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   63篇
  免费   6篇
  国内免费   7篇
化学   28篇
力学   6篇
综合类   9篇
数学   4篇
物理学   29篇
  2023年   1篇
  2022年   2篇
  2021年   2篇
  2020年   1篇
  2019年   2篇
  2018年   1篇
  2017年   1篇
  2016年   2篇
  2015年   1篇
  2014年   4篇
  2013年   10篇
  2012年   6篇
  2011年   3篇
  2010年   11篇
  2009年   6篇
  2008年   2篇
  2007年   2篇
  2006年   2篇
  2005年   1篇
  2004年   2篇
  2003年   1篇
  2002年   2篇
  1998年   1篇
  1995年   1篇
  1993年   1篇
  1991年   1篇
  1989年   2篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
  1978年   1篇
排序方式: 共有76条查询结果,搜索用时 31 毫秒
11.
以大亚湾核电站附近海域为研究区,基于HJ-1B卫星热红外遥感数据IRS4,对核电站温排水空间分布特征进行了识别与验证。首先利用时空插值后的NCEP大气廓线数据,结合近地面气象观测信息对IRS4数据进行大气订正;其次查找表数据建立IRS4宽通道辐亮度与辐射温度转换公式,完成研究区海表温度反演。利用温盐深测量仪,与卫星同步采集了84个离散点的水温,经空间插值获得地面调查海水“体温度”(bulk temperature, BT)的分布,并与海表温度(sea surface temperature, SST)反演结果进行了对比。结果表明,调查区平均BT比平均SST高0.47 ℃。在远离热排放口区域,SST高于BT,两者差异在1.0 ℃以内;在靠近热排放口区域,SST低于BT,并且越接近排放口两者之间差距越大。遥感与地面调查两种手段获得的温升分布基本一致,总温升区域面积相近。遥感手段获得的温升等级较少(小于4级),地面调查获得温升等级较多(大于5级);后者高温升等级(2级以上)区域面积较大,但对于1级温升区面积而言,两种手段差异较小。上午10时左右海表BT与SST差异较小,“肤-体”温差效应可以忽略,在IRS4业务化SST应用中,这一时段的卫星遥感可以作为核电站温排水分布监测的常规手段。  相似文献   
12.
Neutrinos are elementary particles in the Standard Model. Neutrino oscillation is a quantum mechanical phenomenon beyond the Standard Model. Neutrino oscillation can be described by two independent mass-squared differences Δm 21 2 , Δm 31 2 (or Δm 32 2 ) and a 3 × 3 unitary matrix, containing three mixing angles θ 12, θ 23, θ 13, and one charge-parity (CP) phase. θ 12 is about 34° and determined by solar neutrino experiments and the reactor neutrino experiment KamLAND. θ 23 is about 45° and determined by atmospheric neutrino experiments and accelerator neutrino experiments. θ 13 can be measured by either accelerator or reactor neutrino experiments. On Mar. 8, 2012, the Daya Bay Reactor Neutrino Experiment reported the first observation of non-zero θ 13 with 5.2 standard deviations. In June, with 2.5× previous data, Daya Bay improved the measurement of sin22θ 13 = 0.089 ± 0.010(stat) ± 0.005(syst).  相似文献   
13.
以海南三亚湾鹿回头附近海域常见的8种优势造礁石珊瑚的反射率光谱代表该海域珊瑚的反射率光谱,用光纤光谱仪测量它们和此海域常见底质团扇藻、砂的反射率光谱。利用反射率、导数光谱法分析研究了该海域造礁石珊瑚、团扇藻和砂反射率光谱的差异。分析表明500~ 700 nm和珊瑚反射率差异相对较大;珊瑚反射率光谱明显低于砂反射率光谱,反射率谱线整体差异显著。导数分析结果显示造礁石珊瑚、团扇藻和砂的可区分波段为:石珊瑚与团扇藻的一阶导数,主要为415.1~425.6,482~487,514.5~529,577~587.6和631.9~644 nm等波段。二阶导数主要为,413~418.7,427.4~432.5,462.3~470.6,494.4~503.6,551.6~561.4,590~594和639~643 nm波段。四阶导数主要为,412.2~418.4,420.5~425.3,470.9~480.2,481.3~486.9,540.8~545.7,560~568.3和635.6~639.6 nm等波段。石珊瑚与砂的一阶导数,主要为400~413.7,514.5~529.6,576.9~587.6和602.7~667 nm波段。二阶导数主要为,420.5~430.7,446.9~458.8,467.3~472.3,537~544.3,556.8~561.4,582.8~587.2和637.6~649.4 nm。四阶导数主要为,414.4~418.7,419.5~430.3,486.9~495.8,534.2~540.1,579~583.1,622.7~627.5,640~645和665.4~672.8 nm等波段。  相似文献   
14.
We describe here the characteristic features of the ringing we observed following large PMT signals in the Daya Bay reactor antineutrino experiment. We conclude that the ceramic capacitors used in the circuitry of the PMT bases and the HV-signal decouplers are the primary cause for this ringing. We present some possible schemes to reduce the ringing when replacing these ceramic capacitors is not feasible.  相似文献   
15.
