全文获取类型
收费全文 | 607篇 |
免费 | 41篇 |
国内免费 | 30篇 |
专业分类
测绘学 | 27篇 |
大气科学 | 26篇 |
地球物理 | 135篇 |
地质学 | 319篇 |
海洋学 | 32篇 |
天文学 | 77篇 |
综合类 | 18篇 |
自然地理 | 44篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 15篇 |
2021年 | 21篇 |
2020年 | 23篇 |
2019年 | 24篇 |
2018年 | 55篇 |
2017年 | 50篇 |
2016年 | 50篇 |
2015年 | 30篇 |
2014年 | 44篇 |
2013年 | 62篇 |
2012年 | 31篇 |
2011年 | 39篇 |
2010年 | 23篇 |
2009年 | 26篇 |
2008年 | 23篇 |
2007年 | 18篇 |
2006年 | 11篇 |
2005年 | 11篇 |
2004年 | 9篇 |
2003年 | 11篇 |
2002年 | 9篇 |
2001年 | 7篇 |
2000年 | 4篇 |
1999年 | 8篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1993年 | 2篇 |
1992年 | 8篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1966年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有678条查询结果,搜索用时 15 毫秒
111.
Fahad Irfan Siddiqui Syed Baharom Azahar Bin Syed Osman 《Environmental Earth Sciences》2013,70(1):259-267
Precise determination of engineering properties of soil is essential for proper design and successful construction of any structure. The conventional methods for determination of engineering properties are invasive, costly and time-consuming. Electrical resistivity survey is an attractive tool for delineate subsurface properties without soil disturbance. Reliable correlations between electrical resistivity and other soil properties will enable us to characterize the subsurface soil without borehole sampling. This paper presents the correlations of electrical resistivity with various properties of soil. Soil investigations, field electrical resistivity survey and laboratory electrical resistivity measurements were conducted. The results from electrical resistivity tests (field and laboratory) and laboratory tests were analyzed together to understand the interrelation between electrical resistivity and various soil properties. The test results were evaluated using simple and multiple regression analysis. From the data analysis, significant quantitative and qualitative correlations have been obtained between resistivity and moisture content, friction angle and plasticity index. Weaker correlations have been observed for cohesion, unit weight of soil and effective size (D 10). 相似文献
112.
Riaz Hossain Khan Muhammad Qumrul Hassan Mohammad Saiful Islam 《Environmental Earth Sciences》2013,69(8):2499-2512
Water quality and hydrochemistry of Shariatpur district were evaluated in terms of hydrochemical composition and some important physico-chemical parameters. The groundwater of the study area is good for drinking, domestic as well as for irrigation purposes. Among the major ions, shallow tube well waters give higher concentration of Ca2+ which ranges from 24 to 260 mg/L. The deep tubewell waters show higher concentration of Na+ which varies from 74 to 582 mg/L during dry season. Among the trace elements most of the shallow aquifer samples show higher concentration of Fe2+, Mn2+ and As. Concentration of Fe2+ varies from 0.655 to 18.8 mg/L, and Mn2+ from trace to 0.868 mg/L during dry period. Hydrochemical analyses reveal significant seasonal variation in water quality of shallow aquifer. Both the shallow aquifer and the surface water of the study area are predominantly of Ca–Mg–HCO3 type, while the deep aquifer water is mainly of Na–K–Cl–SO4 type with slight inclination to Ca–Mg–HCO3 type. The study area is suitable for groundwater development if comprehensive and holistic approaches towards water resource management are taken into consideration. 相似文献
113.
Eslam A. Al-Hogaraty Hassan K. Garamoon Farouk El-Baz Reinhard Zölitz-Möller Mohamed A. Abdel Moati 《Arabian Journal of Geosciences》2013,6(11):4093-4107
Wadi Wurayah area is one of the major wadis originating and running on the Oman Mountains and drains into the Oman Gulf. These wadis in general and Wadi Wurayah in particular are characterized with a rich diversity of rare and mountainous and freshwater habitats and species. These wadis contain unequal, representative, and sensitive areas of the dry lands ecosystem with natural, outstanding landscapes and cultural heritage, while the socioeconomic situation indicates that it has enough socioeconomic infrastructures to develop new alternatives ecologically and economically sustainable. As most of the United Arab Emirates and the region, the study area is undergoing dramatic changes linked to economic diversification and promotion of tourism. Established under the UNESCO’s Man and the Biosphere Program, Wurayah Biosphere Reserve represents protected areas intended to demonstrate well-balanced relationship between conservation of biodiversity and an appropriate local development. The main objectives of this study are to develop an environmental information system to understand the dynamics of human activities associated to land use in the study area, highlight the threats to the environment, educate people about the basic environmental issues and positive traditional practices, and promote tourism. Based on the gained results, the concept of biosphere reserve as a model is to implement ideas of sustainable land use in practice. 相似文献
114.
