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   17篇
  免费   2篇
  国内免费   10篇
化学   20篇
力学   1篇
数学   3篇
物理学   5篇
  2018年   1篇
  2013年   1篇
  2004年   2篇
  2003年   4篇
  2002年   2篇
  2001年   4篇
  2000年   1篇
  1998年   1篇
  1997年   2篇
  1996年   1篇
  1995年   1篇
  1993年   2篇
  1990年   1篇
  1965年   3篇
  1964年   2篇
  1963年   1篇
排序方式: 共有29条查询结果,搜索用时 250 毫秒
1.
Derivatives of 2,3-(1,4-dialkoxyaceno)norbornadiene underwent ring-opening metathesis polymerization (ROMP) upon the catalysis of a ruthenium complex to afford the corresponding polymers. The polymeric materials containing anthracene chromophores emit white electro-luminescence, which can be fabricated into light-emitting diodes (LED). The broad emission band is composed of a blue emission from anthracene and a red emission from aggregates. A single layer device, ITO/polymer/Ca/Al, can be turned on at 7V and exhibits maximum intensity 427 cd/m2 at 15 V. A double layer device, ITO/polymer/TPBI/Mg:Ag (TPBI = (2,2′,2"-(1,3,5-benzenetriyl)-tris(1-phenyl-1H-benzimidazole)) displayed blue light with turn-on voltage 6 V and maximal intensity 930 cd/m2 at 15 V.Derivatives of bisindolylmaleimide were found to form amorphous solid films which exhibit intensive red luminescence. The property of forming glasses can be ascribed to the nonplanar geometry of these molecules. LED devices were fabricated by a layer of pure dye sandwiched between two charge transporting films. The yellow emission spectrum of the devices utilizing Alq (tris(8-hydoxyquinolinato)aluminum) contains a green component from Alq. Pure red emissions can be achieved by replacing Alq with TPBI. Typical devices can be turned on at ~3 V with maximal intensity 2000 cd/m2. White color devices are under current investigation, in which the green Alq layer is replaced by its blue derivative (bis(2-methyl-8-hydoxyquinolinato)(phenolato)aluminum).  相似文献   
2.
本文研究了TBH与各种胺组成的引发系统对丙烯腈水溶液聚合的影响,发现胺的结构对聚合速度与转化率有极大的影响,其聚合速度顺序为:Et_3N、HEA>TEA>DMA,MEA>TEA·HCl。其中以 TBH-TEA体系效果最好,聚合速度快,转化率也高。此外,聚合反应中大致有着这样的规律,诱导期与聚合速度有较明显的平行关系,即诱导期短,聚合速度大,诱导期长,聚合速度小;而诱导期又与这些三极胺的碱性(pK_b)也有一定的平行关系,碱性强的(pK_b小)诱导期短,碱性弱的(pK_b大)诱导期长。 在所用的引发体系中,TBH-TEA及BPO-TEA体系,聚合速度与转化率随着TEA 浓度的增加而增加,但在 TBH-Et_3N、TBH-HEA 及 TBH-DMA 体系时,随着胶的浓度增加前二者聚合速度虽然增加但转化率反而下降,而后一体系则聚合速度与转化率都呈下降。  相似文献   
3.
The methanolic extract from a Chinese endemic Chrysanthemum plant, Dendranthema indicum var. aromaticum, was found to show high antifeeding activity against Pieris brassicae L., and by bioassay-guided separation, the active component, B-ring-homo-tonghaosu, 2-(2‘,4‘-hexadiynylidene)-1,6-dioxaspiro-[4,5]-dec-3-ene (2) was isolated. Its structure was elucidated by comparing its spectroscopic data with those of 2 reported in the literatures. Furthermore new convenient total synthesis methods of B-ring-homo-tonghaosu were also developed to confirm its structure and make its further application in crop protection available. In addition, extensive comparison of spectroscopic data showed that the structure of compound 21 reported in literature should be revised to 2.  相似文献   
4.
Approaches toward the synthesis of iridoids and 9-isocyanopupukeanane starting from cy-clopentadiene are discussed.  相似文献   
5.
