全文获取类型
收费全文 | 496篇 |
免费 | 50篇 |
国内免费 | 33篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 31篇 |
地球物理 | 128篇 |
地质学 | 304篇 |
海洋学 | 19篇 |
天文学 | 27篇 |
综合类 | 36篇 |
自然地理 | 24篇 |
出版年
2023年 | 8篇 |
2022年 | 21篇 |
2021年 | 46篇 |
2020年 | 32篇 |
2019年 | 26篇 |
2018年 | 87篇 |
2017年 | 50篇 |
2016年 | 66篇 |
2015年 | 42篇 |
2014年 | 35篇 |
2013年 | 42篇 |
2012年 | 15篇 |
2011年 | 22篇 |
2010年 | 7篇 |
2009年 | 17篇 |
2008年 | 8篇 |
2007年 | 4篇 |
2006年 | 9篇 |
2005年 | 4篇 |
2004年 | 2篇 |
2003年 | 4篇 |
2002年 | 4篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1986年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有579条查询结果,搜索用时 15 毫秒
441.
Feed forward neural network and interpolation function models to predict the soil and subsurface sediments distribution in Bam,Iran 总被引:1,自引:1,他引:0
Khalil Rezaei Bernard Guest Anke Friedrich Farajollah Fayazi Muhammad Nakhaei Ali Beitollahi Seyed Mahmoud Fatemi Aghda 《Acta Geophysica》2009,57(2):271-293
An application of the artificial neural network (ANN) approach for predicting mean grain size using electric resistivity data
from Bam city is presented. A feed forward back propagation network was developed employing 45 sets of input data. The input
variables in the ANN model are the electrical resistivity, water table as a Boolean value and depth; the output is the mean
grain size. To demonstrate the authenticity of this approach, the network predictions are compared with those from interpolation
methods and the same data. This comparison shows that the ANN approach performs better results. The predicted and observed
mean grain size values were compared and show high correlation coefficients. The ANN approach maps show a high degree of correlation
with well data based grain size maps and can therefore be used conservatively to better understand the influence of input
parameters on sedimentological predictions. 相似文献
442.
Pollution resulting from terrestrial and aquatic trace elements has become a severe problem across the world. Organic carbon(OC) content has a high affinity for metallic contaminants and it acts as a significant sink for trace elements. The decomposition of OC content directly influences the bioavailability of trace elements. The decomposition of OC content and OC distribution vary spatially, these processes affect the release of trace elements and need further research. In the current study, se... 相似文献
443.
塔里木盆地西部白垩纪—古近纪发生了大规模的海侵事件,形成一个喇叭状向西开口的海湾,该海湾属于东特提斯洋的一个分支。该地区白垩纪—古近纪海相地层记录了东特提斯洋演化和一系列重大地质事件,具有重要的研究价值,但对其地层的研究仍相对薄弱,对重大地质事件的研究还不够深入。本文拟通过详细的岩石地层、生物地层和其他地层方法,完善地层划分与对比框架,并在此基础上讨论Cenomanian/ Turonian界线大洋缺氧事件(OAE2)、白垩纪/古近纪界线(K/Pg)、古新世—始新世极热事件(PETM)、特提斯海进与海退等一系列重大地质事件。塔里木盆地白垩纪—古近纪海相或海陆过渡相地层自下而上为克孜勒苏群、库克拜组、乌依塔克组、依格孜牙组、吐依洛克组、阿尔塔什组、齐姆根组、盖吉塔格组、卡拉塔尔组、乌拉根组和巴什布拉克组,上述地层中含有丰富的有孔虫、介形虫、钙质超微、沟鞭藻、孢粉、双壳类、腹足类等化石,以及少量菊石、腕足类、海胆和鲨鱼牙齿等化石。综合的生物地层和年代地层研究表明,克孜勒苏群的时代为早白垩世Barremian-Albian期,库克拜组—依格孜牙组的时代为晚白垩世Cenomanian-Maastrichtian期(Cenomanian/Turonian界线可能位于库克拜组三段),吐依洛克组的时代为白垩纪—古近纪过渡期;阿尔塔什组的时代为古新世早中期,齐姆根组为古新世晚期—始新世最早期,盖吉塔格组—乌拉根组的时代为中始新世中晚期,巴什布拉克组的时代为晚始新世,但不排除最上部进入渐新世早期。塔里木盆地的海侵开始于克孜勒苏群中上部沉积期(Albian晚期—Aptian早期),但规模很有限,大规模的海侵始于晚白垩世Cenomanian早期;从晚白垩世—古新世,共经历了5次大规模的海侵—海退事件;大约41 Ma前后,海水退出盆地南部的昆仑山山前,34 Ma前后,海水退出盆地北部的天山山前。上述海侵—海退事件可能受构造和全球海平面变化的双重影响,但构造事件对海侵的启动和结束可能更具决定性的影响。阐述了塔里木盆地西部白垩纪—古近纪海相地层所记录的OAE2、K/Pg界线、PETM和特提斯海侵—海退等事件,其中笔者及团队第一次在塔里木盆地西部齐姆根组中所发现和报道的PETM事件,将有助于揭示全球近岸地区PETM的特征和生物-环境响应。在未来的研究中,需要进一步厘清塔里木盆地西部地层序列,建立更加精细的生物地层和年代地层框架,加强对PETM和特提斯海侵—海退等重大地质事件的研究。 相似文献
