全文获取类型
收费全文 | 1062篇 |
免费 | 333篇 |
国内免费 | 245篇 |
专业分类
测绘学 | 19篇 |
大气科学 | 58篇 |
地球物理 | 506篇 |
地质学 | 766篇 |
海洋学 | 195篇 |
天文学 | 15篇 |
综合类 | 40篇 |
自然地理 | 41篇 |
出版年
2024年 | 13篇 |
2023年 | 33篇 |
2022年 | 51篇 |
2021年 | 47篇 |
2020年 | 56篇 |
2019年 | 63篇 |
2018年 | 46篇 |
2017年 | 48篇 |
2016年 | 59篇 |
2015年 | 44篇 |
2014年 | 74篇 |
2013年 | 74篇 |
2012年 | 48篇 |
2011年 | 81篇 |
2010年 | 45篇 |
2009年 | 71篇 |
2008年 | 73篇 |
2007年 | 61篇 |
2006年 | 72篇 |
2005年 | 62篇 |
2004年 | 53篇 |
2003年 | 49篇 |
2002年 | 53篇 |
2001年 | 54篇 |
2000年 | 51篇 |
1999年 | 35篇 |
1998年 | 30篇 |
1997年 | 31篇 |
1996年 | 33篇 |
1995年 | 24篇 |
1994年 | 27篇 |
1993年 | 17篇 |
1992年 | 14篇 |
1991年 | 5篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 10篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有1640条查询结果,搜索用时 0 毫秒
51.
核废物处置试验场环境地质研究综述 总被引:1,自引:0,他引:1
介绍了国外核废物处理试验场有关环境地质研究现状与进展。据核废物的放射性不同,目前或未来处置的方式不一样:中-低放射性废物(ILW-LLW)一般采用浅层处置,多置于粘土层或沉积岩层中;高放射性废物(HLW)一般通过竖井或平巷处置于深部的花岗岩或岩盐中。根据母岩的类别不同,本文分花岗岩、岩盐、粘土及其它四部分,对不同的试验场的研究计划、内容、方法、进展等进行了评述。 相似文献
52.
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
53.
54.
Vertical migration of municipal wastewater in deep injection well systems,South Florida,USA 总被引:1,自引:2,他引:1
Deep well injection is widely used in South Florida, USA for wastewater disposal largely because of the presence of an injection zone (“boulder zone” of Floridan Aquifer System) that is capable of accepting very large quantities of fluids, in some wells over 75,000 m3/day. The greatest potential risk to public health associated with deep injection wells in South Florida is vertical migration of wastewater, containing pathogenic microorganisms and pollutants, into brackish-water aquifer zones that are being used for alternative water-supply projects such as aquifer storage and recovery. Upwards migration of municipal wastewater has occurred in a minority of South Florida injection systems. The results of solute-transport modeling using the SEAWAT program indicate that the measured vertical hydraulic conductivities of the rock matrix would allow for only minimal vertical migration. Fracturing at some sites increased the equivalent average vertical hydraulic conductivity of confining zone strata by approximately four orders of magnitude and allowed for vertical migration rates of up 80 m/year. Even where vertical migration was rapid, the documented transit times are likely long enough for the inactivation of pathogenic microorganisms. 相似文献
55.
天然类似物研究是国际上新兴起的一门边缘科学。本文结合我国实际情况,综述研究的意义以及我国开展这项研究的有利条件、课题优选和具体开发内容。 相似文献
56.
In an attempt to reduce the threat of global warming, it has been proposed that the rise of atmospheric carbon dioxide concentrations be reduced by the ocean disposal of CO2 from the flue gases of fossil fuel-fired power plants. The release of large amounts of CO2 into mid or deep ocean waters will result in large plumes of acidified seawater with pH values ranging from 6 to 8. In an effort to determine whether these CO2-induced pH changes have any effect on marine nitrification processes, surficial (euphotic zone) and deep (aphotic zone) seawater samples were sparged with CO2 for varying time durations to achieve a specified pH reduction, and the rate of microbial ammonia oxidation was measured spectrophotometrically as a function of pH using an inhibitor technique. For both seawater samples taken from either the euphotic or aphotic zone, the nitrification rates dropped drastically with decreasing pH. Relative to nitrification rates in the original seawater at pH 8, nitrification rates were reduced by ca. 50% at pH 7 and more than 90% at pH 6.5. Nitrification was essentially completely inhibited at pH 6. These findings suggest that the disposal of CO2 into mid or deep oceans will most likely result in a drastic reduction of ammonia oxidation rates within the pH plume and the concomitant accumulation of ammonia instead of nitrate. It is unlikely that ammonia will reach the high concentration levels at which marine aquatic organisms are known to be negatively affected. However, if the ammonia-rich seawater from inside the pH plume is upwelled into the euphotic zone, it is likely that changes in phytoplankton abundance and community structure will occur. Finally, the large-scale inhibition of nitrification and the subsequent reduction of nitrite and nitrate concentrations could also result in a decrease of denitrification rates which, in turn, could lead to the buildup of nitrogen and unpredictable eutrophication phenomena. Clearly, more research on the environmental effects of ocean disposal of CO2 is needed to determine whether the potential costs related to marine ecosystem disturbance and disruption can be justified in terms of the perceived benefits that may be achieved by temporarily delaying global warming. 相似文献
57.
