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111.
Paulo Debiagi Coskun Yildiz Marcel Richter Jochen Ströhle Bernd Epple Tiziano Faravelli Christian Hasse 《Proceedings of the Combustion Institute》2021,38(3):4053-4061
Coal combustion releases elevated amounts of pollutants to the atmosphere including SOX. During the pyrolysis step, sulfur present in the coal is released to the gas phase as many different chemical species such as H2S, COS, SO2, CS2, thiols and larger tars, also called SOX precursors, as they form SOX during combustion. Understanding the sulfur release process is crucial to the development of reliable kinetic models, which support the design of improved reactors for cleaner coal conversion processes. Sulfur release from two bituminous coals, Colombian hard coal (K1) and American high sulfur coal (U2), were studied in the present work. Low heating rate (LHR) experiments were performed in a thermogravimetric analyzer coupled with mass spectrometry (TG-MS), allowing to track the mass loss and the evolution of many volatile species (CO, CO2, CH4, SO2, H2S, COS, HCl and H2O). High heating rate (HHR) experiments were performed in an entrained flow reactor (drop-tube reactor – DTR), coupled with MS and nondispersive infrared sensor (NDIR). HHR experiments were complemented with CFD simulation of the multidimentional reacting flow field. A kinetic model of coal pyrolysis is employed to reproduce the experiments allowing a comprehensive assessment of the process. The suitability of this model is confirmed for LHR. The combination of HHR experiments with CFD simulations and kinetic modeling revealed the complexity of sulfur chemistry in coal combustion and allowed to better understand of the individual phenomena resulting in the formation of the different SOX precursors. LHR and HHR operating conditions lead to different distribution of sulfur species released, highly-dependent on the gas-phase temperature and residence time. Higher retention of total sulfur in char is observed at LHR (63%) when compared to HHR (37–44%), at 1273 K. These data support the development of reliable models with improved predictability. 相似文献
112.
Time and temperature induced phase transformation in L‐isoleucine hydrochloride monohydrated crystal
Ricardo S. Ferreira Júnior Geanso M. Moura Andreia C. Pereira Paulo R. da Silva Ribeiro Luzeli M. da Silva Adenilson O. dos Santos 《Crystal Research and Technology》2016,51(12):738-741
Semi organic crystals have been intensively studied aiming applications in nonlinear optical (NLO). Such applicability requires crystals with both high quality and thermal stability, which make the full characterization of this material a topic issue. In this paper, single crystals of L‐isoleucine hydrochloride monohydrated (L‐Ile.H2O.HCl) was synthesized by slow evaporation technique and characterized by thermal analysis and X‐ray diffraction (XRD) measurements. XRD results at 298 K showed that the sample crystallize with the orthorhombic structure, and the lattice parameters obtained by Rietveld refinement were a = 5.873(3) Å, b = 24.814(4) Å, and c = 6.873(5) Å. Thermal analysis measurements shows four decomposition stages between 328 ‐480 K which were associated with loss of water by desolvation, loss crystallization water and decomposition of L‐Ile.HCl. XRD measurements as a function of temperature up to 428 K show an irreversible phase transformation. This transformation was obtained after 32 hours keeping the L‐Ile.HCl.H2O sample at 413 K. The analysis shows that phase transformation occurs due to water and chlorine losses without destroy the amino acid carbon chain and in the end of transformation only the precursor amino acid remains. L‐Ile.HCl.H2O present low thermal stability and the phase transformation is time and temperature dependent. 相似文献
113.
Paulo A. Machicao Scott R. Burt Ryan K. Christensen Nathan B. Lohner J.D. Singleton Matt A. Peterson 《Tetrahedron letters》2017,58(24):2318-2321
Treatment of N-[(4-hydroxy-6-phenyl)pyrimidin-2-yl]cyanamide with 1° alkyl or arylamines in isopropyl alcohol for only 10 min at 110–120 °C under microwave conditions gave the corresponding N′-alkyl(aryl)guanidine derivatives in excellent yields (65–84%). Isolated yields were greatest when >1.0 equiv. of amines were employed, but excellent results were also obtained when aryl and alkylamines were reacted with a more atom-economical loading (1.0 equiv.; 70% and 72% ave. yields, respectively). Arylamines with either highly electron withdrawing substituents (e.g. CO2H) or pi-deficient heterocycles (e.g. variously substituted aminopyridines) did not work well under these conditions, and reaction with ureas and/or amino acids did not give detectable products. Work-up was exceedingly simple, and involved simple collection and washing of product on a sintered glass funnel. Products were obtained in analytically pure form and required approximately 1 h to prepare, start to finish. 相似文献
114.
