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141.
Valentina Domenici Dr. Alberto Marini Dr. Carlo A. Veracini Prof. Corrado Malanga Dr. Rita Menicagli Prof. 《Chemphyschem》2009,10(15):2679-2691
The molecular dynamics of a ferroelectric liquid crystal, denoted ZLL 7/* , is investigated by means of 2H NMR relaxation. The spin–lattice (T1Q and T1Z) and spin–spin (T2) relaxation times of two isotopomers of ZLL 7/* , labeled on the phenyl and biphenyl fragments, are measured and their behavior upon passing from the SmA to the hexatic phase, through the ferroelectric SmC*, antiferroelectric SmC*A, and re‐entrant ferroelectric SmC*re phases, is discussed. A comparison between the measured T2 and T2*, directly related to the experimental linewidth, provides information on the heterogeneity of the system, thus allowing confirmation of previous hypotheses concerning the structural and ordering properties of the SmC*A and SmC*re phases. The possibility to look at different sites of the core of the ZLL 7/* smectogen reveals a peculiar sensitivity of the phenyl moiety with respect to the biphenyl fragment, which may be justified by its vicinity to the chiral centers. Interestingly, the trend of the longitudinal relaxation times is characterized by a minimum that corresponds to the SmC*A and SmC*re phases, which is reproducible for the two isotopomers and at several Larmor frequencies. A quantitative analysis of T1Q and T1Z is performed in the SmA and SmC* phases, for which the narrowing regime approximation is valid. A multifrequency approach is applied to self‐consistently determine the diffusion coefficients for the overall molecular motions, namely spinning and tumbling, and the internal rotations around the para axes of the phenyl and biphenyl fragments. The effect of the magnetic field in unwinding the helical structure of the SmC* phase (for H>9 T) allows observation of a sensitive change in the rotational diffusion coefficients in the frustrated unwound SmC* phase with respect to the SmC* phase. 相似文献
142.
Giuseppe Buttazzo Serena Guarino Lo Bianco Michele Marini 《Journal of Mathematical Analysis and Applications》2018,457(2):1153-1172
In this paper we generalize some classical estimates involving the torsional rigidity and the principal frequency of a convex domain to a class of functionals related to some anisotropic nonlinear operators. 相似文献
143.
Stilbeneylsydnone derivatives were synthesized by a sequence of reactions in good yields. Irradiation of 3-stilbeneyl-4-methylsydnone 4 gives 1H-1,2-benzodiazepine derivative 7 as the main product along with 2-methylquinoline derivative 20. Irradiation of 3-stilbeneyl-4-phenylsydnone 5 afforded only 1H-1,2-benzodiazepine derivative 8 whereas on irradiation of 4-unsubstituted 3-stilbeneylsydnone 3 no benzodiazepine derivative was detected. An efficient novel photochemical approach to 1H-1,2-benzodiazepines has been found from the new 3-(o-stilbeneyl)-4-substituted-sydnones via intramolecular 1,7-electrocyclization reaction of the photogenerated nitrile imines. 相似文献
144.
Malacea R Daran JC Duckett SB Dunne JP Godard C Manoury E Poli R Whitwood AC 《Dalton transactions (Cambridge, England : 2003)》2006,(27):3350-3359
Ir(CO)[CpFe{eta5-C5H3(PPh2)CH2SR}]Cl [R = Ph and (t)Bu], containing a kappa2:P,S ligand, undergoes H2 addition across the S-Ir-CO axis under kinetic control to form two distinct diastereoisomeric products, which then rearrange via S dissociation in a process that can be hijacked for useful catalysis, but ultimately form a single diastereoisomer of the thermodynamic product where the hydride ligands are trans to chloride and phosphine. 相似文献
145.
Crociani B Antonaroli S Marini A Matteoli U Scrivanti A 《Dalton transactions (Cambridge, England : 2003)》2006,(22):2698-2705
The complexes [Pd(eta2-dmfu)(P-N)] [P-N = 2-(PPh2)C6H4-1-CH=NR, R = C(6)H(4)OMe-4; CHMe2; C6H3Me2-2,6; C6H3(CHMe2)-2,6] react with an excess of BrC6H4R1-4 (R1= CF3; Me) yielding the oxidative addition products [PdBr(C6H4R1-4)(P-N)] at different rates depending on R [C6H4OMe-4 > C6H3(CHMe2)-2,6 > CHMe2 approximately C6H3Me2-2,6] and R1 (CF3> Me). In the presence of K2CO3 and activated olefins (ol = dmfu, fn), the latter compounds react with an excess of 4-R2C6H4B(OH)2 (R2= H, Me, OMe, Cl) to give [Pd(eta2-ol)(P-N)] and the corresponding biaryl through transmetallation and fast reductive elimination. The transmetallation proceeds via a palladium(II) intermediate with an O-bonded boron anion, the formation of which is markedly retarded by increasing the bulkiness of R. The intermediate was isolated for R = CHMe2, R1 = CF3 and R2= H. The boron anion is formulated as a diphenylborinate anion associated with phenylboronic acid and/or as a phenylboronate anion associated with diphenylborinic acid. In general, the oxidative addition proceeds at a lower rate than transmetallation and represents the rate-determining-step in the coupling reaction of aryl bromides with arylboronic acids catalyzed by [Pd(eta2-dmfu)(P-N)]. 相似文献
146.
Artificial neural networks (ANNs) are non-linear computational tools suitable to a great host of practical application due to their flexibility and adaptability. However, their application to the resolution of chemometric problems is relatively recent (early 1990s).In this communication, different artificial neural networks architectures are presented and their application to different kinds of chemometric problems (mainly classification and regression) is discussed by means of examples taken from the authors' experience, stressing the pros and cons of ANNs with respect to traditional chemometric techniques. 相似文献
147.
A. Marini V. Berbenni G. Bruni A. Maggioni M. Villa 《Journal of Thermal Analysis and Calorimetry》1999,56(2):699-715
The heat capacity calibration ‘constants’ of a commercial MTDSC system (TA 3100) were determined in a variety of experimental
conditions. For a given modulation frequency, the calibration constants are the same within a few percents for different temperatures,
and over a wide range of modulation amplitudes and scan rates. This variation decreases below 1% if hidden instrumental constraints
are taken into account, which are related with the capability of the control system to achieve the desired temperature program.
On the other hand, the calibration constant changes substantially with the period, and takes anomalously high values for the
short modulation periods (20+40 s). Rules to optimize the accuracy of the system are given.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
148.
149.
G. Bruni A. Marini V. Berbenni R. Riccardi M. Villa 《Journal of inclusion phenomena and macrocyclic chemistry》1999,35(3):517-530
The ketoprofen/beta-cyclodextrin (-CD) inclusion compounds may be conveniently obtained through a solid state reaction at room temperature in the presence of saturated water vapour. Relative to the corresponding complexes produced with the usual coprecipitation method, the new compounds have a higher ketoprofen content and/or different properties. In particular, the formation reaction is not accompanied by a loss of hydration water, which is released in distinct stages upon heating. The thermodynamics of the dehydration process is discussed. 相似文献
150.