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   152篇
  免费   6篇
  国内免费   3篇
测绘学   1篇
大气科学   20篇
地球物理   35篇
地质学   88篇
海洋学   11篇
天文学   3篇
自然地理   3篇
  2022年   8篇
  2021年   7篇
  2020年   8篇
  2019年   2篇
  2018年   18篇
  2017年   15篇
  2016年   21篇
  2015年   7篇
  2014年   8篇
  2013年   16篇
  2012年   7篇
  2011年   6篇
  2010年   11篇
  2009年   5篇
  2008年   2篇
  2007年   1篇
  2006年   7篇
  2003年   3篇
  2001年   3篇
  2000年   2篇
  1999年   2篇
  1996年   1篇
  1978年   1篇
排序方式: 共有161条查询结果,搜索用时 31 毫秒
121.
The present research evaluated the relation between the normalized difference vegetation index (NDVI) changes and the climate change during 2000–2014 in Qazvin Plain, Iran. Daily precipitation and mean temperature values during 2015–2040 and 2040–2065 were predicted using the statistical downscaling model (SDSM), and these values were compared with the values of the base period (2000–2014). The MODIS images (MOD13A2) were used for NDVI monitoring. In order to investigate the effects of climate changes on vegetation, the relationship between the NDVI and climatic parameters was assessed in monthly, seasonal, and annual time periods. According to the obtained results under the B2 scenario, the mean annual precipitation at Qazvin Station during 2015–2040 and 2040–2065 was 6.7 mm (9.3%) and 8.2 mm (11.36%) lower than the values in the base period, respectively. Moreover, the mean annual temperature in the mentioned periods was 0.7 and 0.92 °C higher than that in the base period, respectively. Analysis of the correlations between the NDVI and climatic parameters in different periods showed that there is a significant correlation between the seasonal temperature and NDVI (P < 0.01). Moreover, the NDVI will increase 0.009 and 0.011 during 2015–2040 and 2040–2065, respectively.  相似文献   
122.
123.
124.
The fate and behavior of organochlorine pesticides (OCPs) in the Segara Anakan Estuarine ecosystem was studied in the Indonesian tropical climate, which is characterized by heavy rainfall in the rainy season and low rainfall in the dry season. Since OCPs have high affinity for soil, a field study on the dissipation and degradation pattern of soil‐applied 1,1,1‐trichloro‐2,2‐bis (4‐chlorophenyl) ethane (p,p′‐DDT) and 1,1‐dichloro‐2,2‐bis (4‐chlorophenyl) ethylene (p,p′‐DDE) as model OCPs was carried out. They occurred at a faster rate in the biphasic mode in wet conditions and at a slower rate in dry conditions. In wet conditions, the conversion from p,p′‐DDT to p,p′‐DDE and p,p′‐DDD (1,1‐dichloro‐2,2‐bis (4‐chlorophenyl) ethane) was governed by a parallel reaction. In dry conditions, only p,p′‐DDE was formed. The fate and behavior of OCPs in sediment estuary are similar to those in soil under wet conditions, except that their sorption‐desorption constants are influenced by estuarine surface water salinity. In the dry season, due to high salinity, the sediment acts as an OCP sink and a secondary source for the ecosystem, causes higher OCP concentration of local bio‐monitors, i. e., Geloina spp. and Mugil spp. In the rainy season, high water inflow washed the desorbed OCP pesticides out of the estuarine ecosystem, and caused lower concentrations of bio‐monitors. A risk evaluation for the uptake of OCP pesticides during the dry season suggests that adult fish meal consumers are safe, but risk management is required for pregnant woman.  相似文献   
125.
There is growing pressure from regulators on operators to adhere to increasingly stricter regulations related to the environment and safety. Hence, operators are required to predict and contain risks related to hydrocarbon production and their infrastructure in order to maintain their licence to operate. A deeper understanding of production optimisation and production‐related risk requires strengthened knowledge of reservoir behaviour and overburden dynamics. To accomplish this, sufficient temporal and spatial resolution is required as well as an integration of various sources of measurements. At the same time, tremendous developments are taking place in sensors, networks, and data analysis technologies. Sensors and accompanying channels are getting smaller and cheaper, and yet they offer high fidelity. New ecosystems of ubiquitous wireless communications including Internet of Things nowadays allow anyone to affordably connect to the Internet at any time and anywhere. Recent advances in cloud storage and computing combined with data analytics allow fast and efficient solutions to handle considerable amounts of data. This paper is an effort to pave the way for exploiting these three fundamental advances to create Internet of Things‐based wireless networks of seismic sensors. To this aim, we propose to employ a recently developed Internet of Things‐based wireless technology, so‐called low‐power wide‐area networks, to exploit their long range, low power, and inherent compatibility to cloud storage and computing. We create a remotely operated minimum‐maintenance wireless solution for four major seismic applications of interest. By proposing appropriate network architecture and data coordination (aggregation and transmission) designs, we show that neither the low data rate nor the low duty cycle of low‐power wide‐area networks imposes fundamental issues in handling a considerable amount of data created by complex seismic scenarios as long as the application is delay tolerant. In order to confirm this claim, we cast our ideas into a practical large‐scale networking design for simultaneous seismic monitoring and interferometry and carry out an analysis on the data generation and transmission rates. Finally, we present some results from a small‐scale field test in which we have employed our Internet of Things‐based wireless nodes for real‐time seismic quality control over clouds.  相似文献   
126.
