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961.
Arno R. Bohm 《International Journal of Theoretical Physics》2003,42(10):2317-2338
These notes review a consistent and exact theory of quantum resonances and decay. Such a theory does not exist in the framework of traditional quantum mechanics and Dirac's formulation. But most of its ingredients have been familiar entities, like the Gamow vectors, the Lippmann-Schwinger (in- and out-plane wave) kets, the Breit-Wigner (Lorentzian) resonance amplitude, the analytically continued S-matrix, and its resonance poles. However, there are inconsistencies and problems with these ingredients: exponential catastrophe, deviations from the exponential law, causality, and recently the ambiguity of the mass and width definition for relativistic resonances. To overcome these problems the above entities will be appropriately defined (as mathematical idealizations). For this purpose we change just one axiom (Hilbert space and/or asymptotic completeness) to a new axiom which distinguishes between (in-)states and (out)observables using Hardy spaces. Then we obtain a consistent quantum theory of scattering and decay which has the Weisskopf-Wigner methods of standard textbooks as an approximation. But it also leads to time-asymmetric semigroup evolution in place of the usual, reversible, unitary group evolution. This, however, can be interpreted as causality for the Born probabilities. Thus we obtain a theoretical framework for the resonance and decay phenomena which is a natural extension of traditional quantum mechanics and possesses the same arrow-of-time as classical electrodynamics. When extended to the relativistic domain, it provides an unambiguous definition for the mass and width of the Z-boson and other relativistic resonances. 相似文献
962.
A concise stereoselective 3-step conversion of methyl α-d-mannopyranoside to α-d-2,3,4,6-tetra-O-methyl-mannosylacetic acid is described. After methylation of the alcohol functions, an allylation is performed. The resulting alkene undergoes oxidative cleavage to the acid, an alkylated C-sugar, appropriate for attachment to peptides or other drug candidates for solubility enhancement. 相似文献
963.
Yyves Verbandt Bart Verwilghen Peter Cloetens Luk Van Kempen Hugo Thienpont Irina Veretennicoff Greta Van Vinckenroy W. Patrick De Wilde Marc R. H. Voet 《Optical Review》1997,4(1):A75-A79
An analytical model for the pressure and strain sensitivity of highly-birefringent fibers is proposed which is in excellent agreement with numerical calculations. Results of polarimetry and coherence-multiplexing experiments are presented and a novel method for accurately splicing this kind of fibers is demonstrated. 相似文献
964.
Arno F. Stassen Eugenia Martínez Ferrero Carlos Giménez-Saiz Eugenio Coronado Jaap G. Haasnoot Jan Reedijk 《Monatshefte für Chemie / Chemical Monthly》2003,134(2):255-264
Summary. The synthesis, crystal structure and physical properties of the complex obtained from the reaction between the polyoxometalate
anion [PMo12O40]3−, copper(II) and the ligand 1-(2-chloroethyl)tetrazole (teec) are described. This compound has been synthesized as a model for designing materials containing both magnetic polyoxometalate
anions and iron(II) spin-crossover cations.
The compound, with formula [Cu(teec)5]2[Cu(teec)6][PMo12O40]2·2H2O, consists of alternating layers of polyoxometalates and cationic complexes. Both, five and six coordinated Cu(II) ions are
present, each positioned in different layers. Despite these layers having a similar width, the layer of pentacoordinated Cu(II)
ions contains twice as many cationic complexes as the layer of hexacoordinated Cu(II) ions. This unusual coexistence of complexes
with different coordination number is most likely caused by the steric hindrance induced by the bulky polyoxometalates in
the layer of pentacoordinated Cu(II) which prevents the presence of a sixth teec ligand.
Corresponding author. E-mail: haasnoot@chem.leidenuniv.nl
Received June 5, 2002; accepted June 12, 2002 相似文献
965.
966.
Hugo Bianchi Horacio R. Corti Roberto Fernandez-Prini 《Journal of solution chemistry》1992,21(11):1107-1114
The conductivities of dilute aqueous mixtures of NaCl-MgCl2 have been determined at various ionic compositions and at 25°C. These results are used to assess the applicability of modern theories of electrolytic conductivity. 相似文献
967.
We present a recent experiment [1] using space-like beamsplitters in motion revealing a new feature of quantum nonlocality:
The correlations caused by two-particle quantum entanglement are not only independent of distance (as we already know from
the conventional Bell-type experiments) but also independent of the time-ordering between the two single-photon measurements.
Hence, it seems impossible to cast them in any real time ordering and maintain a causal explanation in which an earlier event
influences a later one by arbitrarily fast communication. 相似文献
968.
969.
Dongre C van Weerd J Besselink GA Vazquez RM Osellame R Cerullo G van Weeghel R van den Vlekkert HH Hoekstra HJ Pollnau M 《Lab on a chip》2011,11(4):679-683
We introduce a principle of parallel optical processing to an optofluidic lab-on-a-chip. During electrophoretic separation, the ultra-low limit of detection achieved with our set-up allows us to record fluorescence from covalently end-labeled DNA molecules. Different sets of exclusively color-labeled DNA fragments-otherwise rendered indistinguishable by spatio-temporal coincidence-are traced back to their origin by modulation-frequency-encoded multi-wavelength laser excitation, fluorescence detection with a single ultrasensitive, albeit color-blind photomultiplier, and Fourier analysis decoding. As a proof of principle, fragments obtained by multiplex ligation-dependent probe amplification from independent human genomic segments, associated with genetic predispositions to breast cancer and anemia, are simultaneously analyzed. 相似文献
970.
Gowda CM Vasconcelos F Schwartz E van Eck ER Marsman M Cornelissen JJ Rowan AE de Wijs GA Kentgens AP 《Physical chemistry chemical physics : PCCP》2011,13(28):13082-13095
Carbazole functionalized polyisocyanides are known to exhibit excellent electronic properties (E. Schwartz, et al., Chemistry of Materials, 2010, 22, 2597). The functionalities and properties of such materials crucially depend on the organization and stability of the polymer structure. We combine solid-state Nuclear Magnetic Resonance (NMR) experiments with first-principles calculations of isotropic chemical shifts, within the recently developed converse approach, to rationalize the origin of isotropic chemical shifts in the crystalline monomer l-isocyanoalanine 2-(9H-carbazol-9-yl) ethyl amide (monomer 1) and thereby gain insight into the structural organization of its polymer (polymer 2). The use of state-of-the-art solid-state NMR experiments combined with Density Functional Theory (DFT) based calculations allows an unambiguous assignment of all proton and carbon resonances of the monomer. We were able to identify the structure stabilising interactions in the crystal and understand the influence of the molecular packing in the crystal structure on the chemical shift data observed in the NMR spectra. Here the Nuclear Independent Chemical Shift (NICS) approach allows discriminating between 'physical' interactions amongst neighboring molecules such as ring-current effects and 'chemical' interactions such as hydrogen bonding. This analysis reveals that the isocyanide monomer is stabilized by multiple hydrogen bonds such as a bifurcated hydrogen bond involving -N-H, -C-H and O=C- moieties and Ar-H···C≡N- hydrogen bonding (Ar = aromatic group). Based on the geometrical arrangement it is postulated that the carbazole units are involved in the weak σ-π interactions giving rise to a Herringbone packing of the molecules. The chemical shift analysis of the polymer spectra readily establishes the existence of N-H···O=C hydrogen bonds despite the limited resolution exhibited by the polymer spectra. It is also elucidated that the relative arrangement of the carbazole units in the polymer differs significantly from that of the monomer. 相似文献