年 | 20篇 |
1998年 | 15篇 |
1997年 | 11篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 8篇 |
1993年 | 22篇 |
1992年 | 9篇 |
1991年 | 16篇 |
1990年 | 15篇 |
1989年 | 13篇 |
1988年 | 13篇 |
1987年 | 14篇 |
1986年 | 13篇 |
1985年 | 14篇 |
1984年 | 17篇 |
1983年 | 11篇 |
1982年 | 13篇 |
1981年 | 16篇 |
1980年 | 22篇 |
1979年 | 13篇 |
1978年 | 16篇 |
1977年 | 22篇 |
1976年 | 28篇 |
1975年 | 12篇 |
1973年 | 11篇 |
1972年 | 8篇 |
1971年 | 9篇 |
排序方式: 共有1858条查询结果,搜索用时 0 毫秒
31.
Numerical morphological modelling of braided rivers is increasingly used to explore controls on river pattern and for applied environmental management. This article reviews and presents a taxonomy of braided river morphodynamic models and discusses the challenges facing model development and use, illustrating these challenges with a case example. The taxonomy is contextualised by an initial discussion of the physical mechanisms of braiding. The taxonomy differentiates between reach‐scale and catchment‐scale models. Reach‐scale models are usually physics‐based, which are further divided based upon the mathematical approach used to solve equations (analytical or numerical) and their dimensionality (1D, 2D or 3D). Cellular automata models are one type of numerical model that replace at least some physical processes with expedient rules. A 2D physics‐based approach encapsulates sufficient process complexity to provide behavioural predictions. Predictions from catchment‐scale landscape evolution models have potential for providing boundary conditions. Future progress in physics‐based modelling needs to address three challenges: (i) representation of flow and sediment transport; (ii) temporal and spatial scaling; and (iii) model calibration, sensitivity, uncertainty and validation. The key problem for addressing these is the dearth of laboratory or natural experiment datasets. To show that progress can be made by comparing reach‐scale predictions to high‐resolution observations, a case study of monitoring and modelling, conducted in the Rees River, New Zealand, is presented. Hydraulic predictions of cellular automata and shallow water equation (Delft3d) models are compared to observed inundation extent. The efficacy of high‐resolution, multi‐temporal morphological data for assessing 2D physics‐based morphodynamic model predictions is also demonstrated. 相似文献
32.
33.
The recent articles by Vardi et al., “Tracing sickle blade levels of wear and discard patterns: a new sickle gloss quantification method” (Journal of Archaeological Science 37 (2010) 1716–1724), and Goodale et al., “Sickle blade life-history and the transition to agriculture: an early Neolithic case study from Southwest Asia” (Journal of Archaeological Science 37 (2010) 1192–1201), are two papers that seek to address interesting archaeological questions through the development of new approaches to measuring the duration of stone tool use. Here comment is made on the fashion in which research design and analytic procedures contribute to limit the capabilities of each of the techniques presented. Whilst the authors support the investigation of novel techniques, in order for the results of any use-wear analysis to be accepted as reliable the methods employed must be demonstrably sound. 相似文献
34.
A new method for modelling archaeological resource potential is presented that avoids some of the mathematical violations and inconsistencies of previously-favoured techniques. The Minanha research area in west-central Belize and a database of other Maya centres from within Belize are used as a case study for demonstrating the utility of the proposed modelling technique. 相似文献
35.
James Fairhall 《Irish Studies Review》2012,20(4):367-387
This article explores the ecological and ideological context of a passage in which two nationalists lament Ireland's treeless state. Although Joyce satirises these professed tree-lovers and the cause of reforestation, the passage alludes to a lively, serious topic in fin de siècle discourse. While Catholic nationalists blamed the loss of the island's once-vast, oak-dominated forests on British colonialism, a history elided by unionists, they shared a belief in the economic benefits of reforestation. Like Joyce, both sides knew little of Ireland's post-Ice Age natural history and did not appreciate the cultural importance of forest ecosystems to ancient Celtic peoples. Today, the Republic's profit-based plantations of conifers enact the materialist ideology of c.1904 reforestation advocates while overlooking the environmental and cultural benefits of restoring the biodiversity of native deciduous forests. 相似文献
36.
37.
38.
39.
40.