全文获取类型
收费全文 | 4715篇 |
免费 | 855篇 |
国内免费 | 753篇 |
专业分类
测绘学 | 417篇 |
大气科学 | 241篇 |
地球物理 | 326篇 |
地质学 | 3097篇 |
海洋学 | 360篇 |
天文学 | 4篇 |
综合类 | 497篇 |
自然地理 | 1381篇 |
出版年
2024年 | 19篇 |
2023年 | 60篇 |
2022年 | 153篇 |
2021年 | 221篇 |
2020年 | 161篇 |
2019年 | 169篇 |
2018年 | 141篇 |
2017年 | 173篇 |
2016年 | 147篇 |
2015年 | 162篇 |
2014年 | 264篇 |
2013年 | 286篇 |
2012年 | 247篇 |
2011年 | 265篇 |
2010年 | 301篇 |
2009年 | 266篇 |
2008年 | 244篇 |
2007年 | 275篇 |
2006年 | 333篇 |
2005年 | 283篇 |
2004年 | 255篇 |
2003年 | 269篇 |
2002年 | 275篇 |
2001年 | 265篇 |
2000年 | 239篇 |
1999年 | 175篇 |
1998年 | 141篇 |
1997年 | 115篇 |
1996年 | 79篇 |
1995年 | 82篇 |
1994年 | 61篇 |
1993年 | 48篇 |
1992年 | 40篇 |
1991年 | 27篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 14篇 |
1987年 | 13篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有6323条查询结果,搜索用时 359 毫秒
331.
332.
矿产资源开采必须实行有偿取得,有偿出让的本质是出让矿产资源储量,矿产资源的开发利用都是围绕矿产资源储量,离开矿产资源储量,采矿权的有偿出让就无从谈起。介绍了当前储量动态管理现状,提示了存在的问题,并就如何加强对矿产资源储量监管提出了对策并进行了探讨。 相似文献
333.
334.
Assessment of Exploration Bias in Data-Driven Predictive Models and the Estimation of Undiscovered Resources 总被引:3,自引:0,他引:3
The spatial distribution of discovered resources may not fully mimic the distribution of all such resources, discovered and
undiscovered, because the process of discovery is biased by accessibility factors (e.g., outcrops, roads, and lakes) and by
exploration criteria. In data-driven predictive models, the use of training sites (resource occurrences) biased by exploration
criteria and accessibility does not necessarily translate to a biased predictive map. However, problems occur when evidence
layers correlate with these same exploration factors. These biases then can produce a data-driven model that predicts known
occurrences well, but poorly predicts undiscovered resources.
Statistical assessment of correlation between evidence layers and map-based exploration factors is difficult because it is
difficult to quantify the “degree of exploration.” However, if such a degree-of-exploration map can be produced, the benefits
can be enormous. Not only does it become possible to assess this correlation, but it becomes possible to predict undiscovered,
instead of discovered, resources.
Using geothermal systems in Nevada, USA, as an example, a degree-of-exploration model is created, which then is resolved into
purely explored and unexplored equivalents, each occurring within coextensive study areas. A weights-of-evidence (WofE) model
is built first without regard to the degree of exploration, and then a revised WofE model is calculated for the “explored
fraction” only. Differences in the weights between the two models provide a correlation measure between the evidence and the
degree of exploration.
The data used to build the geothermal evidence layers are perceived to be independent of degree of exploration. Nevertheless,
the evidence layers correlate with exploration because exploration has preferred the same favorable areas identified by the
evidence patterns. In this circumstance, however, the weights for the “explored” WofE model minimize this bias. Using these
revised weights, posterior probability is extrapolated into unexplored areas to estimate undiscovered deposits. 相似文献
335.
Elana Wilson 《Area》2007,39(3):323-330
In this article, I trace the efforts of a development team working to promote a Canadian approach to natural resources management in the Russian North. These development workers used two communication strategies related to time and history to render Canadian knowledge mobile and applicable to a new location: (1) imagining today's Russian North as equivalent to the Canadian northern past and (2) reframing and idealising the Canadian past and present to make the governance export less discursively 'messy' for an outside audience. The relative failure of these communicative strategies points to the need for richer dialogue in efforts to move knowledge cross-culturally. 相似文献
336.
Bruno MOLINO Rosa VIPARELLI Annamaria DE VINCENZO 《国际泥沙研究》2007,22(4):273-281
Knowledge of the morphological dynamics of a water course is essential for management of reservoir siltation. With an example of sedimentation in a reservoir in Basilicata, Italy, this paper demonstrates the effect on reservoir siltation of the hydraulic works, which are aimed to reduce sediment transport along the fluvial network and to prevent part of the sediment discharge from reaching the lake. The effect depends on the river type and on the the geological features of river basin slopes. The paper also shows how mass erosion can significantly contribute to development of reservoir siltation. Finally, preliminary results are provided about the time needed for river training works to be effective. 相似文献
337.
338.
339.
340.
基于GIS的地热资源与环境管理信息系统的研制 总被引:2,自引:0,他引:2
如何实现地热资源的可持续开发与利用,保证资源与环境协同发展,已经成为一个亟待解决的问题。将GIS与地热工程分析相结合,借助信息技术,建立了地热资源与环境管理信息系统,这一系统的特点就是以长观数据与地热工程分析结果作为数据源,将信息化管理和科学决策结合在一起,实现集信息管理,资源评价与科学决策为一体的信息系统。 相似文献