全文获取类型
收费全文 | 417篇 |
免费 | 43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 | 262篇 |
海洋学 | 18篇 |
天文学 | 18篇 |
综合类 | 31篇 |
自然地理 | 22篇 |
出版年
2023年 | 8篇 |
2022年 | 19篇 |
2021年 | 47篇 |
2020年 | 32篇 |
2019年 | 26篇 |
2018年 | 78篇 |
2017年 | 40篇 |
2016年 | 60篇 |
2015年 | 36篇 |
2014年 | 28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 |
排序方式: 共有493条查询结果,搜索用时 15 毫秒
71.
Natural Hazards - The original article was updated and corrected due to numbering errors in Figure 8’s subfigures and the placement of some of the article’s other figures. Additional... 相似文献
72.
73.
74.
Sumaira Khan Tasneem G. Kazi Muhammad B. Arain Nida F. Kolachi Jameel A. Baig Hassan I. Afridi Abdul Q. Shah 《洁净——土壤、空气、水》2013,41(8):808-815
Sequential extraction procedures are widely used to characterize the different operational fractions with different potential toxicity of metals in environmental solid samples. The present work describes the application of different analytical approaches for sequential extraction of aluminum to evaluate its mobility, availability, and persistent chemical forms in sediment samples of different fresh water ecosystems (lake, canal, and river). The conventional BCR three‐stage sequential extraction procedure (C‐BCR) was modified at each stage, by applying ultrasonic device (U‐BCR), in order to shorten the required shaking time of 16 h for each three steps (excluding the hydrogen peroxide digestion in step 3, which was not performed with ultrasonic bath), could be completed in 40, 50, and 45 min, respectively. The aluminum in all extracts were determination by atomic absorption spectrometry using nitrous oxide – acetylene flame. The accuracy of results obtained from C‐BCR and proposed U‐BCR was verified with literature reported values of certified sediment sample (BCR 701). The overall recoveries of aluminum obtained by proposed U‐BCR were found in the range of 96.7–113% of those values obtained with C‐BCR for all fractions. Use of ultrasonic device, provided a large saving in extraction time relative to conventional shaking. It was observed that major part of Al in real sediment samples (80–83% of total Al) were bound to residual fraction. The acid soluble fraction of aluminum extracted by 0.11 mol/L CH3COOH has good correlation with aluminum content in corresponding water samples of each ecosystem. 相似文献
75.
Wahiduzzaman Md Ali Md. Arfan Luo Jing-Jia Wang Yu Uddin Md. Jalal Shahid Shamsuddin Islam A. R. M. Towfiqul Mondal Sanjit Kumar Siddiki Ubaydur Rahaman Bilal Muhammad Qiu Zhongfeng Dambul Ramzah Eibek Kutubuddin Haque Md. Emdadul 《Theoretical and Applied Climatology》2022,147(1-2):325-346
Theoretical and Applied Climatology - The present study examines the effects of convective available potential energy (CAPE), temperature and humidity on the spatiotemporal variation of... 相似文献
76.
Climatic data from four meteorological stations in Iraq (Mosul, Baghdad, Basra, and Rutba) were obtained. The recorded temperature data since 1960 till 2007 and rainfall and evaporation data since 1960 till 2008 and 1970 till 2008, respectively, were used and interpreted. This study showed an increase in temperature of about 5°C/47?years and an increase in evaporation rate with a decrease in the rainfall rate. Carbon dioxide in the atmosphere appears to be a factor controlling climate change. Basra climate, due to its location which is nearest to the Arabian Gulf, is expressed as a coastal climate and has a different behavior from Mosul, Baghdad, and Rutba, which are considered as terrestrial climates. 相似文献
77.
Mohammad Wasim Mohammad Arif Sajid Iqbal Muhammad Daud 《Geostandards and Geoanalytical Research》2013,37(1):87-93
The International Atomic Energy Agency (IAEA) organised a proficiency test (PT), IAEA‐CU‐2010‐02, for the determination of elements in sewage sludge. The PT sample was analysed by semi‐absolute standardless k0‐instrumental neutron activation analysis (k0‐INAA). Results for seven elements (As, Co, Cr, Fe, Hg, Se, Zn) were submitted to the IAEA by our laboratory. All of our results were scored ‘acceptable’ by the ‘result evaluation criteria’ adopted by the IAEA. The same analytical methodology produced quantitative results for twenty‐six additional elements. In total, thirty‐six elements were determined with uncertainty varying from 4 to 11%. This paper presents the provisional mass fractions of twenty‐six additional elements (Ag, Al, Br, Ca, Ce, Cl, Dy, Eu, Ga, Hf, I, K, La, Mg, Mn, Na, Rb, Sb, Sc, Sm, Ta, Tb, Th, V, U, W) not reported by the IAEA. The analytical methodology was discussed with important sources of spectral, nuclear and fission‐product interferences. It was shown that the important components of uncertainties were the k0 factor, Q0 factor, detector efficiency, mass and counting statistics. The methodology was validated by analysing the IAEA‐S7 reference material. 相似文献
78.
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
79.
Thermodynamics of a large family of black holes from electrovacuum solutions of Einstein’s equations is studied. This family includes rotating and non-accelerating black holes with NUT charge, and rotating and accelerating black holes. The surface gravity, Hawking temperature and the area laws for these black holes are presented. The first law of thermodynamics is also given. An interesting outcome of our analysis is the restriction obtained on the magnitude of acceleration for these black holes. 相似文献
80.
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