全文获取类型
收费全文 | 549篇 |
免费 | 22篇 |
国内免费 | 9篇 |
专业分类
测绘学 | 22篇 |
大气科学 | 17篇 |
地球物理 | 113篇 |
地质学 | 312篇 |
海洋学 | 33篇 |
天文学 | 28篇 |
综合类 | 24篇 |
自然地理 | 31篇 |
出版年
2023年 | 3篇 |
2022年 | 13篇 |
2021年 | 11篇 |
2020年 | 19篇 |
2019年 | 13篇 |
2018年 | 36篇 |
2017年 | 33篇 |
2016年 | 42篇 |
2015年 | 20篇 |
2014年 | 41篇 |
2013年 | 49篇 |
2012年 | 27篇 |
2011年 | 28篇 |
2010年 | 26篇 |
2009年 | 26篇 |
2008年 | 21篇 |
2007年 | 16篇 |
2006年 | 18篇 |
2005年 | 9篇 |
2004年 | 14篇 |
2003年 | 12篇 |
2002年 | 10篇 |
2001年 | 13篇 |
2000年 | 3篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 2篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1964年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有580条查询结果,搜索用时 15 毫秒
1.
MohammedHazaea HUKe MohammedMattash CHENBing M.O.AI-JabaliAref MohammedAbdussalam 《东北亚地学研究》2004,7(2):181-184
The chemical composition of several thermal springs around Changbaishan area has been investigated. Cenozoic basaltic rocks are widely distributed in Northeast China and geothermal characteristics have been described. About one hundred hot springs exist around Changhaishan Volcano at the border between China and D.P.R.Korea with high temperature about 82~C. The pH values of the spring water range from 6.9 to 7.1 and the total flow rate is about 4.8 L/sec. The chemical composition of the thermal springs is sodium carbonate; the high-mineral contents of thermal water are believed to have medicinal properties. Bathhouses are already built along the hot springs to take the advantage of the supposed healing properties. The high quality of those hot springs is believed to be utilitized for mineral water. The chemical equilibrium temperatures were estimated at about 160℃ based on the Na-K-Ca geochemical thermometer. 相似文献
2.
H. M. Hussein K. M. Abou Elenean I. A. Marzouk A. Peresan I. M. Korrat E. Abu El-Nader G. F. Panza M. N. El-Gabry 《Natural Hazards》2008,47(3):525-546
The aim of the present work is to compile and update a catalogue of the instrumentally recorded earthquakes in Egypt, with
uniform and homogeneous source parameters as required for the analysis of seismicity and seismic hazard assessment. This in
turn requires a detailed analysis and comparison of the properties of different available sources, including the distribution
of events with time, the magnitude completeness, and the scaling relations between different kinds of magnitude reported by
different agencies. The observational data cover the time interval 1900–2004 and an area between 22°–33.5° N and 25°–36° E.
The linear regressions between various magnitude types have been evaluated for different magnitude ranges. Using the best
linear relationship determined for each available pair of magnitudes, as well as those identified between the magnitudes and
the seismic moment, we convert the different magnitude types into moment magnitudes M
W, through a multi-step conversion process. Analysis of the catalogue completeness, based on the M
W thus estimated, allows us to identify two different time intervals with homogeneous properties. The first one (1900–1984)
appears to be complete for M
W ≥ 4.5, while the second one (1985–2004) can be considered complete for magnitudes M
W ≥ 3. 相似文献
3.
Risk-based decision-making for drilling waste discharges using a fuzzy synthetic evaluation technique 总被引:5,自引:0,他引:5
Offshore petroleum drilling wastes contain toxic substances that are potentially harmful to the marine ecosystem. Despite environmentally benign characteristics, wastes associated with synthetic-based fluids still contain a certain amount of pollutants due to contamination with formation oil and the presence of trace heavy metals in barite, which may pose risk when discharged into the marine environment. A framework is presented here for a decision support system for the selection of the best drilling waste discharge option. Uncertainties in the quantification of risk, cost and technical feasibility are expressed by fuzzy numbers. An analytical hierarchy process with a technique called fuzzy synthetic evaluation is employed to determine the best management alternative (discharge scenario). 相似文献
4.
Jonas Ardö Meelis Mölder Bashir Awad El-Tahir Hatim Abdalla Mohammed Elkhidir 《Carbon balance and management》2008,3(1):1-18
Background
Large spatial, seasonal and annual variability of major drivers of the carbon cycle (precipitation, temperature, fire regime and nutrient availability) are common in the Sahel region. This causes large variability in net ecosystem exchange and in vegetation productivity, the subsistence basis for a major part of the rural population in Sahel. This study compares the 2005 dry and wet season fluxes of CO2 for a grass land/sparse savanna site in semi arid Sudan and relates these fluxes to water availability and incoming photosynthetic photon flux density (PPFD). Data from this site could complement the current sparse observation network in Africa, a continent where climatic change could significantly impact the future and which constitute a weak link in our understanding of the global carbon cycle.Results
The dry season (represented by Julian day 35–46, February 2005) was characterized by low soil moisture availability, low evapotranspiration and a high vapor pressure deficit. The mean daily NEE (net ecosystem exchange, Eq. 1) was -14.7 mmol d-1 for the 12 day period (negative numbers denote sinks, i.e. flux from the atmosphere to the biosphere). The water use efficiency (WUE) was 1.6 mmol CO2 mol H2O-1 and the light use efficiency (LUE) was 0.95 mmol CO2 mol PPFD-1. Photosynthesis is a weak, but linear function of PPFD. The wet season (represented by Julian day 266–273, September 2005) was, compared to the dry season, characterized by slightly higher soil moisture availability, higher evapotranspiration and a slightly lower vapor pressure deficit. The mean daily NEE was -152 mmol d-1 for the 8 day period. The WUE was lower, 0.97 mmol CO2 mol H2O-1 and the LUE was higher, 7.2 μmol CO2 mmol PPFD-1 during the wet season compared to the dry season. During the wet season photosynthesis increases with PPFD to about 1600 μmol m-2s-1 and then levels off.Conclusion
Based on data collected during two short periods, the studied ecosystem was a sink of carbon both during the dry and wet season 2005. The small sink during the dry season is surprising and similar dry season sinks have not to our knowledge been reported from other similar savanna ecosystems and could have potential management implications for agroforestry. A strong response of NEE versus small changes in plant available soil water content was found. Collection and analysis of flux data for several consecutive years including variations in precipitation, available soil moisture and labile soil carbon are needed for understanding the year to year variation of the carbon budget of this grass land/sparse savanna site in semi arid Sudan. 相似文献5.
