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71.
The regression diagnostics algorithm REGDIA in S-Plus is introduced to examine the accuracy of pK
a predicted with four programs: PALLAS, MARVIN, PERRIN and SYBYL. On basis of a statistical analysis of residuals, outlier
diagnostics are proposed. Residual analysis of the ADSTAT program is based on examining goodness-of-fit via graphical diagnostics
of 15 exploratory data analysis plots, such as bar plots, box-and-whisker plots, dot plots, midsum plots, symmetry plots,
kurtosis plots, differential quantile plots, quantile-box plots, frequency polygons, histograms, quantile plots, quantile-quantile
plots, rankit plots, scatter plots, and autocorrelation plots. Outliers in pK
a relate to molecules which are poorly characterized by the considered pK
a program. Of the seven most efficient diagnostic plots (the Williams graph, Graph of predicted residuals, Pregibon graph,
Gray L–R graph, Index graph of Atkinson measure, Index graph of diagonal elements of the hat matrix and Rankit Q–Q graph of
jackknife residuals) the Williams graph was selected to give the most reliable detection of outliers. The six statistical
characteristics, Fexp,R2,RP2,MEP,AIC{F_{\rm exp},R^{2},R_{\rm P}^{2},{\it MEP},{\it AIC}}, and s in pK
a units, successfully examine the specimen of 25 acids and bases of a Perrin’s data set classifying four pK
a prediction algorithms. The highest values Fexp,R2,RP2{F_{\rm exp},R^{2},R_{\rm P}^{2}} and the lowest value of MEP and s and the most negative AIC have been found for PERRIN algorithm of pK
a prediction so this algorithm achieves the best predictive power and the most accurate results. The proposed accuracy test
of the REGDIA program can also be extended to test other predicted values, as log P, log D, aqueous solubility or some physicochemical properties. 相似文献
72.
We investigate the properties of dissipative full discretizations for the equations of motion associated with models of flow and radiative transport inside stars. We derive dissipative space discretizations and demonstrate that together with specially adapted total-variation-diminishing (TVD) or strongly stable Runge-Kutta time discretizations with adaptive step-size control this yields reliable and efficient integrators for the underlying high-dimensional nonlinear evolution equations. For the most general problem class, fully implicit SDIRK methods are demonstrated to be competitive when compared to popular explicit Runge-Kutta schemes as the additional effort for the solution of the associated nonlinear equations is compensated by the larger step-sizes admissible for strong stability and dissipativity. For the parameter regime associated with semiconvection we can use partitioned IMEX Runge-Kutta schemes, where the solution of the implicit part can be reduced to the solution of an elliptic problem. This yields a significant gain in performance as compared to either fully implicit or explicit time integrators. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
73.
3He NMR studies on helium–pyrrole,helium–indole,and helium–carbazole systems: a new tool for following chemistry of heterocyclic compounds 下载免费PDF全文
The 3He nuclear magnetic shieldings were calculated for free helium atom and He–pyrrole, He–indole, and He–carbazole complexes. Several levels of theory, including Hartree–Fock (HF), Second‐order Møller‐Plesset Perturbation Theory (MP2), and Density Functional Theory (DFT) (VSXC, M062X, APFD, BHandHLYP, and mPW1PW91), combined with polarization‐consistent pcS‐2 and aug‐pcS‐2 basis sets were employed. Gauge‐including atomic orbital (GIAO) calculated 3He nuclear magnetic shieldings reproduced accurately previously reported theoretical values for helium gas. 3He nuclear magnetic shieldings and energy changes as result of single helium atom approaching to the five‐membered ring of pyrrole, indole, and carbazole were tested. It was observed that 3He NMR parameters of single helium atom, calculated at various levels of theory (HF, MP2, and DFT) are sensitive to the presence of heteroatomic rings. The helium atom was insensitive to the studied molecules at distances above 5 Å. Our results, obtained with BHandHLYP method, predicted fairly accurately the He–pyrrole plane separation of 3.15 Å (close to 3.24 Å, calculated by MP2) and yielded a sizable 3He NMR chemical shift (about ?1.5 ppm). The changes of calculated nucleus‐independent chemical shifts (NICS) with the distance above the rings showed a very similar pattern to helium‐3 NMR chemical shift. The ring currents above the five‐membered rings were seen by helium magnetic probe to about 5 Å above the ring planes verified by the calculated NICS index. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
74.
75.
Klaudia Radula‐Janik Teobald Kupka Krzysztof Ejsmont Zdzislaw Daszkiewicz Stephan P. A. Sauer 《Magnetic resonance in chemistry : MRC》2013,51(10):630-635
Structures of selected 3,6‐dihalogeno‐N‐alkyl carbazole derivatives were calculated at the B3LYP/6‐311++G(3df,2pd) level of theory, and their 13C nuclear magnetic resonance (NMR) isotropic shieldings were predicted using density functional theory (DFT). The model compounds contained 9H, N‐methyl and N‐ethyl derivatives. The relativistic effect of Br and I atoms on nuclear shieldings was modeled using the spin–orbit zeroth‐order regular approximation (ZORA) method. Significant heavy atom shielding effects for the carbon atom directly bonded with Br and I were observed (~?10 and ~?30 ppm while the other carbon shifts were practically unaffected). The decreasing electronegativity of the halogen substituent (F, Cl, Br, and I) was reflected in both nonrelativistic and relativistic NMR results as decreased values of chemical shifts of carbon atoms attached to halogen (C3 and C6) leading to a strong sensitivity to halogen atom type at 3 and 6 positions of the carbazole ring. The predicted NMR data correctly reproduce the available experimental data for unsubstituted N‐alkylcarbazoles. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
76.
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78.
Milling of electroluminescent ZnS-Cu powders causes changes in their structure. In its consequence centers of lumincescence are destroyed, the integral intensity of electroluminescent, photoluminescent and roentgenoluminescent radiation decreases and the spectral intensity of luminescent radiation changes, too. On this basis the location of centres of luminescence and forming of glow-complexes in ZnS-Cu crystallites are discussed. The results show that the emission of ZnS-Cu powders is probably due to two glow-complexes. The centers of luminescence of one of them are located near the borders of coherent domains while the centers of the other glow-complex are inside coherent domains of the luminescent powder. 相似文献
79.
Karl Jug Hans-Peter Schluff Hans Kupka Rüdiger Iffert 《Journal of computational chemistry》1988,9(8):803-809
Small Sin and Aln clusters (n = 3–10) were studied with the semiempirical molecular orbital method (MO) method SINDO1. For each n, various structures were optimized to determine the most stable structure. To obtain good qualitative agreement with available ab initio calculations d orbitals had to be omitted from the basis set. Both silicon and aluminum tend to build three-dimensional structures rather than two- or one-dimensional structures, except for n = 3 or 4. The structure growth was studied by approaching various sites of stable structures with one or more atoms. It was found that silicon and aluminum exhibit different structure growth, and consequently, different most-stable structures. Ionization potentials, HOMO -LUMO energy differences, binding energies per atom, and average atomic valencies are presented. 相似文献
80.
Mirosław Gibas Tomasz Kupka Marta Tanasiewicz Witold Malec 《Macromolecular Symposia》2004,210(1):237-240
The procedure of restoring missing crown part of a human tooth with use of experimental materials, including new functional dimethacrylate monomers, is presented. The essential steps are precise evaluation of root canal cavities and providing a good adhesion of restorative materials to tooth structures. Magnetic resonance microscopy is considered to be a valuable supporting technique in restorative dentistry. 相似文献