444.
MD Nurul Islam Siddique Zaied Bin Khalid M. Zamri Bin Ibrahim Muhammad Syarifuddin Yahya 《洁净——土壤、空气、水》2023,51(2):2200031
A comparative study of methane recovery by co-digesting kitchen waste and saline sewage sludge is performed to evaluate its feasibility for waste minimization. The experiment is performed at 37 °C having a mixing speed of 100 rpm and pH of 6.49–7.5 in anaerobic mixed batch reactors. The higher salinity level of the saline sewage sludge reduces the degradation rate of kitchen waste causing an enhancement in soluble chemical oxygen demand by 133% compared with 280% when co-digesting with the non-saline sample. The inhibitory behavior is in line with the low volatile solid elimination efficiency of 31% of saline against 55% of non-saline sludge. The Gompertz modeling, based on the outcomes, fits the cumulative methane generation trends quite well, with a strong correlation coefficient (>0.994). Besides, use of the non-saline sludge results in three times more methane production than the saline sample digestion. Sludge recovery is 0.07 m3 sludge m−3 wastewater, and water recovery is 0.84 m3 m−3 wastewater. The liquid produced from the fermentation of the slurry can be used for irrigation as well as fertilization. Kitchen waste co-digestion with both sludge samples has been proven to be a practical method for exploiting the extra digestion capacity of wastewater treatment plants currently in operation, but it is more practical for non-saline sludge. 相似文献
445.
Sobia Ashraf Farhat Abbas Muhammad Ibrahim Umer Rashid Shoaib Khalid Hammad Raza Ahmad Khalid Rehman Hakeem Tahir Majeed 《地理学报(英文版)》2015,(2):225-235
Groundwater is the most appropriate and widely used source of drinking water,which is increasingly threatened by pollution from industrial and agricultural activities.To check the severity of the problem,156 groundwater samples were collected from various depths(60-110 ft) of 52 different localities in Faisalabad city,the third largest metropolis in Pakistan,and analyzed for the metals(Zn,Cu,Cd,Ni,Pb,Mn and Fe) concentration in 2009.Quantification was done by using Flame Atomic Absorption Spectrophotometer technique and the results were compared with WHO standards for drinking water quality.Results showed that the levels of Cu,Mn and Fe were below the WHO standards while the concentrations of Zn,Cd,Ni and Pb were above the recommended levels of safe drinking water.Correlation analysis among the occurrence of these heavy metals revealed a highly significant and positive correlation of Mn with Zn and Fe.A significant and positive correlation of Cd was also found with Cu and groundwater depth showing that there is strong association between Cu-Cd pair and that the Cd concentration varies with depth of groundwater in the study area.Regional patterns of heavy metals occurrence were mapped using Geographical Information System(GIS) for the identification and demarcation of risk areas.The concentration maps may be used by policymakers of the city to mitigate groundwater pollution. 相似文献
446.
