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991.
Separation quality on glass microfluidic devices fabricated from photomasks of different optical resolutions was compared by measuring the dispersion (apparent diffusion) coefficients of a set of standard compounds separated on these devices. Currently, the channel manifolds of most microfluidic devices are patterned using chrome photomasks. A much cheaper, more robust alternative to chrome photomasks are laser photoplotted masks. The primary disadvantage to using laser photoplots is that the optical resolution of these masks is not as high as that of chrome masks, and this feature increases the side-wall roughness of etched channel manifolds patterned using such masks. The increased wall roughness may affect the fluid flow within the channels and, therefore, the separation quality. To determine the effect of increased sidewall channel roughness, microchip channel manifolds were patterned in soda lime glass using a chrome photomask and laser photoplots printed at resolutions of 620, 1240, 3100 and 6200 dots per centimetre (dpc). Separations were performed on these devices using dilute solutions of fluorescently labeled amino acids. The peak variances of the amino acids were calculated at increasing distances down the separation channel and plotted as a function of migration time. From this plot, dispersion coefficients of the analytes were measured. This allowed for a reliable, relatively easy, direct separation analysis among microchips fabricated from the various photomasks. After multiple separations using microchips fabricated from each resolution mask, we found that the change in sidewall surface roughness did not significantly affect the dispersion coefficients measured, and thus the separation quality. The lower mask resolution limit, rather, was governed by the fidelity to which the mask could capture the original CAD design. 相似文献
992.
Hayer A de Halleux V Köhler A El-Garoughy A Meijer EW Barberá J Tant J Levin J Lehmann M Gierschner J Cornil J Geerts YH 《The journal of physical chemistry. B》2006,110(15):7653-7659
A concept for highly ordered solid-state structures with bright fluorescence is proposed: liquid crystals based on tetraethynylpyrene chromophores, where the rigid core is functionalized with flexible, promesogenic alkoxy chains. The synthesis of this novel material is presented. The thermotropic properties are studied by means of differential scanning calorimetry (DSC), cross-polarized optical microscopy (POM), and X-ray diffraction. The mesogen possesses an enantiotropic Col(h) phase over a large temperature range before clearing. The material is highly fluorescent in solution and, most remarkably, in the condensed state, with a broad, strongly red shifted emission. Fluorescence quantum yields (Phi(F)) have been determined to be 70% in dichloromethane solution and 62% in the solid state. Concentration- and temperature-dependent absorption and emission studies as well as quantum-chemical calculations on isolated molecules and dimers are used to clarify the type of intermolecular interactions present as well as their influence on the fluorescence quantum yield and spectral properties of the material. The high luminescence efficiency in the solid state is ascribed to rotated chromophores, leading to an optically allowed lowest optical transition. 相似文献
993.
Felim A Toussaint A Phillips CR Leca D Vagstad A Fensterbank L Lacôte E Malacria M 《Organic letters》2006,8(2):337-339
[reaction: see text] One-pot hypervalent iodine-mediated oxidations of arylsulfinamides to arylsulfonimidates is reported. Contrary to the case of alkylsulfinamides, use of iodosobenzene was not satisfactory. The reaction worked best with diacetoxyiodosobenzene (DIB) and a mild base (MgO). The influence of substituents on the iodine(III) reagent arene has been examined. 相似文献
994.
Taglienti A Cellesi F Crescenzi V Sequi P Valentini M Tirelli N 《Macromolecular bioscience》2006,6(8):611-622
[Chemical structure: see text] The interactions between a biomaterial and biomolecules present in body fluids often determine the fate of the biomaterial. This paper presents a study on hyaluronan (HA)-containing materials (in soluble or colloidal form) that focuses on their interactions with lipids and proteins and for the first time uses PFG NMR as an analytical technique for probing these events. The interactions of HA-based polymers with phospholipids (DPPC and DPPG liposomes) are shown to depend both on charge and hydrophobicity factors. Despite the difference in behavior between albumin (substantially non-adhesive) and fibrinogen (adhesive), the interactions of the polymers with proteins do not seem to be based on hydrophobic effects but on surface polar interactions. 相似文献
995.
A specific, sensitive, precise, and accurate method for the determination of abscisic acid (ABA) in grapevine leaf tissues
is described. The method employs high-performance liquid chromatography and electrospray ionization–mass spectrometry (LC-ESI-MS)
in selected ion monitoring mode (SIM) to analyze ABA using a stable isotope-labeled ABA as an internal standard. Absolute
recoveries ranged from 72% to 79% using methanol/water pH 5.5 (50:50 v/v) as an extraction solvent. The best efficiency was
obtained when the chromatographic separation was carried out by using a porous graphitic carbon (PGC) column. The statistical
evaluation of the method was satisfactory in the work range. A relative standard deviation (RDS) of < 5.5% and < 6.0% was
obtained for intra-batch and inter-batch comparisons, respectively. As for accuracy, the relative error (%Er) was between
−2.7 and 4.3%, and the relative recovery ranged from 95% to 107%. 相似文献
996.
