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71.
Dominik Cin
i Branko Kaitner 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(2):o101-o104
In the title compounds, C7H8NO2+·Br−, (I), and C7H8NO2+·I−, (II), the asymmetric unit contains a discrete 3‐carboxyanilinium cation, with a protonated amine group, and a halide anion. The compounds are not isostructural, and the crystal structures of (I) and (II) are characterized by different two‐dimensional hydrogen‐bonded networks. The ions in (I) are connected into ladder‐like ribbons via N—H...Br hydrogen bonds, while classic cyclic O—H...O hydrogen bonds between adjacent carboxylic acid functions link adjacent ribbons to give three characteristic graph‐set motifs, viz. C21(4), R42(8) and R22(8). The ions in (II) are connected via N—H...I, N—H...O and O—H...I hydrogen bonds, also with three characteristic graph‐set motifs, viz. C(7), C21(4) and R42(18), but an O—H...O interaction is not present. 相似文献
72.
Harding ME Vázquez J Ruscic B Wilson AK Gauss J Stanton JF 《The Journal of chemical physics》2008,128(11):114111
Effects of increased basis-set size as well as a correlated treatment of the diagonal Born-Oppenheimer approximation are studied within the context of the high-accuracy extrapolated ab initio thermochemistry (HEAT) theoretical model chemistry. It is found that the addition of these ostensible improvements does little to increase the overall accuracy of HEAT for the determination of molecular atomization energies. Fortuitous cancellation of high-level effects is shown to give the overall HEAT strategy an accuracy that is, in fact, higher than most of its individual components. In addition, the issue of core-valence electron correlation separation is explored; it is found that approximate additive treatments of the two effects have limitations that are significant in the realm of <1 kJ mol(-1) theoretical thermochemistry. 相似文献
73.
Jasper AW Klippenstein SJ Harding LB Ruscic B 《The journal of physical chemistry. A》2007,111(19):3932-3950
The CH3 + OH bimolecular reaction and the dissociation of methanol are studied theoretically at conditions relevant to combustion chemistry. Kinetics for the CH3 + OH barrierless association reaction and for the H + CH2OH and H + CH3O product channels are determined in the high-pressure limit using variable reaction coordinate transition state theory and multireference electronic structure calculations to evaluate the fragment interaction energies. The CH3 + OH --> 3CH2 + H2O abstraction reaction and the H2 + HCOH and H2 + H2CO product channels feature localized dynamical bottlenecks and are treated using variational transition state theory and QCISD(T) energies extrapolated to the complete basis set limit. The 1CH2 + H2O product channel has two dynamical regimes, featuring both an inner saddle point and an outer barrierless region, and it is shown that a microcanonical two-state model is necessary to properly describe the association rate for this reaction over a broad temperature range. Experimental channel energies for the methanol system are reevaluated using the Active Thermochemical Tables (ATcT) approach. Pressure dependent, phenomenological rate coefficients for the CH3 + OH bimolecular reaction and for methanol decomposition are determined via master equation simulations. The predicted results agree well with experimental results, including those from a companion high-temperature shock tube determination for the decomposition of methanol. 相似文献
74.
Renata Toplak Jurij Svete Branko Stanovnik Simona Goli Grdadolnik 《Journal of heterocyclic chemistry》1999,36(1):225-235
Methyl 2-(benzyloxycarbonyl)aimno-3-dimemylaminopropenoate ( 2 ) was prepared from methyl N-(benzyloxycarbonyl)glycinate ( 1 ) and t-butoxybis(dimethylamino)methane, and used as a reagent for preparation of substituted 3-(benzyloxycarbonyl)amino-4H-quinolizin-4-ones 5 and 6 , ?2H-pyran-2-ones 17–19 , ?2H-1-benzopyran-2-ones 28–31 , and -naphthopyrans 32–35 , ?2H-pyrano[3,2-c]pyridine-2,5-dione 46 , -pyrano-[4,3-b]pyran-2,5-dione 47 , -pyrano[3,2-c]benzopyran-2,5-dione 48 , -pyrano[2,3-c]pyrazol-6-ones 49 and 50 , -pyrano[2,3-d]pyrirnidin-7-ones 51 and 52 derivatives. In the reaction of 2 with 1,3-diketones trisubsti tuted pyrroles 14–16 were formed. Selective removal of benzyloxycarbonyl group was achieved by cat alytic transfer hydrogenation with Pd/C in the presence of cyclohexene to afford free 3-amino compounds 7 , 8 , 20 , 36–38 and 53–57 in yields better than 80%. 相似文献
75.
