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821.
822.
An approach to evaluate the second-order exchange-induction energies of symmetry-adapted intermolecular perturbation theory (SAPT) for single-determinant ground-state monomer wavefunctions has been derived. This approach is correct to all orders of the intermonomer overlap, that is, it takes multiple electron exchange between the monomers into account. The resulting formulae can be written in a compact way and implemented efficiently. Here, the method is employed to investigate the performance of the S 2- or single-exchange approximation at the Hartree-Fock-SAPT level. The list of test systems comprises the prototypical van der Waals- and hydrogen-bridge complexes Ne2, Ar–HF, and (H2O)2, but also the systems HeCl?, NeNa+ and Li+F? involving closed-shell ions. It was found that the errors introduced by the S 2-approximation are more pronounced for the second-order exchange-induction energy than for the first-order exchange energy. While these errors tend to be negligible throughout the well region of complexes such as the neon dimer, they start to be significant in the repulsive part of the well regions of systems such as the water dimer, and in particular for the ionic lithium fluoride molecule. The consequences of these findings for the Hartree-Fock level estimate of higher-order induction plus exchange-induction energies, which is frequently employed in SAPT are also discussed. 相似文献
823.
Dr. Yoichi Hoshimoto Keita Ashida Yukari Sasaoka Dr. Ravindra Kumar Prof. Dr. Ken Kamikawa Prof. Dr. Xavier Verdaguer Prof. Dr. Antoni Riera Prof. Dr. Masato Ohashi Prof. Dr. Sensuke Ogoshi 《Angewandte Chemie (International ed. in English)》2017,56(28):8206-8210
The nickel(0)-catalyzed carbonylative cycloaddition of 1,5- and 1,6-ene-imines with carbon monoxide (CO) is reported. Key to this reaction is the efficient regeneration of the catalytically active nickel(0) species from nickel carbonyl complexes such as [Ni(CO)3L]. A variety of tri- and tetracyclic γ-lactams were thus prepared in excellent yields with 100 % atom efficiency. Preliminary results on asymmetric derivatives promise potential in the synthesis of enantioenriched polycyclic γ-lactams. 相似文献
824.
Rafa? Janus Piotr Natkański Anna Wach Marek Drozdek Zofia Piwowarska Pegie Cool Piotr Ku?trowski 《Journal of Thermal Analysis and Calorimetry》2012,110(1):119-125
Thermogravimetry, diffuse reflectance infrared Fourier transform spectroscopy, and X-ray photoelectron spectroscopy (XPS) were used for the studying of thermally induced structural changes of polyacrylonitrile (PAN) deposited on the surface of SBA-15 type mesoporous silica. Polymer was introduced onto the support by the precipitation polymerization of acrylonitrile in aqueous suspension of SBA-15. Low temperature transformation (to 723?K) of the deposited PAN was analyzed. It was found that at about 523?K, exothermic cyclization of polymer chains to the so-called ladder form of PAN occurred. However, the total cyclization of PAN required higher carbonization temperatures, at which gradual dehydrogenation followed by graphitization was initiated. XPS revealed that the cyclic form of PAN and a relatively large amount of carbonyl species, formed during the carbonization of the PAN/SBA-15 composite at 623?K, were responsible for the high sorption capacity in the methyl?Cethyl ketone (MEK) vapor elimination. The efficiency in the MEK adsorption was also influenced by the content of PAN-derived carbon deposited on the SBA-15 surface. 相似文献
825.
