全文获取类型
收费全文 | 824篇 |
免费 | 61篇 |
国内免费 | 37篇 |
专业分类
测绘学 | 21篇 |
大气科学 | 53篇 |
地球物理 | 43篇 |
地质学 | 226篇 |
海洋学 | 92篇 |
综合类 | 57篇 |
自然地理 | 430篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 28篇 |
2021年 | 35篇 |
2020年 | 29篇 |
2019年 | 32篇 |
2018年 | 34篇 |
2017年 | 62篇 |
2016年 | 46篇 |
2015年 | 42篇 |
2014年 | 57篇 |
2013年 | 37篇 |
2012年 | 29篇 |
2011年 | 35篇 |
2010年 | 28篇 |
2009年 | 39篇 |
2008年 | 29篇 |
2007年 | 34篇 |
2006年 | 41篇 |
2005年 | 20篇 |
2004年 | 14篇 |
2003年 | 25篇 |
2002年 | 24篇 |
2001年 | 24篇 |
2000年 | 24篇 |
1999年 | 20篇 |
1998年 | 20篇 |
1997年 | 21篇 |
1996年 | 13篇 |
1995年 | 14篇 |
1994年 | 8篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 9篇 |
1990年 | 3篇 |
1989年 | 8篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1982年 | 3篇 |
1980年 | 1篇 |
排序方式: 共有922条查询结果,搜索用时 15 毫秒
51.
中亚各国在咸海流域水资源问题上的冲突与合作 总被引:6,自引:1,他引:6
咸海流域是中亚社会发展进程中水资源供需矛盾和生态环境问题表现最为突出的区域,已严重妨碍了经济发展和社会稳定,甚至严重影响到中亚国家间的关系. 在解决咸海问题上,中亚各国虽然都表现出了极度忧虑和希望合作解决共同问题的诚意,签订了一系列的多边和双边合作协议,付诸了较多的行动;发达国家和国际组织也多方介入,大力援助、积极斡旋,但仍未从根本上缓解咸海危机. 深入分析介绍了咸海流域的水资源及开发利用情况、中亚各国在咸海流域水资源问题上的冲突以及开展的一系列合作,探讨了咸海危机的潜在水冲突,提出了合理利用水资源,实现流域一体化管理,化解咸海危机的对策措施. 相似文献
52.
试论海洋经济地理学 总被引:4,自引:0,他引:4
张耀光 《云南地理环境研究》1991,3(1):38-45
作者认为海洋经济地理学属于经济地理学范畴,其研究对象为海洋产业布局,以及海洋经济体系的形成过程、结构特点和发展规律。海洋产业可分为传统的、新兴的和未来的三种,作者探讨了它们的内容及其与国民经济建设的关系。我国海洋经济地理学研究的重点,80年代以海岸带、90年代以海岛为主,以后将以大陆架和专属经济区为主。海洋经济地理学的研究方法以系统方法为主,文章结合作者住长山群岛的实践,阐述了海洋开发的若干问题,提出开展海洋经济地理研究的同时,要开展更广泛的海洋人文地理研究。 相似文献
53.
国家经济地图集的设计和制图可视化的方法技术 总被引:2,自引:2,他引:2
国家经济地图集是第一部全面,系统反映我国当前经济社会发展面貌和空间分布的大型科学参考地图集,它的编制是一项重大的制图系统工程,本文简要地阐述了图集编制研究的主要方面,包括从分析我国经济社会发展和现状出发,确定图集设计总体目标,为科学和形象地表达我国经济社会特征,而采用的可视化方法技术,以及智能化的计算机制图系统在图集制中的应用。 相似文献
54.
55.
56.