The aim of this study was to isolate and molecularly characterize Streptococcus pneumoniae in samples collected from the aquatic environment in Lebanon. For this purpose, 57 samples of ground waters, sea water, sediments and crabs were collected. Biochemical tests as well as PCR were used for further identification and molecular characterization of 46 suspected isolates using specific primers for the lytA-gene and protein 2B-gene. The confirmed isolates were evaluated for their antimicrobial resistance, using the minimum inhibitory concentration method. Crab samples exhibited a high contamination level of an average count of 8.2 x 10(4)CFU/g. In water samples, the highest contamination was recorded near a coastal landfill with a bacterial count of 1.8 x 10(3)CFU/ml whereas the lowest bacterial counts (non detectable) were observed in ground water samples. Twenty out of the 46 suspected isolates came from sea water, and 17 out of those were characterized by PCR as S. pneumoniae. Testing the antimicrobial resistance of the 20 isolates to various antimicrobials showed that all sea water isolates were resistant to vancomycin, gentamicin, and oxacillin (100%), whereas 62.5% were resistant to clindamycin, and only 25% were erythromycin resistant. Resistance rates were higher in the case of fresh water samples, with 57% resistance to erythromycin, and 100% resistance to vancomycin, gentamicin, clindamycin and oxacillin. Alternatively, all tested crab isolates were susceptible to erythromycin. However, they showed a high resistance of 80% against vancomycin, gentamicin, clindamycin and 100% against oxacillin.  相似文献   
127.
Ground motion prediction equations (GMPEs) have a major impact on seismic hazard estimates, because they control the predicted amplitudes of ground shaking. The prediction of ground-motion amplitudes due to mega-thrust earthquakes in subduction zones has been hampered by a paucity of empirical ground-motion data for the very large magnitudes (moment magnitude (M) $>$ 7) of most interest to hazard analysis. Recent data from Tohoku M9.0 2011 earthquake are important in this regard, as this is the largest well-recorded subduction event, and the only such event with sufficient data to enable a clear separation of the overall source, path and site effects. In this study, we use strong-ground-motion records from the M9 Tohoku event to derive an event-specific GMPE. We then extend this M9 GMPE to represent the shaking from other M $>$ 7 interface events in Japan by adjusting the source term. We focus on events in Japan to reduce ambiguity that results when combining data in different regions having different source, path and site effect attributes. Source levels (adjustment factors) for other Japanese events are determined as the average residuals of ground-motions with respect to the Tohoku GMPE, keeping all other coefficients fixed. The mean residuals (source terms) scale most steeply with magnitude at the lower frequencies; this is in accord with expectations based on overall source-scaling concepts. Interpolating source terms over the magnitude range of 7.0–9.0, we produce a GMPE for large interface events of M7–M9, for NEHRP B/C boundary site conditions (time-averaged shear-wave velocity of 760 m/s over the top 30 m) in both fore-arc and back-arc regions of Japan. We show how these equations may be adjusted to account for the deeper soil profiles (for the same value of $\hbox {V}_\mathrm{S30})$ in western North America. The proposed GMPE predicts lower motions at very long periods, higher motions at short periods, and similar motions at intermediate periods, relative to the simulation-based GMPE model of Atkinson and Macias (2009) for the Cascadia subduction zone.  相似文献   
128.
129.
Discovery of the remains of belemnites referred to the Hibolithes sp. from the Jurassic–Cretaceous Pedawan Formation in Sarawak, on the island of Borneo(Malaysia) comprises four fragments of belemnite rostra. The specimens are characterized by multiple fractures and vein filling. Two fragments measuring about 130 mm are relatively intact, with only part of the alveolar region missing; a third piece represents the middle part of a rostrum, and the fourth specimen is too fragmentary to be assigned to any specific part of the rostrum. Based on specimen characteristics, a Tithonian–Hauterivian age is plausible. The sedimentary succession that yielded the belemnite material comprises thick shale that reflects the Te division of Bouma sequence. The occurrence of a Hibolithes taxon in the uppermost Jurassic to lowermost Cretaceous Pedawan Formation sediments in Borneo reflects a near to global palaeobiogeographic distribution of this genus.  相似文献   
130.
In present paper, wavelet analysis of total dissolved solid that monitored at Nazlu Chay (northwest of Iran), Tajan (north of Iran), Zayandeh Rud (central of Iran) and Helleh (south of Iran) basins with various climatic conditions, have been studied. Daubechies wavelet at suitable level (db4) has been calculated for TDS of each selected basins. The performance of artificial neural networks (ANN), two different adaptive-neurofuzzy inference system (ANFIS) including ANFIS with grid partition (ANFIS-GP) and ANFIS with subtractive clustering (ANFIS-SC), gene expression programming (GEP), wavelet-ANN, wavelet-ANFIS and wavelet-GEP in predicting TDS of mentioned basins were assessed over a period of 20 years at twelve different hydrometric stations. EC (μmhos/cm), Na (meq L?1) and Cl (meq L?1) parameters were selected (based on Pearson correlation) as input variables to forecast amount of TDS in four studied basins. To develop hybrid wavelet-AI models, the original observed data series was decomposed into sub-time series using Daubechies wavelets at suitable level for each basin. Based on the statistical criteria of correlation coefficient (R), root mean square error (RMSE) and mean absolute error (MAE), the hybrid wavelet-AI models performance were better than single AI models in all basins. A comparison was made between these artificial intelligence approaches which emphasized the superiority of wavelet-GEP over the other intelligent models with amount of RMSE 18.978, 6.774, 9.639 and 318.363 mg/l, in Nazlu Chay, Tajan, Zayandeh Rud and Helleh basins, respectively.  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