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961.
A new Alkaline-Alkaline-Earth-Copper-Oxovanadate: Kba3Ca4Cu3V7O28 . Single crystals of Kba3Ca4Cu3V7O28 were prepared by solid state reactions below the melting point of the reaction mixture. It crystallizes with hexagonal symmetry, space group C?P63mc, a=11.160, c=12.428 Å, Z=2. Kba3Ca4Cu3V7O28 represents a new structure type with special coordination polyhedra around Ba2+, trigonal prisms and octahedra around Ca2+ and Cu2+ inside square pyramids. The crystal structure will be shown and discussed. 相似文献
962.
David T. Connor Patricia A. Young Maximilian Von Strandtmann 《Journal of heterocyclic chemistry》1981,18(4):697-702
3-Aminochromone and 3-aminocoumarin were condensed with diethyl ethoxymethylenemalonate and with dimethyl acetylenedicarboxylate to give intermediates, which were thermally cyclized to give 4,10-dihydro-4,10-dioxo-lH-[1]-benzopyrano[3,2-b]pyridinecarboxylates and 1,5-dihydro-1,5-dioxo-4H-[1]-benzopyrano-[3,4-b]pyridinecarboxylates. 2-Aminochromone was converted to 4,5-dihydro-4,5-dioxo-1H-[1]-benzopyrano-[2,3-b]pyridinecarboxylate via an intermediate condensation product with diethyl ethoxymethylenemalonate. These esters were hydrolyzed to the corresponding carboxylic acids (21, 30, 36, 50, and 60). Attempts to prepare 4,5-dihydro-4,5-dioxo-1H-[1]-benzopyrano[4,3-b]pyridinecarboxylates from 4-aminocoumarin were unsuccessful. 相似文献
963.
Hydrogen exchange reactions between lithium and sodium compounds, MX (M=Li: X=H, CH3, NH2, OH, F; M=Na: X=CH3), and the corresponding hydrides, HX, have been modelled by means of ab initio calculations including electron correlation and zero point energy (ZPE) corrections. Small or no activation barriers (from the initial complexes) are encountered in systems involving lone pairs (10.8, 2.4, 0.0 kcal/mol for X=NH2, OH, F, respectively). Since the association energies of the initial complexes are much larger (21.0, 20.4, 23.5 kcal/mol, respectively; MP2/6–31+G*/6–31+G* + ZPE), such exchange reactions should occur spontaneously in the gas phase. The methyl systems (X=CH3) have the largest barriers: 26.7 (M=Li) and 31.7 (M=Na) kcal/mol (MP2/6–31+G*/6–31G* + ZPE), and the initial complexes are only weakly bound. The significance of these systems as models for hydrogen exchange reactions in complexes of electropositive transition metals is discussed. However, the gegenion-free exchange of hydrogen between CH3 and CH4 has a much lower, 11.8 kcal/mol barrier (MP2/6–31+G*/6–31+G* + ZPE). All the transition structures are highly ionic (charges on the metals > +0.8). The effect of aggregation has been considered by examining the hydrogen exchange between (LiX)2 and HX(X=H, CH3, NH2, OH). Although these dimer reactions formally involve six, instead of four electrons, no “aromatic” preference is observed. 相似文献
964.
965.
Lech Kozerski Krystyna Kamienska-Trela Lidia Kania Wolfgang Von Philipsborn 《Helvetica chimica acta》1983,66(7):2113-2128
The pulse sequence INEPT was used to obtain proton-coupled 15N-NMR spectra in natural isotope abundance for enamines substituted in 2-position with electron-with-drawing groups. The chemical shifts and coupling constants are discussed in terms of their relationship to structural features such as multiple N-alkyl substitution, double-bond configuration, H-bonding, N-lone-pair delocalization within the conjugated system, and steric effects. It is concluded that 15N chemical shifts are a sensitive probe for local structural modifications at the N-atom and conformational changes in a remote part of a conjugated molecule, while one-bond N,H-coupling essentially reflects N-hybridization and subtle local geometric distortions. Stereospecific three-bond N,H spin coupling to olefinic protons (4.0 ± 0.2 Hz) has been found a characteristic feature of (Z)-isomers in all investigated compounds, whereas two-bond coupling to olefinic protons (2J(N,H) = 0.5 to 5 Hz) is observed in (E)-isomers. The sensitivity to solvents and steric properties of remote substituents renders geminal coupling a useful probe for studying electronic effects in the C? N bond. 相似文献
966.
Crown Ether Complexes of Lead(II). The Crystal Structures of [PbCl(18-Krone-6)][SbCl6], [Pb(18-Krone-6)(CH3CN)3][SbCl6]2 und [Pb(15-Krone-5)2][SbCl6]2 . [PbCl(18-crown-6)][SbCl6] has been prepared in low yield besides [Pb(CH3)2(18-crown-6)][SbCl6]2 by the reaction of Pb(CH3)2Cl2 with antimony pentachloride in acetonitrile solution in the presence of 18-crown-6, forming pale-yellow crystals. The other two title compounds are formed as colourless crystals by the reaction of PbCl2 with antimony pentachloride in acetonitrile solutions in the presence of 18-crown-6 and 15-crown-5, respectively. The complexes were characterized by IR spectroscopy and by crystal structure determinations. [PbCl(18-crown-6)][SbCl6]: Space group P21/c, Z = 8, 5 003 observed unique reflections, R = 0.046. Lattice dimensions at - 80°C: a = 1 386.9; b = 1 642.7; c = 2 172.1 pm, β = 92.95°. The lead atom in the cation [PbCl(18-crown-6)]+ is surrounded in an almost hexagonal-planar construction by the six oxygen atoms of the crown ether and an axially oriented Cl atom. [Pb(18-crown-6)(CH3CN)3][SbCl6]2: Space group P1 , Z = 2, 6 128 observed unique reflections, R = 0.076. Lattice dimensions at - 70°C: a = 1 228.0; b = 1 422.9; c = 1 463.2 pm, α = 69.08°; β = 65.71°; γ = 64.51°. In the cation [Pb(18-crown-6)(CH3CN)3]2+ the lead atom is coordinated by the six oxygen atoms of the crown ether and by the three nitrogen atoms of the acetonitrile molecules. The structure determination is restricted by disorder. [Pb( 15-crown-5)2][SbCI6]2: Space group P63/m, Z = 6, 5 857 observed unique reflections, R = 0.059. Lattice dimensions at -70°C: a = b = 2 198.5; c = 1499.4 pm, α = β = 90°, γ = 120°. In the cation [Pb(l5-crown-5)2]2 the lead atom is sandwich-like coordinated by the ten oxygen atoms of the two crown ether molecules. The structure determination is restricted by disorder. 相似文献
967.
