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751.
Shing TK Kwong CS Cheung AW Kok SH Yu Z Li J Cheng CH 《Journal of the American Chemical Society》2004,126(49):15990-15992
This article describes an efficient synthesis of a potent trehalase inhibitor, 1,1'-N-linked pseudodisaccharide 1 (consisting of two valienamines), in 14 steps with an overall yield of 12% and a first synthesis of 2 (consisting of two 2-epi-valienamines) in 15 steps with an overall yield of 24% from (-)-quinic acid. The synthesis involves a stereospecific palladium-catalyzed coupling reaction between an allylic amine and an allylic chloride as the crucial step. The acetonide blocking groups were shown to be the best hydroxyl protecting groups, compatible with the palladium-catalyzed allylic amination reaction that afforded high yields of the 1,1'-N-linked pseudodisaccharides with a minimum amount of an elimination diene side product. 相似文献
752.
Aryl diazonium salts occupy a privileged role in synthetic chemistry owing to their ready availability and versatile reactivity. While their applications in accessing diversely functionalized arene derivatives via denitrogenation‐coupling and reduction/addition reactions have been well recognized by practitioners in both academia and industry, recent renaissance in chemical transformations of retaining the key N2‐unit has emerged as a powerful technique to construct various N‐heterocycles. This review covers the history and latest advances in cyclization and cycloaddition reactions using aryl diazonium salts as N2‐annulation synthons. The scope, applications, and opportunities in exploring new chemical space by this sustainable strategy are summarized and discussed. 相似文献
753.
754.
755.
Resonance Raman spectra of nickel, chromium, and copper porphyrins, excited at their Soret maxima, show decreasing scattering intensity due to depolarized modes. This order correlates with diminished 1Q(0-0) absorption in the porphyrins. The data are interpreted in terms of Jahn-Teller distortions in both Q and B states. General agreement between predicted and observed excitation profiles of nickel etioporphyrin I support a vibronic treatment of the excited states. The effect of tight focusing of the incident beam is to quench most Raman scattering intensity, except the 1384 cm?1 line of the nickel complex. 相似文献
756.
Che CM Xia BH Huang JS Chan CK Zhou ZY Cheung KK 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(18):3998-4006
Reactions of MS4(2-) (M = Mo, W) with M'(PCy3)X (M'=Ag/Au, X= ClO4/Cl) and [Cu2(dcpm)2(MeCN)2](ClO4)2 (dcpm = bis(dicyclohexylphosphino)methane) afforded heterometallic sulfido clusters [M'2(PCy3)2(MS4)] (M=Mo, M'=Au: 2; M=W, M'=Ag: 3, Au: 4) and [Cu4(dcpm)4(MS4)](ClO4)2 (M=Mo: 5 x (ClO4)2, W: 6 x (ClO4)2), all of which, except 4, have been characterized by X-ray structure determination. Clusters 5 x(ClO4)2 and 6 x (ClO4)2 feature unusual 16-membered [Cu4P5C4] metallamacrocycles formed on the respective tetrathiometalate anion templates and have unusually long Cu-S bonds and Cu...M distances for metal sulfur clusters that contain a saddle-shaped [Cu4MS4] core. Low-energy absorption bands are observed in their electronic spectra at approximately 562 and 467 nm, respectively, assignable to MMCT transitions; quasireversible reduction waves are observed with E(1/2) = -1.43 (52+) and -1.78 V (62+) versus FeCp2(0/+); and they are emissive either in the solid state or in solution. The emission of 6(2+) can be quenched by both electron acceptors, such as methylviologen, or electron donors, such as aromatic amines, with the excited state reduction potential E(62+*/6+) estimated to be approximately 1.13V versus a normal hydrogen electrode. 相似文献
757.
Kai-Leung Cheung 《Journal of organometallic chemistry》2004,689(24):4451-4462
The present work provides a brief summary review of the chemistry of luminescent gold(I) alkynyls and their ability to form heterometallic complexes. A series of luminescent heterometallic gold(I)-rhenium(I) alkynyl complexes has been synthesized and characterized. Their electrochemical and photophysical properties have been studied and their emission origins elucidated. 相似文献
758.
Chao HY Lu W Li Y Chan MC Che CM Cheung KK Zhu N 《Journal of the American Chemical Society》2002,124(49):14696-14706
A family of mono- and binuclear Cy(3)P-supported gold(I) complexes containing various pi-conjugated linear arylacetylide ligands, including the two homologous series (Cy(3)P)Au(Ctbd1;CC(6)H(4))(n)()(-)(1)(Ctbd1;CPh) and (Cy(3)P)Au(Ctbd1;CC(6)H(4))(n)()Ctbd1;CAu(PCy(3)) (n = 1-4), have been prepared. X-ray crystal analyses revealed no intermolecular aurophilic interactions in their crystal lattice. The lowest-energy singlet transitions are predominately intraligand in nature and exhibit both phenyl and acetylenic (1)(pipi) character. Strong photoluminescence is detected in solid and solution states under ambient conditions, with lifetimes in the microsecond regime. For complexes with a single arylacetylide group, only phosphorescence from the arylacetylide (3)(pipi) state is observed. Vibrational spacings in the solid-state emission spectra can be attributed to a combination of phenyl ring deformation and symmetric phenyl ring and Ctbd1;C stretches. Additional delayed-fluorescence emission is recorded for complexes with multiple p-arylacetylide units, and this is attributed to a triplet-triplet annihilation process. The phosphorescence energy of these complexes are readily modified by altering the length of the conjugated arylacetylide system, while the intensity of phosphorescence relative to fluorescence decreases when the p-arylacetylide chain is elongated. Information regarding the nature and relative energies of arylacetylide singlet and triplet excited states has been derived from the two homologous series and extrapolated to polymeric arylacetylide species. The (3)(pipi) excited-state reduction potentials E degrees [Au(+)/Au] (Au = 1a, 2, and 4) are estimated to be -1.80, -1.28, and -1.17 V versus SSCE, respectively. 相似文献
759.
The two perfluoro-azadienes CF2N.CRCF2 (R = CF3 or CF2Cl) show temperature dependent 19F n.m.r. spectra, with non-equivalent fluorine nuclei of the CF2N portion at low temperatures, which coalesce due to inversion at the nitrogen at higher temperatures (ΔG3 = 60 kJ mol?1). N.m.r. parameters have been obtained. One of the five-bond FF coupling constants is much larger (. 24 Hz) than the remainder (0·5–5·5 Hz), possibly due to ‘through-space’ coupling of fluorines in the -skew conformation. 相似文献
760.