首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   236篇
  免费   10篇
  国内免费   4篇
测绘学   4篇
大气科学   5篇
地球物理   63篇
地质学   148篇
海洋学   8篇
天文学   9篇
综合类   1篇
自然地理   12篇
  2023年   1篇
  2022年   5篇
  2021年   5篇
  2020年   15篇
  2019年   6篇
  2018年   15篇
  2017年   20篇
  2016年   16篇
  2015年   10篇
  2014年   20篇
  2013年   22篇
  2012年   10篇
  2011年   13篇
  2010年   14篇
  2009年   7篇
  2008年   6篇
  2007年   9篇
  2006年   5篇
  2005年   2篇
  2004年   3篇
  2003年   1篇
  2002年   4篇
  2001年   4篇
  1999年   4篇
  1998年   1篇
  1997年   2篇
  1996年   1篇
  1995年   1篇
  1994年   4篇
  1993年   2篇
  1992年   5篇
  1991年   3篇
  1990年   1篇
  1988年   1篇
  1986年   4篇
  1985年   1篇
  1983年   1篇
  1982年   1篇
  1981年   2篇
  1980年   1篇
  1979年   1篇
  1976年   1篇
排序方式: 共有250条查询结果,搜索用时 31 毫秒
81.
The emissions from palm oil industry through incineration and open burning are the major sources of air pollutions contribution in Malaysia. The consequence of increasing the particulate concentration, the particulate matter dissolves with vapour and grows into droplets when the humidity exceeds approximately 70% and causing opaque situation known as haze. This work focuses on the dispersion particulate matter from palm oil mill. Gaussian Plume Model from a point source, subject to various atmospheric conditions is used to calculate particulate matter concentration then display the distribution of plume dispersion using geographic information system. Atmospheric Stability, mixing height, wind direction, wind speed, natural and artificial features play an important role in dispersion process. Study on the dispersion of particulate matters and the haze potential are presented as a case study in this paper. The data obtained will be served as the purpose of modeling the transport of particulate matter for obtaining permits and prevention of significant deterioration to the environment.  相似文献   
82.
83.
Sabkha deposits cover extensive areas along the Red Sea and the Arabian Gulf shores. They are the site of huge industrial complexes in spite of their low bearing capacity of its upper part. The strength of the Sabkha soil is controlled by several factors, among them are the evaporatic salts that cement the grains. The Standard Penetration Test (SPT) is used extensively in this terrain but its results are misleading. The Sabkha soil that may give high N value will lose most of its strength upon wetting as part of the salts are dissolved. Therefore, the design N value was adjusted for Sabkhas to account for salt migration, by relating the SPT (N) value to the Sabkha moisture and salt content. A steel structure factory that was placed in an eastern Saudi Arabian virgin Sabkha deposits was considered. After a few years of operation fresh water leaked through the ground and caused signi.cant differential collapse settlement which threatened the functional integrity of the superstructure. The differential settlement was con.ned to one area of the structure indicating that localized conditions must have contributed to the observed settlement. The subsurface conditions and the geotechnical properties of the site are presented. A statistical model was developed that quanti.es the effect of the moisture and salt content on SPT (N) values. A simple site procedure is suggested to correct the design N value in similar cases. It was found that the increase in the moisture content could reduce the SPT (N) values by as much as 60, good agreements were found between the measured and predicted N values.  相似文献   
84.
The paper deals with the structural position of the Logar ultrabasite massif with respect to the folded Kabul block. The ultrabasite is composed of a thick tectonic mantle in the ophiolite belt in the northern portion of south eastern Afghanistan. Magnetometric data together with geological investigations make it possible to understand the tectonic nature of the massif contacts.  相似文献   
85.
