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971.
This paper deals with the dynamic response of infinite double Euler–Bernoulli beam supported by elastic foundation with stochastic stiffness subjected to an oscillating moving load, which is the first research in relevant literature review. In this matter, equations of motion for double beam are formulated in a moving frame of reference. Moreover, by employing the first order perturbation theory and calculating contour integration, the response of double beam is obtained analytically and validated by a stochastic finite element model. Sensitivity analyses on the various parameters of closed form solution such as velocity, load frequency, coefficient of variation of soil foundation and rail and slab bending stiffness show the significant effect of load frequency on the dynamic response of the doubled beam. From practical point of view, the obtained results of the present study can be utilized efficiently in analysis and design of slab track systems. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
972.
973.
Interception losses in stands of non‐native trees in Hawaiian forests and their potential negative impacts on fresh water availability are poorly understood. In this study, a canopy water balance analysis was conducted to estimate interception losses using measurements of rainfall (RF), throughfall (TF), and stemflow (SF) at three locations, each dominated by one or more of the following non‐native tree species: Psidium cattleianum Sabine (Strawberry guava), Schinus terebinthifolius Raddi (Christmas berry), Syzygium cumini (L.) Skeels (Java plum), and Coffea arabica L. (Coffee). Mean TF expressed as percentage of total RF was the lowest (43.3%) under a monotypic stand of P. cattleianum and the highest (56.5%) under mixture of S. terebinthifolius, P. cattleianum, and S. cumini. Observed SF was highest (33.9%) under P. cattleianum and lowest (3.6%) under a mixture of S. terebinthifolius, P. cattleianum, and S. cumini. The relatively high SF under P. cattleianum can be attributed to its smooth bark, stem density, and steep branching. The mean observed canopy interception varied between 23% under P. cattleianum and 45% at the site dominated by C. arabica. Mean direct TF coefficients from individual events at each location ranged from a low of 0.36 under the canopy dominated by C. arabica to a high of 0.51 under the canopy dominated by S. terebinthifolius, P. cattleianum, and S. cumini. In contrast, the mean SF partitioning coefficients from individual storm events at each location ranged from a low of 0.05 under the canopy dominated by S. terebinthifolius, P. cattleianum, and S. cumini to a high of 0.37 under P. cattleianum. Mean canopy storage capacity was highest (1.90) at the site dominated by S. terebinthifolius, P. cattleianum, and S. cumini whereas trunk storage capacity was highest (0.54) under the P. cattleianum. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
974.
In this study, an approach is presented for handling hydraulic uncertainties in the prediction of floodplain. Different factors affect river flood characteristics. Furthermore, the high changeability of flooding conditions leads to high variability of the inundation. River morphology is one of the most effective factors in river flood characteristics. This factor is influenced by sedimentation and erosion in the river cross sections, which affects the discharge variation. The depth and the width of the river cross section lead to an increase or decrease in the river flow path. This results in changes in the extent of the floodplain based on the generated rainfall. The inundated region boundaries are determined by utilizing the mean first‐order second‐moment analysis. The proposed method is applied to the Kajoo River in the south‐eastern part of Iran. Determination of floodplain uncertainty is a damage‐reduction policy in this region. Also, it is useful to prepare the necessary activities for overcoming the flood hazards. Climate change is the second effective factor on the floodplain uncertainties. Climate change affects the magnitude, extent and depth of inundation and it may intensify the flood problem. Therefore, the future rainfall pattern of the study area under climate change is simulated to evaluate its impacts on the river flow characteristic. Subsequently, a hydraulic routing model is used to determine floodplain. Finally, the copula function is used to estimate the joint probability of the changes in the inundation area due to changes in river morphology and the rainfall changes due to impacts of climate change. Results show that the uncertainties of the extent of floodplain are affected by climate change and river morphology, leading to noticeable changes in the magnitude and frequency of floods. Evaluating these impacts and estimating corresponding river discharges will help in the study of river dynamics, and will also contribute towards devising effective mitigation and management strategies. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
975.
976.
An investigation of the Iranian climatic changes by considering the precipitation, temperature, and relative humidity parameters 总被引:5,自引:2,他引:3
Mohammad Reza Kousari Mohammad Reza Ekhtesasi Mehdi Tazeh Mohammad Ali Saremi Naeini Mohammad Amin Asadi Zarch 《Theoretical and Applied Climatology》2011,103(3-4):321-335
The present study tends to describe the survey of climatic changes in the case of the eastern and central areas of Iran and, to some extent, the northern parts. The monthly and yearly change trends in the minimum, maximum and mean temperatures, relative humidity, and the precipitation were surveyed for 26 synoptic stations in Iran during a 55-year period. The study was carried out by using the ??-Kendall test. The results showed the same temperature changes for the centrally located stations as the eastern and northern ones. Most of the stations in Zagros showed no significant temperature changes. A significant decrease in the precipitation was seen in summer in different stations. Most of the eastern and centrally located stations showed a decrease in relative humidity trend, while this condition was not recorded in Zagros and northern part of Iran. The present results also showed that the upward trend of minimum air temperature had an effect in increasing the mean air temperature in the stations with temperature ascending trend. This effect of minimum temperature was significantly more than that of the maximum temperature, which could be the result of increasing the amount of greenhouse gases and the reflection of received thermal energies, from land through the night. This increase in the temperature and a decrease in relative humidity would cause an increase in the evaporation of the received precipitation. 相似文献
977.
