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121.
The effect of the inclusion of the exact exchange into self-interaction corrected generalized gradient approximation density
functional theory (GGA-DFT) for the simplest hydrogen abstraction reaction, H + H2 → H3 → H2 + H, is presented using a triple-zeta augmented 6-311++G(d,3pd) basis set. The introduction of the self-interaction correction has a considerably larger effect on molecular geometry and
vibrational frequencies than the inclusion of the exact exchange. We investigate the influence of the self-interaction error
on the shape of the potential energy surface around the transition state of the hydrogen abstraction reaction. The decomposition
of the self-interaction error into correlation and exchange parts shows that the exchange self-interaction error is the main
component of the energy barrier error. The best agreements with the experimental barrier height were achieved by self-interaction
corrected B3LYP, B-LYP and B3PW functionals with errors of 1.5, 2.9 and 3.0 kcal/mol, respectively.
Received: 13 August 1997 / Accepted: 14 November 1997 相似文献
122.
Dual-functionalised ionic liquids: synthesis and characterisation of imidazolium salts with a nitrile-functionalised anion 总被引:1,自引:0,他引:1
Zhao D Fei Z Ohlin CA Laurenczy G Dyson PJ 《Chemical communications (Cambridge, England)》2004,(21):2500-2501
A series of 'dual-functionalised' ionic liquids, comprising imidazolium cations with various functionalities and the nitrile functionalised anion [CH3CH(BF3)CH2CN]- have been prepared; some exhibit very low viscosities-a highly valuable property in many applications. 相似文献
123.
Kovacs J Joo F Benyei AC Laurenczy G 《Dalton transactions (Cambridge, England : 2003)》2004,(15):2336-2340
In aqueous solutions under mild conditions, [Ru(H(2)O)(6)](2+) was reacted with various water-soluble tertiary phosphines. As determined by multinuclear NMR spectroscopy, reactions with the sulfonated arylphosphines L =mtppms, ptppms and mtppts yielded only the mono- and bisphosphine complexes, [Ru(H(2)O)(5)L](2+), cis-[Ru(H(2)O)(4)L(2)](2+), and trans-[Ru(H(2)O)(4)L(2)](2+) even in a high ligand excess. With the small aliphatic phosphine L = 1,3,5-triaza-7-phosphatricyclo-[3.3.1.1(3,7)]decane (pta) at [L]:[Ru]= 12:1, the tris- and tetrakisphosphino species, [Ru(H(2)O)(3)(pta)(3)](2+), [Ru(H(2)O)(2)(pta)(4)](2+), [Ru(H(2)O)(OH)(pta)(4)](+), and [Ru(OH)(2)(pta)(4)] were also detected, albeit in minor quantities. These results have significance for the in situ preparation of Ru(II)-tertiary phosphine catalysts. The structures of the complexes trans-[Ru(H(2)O)(4)(ptaMe)(2)](tos)(4)x2H(2)O, trans-[Ru(H(2)O)(4)(ptaH)(2)](tos)(4)[middle dot]2H(2)O, and trans-mer-[RuI(2)(H(2)O)(ptaMe)(3)]I(3)x2H(2)O, containing protonated or methylated pta ligands (ptaH and ptaMe, respectively) were determined by single crystal X-ray diffraction. 相似文献
124.
Cheng X Canavan HE Stein MJ Hull JR Kweskin SJ Wagner MS Somorjai GA Castner DG Ratner BD 《Langmuir : the ACS journal of surfaces and colloids》2005,21(17):7833-7841
Surface-immobilized poly(N-isopropyl acrylamide) (pNIPAM) is currently used for a wide variety of biosensor and biomaterial applications. A thorough characterization of the surface properties of pNIPAM thin films will benefit those applications. In this work, we present analysis of a plasma-polymerized NIPAM (ppNIPAM) coating by multiple surface analytical techniques, including time-of-flight secondary-ion mass spectrometry (ToF-SIMS), contact angle measurement, atomic force microscopy (AFM), and sum frequency generation (SFG) vibrational spectroscopy. ToF-SIMS data show that the plasma-deposited NIPAM polymer on the substrate is cross-linked with a good retention of the monomer integrity. Contact angle results confirm the thermoresponsive nature of the film as observed by a change of surface wettability as a function of temperature. Topographic and force-distance curve measurements by AFM further demonstrate that the grafted film shrinks or swells depending on the temperature of the aqueous environment. A clear transition of the elastic modulus is observed at 31-32 degrees C. The change of the surface wettability and mechanical properties vs temperature are attributed to different conformations taken by the polymer, which is reflected on the outmost surface as distinct side chain groups orienting outward at different temperatures as measured by SFG. The results suggest that a ppNIPAM thin film on a substrate experiences similar mechanical and chemical changes to pNIPAM bulk polymers in solution. The SFG result provides evidence supporting the current theory of the lower critical solution temperature (LCST) behavior of pNIPAM. 相似文献
125.
