全文获取类型
收费全文 | 946篇 |
免费 | 35篇 |
国内免费 | 23篇 |
专业分类
测绘学 | 37篇 |
大气科学 | 47篇 |
地球物理 | 180篇 |
地质学 | 601篇 |
海洋学 | 32篇 |
天文学 | 64篇 |
综合类 | 6篇 |
自然地理 | 37篇 |
出版年
2023年 | 4篇 |
2022年 | 34篇 |
2021年 | 37篇 |
2020年 | 33篇 |
2019年 | 24篇 |
2018年 | 77篇 |
2017年 | 85篇 |
2016年 | 63篇 |
2015年 | 42篇 |
2014年 | 64篇 |
2013年 | 79篇 |
2012年 | 41篇 |
2011年 | 51篇 |
2010年 | 37篇 |
2009年 | 40篇 |
2008年 | 33篇 |
2007年 | 21篇 |
2006年 | 24篇 |
2005年 | 25篇 |
2004年 | 18篇 |
2003年 | 16篇 |
2002年 | 16篇 |
2001年 | 8篇 |
2000年 | 11篇 |
1999年 | 11篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1973年 | 3篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1963年 | 1篇 |
排序方式: 共有1004条查询结果,搜索用时 15 毫秒
91.
Ahmed Murad 《中国地球化学学报》2010,29(2):152-156
The stable isotopes of oxygen and hydrogen have been implemented to assess the recharge mechanisms in an area in the UAE bounded to the northwestern part of the Gulf of Oman and the southeastern part of the Arabian Gulf. The conversion of stable isotopes to deuterium excess was utilized as a supportive tool to understand the process of groundwater recharge. The concluding results of this study showed that the origin of moisture is the Mediterranean Sea. The precipitation is the main source of recharge, in which the precipitation having undergone evaporation before recharge occurs. The comparison between regression line for data collected in 1996 and regression line for samples collected in 2006 suggests that the precipitation water which recharged the groundwater, was diluted with groundwater and this dilution is observed from decreasing of the deuterium excess of collected groundwater samples with increasing isotopes of oxygen. The dilution of groundwater with the recharge water suggests modern-day recharge as it is seen from high deuterium excess that exceeded the deuterium excess of LMWL and was close to MMWL. 相似文献
92.
Franziska D.H. Wilke Patrick J. O'Brien Uwe Altenberger Matthias Konrad-Schmolke M. Ahmed Khan 《Lithos》2010,114(1-2):70-85
Metabasites were sampled from rock series of the subducted margin of the Indian Plate, the so-called Higher Himalayan Crystalline, in the Upper Kaghan Valley, Pakistan. These vary from corona dolerites, cropping out around Saif-ul-Muluk in the south, to coesite–eclogite close to the suture zone against rocks of the Kohistan arc in the north. Bulk rock major- and trace- element chemistry reveals essentially a single protolith as the source for five different eclogite types, which differ in fabric, modal mineralogy as well as in mineral chemistry. The study of newly-collected samples reveals coesite (confirmed by in situ Raman spectroscopy) in both garnet and omphacite. All eclogites show growth of amphiboles during exhumation. Within some coesite-bearing eclogites the presence of glaucophane cores to barroisite is noted whereas in most samples porphyroblastic sodic–calcic amphiboles are rimmed by more aluminous calcic amphibole (pargasite, tschermakite, and edenite). Eclogite facies rutile is replaced by ilmenite which itself is commonly surrounded by titanite. In addition, some eclogite bodies show leucocratic segregations containing phengite, quartz, zoisite and/or kyanite. The important implication is that the complex exhumation path shows stages of initial cooling during decompression (formation of glaucophane) followed by reheating: a very similar situation to that reported for the coesite-bearing eclogite series of the Tso Morari massif, India, 450 km to the south-east. 相似文献
93.
The particulate nature of granular soils can be accurately simulated at a microscale level. However, due to the huge spatial extent of geotechnical systems, a model fully constructed at such a scale is almost impossible with current computing technologies. Hence, continuum-based approaches are considered as the practical scale for modeling the majority of problems. Combining both scales enables benefiting from the advantages of both techniques while trying to overcome their drawbacks. Although a significant number of publications have addressed coupling both scales, only a few provide information regarding implementing the proposed procedures. In this study, an efficient co-simulation framework for conducting multiscale analysis is introduced. The framework is based on integrating existing continuum and micromechanical modeling software packages and therefore benefitting from already existing codes. A computational simulation of a rigid pile in contact with granular soil demonstrating the capabilities of such technique is presented. The near-field zone surrounding the pile is modeled using DEM whereas FEM is utilized to model far-field zones that are not affected by the presence of the pile. Results of conducted simulations resemble those obtained from experimental results. The proposed approach appears to be a very effective and promising tool to model boundary value problems of geotechnical systems. 相似文献
94.