Hassan Eltom Mohammed Makkawi Osman Abdullatif Khalid Alramadan 《Arabian Journal of Geosciences》2013,6(11):4323-4335
Subsurface models of hydrocarbon reservoirs are coarse and of low resolution when compared with the actual geologic characteristics. Therefore, the understanding of the three-dimensional architecture of reservoir units is often incomplete. Outcrop analogues are commonly used to understand the spatial continuity of reservoir units. In this study, a Late Jurassic outcrop analogue for the Arab-D reservoir of central Saudi Arabia was used to build a high-resolution model that captures fine geologic details. Subsurface reservoir lithofacies were matched with those from the studied outcrop, and porosity values derived from published core and well log data from the Ain Dar, Uthmanyah, and Shudgum areas of the Ghawar Field, eastern Saudi Arabia, were then applied to the equivalent lithofacies in the outcrop. Maximum, minimum, and average subsurface porosity for each lithofacies were distributed in the facies model using a geostatistical algorithm to produce nine porosity models for the field data. Several realisations were run to visualise the variability in each model and to quantitatively measure the uncertainty associated with the models. The results indicated that potential reservoir zones were associated with grainstone, packstone, and some wackestone layers. Semivariogram analysis of the lithofacies showed good continuity in the N-S direction and less continuity in the E-W direction. The high-resolution lithofacies models detected permeability barriers and isolated low porosity bodies within the potential reservoir zones. This model revealed the porosity distribution in areas smaller than one cell in the subsurface model and highlighted the uncertainty associated with several aspects of the model. 相似文献
115.
Muhammad Irfan Aziz Akbar Mubashir Aziz Ammad Hassan Khan 《Geotechnical and Geological Engineering》2013,31(2):729-738
Rapid urbanization and expansion of metropolitans in the developing world is pressing the need of tall structures with multiple basements. In several such projects, open land is available around excavation site and unsupported deep excavations by maintaining appropriate side slopes offer economical solution. In this research, subsoil stratigraphy of Lahore district was established to be comprising of a top clay stratum 1.5–8 m thick, followed by a sand layer. Considering subsoil data from several geotechnical investigation reports, the effect of four key parameters viz., cohesion of clay layer, friction angle of sand layer, thickness of clay layer at the top and slope inclination of underlying sand layer on safety factor of open excavations was studied. Six hundred twenty-five slope stability analyses were conducted by considering different geometries and soil properties. Based on the results of these analyses, a regression model was suggested to estimate safety factor of open excavations in similar stratigraphy which would be useful in feasibility studies and preliminary design of deep excavations. It was established that the clay layer cohesion was the most dominant contributor to safety factor. 相似文献
116.
This paper presents a new family of interior solutions of Einstein–Maxwell field equations in general relativity for a static spherically symmetric distribution of a charged perfect fluid with a particular form of charge distribution. This solution gives us wide range of parameter, K, for which the solution is well behaved hence, suitable for modeling of superdense star. For this solution the gravitational mass of a star is maximized with all degree of suitability by assuming the surface density equal to normal nuclear density, ρ nm=2.5×1017 kg?m?3. By this model we obtain the mass of the Crab pulsar, M Crab, 1.36M ⊙ and radius 13.21 km, constraining the moment of inertia >?1.61×1038 kg?m2 for the conservative estimate of Crab nebula mass 2M ⊙. And M Crab=1.96M ⊙ with radius R Crab=14.38 km constraining the moment of inertia >?3.04×1038 kg?m2 for the newest estimate of Crab nebula mass, 4.6M ⊙. These results are quite well in agreement with the possible values of mass and radius of Crab pulsar. Besides this, our model yields moments of inertia for PSR J0737-3039A and PSR J0737-3039B, I A =1.4285×1038 kg?m2 and I B =1.3647×1038 kg?m2 respectively. It has been observed that under well behaved conditions this class of solutions gives us the overall maximum gravitational mass of super dense object, M G(max)=4.7487M ⊙ with radius $R_{M_{\max}}=15.24~\mathrm{km}$ , surface redshift 0.9878, charge 7.47×1020 C, and central density 4.31ρ nm. 相似文献
117.
