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   175篇
  免费   1篇
  国内免费   9篇
化学   138篇
物理学   26篇
综合类   21篇
  2024年   1篇
  2023年   21篇
  2022年   1篇
  2020年   2篇
  2019年   1篇
  2018年   2篇
  2017年   3篇
  2015年   5篇
  2014年   7篇
  2013年   16篇
  2012年   11篇
  2011年   7篇
  2010年   4篇
  2009年   8篇
  2008年   10篇
  2007年   6篇
  2006年   4篇
  2005年   6篇
  2004年   6篇
  2003年   8篇
  2002年   7篇
  2001年   6篇
  2000年   5篇
  1999年   2篇
  1998年   8篇
  1997年   5篇
  1996年   3篇
  1995年   3篇
  1994年   1篇
  1992年   4篇
  1991年   2篇
  1990年   4篇
  1988年   3篇
  1987年   2篇
  1980年   1篇
排序方式: 共有185条查询结果,搜索用时 15 毫秒
21.
The copper(I)‐mediated generation of ‐OCF2CF2‐ moieties by the oxycupration of tetrafluoroethylene (TFE) using either copper aryloxides or alkoxides is disclosed. The key intermediates, 2‐aryloxy‐1,1,2,2‐tetrafluoroethyl and 2‐alkoxy‐1,1,2,2‐tetrafluoroethyl copper complexes, were obtained from the reaction of the corresponding aryloxy and alkoxy copper complexes with TFE, and their structures in solution and in the solid state were unambiguously determined by multinuclear NMR spectroscopy and X‐ray diffraction analysis. These copper complexes subsequently reacted with aryl iodides (ArI) to afford ROCF2CF2Ar (R=aryl or alkyl) in high yields.  相似文献   
22.
合成了二苯并18冠6冠醚配合物:[K(DB18C6)]2[Co(NCS)4]C3H6O,并通过元素分析、红外光谱及X-射线单晶衍射对结构进行了分析.配合物为:单斜晶系、空间群C2/C.晶体学数据:a=2.051(8),b=1.517 4(7),c=1.912 5(8)nm,β=92.422(8)°,V=5.927(4)nm3,Z=4,Dcalc=1.352 g·cm-3,F(000)=2 516,R1=0.061,wR=0.126 5.配合物由两个[K(DB18C6)]+配阳离子、一个[Co(NCS)4]2-配阴离子和一个C3H6O分子组成.四个硫氰酸根的氨原子与钴原子配位,[Co(NCS)4]2-为四面体构型.K+除与冠醚环6个氧原子成键外还与丙酮氧原子配位成键.  相似文献   
23.
以杯「4」芳烃和环氧氯丙烷反应,合成杯「4」芳烃环氧丙醚:25,27-二(2‘,3’-环氧丙氧基)-26,28-二羟基杯「4」芳烃,并通过^1H-NMR,IR以及元素分析对其结构进行表征。  相似文献   
24.
Treatment of an acetonitrile solution of CuI with 1, 10‐dithia‐18‐crown‐6 (1, 10DT18C6) in the presence of Rb2CO3 leads to formation of the lamellar coordination polymer [Rb{Cu4I5(1, 10DT18C6)2}] ( 1 ).The anionic network of 1 is composed of parallel [(Cu4I5)] chains linked by bridging thiacrown ether ligands, pairs of which coordinate the Rb+ counter cations. [Cs{Cu5I6(1, 10DT18C6)2}] ( 2 ) can be prepared under similar conditions but contains separated helical anionic chains. In this case 1, 10DT18C6 ligands bridge copper atoms of individual chains in an intrastrand manner. In contrast the coordination networks in [(CuCN)2(1, 10DT18C6)] ( 3 ) and [K2{Cu12(CN)14(1, 10DT18C6)3} · CH3CN] ( 4 ) are both three‐dimensional and based on CuCN‐containing sheets bridged by 1, 10DT18C6 ligands. In the latter compound pairs of K+ cations are coordinated by groups of three thiacrown ether molecules. The neutral network of 3 can imbibe up to 31 % KNO3 per 1, 10DT18C6 pair without loss of lattice integrity.  相似文献   
25.