Through their consumption behavior, households are responsible for 72% of global greenhouse gas emissions. Thus, they are key actors in reaching the 1.5 °C goal under the Paris Agreement. However, the possible contribution and position of households in climate policies is neither well understood, nor do households receive sufficiently high priority in current climate policy strategies. This paper investigates how behavioral change can achieve a substantial reduction in greenhouse gas emissions in European high-income countries. It uses theoretical thinking and some core results from the HOPE research project, which investigated household preferences for reducing emissions in four European cities in France, Germany, Norway and Sweden. The paper makes five major points: First, car and plane mobility, meat and dairy consumption, as well as heating are the most dominant components of household footprints. Second, household living situations (demographics, size of home) greatly influence the household potential to reduce their footprint, even more than country or city location. Third, household decisions can be sequential and temporally dynamic, shifting through different phases such as childhood, adulthood, and illness. Fourth, short term voluntary efforts will not be sufficient by themselves to reach the drastic reductions needed to achieve the 1.5 °C goal; instead, households need a regulatory framework supporting their behavioral changes. Fifth, there is a mismatch between the roles and responsibilities conveyed by current climate policies and household perceptions of responsibility. We then conclude with further recommendations for research and policy. 相似文献
58.
Duke U. Ophori 《Hydrogeology Journal》1998,6(2):193-203
Flow of groundwater with variable density and viscosity was simulated at the Atikokan Research Area (ARA) in northwestern
Ontario, Canada. An empirical viscosity–concentration equation was modified to include total-dissolved-solids (TDS) data from
the ARA. The resulting equation was used successfully to estimate reasonably accurate viscosity values over the expected range
of temperature and concentration, in comparison with experimental values derived for sodium chloride solutions. A three-dimensional
finite-element code, MOTIF, developed by Atomic Energy of Canada Limited, was used in the simulations. The inclusion of the
effects of depth-increasing temperature and TDS-dependent fluid-density distribution, while maintaining only a temperature-dependent
viscosity relationship in a simulation, resulted in a more penetrative flow against expected buoyancy effects (i.e., the physics
of the system was not honored). Accounting for concentration in the viscosity equation caused water to be less penetrative
and more in accordance with the expected physics of the system. A conclusion is that fluid concentration should be considered
simultaneously in calculating the density and viscosity of a fluid during modeling of variable-density flow in areas underlain
by fluids with high TDS. Results of simulations suggest that both flow directions and magnitudes should be employed simultaneously
during the calibration of a model. Large-scale groundwater movement in the ARA may be analyzed with carefully selected vertical
no-flow boundaries. By incorporating the geothermal temperature gradient, groundwater recharge increases by 12%; thus, this
gradient plays a significant role in groundwater flow at the ARA. Variability in the fluid concentration at the ARA neither
decreases nor increases recharge into the groundwater system. The hypothesis that an isolated continuous regional flow system
may exist at depth in the ARA is not supported by these simulations.
Received, September 1996 Revised, September 1997, February 1998 Accepted, February 1998 相似文献
59.
兴蒙造山带位于中亚造山带东段, 作为古亚洲构造域的重要组成部分, 由西伯利亚板块与华北板块碰撞拼合而成, 其经历了大陆裂解、洋盆扩张、洋壳俯冲消减和碰撞拼合造山等复杂的构造演化过程.为了利用壳幔结构约束造山带演化的深部过程, 跨越华北地块北缘、松辽—锡林浩特地块、兴安地块以及索伦—西拉木伦缝合带和二连—贺根山缝合带, 实施了一条520 km长的深地震测深剖面, 获得了高质量的人工源大当量的宽角反射和折射地震资料, 并采用地震动力学射线方法获得地壳速度结构.结果显示: (1)研究区地壳平均速度为6.15~6.3 km·s-1, Pn波速度为7.8~8.2 km·s-1; (2)地壳厚度约为36.1~42.2 km, 最厚位置(~42.2 km)对应地表大兴安岭主峰, 说明大兴安岭在此位置存在山根; (3)地壳速度在1.5~6.8 km·s-1范围内, 认为在该区地壳内不存在洋壳物质; (4)主要断裂带或缝合带位于速度等值线变化剧烈的梯度带上; (5)速度结构显示研究区具有明显的横向分区和纵向分层的特点.地壳内速度剧烈变化特征表明兴蒙造山带的地壳物质组成不均匀, 尤其中下地壳, 速度等值线起伏剧烈.这种复杂的地壳速度结构应该与中生代以来多板块汇聚引发的多期区域性伸展和挤压作用有关.
相似文献60.
在谷德振先生“水文地质结构”学术思想指引下,本文提出建立结构水文地质学的设想,论述了其基础理论框架。从方法论角度将矿山水害防控分为被动防控和主动防控两种方法。以结构水文地质学指导煤矿高势能突水溃砂防控,分析了被动防控可能产生突水溃砂灾害的机理; 提出了主动地质工程防控的原理,包括地质材料性质改造、结构隔水性能重构、赋存水动力环境改造、减轻采掘诱发覆岩破坏等具体方法。抛砖引玉,以期催生符合中国矿山防治水实践需要的创新理论和方法。 相似文献