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121.
M. Ayranov U. Krähenbühl S. Röllin M. Burger 《Journal of Radioanalytical and Nuclear Chemistry》2009,279(2):475-480
We applied three techniques (DF-ICP-MS, PERALS and alpha-spectrometry) for the determination of minor actinides at environmental
levels. For each method the limit of detection and the resolution were estimated in order to study the content and isotopic
composition of the actinides. Two international reference materials, IAEA-135 (Irish Sea Sediment) and IAEA-300 (Baltic Sea
sediment) were analyzed for activity concentrations of 238Pu, 239Pu, 240Pu, 241Pu and 241Am. The sensitivities of the three determination techniques were compared. 相似文献
122.
Julia Schöffel Andrey Yu. Rogachev Dr. Serena DeBeer George Dr. Peter Burger Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(26):4734-4738
An N for Ir : The synthesis and X‐ray crystal structure of a late‐transition‐metal complex with a terminal nitrido ligand and its hydrogenation to the related amido complex are reported (see scheme).
123.
A hyperspectral image in the near infrared contains thousands of position-referenced spectra. After imaging reference materials of known composition it is possible to build Partial Least Squares (PLS) regression models for predicting unknown compositions from new images or spectra. In this paper a comparison is made between spectra from a hyperspectral image and spectra from two spectrometers: a scanning grating instrument with rotating sample holders and an FT-NIR instrument utilizing a fiber-optic probe. The raw spectra and the quality of the PLS calibration models and predictions are compared. Two sample datasets consist of a set of 13 designed artificial mixtures of pure constituents and a selection of 13 sampled cheeses. The prediction error from the hyperspectral image spectra is between that of the two spectrometers. For a typical food sample, the average bias [and replicate standard deviation] was -0.6% [0.5%] for protein and -0.2% [1.3%] for fat. Comparable values for the best spectrometer were -0.2% bias for protein and -0.5% for fat. Some of the advantages of working with hyperspectral images are highlighted: the simultaneous exploration of representations of both spectral and spatial data, and the analysis of concentration profiles and concentration maps all contribute to better characterization of organic and biological materials. 相似文献
124.
A better understanding of cosmic-ray modulation in the heliosphere can only be gained through a proper understanding of the effects of turbulence on the diffusion and drift of cosmic rays. We present an ab initio model for cosmic-ray modulation, incorporating for the first time the results yielded by a two-component turbulence transport model. This model is solved for periods of minimum solar activity, utilizing boundary values chosen so that model results are in fair to good agreement with spacecraft observations of turbulence quantities, not only in the solar ecliptic plane but also along the out-of-ecliptic trajectory of the Ulysses spacecraft. These results are employed as inputs for modelled slab and 2D turbulence energy spectra. The latter spectrum is chosen based on physical considerations, with a drop-off at the very lowest wavenumbers commencing at the 2D outerscale. There currently exist no models or observations for this quantity, and it is the only free parameter in this study. The modelled turbulence spectra are used as inputs for parallel mean free path expressions based on those derived from quasi-linear theory and perpendicular mean free paths from extended nonlinear guiding center theory. Furthermore, the effects of turbulence on cosmic-ray drifts are modelled in a self-consistent way, employing a recently developed model for drift along the wavy current sheet. The resulting diffusion coefficients and drift expressions are applied to the study of galactic cosmic-ray protons and antiprotons using a three-dimensional, steady-state cosmic-ray modulation code, and sample solutions in fair agreement with multiple spacecraft observations are presented. 相似文献
125.
Kenfack CA Klymchenko AS Duportail G Burger A Mély Y 《Physical chemistry chemical physics : PCCP》2012,14(25):8910-8918
The electronic transitions occurring in 4-(N,N-dimethylamino)-3-hydroxyflavone (DMAF) and 2-furanyl-3-hydroxychromone (FHC) were investigated using the TDDFT method in aprotic and protic solvents. The solvent effect was incorporated into the calculations via the PCM formalism. The H-bonding between solute and protic solvent was taken into account by considering a molecular complex between these molecules. To examine the effect of the H-bond on the ESIPT reaction, the absorption and emission wavelengths as well as the energies of the different states that intervene during these electronic transitions were calculated in acetonitrile, ethanol and methanol. The calculated positions of the absorption and emission wavelengths in various solvents were in excellent agreement with the experimental spectra, validating our approach. We found that in DMAF, the hydrogen bonding with protic solvents makes the ESIPT reaction energetically unfavourable, which explains the absence of the ESIPT tautomer emission in protic solvents. In contrast, the excited tautomer state of FHC remains energetically favourable in both aprotic and protic solvents. Comparing our calculations with the previously reported time-resolved fluorescence data, the ESIPT reaction of DMAF in aprotic solvents is reversible because the emitting states are energetically close, whereas in FHC, ESIPT is irreversible because the tautomer state is below the corresponding normal state. Therefore, the ESIPT reaction in DMAF is controlled by the relative energies of the excited states (thermodynamic control), while in FHC the ESIPT is controlled probably by the energetic barrier (kinetic control). 相似文献
126.