We present the bundle (Aff(3)Λ)(ℝ3), with a geometric Dirac equation on it, as a three-dimensional geometric interpretation of the SM fermions. Each (ℂΛ)(ℝ3) describes an electroweak doublet. The Dirac equation has a doubler-free staggered spatial discretization on the lattice space (Aff(3)ℂ)(ℤ3). This space allows a simple physical interpretation as a phase space of a lattice of cells. We find the SM SU(3) c ×SU(2) L ×U(1) Y action on (Aff(3)Λ)(ℝ3) to be a maximal anomaly-free gauge action preserving E(3) symmetry and symplectic structure, which can be constructed using two simple types of gauge-like lattice fields: Wilson gauge fields and correction terms for lattice deformations. The lattice fermion fields we propose to quantize as low energy states of a canonical quantum theory with ℤ2-degenerated vacuum state. We construct anticommuting fermion operators for the resulting ℤ2-valued (spin) field theory. A metric theory of gravity compatible with this model is presented too.  相似文献   
26.

A chromoionophore-derived calix[4]crown, 1 , possessing an effective signal-controllable function by metal ionic inputs has been newly synthesized, whose function is mainly of our interest, by transforming the process of receptor activation to one that may be detected by an optical signal (i.e. color change), the basic feature of antagonist-agonist competition may be reproduced readily and visually detected. The process would be particularly new within the field of optical read-out receptors. Further, from the standpoint of material sciences, the controllable signal function may not only be welcome for molecular information processing, but also contribute to the design of new sensory materials.  相似文献   
27.
3,4‐Dibromo‐5‐[2‐bromo‐3,4‐dihydroxy‐6‐(methoxymethyl)benzyl]benzene‐1,2‐diol ( 2 ), a natural product, has been synthesized for the first time starting from (3‐bromo‐4,5‐dimethoxyphenyl)methanol ( 5 ) in five steps and with an overall yield of 34%. The reaction of some methoxymethyl‐substituted aryl methyl ethers with BBr3, followed by the addition of MeOH, afforded the corresponding methoxymethyl‐substituted arylphenols in high yields.  相似文献   
28.
Xiaolu Jiang 《Tetrahedron》2010,66(52):9828-9834
Gold(I) and (III) salts have been found to be highly effective at the catalysis of ether formation from alcohols. Intramolecular ether formation of a 1,5-diol was also achieved, with a stereoselectivity that indicates that an SN1 mechanism predominates. In an attempt to form a seven-membered ring, a stable 14-membered dimer product was also formed. Attempts to control the diastereoselectivity of the reaction using a chiral anionic counterion did not give products with a high de.  相似文献   
29.
The GC-SAFT equation of state proposed by Tamouza et al. (2004) [51], extended to polar molecular fluids NguyenHuynh et al. (2008) [32], is here applied to model vapor-liquid phase equilibria of various binary mixtures containing at least one oxygenated compound belonging to ethers, ketones or aldehydes chemical families.These systems are modeled using a polar version of the three different versions of SAFT-EOS (original, VR-SAFT and PC-SAFT) in a predictive manner: binary interaction parameters kij and lij are all set to zero.In the case of alcohol + ether, +ketone, +aldehyde systems, a cross-association interaction between an oxygenated compound (non self-associating compound) and an alcohol is necessary to model/predict accurately the mixture VLE. The corresponding association parameters are assumed to be equal to the self-association parameters of pure 1-alkanols.The above-cited systems have been treated in a comprehensive manner. The general agreement between polar GC-SAFT and experimental data is good (within 4-5% deviation on pressure), similar to the one obtained on previously investigated systems using GC-SAFT.  相似文献   
30.
研究了二苯并18-冠-6(DB18-C-6)与(NH4)2[Pd(SCN)4]的反应,通过元素分析、红外光谱、单晶X射线衍射对生成的配合物[NH4(DB18-C-6)]2[Pd(SCN)4](1)进行了结构分析.1为三斜晶系,空间群P-1,晶体学数据:a=0.8705(3)nm,b=1.1954(4)nm,c=1.3044(4)nm,α=73.216(5)°,β=78.897(5)°,γ=81.105(6)°,V=1.2682(7)nm3,Z=1,F(000)=568,R1=0.0301,wR2=0.0431.配合物由二个[NH4(DB18-C-6)]+配阳离子和一个[Pd(SCN)4]2-配阴离子组成,二者通过N-H…N氢键形成中性配合物,配合物中不存在阳离子-π相互作用.  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