Steady shear viscosity, dynamic viscosity, dynamic modulus, and normal force were measured via rotational rheometry for concentrated solutions of racemic mixtures of poly(benzyl-glutamate) and poly(benzyl-D-glutamate) in m-cresol. A transition from the isotropic state to liquid-crystalline order with increase in concentration was indicated by optical anisotropy and maxima in all four material functions. This occurred at a critical concentration higher than the Flory prediction. Over a well-defined range of concentrations and shear stresses, some of the liquid-crystalline solutions exhibited negative first normal-stress differences that were not due to inertial effects. 相似文献
126.
127.
P l Herczegh Imre Kov cs L szl Szil gyi Ferenc Sztaricskai
Amaya Berecibar
Claude Riche Ang le Chiaroni Alain Olesker Gabor Lukacs 《Tetrahedron》1994,50(48):13671-13686Diastereoselective hetero Diels-Alder reactions of sugar derived azomethines 4a–4g have been used for the construction of chiral piperidones 6 and 7. Configuration of the major products was 6,1′-threo in every case. The enone system of 6 and 7 was reduced diastereoselectively and subsequently swainsonine-analog hydroxyindolizidines 28–32 were prepared by an intramolecular reductive amination. 相似文献
128.
129.
Jungmee Kang Gabor Erdodi Joseph P. Kennedy Emel Yilgor Iskender Yilgor 《Journal of polymer science. Part A, Polymer chemistry》2009,47(22):6180-6190
Novel polyurethanes consisting of polyisobutylene (PIB)/poly(tetramethylene oxide) (PTMO) or PIB/poly(hexamethylene carbonate) (PC) soft co‐segments in combination with 4,4′‐methylene‐bis(cyclohexyl isocyanate)/1,6‐hexanediol, 1,4‐butanediol, or 1,6‐hexamethylene diamine hard segments exhibit excellent mechanical properties (upto 31 MPa tensile strength with 700% elongation) together with unprecedented oxidative/hydrolytic stability. A structural model of the morphology of these polyurethanes was developed that reflects this combination of properties. The key new elements of our model are H bridges between the PTMO and PC type soft and urethane hard segments, which compatibilize the soft and hard domains, and the presence of large quantities of chemically resistant PIB soft segments that protect the other oxidatively/hydrolytically vulnerable constituents. A variety of FTIR, DSC, SAXS, AFM, and DMTA experiments strongly support the proposed morphological model. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6180–6190, 2009 相似文献
130.
Gabor Erdodi Jungmee Kang Joseph P. Kennedy Emel Yilgor Iskender Yilgor 《Journal of polymer science. Part A, Polymer chemistry》2009,47(20):5278-5290
The synthesis, characterization, and structure–property behavior of polyurethanes containing polyisobutylene (PIB)/poly(tetramethylene oxide) (PTMO) soft co‐segments and bis(4‐isocyanatocyclohexyl)methane (HMDI)/hexanediol (HDO) hard segments is presented. The mechanical (stress/strain, hardness, and hysteresis) properties of these novel polyurethanes were investigated over a broad composition range. PIB‐based polyurethanes with HMDI/HDO hard segments showed better mechanical properties than earlier polyurethanes containing highly crystalline hard segments. The addition of moderate amounts (20% by weight) of PTMO significantly increased both tensile strengths and elongation. In the presence of larger amounts of PIB, these polyurethanes are expected to possess oxidative/hydrolytic/enzymatic stabilities superior to commercially available polyurethanes. These polyurethanes are softer and exhibit hysteresis superior to or comparable with conventional polyurethanes. According to initial thermal studies, these materials show good melt processibility. Overall, the mechanical properties of PIB based hybrid polyurethanes are similar to commercially important polyurethane type biomaterials. Our results show that the incorporation of PTMO segments to PIB‐based polyurethanes significantly improves elastomeric properties. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5278–5290, 2009 相似文献