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21.
从豆甾醇出发,通过10步反应,合成得到具有显著细胞毒活性的24-亚甲基胆甾-5-烯-3β,19-二醇(1),总产率为16%.目标产物1的熔点、[α]值和波谱数据与天然产物一致.化合物1的合成是首次报道,它对人体鼻咽癌(CN2)和胃癌(Mgc803)细胞有显著抑制活性. 相似文献
22.
Addition and Substitution Reactions at Tetrafluoro- and Tetrachlorodiborane(4) From equimolar mixtures of B2F4 and MenN(SiMe3)3-n (n = 0–3) the mono-addition products 1–4 are formed at low temperatures. By elimination of Me3SiF the adduct 2 gives the dimeric monosubstituted diborane 8 , which slowly decomposes at room temperature to the aminoborane 6 and (BF)n. The course of the reactions was studied by means of 11B and 19F NMR spectroscopy and by measuring the vapor pressures. According to the 11B and 31P NMR spectra the reaction of B2Cl4 with PCl5 or [Me4N]Cl in liquid hydrogen chloride at 0°C does not yield [PCl4]2+[B2Cl6]2? or [Me4N]2+[B2Cl6]2? but gives [PCl4]+[BCl4]?, PCl3 and BCl3 or [Me4N]+[BCl4]? and BCl3 besides (BCl)n. 相似文献
23.
Keshtov M. L. Rusanov A. L. Keshtova S. V. Petrovskii P. V. Shchegolikhin A. A. 《Russian Chemical Bulletin》2002,51(1):117-123
A series of previously unknown unsymmetrical difluoroaromatic compounds, viz., p-fluorobenzoylphenyl(p-fluorophenyl)-substituted imidazoles, pyrazines, and quinoxalines, were synthesized according to multistep procedures with the use of chloral as the key compound. The reactivities of the resulting difluoroaromatic compounds were estimated based on 19F and 13C NMR spectral data and the results of quantum-chemical calculations. The calculated charge densities on the Cipso atoms correlate linearly with the experimental chemical shifts in the 19F and 13C NMR spectra. Difluoroaromatic compounds, which are characterized by F > –110 and C > 163 and by the charge density on the Cipso atom higher than 0.08 e, are sufficiently activated to be used for the preparation of high-molecular-weight polyethers. 相似文献
24.
New activated bis- and tetrafluoroaromatic compounds containing the bis-phenylquinoxaline fragments, viz., methylene-bis-6(7),6"(7")-{2-(p-fluoro)phenyl-3[4-(p-fluorobenzoyl)phenyl]quinoxalines}, were prepared according to multistep procedures with the use of chloral as the starting compound. The presence of the activating carbonyl groups in the para positions with respect to two fluorine atoms opens up the possibility of the use of these monomers for the synthesis of high-molecular-weight aromatic quinoxaline-containing polyether ketones. 相似文献
25.
The excess Gibb's free energy of mixing, GE, for ethyl iodide+toluene at 25°C have been obtained from the measured vapor pressuure data. The HE and GE values for ethyl iodide+toluene are positive throughout the ethyl iodide concentration range and GE>HE. The results have been analyzed in terms of Flory and ideal associated model theory of nonelectrolyte solutions. It has been observed that the ideal associated model approach which assumes the presence of AN and A2B molecular species describes well (within±10 J-mol–1 in the worst case) the general dependence of HE on XA (mole fraction of ethyl iodide) over the whole composition range for ethyl iodide+toluene mixtures. The equilibrium constants for A+A AB and 2A+BA2B reactions along with the enthalpies of formation of AB and A2B molecular species have been calculated. 相似文献
26.
Facile synthesis of 6(E)-geranylgeraniol-19-oic acid 1,a naturally occurring alicyclic diterpene acid, by a Horner-Wadsworth-Emmons olefination of two readily available fragments 2 and 3,is described. 相似文献
27.
Uwe Klingebiel Gerhild Wendenburg Anton Meller 《Monatshefte für Chemie / Chemical Monthly》1979,110(2):289-296
Lithium salts of hydrazines react with fluorosilanes under formation of fluorosilylhydrazines and LiF. Five membered rings are obtained in the reaction of bis(fluorosilyl)-hydrazines with lithiated amines. The mass,1H-and19F-nmr spectra of the compounds are reported. 相似文献
28.
29.
W. Wojnowski J. Pikies K. Peters E.-M. Peters D. Thiery H. G. Von Schnering 《无机化学与普通化学杂志》1994,620(2):377-384
Formation and Structures of N-(tri-t-butoxysilyl)aniline Compounds Para-substituted N-(tri-t-butoxysilyl)anilines (t-BuO)3SiNRC4H4X-p, R = H, CH3, with substituents of high electron affinity (X = CN, NO2) were prepared by a one-pot reaction of tri-t-butoxychlorsilane, potassium t-butanolate and substituted anilines. Corresponding compounds with substituents of low electron affinity (X = OMe, H) preferably were prepared by metalation of anilines with sodium amide. Four crystal structures were determined. N-(tri-t-butoxysilyl)-p-nitro-aniline, N-methyl-(N-tri-t-butoxysilyl)-p-nitroaniline and N-(tri-t-butoxysilyl)-p-cyanoaniline crystallize at 298 K monoclinically, N-(tri-t-butoxysilyl)aniline crystallizes orthorhombically. 相似文献
30.
Two-dimensional (2D) NMR is an invaluable technique for the complete analysis and assignment of chemical structures. Although 19F/19F COSY experiments are routinely used for assignments in perfluorochemicals, interpretation can be difficult because four-bond (4JFF) coupling constants are typically 5-10-fold larger than vicinal (3JFF) coupling constants. Furthermore, the dependence of long range coupling constants on stereochemistry is not always known. Fluorine-fluorine NOESY correlations represent an enhancement in the arsenal of 2D 19F NMR experiments. The NOESY and COSY spectra of 2,2,3,3,4,4,4-heptafluorobutanol and a telomeric perfluorochemical iodide show that COSY identifies the 1,4-fluorine interactions whereas NOESY identifies the vicinal fluorine atoms. The combined experiments have been used to unambiguously assign all of the fluorines in a mixture of cis- and trans-perfluoro-1,3-dimethylcyclohexane and in a substituted perfluorotetrahydrofuran. 相似文献