全文获取类型
收费全文 | 3829篇 |
免费 | 700篇 |
国内免费 | 1353篇 |
专业分类
测绘学 | 600篇 |
大气科学 | 2451篇 |
地球物理 | 705篇 |
地质学 | 918篇 |
海洋学 | 390篇 |
天文学 | 17篇 |
综合类 | 225篇 |
自然地理 | 576篇 |
出版年
2024年 | 30篇 |
2023年 | 61篇 |
2022年 | 112篇 |
2021年 | 133篇 |
2020年 | 174篇 |
2019年 | 203篇 |
2018年 | 151篇 |
2017年 | 217篇 |
2016年 | 196篇 |
2015年 | 190篇 |
2014年 | 270篇 |
2013年 | 313篇 |
2012年 | 259篇 |
2011年 | 261篇 |
2010年 | 212篇 |
2009年 | 276篇 |
2008年 | 247篇 |
2007年 | 352篇 |
2006年 | 302篇 |
2005年 | 242篇 |
2004年 | 230篇 |
2003年 | 226篇 |
2002年 | 182篇 |
2001年 | 170篇 |
2000年 | 188篇 |
1999年 | 146篇 |
1998年 | 110篇 |
1997年 | 83篇 |
1996年 | 82篇 |
1995年 | 54篇 |
1994年 | 62篇 |
1993年 | 46篇 |
1992年 | 32篇 |
1991年 | 24篇 |
1990年 | 10篇 |
1989年 | 14篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有5882条查询结果,搜索用时 15 毫秒
11.
Exurbia from the bottom-up: Confronting empirical challenges to characterizing a complex system 总被引:2,自引:0,他引:2
Daniel G. Brown Derek T. Robinson Li An Moira Zellner William Rand Rick Riolo Bobbi Low 《Geoforum》2008,39(2):805-818
We describe empirical results from a multi-disciplinary project that support modeling complex processes of land-use and land-cover change in exurban parts of Southeastern Michigan. Based on two different conceptual models, one describing the evolution of urban form as a consequence of residential preferences and the other describing land-cover changes in an exurban township as a consequence of residential preferences, local policies, and a diversity of development types, we describe a variety of empirical data collected to support the mechanisms that we encoded in computational agent-based models. We used multiple methods, including social surveys, remote sensing, and statistical analysis of spatial data, to collect data that could be used to validate the structure of our models, calibrate their specific parameters, and evaluate their output. The data were used to investigate this system in the context of several themes from complexity science, including have (a) macro-level patterns; (b) autonomous decision making entities (i.e., agents); (c) heterogeneity among those entities; (d) social and spatial interactions that operate across multiple scales and (e) nonlinear feedback mechanisms. The results point to the importance of collecting data on agents and their interactions when producing agent-based models, the general validity of our conceptual models, and some changes that we needed to make to these models following data analysis. The calibrated models have been and are being used to evaluate landscape dynamics and the effects of various policy interventions on urban land-cover patterns. 相似文献
12.
13.
David P. Bacon Nash’at N. Ahmad Thomas J. Dunn Michael C. Monteith Ananthakrishna Sarma 《Natural Hazards》2008,44(3):317-327
By definition, a crisis is a situation that requires assistance to be managed. Hence, response to a crisis involves the merging
of local and non-local emergency response personnel. In this situation, it is critical that each participant: (1) know the
roles and responsibilities of each of the other participants; (2) know the capabilities of each of the participants; and (3)
have a common basis for action. For many types of natural disasters, this entails having a common operational picture of the unfolding events, including detailed information on the weather, both current and forecasted, that may impact on either
the emergency itself or on response activities. The Consequences Assessment Tool Set (CATS) is a comprehensive package of
hazard prediction models and casualty and damage assessment tools that provides a linkage between a modeled or observed effect
and the attendant consequences for populations, infrastructure, and resources, and, hence, provides the common operational
picture for emergency response. The Operational Multiscale Environment model with Grid Adaptivity (OMEGA) is an atmospheric
simulation system that links the latest methods in computational fluid dynamics and high-resolution gridding technologies
with numerical weather prediction to provide specific weather analysis and forecast capability that can be merged into the
geographic information system framework of CATS. This paper documents the problem of emergency response as an end-to-end system
and presents the integrated CATS–OMEGA system as a prototype of such a system that has been used successfully in a number
of different situations. 相似文献
14.
Flaring of associated gas from oil exploitation has several consequences on the environment. This study explores the spatial
variability effects of gas flaring on the growth and development of cassava (Manihot esculenta), waterleaf (Talinum triangulare), and pepper (Piper spp.) crops commonly cultivated in the Niger Delta, Nigeria. Data was collected on soil and atmospheric temperature and moisture
at a 20-m interval, starting at 40 m from the flare point to a distance of 140 m. Lengths and widths of crop leaves, height
of crop plants and cassava yields were measured at the specified distances. The amino acid, ascorbic acid, starch, and sugar
constituents of the cassava yields were determined. The results suggest that a spatial gradient exists in the effects of gas
flares on crop development. Retardation in crop development manifests in decreased dimensions of leaf lengths and widths of
cassava and pepper crops closer to the gas flare point. Statistical analysis also confirms that cassava yields are higher
at locations further away from the flare point. In addition, the amount of starch and ascorbic acid in cassava decreased when
the plant is grown closer to the gas flare. High temperatures around the gas flare appear to be the most likely cause of this
retardation. The waterleaf crop, on the other hand, appears to thrive better around the gas flare point. 相似文献
15.
Historical space as narrative medium: on the configuration of spatial narratives of time at historical sites 总被引:1,自引:0,他引:1
This paper examines how narratives of history are organized spatially at historical sites and memorial spaces, especially
in urban settings and in places invested with a sense of collective memory. Much recent research has focused on landscape,
memory, and place and how relationships of political and social power influence the representation of historical events in
public spaces. Although the meaning of such sites may be hotly contested for long periods of time, we focus here on narrative
theory and the related, but unexplored, issue of how such historical stories are configured on the ground at actual historical
sites. We identify a number of narrative strategies which are frequently used to configure historical stories in space. Declamatory
strategies using markers presenting a snapshot of an event are common, but sequential and non-sequential linear strategies
are also used, as are thematic strategies that cross-cut space and time to present complex historical stories at various spatial
scales. Examples are drawn from a range of historical sites in North America, Europe and Israel. 相似文献
16.
This paper explores the links between a strategic policy, urban consolidation, and house prices by examining the changes in
the mix of housing and in house price for the period 1991–2004. We contend that urban consolidation could be seen as a source
of additional supply, (which might be expected to be felt in lower prices and so contribute to a local policy objective) but
also as a stimulus to demand (by developers who could bid up the price of lots where it was understood more housing could
be built). Analyses were carried out at the metropolitan and sub-regional scales using correlation tests. The research finds
very weak statistical connections, and concludes that this policy has not been associated with price changes. 相似文献
17.
18.
19.
20.