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131.
Espa D Pilia L Marchiò L Mercuri ML Serpe A Barsella A Fort A Dalgleish SJ Robertson N Deplano P 《Inorganic chemistry》2011,50(6):2058-2060
The synthesis and full characterization of the redox-active nickel triad mixed-ligand dithiolene complexes based on Bz(2)pipdt = 1,4-dibenzylpiperazine-3,2-dithione and dmit = 2-thioxo-1,3-dithiole-4,5-dithiolate ligands are reported. These complexes show a reversibly bleacheable solvatochromic peak and a remarkably high negative molecular first hyperpolarizability, whose values depend on the metal being highest for the platinum(II) compound. 相似文献
132.
133.
Espa D Pilia L Marchiò L Artizzu F Serpe A Mercuri ML Simão D Almeida M Pizzotti M Tessore F Deplano P 《Dalton transactions (Cambridge, England : 2003)》2012,41(12):3485-3493
The mixed-ligand dithiolene complex [Pt(Bz(2)pipdt)(dcbdt)] (1) bearing the two ligands Bz(2)pipdt = 1,4-dibenzyl-piperazine-3,2-dithione and dcbdt = dicyanobenzodithiolato, has been synthesized, characterized and studied to evaluate its second-order optical nonlinearity. The dithione/dithiolato character of the two ligands gives rise to an asymmetric distribution of the charge in the molecule. This is reflected by structural data showing that in the C(2)S(2)PtS(2)C(2) dithiolene core the four sulfur atoms define a square-planar coordination environment of the metal where the Pt-S bond distances involving the two ligands are similar, while the C-S bond distances in the C(2)S(2) units exhibit a significant difference in Bz(2)pipdt (dithione) and dcbdt (dithiolato). 1 shows a moderately strong absorption peak in the visible region, which can be related to a HOMO-LUMO transition, where the dcbdt ligand (dithiolato) contributes mostly to the HOMO, and the Bz(2)pipdt one (dithione) mostly to the LUMO. Thus this transition has ligand-to-ligand charge transfer (CT) character with some contribution of the metal and undergoes negative solvatochromism and molecular quadratic optical nonlinearity (μβ(0) = -1296 × 10(-48) esu), which was determined by the EFISH (electric-field-induced second-harmonic generation) technique and compared with the values of similar complexes on varying the dithiolato ligand (mnt = maleonitriledithiolato, dmit = 2-thioxo-1,3-dithiole-4,5-dithiolato). Theoretical calculations help to elucidate the role of the dithiolato ligands in affecting the molecular quadratic optical nonlinearity of these complexes. 相似文献
134.
Carlos Henrique Marchi Leandro Alberto Novak Cosmo Damião Santiago Ana Paula da Silveira Vargas 《Applied Mathematical Modelling》2013,37(12-13):7386-7397
A theoretical basis is presented for the repeated Richardson extrapolation (RRE) to reduce and estimate the discretization error of numerical solutions for heat conduction. An example application is described for the 2D Laplace equation using the finite difference method, a domain discretized with uniform grids, second-order accurate approximations, several variables of interest, Dirichlet boundary conditions, grids with up to 8,193 × 8,193 nodes, a multigrid method, single, double and quadruple precisions and up to twelve Richardson extrapolations. It was found that: (1) RRE significantly reduces the discretization error (for example, from 2.25E-07 to 3.19E-32 with nine extrapolations and a 1,025 × 1,025 grid, yielding an order of accuracy of 19.1); (2) the Richardson error estimator works for numerical results obtained with RRE; (3) a higher reduction of the discretization error with RRE is achieved by using higher calculation precision, a larger number of extrapolations, a larger number of grids and correct error orders; and (4) to obtain a given value error, much less CPU time and RAM memory are required for the solution with RRE than without it. 相似文献
135.
F De Marchi R Seraglia L Molin P Traldi M De Rosso A Panighel A Dalla Vedova M Gardiman M Giust R Flamini 《Journal of mass spectrometry : JMS》2012,47(9):1113-1119
Triglyceride profile of seed oil samples from 32 hybrid grape varieties not studied before was investigated. A new method for the analysis of triacylglycerols (TAGs) has been developed based on the direct infusion in the electrospray ionization (ESI) source and employing tetrahydrofuran/methanol/water (85:10:5 v|v|v) as solvent; the formation of [M?+?Na](+) ions in high yield has been observed. TAGs were identified by ESI-tandem mass spectrometry analysis, and the matrix-assisted-laser-desorption-ionization and time-of-flight profile of samples was determined. Six were the principal TAGs identified in seed oil: trilinolein (LLL) was the most abundant (43%), followed by dilinoleoyl-oleoylglycerol (LOL, 23%), and dilinoleoyl-palmitoylglycerol (LPL, 15%). Compounds present in lower concentration were LSL and LOO (11%), LOP (6%), and LSP (2%). Compared with seed oils produced from V. Vinifera grapes, some significant differences in the relative abundances of TAGs were found, in particular hybrid grape seed oils showed higher LOL and lower LPL content, respectively. Among the samples studied, a particularly high content of LLL (rich in unsaturated fatty acids) was found in seed oils from two red varieties. Copyright ? 2012 John Wiley & Sons, Ltd. 相似文献
136.
