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   22篇
  免费   1篇
  国内免费   73篇
教育与普及   1篇
理论与方法论   8篇
综合类   87篇
  2015年   1篇
  2013年   1篇
  2012年   1篇
  2011年   1篇
  2010年   2篇
  2009年   1篇
  2008年   2篇
  2007年   5篇
  2005年   45篇
  2004年   21篇
  2003年   11篇
  2001年   1篇
  1999年   2篇
  1996年   2篇
排序方式: 共有96条查询结果,搜索用时 156 毫秒
1.
2.
Recently ,hazardscausedbysuspendedparticu latematter (SPM ) ,especiallybyparticleswithdiam etersmallerthan 1.0 μm (PM 1.0 ) (calledsub mi cronparticles) ,havereceivedmuchattentionintheenvironmentalresearch[1] .Combustion processcaninherentlyresultintheformationofsub micronparti clesanditisamajorsourceofatmosphericloadingofsuch particles .Thesecombustiondevicesincludesmelters,coalcombustion ,waste to energyincinera tors ,andcementkilns .Althoughenvironmentalreg ulationsaredesignedandusedunde…  相似文献   
3.
Inbroadbandarraysignalprocessing ,thespec tralcharacteristicsofthetargetaremostlyusedintargetdetectionandtargetclassification .Sincetheradiatednoiseofthetargetgenerallyspreadsoverawidefrequencyband ,distortioninthepowerspec trummightappearifthebeamformerresponsevarieswithfrequency .Theso calledfrequencyinvariantbeamformer (FIB)techniqueisrequiredasaremedy .AnFIBisabeamformerinwhichtheresponseisap proximatelyconstantoversomedesignbandwidth .InRef .[1],anapproachtodesigningbroadbandbeamformer…  相似文献   
4.
Cucumber (Cucumis sativus L.) is an annualclimber originated from the tropic rain forest area inthe south of Himalayas, which belongs to the Cucur bitaceae family. Cucumber is one of the importantvegetables in the world, and its planting area is sec ond only to that of tomato[1]. However genetics re search on cucumber obviously drops behind that of thelatter. The classic genetic map of cucumber, with sixlinkage groups, is composed of more than 100 genesfor color, morphology, and dise…  相似文献   
5.
Deformable model is a curve or a surface drivenpartial differential equations (PDE) method for imagesegmentation and pattern recognition. Two types ofdeformable models have been developed previously.One is the parametric deformable model proposed byKass et al.[1], which formulates the curve explicitlyin the parametric form. The other is the geometricdeformable model, which implicitly characterizes thecurve by a level set function developed by Osher,Sethian and implement…  相似文献   
6.
从剑桥晶体结构数据库(CSD)中系统地提取了17个邻羟基偶氮苯的晶体结构数据,用自编的FORTRAN程序对它们的几何参数进行了计算.结果表明:邻羟基偶氮苯晶体中普遍存在着偶氮一醌腙互变异构平衡,这些化合物中均存在很强的六元环分子内氢键且为近平面构型,对应的相关键长呈有规律的变化.  相似文献   
7.
1"特菜"是一个动态概念 "特菜"英文名称为"Special Vegetable".美国加州大学蔬菜专业学生有一门必修课就称为Special Vegetable,它重点介绍非美国本土生产种植的蔬菜,如中国的莲藕、茭白、香椿、蒜苔等.国内特菜在不同时期所包含的范围也不尽相同,20世纪80年代的特菜主要指从国外引进的蔬菜品种,如青花菜、结球生菜、紫甘蓝、西芹等.  相似文献   
8.
Anabarites belong to small shelly fossils (SSF), which occur widely in the Lower Cambrian strata of Yangtze Platform in South China. They are phosphate shell in composition and represent the earliest stage of the Cambrian bioradiation of Bilateria, the so-called “Cambrian Explosion”. In this study, we attempted to separate Anabarites fossils from Lower Cambrian dolostones, and we obtained samples of both the fossils (SSF) and the granular phosphates (GP). Isotopic analyses were performed on samples of SSF, GP, and matrix dolostone (DH-23). The results showed that the δ30Si values of the quartz filling in fossils celoms, and the siliceous materials in granular phosphates are -0.6‰ and -0.7‰, which is different from normal sedimentary siliceous rocks from the Lower Cambrian strata (0—0.7‰) as reported by Li et al., but is consistent with the data for siliceous rocks and cherts of submarine hydrothermal origin. It is likely that a later hydrothermal replacement could have taken place in the SSF-bearing sedimentary rocks. The oxygen isotope values of the phosphate of SSF and GP are 16.8‰ and 17.0‰, respectively. These are significantly higher than the Neoproterozoic phosphate ores (10.9‰—13.9‰) as reported by Ling et al., hence, late diagenesis and hydrothermal replacement may not have caused a significant change in the oxygen isotope compositions of the small shelly fossils, and the calculated temperatures (25.4—26.3℃) for palaeo-seawater using a SSF phosphate oxygen isotope thermometer are therefore considered here as the upper limit of seawater temperature in the Early Cambrian ocean of the Yangtze Platform.  相似文献   
9.
To efficiently use the array aperture and avoid the complicated parameter pairing computation,this paper proposes a new cumulant-based algorithm for localizing near-field narrowband sources.Firstly,this algorithm proposes a symmetric uniform linear ar- ray (ULA),and constructs three cumulant matrices by using the fourth-order cumulants of some properly chosen sensor outputs;second- ly,unlike the conventional parallel factor (PARAFAC) analysis models in data or subspace domain,it forms a three-way array (TWA) in the fourth-order cumulant domain using the three matrices,and analyzes the uniqueness of its low-rank decomposition;thirdly,it jointly estimates the frequency,the direction-of-arrival (DOA),and the range of each near-field source from the matrices via the low-rank de- composition of the TWA.The simulation results are presented to validate the performance of our proposed method.  相似文献   
10.
世界上,一项发明、一项新技术可以通过申请专利,保护发明者的权益。在农业领域,对新品种的发现和培育,同样可以获得专利保护,这就是“植物新品种保护制度”。  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