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131.
The aromatic thioketone xanthione has been investigated by means of the optically detected magnetic resonance (ODMR) technique in a n-hexane matrix at ≈ 1.1 K. It was established that the short-lived red emission, which is characteristic for many thione molecules, is phosphorescence. At high temperatures (77 K) this phosphorescence originates mainly (>80%) from the T1z (n, π*) sublevel (kz(r) >kx(r), ky(r). At low temperature (1.1 K) the intersystem crossing following S2 (π, π*) ← S0 excitation is a highly spin-sublevel selective process which populates predominantly the T1x and T1y, levels. Hence, the slow spin—lattice relaxation phosphorescence at low temperature originates from these sublevels. A value of 0.0611 cm?1 was obtained for the zero-field parameter |E|/hc. A lower limit of 0.66 cm?1 has been found for the zero-field parameter |D|/hc. This value is considerably larger than those observed for ketones, and it is shown that spin—orbit coupling contributes strongly to the zero-field splitting. 相似文献
132.
Norton P. Peet Shyam Sunder Robert J. Barbuch Edward W. Huber Ester M. Bargar 《Journal of heterocyclic chemistry》1987,24(6):1531-1535
Treatment of o-nitrobenzenesulfonyl chloride ( 3 ) with 5-aminotetrazole (5-AT) gave [(2-nitrophenyl)-sulfonyl]carbamimidic azide ( 6 ), a ring-opened isomer of the expected N-(1H-tetrazol-5-yl)-2-nitrobenzenesulfonamide ( 4 ). Sulfonylcarbamimidic azide 6 was converted to 2-amino-N-(aminoiminomethyl)benzene-sulfonamide ( 7 ) with ethanolic stannous chloride, and to 3-amino-1,2,4-thiadiazine 1,1-dioxide ( 8 ) with sodium dithionite. Methanesulfonyl chloride ( 9 ) and 5-AT gave 2-(methylsulfonyl)carbamimidic azide ( 10 ), which isomerized to 5-[(methylsulfonyl)amino]-1H-tetrazole ( 11 ) in warm ethanol. Attempted cycloaddition of 2-(phenylsulfonyl)carbamimidic azide ( 13 ) and ethyl vinyl ether led only to alkylated tetrazole products. In addition, other tetrazole-alkylating reactions are described. Isomers produced from these alkylations were differentiated with 13C nmr spectroscopy. 相似文献
133.
Inhaltsübersicht. Triorganoantimon- und Triorganobismutdicarboxylate R3M[O2C(CH2)n-2-C4H3X]2 (M = Sb, R = CH3, C6H11, C6H5, 4-CH3OC6H4; M = Bi, R = C6H5, 4-CH3C6H4; n = 0, X = O, S, NH, NCH3. M = Sb, R = CH3, C6H5; M = Bi, R = C6H5; n = 1, X = O, S. M = Sb, R = C6H11, n = 1, X = S; R = 4-FC6H4, n = 0, X = O, S, NCH3; R = 2,4,6-(CH3)3C6H2, n = 0, X = O, S, NH) wurden durch Reaktionen von R3Sb(OH)2 (R = CH3, C6H11, 2,4,6-(CH3)3C6H2), R3SbO (R = C6H5, 4-CH3OC6H4, 4-FC6H4) bzw. R3BiCO3 mit den entsprechenden fünfgliedrigen heterocyclischen Carbonsäuren 2-C4H3X(CH2)nCOOH dargestellt. Auf der Basis schwingungsspektroskopischer Daten wird für alle Verbindungen eine trigonal bipyramidale Umgebung vom M (zwei O-Atome von einzähnigen Carboxylatliganden in den apikalen, drei C-Atome von R in den äquatorialen Positionen) vorgeschlagen, ferner eine schwache Wechselwirkung zwischen O(=C) jeder Carboxylatgruppe und M. Die Kristallstrukturbestimmung von (C6H5)3Sb(O2C–2-C4H3S)3 stützt diesen Vorschlag. Die Verbindung kristallisiert triklin [Raumgruppe P$1; a = 891,8(14), b = 1058,2(12), c = 1435,6(9) pm, α = 68,53(8), β = 85,47(9), γ = 85,99(11)°; Z = 2; d(ber.) = 1,607 Mg m–3; V(Zelle) = 1255,6 Å3; Strukturbestimmung anhand von 3947 unabhängigen Reflexen (Fo > 3σ(F2o)), R(ungewichtet) = 0,037]. Sb bindet drei C6H5-Gruppen in der äquatorialen Ebene [mittlerer Abstand Sb–C: 211,1(5)pm] und zwei einzähnige Carboxylatliganden in den apikalen Positionen einer verzerrten trigonalen Bipyramide [mittlerer Abstand Sb–O: 212,0(4) pm]. Aus den relativ kurzen Sb – O(=C)-Abständen [274,4(4) und 294,9(4) pm] und aus der Aufweitung des dem O(=C)-Atom nächsten äquatorialen C–Sb–C-Winkels auf 145,9(2)° [andere C-Sb-C-Winkel: 104,4(2), 109,5(2)°] wird auf schwache Sb–O(=C)-Koordination geschlossen. Schließlich wird eine Korrelation zwischen dem (+, –)I-Effekt des Organoliganden R an M (M = Sb, Bi) und der Stärke der M–O(=C)-Koordination in den Dicarboxylaten R3M[O2C(CH2)n–2-C4H3X]2 vorgeschlagen. Triorganoanümony and Triorganobismuth Derivatives of Carbonic Acids of Five-membered Heterocycles. Crystal and Molecular Structure of (C6H5)3Sb(O2C–2-C4H3S)2 Triorganoantimony- and triorganobismuth dicarboxylates R3M[O2C(CH2)n–2-C4H3X]2 (M = Sb, R = CH3, C6H11, C6H5, 4-CH3OC6H4; M = Bi, R = C6H5, 4-CH3C6H4; n = 0, X = O, S, NH, NCH3. M = Sb, R = CH3, C6H5; M = Bi, R = C6H5; n = 1, X = O, S. M = Sb, R = C6H11, n = 1, X = S; R = 4-FC6H4, n = 0, X = O, S, NCH3; R = 2,4,6-(CH3)3C6H2, n = 0, X = O, S, NH) have been prepared by reaction of R3Sb(OH)2 (R = CH3, C6H11; 2,4,6-(CH3)3C6H2), R3SbO (R = C6H5, 4-CH3OC6H4, 4-FC6H4) or R3BiCO3 with the appropriate five-membered heterocyclic carboxylic acid. From vibrational data for all compounds a trigonal bipyramidal environment around M (two O atoms of unidendate carboxylate ligands in apical, three C atoms (of R) in equatorial positions) is proposed and also an additional weak interaction of O(=C) of each carboxylate group and M. The crystal structure determination of Ph3Sb(O2C–2-C4H3S)2 gives additional prove to this proposal. It crystallizes triclinic [space group P$1; a = 891.8(14), b = 1058.2(12), c = 1435.6(9) pm, α = 68.53(8), β = 85.47(9), γ = 85.99(11)°; Z = 2; d(calc.) = 1.607 Mg m–3; Vcell = 1255.6 Å3; structure determination from 3 947 independent reflexions (Fo > 3σ(F2o)), R(unweighted) = 0.037]. Sb is bonding to three C6H5 groups in the equatorial plane [mean distance Sb–C: 211.1(5) pm] and two unidentate carboxylate ligands in the apical positions of a distorted trigonal bipyramid [mean distance Sb–O: 212.0(4) pm]. From the relatively short Sb–O(=C) distances [274.4(4) and 294.9(4) pm] and from the enlarged value of the equatorial C–Sb–C angle next to the O(=C) atom [145.9(2)°; other C–Sb–C angles: 104.4(2), 109.5(2)°] additional weak Sb–O(=C) coordination is inferred. Finally a correlation between the (+, –) I-effect of the organic ligands It at M and the strength of the M–O = C interaction is suggested. 相似文献
134.
A Study of the Probe Effect on the Apparent Image of Biological Atomic Force Microscopy 总被引:1,自引:0,他引:1
Xue Mei WANG * Lei QIN Long BA Zu Hong LU The State Key Lab of Coordination Chemistry Nanjing University Nanjing National Lab of Molecular Biomolecular Electronics Southeast University Nanjing 《中国化学快报》2001,(12)
The atomic force microscopy (AFM) possesses high spatial resolution and it is compatible with liquid environments. AFM can provide possibility to study a wide range of biological problems at the molecular level and acquire topological information at nanometre resolution under physiological conditions1,2. However, a major problem for image reconstruction of biological specimens is that structures of most biological molecules are very soft and delicate, which could be easily deformed and dama… 相似文献
135.
136.
The 20S proteasome is a large multicomponent protease complex. Relatively little is known about the mechanisms that control substrate specificity of its multiple active sites. We present here the crystal structure at 2.95 A resolution of a beta2-selective inhibitor (MB1) bound to the yeast 20S proteasome core particle (CP). This structure is compared to the structure of the CP bound to a general inhibitor (MB2) that covalently modified all three (beta1, beta2, beta5) catalytic subunits. These two inhibitors differ only in their P3 and P4 residues, thereby highlighting binding interactions distal to the active site threonine that control absolute substrate specificity of the complex. Comparisons of the CP-bound structures of MB1, MB2, and the natural products epoxomycin and TMC-95A also provide information regarding general binding modes for several classes of proteasome inhibitors. 相似文献
137.
138.
139.
Partial ionization cross section experiments have been carried out recently at the University of Innsbruck for three types of hydrocarbons, i.e. acetylene, ethylene and propene. Cross section data fits are generated and compared to the compilation of earlier experimental data summarized in the online database HYDKIN [www.hydkin.de]. New data fits are brought into a suitable form to be incorporated into the database. In order to illuminate underlying dissociation mechanisms the energy dependence of branching ratios above energies of 20 –30 eV is reviewed in light of the present results (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
140.
A continuous surface wetting transition, pinned to a solid-liquid-liquid-vapor tetra coexistence point, is studied by x-ray reflectivity in liquid Ga-Bi binary alloys. The short-range surface potential is determined from the measured temperature evolution of the wetting film. The thermal fluctuations are shown to be insufficient to induce a noticeable breakdown of mean-field behavior, expected in short-range-interacting systems due to their d(u) = 3 upper critical dimensionality. 相似文献