全文获取类型
收费全文 | 244篇 |
免费 | 3篇 |
国内免费 | 2篇 |
专业分类
化学 | 245篇 |
晶体学 | 2篇 |
物理学 | 2篇 |
出版年
2024年 | 2篇 |
2023年 | 41篇 |
2022年 | 2篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 1篇 |
2015年 | 3篇 |
2014年 | 8篇 |
2013年 | 23篇 |
2012年 | 18篇 |
2011年 | 3篇 |
2010年 | 4篇 |
2009年 | 6篇 |
2008年 | 14篇 |
2007年 | 18篇 |
2006年 | 12篇 |
2005年 | 12篇 |
2004年 | 8篇 |
2003年 | 4篇 |
2002年 | 5篇 |
2000年 | 5篇 |
1999年 | 6篇 |
1998年 | 10篇 |
1997年 | 6篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1985年 | 1篇 |
1982年 | 2篇 |
1979年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有249条查询结果,搜索用时 15 毫秒
1.
Dehydrogenation of alcohols into aldehydes and ketones by Ru3(CO)12/PPh3 based homogeneous catalysis has been investigated as an alternative for the classical Oppenauer oxidation. Several catalytic systems have been screened in the Oppenauer-like oxidation of alcohols. A systematic study of various combinations of Ru3(CO)12, mono- and bidentate ligands and hydride acceptors was performed to enable dehydrogenation of primary alcohols to stop at the aldehyde stage. Among many H-acceptors screened, diphenylacetylene (tolane) proved the most suitable judged from its smooth reduction. Electron rich and deficient analogues of tolane have been synthesized and, based on competition experiments between these H-acceptors, a tentative catalytic cycle for the Ru3(CO)12/PPh3-catalyzed dehydrogenations has been proposed. 相似文献
2.
Polyol Metal Complexes. 27. Bis-Diolato Antimonates(III ) with Guanosine as the Diol The complex anions of K3[SbIII(Guo1,2′,3′H?3)2] · 10 H2O ( 1 ) and [Co(NH3)6][SbIII(Guo1,2′,3′H?3)2] · 9 H2O ( 2 ) are four-coordinate homoleptic bis(diolato)antimonate(III ) species. The guanosine trianions act as carbohydrate ligands through their cis-furanoidic ribosyl moiety, thus forming no nucleobase–metal bonds. 相似文献
3.
Guido Kickelbick Dieter Rutzinger Thomas Gallauner 《Monatshefte für Chemie / Chemical Monthly》2002,133(8):1157-1164
Summary. Hexadentate ligands were formed by the reaction of primary dimethylaminoethyl- or methoxyethylamines with formaldehyde. The
resulting N, N′, N″-functionalized hexahydro-1,3,5-triazines contain pending amino or ether functionalities which are able to coordinate to
metals in addition to the ring nitrogen atoms. Both ligands were reacted with CuBr, and novel tricopper clusters were isolated
and characterized by X-ray structure analysis. In these compounds a ring nitrogen atom, the pending amino or ether functionality,
and two bridging bromine atoms coordinate each of the copper atoms.
Received January 22, 2002; accepted (revised) March 22, 2002 相似文献
4.