Thales R. de Moura Sahra L. Cavalcanti Paulo R. D. V. de Godoy Elza T. Sakamoto-Hojo Fillipe V. Rocha Eduardo T. de Almeida Victor M. Deflon Antonio E. Mauro Adelino V. G. Netto 《Transition Metal Chemistry》2017,42(6):565-574
Complexes of the type cis-[PdX2(imzt)(PPh3)] {imzt = imidazolidine-2-thione; PPh3 = triphenylphosphine; X = Cl (1), Br (2), I (3), SCN (4)} have been synthesized and characterized by elemental analyses, molar conductance, IR and 1H NMR spectroscopies. The complex 1·MeOH was obtained from the reaction of [PdCl2(CH3CN)2], imidazolidine-2-thione and triphenylphosphine in CHCl3/CH3OH. Complexes 2·MeOH, 3 and 4 were prepared by metathesis of the chlorido ligands in 1 with bromide, iodide and thiocyanate, respectively. Elemental analyses showed good agreement with the expected mononuclear compositions, while the molar conductivities of the complexes in DMF were consistent with their nonelectrolytic nature. NMR spectra confirmed coordination of the imidazolidine-2-thione and triphenylphosphine ligands. Single-crystal X-ray diffraction determination of 1·CH3OH showed that the coordination geometry around PdII is nearly square planar, with the chlorido ligands in a cis configuration. All four complexes have been tested in vitro by XTT assay for their cytotoxicity against human glioblastoma cell line (U87MG). The binding of 1 with guanosine was studied by 1H NMR spectroscopy, revealing that the coordination takes place via N7. 相似文献
115.
Eduardo Lutterbach Bandeira Marcelo Amorim Savi Paulo Cesar da Camara Monteiro Jr. Theodoro Antoun Netto 《Archive of Applied Mechanics (Ingenieur Archiv)》2006,76(3-4):133-144
This contribution deals with the nonlinear analysis of shape memory alloy (SMA) adaptive trusses employing the finite element method. Geometrical nonlinearities are incorporated into the formulation together with a constitutive model that describes different thermomechanical behaviors of SMA. It has four macroscopic phases (three variants of martensite and an austenitic phase), and considers different material properties for austenitic and martensitic phases together with thermal expansion. An iterative numerical procedure based on the operator split technique is proposed in order to deal with the nonlinearities in the constitutive formulation. This procedure is introduced into ABAQUS as a user material routine. Numerical simulations are carried out illustrating the ability of the developed model to capture the general behavior of shape memory bars. After that, it is analyzed the behavior of some adaptive trusses built with SMA actuators subjected to different thermomechanical loadings. 相似文献
116.
Joo Paulo A. Martins Reinaldo F. Tefilo Mrcia M. C. Ferreira 《Journal of Chemometrics》2010,24(6):320-332
An evaluation of computational performance and precision regarding the cross‐validation error of five partial least squares (PLS) algorithms (NIPALS, modified NIPALS, Kernel, SIMPLS and bidiagonal PLS), available and widely used in the literature, is presented. When dealing with large data sets, computational time is an important issue, mainly in cross‐validation and variable selection. In the present paper, the PLS algorithms are compared in terms of the run time and the relative error in the precision obtained when performing leave‐one‐out cross‐validation using simulated and real data sets. The simulated data sets were investigated through factorial and Latin square experimental designs. The evaluations were based on the number of rows, the number of columns and the number of latent variables. With respect to their performance, the results for both simulated and real data sets have shown that the differences in run time are statistically different. PLS bidiagonal is the fastest algorithm, followed by Kernel and SIMPLS. Regarding cross‐validation error, all algorithms showed similar results. However, in some situations as, for example, when many latent variables were in question, discrepancies were observed, especially with respect to SIMPLS. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
117.
