全文获取类型
收费全文 | 487篇 |
免费 | 12篇 |
专业分类
化学 | 220篇 |
晶体学 | 4篇 |
力学 | 88篇 |
数学 | 85篇 |
物理学 | 102篇 |
出版年
2022年 | 4篇 |
2021年 | 12篇 |
2020年 | 4篇 |
2019年 | 10篇 |
2018年 | 12篇 |
2017年 | 6篇 |
2016年 | 13篇 |
2015年 | 14篇 |
2014年 | 9篇 |
2013年 | 26篇 |
2012年 | 30篇 |
2011年 | 26篇 |
2010年 | 13篇 |
2009年 | 20篇 |
2008年 | 14篇 |
2007年 | 23篇 |
2006年 | 21篇 |
2005年 | 11篇 |
2004年 | 17篇 |
2003年 | 14篇 |
2002年 | 17篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 9篇 |
1997年 | 4篇 |
1996年 | 11篇 |
1995年 | 11篇 |
1994年 | 8篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1985年 | 3篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 3篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1969年 | 3篇 |
1968年 | 3篇 |
1966年 | 3篇 |
1963年 | 4篇 |
1962年 | 4篇 |
1961年 | 3篇 |
1959年 | 4篇 |
排序方式: 共有499条查询结果,搜索用时 265 毫秒
441.
B. S. Maruthiprasad M. N. Sastri S. Rajagopal K. Seshan K. R. Krishnamurthy T. S. R. Prasada Rao 《Journal of Thermal Analysis and Calorimetry》1988,34(4):1023-1030
Thermal analysis of alumina precursors prepared by two different PFHS (precipitation from homogeneous solution) methods and a conventional method is described. All three precursors exhibit distinct thermal behaviour patterns, marked by multiple phase transformations, to yield-Al2O3 ultimately. Thermal analysis studies, coupled with XRD, IR and elemental analysis data, indicate that the precursors obtained by the PFHS methods are monophasic in nature, and hence yield relatively small, uniform microspheroidal alumina in comparison with the alumina obtained by the conventional method.
One of us BSM thanks the University Grants Commission, India, for the award of a Research Fellowship. 相似文献
Zusammenfassung Die Thermoanalyse von Aluminiumoxidpräkursoren, hergestellt durch zwei verschiedene PFHS (Precipitation From Homogeneous Solution) und eine herkömmliche Methode, wurde beschrieben. Alle drei Präkursoren zeigen ausgeprägte thermische Verhaltensformen, gekennzeichnet durch Mehrfachphasenübergange zur letztendlichen Bildung von-Al2O3. Die Thermoanalysen, verbunden mit Röntgendiffraktions-, Infrarot- und Elementaranalysen zeigen, dass die durch PFHS-Methoden erhaltenen Präkursoren über Einphasen verfügen und verglichen zu herkömmlich hergestelltem Aluminiumoxid relativ kleines, einheitliches Kugelaluminiumoxid liefern.
« » , - , . «» , -l23. , , , « », , , .
One of us BSM thanks the University Grants Commission, India, for the award of a Research Fellowship. 相似文献
442.
E. S. Rajagopal 《Colloid and polymer science》1961,175(2):126-129
Summary A working model is given for the rate of ultrasonic emulsification, considering the dispersion at the interface (areaA) and the coagulations in the volumeV of the emulsion. A bimolecular coagulation leads to the equationc=c
∞tanhbt;c
∞=(Aα/Vβ)1/2;b=(Aαβ/V)1/2 while a monomolecular coagulation givesc=c
∞{1−exp (−at)};c
∞=Aα/Vβ;a=β.
The experiments on the dependence of c∞,a andb uponA andV favour the bimolecular coagulation. The results are satisfactorily explained on general theoretical grounds.
Zusammenfassung Ein Arbeitsmodell für die Geschwindigkeit der Ultraschallemulgierung wird entwickelt, das Dispersion in der Grenzfl?che (Fl?cheA) und Koagulation im Volumen (V) der Emulsion annimmt. Eine bimolekulare Koagulation führt zu der Gleichung:c=c ∞ tanhbt;c ∞=(Aα/Vβ)1/2;b=(Aαβ/V)1/2, eine monomolekulare dagegen zu:c=c ∞{1−exp (at−)};c ∞=Aα/Vβ;α=β. Die Versuche über die Abh?ngigkeit vonc ∞,a undb vonA undV scheinen für bimolekulare Koagulation zu sprechen. Die Ergebnisse werden auf der Basis dieser einfachen theoretischen Grundlagen befriedigend erkl?rt.相似文献
443.
