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排序方式: 共有429条查询结果,搜索用时 15 毫秒
81.
Tomislav Došlić Ivica Martinjak Riste Škrekovski Sanja Tipurić Spužević Ivana Zubac 《Journal of mathematical chemistry》2018,56(10):2995-3013
We propose and investigate a new bond-additive structural invariant as a measure of peripherality in graphs. We first determine its extremal values and characterize extremal trees and unicyclic graphs. Then we show how it can be efficiently computed for large classes of chemically interesting graphs using a variant of the cut method introduced by Klav?ar, Gutman and Mohar. Explicit formulas are presented for several classes of benzenoid graphs and Cartesian products. At the end we state several conjectures and list some open problems. 相似文献
82.
A highly enantio- and diastereoselective intramolecular Stetter reaction has been developed. Subjection of alpha,alpha-disubstituted Michael acceptors to an asymmetric intramolecular Stetter reaction results in a highly enantioselective conjugate addition and a diastereoselective proton transfer. Available evidence suggests the diastereoselective protonation occurs via intramolecular delivery to the sterically more hindered face of the enolate. The scope of the trisubstituted Michael acceptors has been examined and found to be broad with respect to the size of the alpha-substituent and nature of the Michael acceptor. Aliphatic and aromatic aldehydes were examined and found to afford the desired product in good overall yield with high enantio- and diastereoselectivity. 相似文献
83.
Ante Graovac Hendrik J. Monkhorst Tomislav Zivkovic 《International journal of quantum chemistry》1973,7(2):233-251
Slater orbital r12?1 integrals are calculated with a numerical Fourier-transform method based on a formulation first given by Bonham, Peacher and Cox. Spherical wave expansions are introduced that decouple the Feynman integrations for the charge distribution Fourier transforms. The Feynman integrals are evaluated semianalytically, and their properties are analyzed in detail. The final computational step involves a numerical integration over charge distribution quantities. Results for (coplanar) multicenter exchange integrals over 1s orbitals are given. As long as the charge distributions are overlapping considerably, the method gives good results, even when these distributions are highly asymmetric. The method as presently implemented fails when highly disconnected charge distributions are involved. 相似文献
84.
Tomislav P. Živković 《Theoretical chemistry accounts》1983,62(4):335-350
An alternative approach to the treatment of the quantum chemical problems combining both, the MO and VB theory, is proposed. This approach retains the concept of resonance from the VB method, but it treats each particular bond in the MO sense. The method is illustrated with a few examples. Relative stabilities of benzene, pentalene and cyclobutadiene are derived. A Hückel (4m + 2) rule is derived for the annulenes. The charge polarisation in the case of the pentalene molecule is explained. A distortion of the pentalene molecule is considered and it is shown that within this approach the distortion depends on the charge polarisation. 相似文献
85.
Tomislav J. Janjić Lidija B. Pfendt Mirjana B. Pasulj 《Monatshefte für Chemie / Chemical Monthly》1984,115(2):125-133
Heterogeneous equilibria in saturated solutions of sparingly soluble diprotic acids: 1,2-, 1,3- and 1,4-benzenedicarboxylic acid, and octanedioic acid, respectively, at ionic strengthI=1 (NaCl) and the temperature of 25 °C, have been investigated. The corresponding equilibrium constants were determined by the application of three independent methods: the formation function method, the method of protons bound to the acid in the solution and the solubility method. The results obtained by these three different methods are in good agreement.
Untersuchung heterogener Gleichgewichte in gesättigten Lösungen schwerlöslicher diprotischer Säuren
Zusammenfassung Es wurden die heterogene Gleichgewichte in gesättigten Lösungen schwerlöslicher diprotischer Säuren (Benzol-1,2-, -1,3- und-1,4-dicarbonsäuren und Oktandisäure) bei einer IonenstärkeI=1 (NaCl) und der Temperatur von 25 °C untersucht. Die entsprechende Gleichgewichtskonstanten wurden mit drei unabhängigen Methoden bestimmt: mit der Methode der Bildungsfunktion, der Methode der an die Säure in Lösung gebundenen Protonen, bzw. mit der Methode der Löslichkeitsbestimmung. Die erhaltenen Ergebnisse stehen in guter Übereinstimmung.相似文献
86.
