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671.
In this paper we examine the significance of gestures in a setting where two students try to make sense of, and solve, mathematical problems involving speed and time. We are particularly interested in exploring the claims that gesture serves various signaling functions in collaborative problem-solving communication generally and in mathematics problem-solving more specifically, and that gesture has a diagnostic role for the collaborators and for teachers. The overall purpose of our paper is to illustrate the integral role of gesture in dyadic communication where core problem domain concepts may be difficult to explicate. 相似文献
672.
C J Creighton C H Reynolds D H Lee G C Leo A B Reitz 《Journal of the American Chemical Society》2001,123(50):12664-12669
Nicotinic acetylcholine receptors (nAChRs) are membrane-bound, pentameric ligand-gated ion channels associated with a variety of human disorders such as Alzheimer's disease, Parkinson's disease, schizophrenia, and pain. Most known nAChRs contain an unusual eight-membered disulfide-containing cysteinyl-cysteine ring, ox-[Cys-Cys], as does the soluble acetylcholine binding protein (AChBP) found in the snail Lymnaea stagnalis. The cysteinyl-cysteine ring is located in a region implicated in ligand binding, and conformational changes involving this ring may be important for modulation of nAChR function. We have studied the preferred conformations of Ac-ox-[Cys-Cys]-NH2 by NMR in water and computationally by Monte Carlo simulations using the OPLS-AA force field and GB/SA water model. ox-[Cys-Cys] adopts four distinct low-energy conformers at slightly above 0 degrees C in water. Two populations are dependent on the peptide omega2 dihedral angle, with the trans amide favored over the cis amide by a ratio of ca. 60:40. Two ox-[Cys-Cys] conformers with a cis amide bond (C+ and C-) differ from each other primarily by variation of the chi3 dihedral angle, which defines the orientation of the helicity about the S-S bond (+/- 90 degrees ). Two trans amide conformers have the same S-S helicity (chi3 approximately -90 degrees ), but are distinguished by a backbone rotation about phi2 and psi1 (T- and T'-). The ratio of T-/T'-/C+/C- is 47:15:29:9. The orientation of the pendant moieties from the eight-membered ring is more compact for the major trans conformer (T-) than for the extended conformations adopted by T'-, C+, and C-. These conformational preferences are also observed in tetrapeptide and undecapeptide fragments of the human alpha7 subtype of the nAChR that contains the ox-[Cys-Cys] unit. Conformer T- is nearly identical to the conformation seen in the X-ray structure of ox-[Cys(187)-Cys(188)] found in the unliganded AChBP, and is a Type VIII beta-turn. 相似文献
673.
Peter J. Branton Philip A. Reynolds Andrew Studer Kenneth S.W. Sing John W. White 《Adsorption》1999,5(1):91-96
Adsorption isotherms of carbon tetrachloride at temperatures between 273 and 323 K have been determined on the pure silica form of MCM-41 of pore diameter ca. 3.4 nm. All isotherms were of Type V, the isotherms at 273, 288 and 303 K showing hysteresis loops, whereas the isotherm at 323 K was completely reversible. Despite the questionable validity of the Kelvin equation when applied to narrow mesopores, changes in the relative pressure positions of capillary condensation and evaporation as a function of the temperature appear to be well described. Neutron diffraction measurements at 200 and 273 K show significant changes in the physical properties of the adsorbed CCl4 in the MCM-41 from those of bulk adsorbate. The results also suggest a highly heterogeneous surface and appear to show some flexibility in the pore walls upon pore filling. The conditions required for first order reversible capillary condensation are discussed. 相似文献
674.
T.W. Hijmans P.W.H. Pinkse A.P. Mosk M. Weidemüller M.W. Reynolds J.T.M. Walraven C. Zimmermann 《Hyperfine Interactions》2000,127(1-4):175-180
We show that resonant enhanced two photon spectroscopy is a very powerful and promising diagnostic method for trapped atomic
hydrogen and antihydrogen. This method, in which photons of different wavelengths are used to excite H atoms from the 1S to
the 3D or 3S level, uses the resonant enhancement of the intermediate 2P level to obtain high sensitivity while at the same
time offering potentially much higher spectral resolution than single photon (Lyman α) excitation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
675.
