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91.
Modeling urban street patterns 总被引:3,自引:0,他引:3
Urban street patterns form planar networks whose empirical properties cannot be accounted for by simple models such as regular grids or Voronoi tesselations. Striking statistical regularities across different cities have been recently empirically found, suggesting that a general and detail-independent mechanism may be in action. We propose a simple model based on a local optimization process combined with ideas previously proposed in studies of leaf pattern formation. The statistical properties of this model are in good agreement with the observed empirical patterns. Our results thus suggest that in the absence of a global design strategy, the evolution of many different transportation networks indeed follows a simple universal mechanism. 相似文献
92.
We present a dynamic scanning force and Kelvin microscopy study of Suzuki precipitates on clean (001) surfaces of UHV cleaved NaCl : Mg2+. Nanometer sized precipitates with a rectangular shape on flat terraces and also at steps were found. Images with atomic resolution confirm that the precipitates are embedded in the NaCl matrix and permit the identification of each type of ion in the unit cell of the Suzuki structure. Kelvin microscopy images show always a strong bright contrast at the precipitates, which is probably due to the negative cation vacancies in the Suzuki structure. 相似文献
93.
Kornauth Wilh Bersch A. Philips Donner Dr. Louise H. Weller C. Schweitzer Ch. L. Penny Ed. van Melckebeke H. J. Wheeler B. Hartwell Knorr W. Büttner Barthé W. Jerwitz C. F. Parker Gust Christ Ferdinand Kryz J. Katz H. Göckel R. Jabota J. J. L. von Rijn F. Baum Joseph Nerking A. E. Taylor J. Gadamer C. Th. L. Hagemann C. A. Neufeld Christ. Kob und Co. 《Analytical and bioanalytical chemistry》1902,41(11):686-695
94.
95.
Morgner N Barth HD Brutschy B Scheffer U Breitung S Göbel M 《Journal of the American Society for Mass Spectrometry》2008,19(11):1600-1611
A new laser-based mass spectrometry method, called laser induced liquid bead ion desorption (LILBID), was applied to investigate RNA:ligand interactions. As model system the HIV Tat:TAR transactivation complex and its binding behavior were analyzed. TARwt of HIV Type 1 and Type 2 and different artificial mutants were compared regarding their binding to Tat and different peptide ligands. Specific and nonspecific association to TAR was deduced, with the bulge being the well known specific binding site of TAR. In the case of triple arginine (RRR) as a nonspecific ligand, multiple electrostatic binding to TAR was found at higher concentration of RRR. This contrasted with the formation of only ternary complexes in competitive binding studies with TAR, Tat, and potential inhibitors. The fact that the stoichiometries of the complexes can be determined is a major advantage of MS methods over the widely applied fluorimetric methods. A quantitative evaluation of the spectra by a numeric model for ternary complex formation allows conclusions about the role and strength of the binding sites of the RNAs, the specificity and affinity of different ligands, the determination of apparent IC50 and KD values, and a comparison of the binding efficiencies of potential inhibitors. 相似文献
96.
Dynamic Nuclear Polarization Provides New Insights into Chromophore Structure in Phytochrome Photoreceptors 下载免费PDF全文
Daniel Stöppler Dr. Chen Song Dr. Barth‐Jan van Rossum Michel‐Andreas Geiger Christina Lang Prof. Dr. Maria‐Andrea Mroginski Dr. Anil Pandurang Jagtap Prof. Dr. Snorri Th. Sigurdsson Prof. Dr. Jörg Matysik Prof. Dr. Jon Hughes Prof. Dr. Hartmut Oschkinat 《Angewandte Chemie (International ed. in English)》2016,55(52):16017-16020
97.
Auwärter W Klappenberger F Weber-Bargioni A Schiffrin A Strunskus T Wöll C Pennec Y Riemann A Barth JV 《Journal of the American Chemical Society》2007,129(36):11279-11285
We present a combined low-temperature scanning tunneling microscopy and near-edge X-ray adsorption fine structure study on the interaction of tetrapyridyl-porphyrin (TPyP) molecules with a Cu(111) surface. A novel approach using data from complementary experimental techniques and charge density calculations allows us to determine the adsorption geometry of TPyP on Cu(111). The molecules are centered on "bridge" sites of the substrate lattice and exhibit a strong deformation involving a saddle-shaped macrocycle distortion as well as considerable rotation and tilting of the meso-substituents. We propose a bonding mechanism based on the pyridyl-surface interaction, which mediates the molecular deformation upon adsorption. Accordingly, a functionalization by pyridyl groups opens up pathways to control the anchoring of large organic molecules on metal surfaces and tune their conformational state. Furthermore, we demonstrate that the affinity of the terminal groups for metal centers permits the selective capture of individual iron atoms at low temperature. 相似文献
98.
Alexei A. Gridnev Patricia M. Cotts Chris Roe Howard Barth 《Journal of polymer science. Part A, Polymer chemistry》2001,39(7):1099-1105
Low molecular weight (MW) polystyrenes were synthesized by radical polymerization in the presence of catalytic chain‐transfer agents. Synthetic conditions are controlled to produce molecules containing one methyl group at one end as well as a double bond at the other end, capped with a phenyl group. Individual oligomers were separated by liquid chromatography, and the properties were analyzed using NMR, ultraviolet–visible (UV–vis) spectroscopy, and size exclusion chromatography with light scattering. The UV–vis spectra, proton NMR spectra, and differential refractive‐index increments exhibit an MW dependence of up to six–eight monomer units. The obtained dependencies can be used for precise characterization of the molecular weight distribution of polystyrene obtained by catalytic chain transfer. The double‐bonded end groups were found to be exclusively in the transconfiguration for all oligomers. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1099–1105, 2001 相似文献
99.
Partial vapor pressures were measured for the volatiles of solutions of polysulfone or polyethersulfone in mixtures of N,N‐dimethylformamide (DMF, solvent) and water or acetone (precipitants) by means of headspace gas chromatography. The results demonstrate that the enrichment of water in the gas phase increases exponentially with rising polymer concentration, in contrast to that of acetone which remains constant. The reinforced expulsion of water resulting from the presence of polymers is theoretically conceivable and should be useful in the field of separation techniques. 相似文献
100.
Johannes V. Barth 《Surface science》2009,603(10-12):1533-1541
Surface coordination chemistry has been traditionally associated with analogies between metal–ligand bonding in coordination compounds and chemisorptive interactions, the anchoring of metal complexes or other units for interface functionalisation, or the chemistry of oxide surfaces. However, more recently it became clear that well-defined surfaces similarly represent versatile platforms to conduct metal–ligand reactions in two dimensions and engineer unique coordination compounds or layers by novel complexation or metal-directed assembly protocols. This approach presents a versatile strategy to realize coordinatively unsaturated species as well as metal–organic polymers and networks with distinct shape and functional properties. 相似文献