全文获取类型
收费全文 | 415篇 |
免费 | 44篇 |
国内免费 | 33篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 22篇 |
地球物理 | 112篇 |
地质学 | 265篇 |
海洋学 | 17篇 |
天文学 | 18篇 |
综合类 | 28篇 |
自然地理 | 22篇 |
出版年
2023年 | 8篇 |
2022年 | 19篇 |
2021年 | 44篇 |
2020年 | 32篇 |
2019年 | 25篇 |
2018年 | 78篇 |
2017年 | 40篇 |
2016年 | 60篇 |
2015年 | 36篇 |
2014年 | 29篇 |
2013年 | 38篇 |
2012年 | 13篇 |
2011年 | 19篇 |
2010年 | 6篇 |
2009年 | 12篇 |
2008年 | 7篇 |
2007年 | 2篇 |
2006年 | 3篇 |
2005年 | 2篇 |
2004年 | 2篇 |
2003年 | 1篇 |
2002年 | 1篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1986年 | 1篇 |
1978年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有492条查询结果,搜索用时 15 毫秒
301.
Ionic liquid as a medium to remove iron and other metal ions: a case study of the North Kelantan Aquifer,Malaysia 总被引:1,自引:1,他引:0
Nur Hayati Hussin Ismail Yusoff Yatimah Alias Sharifah Mohamad Nurul Yani Rahim Muhammad Aqeel Ashraf 《Environmental Earth Sciences》2014,71(5):2105-2113
An alternative iron removal treatment method using liquid-liquid extraction with the room-temperature ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, as a solvent medium was studied. The chelating agent 1,10-phenanthroline was used as the extractant. The extraction of Fe(III) and Fe(II) was influenced significantly by the pH of the aqueous phase. The successful removal of iron was achieved; more than 95 % of the initial iron concentration was removed from the groundwater samples. However, detailed research is needed before the ionic liquid method can replace the conventional groundwater treatment protocol because the recovery rate was very low upon reuse (approximately 25–60 %). This low recovery was due to the ion exchange process; the appearance of anions from ionic liquids was also detected in groundwater samples. 相似文献
302.
303.
Muhammad Nauman Malik Mehdi Murtuza Iqbal Asif Bakar Muhammad Saifullah Abu Brahim Aissa Dk Nur Afiqah Jalwati Puteri Amer Farhan Rafique 《地下水科学与工程》2014,7(4):373-382
In many circumstances involving heat and mass transfer issues, it is considered impractical to measure the input flux and the resulting state distribution in the domain. Therefore, the need to develop techniques to provide solutions for such problems and estimate the inverse mass flux becomes imperative. Adaptive state estimator (ASE) is increasingly becoming a popular inverse estimation technique which resolves inverse problems by incorporating the semi-Markovian concept into a Bayesian estimation technique, thereby developing an inverse input and state estimator consisting of a bank of parallel adaptively weighted Kalman filters. The ASE is particularly designed for a system that encompasses independent unknowns and /or random switching of input and measurement biases. The present study describes the scheme to estimate the groundwater input contaminant flux and its transient distribution in a conjectural two-dimensional aquifer by means of ASE, which in particular is because of its unique ability to efficiently handle the process noise giving an estimation of keeping the relative error range within 10% in 2-dimensional problems. Numerical simulation results show that the proposed estimator presents decent estimation performance for both smoothly and abruptly varying input flux scenarios. Results also show that ASE enjoys a better estimation performance than its competitor, Recursive Least Square Estimator (RLSE) due to its larger error tolerance in greater process noise regimes. ASE’s inherent deficiency of being slower than the RLSE, resulting from the complexity of algorithm, was also noticed. The chosen input scenarios are tested to calculate the effect of input area and both estimators show improved results with an increase in input flux area especially as sensors are moved closer to the assumed input location. 相似文献
304.
Middle and Late Permian palynoflora in Tianshan Township,southeast of Bogda Mountain,Xinjiang, China
The Permian is one of the most important periods during which the vegetative earth witnessed the transition from icehouse to greenhouse climate and the global environment changes. Organisms on the planet en-countered great challenge and the demise of swamp caused the extinction of arborescent lycopods and the rising of Mesophytic plants accomplished the floral transition from the Paleophytic to Mesophytic vegetation. In order to depict the climatic changes and floral succession in the middle and high latitudes of the North Hemisphere, palynological investigation was engaged, and 40 samples collected from the uppermost of Taerlang Formation, Hongyanchi Formation and Quanzijie Formation in the Tianshan Town, Turpan-Hami Basin, eastern Xinjiang, China. The result shows that the palynoflora in the studied area is composed of 50 species of 33 genera, domi-nated by disaccites and striatiti gymnosperm pollen, and characterized by diverse Protohaploxypinus, Hamia-pollenites, Alisporites and Klausipollenites. It is quite similar to those Middle and Late Permian palynological as-semblages reported in the Dalongkou section and other localities in southern margin of Junggar Basin, and aged at Middle and Late Permian. The diversity of typical Angara and sub-Angara pollen, such as Falcisporites, Alisporites, Protohaploxypinus, Vittatina, Lunatisporites, Hamiapollenites, etc. indicates that the studied palyno-flora belonged to the sub-Angara phytoprovince, while the presence of Lueckisporites virkkiae implied Euramerica pollen intruded northward sometimes. The paleoclimate of the studied area might be warm and humid with fluc-tuated dry seasons during the late Guadalupian and early Lopingian time. 相似文献
305.