Numerical modeling of the Rideau Valley Watershed 总被引:1,自引:0,他引:1
Ferdous Ahmed 《Natural Hazards》2010,55(1):63-84
Using the Mike11 modeling system by the Danish Hydraulic Institute, a detailed model of the Rideau Valley Watershed was constructed.
It includes 532 km of rivers and lakes, 106 basins, 122 bridges and culverts, and 20 water control structures. The model was
calibrated using measured streamflow data for a time period of 5 years; additional 5 years of data was used for validation.
Various methods, both qualitative and quantitative, were used to evaluate the model performance. It was found that the model
can simulate the hydrological response with a reasonable to high degree of accuracy. This model is now being used for various
watershed management purposes, including flood forecasting, dam safety assessment, quantification of wetland functions, and
derivation of design flows. 相似文献
95.
Hydrochemistry and Classification of Groundwater Resources of Ishwardi Municipal Area,Pabna District,Bangladesh 总被引:2,自引:0,他引:2
Golzar Hossain M. Farhad Howladar Lutfun Nessa Syed Samsuddin Ahmed Chowdhury Quamruzzaman 《Geotechnical and Geological Engineering》2010,28(5):671-679
The chemical property of groundwater depends largely on the mineralogical composition of the rocks through which the water
has moved and the rate of movement and these characteristics of surface water depend on organic and inorganic reactions, industrial
effluents, rainfall and temperature etc. The underground water tends to contain more dissolved materials than those in surface
water because of their more intimate and longer contact with organic materials of soil and rock particles. The groundwater
of the studied area is dominant of alkaline earth’s (Ca2+ and Mg2+) and weak acids (HCO3
−) which may be classified as Magnesium-Bicarbonate and Calcium Carbonate types. Genetically, the groundwater of the area belongs
to both “Normal Chloride” “Normal Sulphate” and “Normal Carbonate” to “Super Carbonate” group. Based on EC, SAR and RC, the
groundwater of the area varies from good–excellent quality for irrigation purposes with low alkali hazard and medium salinity
hazard. 相似文献
96.
Modelling of paleo-saltwater intrusion in the northern part of the Nubian Aquifer System, Northeast Africa 总被引:2,自引:2,他引:0
A numerical groundwater model of the Nubian Aquifer System was established to prove the influence of rising seawater levels on the groundwater salinity in northern Egypt over the last 140,000 years. In addition, the impact of a groundwater recharge scenario for these 140,000 years, involving climatic change, on the saltwater/freshwater interface was investigated. Saltwater intrusion induced by rising water levels of the Mediterranean Sea led to salinisation from the Mediterranean Sea to the Qattara depression. This modeling approach was supported by a density-driven model setup and calculation. The modelled saltwater/freshwater interfaces partially fitted the observed ones, especially in the southern half of the Qattara depression. In other parts of the northern Nubian Aquifer System, the ingression of salt water was modelled adequately, but in the west, small regions of the measured interface were not. The development in the Qattara depression (Egypt) and Sirte basin (Libya) were investigated in more detail. The different behaviour in the Sirte basin may be due to high evapotranspiration rates in some former periods, salt solutions from the pre-Quaternary layers or saltwater infiltration from sabkha-like recent salt-bearing sediments. 相似文献
97.
Adsorption of copper, nickel and lead ions from synthetic semiconductor industrial wastewater by palm shell activated carbon 总被引:4,自引:4,他引:0
Y. B. Onundi M.Sc. A. A. Mamun Ph.D. M. F. Al Khatib Ph.D. Y. M. Ahmed M.Sc. 《International Journal of Environmental Science and Technology》2010,7(4):751-758
Granular activated carbon produced from palm kernel shell was used as adsorbent to remove copper, nickel and lead ions from a synthesized industrial wastewater.Laboratory experimental investigation was carried out to identify the effect of pH and contact time on adsorption of lead, copper and nickel from the mixed metals solution. Equilibrium adsorption experiments at ambient room temperature were carried out and fitted to Langmuir and Freundlich models. Results showed that pH 5 was the most suitable, while the maximum adsorbent capacity was at a dosage of 1 g/L, recording a sorption capacity of 1.337 mg/g for lead, 1.581 mg/g for copper and 0.130 mg/g for nickel. The percentage metal removal approached equilibrium within 30 min for lead, 75 min for copper and nickel, with lead recording 100 %, copper 97 % and nickel 55 % removal, having a trend of Pb2+ > Cu2+ > Ni2+. Langmuir model had higher R2 values of 0.977, 0.817 and 0.978 for copper, nickel and lead respectively, which fitted the equilibrium adsorption process more than Freundlich model for the three metals. 相似文献
98.
