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81.
Engelbert Reusch Dr. Fabian Holzmeier Marius Gerlach Prof. Dr. Ingo Fischer Dr. Patrick Hemberger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(72):16652-16659
The reaction products of the picolyl radicals at high temperature were characterized by mass-selective threshold photoelectron spectroscopy in the gas phase. Aminomethylpyridines were pyrolyzed to initially produce picolyl radicals (m/z=92). At higher temperatures further thermal reaction products are generated in the pyrolysis reactor. All compounds were identified by mass-selected threshold photoelectron spectroscopy and several hitherto unexplored reactive molecules were characterized. The mechanism for several dissociation pathways was outlined in computations. The spectrum of m/z=91, resulting from hydrogen loss of picolyl, shows four isomers, two ethynyl pyrroles with adiabatic ionization energies (IEad) of 7.99 eV (2-ethynyl-1H-pyrrole) and 8.12 eV (3-ethynyl-1H-pyrrole), and two cyclopentadiene carbonitriles with IE′s of 9.14 eV (cyclopenta-1,3-diene-1-carbonitrile) and 9.25 eV (cyclopenta-1,4-diene-1-carbonitrile). A second consecutive hydrogen loss forms the cyanocyclopentadienyl radical with IE′s of 9.07 eV (T0) and 9.21 eV (S1). This compound dissociates further to acetylene and the cyanopropynyl radical (IE=9.35 eV). Furthermore, the cyclopentadienyl radical, penta-1,3-diyne, cyclopentadiene and propargyl were identified in the spectra. Computations indicate that dissociation of picolyl proceeds initially via a resonance-stabilized seven-membered ring. 相似文献
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Fabian H. Gaioli Edgardo T. Garcia Alvarez Diego G. Arbo 《International Journal of Theoretical Physics》1999,38(1):183-198
This paper generalizes some previous resultspresented in Gaioli et al. [Int. J. Theor. Phys. 36,2167 (1997)]. We evaluate the autocorrelation functionof the stochastic acceleration and study the asymptotic evolution of the mean occupation number of aharmonic oscillator playing the role of a Brownianparticle. We also analyze some deviations from the Bosepopulation at low temperatures and compare it with the deviations from the exponential decay lawof an unstable quantum system. 相似文献
85.
Ahmed Al‐Harrasi Dr. Fabian Pfrengle Dipl.‐Chem. Vladimir Prisyazhnyuk Dr. Shahla Yekta Dr. Peter Koóš Dr. Hans‐Ulrich Reissig Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(43):11632-11641
1,3‐Dioxolanyl‐substituted 1,2‐oxazines, such as syn‐ 1 and anti‐ 1 , rearrange under Lewis acidic conditions to provide bicyclic products 2 – 5 . Subsequent reductive transformations afforded enantiopure 3‐aminopyran derivatives such as 7 and 9 or their protected diastereomers 16 and 18 , which can be regarded as carbohydrate mimetics. An alternative sequence of transformations including selective oxidation of the primary hydroxyl groups in 21 and 24 led to two protected β‐amino acid derivatives with carbohydrate‐like backbone (sugar amino acids). Treatment of bicyclic ester 23 with samarium diiodide cleaved the N? O bond and furnished the unusual β‐lactam 27 in excellent yield. Alternatively, γ‐amino acid derivative 29 was efficiently prepared in a few steps. Fairly simple transformations gave azides 32 and 35 or alkyne 30 which are suitable substrates for the construction of oligosaccharide mimetics such as 34 by copper iodide catalyzed cycloadditions. With this report we demonstrate that enantiopure rearrangement products 2 – 5 are protected precursors of a variety of polyfunctionalized pyran derivatives with great potential for chemical biology. 相似文献
86.
L. Nyulászi T. Pasinszki J. Réffy T. Veszprémi J. Fabian W. Thiel 《Structural chemistry》1990,1(4):367-370
The Hel UPS spectra of acetamidine, perimidine, and four 2-substituted perimidine derivatives have been recorded and interpreted using ab initio and MNDO quantum-chemical calculations. A large interaction between the naphthalene and amidine fragment was concluded from the lowest ionization energy. The color-determining band of these compounds is strongly affected by the intramolecular charge-transfer transitions, which are of low energy because of the low ionization energy of the perimidine moiety. 相似文献
87.
Angel L. Esteban Maria P. Galache Francisco Mora Ernesto Diez Jesus San Fabian 《Journal of computational chemistry》1989,10(7):887-895
An equation is formulated on the basis of theoretical INDO/FPT calculations which describes the angular dependence of the propanic long-range coupling constant 4JMeH in substituted HCCCH3 fragments. This equation is a truncated Fourier series in the torsion angle ?, HCCMe, which takes into account the dependence of the Fourier coefficients on the bond angle θ, CCMe. The substituent effects are assumed to be additive. Some parameters in the equation may be obtained from the 4JMeH couplings in propane and neopentane derivatives. The calculated effect upon 4JMeH of changes in the bond angle θ is significant and it seems to be in part the cause of some effects which have been attributed to conformational dependence. 相似文献
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