Uro Groelj Ale Drobni
Simon Re
nik Jurij Svete Branko Stanovnik Amalija Golobi
Nina Lah Ivan Leban Anton Meden Simona Goli
‐Grdadolnik 《Helvetica chimica acta》2001,84(11):3403-3417
Cycloadditions of various 1,3‐dipoles to (5Z)‐1‐acyl‐5‐(cyanomethylidene)‐3‐methylimidazolidine‐2,4‐diones 8 or 9 , prepared in 3 steps from hydantoin ( 1 ) (Schemes 1 and 2), were studied. In all cases, reactions proceeded regio‐ and stereoselectively. The type of product depended on the 1,3‐dipole and/or dipolarophile employed as well as on reaction conditions. Thus, with stable dipoles under neutral conditions, spirohydantoin derivatives 12 – 16 were obtained (Scheme 2), while under basic or acidic conditions, pyrazole‐ or isoxazole‐5‐carboxamides 18 and 23 – 26 and carboxylate 27 were formed via aromatization of the newly formed dihydroazole ring, followed by the simultaneous cleavage of the hydantoin ring (Schemes 3 – 5). 相似文献
76.
The transformation of ethyl 3-{[1-(alkoxycarbonyl)-2-(dimethylamino)ethenyl]amino}2-cyanoprop-2-enoates 2 to dialkyl 3-aminopyrrole-2,4-dicarboxylates 3 in good yields is described. 相似文献
77.
Branko S. Jursic 《International journal of quantum chemistry》1997,62(5):515-520
The isomerization of difluorovinylidene: C = CF2 into difluoroacetylene FCCF was systematically studied using density functional theory (DFT) methods with the 6-311 + G(2 p, 2 p) Gaussian-type basis set. The computed geometries for the reactant, product, and transition state as well as the enthalpy and reaction barrier were compared with the previously computed values obtained by the LSD and NLSD DFT methods and the ab initio CCSD method. The suitability of some of the DFT methods for the computation of this system was discussed and the best estimated computational data were selected. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 62: 515–520, 1997 相似文献
78.
79.
Tomislav Friščić Dr. Ernest Meštrović Dr. Dijana Škalec Šamec Branko Kaitner Prof. Dr. László Fábián Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(46):12644-12652
Liquid‐assisted grinding (LAG) was used to combine three levels of molecular self‐assembly into a one‐pot mechanochemical approach for the construction of metal–organic materials. The approach was applied for the construction of three adducts of cobalt(II) dibenzoylmethanate with isonicotinamide, nicotinamide and imidazole, to screen for their inclusion compounds. The one‐pot process consists of: i) The coordination‐driven binding of addends to the equatorially‐protected metal ion, resulting in “wheel‐and‐axle”‐shaped complexes; ii) self‐assembly of resulting complexes by way of hydrogen‐bonded synthons to form metal–organic inclusion hosts; iii) in situ inclusion of the grinding liquid in the resulting host. This approach provided quantitatively and within 20 min the known inclusion compounds of the bis(isonicotinamide) adduct in a single synthetic step. Changing the liquid phase in LAG was used to explore the inclusion behaviour of new wheel‐and‐axle adducts with nicotinamide and imidazole, revealing several inclusion compounds, as well as two polymorphs, of the bis(nicotinamide) host. Preliminary results suggest that one‐pot LAG is superior to solution synthesis in screening for metal–organic inclusion compounds. The difference between the methods is rationalised in terms of reactant solubility and solvent competition. In contrast to the nicotinamide adduct, the bis(imidazole) adduct did not form inclusion compounds. The difference in the inclusion properties of the two adducts is rationalised by structural information gathered by single crystal and powder X‐ray diffraction. 相似文献
80.
Classical and quantum mechanics based on an extended Heisenberg algebra with additional canonical commutation relations for
position and momentum coordinates are considered. In this approach additional noncommutativity is removed from the algebra
by a linear transformation of coordinates and transferred to the Hamiltonian (Lagrangian). This linear transformation does
not change the quadratic form of the Hamiltonian (Lagrangian), and Feynman’s path integral preserves its exact expression
for quadratic models. The compact general formalism presented here can be easily illustrated in any particular quadratic case.
As an important result of phenomenological interest, we give the path integral for a charged particle in the noncommutative
plane with a perpendicular magnetic field. We also present an effective Planck constant ħ
eff which depends on additional noncommutativity. 相似文献