The Shoushan Basin is an important hydrocarbon province in the Western Desert, Egypt, but the origin of the hydrocarbons is not fully understood. In this study, organic matter content, type and maturity of the Jurassic source rocks exposed in the Shoushan Basin have been evaluated and integrated with the results of basin modeling to improve our understanding of burial history and timing of hydrocarbon generation. The Jurassic source rock succession comprises the Ras Qattara and Khatatba Formations, which are composed mainly of shales and sandstones with coal seams. The TOC contents are high and reached a maximum up to 50%. The TOC values of the Ras Qattara Formation range from 2 to 54 wt.%, while Khatatba Formation has TOC values in the range 1-47 wt.%. The Ras Qattara and Khatatba Formations have HI values ranging from 90 to 261 mgHC/gTOC, suggesting Types II-III and III kerogen. Vitrinite reflectance values range between 0.79 and 1.12 VRr %. Rock−Eval Tmax values in the range 438-458 °C indicate a thermal maturity level sufficient for hydrocarbon generation. Thermal and burial history models indicate that the Jurassic source rocks entered the mature to late mature stage for hydrocarbon generation in the Late Cretaceous to Tertiary. Hydrocarbon generation began in the Late Cretaceous and maximum rates of oil with significant gas have been generated during the early Tertiary (Paleogene). The peak gas generation occurred during the late Tertiary (Neogene).  相似文献   
86.
This paper examines the impact of Community Based Fisheries Management (CBFM) on fishing households’ welfare in Bangladesh. It analyses how the various types of livelihood assets contribute to fishers’ household incomes. The study found that fishers in CBFM project areas have improved their access to different assets including social, human, physical, financial and natural capitals. The regression results show that social capital contributed significantly to household income, indicating that social factors play very important roles in poverty alleviation in Bangladesh. Future poverty alleviation policy options need to give priority to investments in human, physical and natural capital assets.  相似文献   
87.
The problem of gravitational instability of an infinite homogenous fluid has been considered in the presence of a non-vertical magnetic field. A non-linear relation between the magnetic field and the magnetic induction proposed by P.H. Roberts (1981) in the context of neutron stars has been used. The dispersion relations have been obtained. It has been found that Jeans's criterion for instability is unaffected by this non-linear relationship even if the effect due to rotation is considered in the presence of a non-vertical magnetic field.  相似文献   
88.
89.
Earthquake prediction is currently the most crucial task required for the probability, hazard, risk mapping, and mitigation purposes. Earthquake prediction attracts the researchers' attention from both academia and industries. Traditionally, the risk assessment approaches have used various traditional and machine learning models. However, deep learning techniques have been rarely tested for earthquake probability mapping. Therefore, this study develops a convolutional neural network (CNN) model for earthquake probability assessment in NE India. Then conducts vulnerability using analytical hierarchy process (AHP), Venn's intersection theory for hazard, and integrated model for risk mapping. A prediction of classification task was performed in which the model predicts magnitudes more than 4 Mw that considers nine indicators. Prediction classification results and intensity variation were then used for probability and hazard mapping, respectively. Finally, earthquake risk map was produced by multiplying hazard, vulnerability, and coping capacity. The vulnerability was prepared by using six vulnerable factors, and the coping capacity was estimated by using the number of hospitals and associated variables, including budget available for disaster management. The CNN model for a probability distribution is a robust technique that provides good accuracy. Results show that CNN is superior to the other algorithms, which completed the classification prediction task with an accuracy of 0.94, precision of 0.98, recall of 0.85, and F1 score of 0.91. These indicators were used for probability mapping, and the total area of hazard (21,412.94 km2), vulnerability (480.98 km2), and risk (34,586.10 km2) was estimated.  相似文献   
90.
Quartz and iron (hydr)oxide are reactive surface phases that are often associated with one another in soils and sediments. Despite the several studies on the coating of quartz with iron oxides, the reactivity of dissolved species (Si) leached from quartz with iron (hydr)oxides has received limited attention. In this study, goethite synthesized on quartz substrates were characterized using field emission scanning electron microscopy, X-ray diffraction (XRD), transmission electron microscopy, and Fourier-transform infrared (FT-IR) spectroscopy. The SEM characterization revealed that bundles of thin parallel aligned goethite rods were formed at pH?>?10, while large pseudohexagonal crystals of twinned goethite needles were synthesized at pH?≤?10 after dehydration and hydration in the alkaline media. TEM analysis showed expanded and distorted lattice spacing of the crystal structure of iron (hydr)oxide due to silica incorporation. The characterization showed that silica increased the crystallite size of the goethite and transformed its acicular texture to a larger, twinned needle structure. FT-IR and XRD analyses revealed band shifts in crystal bonds as well as new bond formations, which indicate the presence of changes in the chemical environment of Fe–O and Si–O bonds. Thus, the presence of sorbed silicates modifies the crystal and lattice structure of goethite.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号