Black shales of the Paleocene Patala Formation are proven source rocks for conventional hydrocarbons in southern Potwar Basin of Pakistan and are assumed to be effective source rocks towards north in the Margalla Hill Range of Pakistan. In this regard, the current study focuses on source rock geochemistry of the Paleocene Patala Formation to assess its source rock potential, organic matter types and thermal maturity levels in the Mar-galla Hill Range of North Pakistan. Source rock generative potential, kerogen types and thermal maturation of the analysed rock samples were unraveled by using Rock-Eval pyrolysis Tmax, TOC (total organic carbon) and vitrinite reflectance ( R0 ) analyses. TOC analysis coupled with S2 yield revealed poor to fair source rock quality encountered within the formation. The pyrolysis Tmax vs Hydrogen Index ( HI) , showed mostly Type Ⅲ kerogen dominated by thermally immature to mature organic matter. The HI and genetic potential is low and revealed poor hydrocarbon generation potential of the formation. The S1 vs TOC plots confirm the indigenous nature of the hydrocarbons hosted by Patala Formation. The vitrinite reflectance outcomes indicated immature to mature source rock beds lying in dry gas zone. The HI and OI signatures and abundance of Type Ⅲ kerogen are indica-ting dominance of terrestrial organic matter within the formation. Overall, the investigated Patala Formation ex-posed at the studied section of Margalla Hill Range, Pakistan acts as a poor source rock unit for liquid hydrocar-bon generation but holds prospects for dry gas generation in the study area. 相似文献
306.
The attitude dynamics of a rigid artificial satellite subject to a gravity gradient and Lorentz torques in a circular orbit are considered. Lorentz torque is developed on the basis of the electrodynamic effects of the Lorentz force acting on the charged satellite's surface. We assume that the satellite is moving in a Low Earth Orbit in the geomagnetic field, which is considered to be a dipole. Our model of torque due to the Lorentz force is developed for an artificial satellite with a general shape, and the nonlinear differential equations of Euler are used to describe its attitude orientation. All equilibrium positions are determined and conditions for their existence are obtained.The numerical results show that the charge q and radius ρ0of the center of charge for the satellite provide a certain type of semi-passive control for the attitude of the satellite. The technique for this kind of control would be to increase or decrease the electrostatic screening on the satellite. The results obtained confirm that the change in charge can affect the magnitude of the Lorentz torque, which can also affect control of the satellite. Moreover, the relationship between magnitude of the Lorentz torque and inclination of the orbit is investigated. 相似文献
307.
Effects of climate anomaly on rainfall,groundwater depth,and soil moisture on peatlands in South Sumatra,Indonesia
下载免费PDF全文
![点击此处可从《地下水科学与工程》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Muhammad Irfan Sri Safrina Erry Koriyanti Netty Kurniawati Khairul Saleh Iskhaq Iskandar 《地下水科学与工程》2023,11(1):81-88
Climate anomalies can cause natural disasters such as severe fires and floods on peatlands in South Sumatra. Factors that affect the natural disasters on peatlands include rainfall, groundwater level, and soil moisture. This paper aims to study the effect of the climate anomalies in 2019 and 2020 and effects of these influencing factors on peatlands in South Sumatra. The data used in this study was derived from in-situ measurement at two SESAME’s measurement stations in the study area. The results indicate that in the 2019 dry season, the rainfall was minimal, the lowest groundwater table depth was ?1.14 m and the lowest soil moisture was 3.4%. In the 2020 dry season, rainfall was above the monthly average of 100 mm, the lowest groundwater level was ?0.44 m, and the lowest soil moisture was 26.64%. There is also a strong correlation between soil moisture and groundwater table depth. The correlation between the two is stronger when there is less rainfall. 相似文献
308.