First-arrival waveforms remain underutilized in crustal refraction–reflection seismology by mostly reducing them to traveltime picks. However, as in earthquake seismology, the waveforms also contain important information about shallow near-receiver structures. We illustrate the use of three-component waveform analysis on the records from the ACCRETE wide-angle data set (SE Alaska and British Columbia; 1994), apply the Receiver Function (RF) methodology to the codas of P -wave arrivals, and draw two important conclusions. First, the P -wave polarization azimuths are found to be controlled by the near-receiver structures and virtually unrelated to the source–receiver backazimuths, from which they deviate by up to ∼40°. This observation might be important for studies of anisotropy and also for earthquake RF studies. Second, after correcting for the polarization azimuths, clear P / S mode conversions are reliably detected within 80–400 ms following the primary arrivals. The conversions are interpreted as originating at the base of the sedimentary cover of the fjord channel. In most cases, imaging of the basement requires only several records; however, notable exceptions are also found and interpreted as caused by multipathing, localized scattering, and onsets of crustal and Moho reflections. The ACCRETE example shows that RF methodology could be useful for constraining sediment thickness and deriving P - and S -wave receiver statics in land refraction surveys where collocated reflection profiles are not available. In addition, RFs from repeatable controlled sources could be useful for testing and calibration of RF techniques. 相似文献
447.
Natural Hazards - With increasing environmental pressure and the promotion of structural reforms on the supply side, a trend of transformation and upgrading is inevitable in coal-fired power... 相似文献
448.
Natural Hazards - Agriculture involves multiple risks of which environmental and production threats are major ones. Farmers’ risk attitudes and risk perceptions have a significant role in... 相似文献
449.
Improving seismic resolution is essential for obtaining more detailed structural and stratigraphic information. We present a new algorithm to increase seismic resolution with a minimum of user‐defined parameters. The algorithm inherits useful properties of both the short‐time Fourier transform and the cepstrum to smooth and broaden the frequency spectrum at each translation of the spectral decomposing window. The key idea is to replace the amplitude spectrum with its logarithm in each window of the short‐time Fourier transform. We describe the mathematical formulation of the algorithm and its testing on synthetic and real seismic data to obtain broader frequency spectra and thus enhance the seismic resolution. 相似文献
450.
Mohammad Amjad Sabir S. Shafiqur Rehman Muhammad Umar Amir Waseem Muhammad Farooq Fariduulah Muhammad Irshad 《Water Resources》2014,41(5):612-618
Pakistan is facing acute power dearth these days due to which people are suffering from privation and their economic condition is deflating. Expensive imported fossil fuel for thermal power generation is pressing them hard and exacerbating the situation. The total power produced in the country by all means is less by 4000 MW than the requirement of Pakistan. So this is the prime time to think about exploring aboriginal and renewable power resources. This article converses about hydro power resources of Swat, North Pakistan, one of the most promising areas in hydro power production. The area drained by the Swat River and its tributary net work is a part of Kohistan Himalayas and has a potential of more than 1000 MW that can contribute 25% to the total energy shortfall in the country and the same is 150% more than the shortfall experienced in the province of Khyber Pakhtunkhwa that hosts Swat Valley. Due to great relief difference acquired within a small stretch, the perennial Swat River and its tributaries become pertinent for power production as high head projects and also gain importance in irrigation as well. 相似文献