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91.
Ede Kapuy Ferenc Bartha Ferenc Bogr Zoltn Cspes Cornelia Kozmutza 《International journal of quantum chemistry》1990,38(2):139-147
Diagrammatic formulation of the MBPT is applied when the occupied and the virtual canonical orbitals are separately localized by unitary transformations. In this localized representation, due to the off-diagonal Fock matrix elements, the perturbation operator contains extra terms generating the so-called localization corrections. These corrections enter the perturbation energy in third and higher orders. Their magnitude depends on the type of localization, but they represent only a small fraction of the canonical corrections. The calculation of the localization corrections, however, does not need a significant amount of extra computer time. It is shown that by introducing an “order of neighborhood” local and nonlocal effects of the electron correlation can be separated and the contribution of the nonlocal effects can be neglected to a good approximation. Ab initio calculations have been carried out for the normal saturated hydrocarbons: C2n+1H4n+4 and for the all-trans conjugated polyenes C2n+2H2n+4. As to the ratio of the local and nonlocal corrections, it is shown that there is only a quantitative difference for these two kinds of systems (strongly or weakly localizable). Neglecting nonlocal effects, considerable amount of computer time can be saved. 相似文献
92.
Elemental I(2) and Br(2) cleanly react with the 3:3 Pt(ii) metallamacrocycle of 3,3,3',3'-tetra(n-butyl)-1,1'-terephthaloylbis(thiourea)(cis-[Pt(II)(3)(L(p)(1)-S,O)(3)]3), in chloroform at room temperature, to yield oxidative addition products; (195)Pt NMR studies reveal that a stepwise oxidative addition readily occurs to each of the Pt(ii) centres in the metallamacrocycle to yield the mixed valence species cis-[Pt(II)(2)Pt(IV)I(2)(L(p)(1)-S,O)(3)] and cis-[Pt(II)Pt(IV)(2)I(4)(L(p)(1)-S,O)(3)], and the fully oxidised cis-[Pt(IV)(3)I(6)(L(p)(1)-S,O)(3)] in solution, depending on the mole ratio I(2):3. Similar results are obtained on treatment of solutions of 3 with elemental Br(2). Treatment of the corresponding 2:2 Pt(ii) complex of 3,3,3',3'-tetraethyl-1,1'-isophthaloylbis(thiourea)(cis-[Pt(II)(2)(L(m)(1)-S,O)(2)]4) with iodine, results in facile oxidative addition to yield cis-[Pt(IV)(2)(L(m)(1)-S,O)(2)I(4)], with a trans-Pt(iv)-iodo arrangement. Molecules in the crystal structure of 5 have their trans-Pt(iv)-iodo axes essentially aligned, with very close intermolecular iodide contacts (3.775(1)A), resulting in chains of weakly bound metallamacrocycles in the solid. An alternative electrolytic synthesis method, using a simple two-compartment glass cell containing 4 and a chosen halide salt in dichloromethane, led to the formation of cis-[Pt(IV)(2)(L(m)(1)-S,O)(2)Br(4)] 6 and cis-[Pt(IV)(2)(L(m)(1)-S,O)(2)Cl(4)] 7, completing characterization of a series of first-reported trans-Pt(iv)-X (X=I, Br, Cl) metallamacrocyclic complexes. 相似文献
93.
Neuvonen H Neuvonen K Koch A Kleinpeter E 《The journal of physical chemistry. A》2005,109(28):6279-6289
Equilibria between the Z (tau1= 0 degrees) and E (tau1= 180 degrees) conformers of p-substituted phenyl acetates 4 and trifluoroacetates 5 (X = OMe, Me, H, Cl, CN, NO2) were studied by ab initio calculations at the HF/6-31G* and MP2/6-31G* levels of theory. The preference for the Z conformer, DeltaE(HF), was calculated to be 5.36 kcal mol(-1) and 7.50 kcal mol(-1) for phenyl acetate and phenyl trifluoroacetate (i.e., with X = H), respectively. The increasing electron-withdrawing ability of the phenyl substituent X increases the preference of the Z conformer. An excellent correlation with a negative slope was observed for both series between DeltaE of the E-Z equilibrium and the Hammett sigma constant. By using an appropriate isodesmic reaction, it was shown that electron-withdrawing substituents decrease the stability of both conformers, but the effect is higher with the E conformer. Electron-withdrawing phenyl substituents decrease the delocalization of the lone pair of the ether oxygen to the C=O antibonding orbital (nO--> pi*C=O) in both the E and Z forms and in both series studied; this effect is higher in the E conformer than in the Z conformer. The nO --> pi*C=O electron donation has a minimum value with tau1= 90 degrees and a maximum value with tau1= 0 degrees (the Z conformer), the value with tau1= 180 degrees (the E conformer) being between these two values, obviously due to steric hindrance. The effects of the phenyl substituents on the reactivity of the esters studied are discussed in terms of molecular orbital interactions. ED/EW substituents adjust the availability of the pi*C=O antibonding orbital to interact with the lone pair orbital of the attacking nucleophile and therefore affect the reactivity: EW substituents increase and ED substituents decrease it. Excellent correlations were observed between the rate coefficients of nucleophilic acyl substitutions and pi*C=O occupancies of the ester series 4 and 5. 相似文献
94.
Patrick Koch Carl Djerassi Vijai Lakshmi Francis J. Schmitz 《Helvetica chimica acta》1983,66(8):2431-2436
Thirty-two sterols are identified in the sponge Hyrtios sp. In addition to fourteen monohydroxylated compounds, the sterol fraction contains eight functionalized sidechain sterols, three of them new: 3 β-hydroxy-24-norchol-5-en-23-al (19) , (22-trans)-3 β-hydroxycholest-5, 22-dien-24-one (20) and (22R, 23R, 24S) or (22S, 23S, 24S)- 22,23-epoxy-24-methylchoest-5-en-3 β-ol (24). The probable biological origin, rather than artifact production, of these undescribed components is discussed. 相似文献
95.
