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排序方式: 共有5271条查询结果,搜索用时 15 毫秒
941.
CM Silva MF Duarte ML Mira MH Florêncio K Versluis AJ Heck 《Rapid communications in mass spectrometry : RCM》1999,13(12):1098-1103
Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
942.
J. Ellis G.G. Ross J. Williams 《The European Physical Journal C - Particles and Fields》1999,10(3):443-460
We suggest that the pseudo-rapidity cut dependence of diffractive deep-inelastic scattering events at HERA may provide a
sensitive test of models of diffraction. A comparison with the experimental cross section shows that the Donnachie-Landshoff
model and a simple two-gluon exchange model of the pomeron model are disfavoured. However a model with a direct coupling of
the pomeron to quarks is viable for a harder quark–pomeron form factor, as is a model based on the leading-twist operator
contribution. We also consider a direct-coupling scalar pomeron model. We comment on the implications of these results for
the determination of the partonic structure of the pomeron.
Received: 5 March 1999 / Published online: 3 August 1999 相似文献
943.
We give sufficient conditions for the existence of positive solutions to some semilinear elliptic equations in bounded domains
with Dirichlet boundary conditions. We impose mild conditions on the domains and lower order (nonlinear) coefficients of
the equations in that the bounded domains are only required to satisfy an exterior cone condition and we allow the coefficients
to have singularities controlled by Kato class functions. Our approach uses an implicit probabilistic representation, Schauder's
fixed point theorem, and new a priori estimates for solutions of the corresponding linear elliptic equations. In the course
of deriving these a priori estimates we show that the Green functions for operators of the form on D are comparable when one modifies the drift term b on a compact subset of D. This generalizes a previous result of Ancona [2], obtained under an condition on b, to a Kato condition on .
Received: 21 April 1998 / in final form 26 March 1999 相似文献
944.
X. Chen M. C. Davies C. J. Roberts S. J. B. Tendler P. M. Williams N. A. Burnham 《Surface science》2000,460(1-3):292-300
Tapping mode (TM, also called intermittent contact mode) atomic force microscopy (AFM) has been routinely used in many laboratories. However, consistent or deliberate control of measuring conditions and interpretation of results are often difficult. In this article, we demonstrate how measurement parameters (drive frequency, cantilever stiffness and oscillation amplitude) affect the tapping tip's state. This has been done by systematic dynamic force measurements performed on mica and polystyrene surfaces together with computer simulations. Our study shows the following results. (1) Weaker cantilevers, smaller amplitude and higher drive frequency (around the resonance) lead to an extension of the attractive region (greater phase lag) in amplitude–phase–distance curves and thus can help to achieve stable high-setpoint TM imaging with minimal tip–sample pressure. (2) Bistability of tapping tips often exists and may cause height artefacts if the setpoint falls in the bistable region. (3) Tapping tips with high vibrating energy (stiff cantilevers and large amplitude) driven at resonance are only slightly perturbed by tip–sample interactions and usually remain monostable during the sweep of the scanner position. This can help to achieve good phase contrast without significant artefacts when the setpoint falls in a continuous negative–positive phase shift transition region. (4) Low energy cantilevers (compliant cantilevers and small amplitude) usually result in large phase shift and can be used to acquire large phase contrast images. However, height artefacts will occur when the setpoint falls in the bistable region usually existing for such cantilevers. (5) Computer simulations are useful in understanding the bistability in dynamic force curves and determining either material properties or the optimal imaging parameters. 相似文献
945.
946.
Patricia A. M. Williams Evelina G. Ferrer Karina A. Pasquevich Enrique J. Baran Zulema Chaia Eduardo E. Castellano Oscar E. Piro 《无机化学与普通化学杂志》2000,626(12):2509-2514
The crystal structure of the complexes [Cu(sac)2(bzim)2(H2O)] ( 1 ) and [Cu(sac)2(bzim)(H2O)(EtOH)] · 2 EtOH ( 2 ) (sac = saccharinate anion; bzim = benzimidazole; EtOH = ethanol) was determined by single crystal X‐ray diffractometry. Complex 1 crystallizes in the monoclinic C2/c space group with Z = 8 whereas complex 2 belongs to the triclinic P1 space group with Z = 2. Room temperature magnetic susceptibilities as well as electronic and IR spectra of both complexes were discussed. Their thermal behaviour was investigated by means of TG and DTA methods. 相似文献
947.
948.
Masumi Asakawa Peter R. Ashton Vincenzo Balzani Alberto Credi Christoph Hamers Gunter Mattersteig Marco Montalti Andrew N. Shipway Neil Spencer J. Fraser Stoddart Malcolm S. Tolley Margherita Venturi Andrew J. P. White David J. Williams 《Angewandte Chemie (International ed. in English)》1998,37(3):333-337
A mechanical switch in a [2]catenane , made up of a cyclobis(paraquat-p-phenylene) tetracation interlocked with a macrocyclic polyether containing a redox-active tetrathiafulvalene (TTF) unit and a 1,5-dioxynaphthalene ring system, can be thrown either chemically or electrochemically. The neutral TTF unit resides “inside” the tetracationic cyclophane in the reduced state and “alongside” it in the oxidized species (TTF+/ TTF2+). Switching between the reduced (I4+) and oxidized state (I5+(I6+)) is accompanied by a dramatic color change. 相似文献
949.
Ramn Vilar D. Michael P. Mingos Andrew J. P. White David J. Williams 《Angewandte Chemie (International ed. in English)》1998,37(9):1258-1261
An anion is encapsulated in the center of the new cage compound [Ni6(atu)8X]X3 (X=Cl—for the structure see picture—or Br; Hatu=amidinothiourea). A combination of Lewis acid–base and hydrogen-bonding interactions cause the square-planar [Ni(Hatu)2]2+ units, after deprotonation, to assemble to form this compound. A remarkable feature is the anion dependence of the cage formation; nitrate, acetate, and perchlorate are unsuitable as templates. 相似文献
950.
Emako Miyoshi Tomohisa Takaya Katsuyoshi Nishinari Peter A. Williams 《Macromolecular Symposia》1997,120(1):271-280
The interaction between gellan gum (GELL) and konjac glucomannan (KGM) with and without sodium chloride, potassium chloride, calcium chloride and magnesium chloride has been monitored using mechanical spectroscopy and differential scanning calorimetry (DSC). The rheological results indicated that the synergism occurred at sufficient low temperatures where individual helices of GELL molecules were sufficiently aggregated. With progressive addition of monovalent cations, storage shear modulus G' and loss shear modulus G” for mixtures gradually increased, and not only the helix-coil transition temperature of GELL molecules in mixtures but also the sol-gel transition temperature for mixtures shifted to higher temperatures with increasing concentration of salts. Moreover, in the presence of sufficient monovalent cations, mixtures formed an elastic gel with large thermal hysteresis. In the presence of divalent cations, the synergistic interaction was promoted up to a certain concentration, however, with more progressive addition of divalent cations, the main structure formed by aggregates of GELL helices would be smaller, so that mixtures could not form a gel in the presence of excessive divalent cations. DSC results indicated that the intermolecular binding complexes between GELL and KGM molecules would not occur, but KGM markedly influenced the disorder-order transition of GELL molecules. We have suggested that KGM was attached to the surface of large aggregates of GELL helices, and since cations promote GELL self-aggregation by a screening effect, the synergistic interaction between GELL and KGM was promoted with increasing concentration of salts. However, excessive divalent cations formed various aggregates of GELL helices with different thermal stabilities, so that the phase-separation in GELL/KGM mixtures was promoted in the presence of excessive divalent cations. 相似文献