本文报导了第三丁基乙烯基酮在不同溶剂中应用各种负离子引发剂的聚合研究。以正丁基锂为引发剂,吡啶或四氢呋喃为溶剂时,都是均相聚合,得到无定形聚合物,它们的软化温度为40—180°之间,如果以苯、甲苯、二甲苯或正庚烷为溶剂,则都是非均相聚合,得到结晶性聚合物,有着高达260—280°之间的熔点。上述结晶性与无定形聚第三丁基乙烯基酮的红外光谱有着显著的不同,结晶性聚合物具有特征的吸收峯,以1100厘米~(-1)与1330厘米~(_1)二处最为明显。还研究了不同比例的混合物的红外光谱,当结晶性聚合物含量降至 87%以下时,则 1100厘米~(-1) ,1290厘米~(-1)及 1330厘米~(-1)三处吸收峯逐渐减弱,当减少至13%时则与无定形聚合物的光谱一致。此外金属锂、钠与钾都能引发聚合第三丁基乙烯基酮,也试用了NaH,LiAlH_4,RONa,ROK,RMgX,二苯酮以及二苯酮钠等引发剂进行非均相聚合。  相似文献   
6.
Asymmetric catalysis is one of the most challenging and formidable endeavor in organic synthesis. The development of chiral auxiliaries is a key in the asymmetric catalysis. Azulenoids, a parent structure of bicyclo[5.3.0]decapentaene with 10 πelectrons, are useful as dye materials, medical treatment of inflammation and hypertension, and the development of liquid crystals. In continuing to investigate synthetic application of azulenoids, we have studied to develop novel chiral auxiliaries of BIAZOLs. The BIAZOLs were synthesized from dicyclopentadiene and characterized using spectroscopies.  相似文献   
7.
A systematic prefilter design process for reducing operator-induced rigid body vibrations of rubber tire mounted machines is presented. The contribution of this work is the development of a systematic prefilter design process and interpretation of the results. The class of heavy equipment considered in this work are those machines having rigid body main frame vibrations dominated by linear dynamics. The reduction in machine vibrations is accomplished through the design of prefilters that reduce the machine resonant frequencies from the operator commands. The machine information required for the design process includes the bandwidth of the electro-hydraulic (E/H) valves and rigid body resonant frequencies of the machine mainframe. The prespecified performance in the design process is the desired attenuation of machine resonant frequencies which is related to the acceptable level of machine vibration. The design methodology has been applied to a telescopic boom lift to illustrate the procedure and the effectiveness of the design.  相似文献   
8.
丘锡钧 《物理学报》1965,21(1):208-217
本文研究了在氘核削裂反应中伴随有靶核核心激发的情况。在这种情况下,假定由于核子-核子剩余相互作用,靶核的组态除了通常壳模型组态外,还混杂有核心激发的组态。同样,剩余核的组态主要是某一种核心激发的组态,但也还混杂有别种组态。在这假定下,给出了所考虑的反应过程的微分截面表示式。它表明,反应截面主要由靶核的组态混合所贡献。一般说来,组态的混合程度不大,故可预期截面数值是较小的。公式还表明,反应角分布的特征峯是由核心在激发后留下来的空穴态的轨道角动量量子数所决定的。这二点结论与这类反应的实验结果是一致的。运用这公式具体估计了六个反应事例的核谱因子,在实验误差内,理论值和从实验的估计值大致相合。  相似文献   
9.
Intramolecular radical cyclization reactions are now used routinely to synthesize carbocyclic and heterocyclic structures. We have reported that α-carbonyl radicals 1, generated from the corresponding iodo ketones or enones, underwent intramolecular radical cyclization smoothly to afford products 2.1, 2,3  相似文献   
10.
51. Introduction and Statement of ResultsLet X ~ {Xt, t 2 0} be a standajrd d-dimensional Brownian motion with drift c startedat fiXed XO ~ x:Xo ~ Wb ct, t 2 0,where Wt is the standard d--dimensional Brownian motion, c E R'(d 2 2) is a fixed vector.Denote by P:(.) the probability meajsure on the path space of X corresponding to initialstate XO = x and drift vector c, with E;(.) the corresponding expection operator. Forsimplity, we shall write Pz(.) and Ex(.) to refer to the case c ~ …  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