The industrial fisheries of Fiji have had mixed fortunes. The fresh fish export industry has grown rapidly in importance so that fisheries is now the third most valuable export industry; its positive effect on the economy is mainly in the increase in the purchase of goods and services, such as air freight. The present ‘hands off’ policy by government in the fresh fish export industry should continue until the industry matures. In the longer run, ad valorem royalties should be considered as a mean of capturing resource rents. The government-owned export cannery has been in financial decline, and the maintenance of the social benefits of regional employment generated by the cannery has come at a high cost to government coffers. The future of the cannery, now leased to a private operator, is clouded by the uncertainty of the continuity of concessional access to European markets beyond the year 2000. The main task faced by government is the management of fisheries and fish stocks. The management of the inshore fisheries — vital to the needs of a large proportion of the population — needs additional resources. The capability for management of the industrial fisheries, necessary to maximise long term public benefits, would be enhanced by full cost recovery through a user pays policy. This article is based on a paper presented to the Fiji Update seminar, held at the National Centre for Development Studies, the Australian National University, Canberra, on 19 June 1998. The author wishes to thank Mr Krishna Swamy, Senior Fisheries Officer in the Fiji Fisheries Division, and Mr Grahame Southwick, Managing Director of the Fiji Fish Company Ltd, for their generous provision of information for the preparation of this paper; and Mr Joeli Veitayaki, Coordinator of the Ocean Resources Management Programme, University of the South Pacific, for helpful comments. Any errors or omissions are the author’s responsibility, however. 相似文献
57.
《地学前缘(英文版)》2022,13(6):101435
The past two decades have seen a rapid adoption of artificial intelligence methods applied to mineral exploration. More recently, the easier acquisition of some types of data has inspired a broad literature that has examined many machine learning and modelling techniques that combine exploration criteria, or ‘features’, to generate predictions for mineral prospectivity. Central to the design of prospectivity models is a ‘mineral system’, a conceptual model describing the key geological elements that control the timing and location of economic mineralisation. The mineral systems model defines what constitutes a training set, which features represent geological evidence of mineralisation, how features are engineered and what modelling methods are used. Mineral systems are knowledge-driven conceptual models, thus all parameter choices are subject to human biases and opinion so alternative models are possible. However, the effect of alternative mineral systems models on prospectivity is rarely compared despite the potential to heavily influence final predictions. In this study, we focus on the effect of conceptual uncertainty on Fe ore prospectivity models in the Hamersley region, Western Australia. Four important considerations are tested. (1) Five different supergene and hypogene conceptual mineral systems models guide the inputs for five forest-based classification prospectivity models model. (2) To represent conceptual uncertainty, the predictions are then combined for prospectivity model comparison. (3) Representation of three-dimensional objects as two-dimensional features are tested to address commonly ignored thickness of geological units. (4) The training dataset is composed of known economic mineralisation sites (deposits) as ‘positive’ examples, and exploration drilling data providing ‘negative’ sampling locations. Each of the spatial predictions are assessed using independent performance metrics common to AI-based classification methods and subjected to geological plausibility testing. We find that different conceptual mineral systems produce significantly different spatial predictions, thus conceptual uncertainty must be recognised. A benefit to recognising and modelling different conceptual models is that robust and geologically plausible predictions can be made that may guide mineral discovery. 相似文献
58.
A multi-equation spatial econometric model,with application to EU manufacturing productivity growth 总被引:1,自引:0,他引:1
Bernard Fingleton 《Journal of Geographical Systems》2007,9(2):119-144
A multi-equation spatial econometric model is used to explain variations across EU regions in manufacturing productivity growth
based on recent theoretical developments in urban economics and economic geography. The paper shows that temporal and spatial
parameter homogeneity is an unrealistic assumption, contrary to what is typically assumed in the literature. Constraints are
imposed on parameters across time periods and between core and peripheral regions of the EU, with the significant loss of
fit providing overwhelming evidence of parameter heterogeneity, although the final model does highlight increasing returns
to scale, which is a central feature of contemporary theory.
相似文献
59.
The authors identify a management approach to the problem of incidental catch and utilize that approach to evaluate six management options which are being considered to control incidental catch in the US fishery conservation zone of the Bering Sea. The evaluation is in terms of the ability of management to minimize the impact and control costs of incidental catch. The authors conclude that the use of economic disincentives tends to be preferable due to the inefficiencies and extensive information requirements of the alternative options. 相似文献
60.
Downtowns are responding to decades of decline through a variety of revitalization strategies. The progression and success of downtown renewal efforts are largely rooted in asset-based, mixed-use approaches to revitalization that mirror the evolving economic functions of downtowns. While contemporary economic revitalization strategies provide opportunities, their complexity also creates potential challenges for community organizations tasked with determining the highest and best uses for downtown properties. Accordingly, this article examines how the evolution of downtown economic revitalization strategies has influenced the capacity and expertise required by organizations engaged in the endeavor of downtown market analysis. In particular, we identify applied market analysis challenges arising from organizational deficiencies in expertise, credibility, scope, and technology adoption and propose capacity building opportunities for overcoming these deficits. 相似文献