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731.
Siegfried L McMahon CN Baumeister J Neuburger M Kaden TA Anandaram S Palivan CG 《Dalton transactions (Cambridge, England : 2003)》2007,(42):4797-4810
Two new polytopic ligands L1 and L2 have been synthesized. They consist of a central tren unit to which three 1,4,7,10-tetraazacyclododecane rings are attached via an ethylene and a trimethylene bridge, respectively. The complexation properties of L1 and L2 towards Cu(2+) and Ni(2+) were studied by potentiometric pH titration, UV-Vis, EPR spectroscopy and kinetic techniques. As a comparison, the Cu(2+) and Ni(2+) complexes with L3 (1-(N-methyl-2-aminoethyl-1,4,7,10-tetraazacyclododecane)) were also investigated. The crystal structures of [CuL3H(H(2)O)](ClO(4))(3) and [NiL3Cl](ClO(4)) were solved and show that the side chain in its protonated form is not involved in coordination, whereas deprotonated it binds to the metal ion. The thermodynamically stable 3:1 complexes of L1 or L2 have a metal ion in the three macrocyclic units. However, when three equivalents of Cu(2+) are added to L1 or L2 the metal ion first binds to the tren unit and only then to the macrocycles. The kinetics of the different steps of complexation have been studied and a mechanism is proposed. 相似文献
732.
Aguilar-Arevalo AA Bazarko AO Brice SJ Brown BC Bugel L Cao J Coney L Conrad JM Cox DC Curioni A Djurcic Z Finley DA Fleming BT Ford R Garcia FG Garvey GT Green C Green JA Hart TL Hawker E Imlay R Johnson RA Kasper P Katori T Kobilarcik T Kourbanis I Koutsoliotas S Laird EM Link JM Liu Y Liu Y Louis WC Mahn KB Marsh W Martin PS McGregor G Metcalf W Meyers PD Mills F Mills GB Monroe J Moore CD Nelson RH Nienaber P Ouedraogo S Patterson RB Perevalov D Polly CC Prebys E Raaf JL Ray H Roe BP 《Physical review letters》2007,98(23):231801
The MiniBooNE Collaboration reports first results of a search for nu e appearance in a nu mu beam. With two largely independent analyses, we observe no significant excess of events above the background for reconstructed neutrino energies above 475 MeV. The data are consistent with no oscillations within a two-neutrino appearance-only oscillation model. 相似文献
733.
Mukai T Hufnagel C Kasper A Meno T Tsukada A Semba K Shimizu F 《Physical review letters》2007,98(26):260407
Rubidium-87 atoms are trapped in an Ioffe-Pritchard potential generated with a persistent supercurrent that flows in a loop circuit patterned on a sapphire surface. The superconducting circuit is a closed loop made of a 100 microm wide molecular-beam epitaxy-grown MgB2 stripe carrying a supercurrent of 2.5 A. To control the supercurrent in the stripe, an on-chip thermal switch operated by a focused argon-ion laser is developed. The switch operates as an on/off switch of the supercurrent or as a device to set the current to a specific value with the aid of an external magnetic field. The current can be set even without an external source if the change is in the decreasing direction. 相似文献
734.
Celik L Sinning S Severinsen K Hansen CG Møller MS Bols M Wiborg O Schiøtt B 《Journal of the American Chemical Society》2008,130(12):3853-3865
Molecular modeling and structure-activity relationship studies were performed to propose a model for binding of the neurotransmitter serotonin (5-HT) to the human serotonin transporter (hSERT). Homology models were constructed using the crystal structure of a bacterial homologue, the leucine transporter from Aquifex aeolicus, as the template and three slightly different sequence alignments. Induced fit docking of 5-HT into hSERT homology models resulted in two different binding modes. Both show a salt bridge between Asp98 and the charged primary amine of 5-HT, and both have the 5-HT C6 position of the indole ring pointing toward Ala173. The difference between the two orientations of 5-HT is an enantiofacial discrimination of the indole ring, resulting in the 5-hydroxyl group of 5-HT being vicinal to either Ser438/Thr439 or Ala169/Ile172/Ala173. To assess the binding experimentally, binding affinities for 5-HT and 17 analogues toward wild type and 13 single point mutants of hSERT were measured using an approach termed paired mutant-ligand analogue complementation (PaMLAC). The proposed ligand-protein interaction was systematically examined by disrupting it through site-directed mutagenesis and re-establishing another interaction via a ligand analogue matching the mutated residue, thereby minimizing the risk of identifying indirect effects. The interactions between Asp98 and the primary amine of 5-HT and the interaction between the C6-position of 5-HT and hSERT position 173 was confirmed using PaMLAC. The measured binding affinities of various mutants and 5-HT analogues allowed for a distinction between the two proposed binding modes of 5-HT and biochemically support the model for 5-HT binding in hSERT where the 5-hydroxyl group is in close proximity to Thr439. 相似文献
735.
