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排序方式: 共有651条查询结果,搜索用时 31 毫秒
561.
We define fuzzy symbols as particular fuzzy sets whose membership functions operate between two linearly ordered spaces, and study the operations of maximum and of minimum between two fuzzy symbols. We consider the membership functions of the fuzzy symbols as possibility distributions. We study those of the maximum and the minimum of two non-interactive and weakly non-interactive variables. 相似文献
562.
Giulia Caron Patrick Gaillard Pierre-Alain Carrupt Bernard Testa 《Helvetica chimica acta》1997,80(2):449-462
This study was designed to unravel lipophilicity changes associated with the oxidation state of the S-atom in model compounds, drugs, and metabolites, special attention being given both to intermolecular and intramolecular effects. The methods used were experimental (potentiometry, CPC, and shake-flask techniques to measure lipophilicity, 13C-NMR spectroscopy to investigate tautomeric equilibria) and computational (quenched molecular dynamics and molecular lipophilicity potential). Simple, monofunctional model compounds were used to assess intermolecular forces, as revealed by the Δlog Poct–alk and Δlog Poct–chf parameters. Drugs and their metabolites proved to be good probes to study intramolecular effects in both neutral and anionic forms, as revealed by the difference between calculated and experimental log Poct values (the diff(log Pexp–calc) parameter). Sulindac and its metabolites showed a normal partitioning behavior, whereas the lipophilicity of sulfmpyrazone and its metabolites' was markedly affected by tautomeric and conformational equilibria. 相似文献
563.
GC-MS analytical methods for the determination of personal-care products in water matrices 总被引:1,自引:0,他引:1
Maria Chiara Pietrogrande Giulia Basaglia 《Trends in analytical chemistry : TRAC》2007,26(11):1086-1094
This article discusses the more recent methods combining gas chromatography and mass spectrometry (GC-MS) for analysis of personal-care products (PCPs) in water matrices. We describe different procedures for sample extraction and preparation as well as different instrumental methods commonly used for these compounds. GC-MS and GC-tandem MS (GC-MS2), which are complementary to liquid chromatography combined with MS (LC-MS), allow identification and quantification of PCPs belonging to different classes with the sensitivity and the selectivity necessary for environmental monitoring. The compounds investigated include fragrances (e.g., nitro and polycyclic musks), antimicrobial compounds (e.g., triclosan), ultraviolet blockers (e.g., methylbenzylidene camphor), antioxidants and preservatives (e.g., phenols and p-hydroxybenzoic acid (parabens)) and insect repellents (e.g., N,N-diethyl-m-toluamide (DEET)). We critically review data in the literature by focusing attention on analytical methods devoted to simultaneous detection and quantification of structurally diverse pharmaceuticals and PCPs. 相似文献
564.
Gabriella Capecchi Maria Giulia Faga Gianmario Martra Salvatore Coluccia Maria Francesca Iozzi Maurizio Cossi 《Research on Chemical Intermediates》2007,33(3-5):269-284
Adsorption of organic molecules on TiO2 surfaces is widely used in a number of technological applications, from heterogeneous catalysis, in particular photodegradation of organic pollutants, to dye-sensitized solar cells (DSSCs), where in most cases the dye molecules are grafted to the anatase TiO2 surface through a carboxylic group. In particular, organic/TiO2 systems can be of relevant importance in the modeling of electronic devices, in which the molecular layer is able to finely tune the electric properties, as well as of highly efficient heterogeneous catalysts. A key step is the understanding of the nature of the carbon-oxygen-titanium bonds on such surfaces, which is the specific aim of our combined IR and ab initio study of the adsorption of CH3COOH on TiO2. The experimental determination of the CH3COOH frequency shifts due to the absorption on the P25 (Degussa) TiO2 surface was performed by means of a step-wise procedure, consisting of a preliminary outgassing at 600°C of TiO2, in order to have a high dehydroxilation degree of the surface, followed by IR measurements at increasing CH3COOH pressure and subsequent desorption. Frequency calculations to be compared with experimental results were performed within a cluster approach using GAUSSIAN03 package. In order to make such calculations feasible, we decided to use an ONIOM approach where the model system, i.e., the small portion corresponding to CH3COOH plus the surface atoms, is treated at DFT level while the real system, comprising the bulk atoms, at MSINDO level. Once properly tested the ONIOM approach to characterize the interaction of TiO2 with CH3COOH, we computed the vibrational frequencies and compared them with the results of the IR experiments, providing some insight for the interpretation of the experimental complex vibrational pattern. 相似文献
565.
Prendergast D Grossman JC Williamson AJ Fattebert JL Galli G 《Journal of the American Chemical Society》2004,126(42):13827-13837
We investigate the impact of water on the optical absorption of prototypical silicon clusters. Our clusters contain 5 silicon atoms, tetrahedrally coordinated and passivated with either hydrogen or oxygen. We approach this complex problem by assessing the contributions of three factors: chemical reactivity, thermal equilibration, and dielectric screening. We find that the silanone (Si=O) functional group is not chemically stable in the presence of water and exclude this as a source of significant red shift in absorption in aqueous environments. We perform first principles molecular dynamics simulations of the solvation of a chemically stable, oxygenated silicon cluster with explicit water molecules at 300 K. We find a systematic 0.7 eV red shift in the absorption gap of this cluster, which we attribute to thermally induced fluctuations in the molecular structure. Surprisingly, we find no observable screening impact of the solvent, in contrast with consistent blue shifts observed for similarly sized organic molecules in polar solvents. The predicted red shift is expected to be significantly smaller for larger Si quantum dots produced experimentally, guaranteeing that their vacuum optical properties are preserved even in aqueous environments. 相似文献
566.