Alan P. Marchand G. V. M. Sharma D. Rajagopal Rajesh Shukla Grzegorz Mlosto Romuald Bartnik 《Journal of heterocyclic chemistry》1996,33(3):837-840
Trimethylsilyl azide adds smoothly to the highly strained N-C(3) σ-bond in 3-ethyl-1-azabicyclo[1.1.0]-butane ( 1 ) to afford an adduct, 2 , that reacts in situ with a variety of electrophilic reagents (i.e., ethyl chloroformate, p-toluenesulfonyl chloride, benzoyl chloride, acetyl chloride, and oxalyl chloride) to afford the corresponding N-substituted-3-azido-3-ethylazetidines 3–7 , respectively in 62–72% yield. Similarly, 1 reacts regiospecifically with “mixed anhydrides” (i.e., p-toluenesulfonyl acetate, methanesulfonyl acetate, and benzoyl trifluoromethanesulfonate) to afford the corresponding adducts, 8–10 , respectively) in 38–68% yield. Reaction of p-toluenesulfonyl azide with 1-aza-3-phenylbicyclo[1.1.0]butane ( 12 ) produces two products: N-(p-toluenesulfonyl-3-azido-3-phenylazetidine ( 13 , 15%) and a dimeric product, N-(N'-p-toluenesulfonyl-3′-phenyl-3′-azetidinyl)-3-azido-3-phenylazetidine ( 14 , 28%). Ethyl chloroformate adds to the N-C(3) σ-bond in 1-aza-3-(bromomethyl)bicyclo[1.1.0]butane ( 15 ) to afford N-carboethoxy-3-(bromomethyl)-3-chloroazetidine ( 16 ) in 73% yield. 相似文献
444.
Sivasubramanian VK Ganesan M Rajagopal S Ramaraj R 《The Journal of organic chemistry》2002,67(5):1506-1514
The oxidation of a series of para-substituted phenyl methyl sulfides was carried out with several oxo(salen)iron (salen = N,N'-bis(salicylidine)ethylenediaminato) complexes in acetonitrile. The oxo complex [O=Fe(IV)(salen)](*+), generated from an iron(III) [bond] salen complex and iodosylbenzene, effectively oxidizes the organic sulfides to the corresponding sulfoxides. The formation of [O [double bond] Fe(IV)(salen)](*+) as the active oxidant is supported by resonance Raman studies. The kinetic data indicate that the reaction is first-order in the oxidant and fractional-order with respect to sulfide. The observed saturation kinetics of the reaction and spectral data indicate that the substrate binds to the oxidant before the rate-controlling step. The rate constant (k) values for the product formation step determined using Michaelis-Menten kinetics correlate well with Hammett sigma constants, giving reaction constant (rho) values in the range of -0.65 to -1.54 for different oxo(salen)iron complexes. The log k values observed in the oxidation of each aryl methyl sulfide by substituted oxo(salen)iron complexes also correlate with Hammett sigma constants, giving positive rho values. The substituent effect, UV-vis absorption, and EPR spectral studies indicate oxygen atom transfer from the oxidant to the substrate in the rate-determining step. 相似文献
445.
Summary Complexes of the type M(HXCA)2·nH2O (M = CuII, NiII or CoII; HXCA = 2-hydroxy--4-X-cinnamoyl acetophenone; X = H, Cl, Me or OMe; n = 0 or 2) have been synthesized, and characterized by elemental analysis, i.r., electronic, 1H-n.m.r. and e.s.r. spectroscopies, and magnetic susceptibility measurements. The spectral data indicate that the ligand coordinates through both carbonyl and enolic oxygens. The anhydrous CuII complexes are monomeric and square planar, while the NiII and CoII analogues possess polymeric high-spin octahedral structures. The diaquates and dipyridinates of CoII and NiII have monomeric high-spin octahedral geometries. 相似文献
446.
Periakaruppan Athappan Sankarapandian Sevagapandian Gurusamy Rajagopal 《Transition Metal Chemistry》1995,20(5):472-476
Summary Metal(II) chelates of Schiff bases derived from the condensation of 1,2,3,5,6,7,8,8a-octahydro-3-oxo-N,1-diphenyl-5-(phenylmethylene)-2-naphthalenecarboxamide with o-aminophenol (KAAP), o-aminothiophenol (KAAT) or o-aminobenzoic acid (KAAB) have been prepared and characterized. The complexes are of the type [M(N2X)]2 for M = CuII and M(NX)2·nH2O for M = NiII, CoII and VOII (X = phenolic oxygen, thiophenolic sulphur or carboxylic oxygen; n = 0 or 2). Conductivity data indicate that the complexes are non-ionic. The Schiff bases behave as dibasic tridentate ligands in their copper(II) complexes and as monobasic bidentate ligands in their nickel(II), cobalt(II) and vanadyl(II) complexes. The subnormal magnetic moments of the copper(II) complexes are ascribed to an antiferromagnetic exchange interaction arising from dimerization. Nickel(II) and cobalt(II) complexes are trans octahedral whereas vanadyl(II) complexes are square pyramidal 相似文献
447.
448.
Zusammenfassung Es wird über die Synthese einiger angulärer Furoxanthone mit einer Methylgruppe in -oder -Stellung oder einer Phenylgruppe in der -Stellung des Furanrings berichtet. Ausgegangen wurde von einem Hydroxyxanthon mit einem Orcinkern.
The synthesis of a few angular furano-xanthones carrying a methyl group either in -or in -position or a phenyl group in the -position of the furan ring, starting with an hydroxy xanthone possessing an orcinol nucleus is recorded.相似文献
449.
450.