The bonding situation and energetics of the N-O bond in a series of amine-N-oxides, Ph(x)(CH(3))(3-x)N-O, where x = 0-3, were analyzed experimentally and theoretically. There is a notable nearly linear decrease of the N-O bond dissociation energies (BDEs) for this series with an increasing number of phenyl groups x. This was investigated experimentally by X-ray high angle multipole refinement techniques in combination with subsequent topological analysis of the electron density for the representative (CH(3))(2)PhN-O, 2, and complementary theoretical calculations at the DFT and multireference CASSCF and MR-perturbation theory (MCQDPT2) levels. Both the theoretical and experimental results unambiguously revealed a polar covalent σ-bond for the N-O bond with an essentially identical bonding situation for all amine-N-oxides studied. This apparent disparity between the bonding situation and the trend of BDEs is attributed to the large differences of the relaxation energies of the corresponding amines Ph(x)(CH(3))(3-x)N, (x = 0-3), respectively, the required preparation energies (ΔE(prep)) for the reverse N-O bond forming process. The detailed theoretical analysis of the amines allowed us to trace the trend of larger values of ΔE(prep) for a higher number of phenyl groups x to an increase of n(N) → π*(C-C) delocalization interactions. 相似文献
127.
Meingast C Hardy F Heid R Adelmann P Böhmer A Burger P Ernst D Fromknecht R Schweiss P Wolf T 《Physical review letters》2012,108(17):177004
Thermal expansion data are used to study the uniaxial pressure dependence of the electronic-magnetic entropy of Ba(Fe(1-x)Co(x))2As2. Uniaxial pressure is found to be proportional to doping and, thus, also an appropriate tuning parameter in this system. Many of the features predicted to occur for a pressure-tuned quantum critical system, in which superconductivity is an emergent phase hiding the critical point, are observed. The electronic-magnetic Grüneisen parameters associated with the spin-density wave and superconducting transitions further demonstrate an intimate connection between both ordering phenomena. 相似文献
128.
JA Drewry E Duodu A Mazouchi P Spagnuolo S Burger CC Gradinaru P Ayers AD Schimmer PT Gunning 《Inorganic chemistry》2012,51(15):8284-8291
Src Homology 2 (SH2) domains are the paradigm of phosphotyrosine (pY) protein recognition modules and mediate numerous cancer-promoting protein-protein complexes. Effective SH2 domain mimicry with pY-binding coordination complexes offers a promising route to new and selective disruptors of pY-mediated protein-protein interactions. We herein report the synthesis and in vitro characterization of a library of coordination complex SH2 domain proteomimetics. Compounds were designed to interact with phosphopeptides via a two-point interaction, principally with pY, and to make secondary interactions with pY+2/3, thereby achieving sequence-selective discrimination. Here, we report that lead mimetics demonstrated high target phosphopeptide affinity (K(a) ~ 10(7) M(-1)) and selectivity. In addition, biological screening in various tumor cells for anticancer effects showed a high degree of variability in cytotoxicity among receptors, which supported the proposed two-point binding mode. Several receptors potently disrupted cancer cell viability in breast cancer, prostate cancer, and acute myeloid leukemia cell lines. 相似文献
129.
Qi Li Joel Q. Grim K. B. Ucer A. Burger G. A. Bizarri W. W. Moses R. T. Williams 《固体物理学:研究快报》2012,6(8):346-348
Several outstanding questions, including why complex halide scintillator host structures allow higher light yield and flatter electron energy response than simple monovalent metal halides, have remained unanswered by current models of luminescence in dense ionization tracks. Our measurements of nonlinear quenching kinetic order, recent literature on hot‐electron transport in scintillators, and calculations presented here of hot‐electron velocity from band structure of SrI2 and NaI, lead us to expand our previously described diffusion and nonlinear quenching model to include hot‐electron transport. Trends in multivalent versus monovalent metal halides, heavier versus lighter halides, and halides versus oxides versus semiconductors can be predicted based on optical phonon frequency, thermalized band edge mobilities, velocity in the upper conduction bands, and hole self‐trapping. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
130.
Kattrin Arning Martin Burger Robert S. Eisenberg Heinz W. Engl Lin He 《PAMM》2007,7(1):1120801-1120802
Ion channels are proteins with a hole down theirmiddle that allow ions to move across otherwise impermeable cellmembranes, thereby controlling many important physiological functions. The transport process of the ions can be described using the Poisson-Nernst-Plank equations, a system of coupled nonlinear partial differential equations. Based on this model we derive a simplified surrogate model that captures the main features of the associated current-voltage curves of the ion channel. This surrogate model is then used to identify individual channel parameters based on current data. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献