Marco Arfelli Giulia Mattogno Carla Ferragina Maria Antonietta Massucci 《Journal of inclusion phenomena and macrocyclic chemistry》1991,11(1):15-27
An X-ray photoelectron spectroscopic investigation of-Zr (HP04)2·2 H2O and its intercalation compounds with 1,10-phenanthroline, Co2+-phenanthroline and Cu2+-phenanthroline is described. The analysis of theNls spectra of the compound containing only phenanthroline clearly shows that, on average, more than one nitrogen atom of the diamine interacts with the acid groups of the host, giving protonated species. XPS also provides evidence of the coordination of Co2+ and Cu2+ ions after their diffusion in the phenanthroline--zirconium phosphate intercalation compound. They form mixed N-and O-coordinated species with the diamine and the oxygens of the interlayer region, but the presence of the characteristic peaks of uncoordinated phenanthroline, even at low intensity, shows that the diamine molecules anchored to the host are still present.A comparison is made with the analogous derivatives of -Zr (HPO4)2·H2O and the differences between the two series of compounds are discussed. 相似文献
567.
Cacace F de Petris G Rosi M Troiani A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(16):3653-3659
The course of the reaction of electronically and vibronically excited metastable O(2) (+)((4)Pi(u), nu') ions with O(2), known to produce O(3) (+), was examined by the joint application of computational and mass spectrometric methods. The results show that the reaction does not proceed by a direct mechanism and that it involves instead the intermediacy of the [O(2) (+)((4)Pi(u)) x O(2)] and [O(3) (+)((4)A(2)) x O] complexes, both theoretically characterized, and the latter one positively identified by structurally diagnostic mass spectrometric techniques. The reaction is a potential source of stratospheric ozone, in that O(3) (+) ions are known to undergo efficient charge exchange with oxygen to yield neutral O(3). 相似文献
568.
Rossi G Ferrando R Rapallo A Fortunelli A Curley BC Lloyd LD Johnston RL 《The Journal of chemical physics》2005,122(19):194309
Genetic algorithm global optimization of Ag-Pd, Ag-Au, and Pd-Pt clusters is performed. The 34- and 38-atom clusters are optimized for all compositions. The atom-atom interactions are modeled by a semiempirical potential. All three systems are characterized by a small size mismatch and a weak tendency of the larger atoms to segregate at the surface of the smaller ones. As a result, the global minimum structures exhibit a larger mixing than in Ag-Cu and Ag-Ni clusters. Polyicosahedral structures present generally favorable energetic configurations, even though they are less favorable than in the case of the size-mismatched systems. A comparison between all the systems studied here and in the previous paper (on size-mismatched systems) is presented. 相似文献
569.
Cecchet F Fioravanti G Marcaccio M Margotti M Mattiello L Paolucci F Rapino S Rudolf P 《The journal of physical chemistry. B》2005,109(39):18427-18432
Ordered thin layers of a spirobifluorene derivative containing an amino group were formed by grafting them onto a self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid (11-MUA) on gold. Either physical (H-bonding) or chemical bonding (activated by EDCl) was investigated. X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy confirmed that both methods can be used to effectively graft 2-amino-9,9'-spirobifluorene molecules onto the SAM surface, giving high surface coverages, with a significantly higher packing in the case of chemisorbed films. EIS measurements also showed that the covalently bonded spirobifluorene SAMs act as an effective barrier to both ion penetration and heterogeneous electron transfer. 相似文献
570.
Fabio Sciubba Maria Enrica Di Cocco Giulia Angori Mariangela Spagnoli Flavio Roberto De Salvador Petra Engel 《Natural product research》2020,34(14):2043-2050
AbstractBacterial canker of Actinidia, caused by the bacterium Pseudomonas syringae pv. actinidiae (Psa), is the most serious disease of these plants worldwide. Leaves of three species of Actinidia, namely A. chinensis var. chinensis, A. chinensis var. deliciosa and A. arguta, having different degrees of tolerance to Psa, were analyzed by Nuclear Magnetic Resonance spectroscopy. Aqueous extracts of leaves were studied and several metabolites, classified as organic acids, amino acids, carbohydrates, phenols and other metabolites, were identified by 1D and 2D NMR experiments and quantified. The metabolic profiles of these species were compared through univariate statistical analysis ANOVA and multivariate PCA. Levels of metabolites with known antibacterial activity, such as caffeic and chlorogenic acids, were observed to be higher in the A. arguta samples. Moreover, these metabolites have different Pearson correlation patterns among the three Actinidia species, suggesting a difference at the phenylpropanoid biosynthetic pathway. 相似文献