C. Lavilla A. Alla A. Martínez de Ilarduya E. Benito M.G. García‐Martín J.A. Galbis S. Muñoz‐Guerra 《Journal of polymer science. Part A, Polymer chemistry》2012,50(16):3393-3406
Random poly(hexamethylene terephthalate‐co‐galactarate)s and poly(dodecamethylene terephthalate‐co‐galactarate)s copolyesters covering the whole range of compositions were obtained with weight‐average molecular weights of ~30,000–50,000 g mol?1 by melt polycondensation. They were thermally stable above 300 °C, and displayed Tg in the +20 to ?20 °C range with values steadily decreasing with the content in galactarate units. All the copolyesters were semicrystalline with Tm between 50 and 150 °C and those made from dodecanediol were able to crystallize from the melt at a crystallization rate depending on composition. Copolyesters containing up to 50% of galactaric units retained the crystal structure of their respective polyterephthalate homopolyesters, whereas they adopted the structure of the respective polygalactarates when the content in Galx units reached 70%. Stress‐strain essays revealed decay in the mechanical parameters as the aromatic units were replaced by Galx. Incubation in aqueous buffer revealed that hydrolysis of the polyesters were largely enhanced by copolymerization and evidenced the capacity of the Galx unit for making aromatic polyesters susceptible to biodegradation. A detailed NMR analysis complemented by SEM observations indicated that hydrolysis took place by preferred splitting of galactarate ester bonds with releasing of alkanediol and Galx‐diacid. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
826.
827.
Magdalena Wirkowska Ewa Ostrowska-Lig?za Agata Górska Piotr Koczoń 《Journal of Thermal Analysis and Calorimetry》2012,110(1):137-143
The aim of this research was to analyse composition, fatty acids distribution and oxidative stability of fats extracted from four samples of baby formulas. The fats were oxidized in a differential scanning calorimeter (DSC) under polythermal (dynamic) conditions and at normal pressure. The DSC experiments were carried out in an oxygen flow atmosphere using different, linearly programmed, heating rates in the range of 4?C12.5?°C/min. The extrapolated onset temperatures were determined using DSC exotherms and used for the assessment of the thermal oxidative stabilities of the samples. Activation energies (E a), pre-exponential factors (Z) and reaction rate constants (k) for oil oxidation under DSC conditions were calculated using the Ozawa?CFlynn?CWall method and the Arrhenius equation. The melting characteristics of the studied fats were obtained. The fats extracted from the agglomerated samples with higher onset temperatures were more stable than the fats extracted from the initial samples of baby formulas. 相似文献
828.
A model of spring-block on a moving plate with a nonlinear periodic substrate potential whose shape can be varied continuously as a function of a shape parameter is investigated. The dynamical study of the system for different values of the shape parameter involves the analysis of phase space, the construction of bifurcation diagrams, and the computation of the largest Lyapunov exponent. A smart damper associated with drag coefficient is proposed to reduce stick-slip and chaotic motions. The domain of validity of the control method is derived. 相似文献
829.
830.
Magaly A. M. Lyra José L. Soares-Sobrinho Regina C. B. Q. Figueiredo Jana M. Sandes ádley A. N. Lima R?mulo P. Tenório Danilo A. F. Fontes Fabiana L. A. Santos Larissa A. Rolim Pedro J. Rolim-Neto 《Journal of inclusion phenomena and macrocyclic chemistry》2012,73(1-4):397-404
The current chemotherapy for Chagas disease is still based on benznidazole, which has low solubility, but complexation with cyclodextrins provides a way of increasing the solubility. The objective of this work was to characterize the inclusion complexes formed between benznidazole (BNZ) and randomly 2-methyled-β-cyclodextrin (RM-β-CD) in aqueous solution and study cytotoxicity and trypanocidal. BNZ:RM-β-CD solution complex systems were prepared and characterized using the phase solubility diagram, nuclear magnetic resonance and a photostability assays, also to investigate the in vitro trypanocidal activity with epimastigote forms of Trypanossoma cruzi and the study of cytotoxicity against mammal cells. The phase-solubility diagram displayed an A L-type feature, providing evidence of the formation of soluble inclusion complexes. The continuous variation method showed the existence of a complex with 1:1 stoichiometry. Toxicity assays demonstrated that inclusion complexes were able to reduce the toxic effects caused by benznidazole alone and that this did not interfere with the trypanocidal activity of the benznidazole. The use of inclusion complexes benznidazole:cyclodextrin is thus a promising alternative for the development of a safe and stable liquid formulation and a new option for the treatment of Chagas disease. 相似文献