象山港潮间带大型底栖动物次级生产力初探   总被引:2,自引:0,他引:2  
通过2006~2007年对象山港滩涂潮间带大型底栖动物春、夏、秋、冬的4次调查,利用Brey经验公式进行了大型底栖动物栖息丰度、生物量、次级生产力和P/B值的研究.结果表明:该海域年平均栖息丰度为680.2ind m-2;年平均生物量(以去灰干重计)为16.82g m-2;年平均次级生产力(以去灰干重计)为17.26g (m2 a)-1;P/B值为0.91~1.18a-1.由此得出象山港大型底栖动物次级生产力湾口和湾底大于湾中,这与象山港是一个深入内陆的半封闭狭长型海湾有关;P/B值从湾口到湾底依次升高,说明象山港湾口的大型底栖动物群落中个体小、生活史短、代谢快,湾底的大型底栖动物群落生活史较长,且物种组成基本稳定.  相似文献   
16.
海宁市旅游资源丰富,钱江潮、鱼鳞石塘、海神庙、皮革等具有很高的知名度,但是开发深度不足,旅游形象模糊.海宁市位于浙江省杭州湾产业带核心地带,随着钱江十桥等跨海大桥的建设,海宁市的区位将进一步优化,但在今后相当长时段内,旅游业的竞争将日益加剧,海宁市旅游业的结构升级亟待解决.在充分调研的基础上,认为海宁市旅游资源要统筹规划,高标准开发,确立了海宁市作为浙北旅游增长极的地位,进行了旅游形象重新设计,并提出若干开发思路.  相似文献   
17.
A three factor Doehlert design was applied to optimize the extraction of elements in marine invertebrate samples (oyster, mussel and clam) using centrifugation with diluted acids. The factors were: concentration of acid mixture (HCl + HNO3 + H3CCOOH; 1–3 mol L− 1), centrifugation time (10–40 min), and rotation velocity (6000–10,000 rpm). In order to evaluate the ultrasound effect on the extraction of trace metals, a portion of the certified oyster tissue sample (NIST 1556b; 0.250 g) was sonicated for 15 min and then the solution was centrifuged at the optimized conditions. The optimized procedure was then applied to nine marine invertebrate samples (oysters, clams and mussels) collected at Todos os Santos Bay, Bahia, Brazil. The optimized condition of the developed method was: 20 min of centrifugation at 9000 rpm using the acid mixture 1.0 mol L− 1. The effect of sonication prior centrifugation was very variable, but it promoted a significant increase in the extraction (12 to 44%) of some trace elements. Moreover, the combination of the centrifugation with sonication offered other advantages, such as improvement of the precision and accuracy, both demonstrated using the oyster tissue reference sample. The results of major and trace elements in marine invertebrate samples showed that elements such us Cd and Cu in oyster samples and Zn in mussel and clam samples were above recommendations, suggesting that its consumption may impose health risks.  相似文献   
18.
The reaction of polystyrene with hydroxyl radicals, generated by the photolysis (λ > 300 nm) of H2O2, has been studied at 25° in dichloromethane solution, both under vacuum conditions and in presence of O2. Spectroscopic analyses suggest the presence of phenols and hydroxymucondialdehydes (when O2 is present) among the reaction products, indicating that OH addition occurs at the phenyl groups of the polymer. By comparison with initiated oxidation reactions under the same conditions, it is concluded that the OH radicals undergo mainly addition reactions. A mechanism has been produced to account for the products. The significance of OH addition reactions in the oxidation of polystyrene is considered, the OH radicals being produced by hydroperoxide decomposition during oxidation, and the products having been previously identified as containing mucondialdehydes.  相似文献   
19.
Differential pulse anodic stripping voltammetry (DPASV) using a Nafion-coated thin mercury film electrode (NCTMFE) was implemented to determine the dissolved copper speciation in saline estuarine waters containing high concentrations of dissolved organic matter (DOM). The study used model ligands and estuarine water from San Francisco Bay, California, USA to demonstrate that the NCTMFE is more effective at distinguishing between electrochemically inert and labile copper species when compared to the conventional thin mercury film electrode (TMFE). Copper titration results verify that the NCTMFE better deals with high concentrations of DOM by creating a size-exclusion barrier that prevents DOM from interacting with the mercury electrode when performing copper speciation measurements. Pseudovoltammograms were used to illustrate that copper complexes found in natural waters were more apt to be electrochemically inert at the NCTMFE relative to the TMFE when subjected to high negative overpotentials. Copper speciation results using the NCTMFE from samples collected in San Francisco Bay estimated that >99.9% of all copper was bound to strong copper-binding ligands. These L1-class ligands exceeded the concentration of total dissolved copper in all samples tested and control the equilibrium of ambient [Cu2+] in the San Francisco Bay estuary.  相似文献   
20.
As a primary parameter in the water quality model for shallow bays, the dispersion coefficient is traditionally determined with a trial-and-error method, which is time-consuming and requires much experience. In this paper, based on the measured data of chemical oxygen demand (COD), the dispersion coefficient is calculated using an inversion method. In the process, the regularization method is applied to treat the ill-posedness, and an operator identity perturbation method is used to obtain the solu- tion. Using the model with an inverted dispersion coefficient, the distributions of COD, inorganic nitrogen (IN), and inorganic phosphorus (IP) in Bohai Bay are predicted and compared with the measured data. The results indicate that the method is feasible and the inverted dispersion coefficient can be used to predict other pollutant distribution. This method may also be further extended to the inversion of other parameters in the water quality model.  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