The transmission of polar effects through the bicyclo[2.2.2]octane framework has been investigated by ascertaining how the geometry of a phenyl group at a bridgehead position is affected by a variable substituent at the opposite bridgehead position. We have determined the molecular structure of several Ph-C(CH(2)-CH(2))(3)C-X molecules (where X is a charged or dipolar substituent) from HF/6-31G and B3LYP/6-311++G molecular orbital calculations and have progressively replaced each of the three -CH(2)-CH(2)- bridges by a pair of hydrogen atoms. Thus the bicyclo[2.2.2]octane derivatives were changed first into cyclohexane derivatives in the boat conformation, then into n-butane derivatives in the anti-syn-anti conformation, and eventually into assemblies of two molecules, Ph-CH(3) and CH(3)-X, appropriately oriented and kept at a fixed distance. For each variable substituent the deformation of the benzene ring relative to X = H remains substantially the same even when the substituent and the phenyl group are no longer connected by covalent bonds. This provides unequivocal evidence that long-range polar effects in bicyclo[2.2.2]octane derivatives are actually field effects, being transmitted through space rather than through bonds. Varying the substituent X in a series of Ph-C(CH(2)-CH(2))(3)C-X molecules gives rise to geometrical variation (relative to X = H) not only in the benzene ring but also in the bicyclo[2.2.2]octane cage. The two deformations are poorly correlated. The rather small deformation of the benzene ring correlates well with traditional measures of long-range polar effects in bicyclo[2.2.2]octane derivatives, such as sigma(F) or sigma(I) values. The much larger deformation of the bicyclo[2.2.2]octane cage is controlled primarily by the electronegativity of X, similar to deformation of the benzene ring in Ph-X molecules. Thus the field and electronegativity effects of the substituent are well separated and can be studied simultaneously, as they act on different parts of the molecular skeleton. 相似文献
997.
Ring and open-chain S3O sulfur oxides are detected by neutralization-reionization experiments. 相似文献
998.
The air stable asarone-derived Ru carbene 16, a robust olefin metathesis catalyst, can be easily separated after reaction by deposition on silica gel and reused up to nine times. This procedure provides products of excellent purity with low Ru content. 相似文献
999.
Tortosa-Estorach C Ruiz N Masdeu-Bultó AM 《Chemical communications (Cambridge, England)》2006,(26):2789-2791
High selectivity in acids is obtained in the first example of hydrocarboxylation of 1-octene in supercritical carbon dioxide using a Pd/P(4-C6H4-CF3)3 catalyst system and a perfluorinated surfactant. 相似文献
1000.
Campanelli AR Arcadi A Domenicano A Ramondo F Hargittai I 《The journal of physical chemistry. A》2006,110(5):2045-2052
The molecular structures of ethynylbenzene and s-triethynylbenzene have been accurately determined by gas-phase electron diffraction and ab initio/DFT MO calculations and are compared to that of p-diethynylbenzene from a previous study [Domenicano, A.; Arcadi, A.; Ramondo, F.; Campanelli, A. R.; Portalone, G.; Schultz, G.; Hargittai, I. J. Phys. Chem. 1996, 100, 14625]. Although the equilibrium structures of the three molecules have C2v, D3h, and D2h symmetry, respectively, the corresponding average structures in the gaseous phase are best described by nonplanar models of Cs, C3v, and C2v symmetry, respectively. The lowering of symmetry is due to the large-amplitude motions of the substituents out of the plane of the benzene ring. The use of nonplanar models in the electron diffraction analysis yields ring angles consistent with those from MO calculations. The molecular structure of ethynylbenzene reported from microwave spectroscopy studies is shown to be inaccurate in the ipso region of the benzene ring. The variations of the ring C-C bonds and C-C-C angles in p-diethynylbenzene and s-triethynylbenzene are well interpreted as arising from the superposition of independent effects from each substituent. In particular, experiments and calculations consistently show that the mean length of the ring C-C bonds increases by about 0.002 A per ethynyl group. MO calculations at different levels of theory indicate that though the length of the C[triple bond]C bond of the ethynyl group is unaffected by the pattern of substitution, the C(ipso)-C(ethynyl) bonds in p-diethynylbenzene are 0.001-0.002 A shorter than the corresponding bonds in ethynylbenzene and s-triethynylbenzene. This small effect is attributed to conjugation of the two substituents through the benzene ring. Comparison of experimental and MO results shows that the differences between the lengths of the C(ipso)-C(ethynyl) and C(ipso)-C(ortho) bonds in the three molecules, 0.023-0.027 A, are correctly computed at the MP2 and B3LYP levels of theory but are overestimated by a factor of 2 when calculated at the HF level. 相似文献