Jeffery S. Reynolds Tamara L. Troy Ralf H. Mayer Alan B. Thompson David J. Waters Karen K. Cornell Paul W. Snyder Eva M. Sevick-Muraca 《Photochemistry and photobiology》1999,70(1):87-94
We present near-infrared frequency-domain photon migration imaging for the lifetime sensitive detection and localization of exogenous fluorescent contrast agents within tissue-simulating phantoms and actual tissues. We employ intensity-modulated excitation light that is expanded and delivered to the surface of a tissue or tissue-simulating phantom. The intensity-modulated fluorescence generated from within the volume propagates to the surface and is collected using a gain-modulated image-intensified charge-coupled device camera. From the spatial values of modulation amplitude and phase of the detected fluorescent light, micromolar volumes of diethylthiatricarbocyanine iodide (tau = 1.17 ns) and indocyanine green (ICG) (tau = 0.58 ns) embedded 1.0 cm deep in a tissue phantom are localized and discriminated on the basis of their lifetime differences. To demonstrate the utility of frequency-domain fluorescent measurements for imaging disease, we image the fluorescence emitted from the surface of in vivo and ex vivo canine mammary gland tissues containing lesions with preferential uptake of ICG. Pathology confirms the ability to detect spontaneous mammary tumors and regional lymph nodes amidst normal mammary tissue and fat as deep as 1.5 cm from the tissue surface. 相似文献
676.
677.
Thomas Raistrick Matthew Reynolds Helen F. Gleeson Johan Mattsson 《Molecules (Basel, Switzerland)》2021,26(23)
Liquid Crystal Elastomers (LCEs) combine the anisotropic ordering of liquid crystals with the elastic properties of elastomers, providing unique physical properties, such as stimuli responsiveness and a recently discovered molecular auxetic response. Here, we determine how the molecular relaxation dynamics in an acrylate LCE are affected by its phase using broadband dielectric relaxation spectroscopy, calorimetry and rheology. Our LCE is an excellent model system since it exhibits a molecular auxetic response in its nematic state, and chemically identical nematic or isotropic samples can be prepared by cross-linking. We find that the glass transition temperatures () and dynamic fragilities are similar in both phases, and the -dependence of the relaxation shows a crossover at the same for both phases. However, for , the behavior becomes Arrhenius for the nematic LCE, but only more Arrhenius-like for the isotropic sample. We provide evidence that the latter behavior is related to the existence of pre-transitional nematic fluctuations in the isotropic LCE, which are locked in by polymerization. The role of applied strain on the relaxation dynamics and mechanical response of the LCE is investigated; this is particularly important since the molecular auxetic response is linked to a mechanical Fréedericksz transition that is not fully understood. We demonstrate that the complex Young’s modulus and the relaxation time remain relatively unchanged for small deformations, whereas for strains for which the auxetic response is achieved, significant increases are observed. We suggest that the observed molecular auxetic response is coupled to the strain-induced out-of-plane rotation of the mesogen units, in turn driven by the increasing constraints on polymer configurations, as reflected in increasing elastic moduli and relaxation times; this is consistent with our recent results showing that the auxetic response coincides with the emergence of biaxial order. 相似文献
678.
The synthesis, characterization and electrochemical polymerization, along with redox switching behavior of the resultant polymers, of 1,4-bis(2-(3,4-ethylenedioxy)thienyl)–2,5-difluorobenzene ( 1 ) and 1,4-bis(2-thienyl)–2,5-difluorobenzene ( 2 ) is presented. Compounds 1 and 2 were synthesized by a Pd°-catalyzed cross-coupling and in good yields (85% and 84%, respectively). Both monomers electropolymerize to form electroactive redox switchable films, with the more electron-rich 3,4-ethylenedioxythiophene derivative polymerizing and switching at lower potentials. The electronic band gaps were determined to be 1.9 eV for P1 and 2.3 eV for P2. Thin films of P1 and P2 were found to be electrochromic and exhibit color changes of red-to-blue/black for P1 and yellow-to-black for P2. These results are compared with various substituted bis(heterocycle)benzene derivatives in order to present a series of structure to property relationships. © 1998 John Wiley & Sons, Ltd. 相似文献
679.
680.