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排序方式: 共有873条查询结果,搜索用时 15 毫秒
781.
782.
Michael I. Bruce Trevor W. Hambley Michael R. Snow A.Geoffrey Swincer 《Journal of organometallic chemistry》1984,273(3):361-376
Reactions between MX(PPh3)2(η-C5H5) (M = Ru, X = Cl; M = Os, X = Br) and 2-CH2CHC6H4PPh2 afford Ph2)(η-C5H5); the Os complex is obtained in two isomeric forms. The X-ray structure of the major isomer shows the CC double bond (OsC, 2.214, 2.195 Å; CC, 1.57 Å) is almost coplanar with the OsBr vector, with the terminal C cis to Br; the minor isomer is assumed to have the alternative, more sterically congested conformation, with the β-C cis to Br. The chlororuthenium complex reacts with NaOMe/MeOH to give the corresponding hydrido complex, which also exists as two isomers in solution; reaction of this complex with CS2 gives the expected dithio acid derivative Ph2)(η-C5H5), together with small amounts of a complex assumed to be Ph2](η-C5H5). The X-ray structure of the major product reveals an unusual η3-S2C mode of coordination of the dithio acid fragment (RuS, 2.418, 2.426(1) Å; RuC 2.175(4) Å). Crystals of OsBr(η2-CH2CHC6H4P)Ph2)( η-C5H5) are monoclinic, space group P21/n, with a 12.696(2), b 21.719(6), c 15.929(3) Å, β 79.77(2)°, Z = 8; 2867 data (I > 2.5σ(I)) were refined to R = 0.040, Rw = 0.044. Crystals of Ph2)(η-C5H5) are orthorhombic, space group Pbca, with a 8.921(2), b 15.982(9), c 32.216(5) Å, Z = 8; 1685 data (I > 2.5σ(I)) were refined to R = 0.027, Rw = 0.030. 相似文献
783.
The electronic structure and metal-metal bonding in the classic d(7)d(7) tetra-bridged lantern dimer [Pt(2)(O(2)CCH(3))(4)(H(2)O)(2)](2+) has been investigated by performing quasi-relativistic Xalpha-SW molecular orbital calculations on the analogous formate-bridged complex. From the calculations, the highest occupied and lowest unoccupied metal-based levels are delta(Pt(2)) and sigma(Pt(2)), respectively, indicating a metal-metal single bond analogous to the isoelectronic Rh(II) complex. The energetic ordering of the main metal-metal bonding levels is, however, quite different from that found for the Rh(II) complex, and the upper metal-metal bonding and antibonding levels have significantly more ligand character. As found for the related complex [W(2)(O(2)CH)(4)], the inclusion of relativistic effects leads to a further strengthening of the metal-metal sigma bond as a result of the increased involvement of the higher-lying platinum 6s orbital. The low-temperature absorption spectrum of [Pt(2)(O(2)CCH(3))(4)(H(2)O)(2)](2+) is assigned on the basis of Xalpha-SW calculated transition energies and oscillator strengths. Unlike the analogous Rh(II) spectrum, the visible and near-UV absorption spectrum is dominated by charge transfer (CT) transitions. The weak, visible bands at 27 500 and 31 500 cm(-)(1) are assigned to Ow --> sigma(Pt(2)) and OAc --> sigma(Pt(2)) CT transitions, respectively, although the donor orbital in the latter transition has around 25% pi(Pt(2)) character. The intense near-UV band around 37 500 cm(-)(1) displays the typical lower energy shift as the axial substituents are changed from H(2)O to Cl and Br, indicative of significant charge transfer character. From the calculated oscillator strengths, a number of transitions, mostly OAc --> sigma(Pt-O) CT in nature, are predicted to contribute to this band, including the metal-based sigma(Pt(2)) --> sigma(Pt(2)) transition. The close similarity in the absorption spectra of the CH(3)COO(-), SO(4)(2)(-), and HPO(4)(2)(-) bridged Pt(III) complexes suggests that analogous spectral assignments should apply to [Pt(2)(SO(4))(4)(H(2)O)(2)](2)(-) and [Pt(2)(HPO(4))(4)(H(2)O)(2)](2)(-). Consequently, the anomalous MCD spectra reported recently for the intense near-UV band in the SO(4)(2)(-) and HPO(4)(2)(-) bridged Pt(III) complexes can be rationalized on the basis of contributions from either SO(4) --> sigma(Pt-O) or HPO(4) --> sigma(Pt-O) CT transitions. The electronic absorption spectrum of [Rh(2)(O(2)CCH(3))(4)(H(2)O)(2)] has been re-examined on the basis of Xalpha-SW calculated transition energies and oscillator strengths. The intense UV band at approximately 45 000 cm(-)(1) is predicted to arise from several excitations, both metal-centered and CT in origin. The lower energy shoulder at approximately 40 000 cm(-)(1) is largely attributed to the metal-based sigma(Rh(2)) --> sigma(Rh(2)) transition. 相似文献
784.