Marcelo Godoi Marcio W. Paixão Paulo H. Schneider Antonio L. Braga 《Tetrahedron》2010,66(6):1341-11355
A new class of amino-phosphinite chiral ligands was prepared and applied in zinc-catalyzed addition of aryl boronic acids to aldehydes; the reaction furnished the diarylmethanols in excellent yields and with a high level of enantioselectivity (up to 93% ee). 相似文献
118.
Maurício Hilgemann Fritz Scholz Heike Kahlert Leandro Machado de Carvalho Marcelo Barcellos da Rosa Ulrike Lindequist Martina Wurster Paulo C. do Nascimento Denise Bohrer 《Electroanalysis》2010,22(4):406-412
A new electrochemical assay has been developed which is based on quantifying the attack of OH. radicals on a self‐assembled thiol monolayer on electrodes in the presence and absence of antioxidants. The OH. radicals were produced in Fenton solutions. The radical scavengers diminish the concentration of the OH. radicals in the Fenton solution, and the extent of thiol layer destruction is monitored with the help of a redox probe in solution, the signal of which is only generated at SAM‐free electrode surface. The results of the electrochemical assay were compared with those of the standard DPPH. assay. In case of each plant extract, an excellent linear correlation was observed between the radical scavenging activity and the concentration of plant extracts; however, the scavenging properties of different plants strongly differ in the electrochemical and the DPPH. assay. Since the proposed new method probes the reactivity of radical scavengers towards OH., one of the most important reactive oxygen radicals in tissues, it is supposed to provide much more relevant information than the DPPH. or other assays. 相似文献
119.
Jesús Martínez-Sánchez Rufina Bastida Alejandro Macías Harry Adams David E. Fenton Paulo Pérez-Lourido Laura Valencia 《Polyhedron》2010
Acetate and perchlorate dinuclear metal complexes of Co(II), Cu(II) and Zn(II) with the cresolate polypodal ligand having mixed phenolate and pyridyl pendant functionalities, H3L, have been synthesized. The complexes were characterized by microanalysis, LSI mass spectrometry, IR, UV–Vis spectroscopy, magnetic studies and conductivity measurements. Crystal structures of H3L, [Cu2(HL)(OAc)(H2O)2](OAc)·1.5H2O and [Zn2L(CH3OH)3](ClO4)CH3OH·2H2O complexes, have been also determined. 相似文献
120.
The rigid [6]ferrocenophane, L1, was synthesised by condensation of 1,1′-ferrocene dicarbaldehyde with trans-1,2-diaminocyclohexane in high dilution at r.t. followed by reduction. When other experimental conditions were employed, the [6,6,6]ferrocenephane (L2) was also obtained. Both compounds were characterised by single crystal X-ray crystallography. The protonation of L1 and its metal complexation were evaluated by the effect on the electron-transfer process of the ferrocene (fc) unit of L1 using cyclic voltammetry (CV) and square wave voltammetry (SWV) in anhydrous CH3CN solution and in 0.1 M nBu4NPF6 as the supporting electrolyte. The electrochemical process of L1 between −300 and 900 mV is complicated by amine oxidation. On the other hand, an anodic shift from the fc/fc+ wave of L1 of 249, 225, 81 and 61 mV was observed by formation of Zn2+, Ni2+, Pd2+ and Cu2+ complexes, respectively. Whereas Mg2+ and Ca2+ only have with L1 weak interactions and they promote the acid-base equilibrium of L1. This reveals that L1 is an interesting molecular redox sensor for detection of Zn2+ and Ni2+, although the kinetics of the Zn2+ complex formation is much faster than that of the Ni2+ one. The X-ray crystal structure of [PdL1Cl2] was determined and showed a square–planar environment with Pd(II) and Fe(II) centres separated by 3.781(1) Å. The experimental anodic shifts were elucidated by DFT calculations on the [ML1Cl2] series and they are related to the nature of the HOMO of these complexes and a four-electron, two-orbital interaction. 相似文献