全文获取类型
收费全文 | 5183篇 |
免费 | 497篇 |
国内免费 | 310篇 |
专业分类
测绘学 | 1051篇 |
大气科学 | 284篇 |
地球物理 | 788篇 |
地质学 | 1427篇 |
海洋学 | 1103篇 |
天文学 | 12篇 |
综合类 | 474篇 |
自然地理 | 851篇 |
出版年
2024年 | 11篇 |
2023年 | 21篇 |
2022年 | 74篇 |
2021年 | 124篇 |
2020年 | 161篇 |
2019年 | 155篇 |
2018年 | 134篇 |
2017年 | 254篇 |
2016年 | 198篇 |
2015年 | 238篇 |
2014年 | 301篇 |
2013年 | 382篇 |
2012年 | 306篇 |
2011年 | 341篇 |
2010年 | 302篇 |
2009年 | 303篇 |
2008年 | 352篇 |
2007年 | 338篇 |
2006年 | 333篇 |
2005年 | 274篇 |
2004年 | 234篇 |
2003年 | 171篇 |
2002年 | 190篇 |
2001年 | 150篇 |
2000年 | 111篇 |
1999年 | 131篇 |
1998年 | 77篇 |
1997年 | 72篇 |
1996年 | 38篇 |
1995年 | 44篇 |
1994年 | 32篇 |
1993年 | 29篇 |
1992年 | 17篇 |
1991年 | 13篇 |
1990年 | 15篇 |
1989年 | 11篇 |
1988年 | 16篇 |
1987年 | 9篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有5990条查询结果,搜索用时 0 毫秒
911.
912.
《Marine Policy》2014
A multi-objective programming model has been applied to investigate conflicting goals of the Norwegian cod fisheries. The goals included in this article are economic rent and employment. Fisheries managers are confronted with the problem of how best to allocate the total allowable catch (TAC) of cod among eight vessel groups. Compromise solutions taking into account both objectives by giving them equal weights in the multi-objective programming model are calculated and discussed. This article is an extension of an earlier article in which the trade-off analysis was performed using data only for North Norway and one particular year. The present analysis includes the entire Norwegian cod fisheries and is carried out using time series data for 2003–2007, examining the annual variations of key economic and technological parameters of the cod fisheries. Based on the results from compromise programming, the article discusses management and policy implications of reallocation of the TAC by vessel groups. 相似文献
913.
R. A. Crichton 《Geotechnical and Geological Engineering》1994,12(3):183-212
Summary The legislative framework within which the disposal of sewage sludge is managed in England and Wales and the methods employed are outlined. Those factors which affect management decisions are analysed and consideration is given to the environmental implications of those decisions. Sewage processes and sludge disposal are considered, and the problems, especially those of heavy metal contamination, are addressed. An indication is given as to how the Water Services Companies are likely to implement the more stringent controls on disposal. Finally, the future of sludge management in England and Wales is discussed.Abbreviations BAT
Best available technology
- BATNEEC
Best available technology not entailing excessive cost
- BOD5
Biochemical oxygen demand
- BPEO
Best practicable environmental option
- CBI
Confederation of British Industry
- CEST
Centre for Exploitation of Science and Technology
- COD
Chemical oxygen demand
- CSC
Customer Services Committee
- DAF
Dissolved air flotation
- DG
Director General
- DoE
Department of the Environment
- DS
Dried solids 相似文献
914.
《The Journal of geography》2012,111(2):54-58
To make sense of spatial data, information and concepts strong geographic literacy skills are a prerequisite, yet existing studies suggest a global decline in these skills. Current geographic tools predominantly focus on mapping tasks that do not necessarily lead to an understanding of the broader geographic relevance of location. This article argues that in order to improve geographic literacy exercises should test an understanding of location and employ techniques to correct deficiencies. To support this argument this study offers evidence on the effectiveness of online quizzes in improving geographic literacy skills of first-year undergraduate geography students. 相似文献
915.
内陆河小流域综合治理对景观格局的影响——以童子坝河流域为例 总被引:2,自引:1,他引:2
以1987年、2000年、2008年3期Landsat TM影像为信息源,在GIS 技术和景观分析软件Fragstats3.3支持下,获得了民乐县童子坝河流域研究区不同时期的景观类型信息和描述景观格局特征的8个景观指数数据,利用这些数据分析了实施综合治理前后流域景观格局的变化。结果表明:①在类型水平上,各种草地景观类型的斑块呈现边缘整齐、形状规则的特点,斑块的破碎化程度减小,聚合度增加;特别是高覆盖度草地的斑块数目、平均斑块面积都呈增加趋势,斑块边界形状变得连续、规则,显现出人为干扰的痕迹;河床、河漫滩景观的斑块数目减少,斑块边界形状趋于规整,贯穿连通性增强\.②在景观水平上,景观空间格局规整有序,景观多样性提高,异质性增加,破碎化程度减小,空间连接性增强,以高覆盖度草地为主的景观优势显著体现出来。③综合治理措施实施对童子坝河流域景观格局的影响是积极有效的,这可为内陆河小流域继续开展生态环境建设提供科学依据。 相似文献
916.
一种数据网格的元数据分类管理机制研究 总被引:2,自引:0,他引:2
网格环境下数据发现和访问的关键问题是应用元数据管理和拷贝元数据管理,针对这一问题,提出了一种元数据分类管理机制。该机制定义了数据模型和应用元数据模式,采用了分类存储的方式对不同的元数据进行管理,并设计了一个基于向导的查询智能体 相似文献
917.
Activity patterns, social behaviour, and reproductive success of Arabian oryx were monitored in a reintroduced population in Mahazat as-Sayd Protected Area, Saudi Arabia. During the first year of the study, precipitation was 38% lower than the long-term average, whereas rainfall in the following year resulted in precipitation that was 92.8% of the long-term average. These dramatically different rainfall conditions corresponded with distinct patterns in various environmental parameters (air and soil temperature, humidity, wind speed, solar radiation, air pressure). Daily activity patterns, the frequency of social behaviours, and foraging activity were significantly reduced during the drought period. The frequency of reproductive behaviour was significantly related to daytime, air temperature and radiation, with a pronounced reduction of reproductive activities during the drought. Monthly rates of conceptions were considerably lower during the drought. Our results substantiate the idea that extended dry periods affect the population development of Oryx, but also raise questions about habitat suitability and carrying capacity. Future management of Arabian oryx should consider extreme climatic events as factors influencing various aspects of the ecology and behaviour of this species. This aspect may become even more important in the face of climate change, including a future increase of extreme climatic events. 相似文献
918.
919.
920.
Research shows that flood damage potential has increased significantly in the last 15 years. At the same time, flood policy has shifted away from simplistic flood defence towards 'living with floods' and 'making space for water'. This paper explores the mis-match between the aspiration in policy ideals, the reality of rising potential economic damages and the inability of the flood risk appraisal process to match the aspiration with the reality. Unless investment appraisal procedures are changed, the increase in damages will undermine policy changes that seek a different pattern of flood risk management, away from economically dominated decision-criteria towards more sustainable objectives. 相似文献