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771.
Abstract— The fluorescence properties of three ortho aminobenzoate local anesthetics have been determined in a variety of solvents. Results from these studies have been used to deduce how these drugs interact with phosphatidylcholine bilayers. The emission energy, fluorescence quantum yield and lifetime exhibited a biphasic dependence on solvent polarity. In aprotic solvents, alcohols and in ethanol-water mixtures containing less than 40% water, quantum yields and lifetimes were high (approximately 0.55 and 8.5 ns respectively). In ethanol-water mixtures containing >40% water, the strong fluorescence quenching was primarily due to an increase in the rate of non-radiative deactivation of the excited state. Both the radiative ( kr ) and non-radiative ( knr ) rate constants show a biphasic dependence on solvent polarity. These studies suggest the presence of two singlet excited states for these molecules, a polar singlet excited state, S1-p and a charge transfer excited state, S1-ct with the latter predominating in ethanol-water mixture containing >40% water. In egg phosphatidylcholine bilayers, the fluorescence, lifetime and quantum yield are consistent with the view that these drugs are localized within the lipid head group region where the charge-transfer excited state can be stabilized by intermolecular hydrogen bonding. 相似文献
772.
Michael Reed 《Communications in Mathematical Physics》1969,11(4):346-357
A self-interaction with damped off-diagonal coefficients is used to illustrate techniques for dealing directly with Hamiltonians in strange representations of the CCR. 相似文献
773.
Could temporal order differences underlie 2-month-olds' discrimination of English voicing contrasts?
P W Jusczyk B S Rosner M A Reed L J Kennedy 《The Journal of the Acoustical Society of America》1989,85(4):1741-1749
Previous studies have shown that infants discriminate voice onset time (VOT) differences for certain speech contrasts categorically. In addition, investigations of nonspeech processing by infants also yield evidence of categorical discrimination of temporal-order differences. These findings have led some researchers to argue that common auditory mechanisms underlie the infant's discrimination of timing differences in speech and nonspeech contrasts [e.g., Jusczyk et al., J. Acoust. Soc. Am. 67, 262-270 (1980)]. Nevertheless, some discrepancies in the location of the infant's category boundaries for different kinds of contrasts have been noted [e.g., Eilers et al. (1980)]. Because different procedures were used to study the different kinds of contrasts, interpretation of the discrepancies between the studies has been difficult. In the present study, three different continua were examined: [ba]-[pa] stimuli, which differed in VOT; [du]-[tu] stimuli, which differed in VOT but which lacked format transitions; nonspeech formant onset time (FOT) stimuli that varied in the time that lower harmonics increased in amplitude. An experiment with adults indicated a close match between the perceptual boundaries for the three series. Similarly, tests with 2-month-old infants using high amplitude sucking procedure yielded estimates of perceptual category boundaries at between 20 and 40 ms for all three stimulus series. 相似文献
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778.
John C. Kotz Cynthia L. Nivert Joel M. Lieber Richard C. Reed 《Journal of organometallic chemistry》1975,84(2):255-267
Complexes of the organometallic ligand (h5-C5H5)Fe[(h5-C5H3)(1-CH2NMe2)(2-PPh2)] (FcCNP) have been prepared with the carbonyls of chromium, molybdenum, tungsten, iron, and cobalt and with borane. With the Group VIB metals, the ligand forms complexes of the type (FcCNP)M(CO)4 in which the FcCNP ligand is chelating. However, in the case of (FcCNP)Fe(CO)4 and [(FcCNP)2Co(CO)3]BPh4 the ligand is monodentate, the phosphorus acting as the donor atom. Infrared and NMR data were used to establish the mode of coordination in each case. The electrochemistry of the Group VIB metal carbonyl complexes has been investigated, the chromium complex being of particular interest. The cyclic voltammogram of (FcCNP)Cr(CO)4 consists of two, reversible, one electron redox waves at Epeak, anodic + 0.54 V and + 0.96 V (vs. SCE in CH2Cl2), and a third, irreversible wave at Epeak, anodic + 1.47 V. At + 0.54 V the solution color changed from yellow to orange and the v(CO) bands shifted from 2011 w, 1891 s, and 1831 s (cm?1) in the neutral complex to 2080 m, 2000 s, and 1970 s (cm?1) in the singly oxidized species. At + 0.96 V, the color changed further to blue-green, but no additional shift in v(CO) was observed. On the basis of this information, it is concluded that the first redox wave represents the process Cr0 → Cr+ and the second wave Fe2+ → Fe3+. Other aspects of the electrochemistry of the Group VIB metal carbonyl complexes are discussed. 相似文献
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780.