Differential thermal analysis (DTA) is an effective means for studying chemical reactions, but its application to reaction kinetics is handicapped by the involvement of temperature feedback from the reaction heat and by the solvent dependence of the thermal conductivity.General, empirical relationships are derived from digital computer application which allow to transform half width and shape index of a DTA curve of any first-order process in a uniformly temperated sample to the values of the corresponding rate curve at linearly increased temperature.The expressions are complemented by some new relationships for an n-order reaction and are useful for the kinetic study of complex processes. 相似文献
96.
Matthias HeydenreichAndreas Koch László LázárIstván Szatmári Reijo SillanpääErich Kleinpeter Ferenc Fülöp 《Tetrahedron》2003,59(11):1951-1959
Starting from the 1′- or 2′-phenyl-substituted 1-(2′-hydroxyethyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline diastereomers 3 and 6, 4-unsubstituted and 4-(p-nitrophenyl)- and 4-oxo-substituted 1-phenyl- and 2-phenyl-9,10-dimethoxy-2H,4H-1,6,7,11b-tetrahydro-1,3-oxazino[4,3-a]isoquinolines (7-12) were prepared. The relative configurations and the predominant conformations of the products were determined by NMR spectroscopy, by quantum chemical calculations and, for (2R∗,4S∗,11bR∗)-9,10-dimethoxy-4-(p-nitrophenyl)-2-phenyl-2H,4H-1,6,7,11b-tetrahydro-1,3-oxazino[4,3-a]isoquinoline (11), by X-ray diffraction. 相似文献
97.
K. H. Koch und K. Ohls 《Fresenius' Journal of Analytical Chemistry》1969,247(3-4):239-243
Zusammenfassung Ein neues lösungsspektrographisches Zerstäubungsverfahren wird beschrieben, bei dem die Lösung so zerstäubt wird, daß sie die Graphitelektroden nicht berührt. Mit diesem Verfahren könnten 10–3 bis 10–5 % Al, B, Cr, Cu, Mg, Mn, Mo, Ni, Si, Sn, Ti, V und Zr in Eisen und Stahl bestimmt werden.Zur Bestimmung von Verunreinigungen oder Einschlüssen in Stahl wird ein spektrographisches Verfahren mit Preßlingselektroden empfohlen, das nur 0,1–1 mg Rückstand benötigt. Oxide von Al, B, Ca, Co, Cu, Cr, Fe, Mg, Mn, Mo, Nb, Ni, Pb, Si, Sn, Sr, Ti, V, Zn und Zr konnten bis herab zu etwa 10–7 g erfaßt werden.
Methods for the determination of trace elements from metallic samples
The principles of a new spectrographical atomizing-method of solution are described. The solution has to be atomized into a gap without contacting the surface of the graphite electrodes. In this way the exact determination of 10–3 to 10–5 % of Al, B, Cr, Cu, Mg, Mn, Mo, Ni, Si, Sn, Ti, V and Zr in iron and steel is possible.The microanalytical determination of impurities or inclusions in steel has been achieved by a spectrographical method with briquette electrodes. The necessary amount of isolation residue is only 0.1–1 mg. The oxides of Al, B, Ca, Co, Cu, Cr, Fe, Mg, Mn, Mo, Nb, Ni, Pb, Si, Sn, Sr, Ti, V, Zn and Zr can be accurately determined by this procedure. The limit of determination is about 10–7 g.相似文献
98.
Otto P. Strausz Cornelia Kozmutza Ede Kapuy Michael A. Robb Giannoula Theodorakopoulos Imre G. Csizmadia 《Theoretical chemistry accounts》1978,48(3):215-221
Vertical proton affinities were calculated with closed and open shell direct SCF-MO methods for the ground, excited triplet and ionized doublet states of CH2O and CH2OH+.The computed gas phase basicity of CH2O follows the order: CH2O(1
A
1) > CH2O*(3
A
1 or 3
A
2) > CH2O+(2
B
2 or 2
B
1). 相似文献
99.
O. G. Koch 《Fresenius' Journal of Analytical Chemistry》1977,286(1-2):14-19
Zusammenfassung Es wird eine automatisierte Apparatur zur schnellen, massenspektrometrischen Bestimmung von Sauerstoff und Stickstoff in Stahl beschrieben. Die Stahlprobe wird unter Argon im Gleichstrombogen geschmolzen und die extrahierten Gase Kohlenmonoxid und Stickstoff werden massenspektrometrisch bestimmt. Die relative Standardabweichung beträgt ±3–5% für Sauerstoff und ±3–8% für Stickstoff. Die Nachweisgrenzen liegen bei 10 pp106 O2 und 3 pp106 N2. Der Zeitbedarf für eine Analyse beträgt 85 s.Herrn H. Siffrin danke ich für die sorgfältige Durchführung der zahlreichen Versuche. 相似文献
100.
The optical constants in the photon energy range between 4 and 10.5 eV for E ?b on (001) and E ?L and E ⊥ L on the (010) plane are discussed. In particular the influence of macroscopic fields on the optical properties of anisotropic crystals is considered. For E ? a on the (001) plane reflection spectra have been measured at various angles of incidence. These data and results obtained recently by Hymowitz and Clark for several artificially prepared crystal faces are discussed on the basis of the frequency dependend dielectric functions. New information on the directional dispersion of exciton bands is thus obtained. 相似文献