首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   199篇
  免费   6篇
  国内免费   2篇
测绘学   7篇
大气科学   6篇
地球物理   46篇
地质学   83篇
海洋学   7篇
天文学   46篇
综合类   3篇
自然地理   9篇
  2024年   2篇
  2022年   4篇
  2021年   4篇
  2020年   3篇
  2019年   4篇
  2018年   8篇
  2017年   11篇
  2016年   15篇
  2015年   7篇
  2014年   6篇
  2013年   20篇
  2012年   6篇
  2011年   7篇
  2010年   4篇
  2009年   8篇
  2008年   4篇
  2007年   7篇
  2006年   7篇
  2005年   4篇
  2004年   5篇
  2003年   5篇
  2002年   4篇
  2001年   2篇
  2000年   3篇
  1999年   6篇
  1998年   4篇
  1997年   1篇
  1996年   6篇
  1995年   3篇
  1994年   2篇
  1993年   2篇
  1992年   2篇
  1991年   3篇
  1990年   4篇
  1989年   2篇
  1988年   1篇
  1987年   1篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
  1983年   3篇
  1982年   1篇
  1981年   3篇
  1980年   3篇
  1979年   1篇
  1978年   3篇
  1975年   1篇
  1973年   1篇
  1971年   1篇
排序方式: 共有207条查询结果,搜索用时 15 毫秒
91.
Community-based natural resource management in northeast India has a long history. Indigenous knowledge and adaptation are the collective information, with improvement from generation to generation. The expectation is that under community control, local expertise on biodiversity will play a significant role in natural resource management through traditional practices. This paper discusses the characteristics and application of the traditional ecological knowledge of aboriginal peoples in northeast India and its role in natural resource management. Examples are provided in two different eco-cultural landscapes, i.e., Demazong (the Buddhist eco-cultural landscape in Sikkim Himalaya) and the Apatani eco-cultural landscape in Arunachal Pradesh, which illustrate the utility value of traditional ecological knowledge in sustainable natural resource management. Both eco-cultural landscapes are indeed very complex and highly evolved systems with high levels of economic and ecological efficiencies. The paper concludes that traditional ecological knowledge systems and institutions could serve as entry points into the sustainable utilization and management of natural resources. This could be achieved through the exploration of the cultural practices of the local people and integrating useful aspects into the modern natural resource management expertise. With rapidly depleting biodiversity in the developing tropic regions, there is a greater utilization today than ever before of the value of respecting the "Sacred" as a tool towards better conservation of natural resources.  相似文献   
92.
Tilted Bianchi type I cosmological models filled with disordered radiation in presence of a bulk viscous fluid and heat flow are investigated. The coefficient of bulk viscosity is assumed to be a power function of mass density. Some physical and geometric properties of the models are also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
93.
A possible mechanism for screening of the surface magnetic field of an accreting neutron star, by the accreted material, is investigated. We model the material flow in the surface layers of the star by an assumed two-dimensional velocity field satisfying all the physical requirements. Using this model velocity we find that, in the absence of magnetic buoyancy, the surface field is screened (i.e. there is submergence of the field by advection) within the time-scale of material flow of the top layers. On the other hand, if magnetic buoyancy is present, the screening happens over a time-scale that is characteristic of the slower flow of the deeper (and hence, denser) layers. For accreting neutron stars, this longer time-scale turns out to be about 105 yr, which is of a similar order of magnitude to the accretion time-scale of most massive X-ray binaries.  相似文献   
94.
Bengal Fan Miocene sediments were collected during International Ocean Discovery Program Expedition 354 and investigated using petrographic and detrital garnet chemistry analyses. The Miocene Siwalik Group, which is composed of sediments deposited in the Himalayan foreland basin, was also analyzed for comparison with the Bengal Fan data for the provenance change during the Miocene. Our petrographic analyses revealed that the Miocene sediments of the Bengal Fan and Siwalik Group consist predominantly of Higher Himalayan Crystalline (HHC)-derived detritus such as chloritoid, staurolite, sillimanite, and/or kyanite, which appear among the accessory minerals. The chemistry of the detrital garnet varies across the stratigraphy; most of the garnet is rich in almandine and poor in spessartine and pyrope. However, pyrope-rich garnet, which is considered to originate from the HHC core (granulite facies), was found in the lower to upper Miocene deposits. The deposition of HHC-derived detrital garnet began before the Middle Miocene (15 Ma) and before the Late Miocene (10–9 Ma) in the Siwalik Group. The Bengal Fan data, by contrast, indicated that pyrope-rich garnet appeared in the Early Miocene (17.3 Ma) and Late Miocene (8.5–6.5 Ma). We conclude that the Bengal Fan sediments record the erosion of the HHC zone since the Early Miocene that appears in the Siwalik sediments. Furthermore, we found that the HHC-derived inputs decreased from the late Middle Miocene (12 Ma) to the early Middle Miocene (10 Ma) in both the Nepal Himalaya foreland basin and the Bengal Fan. The disappearance of the HHC-derived detritus is probably the result of dilution by Lesser Himalayan detritus, which suggests that the Lesser Himalayan zone, which is composed of metamorphosed and unmetamorphosed sedimentary rocks, was uplifted.  相似文献   
95.
96.
