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61.
Wang X Shindel MM Wang SW Ragan R 《Langmuir : the ACS journal of surfaces and colloids》2010,26(23):18239-18245
Lipid vesicles are designed with functional chemical groups to promote vesicle fusion on template-stripped gold (TS Au) surfaces that does not spontaneously occur on unfunctionalized Au surfaces. Three types of vesicles were exposed to TS Au surfaces: (1) vesicles composed of only 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipids; (2) vesicles composed of lipid mixtures of 2.5 mol % of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-poly(ethylene glycol)-2000-N-[3-(2-pyridyldithio)propionate] (DSPE-PEG-PDP) and 97.5 mol % of POPC; and (3) vesicles composed of 2.5 mol % of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(poly(ethylene glycol))-2000] (DSPE-PEG) and 97.5 mol % POPC. Atomic force microscopy (AFM) topography and force spectroscopy measurements acquired in a fluid environment confirmed tethered lipid bilayer membrane (tLBM) formation only for vesicles composed of 2.5 mol % DSPE-PEG-PDP/97.5 mol % POPC, thus indicating that the sulfur-containing PDP group is necessary to achieve tLBM formation on TS Au via Au-thiolate bonds. Analysis of force-distance curves for 2.5 mol % DSPE-PEG-PDP/97.5 mol % POPC tLBMs on TS Au yielded a breakthrough distance of 4.8 ± 0.4 nm, which is about 1.7 nm thicker than that of POPC lipid bilayer membrane formed on mica. Thus, the PEG group serves as a spacer layer between the tLBM and the TS Au surface. Fluorescence microscopy results indicate that these tLBMs also have greater mechanical stability than solid-supported lipid bilayer membranes made from the same vesicles on mica. The described process for assembling stable tLBMs on Au surfaces is compatible with microdispensing used in array fabrication. 相似文献
62.
Regina Luschtinetz Augusto F. Oliveira Hélio A. Duarte Gotthard Seifert 《无机化学与普通化学杂志》2010,636(8):1506-1512
Density‐functional based calculations were used to investigate self‐assembled monolayers of different alkylphosphonic acids on corundum α‐Al2O3 (0001), bayerite β‐Al(OH)3 (001) and boehmite γ‐AlOOH (010) surface models. Mono‐, bi‐, and tridentate adsorption modes were considered. In addition, the organization of single adsorbed molecules was compared to the organization at full surface coverage. The height (thickness) of the self‐assembled monolayers is always shorter than the length of the phosphonic acid molecules due to tilting of the alkyl chains. Tilt angles at full surface coverage are very similar to the tilt angle of a single adsorbed molecule, which indicates that the density of the self‐assembled monolayers is limited by the density of adsorption sites. The lateral interactions between alkyl chains are evidenced by small torsions of the adsorbed molecules, which may serve to minimize the repulsion forces between interchain hydrogen atoms. Similar tilt angles were obtained for mono‐, bi‐, and tridentate adsorptions. Hence, the coordination mode cannot be characterized by the molecule tilting. 相似文献
63.
França EJ Andrade CG Furlaneto-Maia L Serpa R Oliveira MT Quesada RM Furlaneto MC 《Micron (Oxford, England : 1993)》2011,42(7):726-732
Candida tropicalis has been identified as one of the most prevalent pathogenic yeast species of the Candida-non-albicans (CNA) group. Study of switching in C. tropicalis has not been the subject of extensive research. Therefore, we investigated switching event and characterized the ultrastructural architecture of different phenotypes and biofilm produced in a C. tropicalis clinical strain. Cells switched heritably, reversibly, and at a high frequency between four phenotypes readily distinguishable by the shape of colonies formed on agar at 25°C. SEM analysis was used to verify the architecture of whole Candida colonies at ultrastructural level. The smooth phenotype (parental phenotype) colony showed a hemispherical shape character, while the semi-smooth was characterized by the presence of shallow marginal depressions. The ring and rough phenotypes exhibited more complex architecture and were characterized by the presence of deep central and peripheral depressions areas. The biofilm-forming ability varied among the switch phenotypes. After 12h incubation, the smooth phenotype formed less biofilm compared to the other phenotypes (P<0.05). The electron microscopy analysis revealed that filamentation (pseudohyphae) was associated with ring and rough colonies. The ultrastructural analysis allowed the observation of the arrangement of individual cells within the colonies. At the deep central and peripheral depressions areas of the ring and rough colonies extracellular material was seen in different arrangements. The data presented here open new avenues to study a possible role for extracellular material in the formation and maintenance of the architecture of switch phenotypes in C. tropicalis. It is therefore essential that more strains be investigated to determine the biological significance of extracellular material in C. tropicalis phenotypic switching phenomenon. 相似文献
64.
Regina Schmitt Patrick Mayer Benjamin Kirsch Jan Aurich Charlotte Kuhn Ralf Müller Kaushik Bhattacharya 《PAMM》2014,14(1):383-384
This work is motivated by cryogenic turning which allows end shape machining and simultaneously attaining a hardened surface due to deformation induced martensitic transformations. To study the process on the microscale, a multivariant phase field model for martensitic transformations in conjunction with a crystal plastic material model is introduced. The evolution of microstructure is assumed to follow a time-dependent Ginzburg-Landau equation. To solve the field equations the finite element method is used. Time integration is performed with Euler backward schemes, on the global level for the evolution equation of the phase field, and on the element level for the crystal plastic material law. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
65.
Regina Schmitt Ralf Müller Charlotte Kuhn Herbert M. Urbassek 《Archive of Applied Mechanics (Ingenieur Archiv)》2013,83(6):849-859
A phase field model approach for multivariant martensitic transformations of stable and metastable phases is introduced. The evolution of the microstructure is examined with respect to elastic energy minimization in which one or two martensitic orientation variants are considered. In this context, the martensitic nucleation behavior is simulated for different activation barriers. Furthermore, the influence of time-dependent external loads on the formation of the different phases is studied. The numerical implementation is performed with finite elements and an implicit time integration scheme. 相似文献
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69.
Regina C. Fischer R. Wittlinger K. Ballschmiter 《Fresenius' Journal of Analytical Chemistry》1992,342(4-5):421-425
Summary Vapor pressures for 133 individual polychlorobiphenyl congeners as subcooled liquids were determined by two different approaches on the basis of gas-chromatographic retention indices obtained with two different non-polar stationary phases. The approach which is based on the retention indices obtained on a methyl-50% octyl polysiloxane phase (SB Octyl 50) and on reference vapor pressures of PCB congeners, and thus contains less approximations, should yield more accurate results than the method which uses retention indices obtained on a methyl polysiloxane phase (OV 101) and reference vapor pressure data taken from the n-alkanes of the retention index system. A systematic deviation is observed between the values obtained by the two different methods. The first method gives constantly slightly higher values for the vapor pressure. This will be caused by the different separation characteristics of the two non-polar stationary phases used, as well as by uncertainties in the reference data for the vapor pressure calculations. 相似文献
70.