Heterobimetallic Complexes with Chelate Ligands from Multidentate Amines and 1,1-Bis(diphenylphosphine)ethene By an addition reaction of bidentate amines Me2N(CH2)nNH2 (n = 2, as-4C2N; 3, as-5C2N) and vinylidene derivatives with an activated double bond CH2 = C(PPh2)2M(CO)4 (M = Cr, Mo, W) were synthesized in dichlormethane unsymmetrical chelate ligands of the type as-4C2N (or as-5C2N)PPM(CO)4. They gave with divalent salts M′Y2 (Y = ac, M′ = Cu, Ni. Y = Cl, M′ = Zn, Cd, Hg) the coloured bimetallic complexes M′Y(as-4C2N) (or as-5C2N)PPM(CO)4 which were characterized by means of IR-, UV/VIS spectroscopic and 1H, 13C and 31P NMR measurements. The molecular structures of the complexes Cuac2(as-5C2N)PPCr(CO)4, I and that of CdCl2(as-4C2N)PPCr(CO)4, II , were acertained by results of single crystal X-ray determinations. In the crystals of I—II , the coordination polyhedron of each chromium(0) central atom containing two phosphorous donor atoms in a four-membered chelate ring and four terminal CO ligands is octahedrally distorted. This coordination sphere is connected at the carbon ring atom via a methylen chain group (spacer) with the bidentate amine ligand, which has a secondary and a tertiary nitrogen donor atom. Both nitrogen atoms are coordinated with the Cuac2 under formation of a new kind of [4 + 2]-coordination in a trischelate complex. The six-membered diamine chelat ring in I has a chair-like conformation. The chromium-cadmium complex II is dimer from which the Cd central atoms obtain the rare coordination number of five. The related five-membered diamine chelate ring has δ conformation. 相似文献
5.
Reactivity of Monophosphine Platinum(0) Complexes with SO2 . The addition reaction of (PPh3)Pt(ViSi) (ViSi = {η2-H2C?CHSiMe2}2O) ( 1 ) with SO2 gives within 30 min the red SO2 complex (PPh3)Pt(η2-H2C?CHSiMe2- OSiMe2CH?CH2)(SO2) ( 2 ). A reaction time of 24 h with SO2 leads to the elimination of the ViSi ligand, and the unstable monomeric intermediate (PPh3)Pt(SO2) cyclo- trimerizes to the stable cluster [Pt(PPh3)(SO2)]3 ( 3 ). 3 is also obtained within 30 min by the reaction of (PPh3)Pt(C2H4)2 ( 4 ) with SO2. The crystal structure of 3 has been determined; space group P21/n, Z = 4, a = 1 606.1(3), b = 1 019.3(1), c = 3 624.6(5) pm, β = 93.67°, R/Rw = 0.102/0.121. 相似文献
6.
The interaction of Amido black 10B (AB) with DNA in basic medium was studied in the presence of cetyltrimethylammonium bromide (CTMAB) based on the measurements of resonance light scattering (RLS), UV–vis, CD spectra, and RLS imaging. The interaction has been proved to give a ternary complex of CTMAB–DNA–AB in Britton–Robinson buffer of pH 11.55, which exhibits strong negative Cotton effect at 233.3 nm and 642.8 nm, and strong RLS signals characterized at 469 nm. Experiments showed that the enhanced RLS intensities (ΔIRLS) against the mixture of AB and CTMAB are proportional to the concentration of fish sperm DNA (fsDNA) and calf thymus DNA (ctDNA), respectively over the range of 0.03–1.0 and 0.05–1.5 μg ml−1, with the limits of determination (3σ) of 7.3 ng ml−1 for fsDNA and 7.0 ng ml−1 for ctDNA. 相似文献
7.
Mark L. Hlavinka 《Tetrahedron letters》2006,47(29):5049-5053
Simple amides and esters are conveniently deprotonated by Zn(tmp)2 (tmp = 2,2,6,6-tetramethylpiperidinyl anion) to generate Zn enolates. Enolates formed by this method are suitable for use in aldol reactions that tolerate base-sensitive functional groups. Additionally, the Zn enolates are readily coupled with aryl bromides using typical Pd-catalyzed coupling methods. 相似文献
8.
G. Tav?ar 《Journal of fluorine chemistry》2004,125(11):1579-1584
A new class of coordination compounds of the type [Mn+(L)p](AF6−)n and [Mn+(L)r](BF4−)n, where M is Mg, Ca, Sr, Ba, Cd, Pb, lanthanides, A is P, As, Sb, Bi and L is XeF2, XeF4, XeF6, KrF2, was studied. A review of all known coordination compounds with L is XeF2 is given: (a) synthetic routes for the preparation of these compounds; (b) analysis of their crystal structures (molecular, dimer, chain, double chain, layer, strongly interconnected double layers and three-dimensional network); (c) the influence of the ligand XeF2 (small formula volume, linear, semi-ionic, charge of −0.5e on each F ligand); (d) the influence of the central metal ion; (e) the influence of the anions: AF6− and BF4− (the formula volume, Lewis basicity). On the basis of all properties of the metal ions, ligand and anions the obtained variety of the structures is analyzed. 相似文献
9.