Assessment of Trace Metal Contamination of Drinking Water in the Pearl Valley,Azad Jammu and Kashmir
Saboor Javaid Syed Ghulam Sarwar Shah Abdul Jabbar Chaudhary Mohammad Haleem Khan 《洁净——土壤、空气、水》2008,36(2):216-221
The aim of this study was to assess trace metal contamination of drinking water in the Pearl Valley, Azad Jammu and Kashmir (Pakistan). The objectives were to determine physical properties and the dissolved concentration of five trace metals, i. e., lead, copper, nickel, zinc, and manganese, in drinking water samples collected from various sites of municipal water supply, natural water springs and wells in the valley. Concentrations of the metals in the water samples were determined by flame atomic absorption spectrometry. Results showed physical parameters, i. e., appearance, taste and odor within acceptable limits and pH was between 5.5 and 7.0. The observed concentrations of the metals varied between sources of water samples and between sampling sites. Maximum dissolved concentration observed was 4.7 mg/L for Pb and Mn, 4.6 mg/L for Zn, 2.9 mg/L for Ni and 2.8 mg/L for Cu. The observed concentrations of the metals were compared with the World Health Organization's guideline values for drinking water. Overall, the quality of water samples taken from the water springs at Mutyal Mara and Bonjosa was good; however, the water quality was unsuitable for drinking in Kiraki, Kharick, and Pothi Bala localities particularly. Finally, the authors discuss possible causes for increased concentrations of the trace metals in drinking water in the study area. 相似文献
118.
The removal of heavy metals such as Ni(II), Zn(II), Al(III), and Sb(III) from aqueous metal solutions was investigated using novel, cost effective, seaweed derived sorbents. Studies with a laboratory scale fixed‐bed sorption column, using a seaweed waste material (referred to as waste Ascophyllum product (WAP)) from the processing of Ascophyllum nodosum as biosorbent, demonstrated high removal efficiencies (RE) for a variety of heavy metals including Ni(II), Zn(II) and Al(III), with 90, 90 and 74% RE achieved from initial 10 mg/L metal solutions, respectively. The presence of Sb(III) in multi component metal solutions suppressed the removal of Ni(II), Zn(II) and Al(III), reducing the RE to 28, 17 and 24%, respectively. The use of Polysiphonia lanosa as a biosorbent showed a 67% RE for Sb(III), both alone and in combination with other metals. Potentiometric and conductometric titrations, X‐ray photoelectron and mid‐infrared spectroscopic analysis demonstrated that carboxyl, alcohol, sulfonate and ether groups were heavily involved in Sb(III) binding by P. lanosa. Only carboxyl and sulfonate groups were involved in Sb(III) binding by WAP. Furthermore, a greater amount of weak acidic groups (mainly carboxylic functions) were involved in Sb(III) binding by P. lanosa, compared to WAP which involved a greater concentration of strong acidic groups (mainly sulfonates). 相似文献
119.
Md. Mokhlesur Rahman Muhammad Qumrul Hassan Mohammad Saiful Islam S. Z. K. M. Shamsad 《Environmental Geology》2000,40(1-2):31-40
This paper deals with an environmental impact assessment of low water flow in the river Ganges during a dry period at the
Khulna and Mongla port areas in south-western Bangladesh. Large-scale surface water withdrawal in India after commissioning
the Farakka Barrage causes a drastic fall in the Ganges low-flow condition within the Bangladesh territory during every dry
period. The average lowest discharge in the Ganges is 552 m3/s, which is about 73% less than that in the pre-Farakka time. This has caused the deterioration of both surface and groundwater
quality of the study area. Salinity is the principal cause of water quality degradation in the area. Present observation shows
that the surface water of the area is sulphate-chloride dominated, which signifies high salinity whereas the groundwater is
categorized as of medium to high salinity. To maintain the Rupsa River's maximum salinity below 1000 μS/cm the discharge in
the Ganges should be ∼1500 m3/s, whereas that at Garai basin is ∼10 m3/s. If this present situation continues it will be a crippling blow to the environment of the area in the long term. An integrated
multidisciplinary approach to hydrogeological research is urgently required to salvage the area from further deterioration.
Received: 9 August 1999 · Accepted: 8 March 2000 相似文献
120.
The Wadi Badaa (WB) Upper Miocene clays, Cairo-Suez district, Egypt, represent materials for the ceramic production. The clay raw materials are composed mainly of smectite and kaolinite with minor quartz, calcite, and rare feldspar. The plasticity indices vary between 24 and 30%, suggesting that these clays are plastic raw materials. IR bands of the investigated clays were observed at 3695, 3619, 1032, 916, 794, 690, 534, 466, and 423 cm?1 for kaolinite; at 3436, 1635, 916, and 466 cm?1 for smectite; and at 1179, 1104, 794, 690, and 466 cm?1 for quartz. The <2 μm particle sizes of samples are relatively abundant in clays (~33%), which is adequate for uses of the ceramic products because of containing fine particle sizes. The studied WB clays contain 7.95 and 12.35% moisture water and interlayer water, respectively, with a maximum drying shrinkage of 7.87% at room temperature; therefore, the WB clays could be used in the ceramic manufacture. 相似文献