Jiban K. Sarker Mehedi Ahmed Ansary Md. S. Rahman A. M. M. Safiullah 《Environmental Earth Sciences》2010,60(3):643-653
Mymensingh municipality lies in one of the most earthquake-prone areas of Bangladesh. The town was completely destroyed during
the Great Indian Earthquake of 12 June 1897, for which the surface-wave magnitude was 8.1. In this study the 1897 Great Indian
Earthquake was used as a scenario event for developing seismic microzonation maps for Mymensingh. For microzonation purposes
SPT data from 87 boreholes were collected from different relevant organizations. To verify those data ten boreholes of depth
up to 30 m were drilled. Intensity values obtained for different events were calibrated against attenuation laws to check
applicability to the study area. Vibration characteristics at diverse points of the study area were estimated by employing
the one-dimensional wave-propagation software SHAKE. SHAKE discretizes the soil profile into several layers and uses an iterative
technique to represent the non-linear behavior of the soil by adjusting the material properties at each iteration step. The
required input information includes depth, shear wave velocity, damping factor, and unit weight of each soil layer. The liquefaction
resistance factor and the resulting liquefaction potential were estimated to quantify the severity of liquefaction. Quantification
of secondary site effects and the weighting scheme for combining the various seismic hazards were heuristic, based on judgment
and expert opinion. 相似文献
99.
Geochemical study of arsenic and other trace elements in groundwater and sediments of the Old Brahmaputra River Plain,Bangladesh 总被引:1,自引:1,他引:0
Faruque Ahmed M. Hawa Bibi Hiroaki Ishiga Takehiko Fukushima Teruyuki Maruoka 《Environmental Earth Sciences》2010,60(6):1303-1316
The geochemical study of groundwaters and core sediments from the Old Brahmaputra plain of Bangladesh was conducted to investigate
the distribution of arsenic and related trace elements. Groundwaters from tube wells are characterized by pH of 6.4–7.4, dissolved
oxygen (DO) of 0.8–1.8 mg/l, Ca contents of 5–50 mg/l, and Fe contents of 0.2–12.9 mg/l. Arsenic concentrations ranged from
8 to 251 μg/l, with an average value of 63 μg/l. A strong positive correlation exists between As and Fe (r
2 = 0.802; p = 0.001) concentrations in groundwater. The stratigraphic sequences in the cores consist of yellowish silty clays at top,
passing downward into grayish to yellowish clays and sands. The uppermost 3 m and lower parts (from 13 to 31 m) of the core
sediments are oxidized (average oxidation reduction potential (ORP) +170 and +220 mV, respectively), and the ORP values gradually
become negative from 3 to 13 m depths (−35 to −180 mV), indicating that anoxic conditions prevail in the shallow aquifers
of the Brahmaputra plain. Age determinations suggest that clay horizons at ~10 m depth were deposited at around 2,000 and
5,000 years BP (14C ages) during the transgressive phase of sea-level change. Elevated concentrations of As, Pb, Zn, Cu, Ni, Cr, and V are present
in the silts and clays, probably due to adsorption onto clay particles. Significant concentrations of As occur in black peat
and peaty sediments at depths between 9 and 13 m. A strong positive correlation between As and Fe was found in the sediments,
indicating As may be adsorbed onto Fe oxides in aquifer sediments. 相似文献
100.
K M Azam Chowdhury Wensheng Jiang Guimei Liu Md Kawser Ahmed Shaila Akhter 《海洋学报(英文版)》2022,41(4):23-39
In the northern Bay of Bengal, the existence of intense temperature inversion during winter is a widely accepted phenomenon. However, occurrences of temperature inversion during other seasons and the spatial distribution within and adjacent to the Bay of Bengal are not well understood. In this study, a higher resolution spatiotemporal variation of temperature inversion and its mechanisms are examined with mixed layer heat and salt budget analysis utilizing long-term Argo(2004 to 2020) and RAMA(2... 相似文献