In this study, feasibility of using seawater to neutralize alkaline red mud for its safe disposal has been studied using Taguchi’s design of experimental methodology. Parameters such as weight of red mud, volume of seawater, stirring time and temperature were tested at three levels to study their effect on response characteristic, i.e., pH of the neutralized slurry. The analysis of variance showed that volume of seawater added and quantity of red mud are the two significant parameters with 53.59 and 44.92 % contribution each, respectively. Under the optimized parameters, pH value of red mud slurry reaches to about 8.0 which is within disposable limits. When seawater or other Ca- and Mg-rich brines are added to caustic red mud, the pH of the mixture is reduced causing hydroxide, carbonate or hydroxy carbonate minerals to be precipitated. This mechanism of neutralization process has been explained with emphasis on chemical analysis, mineralogy and morphology of the neutralized red mud. The process improved the physical characteristics of red mud with entrained liquor becoming non-hazardous water with reduced alkalinity. The results would be extremely useful in the process of safe disposal of red mud.  相似文献   
97.
The present paper evaluates the temporal and spatial impact of heavy metal containing (Cr, Zn, Cu, Ni, Cd and Fe) effluents of brass, electroplating and tannery industries on chemical and microbiological characteristics of affected soil and groundwater. Therefore, samples were drawn from three sites, S1, S2 and S3, with a longitudinally distant from effluent drain of 20, 200 and 700 m, respectively. In general, the metals concentration exceeded the standard limits not only in the discharged effluents but also in the soil and groundwater. The significant reduction of microbial biomass C and N, soil respiration and microbial coefficient with increasing metal content from S3 to S1 was recorded, the effect being more pronounced in summer. However, the Cmic/Nmic ratio decreased whilst the metabolic quotient ($q_{{\rm CO}_{{\rm 2}} } $ ) increased with increasing metal concentration in soil. The content of Zn (11.5 mg/L) and Bacillus sp. was at maximum in groundwater of brass and electroplating industry site, whereas that of tannery site contained maximum Cr (2.34 mg/L) and Enterobacter sp. The toxic metals adversely polluted the groundwater which made it to harbours Escherichia coli beyond the prescribed limit. To check the soil and groundwater pollution, eco‐friendly measures involving improved effluent treatment technology and site‐specific application of treated effluent are recommended.  相似文献   
98.
The anti-microbial agent triclosan (TCS), and its derivative methyl-triclosan (Me-TCS), are discharged with treated effluents from wastewater treatment plants to receiving environments. We investigated the bioconcentration of TCS and Me-TCS in mussels (Mytilus galloprovincialis) exposed to TCS (100 ng L−1) for 30 days in seawater aquaria (19 ± 2 °C) with fresh phytoplankton as a food source. Bioconcentration increased with time reaching a steady-state around 24–30 days. The bioconcentration factor (log BCF) for TCS were 2.81 L kg−1 (dry weight) and 4.13 L kg−1, when lipid normalised concentrations were used. Mussels were also deployed in cages at four marine locations receiving effluents from WWTPs. The mean (±SD) TCS and Me-TCS concentrations for mussels from these sites were 9.87 (±1.34) and 6.99 (±2.44) μg kg−1. The study showed that mussels can be a useful tool for monitoring pollution of TCS and Me-TCS in marine and estuarine environments.  相似文献   
99.
Laboratory biodegradation batch studies were performed to investigate the degradation behavior of six selected UV filters, namely benzophenone‐3 (BP‐3), 3‐(4‐methylbenzylidene) camphor (4‐MBC), Octyl 4‐methoxycinnamate (OMC), Octocrylene (OC), 2‐(3‐t‐butyl‐2‐hydroxy‐5‐methylphenyl)‐5‐chloro benzotriazole (UV‐326), and 2‐(2’‐hydroxy‐5’‐octylphenyl)‐benzotriazole (UV‐329) in an aquifer microcosm (groundwater and aquifer sediment mixture) under aerobic and anaerobic (nitrate, sulfate, and Fe(III) reducing) conditions within 77 d. The results from the biodegradation experiments showed that the six UV filters were degraded well in the aquifer materials under different redox conditions. Rapid biodegradation was observed for BP‐3 and OMC in the aquifer materials, with their half‐lives of 1.5‐8.8 d and 1.3‐5.2 d, respectively. In most cases, aerobic conditions were more favorable for the degradation of the UV filters in aquifer materials. Relatively slow degradation of 4‐MBC, UV‐326, and UV‐329 under anaerobic conditions was noted with their half‐lives ranging between 47 d and 126 d, indicating potential persistence in anaerobic aquifers. The results showed that redox conditions could have significant effects on biodegradation of the UV filters in aquifers.  相似文献   
100.
Dolostone of Vempalle Formation near Tummalapalle hosts large uranium deposit (>100,000 tonnes with an average grade of 0.045%U3O8). It is a unique type of uranium deposit because carbonate formations have been considered to be among the least uraniferous of all the rocks of the Earth’s crust due to mobility of uranium in aqueous fluid in the presence of carbonate and bicarbonate ions. Vempalle dolostone hosts syn-sedimentary uranium mineralization in the form of discrete uranium phases (pitchblende and coffinite) associated with collophane, and adsorbed uranium in organic matter. The organic matter has played dual role of concentrating uranium from solution and also chemically reducing it to pitchhblende and coffinite.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号