Ng SH Adams CS Hayton TW Legzdins P Patrick BO 《Journal of the American Chemical Society》2003,125(49):15210-15223
Gentle thermolysis of the allyl complex, CpW(NO)(CH(2)CMe(3))(eta(3)-H(2)CCHCMe(2)) (1), at 50 degrees C in neat hydrocarbon solutions results in the loss of neopentane and the generation of transient intermediates that subsequently activate solvent C-H bonds. Thus, thermal reactions of 1 with tetramethylsilane, mesitylene, and benzene effect single C-H activations and lead to the exclusive formation of CpW(NO)(CH(2)SiMe(3))(eta(3)-H(2)CCHCMe(2)) (2), CpW(NO)(CH(2)C(6)H(3)-3,5-Me(2))(eta(3)-H(2)CCHCMe(2)) (3), and CpW(NO)(C(6)H(5))(eta(3)-H(2)CCHCMe(2)) (4), respectively. The products of reactions of 1 with other methyl-substituted arenes indicate an inherent preference of the system for the activation of stronger arene sp(2) C-H bonds. For example, C-H bond activation of p-xylene leads to the formation of CpW(NO)(CH(2)C(6)H(4)-4-Me)(eta(3)-H(2)CCHCMe(2)) (5) (26%) and CpW(NO)(C(6)H(3)-2,5-Me(2))(eta(3)-H(2)CCHCMe(2)) (6) (74%). Mechanistic and labeling studies indicate that the transient C-H-activating intermediates are the allene complex, CpW(NO)(eta(2)-H(2)C=C=CMe(2)) (A), and the eta(2)-diene complex, CpW(NO)(eta(2)-H(2)C=CHC(Me)=CH(2)) (B). Intermediates A and B react with cyclohexene to form CpW(NO)(eta(3)-CH(2)C(2-cyclohexenyl)CMe(2))(H) (18) and CpW(NO)(eta(3)-CH(2)CHC)(Me)CH(2)C(beta)H(C(4)H(8))C(alpha)H (19), respectively, and intermediate A can be isolated as its PMe(3) adduct, CpW(NO)(PMe(3))(eta(2)-H(2)C=C=CMe(2)) (20). Interestingly, thermal reaction of 1 with 2,3-dimethylbut-2-ene results in the formation of a species that undergoes eta(3) --> eta(1) isomerization of the dimethylallyl ligand following the initial C-H bond-activating step to yield CpW(NO)(eta(3)-CMe(2)CMeCH(2))(eta(1)-CH(2)CHCMe(2)) (21). Thermolyses of 1 in alkane solvents afford allyl hydride complexes resulting from three successive C-H bond-activation reactions. For instance, 1 in cyclohexane converts to CpW(NO)(eta(3)-C(6)H(9))(H) (22) with dimethylpropylcyclohexane being formed as a byproduct, and in methylcyclohexane it forms the two isomeric complexes, CpW(NO)(eta(3)-C(7)H(11))(H) (23a,b). All new complexes have been characterized by conventional spectroscopic methods, and the solid-state molecular structures of 2, 3, 4, 18, 19, 20, and 21 have been established by X-ray crystallographic analyses. 相似文献
785.
Klem MT Willits D Young M Douglas T 《Journal of the American Chemical Society》2003,125(36):10806-10807
The preparation and subsequent imaging of a two-dimensional array of a genetically and chemically modified cowpea chlorotic mottle virus (CCMV) is described. The genetic mutation provides symmetrically dispersed exposed thiol groups on the outer surface of the virus capsid. These functional groups can be used to covalently bind the capsid to smooth Au substrate. AFM imaging suggests that the genetic mutation by itself does not promote array formation but, rather, aggregation through disulfide linkages. However, breaking the symmetry of the capsid using a solid-phase approach and chemically passivating the exposed thiol groups with iodoacetic acid results in a capsid with exposed thiols only on one side of the particle. These symmetry-broken capsids were able to form self-assembled monolayers (SAM) on a Au surface. 相似文献
786.
The excess molar volumes VmE {x(CH3OH or CH3CH2OH or CH3(CH2)2OH or CH3CH(OH)CH3 + (1 - x){CH3(CH2)2}2O or CH3C(CH3)2OCH3 or CH3CH2C(CH3)2OCH3} have been calculated from measured values of density over the whole composition range at the temperature 298.15 K in order to investigate OH … O specific interactions. The results are explained in terms of the strong self-association of the alkanols, the specific interaction between the alkanol, and the ether molecules and packing effects upon mixing. The experimental Vmh results presented here, together with the previously reported data for the molar excess enthalpy HmE, has been used to test the Extended Real Associated Solution (ERAS) model. 相似文献
787.
Trevor Ridley Kenneth P. Lawley Mohamed H.S.N. Al-Kahali Robert J. Donovan 《Chemical physics letters》2004,390(4-6):376-379
The first ionization energy of furan (C4H4O) has been determined from a short extrapolation of two nd (n=6–22) Rydberg series observed in the mass-resolved (2 + 1) resonance enhanced multiphoton ionization spectrum as IE=71673 ± 3 cm−1. This value confirms the higher of the two values in the literature. 相似文献
788.
Steve Kolokowsky Trevor Davis 《电子测试》2005,(8):66-69
不论我们购买任何移动办公室的配备,都要携带一堆累赘的电源线。而对于某些可借助通用串行总线(USB)连结端口连至台式机或笔记本电脑的消费性电子装置,以后可能不再需要专门的电源线了,因为通过USB线撷取电源的电子装置已日渐风行。 相似文献
789.
790.
Schur positivity of skew Schur function differences and applications to ribbons and Schubert classes
Ronald C. King Trevor A. Welsh Stephanie J. van Willigenburg 《Journal of Algebraic Combinatorics》2008,28(1):139-167
Some new relations on skew Schur function differences are established both combinatorially using Schützenberger’s jeu de taquin,
and algebraically using Jacobi-Trudi determinants. These relations lead to the conclusion that certain differences of skew
Schur functions are Schur positive. Applying these results to a basis of symmetric functions involving ribbon Schur functions
confirms the validity of a Schur positivity conjecture due to McNamara. A further application reveals that certain differences
of products of Schubert classes are Schubert positive.
For Manfred Schocker 1970–2006.
S.J. van Willigenburg was supported in part by the National Sciences and Engineering Research Council of Canada. 相似文献