Khizar SAMIULLAH Omer DRAZ Riffat YASIN Bilal RASOOL Hafiz MUHAMMAD ISHAQ Muhammad HARIS AZIZ Rana MEHROZ FAZAL Shakila NAZ Tehreem RAZA Romesa NIAZI 《《地质学报》英文版》2022,96(4):1150-1165
A fossil-bearing locality near Padhri village, Dhok Pathan, 55 km away from the tehsil Dina, Jhelum District, in the Potwar Plateau, Middle Siwaliks, Punjab, northern Pakistan, is significantly rich in mammalian fossils. This site has provided an abundant mammalian fossil fauna of Late Miocene age from the Dhok Pathan Formation (Fm.). The recovered material belongs to four families: Equidae (horses), Rhinocerotidae (rhinos), Bovidae (cows), and Suidae (pigs). We discovered a new skull of hipparionine Hipparion theobaldi from this locality along with 22 specimens from the associated assemblage of fossil mammals. The recovered material includes seven other species: the aceratheriine Chilotherium intermedium, boselaphines Tragoportax punjabicus, Selenoportax vexillarius, Pachyportax latidens, the antelope Gazella lydekkeri and suinine Propotamochoerus hysudricus. The specimens are isolated teeth, fragments of maxilla, mandibles and horn cores. The Dhok Pathan Fm. is generally composed of claystone, siltstone and sandstone beds and, based on the mammalian fauna, the Padhri fossil locality is dated as Late Miocene. Thi99s formation was deposited in a subtropical paleoenvironment and the predominance of fossil bovids indicates extremely moist conditions with small but frequent standing water bodies. 相似文献
309.
Pakistan is rich in coal resources, which amount to around 186 billion tons. The Paleocene Padhrar and Darra Adam Khel coalfields are located in the Central Salt Range Punjab Province and the Khyber Pakhtunkhwa Province, Pakistan, respectively. Padhrar coal has not been studied in detail and the Darra Adam Khel coalfields are newly-discovered, so no research has been done, due to security considerations. In this study, an attempt has been made to study the geochemical and mineralogical characteristics of the Padhrar and Darra Adam Khel coals, in order to learn about the coal quality, element enrichment mechanism, sedimentary medium conditions and potentially valuable elements for coal utilization. The Padhrar and Darra Adam Khel coals are low to medium ash, low moisture content, high in volatiles and high total sulfur coal. The vitrinite reflectance in Darra Adam Khel coal is higher than in Padhrar coal, indicating either a greater burial depth or the effects of Himalayan tectonism. The vitrinite content is dominant in the Padhrar and Darra Adam Khel coals, followed by inertinite and liptinite, the major minerals including quartz, clay minerals, calcite and pyrite. The trace elements Ni, As, Be Zn, Ge, Mo, Ta, W, Co and Nb, Sn, Hf, Ta, Pb, Th, Cd, In, Be, V, Cr, Zr, Ag, Li, W and Co are concentrated in some of the Padhrar and Darra Adam Khel coal samples, respectively. The Padhrar coal shows positive Ce, Eu and Gd anomalies, with most of the Darra Adam Khel coal showing negative Ce, Eu and positive Gd anomalies with high LREE. The Al2O3/TiO2 values indicate that the sediment source of the Padhrar and Darra Adam Khel coals is mostly related to intermediate igneous rocks. The Sr/Ba, SiO2 + Al2O3, Fe2O3 + CaO + MgO/SiO2 + Al2O3 and high sulfur content in the Padhrar and Darra Adam Khel coals indicate epithermal and marine water influence with a tidal flat, coal-forming environment and a deltaic coal-forming environment, respectively. 相似文献
310.
Nasar Khan Naveed Anjum Mansoor Ahmad Muhammad Awais Naqib Ullah 《Journal of Earth System Science》2018,127(7):98
Organic geochemical and palynofacies analyses were carried out on shale intervals of the Late Paleocene Patala Formation at Nammal Gorge Section, western Salt Range, Pakistan. The total organic carbon content and Rock-Eval pyrolysis results indicated that the formation is dominated by type II and type III kerogens. Rock-Eval \({T}_{\mathrm{max}}\) vs. hydrogen index (HI) and thermal alteration index indicated that the analysed shale intervals present in the formation are thermally mature. \(S_{1}\) and \(S_{2}\) yields showed poor source rock potential for the formation. Three palynofacies assemblages including palynofacies-1, palynofacies-2 and palynofacies-3 were identified, which are prone to dry gas, wet gas and oil generation, respectively. The palynofacies assessment revealed the presence of oil/gas and gas prone type II and type III kerogens in the formation and their deposition on proximal shelf with suboxic to anoxic conditions. The kerogen macerals are dominated by vitrinite and amorphinite with minor inertinite and liptinite. The kerogen macerals are of both marine and terrestrial origin, deposited on a shallow shelf. Overall, the dark black carbonaceous shales present within the formation act as a source rock for hydrocarbons with poor-to-moderate source rock quality, while the grey shales act as a poor source rock for hydrocarbon generation. 相似文献