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991.
Lindsey G. Mackay Daniel Burke Fong-Ha Liu Nigel Sousou Veronica V. Vamathevan Judy Cuthbertson Chris Mussell Richard B. Myors 《Accreditation and quality assurance》2007,12(9):475-482
A high-accuracy exact-matching isotope dilution mass spectrometry (IDMS) method for 19-norandrosterone (19-NA) in human urine
was developed at NMIA for the certification of a freeze-dried human urine reference material (CRM NMIA MX002). The method
utilised GC/HRMS analysis following hydrolysis, solvent extraction, HPLC fractionation and derivatisation. The method development
included investigation of all potential analytical biases for the different stages of the method and included development
of a confirmatory LC/MS/MS method. The measurement uncertainty of the reference method was rigorously investigated with the
achieved expanded uncertainty being less than 4% at the 95% level of confidence. The method was used in the Comité Consultatif
pour la Quantité de Matière (CCQM) pilot study CCQM-P68 which was an interlaboratory intercomparison for the analysis of 19-NA
in human urine in which four national metrology institutes (NMIs) participated in. The agreement in the results from the NMIA
method with those from the other NMIs was excellent. 相似文献
992.
Dionisia Sanz Almudena Perona RosaM. Claramunt Elena Pinilla M.Rosario Torres Jos Elguero 《Helvetica chimica acta》2006,89(7):1290-1303
The new N‐salicylideneheteroarenamines 1 – 4 were prepared by reacting the biologically relevant 3‐hydroxy‐4‐pyridinecarboxaldehyde ( 5 ) with 1H‐imidazol‐1‐amine ( 6 ), 1H‐pyrazol‐1‐amine ( 7 ), 1H‐1,2,4‐triazol‐1‐amine ( 8 ), and 1H‐1,3,4‐triazol‐1‐amine ( 9 ). Solution 1H‐, 13C‐, and 15N‐NMR were used to establish that the hydroxyimino form A is the predominant tautomer. A combination of 13C‐ and 15N‐CPMAS‐NMR with X‐ray crystallographic studies confirms that the same form is present in the solid state. The stabilities and H‐bond geometries of the different forms, tautomers and rotamers, are discussed by using B3LYP/6‐31G** calculations. 相似文献
993.
Saudan C Ceroni P Vicinelli V Maestri M Balzani V Gorka M Lee SK van Heyst J Vögtle F 《Dalton transactions (Cambridge, England : 2003)》2004,(10):1597-1600
We have investigated the complexation of lanthanide ions (Nd3+, Eu3+, Gd3+, Tb3+, Dy3+) with three cyclam-based ligands (cyclam = 1,4,8,11-tetraazacyclotetradecane), namely 1,4,8,11-tetrakis(naphthylmethyl)cyclam (1), and two dendrimers consisting of a cyclam core appended with four dimethoxybenzene and eight naphthyl units (2) and twelve dimethoxybenzene and sixteen naphthyl units (3). In the free ligands the fluorescence of the naphthyl units is strongly quenched by exciplex formation with the cyclam nitrogens. Complexation with the metal ions prevents exciplex formation and revives the intense naphthyl fluorescence. Fluorescence and NMR titration experiments have revealed the formation of complexes with different metal/ligand stoichiometries in the case of 1, 2 and 3. Surprisingly, the large dendrimer 3 gives rise to a stable [M(3)3]3+ species. Energy transfer from the lowest singlet and triplet excited states of the peripheral naphthyl units to the lower lying excited states of Nd3+, Eu3+, Tb3+, Dy3+ coordinated to the cyclam core does not take place. 相似文献
994.
Eichelberger BR Snow TP Bierbaum VM 《Journal of the American Society for Mass Spectrometry》2003,14(5):501-505
Langevin described a model for the interaction between an ion and a neutral nearly a century ago and since then, many modifications have been introduced to adjust for specific circumstances. This work discusses the induced dipole-induced dipole interaction between an ion and a neutral without a permanent dipole and introduces an anisotropic adjustment. A point polarizable ion model (PPI) and an orientation dependent polarizable ion model (ODPI) are discussed and applied to systems where the ion is highly polarizable and the neutral is only weakly polarizable. Significant deviations from classical Langevin rate constants and significant differences between PPI and ODPI are observed. 相似文献
995.
