全文获取类型
收费全文 | 242篇 |
免费 | 21篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 18篇 |
地球物理 | 79篇 |
地质学 | 112篇 |
海洋学 | 22篇 |
天文学 | 17篇 |
综合类 | 2篇 |
自然地理 | 8篇 |
出版年
2022年 | 8篇 |
2021年 | 10篇 |
2020年 | 7篇 |
2019年 | 6篇 |
2018年 | 14篇 |
2017年 | 22篇 |
2016年 | 22篇 |
2015年 | 11篇 |
2014年 | 22篇 |
2013年 | 24篇 |
2012年 | 5篇 |
2011年 | 12篇 |
2010年 | 13篇 |
2009年 | 14篇 |
2008年 | 9篇 |
2007年 | 5篇 |
2006年 | 7篇 |
2005年 | 7篇 |
2004年 | 5篇 |
2003年 | 8篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1979年 | 2篇 |
排序方式: 共有270条查询结果,搜索用时 15 毫秒
231.
In this paper, we apply lagged correlation analysis to study the effects of vegetation cover on the summer climate in different zones of China, using NOAA/AVHRR normalized difference vegetation index (NDVI) data during the time period from 1982 to 2001 and climate data of 365 meteorological stations across China (precipitation from 1982 to 2001 and temperature from 1982 to 1998). The results show that there are positive correlations between spring NDVI and summer climate (temperature and precipitation) in most zones of China; these suggest that, when the vegetation cover increases, the summer precipitation will increase, and the lagged correlations show a significant difference between zones. The stronger correlations between NDVI in previous season and summer climate occur in three zones (Mid-temperate zone, Warm-temperate zone and Plateau climate zone), and this implies that vegetation changes have more sensitive feedback effects on climate in the three zones in China. 相似文献
232.
Sabtanti Harimurti Anisa Ur Rahmah Abdul Aziz Omar Murugesan Thanapalan 《洁净——土壤、空气、水》2013,41(12):1165-1174
The UV/H2O2 is one of the popular techniques in the advanced oxidation processes (AOPs) and has been applied in the wastewater treatment during recent two decades. UV exposure on the H2O2 generate highly reactive hydroxyl radicals (OH?), which are used to degrade organic contaminants through oxidation processes in wastewater. This present study involves the estimation of hydroxyl radical rate constants of methyldiethanolamine (MDEA) mineralization at different temperatures by using UV/H2O2 in aqueous solution. Laboratory experiments have been conducted and the profile of MDEA mineralization has been established. The hydroxyl radical rate constants and the activation energy of mineralization process have been calculated. The estimated hydroxyl rate constants and the activation energy are in good agreement with those reported in the literature. 相似文献
233.
The X-ray fluorescence and ICP methods were used to analyze 60 outcrop samples of black shale, of which 15 were collected from Belait, 15 from the Setap Shale, 15 from Temburong, and 15 from the Trusmadi formations. The average compositions of the shales from the study area are 64.62%, 63.95%, 62.32%, 63.84% SiO2, 1.84%, 2.14%, 2.04%, 1.99% MgO, 2.55%, 3.12%, 2.89%, 2.72% K2O, 0.32%, 0.30%, 0.32%, 0.53% CaO, 5.86%, 6.06%, 7.14%, 6.60% Fe2O3, 207×10^-6, 180×10^-6, 213×10^-6, 200×10^-6 Rb, and 56×10^-6, 49×10^-6, 50×10^-6, 32×10^-6 Sr for the Setap Shale, Temburong, Belait and Trusmadi samples, respectively. The high Rb/Sr ratios of 3.8, 3.7, 4.2, and 6.1 are attributed to the lowest contents of Sr due to reducing conditions prevailing. The high Rb/K ratio sug- gests either brackish marine or rapid deposition that prevented equilibrium between Rb and K in the shales and marine waters. 相似文献
234.
235.
236.
A. Aziz H. Park S. Kim K. S. Kim 《International Journal of Environmental Science and Technology》2016,13(12):2805-2816
Fe-ZSM-5 zeolites are important for many applications, especially for catalysis and volatile organic carbon removal. However, the inclusion of a high content of iron in the ZSM-5 structure is hindered due to the high pH required for hydrothermal synthesis. To overcome this problem, the synthesis of Fe-ZSM-5 zeolites with a novel iron chelate complex as the iron source (ammonium iron citrate) and a common iron source (iron chloride) was investigated. The synthesized materials were characterized by XRD, BET, SEM, FTIR, XPS and ICP. The total iron content was determined by ICP. Fe-ZSM-5 zeolites prepared by the ammonium iron citrate source method contain the highest iron concentration within the framework of a Mobil five structure, which has a high surface area and crystallinity. The prepared materials were used to remove phenol and ammonium. The catalytic results demonstrated that Fe-ZSM-5 prepared with ammonium iron citrate is the best catalyst. 相似文献
237.