Status of macrobenthic community of Manifa-Tanajib Bay System of Saudi Arabia based on a once-off sampling event 总被引:1,自引:0,他引:1
Joydas TV Krishnakumar PK Qurban MA Ali SM Al-Suwailem A Al-Abdulkader K 《Marine pollution bulletin》2011,62(6):1249-1260
Shallow water bays located in the western Arabian Gulf experience harsh environmental conditions. Some of these bays, including Manifa-Tanajib Bay System (MTBS), were also exposed to the 1991 oil pollution event. This study investigates the status of the macrobenthos in MTBS during 2006. This bay system is characterized by very shallow inner bays with elevated salinity and temperature compared to the rest of the bay area. As a result mainly of the hyper salinity, the inner bay communities are distinct from the outer bay communities. Overall, fairly high species richness with several rare species was observed. High Shannon-Wiener diversity values and ABC plots indicated the healthy status of the polychaete communities, while BOPA index indicated slightly polluted status in 20% of the stations. The oil sensitive amphipods were not completely re-colonized in 20% of the stations, even after 15 years of recovery from the 1991 oil spill. 相似文献
978.
Mohammad Hossein Nouri Gheidari Abdoulrasoul Telvari Hossein Babazadeh Mohammad Manshouri 《Water Resources》2011,38(4):484-493
The probable maximum precipitation which is defined as the maximum precipitation at a particular location for a given duration
is used as a design criterion for major dams. The assumptions of deterministic consideration and an upper limit to probable
maximum precipitation have been repeatedly criticized by hydrologists. Nowadays, multifractal method which strongly contains
physical bases can be used to improve the probable maximum precipitation. In this research, the universal multifractal model
was used to estimate the design probable maximum precipitation for specified exceedence probability in basin of Bakhtiari
Dam, southwest Iran, and its results were compared with statistical and synoptically methods. The results revealed that the
return period of statistical and synoptically probable maximum precipitation, estimated for the different durations, are about
109 and 103–104 years, respectively; also, over periods ranging from 1 to 7 days, the ratios of design probable maximum precipitations, estimated
based on multifractal method for return period of 103–109 years, to statistical and synoptically probable maximum precipitation estimates ranged from 0.61 to 1.1 and 1.33 to 2.37,
respectively. These results indicated that the multifractal method can be used to reasonably estimate the probable maximum
precipitation. 相似文献
979.
Patterns,puzzles and people: implementing hydrologic synthesis 总被引:2,自引:0,他引:2
Sally E. Thompson C. J. Harman R. Schumer J. S. Wilson N. B. Basu P. D. Brooks S. D. Donner M. A. Hassan A. I. Packman P. S. C. Rao P. A. Troch M. Sivapalan 《水文研究》2011,25(20):3256-3266
There have been several calls made for hydrologic synthesis research: namely activities which unify diverse data sources across sites, scales and disciplines to uncover new connections and to promote a holistic understanding of water science. This paper draws on the NSF‐funded Hydrological Synthesis Project (HSP) run by the University of Illinois at Urbana‐Champaign to elucidate mechanisms, benefits and challenges of implementing hydrologic synthesis research from the perspectives of participants in a pilot research study. Two broadly different mechanisms of implementing synthesis were adopted in the HSP: 6‐week Summer Institutes in which Ph.D. students conducted team‐based research under the guidance of faculty mentors, and focused workshops which disseminated knowledge and shared experiences between scientists at many different career levels. The Summer Institutes were a test bed in which new ideas could be explored, assisted students in developing a wide range of skills, and were highly productive, but posed challenges for mentors and students because the ‘new’ research topics initiated during the Institutes' programmes needed to be completed in competition with students' ongoing Ph.D. research or mentor's existing research programs. The workshop‐based model circumvented this conflict and was also highly productive, but did not offer the same opportunity to experiment with new ideas as part of the synthesis research. Leadership, trust, flexibility and long gestation times were all important to bringing synthesis research to a positive resolution. Funding models that embrace the exploratory aspects of synthesis and provide adequate support to mentors and students over these long timescales would facilitate future hydrologic synthesis research. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
980.
The survey of climatic drought trend in Iran 总被引:5,自引:3,他引:2
Hossein Bari Abarghouei Mohammad Amin Asadi Zarch Mohammad Taghi Dastorani Mohammad Reza Kousari Mehdi Safari Zarch 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(6):851-863
Drought is one of the most important natural hazards in Iran. Therefore, drought monitoring has become a point of concern
for most of the researchers. In the present study, the changes and trend of drought was surveyed, under the current global
climate changes, by non parametric Mann–Kendall statistical test for 42 synoptic stations at different places of Iran. Standardized
Precipitation Index (SPI) was calculated to recognize the drought condition at different time scales (3, 6, 9, 12, 18 and
24 months’ time series) for analyzing the drought trend in the recent 30 years. The obtained results have indicated a significant
negative trend of drought in many parts of Iran, especially the South-East, West and South-West regions of the country. According
to the results, although some parts of Iran such as North (around the Caspian Sea) and Northeast show no significant trend
but in other parts of country, the severity of drought has increased during the last 30 years. 相似文献