Von Sonntag J Knolle W Naumov S Mehnert R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(18):4199-4209
The photochemistry of maleimide in aqueous solution is governed by the coexistence of up to three different triplet states, the keto triplet (lambda(max)=250, 330 nm, lambda(min)=290 nm, pK(a)=4.4+/-0.1, tau=5 micros), the deprotonated or enolate triplet (lambda(max)=360, 260 nm, lambda(min)=320 nm, shoulder at 370-380 nm) and a dimer triplet. This biradical is formed by the addition of the keto triplet to the double bond of a ground state maleimide in competition with electron transfer, (k( (3)MI+MI)=2.6 x 10(9) dm(3) mol(-1) s(-1)). Its spectrum is identical to that of the maleimide H-adduct radical (lambda(max)=370-380 (broad), 255 nm (narrow), lambda(min)=290 nm) and its lifetime is 110 ns. While protolysis is confined to maleimide and aqueous solutions, the dimer triplet is also found in acetonitrile. Dimer triplet formation is also observed with N-ethylmaleimide. Time-resolved conductometry and buffer experiments were used to characterise excited state protolysis. Multi-wavelength "global analysis" of the time profiles allowed the separation of the transient spectra and study of the kinetics of the monomer and dimer triplets. The cyclobutane dimer yield (determined by GC) is independent of maleimide concentration. This indicates that the dimer triplet does not contribute significantly to the initiation of free-radical polymerisation. Time-dependent Hartree-Fock calculations agree with the experimental data and further confirm the proposed mechanisms. 相似文献
968.
Jürgen Nuss Raúl Hector Cardoso Gil Wolfgang Hnle Karl Peters Hans Von Georg Schnering 《无机化学与普通化学杂志》1996,622(11):1854-1864
Synthesis, Structure, and Properties of the Tetraarsenidometallates(V) M7[TAs4] (M = K, Rb; T = Nb, Ta) The tetraarsenidometallates(V) M7[TAs4] (M = K, Rb; T = Nb, Ta) have been prepared from RbAs, KAs, Rb3As, K3As, and Nb or Ta in sealed Nb(Ta) ampoules at T = 1100 K. They crystallize in a new structure type oP24 (Pmn21, no. 31); K7[NbAs4]: a = 1019.2(2) pm, b = 916.2(2) pm, c = 830.6(1) pm; K7[TaAs4]: a = 1017.3(2) pm, b = 915.5(2) pm, c = 830.5(2) pm; Rb7[NbAs4]: a = 1059.2(4) pm, b = 952.8(4) pm, c = 860.4(4) pm; Z = 2 formula units per unit cell). The compounds form dark red crystals and they are sensitive against air and moisture. They are semiconductors with Eg = 1.80 eV. The thermal decomposition in dynamical vacuum gives evidence for the existance of K4TAs3 and K2TAs2 (T = Nb, Ta). Main structural units are polar oriented tetrahedra [TAs4] with d (T – As) = 252.2(1) pm; 251.3(1) pm; 253.0(4) pm, respectively. The As atoms are trigonal prismatically coordinated by M and T atoms. These trigonal prisms form anionic and cationic layers [M4As2]2? and ∞2[M3TAs2]2+ alternating along the b axis. The structure is comparable with that of Co2P and can be described as a stuffed shear variant of the Na6□ZnO4 type of structure. 相似文献
969.
C. Von Sonntag 《Tetrahedron》1969,25(24):5853-5861
The UV photolysis (λ = 185 nm) of liquid methanol yields hydrogen, glycol, formaldehyde, methane and traces of ethane in quantum yields of 0·83, 0·78, 0·058, 0·05 and 0·002 resp. (related to φ(H2) = 0·4 of the ethanol-actinometer (5 mole/1 in water)). The isotopic distribution of the hydrogen (85% HD) formed in the photolysis of CH3OD shows, that as in the gasphase2 the scission of the O---H-bond (1) is the major process. CH3OH + hv (λ = 185 nm) → CH3O• + H• (1)
In methanoi-water mixtures (nearly all the light of the wavelength λ = 185 nm is absorbed by methanol) the quantum yields of hydrogen, glycol, methane and ethane are greatly reduced, while the formaldehyde yield remains unaffected. In 1 molar solution φ(H2) = 0·42, φ(glycol) = 0·32 and φ(CH4) = 6 x 10−4 is obtained. Ethane cannot be detected. 相似文献
970.
G. Von Billing 《Commentarii Mathematici Helvetici》1936,9(1):161-165
Ohne Zusammenfassung 相似文献