Robert W. Baker Simon O. Rea Elisabeth M.C. Schenkelaars Angela Totaro 《Tetrahedron》2005,61(15):3733-3743
Racemic 1-(1′-isoquinolinyl)-2-naphthalenemethanol rac-12 was prepared through a ligand coupling reaction of racemic 1-(tert-butylsulfinyl)isoquinoline rac-7 with the 1-naphthyl Grignard reagent 10. Resolution of rac-12 was achieved through chromatographic separation of the Noe-lactol derivatives 14 and 15, providing (R)-(−)-12 of >99% ee and (S)-(+)-12 of 90% ee. The ligand coupling reaction of optically enriched sulfoxide (S)-(−)-7 (62% ee) with Grignard reagent 10 furnished rac-12, with the absence of stereoinduction resulting from competing rapid racemisation of the sulfoxide 7. Reaction of optically enriched (S)-(−)-7 with 2-methoxy-1-naphthylmagnesium bromide was also accompanied by racemisation of the sulfoxide 7, and furnished optically active (+)-1-(2′-methoxy-1′-naphthyl)isoquinoline (+)-3b in low enantiomeric purity (14% ee). The absolute configuration of (+)-3b was assigned as R using circular dichroism spectroscopy, correcting an earlier assignment based on the Bijvoet method, but in the absence of heavy atoms. Optically active 2-pyridyl sulfoxides were found not to undergo racemisation analogous to the 1-isoquinolinyl sulfoxide 7, with the ligand coupling reactions of (R)-(+)- and (S)-(−)-2-[(4′-methylphenyl)sulfinyl]-3-methylpyridines, (R)-(+)-17 and (S)-(−)-17, with 2-methoxy-1-naphthylmagnesium bromide providing (−)- and (+)-2-(2′-methoxy-1′-naphthyl)-3-methylpyridines, (−)-18 and (+)-18, in 53 and 60% ee, respectively. The free energy barriers to internal rotation in 3b and 18 have been determined, and the isoquinoline (R)-(−)-12 examined as a ligand in the enantioselectively catalysed addition of diethylzinc to benzaldehyde; (R)-(−)-12 was also converted to (R)-(−)-N,N-dimethyl-1-(1′-isoquinolinyl)-2-naphthalenemethanamine (R)-(−)-19, and this examined as a ligand in the enantioselective Pd-catalysed allylic substitution of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate. 相似文献
10.
Steffen Blaurock Thomas Koch Olaf Kühl Peter Lönnecke Felicite Majoumo René Sommer 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6-7):1451-1456
Substituted bifunctional phosphorus-based ligands HX(CRR') n PR"H (or -PR" 2 ) [where X = O, S, NR', (substituted) cyclopentadienyl; n = 1, 2, 3; R, R', R" = alkyl, aryl, H] were employed as bridging ligands in the synthesis of early/late bridged transition metal complexes. Synthetic routes to the bifunctional ligands were also developed. First, mononuclear complexes, such as [TpZr(OCH 2 PPh 2 ) 3 ] (Tp = trispyrazolylborato), [Cp 2 Zr(1-O-2-PHR-C 6 H 10 )(Me)] (R = 2,4,6-Pr i 3 C 6 H 2 (Tipp)), [Cp 2 Zr(SCH 2 CH 2 PHR) 2 ] (R = Ph, Mes, Tipp), and phosphinoferrocene derivatives, were prepared. These complexes are suitable precursors for the introduction of a second metal (as in, for example, [TpZr( w -OCH 2 PPh 2 ) 3 Mo(CO) 3 ]). 相似文献