Yahia E.-A. Mohamedzein Mohammed H. Aboud 《Geotechnical and Geological Engineering》2006,24(5):1385-1401
A detailed study was performed to investigate the compressibility and the shear strength of a residual soil in Omdurman, Sudan.
The soil resulted from weathering of sandstone and mudstone. The soil is classified as sandy clayey silt (MH-CH) and is generally
partially saturated. Consolidation tests were performed to study the compressibility of the soil and UU, CIU and insitu tests
(CPT and SPT) were performed to study the shear strength characteristics of the soil. The characteristics of this residual
soil can generally be predicted using correlations proposed in the literature for transported soils. The soil is of low to
medium compressibility and exhibits slight apparent overconsolidation behavior. The soil dilates during shear and shows no
long term effective cohesion. Problems associated with open cuts in this soil are attributed to loss of strength upon saturation. 相似文献
6.
Hussein A. Amery 《The Geographical journal》2002,168(4):313-323
This paper explains how hydropolitical dynamics and spatial variables almost triggered a water war between Israel and Lebanon because the latter was building a pump on the Wazzani Spring, a tributary of the Jordan River. The convergence of a regional drought, history of violent confrontations between the two riparians, distrust, varying development needs and territorial disputes almost culminated in a war between these east Mediterranean neighbours. While most international water disputes in the Middle East will be resolved peacefully, some are likely to trigger violent confrontations threatening political stability in the Middle East in the next few decades. 相似文献
7.
8.
Y. Ali Z. Aslam M. Y. Ashraf G. R. Tahir 《International Journal of Environmental Science and Technology》2004,1(3):221-225
Salt tolerance in eighteen advanced rice genotypes was studied under an artificially salinized (EC=8.5 dSm?1) soil conditions after 90 days of transplanting. The results showed that the yield per plant, chlorophyll concentrations, fertility percentage, and number of productive tillers, panicle length and number of primary braches per panicle of all the genotypes were reduced by salinity. However, genotypes viz. Jhona-349 x Basmati-370, NR-1, DM-59418, DM-63275, DM-64198 and DM-38-88 showed better salinity tolerance than others. 相似文献
9.
H. A. Al-Darwish E. A. Abd El-Gawad F. H. Mohammed M. M. Lotfy 《Environmental Geology》2005,49(2):240-250
Coastal uses and other human activities have inevitably impinged on the Gulf environment; therefore, these regions require continuous monitoring. The investigated area covered the maximum fragments of Dubai coastal region in the Arabian Gulf. The determination of major oxides and trace metal concentrations in Dubai sediments revealed three heavily and moderately contaminated regions. One is in the far northeastern part at Al-Hamriya Sts 1–3 and contaminated by Fe, Cu, Pb, and Zn; the second is in the mid-northeastern part at Dry Docks and contaminated by Cu, Ni, Pb, and Zn; and finally, the third is in the near southwestern part at Dubal and contaminated by Fe, Mg, Cr, Ni, and Zn. Al-Hamriya St 3 represented the highest values of Cu, Pb, and Zn, whereas Dubal exhibited the maximum values of Fe, Mg, Ba, Cr, Mn, Ni, and V. The anthropogenic discharge and natural deposits are the main sources of contamination. In general, all trace and major elements showed the minimal levels at Jebel Ali Sanctuary (Sts 11, 12, 13) except for Sr and Ca, which showed their maximum values. The highest concentrations of Ca and Sr are mainly attributed to carbonate gravel sands and sands, which cover most stations. Each of V and Ni showed negative correlation with TPH, which may be indicated that the source of oil contamination in the region is not related to crude oil but mostly attributable to anthropogenic sources. The significant positive correlation, which was found between trace metals and TOC indicates that organic matter plays an important role in the accumulation of trace metals in case of Cu, Zn, and Pb. 相似文献
10.
Remote sensing data and digital elevation models were utilized to extract the catchment hydrological parameters and to delineate storage areas for the Ugandan Equatorial Lakes region. Available rainfall/discharge data are integrated with these morphometric data to construct a hydrological model that simulates the water balance of the different interconnected basins and enables the impact of potential management options to be examined. The total annual discharges of the basins are generally very low (less than 7% of the total annual rainfall). The basin of the shallow (5 m deep) Lake Kioga makes only a minor hydrological contribution compared with other Equatorial Lakes, because most of the overflow from Lake Victoria basin into Lake Kioga is lost by evaporation and evapotranspiration. The discharge from Lake Kioga could be significantly increased by draining the swamps through dredging and deepening certain channel reaches. Development of hydropower dams on the Equatorial Lakes will have an adverse impact on the annual water discharge downstream, including the occasional reduction of flow required for filling up to designed storage capacities and permanently increasing the surface areas of water that is exposed to evaporation. On the basis of modelling studies, alternative sites are proposed for hydropower development and water storage schemes. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献