全文获取类型
收费全文 | 2302篇 |
免费 | 339篇 |
国内免费 | 609篇 |
专业分类
测绘学 | 427篇 |
大气科学 | 20篇 |
地球物理 | 166篇 |
地质学 | 1991篇 |
海洋学 | 136篇 |
天文学 | 5篇 |
综合类 | 265篇 |
自然地理 | 240篇 |
出版年
2024年 | 17篇 |
2023年 | 36篇 |
2022年 | 97篇 |
2021年 | 111篇 |
2020年 | 95篇 |
2019年 | 114篇 |
2018年 | 92篇 |
2017年 | 107篇 |
2016年 | 134篇 |
2015年 | 134篇 |
2014年 | 182篇 |
2013年 | 174篇 |
2012年 | 151篇 |
2011年 | 154篇 |
2010年 | 138篇 |
2009年 | 147篇 |
2008年 | 162篇 |
2007年 | 145篇 |
2006年 | 155篇 |
2005年 | 106篇 |
2004年 | 140篇 |
2003年 | 68篇 |
2002年 | 74篇 |
2001年 | 91篇 |
2000年 | 64篇 |
1999年 | 71篇 |
1998年 | 48篇 |
1997年 | 40篇 |
1996年 | 27篇 |
1995年 | 16篇 |
1994年 | 17篇 |
1993年 | 14篇 |
1992年 | 15篇 |
1991年 | 4篇 |
1990年 | 12篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 15篇 |
1986年 | 11篇 |
1985年 | 15篇 |
1984年 | 18篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1972年 | 2篇 |
排序方式: 共有3250条查询结果,搜索用时 15 毫秒
791.
本文在分析陈仓区地下水开采现状和水文地质条件的基础上,建立了水文地质概念模型,选用了承压水二维非稳定流数学模型进行描述,采用无越流的无界承压含水层干扰井群法求解该数学模型。 相似文献
792.
四川丹巴白云母矿山公园矿业遗迹资源特征及评价 总被引:1,自引:0,他引:1
四川丹巴白云母矿是我国开发最早的白云母矿之一。在悠久的开采历史中遗存下了十分丰富的矿业遗迹,成为该公园建设的基础。这些遗迹典型、稀有,系统完整,科学价值高,组合独特,具有很高的历史文化价值。此外,公园内配套的自然人文景观丰富,旅游区位条件良好,矿业遗迹开发价值巨大。 相似文献
793.
Józef Kabiesz 《Geotechnical and Geological Engineering》2006,24(5):1131-1147
During hard coal mining operations conducted under conditions of rockburst hazard, one of the most important preventive measures
can be the prediction of occurrence time and location of the strong seismic mine tremors of energy E
s ⩾ 104 J. This is a very difficult task and the way it is being currently performed appears to be unsatisfactory. Therefore, attempts
have been made to use neural networks, specifically trained for this application. The paper presents an approach for determining
an influence of the type and shape of the input data on the efficiency of such a prediction. The considerations are based
on a selected example of the seismic activity recorded during longwall mining operations conducted in one of the Polish mines. 相似文献
794.
Impact of karst water on coal mining in North China 总被引:1,自引:0,他引:1
Coalfields in North China encompass more than ten Provinces. They contain six to seven coal seams in the Permo-Carboniferous
strata. The lower three seams account for 37% of the total reserves and are threatened with intrusion of karst water from
the underlying Ordovician limestone. Hundreds of water inrush incidences have occurred, in which a large amount of water suddenly
flows into tunnels or working faces under high potentiometric pressure. Over 50 mines have been flooded over the last 30 years.
Large-scale dewatering or depressurizing of the karst aquifer was considered essential to avoid water inrushes and keep the
mines safely operational. This practice, however, has caused sinkholes, dry springs, water supply shortage, and groundwater
contamination in the surrounding areas. One alternative water control measure is to make full use of the rock layer between
the coal seam and the karst aquifer as a protective barrier to prevent or constrain water flow from the underlying aquifer
into the mines. Grouting is effective when the hydrogeological conditions are favorable to this technique. Proper design of
the grouting program and experience of the contractor are also important for a successful application. 相似文献
795.
Computer-based landscape evolution models offer the ability to evaluate landscape stability over the short (annual), medium
(decades to hundreds of years) and long-term (thousands of years). Modeling has advantages in that design ideas can be tested,
different surface material properties can be evaluated and risk analysis carried out. Landscape evolution models allow landscape
surface change through time. These models also offer the advantage that the landscape can be evaluated visually as it develops
through time, which is not possible with other types of models. Landscape evolution models can be used for not only soil loss
assessment (i.e. tonnes/hectare/year), but also to evaluate the method of soil loss (i.e. rill or interrill erosion). This
study examines a range of waste rock dump designs for the Minera Alumbrera Ltd. copper mine, Argentina. An erosion assessment
using the SIBERIA erosion model over a 1000-year simulation period demonstrates waste rock dump designs using a conventional
stepped design of backsloping benches and caps with angle of repose slopes provide the lowest average erosion rates and depths
of incision than do other designs. Caution should be applied in interpreting these results as the SIBERIA erosion model is
sensitive to parameter input and in this case was calibrated and run using a generic set of parameters that are not site specific.
Nevertheless, the results provide a guide as to the strengths and weaknesses of different rehabilitation designs and demonstrate
the insights that modeling studies can provide. 相似文献
796.
Celine S.L. Lee Shihua QI Gan Zhang Xiangdong LI 《中国地球化学学报》2006,25(B08):20-20
A sediment core from the Liangzhi Lake, Hubei Province in central China, was used to assess metal usage and accumulation in the past 6000+ years in China. The concentrations of trace metals, including Cr, Cu, Pb, Ni and Zn, and major elements, Ca, Fe and Mg, in the ^14C-dated sediment core were analyzed. Historical trends of metal inputs to the Liangzhi Lake from 5000 B.C. to the present were recorded in the sediments, representing over 6000 years of metal mining and utilization history in China. The concentrations of Cu, Ni, Pb and Zn have increased gradually since 3000 B.C., indicating the start of the Bronze Age era in ancient China, until the period 467-76 B.C. During the period of 467-76 B.C., there had been a rapid increase in the concentrations of these metals in the sediments, indicating the enormous inputs of these metals at that time. This era corresponded well with the Warring States Period (475-221 B.C.) and early Hart Dynasty (206 B.C.-220 A.D.) of China, during which copper and lead were extensively used in making bronze articles, such as vessels, tools and weapons. During 1876 A.D. to the early 1900s, there was also a significant increase in the metal concentrations, such as Cu, Ni and Pb, which could probably reflect the impact of metal emissions during the early industrial development and wars in China. The Pb isotopic analysis showed that the surface and subsurface sediments had lower ^206Pb/^207Pb, and ^208Pb/^207Pb ratios than the deeper layers, affected by mining activities both during the Bronze Age era and modem times. 相似文献
797.
798.
数据仓库是近年来信息领域中迅速兴起的一种技术。本文对此技木和应用进行了讨论,提出了适用于地震信息系统数据仓库的方案设计思想。 相似文献
799.
800.