Tomislav P. Živković 《Journal of mathematical chemistry》2001,30(4):349-373
Generalised n×n eigenvalue equation B|
i
=
i
S
b
|
i
(i=1,...,n) where B and S
b
are n×n Hermitian matrices while S
b
is in addition positive definite is considered. This equation is augmented to a generalised (n+1)(n+1) eigenvalue equation H|
k
=
k
S|
k
(k=1,...,n+1) where Hermitian matrices H and S represent matrices B and S
b
, respectively, augmented by one additional row and one additional column. It is shown how the eigenvalues
k
and the eigenvectors |
k
of the augmented eigenvalue equation can be expressed in terms of the eigenvalues
i
and the eigenvectors |
i
of the original eigenvalue equation. Operation count to obtain by this method all augmented eigenvalues and eigenvectors is of the order O(n
2). Unless matrices involved are of some special kind such as sparse matrices or alike, this operation count is one order of magnitude smaller than operation count required by other presently known methods. In many practical cases operation count to obtain a single selected eigenvalue and/or eigenvector by this method is of the order O(n). In the case of the generalised eigenvalue equation, all other methods usually require again O(n
3) operations, even if only a single eigenvalue and/or eigenvector is required. Thus in many cases of interest operation count to obtain a selected eigenvalue and/or eigenvector by this method is two orders of magnitude smaller than operation count required by other methods. 相似文献
87.
M. Asai T. Aziz J. F. Bailly J. F. Baland S. Banerjee W. Bartl A. Batunin C. Caso F. Diez-Medo B. Epp A. Ferrando F. Fontanelli S. N. Ganguli V. G. Gavrjusev T. Gemesy P. Girtler A. Gurtu R. Hamatsu P. Herquet J. Hrubec Y. Iga V. Khalatyan E. Kistenev J. M. Kohli J. Mac Naughton J. C. Marin M. Markytan L. Montanet G. Neuhofer G. Pinter P. Porth R. Raghavan T. Rodrigo J. M. Salicio J. B. Singh S. Squarcia K. Takahashi L. A. Tikhonova U. Trevisan T. Tsurugai V. Yarba G. Zholobov S. Zotkin EHS-RCBC Collaboration 《Zeitschrift fur Physik C Particles and Fields》1987,34(4):429-435
Production properties and correlations forK s 0 K s 0 ,K s 0 Λ,K s 0 ¯Λ and Λ¯Λ systems in 360 GeV/cpp interactions are presented. All rapidity gap distributions are observed to peak at Δy=0 and the azimuthal angular distributions between the two particles are consistent with being flat. Experimental results are compared with the quark fusion and Lund models of particle production. 相似文献
88.
Tomislav P. Živković 《Journal of mathematical chemistry》2000,28(1-3):267-285
Mathematical formalism of the low rank perturbation method (LRP) is applied to the vibrational isotope effect in the harmonic approximation. A pair of two n-atom isotopic molecules A and B which are identical except for isotopic substitutions at atomic sites is considered. Relations which express vibrational frequencies
k
and normal modes
k
of the perturbed isotopic molecule B in terms of the vibrational frequencies
i
and normal modes
i
of the unperturbed molecule A are derived. In these relations complete specification of the unperturbed normal modes
i
is not required. Only amplitudes |
i
of normal modes
i
at sites affected by the isotopic substitution are needed. 相似文献
89.
Tomislav Fri
i Cristina Mottillo Hatem M. Titi 《Angewandte Chemie (International ed. in English)》2020,59(3):1018-1029
Mechanochemical solvent‐free reactions by milling, grinding or other types of mechanical action have emerged as a viable alternative to solution chemistry. Mechanochemistry offers not only a possibility to eliminate the need for bulk solvent use, and reduce the generation of waste, but it also unlocks the door to a different reaction environment in which synthetic strategies, reactions and molecules previously not accessible in solution, can be achieved. This Minireview examines the potential of mechanochemistry in chemical and materials synthesis, by providing a cross‐section of the recent developments in using ball milling for the formation of molecules and materials based on covalent and coordination bonds. 相似文献
90.