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Experiments were carried out over a 2-dimentional pool with a constant length of 1.5 m and four different slopes.The distributions of velocity,Reynolds stress and turbulence intensities have been studied in this paper.Results show that as flow continues up the exit slope,the flow velocity increases near the channel bed and decreases near the water surface.The flow separation was not observed by ADV at the crest of the bed-form.In addition,the length of the separation zone increases with the increasing of entrance and exit slopes.The largest slope angle causes the maximum normalized shear stress.Based on the experiments,it is concluded that the shape of Reynolds stress distribution is generally dependent on the entrance and exit slopes of the pool.Also,the shape of Reynolds stress distribution is affected by both decelerating and accelerating flows.Additionally,with the increase in the slope angle,secondary currents are developed and become more stable.Results of the quadrant analysis show that the momentum between flow and bed-form is mostly transferred by sweep and ejection events. 相似文献
113.
Hossein Mohammadi Vahab Toufigh Ali Akbar Golafshani Ali Arzeytoon 《Bulletin of Earthquake Engineering》2018,16(2):731-752
In this paper, an innovative seismic lateral force resisting system for tall buildings is introduced. In this system, a novel supplemental part, ribbed bracing system (RBSyst), is attached to Braced Tube System, creating a modified BTS. RBSyst is a supplemental part which is attached to the conventional bracing members to eliminate buckling problem. The behavior of RBSyst under tensile force is similar to that of the conventional braces. However, in compression, it prevents the braces from buckling by length reduction. In order to evaluate the efficiency of this new BTS system by performance-based assessment, two typical 40-story tall buildings with different story modules equipped with this proposed bracing system are modeled numerically. Then, the seismic behavior of these 3-dimensional models are evaluated by nonlinear time history analysis under maximum considered earthquakes and service-level earthquakes. The results of the analysis demonstrate that the performance of the tall buildings equipped with this new BTS system is within the acceptable limits under both service-level and maximum considered earthquake ground motions. Additionally, it is shown that RBSyst part can effectively enhance the seismic behavior of BTS systems. 相似文献
114.
Narges Fathalian Seyedeh Somayeh Hosseini Rad Nasibeh Alipour Hossein Safari 《天文和天体物理学研究(英文版)》2022,(3):143-156
Here,we study the temperature structure of flaring and non-flaring coronal loops,using extracted loops from images taken in six extreme ultraviolet channels rec... 相似文献
115.
The paper presents coastal structures design in the presence of waves by the minimization of a cost function. It aims to show that shape optimization can be efficiently applied to ocean engineering. This is an underlying guiding principle for the design of harbors or offshore breakwaters. We compute the solution of a specific simplified boundary value problem describing the short wave propagation toward a vertical sea cliff or vertical wall and modify accordingly the shape of defense structures in order to minimize a pre-defined cost function taking into account the strength (energy) of the water waves. The optimization procedure relies on a global semi-deterministic search algorithm able to escape from local minima. 相似文献
116.
Ataollah Kavian Maziar Mohammadi Artemi Cerdà Moghadaseh Fallah Leila Gholami 《水文科学杂志》2019,64(3):350-360
The Simulator of Artificial RaInfall (SARI) rainfall simulator (RS) is a newly designed, constructed and calibrated, portable, two-nozzle RS with low water consumption, accurate measurement, easy management and low cost. The raindrop size distribution and velocity and mean rainfall intensity were measured. The best rainfall spatial distribution was achieved with nozzles separated by 50, 60 and 70 cm, and with oscillation angles of 30, 45 and 60°, at a pressure of 60 kPa. The uniformity coefficient varied from 57 to 61% and rainfall intensity from 48 to 101 mm h?1. The raindrop diameter varied from 0.2 to 9.9 mm. The raindrop velocity at the optimum pressure of 60 kPa, which was measured with high-speed photography, ranged from 1.1 to 7.1 m s?1. Comparison with other RSs shows that the SARI simulator is a suitable apparatus to research soil erosion and runoff generation under laboratory and field conditions. 相似文献
117.
Abdollahifard Mohammad Javad Marithoz Grgoire Mohammadi Hesam Soltan 《Stochastic Environmental Research and Risk Assessment (SERRA)》2020,34(1):67-85
Stochastic Environmental Research and Risk Assessment - In many geoscience applications, the data extracted from environmental variables are very limited. Multiple-point geostatistical (MPS)... 相似文献
118.
ANN-Based Prediction of Laboratory-Scale Performance of CO2-Foam Flooding for Improving Oil Recovery
Moosavi Seyedeh Raha Wood David A. Ahmadi Mohammad Ali Choubineh Abouzar 《Natural Resources Research》2019,28(4):1619-1637
Natural Resources Research - Improving oil recovery by CO2 injection continues to gain momentum in mature oil fields due to its favorable industrial and environmental benefits. One remediation for... 相似文献
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Safar Marofi Mohammad Mehdi Sohrabi Kurosh Mohammadi Ali Akbar Sabziparvar Hamid Zare Abyaneh 《Theoretical and Applied Climatology》2011,103(3-4):401-412
In this study, in order to detect probable trends and effects of climatic extreme events of precipitation and temperature as well as maximum relative humidity, dew point temperature, sunshine hours, and wind speed, 12 stations on the northern and southern coastlines of Iran were investigated from 1977 to 2007. For this purpose, 27 indices of precipitation and temperature, which are specified by the Expert Team of the World Meteorological Organization and Climate Variability and Predictability, were calculated by using RClimDex software. The Mann?CKendall method was also used to detect possible trends in the data time series. The results indicate that temperature indices are absolutely consistent with warming. Warm nights, hot days, and hot day and night frequencies increased, while cold spell and cool day and night frequencies declined. The minimum temperature experienced a considerable rise both in its maximum and minimum values. The minimum temperature had a higher increase than the maximum temperature. Therefore, diurnal temperature ranges have experienced dramatic declines. In the northern coastal sites, hot day frequency and hottest day temperature showed higher magnitudes than those of the southern sites as a result of the significant increase in the maximum sunshine hours in northern stations. This enhancement led to a considerable increase in the maximum wind speed. Consequently, relative humidity declined in the northern sites. Precipitation indices indicate few significant trends over the studied period. Temporal precipitation distribution was different from station to station. Three precipitation patterns were detected at individual stations, although an overall regional rainfall pattern was not detectable. On the whole, the results of this study emphasize that the water resources in the studied area are going to become problematic. 相似文献