Positano V Salani B Pepe A Santarelli MF De Marchi D Ramazzotti A Favilli B Cracolici E Midiri M Cianciulli P Lombardi M Landini L 《Magnetic resonance imaging》2009,27(2):188-197
In the clinical MRI practice, it is common to assess liver iron overload by T2* multi-echo gradient-echo images. However, there is no full consensus about the best image analysis approach for the T2* measurements. The currently used methods involve manual drawing of a region of interest (ROI) within MR images of the liver. Evaluation of a representative liver T2* value is done by fitting an appropriate model to the signal decay within the ROIs vs. the echo time. The resulting T2* value may depend on both ROI placement and choice of the signal decay model. The aim of this study was to understand how the choice of the analysis methodology may affect the accuracy of T2* measurements. A software model of the iron overloaded liver was inferred from MR images acquired from 40 thalassemia major patients. Different image analysis methods were compared exploiting the developed software model. Moreover, a method for global semiautomatic T2* measurement involving the whole liver was developed. The global method included automatic segmentation of parenchyma by an adaptive fuzzy-clustering algorithm able to compensate for signal inhomogeneities. Global liver T2* value was evaluated using a pixel-wise technique and an optimized signal decay model. The global approach was compared with the ROI-based approach used in the clinical practice. For the ROI-based approach, the intra-observer and inter-observer coefficients of variation (CoVs) were 3.7% and 5.6%, respectively. For the global analysis, the CoVs for intra-observers and inter-observers reproducibility were 0.85% and 2.87%, respectively. The variability shown by the ROI-based approach was acceptable for use in the clinical practice; however, the developed global method increased the accuracy in T2* assessment and significantly reduced the operator dependence and sampling errors. This global approach could be useful in the clinical arena for patients with borderline liver iron overload and/or requiring follow-up studies. 相似文献
137.
Paola Deplano Luciano Marchiò Flavia Artizzu Maria Laura Mercuri Luca Pilia Gloria Pintus Angela Serpe Eduard B. Yagubskii 《Monatshefte für Chemie / Chemical Monthly》2009,140(7):775-781
Abstract The novel [Ni(Me2pipdt)(dddt)] complex based on the Me2pipdt (1,4-dimethylpiperazine-3,2-dithione) and dddt (5,6-dihydro-1,4-dithine-2,3-dithiolate) ligands has been synthesised
and characterised. Structural data, vibrational marker, solvatochromic behaviour of the typical absorption in the near infrared
region, and approximate theoretical calculations suggest that an unbalanced electron distribution at the dithiolene core occurs
in the ground and excited states. In particular, the dddt ligand gives a prevailing contribution to the HOMO, and Me2pipdt to the LUMO. The charge-transfer character of the HOMO–LUMO transition makes this complex a potential second-order non-linear
optic chromophore.
Graphical Abstract
相似文献
138.
Nicola Marchi Qingshan Teng Minh T Nguyen Linda Franic Nirav K Desai Thomas Masaryk Peter Rasmussen Silvia Trasciatti Damir Janigro 《BMC neuroscience》2010,11(1):34
Background
Stem cells or immune cells targeting the central nervous system (CNS) bear significant promises for patients affected by CNS disorders. Brain or spinal cord delivery of therapeutic cells is limited by the blood-brain barrier (BBB) which remains one of the recognized rate-limiting steps. Osmotic BBB disruption (BBBD) has been shown to improve small molecule chemotherapy for brain tumors, but successful delivery of cells in conjunction with BBBD has never been reported. 相似文献139.
The computation of integrals in higher dimensions and on general domains, when no explicit cubature rules are known, can be "easily" addressed by means
of the quasi-Monte Carlo method. The method, simple in its formulation, becomes computationally inefficient when the space dimension is growing and the integration domain is particularly complex.
In this paper we present two new approaches to the quasi-Monte Carlo method for cubature based on nonnegative least squares and approximate Fekete points.
The main idea is to use less points and especially good points for solving the system of the moments. Good points are here intended as points with good interpolation properties, due to the strict connection between interpolation and cubature.
Numerical experiments show that, in average, just a tenth of the points should be used to maintain the same approximation order of the quasi-Monte Carlo method. The method has been satisfactorily applied to 2- and 3-dimensional problems on quite complex domains. 相似文献
140.
Electrospray ionization mass spectrometry for identification and structural characterization of pregnane glycosides 总被引:1,自引:0,他引:1
Dal Piaz F De Leo M Braca A De Simone F Morelli I De Tommasi N 《Rapid communications in mass spectrometry : RCM》2005,19(8):1041-1052
Pregnane glycosides are a class of naturally occurring substances characterized by some interesting biological activities and widely distributed in the plant kingdom and in some marine organisms. Their toxicity and use in herbal drugs and folk medicines has generated great interest in the chemical characterization of these molecules. In the study reported here the potential of electrospray ionization mass spectrometry (ESI-MS) in the identification and structural characterization of pregnane glycosides was examined. ESI-MS/MS and ESI-MS(n) analyses were performed on 27 different compounds employing two mass spectrometers equipped with a triple-quadrupole or an ion-trap analyzer. The data illustrate the ability of the ESI techniques in the identification of pregnane glycosides, including the nature of the pregnane core, the kind of ester substituents, the types of sugar residues (hexose, deoxyhexose, dideoxyhexose, O-methyldeoxyhexose and O-methyldideoxyhexose), and the primary structure of the saccharide chain. From these data, a generalized fragmentation pathway was proposed by comparing the spectra acquired for all the compounds. Interestingly, similar results were obtained from the two instruments, thus demonstrating that detailed analyses of product ion spectra obtained using a triple-quadrupole mass spectrometer led to structural information comparable to those obtainable in MSn experiments using an ion trap. Different and complementary information was deduced by fragmenting the [M+H]+ or the [M+Na]+ ions, or the protonated aglycone [Agl+H]+ generated by in-source fragmentation. The present evidence clearly suggests that, in order to obtain a complete characterization of pregnane glycosides by MS, all three of these species should be accurately analyzed. 相似文献