Bache N Rand KD Roepstorff P Ploug M Jørgensen TJ 《Journal of the American Society for Mass Spectrometry》2008,19(12):1719-1725
We have previously shown that peptide amide hydrogens undergo extensive intramolecular migration (i.e., complete hydrogen scrambling) upon collisional activation of protonated peptides (Jørgensen et al. J. Am. Chem. Soc. 2005, 127, 2785–2793). The occurrence of hydrogen scrambling enforces severe limitations on the application of gas-phase fragmentation as a convenient method to obtain information about the site-specific deuterium uptake for proteins and peptides in solution. To investigate whether deprotonated peptides exhibit a lower level of scrambling relative to their protonated counterparts, we have now measured the level of hydrogen scrambling in a deprotonated, selectively labeled peptide using MALDI tandem time-of-flight mass spectrometry. Our results conclusively show that hydrogen scrambling is prevalent in the deprotonated peptide upon collisional activation. The amide hydrogens (1H/2H) have migrated extensively in the anionic peptide, thereby erasing the original regioselective deuteration pattern obtained in solution. 相似文献
736.
Cornelia Weiss Joachim Knoth Heinrich Schwenke Holm Geisler Jürgen Lerche Rüdiger Schulz Hans-Jürgen Ullrich 《Mikrochimica acta》2000,133(1-4):65-68
The actual detection limits of total reflection X-ray fluorescence (TXRF) are determined and compared to those of destructive
physical analytical methods like secondary ion mass spectrometry (SIMS) and chemical methods like vapour phase decomposition
in combination with inductively coupled plasma-mass spectrometry (VPD-ICP-MS). The elements Ca, Ti, Cr, Fe, Cu were analyzed
on a Si wafer with 10 nm thermal oxide using TXRF and VPD-ICP-MS. The deviation of the TXRF and the VPD-ICP-MS results is
less than 30%. The thickness, composition and density of a Co/Ti two-layer stack were determined using angle dependent total
reflection and grazing incidence X-ray fluorescence (A-TXRF). The obtained data were compared with X-ray reflectometry (XRR)
and energy filtered transmission electron microscopy (EFTEM). The agreement between TEM and A-TXRF is excellent for the determination
of the thickness of the metal layers. From these results we conclude, that A-TXRF permits the accurate determination of composition,
thickness and density of thin metallic layers.
The results are discussed regarding detection efficiency, acquisition time, accuracy and reproducibility. 相似文献
737.
Tkachenko NH Yaremko ZM Bellmann C Soltys MM 《Journal of colloid and interface science》2006,299(2):686-695
The influence of concentration of nonionic TRITON X-100 and anionic ATLAS G-3300 surfactants, and pH of medium on the size and zeta-potential of TiO2 particles in the water suspensions has been studied. Suspensions have been prepared by mixing of the titanium dioxide in the suitable mediums at 10 min and 6 h correspondingly. It was established, that the duration of mixing of the suspensions has an essential influence on the dependence of zeta-potential and size of particles versus concentration of surfactant. However, the duration of mixing does not influence the dependence of electrical conductivity and pH of the suspensions on concentration of surfactant. It is shown that anionic ATLAS G-3300 surfactant is more effective stabilizator of aqueous suspensions of titanium dioxide, than nonionic surfactants of TRITON X-100. It is found that hydrophobic interaction has important role in the processes of stabilization of suspensions for nonionic surfactant, and for anionic surfactant--moving of psi(delta)-planes into solution's depth. 相似文献
738.
739.
We here present a strategy for reliable prediction of elastic properties from X-ray attenuation coefficients visualized in Computer Tomographic images, as basis for Finite Element models. By example, we show the distribution of the axial normal stress throughout a human mandible, due to a bite on the leftmost premolar. Remarkably, this distribution is not heavily altered if we replace the inhomogeneous material distribution by one discerning merely cortical and trabecular bone, but it is strongly affected by the consideration of material anisotropy. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
740.
Cornelia Kasper 《Chemie in Unserer Zeit》2005,39(6):394-401
The increased expectation of life of the people in the developed nations has enhanced the needs for permanent or temporal substitutions of deseased, injured, or aged organs and tissues. This is one of the great challenges the medicine presently faces. The regenerative medicine comprises developments and applications in the fields of implants, cell‐based therapies and tissue engineering. 相似文献