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81.
Free radicals are generated in liquid solutions by harmonically modulated photolysis of suitable substrates. Harmonic analysis of the absorbance as functions of wavelength and modulation frequency yields the optical spectra and the decay kinetics of the transient species. The experimental technique and the analysis are described in detail. Results on t-butyl, 2-propyl and benzyl radicals generated by photolysis of the corresponding dialkyl resp. dibenzyl ketones are reported. They confirm previous spectral assignments and show that the termination reactions are diffusion controlled. 相似文献
82.
Hanns Fischer 《Hyperfine Interactions》1984,19(1-4):751-770
Muonium-substituted organic free radicals are observed by muon spin rotation when positive muons are stopped in liquid unsaturated compounds. From muon precession frequencies in high external magnetic fields the isotropic muon-electron hyperfine coupling constants are determined. They lead to radical structure assignments. Results of a variety of projects are described which show thatSR can successfully complement conventional physical methods of free radical chemistry: A study of the temperature dependence of the coupling constants of isotopically substituted ethyl radicals yields information on structure and barriers to internal rotation. Rate constants for several radical reactions are extracted from the damping of theSR signals, in particular for unimolecular rearrangements and cis-trans-isomerizations. The theory for the analysis for the case of reversible site exchange is outlined.All results described here were obtained by E. Roduner, P. Burkhard and W. Strub of this laboratory, and B. Webster, M. Ramos and D. McKenna of the University of Glasgow. We all appreciate support from the Swiss National Foundation for Scientific Research, the National Institut for Scientific Investigations of Portugal, the Carnegie Trust for the Universities of Scotland, the Royal Society London and SIN. 相似文献
83.
M. Althoff W. Braunschweig F.J. Kirschfink H.-U. Martyn P. Rosskamp D. Schmitz H. Siebke W. Wallraff J. Eisenmann H.M. Fischer H. Hartmann A. Jocksch G. Knop H. Kolanoski H. Kück V. Mertens R. Wedemeyer G. Zobernig 《Physics letters. [Part B]》1984,149(6):524-532
We have determined the average lifetime of hadrons containing b quarks produced in e+e? annihilation to be . Our method uses charged decay products from both non-leptonic and semileptonic decay modes. 相似文献
84.
K. H. Fischer 《Zeitschrift für Physik B Condensed Matter》1984,55(4):317-324
The dynamics of ann-component vector spin glass with infinite range interactions are investigated near and above the Gabay-Toulouse (GT) line. The local transverse susceptibility
T
for 0 varies along the whole GT lineT
c1
(H) as
v
, with a field and temperature independent critical exponentv=1/2. The longitudinal susceptibility
L
() remains analytic for all (T, H)T
c1
(H), except for a cross-over fromv=1 tov=1/2 forH0 at the freezing temperatureT=T
f
. The dynamic susceptibilities
T
() and
L
() are already coupled above the GT line via self-energy terms. BelowT
c1
(H), this coupling is strongly enhanced by other mechanisms. 相似文献
85.
Thin layers of basic zinc carbonate can be used with good results for separation and multiple identification of carbamate and phenylurea pesticides. Five important substances could be separated by one-dimension TLC. The best results were obtained by the following developing solvents: a) benzene, b) a mixture of benzene/petroleum ether/chloroform (6∶1∶1). The substances are either recognisable in short-wave UV-light, when a fluorescence indicator (F 254 nm) is added, or in day-light, after spraying a solution of 0.1 N AgNO3 in 3 N HNO3, followed by an UV-exposure for about 4 min. 相似文献
86.
The rates of substitution of the group X in 1-X-2-naphthol-6-sulfonic acids (X = H, Cl, Br, and I) by p-chlorobenzenediazonium ions in aqueous solution have been measured. The rates of the halogenated naphthols relative to that of the parent compound (X = H) are 0.0070:0.0089:0.149 for X = Cl, Br, and I respectively. The reaction of 1-bromo-2-naphthol-6-sulfonic acid is catalysed by thiosulfate ions; the relative rate observed for this compound does not, therefore, represent the ipso factor. It is postulated that in its substitution the release of the electrofugal leaving group (Br⊕) is rate-limiting. 相似文献
87.
A first infrared pulse at frequency ν1 interacts with vibrational states in S0 and a second visible pulse at ν2 promotes the excited molecules to the S1 state from where they fluoresce. Tuning the frequency ν2 over 600 cm?1 allows the observation of a detailed spectrum which gives information on vibrational states in S0 and on vibronic states in S1 together with corresponding Franck—Condon factors. The spectra differ drastically from the common broad and featureless absorption and fluorescence bands. 相似文献
88.
Khattari Z Ruschel Y Wen HZ Fischer A Fischer TM 《The journal of physical chemistry. B》2005,109(8):3402-3407
The surface shear viscosity of a myelin mimetic Langmuir monolayer is investigated upon adsorption of myelin basic protein (MBP). We measure an increase of the surface shear viscosity at picomolar concentrations of the protein, suggesting that the globular conformation of MBP changes upon adsorption at the monolayer. The conformational change enables hydrodynamic interactions of the proteins, with a typical separation of hundreds of nanometers. This unfolding is essential for the compactification of the myelin sheath, serving an enhanced saltatory signal transduction in vertebrates. The viscometry used extends the sensitivity of standard surface viscometers toward lower viscosities. 相似文献
89.
Pseudoazulenes of the 1,2-benzoxalene type C (indeno[2,1-b]pyranes) are accessible by two new ways: The title compounds 1–10 were synthesized by acid catalysed cyclodeamination of ketovinylated 2-piperidinoindenes F, the compounds 13–36 by deprotonation of 9H-indeno[2,1-b]pyrylium salts L obtained from indan-2-ones and β-diketones. The aromatic nature of the pseudoazulene system is described in terms of various physical and theoretical results (electronic spectra, resonance energies, HMO calculations). 相似文献
90.
Systematic transition calculations have been performed for all triplet decay channels from 2s2p 23s 3 P of N II. The lifetime of 0.505 ns compares favourably with experiment. Transitions in absorption from the 2s 22p 2 3 P ground state have also been determined along with a number of other triplet transitions. Length and velocity forms of thef-value are in agreement at the 2–3% level for most transitions. 相似文献