Milián L Estellés R Abarca B Ballesteros R Sanz MJ Blázquez MA 《Chemical & pharmaceutical bulletin》2004,52(6):696-699
Four phenanthrene and one aporphine alkaloids semi-synthesized from boldine were evaluated for their inhibitory effect on reactive oxygen species (ROS) generation. ROS generation by neutrophils stimulated with N-formyl-methionyl-leucyl-phenylalanine was inhibited in a concentration dependent manner. Alkaloids exerted similar inhibitory effect in the hypoxanthine-xanthine oxidase system than in stimulated neutrophils, which could be attributed to a direct ROS scavenging activity. None of the alkaloids assayed had any effect on xanthine oxidase activity. Therefore the synthesized alkaloids might constitute an alternative therapy in inflammation disorders in which ROS generation is involved. 相似文献
996.
The 243 coupling constants of eight N-R-pyrazoles [R=H, CH3, C6H5, COCH3, NH2, NO2, SO2CF3, Si(CH3)3] have been calculated and compared with 131 experimental values. The agreement is good and can be used to estimate new couplings. The whole collection has been statistically analyzed. 相似文献
997.
When codeine free base is incorporated into a potassium bromide pellet, its infrared spectrum can show anomalous phenomena between approximately 1100 cm?1 and 750 cm?1. Investigation of the problem indicated that the anomalies are related to rapid formation of the codeine free base monohydrate during sample preparation. 相似文献
998.
In this work, the results of a new method for the preparation of porous silicon (PS) layers with in situ simultaneous functionalization with organic molecules are reported. The molecules of interest are dissolved in the HF ethanoic solution used to prepare the PS layers by partial anodic dissolution of a Si electrode. The method has been proved to be effective with various molecules. In this Communication, the case of PS functionalization with heptyne molecules, studied by FTIR spectroscopy, is reported in detail. The results demonstrate that this new functionalization method, accompanied by a low-level oxidation, is simple, fast, and effective and that it can allow the confinement of the adsorbed molecules selectively in a single layer of a PS stack. 相似文献
999.
Alain Levasseur Mohamed Kbala Mariano Sanz Michel Couzi 《Journal of solid state chemistry》1983,47(3):256-263
Conductivity studies of glasses obtained from the B2O3Li2OLi2MoO4 and B2O3Li2OLi2WO4 systems have been carried out. The presence of the transition element in tetrahedral coordination and with two different oxidation states is discussed. A Raman spectroscopy study shows that the MoO4 or WO4 tetrahedra are slightly compressed by the network forming lattice. 相似文献
1000.
J.J. Lozano E. López-de-Briñas N.B. Centeno R. Guigó F. Sanz 《Journal of computer-aided molecular design》1997,11(4):395-408
The three-dimensional modelling of proteins is a useful tool to fill the gap between the number of sequenced proteins and the number of experimentally known 3D structures. However, when the degree of homology between the protein and the available 3D templates is low, model building becomes a difficult task and the reliability of the results depends critically on the correctness of the sequence alignment. For this reason, we have undertaken the modelling of human cytochrome P450 1A2 starting by a careful analysis of several sequence alignment strategies (multiple sequence alignments and the TOPITS threading technique). The best results were obtained using TOPITS followed by a manual refinement to avoid unlikely gaps. Because TOPITS uses secondary structure predictions, several methods that are available for this purpose (Levin, Gibrat, DPM, NnPredict, PHD, SOPM and NNSP) have also been evaluated on cytochromes P450 with known 3D structures. More reliable predictions on -helices have been obtained with PHD, which is the method implemented in TOPITS. Thus, a 3D model for human cytochrome P450 1A2 has been built using the known crystal coordinates of P450 BM3 as the template. The model was refined using molecular mechanics computations. The model obtained shows a consistent location of the substrate recognition segments previously postulated for the CYP2 family members. The interaction of caffeine and a carcinogenic aromatic amine (MeIQ), which are characteristic P450 1A2 substrates, has been investigated. The substrates were solvated taking into account their molecular electrostatic potential distributions. The docking of the solvated substrates in the active site of the model was explored with the AUTODOCK programme, followed by molecular mechanics optimisation of the most interesting complexes. Stable complexes were obtained that could explain the oxidation of the considered substrates by cytochrome P450 1A2 and could offer an insight into the role played by water molecules. 相似文献