Hammad Tariq Janjuhah Ahmed Mohammad Ahmed Salim Abubaker Alansari Deva Prasad Ghosh 《Arabian Journal of Geosciences》2018,11(9):204
The Luconia Province—offshore Sarawak—is a key hydrocarbon province in Malaysia. However, the gas reservoirs in Central Luconia pose unique problems and challenges as they have partially water-filled microporosity that overprint wireline logs. Microporosity in Central Luconia occurs throughout the Miocene carbonates and is a crucial element that influences fluid flow properties and ultimately the recovery of hydrocarbons. Quantification of macroporosity was achieved using petrographic analysis of thin sections and the FESEM images. The point counting technique was used to estimate the amount of macroporosity from the thin section, which was then subtracted from the total porosity to derive microporosity. The qualitative investigation of the Miocene carbonates indicates the presence of three different types of microporosity namely grain-based microporosity, matrix-based microporosity, and cement-based microporosity. Quantification of microporosity showed that the microporosity varies from sample to sample, ranging from 10 to 60% of the total measured porosity. The depositional texture, mineralogy, and microtexture control this microporosity variation including its abundance and type. The microporosity in Central Luconia is diagenetically controlled based on four major diagenetic mechanisms namely (1) mechanical process/endolithic grains/marine diagenesis; (2) leaching/meteoric diagenesis; (3) cementation/shallow diagenesis; and (4) deeper diagenesis environment. 相似文献
238.
An analytical method is developed to provide a better understanding of bolt shearing across joint planes under lateral confinement.
The study was undertaken in conjunction with a laboratory study of the double shearing of bolts in concrete. A review of various
analytical methods is discussed, and the bending behaviour of the bolts is studied under both elastic and plastic conditions.
Issues examined include; hinge point location, the effect of concrete strength on the bolt-bending behaviour; the influence
of bolt axial loading and bolt diameter on the hinge point position with respect to sheared joint planes. It was found that
the applied axial load on the bolt had a significant bearing on the location of the hinge points in different strength concrete,
particularly at low strengths. The hinge point location is also influenced by the bolt diameter. 相似文献
239.
The black shale samples collected from two Neogene formations in the Klias Peninsula area, West Sabah, have been assessed
and characterized in details by gas chromatography, gas chromatography-mass spectrometry and a variety of organic geochemical
parameters. The aims of this study are to describe the characteristics of organic matter of these sediments in terms of source/type
of the organic matter, assess its thermal maturity and paleoenvironment of deposition, based primarily on biomarker distributions.
The results of both formations do not reveal significant differences within the rock extracts. The gas chromatograms of the
saturated hydrocarbon fractions of the Setap Shale and the Belait formations displayed monomodal n-alkane distributions and
nearly identical regular sterane compositions with a predominance of C27 regular steranes. These are consistent with open marine depositional environments dominated by marine biological matter.
Another related feature of these rock extracts is the presence of a high relative abundance of gammacerane, indicating anoxic
marine hypersaline source depositional environment. The relatively high abundance of common land plant-derived biomarkers,
such as bicadinanes and oleananes, is a clear indication of a major terrigenous input to the source of the extractable organic
matter. The predominance of oleanane biomarkers in both formations is indicative of angiospermis input and Tertiary source
rocks. The high C29/C30 hopane ratios, moderate development of C33–C35 hopanes, high abundance of tricyclic terpanes and a slight predominance of C27 regular sterane over C28 and C29 steranes are characteristic features tending to suggest a significant marine influence on these source rocks, thereby suggesting
a mixed source input. The 22S/(22S+22R)C32 hopane ratio has reached equilibrium, and this is supported by the high maturity level as indicated by the 22S/22SC31–33 extended hopane ratios and 20S/(20S+20R)C29 regular steranes ratios. 相似文献
240.
Pervaiz Sikandar Allah Bakhsh Muhammad Arshad Tariq Rana 《Environmental Earth Sciences》2010,60(5):1113-1129
A geoelectrical resistivity survey using vertical electrical sounding (VES) was conducted at Chaj Doab (land between rivers
Jhelum and Chenab, Pakistan) and Rachna Doab (land between rivers Chenab and Ravi, Pakistan), with the objective of investigating
groundwater conditions. A total of 90 sites were selected with 43 sites in Chaj and 47 sites in Rachna Doabs. The resistivity
meter (ABEM Terrameter SAS 4000, Sweden) was used to collect the VES data by employing a Schlumberger electrode configuration,
with half current electrode spacings (AB/2) ranging from 2 to 180 m and the potential electrode (MN) from 1 to 40 m. The field
data were interpreted using the Interpex IX1D computer software and the resistivity versus depth models for each location
was estimated. The outputs of subsurface layers with resistivities and thickness presented in contour maps and 3-D views by
using SURFER software were created. A total of 102 groundwater samples from nearby hydrowells at different depths were collected
to develop a correlation between the aquifer resistivity of VES and the electrical conductivity (EC) of the groundwater and
to confirm the resulted geophysical resistivity models. From the correlation developed, it was observed that the groundwater
salinity in the aquifer may be considered low and so safe for irrigation if resistivity >45 Ω m, and marginally fit for irrigation
having resistivity between 25 and 45 Ω m. The study area has resistivities from 3.9 to 2,222 Ω m at the top of the unsaturated
layer, between 1.21 and 171 Ω m, in the shallow aquifers, and 0.14–152 Ω m in the deep aquifers of the study area. The results
indicate that the quality of groundwater is better near the rivers and in the shallow layers compared to the deep layers. 相似文献