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101.
Inversion of Configuration at the Phosphorus Nucleophile in the Diastereoselective and Enantioselective Synthesis of P‐Stereogenic syn‐Phosphiranes from Chiral Epoxides
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Jake A. Muldoon Dr. Balázs R. Varga Meaghan M. Deegan Dr. Timothy W. Chapp Ádám M. Eördögh Prof. Russell P. Hughes Prof. David S. Glueck Dr. Curtis E. Moore Prof. Arnold L. Rheingold 《Angewandte Chemie (International ed. in English)》2018,57(18):5047-5051
Nucleophilic substitution results in inversion of configuration at the electrophilic carbon center (SN2) or racemization (SN1). The stereochemistry of the nucleophile is rarely considered, but phosphines, which have a high barrier to pyramidal inversion, attack electrophiles with retention of configuration at P. Surprisingly, cyclization of bifunctional secondary phosphine alkyl tosylates proceeded under mild conditions with inversion of configuration at the nucleophile to yield P‐stereogenic syn‐phosphiranes. DFT studies suggested that the novel stereochemistry results from acid‐promoted tosylate dissociation to yield an intermediate phosphenium‐bridged cation, which undergoes syn‐selective cyclization. 相似文献
102.
BaFCl:Ce^3+和BaFCl:Gd^3+晶体中的发光中心 总被引:1,自引:0,他引:1
运用不同的固相反应条件制备或后处理了几种BaFCl:RE~(3+)(RE=Ce或Gd)晶体,测定了它们的荧光光谱,对照并分析光谱数据和不同条件下可能引入晶体缺陷的情况,推论出晶体中存在有2类发光中心,即由RE_(?)-F_(?)和RE_(?)-F_(?)缔合体构成的中心。 相似文献
103.
Distributions ofn-butane pyrolysis products and activities of catalysts have been analyzed. The catalysts based on magnesium oxide was preparedvia modification with magnesium acetate.n-Butane decomposition is shown to be accelerated due to active surface centers of at least two types. 相似文献
104.
Arnold J. Hoff Peter Gast Sergei A. Dzuba Christiane R. Timmel Catherine E. Fursman P.J. Hore 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1998,54(14):2283-2293
We describe in some detail the new method of distance determination for a photoinduced radical pair. Emphasis is on giving the nuts and bolts of the calculations that result in analytical expressions for in- and out-of-phase electron spin echo (ESE) envelope modulations, pulse flip-angle dependencies, zero- and double-quantum coherences, and the distance between the two radicals. The theoretical results are illustrated by a set of recent experiments on photosynthetic reaction centers. 相似文献
105.
The enantioselective total synthesis of the nonacyclic polypyrrolidinoindoline (−)-idiospermuline is described. Stereocontrolled formation of the vicinal quaternary carbon centers is achieved in a single step by dialkylation of an unsymmetrical prostereogenic dienolate with a tartrate-derived chiral dielectrophile. A catalyst-controlled diastereoselective Heck cyclization is employed to form the diaryl-substituted quaternary center. 相似文献
106.
本文介绍了Kaminsky可溶性配位催化剂的发展特点,并在总结均相催化定向控制机理、α-烯烃的间规聚合以及聚合活性种的性质等方面的最新研究成果基础上.讨论了对配位聚合理论研究的意义。 相似文献
107.
Phosphoester Hydrolysis: The Incoming Substrate Turns the Bridging Hydroxido Nucleophile into a Terminal One
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Dr. Eric Gouré Dr. Michaël Carboni Angélique Troussier Colette Lebrun Dr. Jacques Pécaut Jean‐François Jacquot Patrick Dubourdeaux Dr. Martin Clémancey Dr. Geneviève Blondin Dr. Jean‐Marc Latour 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8064-8068
Identifying the active nucleophile in hydrolysis reactions catalyzed by binuclear hydrolases is a recurrent problem and a matter of intense debate. We report on the phosphate ester hydrolysis by a FeIIIFeII complex of a binucleating ligand. This complex presents activities in the range of those observed for similar biomimetic compounds in the literature. The specific electronic properties of the FeIIIFeII complex allowed us to use 1H NMR and Mössbauer spectroscopies to investigate the nature of the various species present in the solution in the pH range of 5–10. Both techniques showed that the hydrolysis activity is associated to a μ‐hydroxido FeIIIFeII species. Further 1H NMR experiments show that binding of anions or the substrate changes this bonding mode suggesting that a terminal hydroxide is the likely nucleophile in these hydrolysis reactions. This view is further supported by the structure determination of the hydrolysis product. 相似文献
108.
This paper presents the first calculation of the second order optical nonlinearity of the FA color center for second harmonic generation (SHG) in KCl:Li crystals. The real and imaginary components of the nonlinear susceptibility evaluated over a wide spectral range enclosing the resonance region of the center show interesting feature. Second harmonics generation and three wave mixing processes are nonlinear optical effects based on the second order susceptibility of materials and are very effective in providing laser radiation over a wide range of wavelengths. The density matrix formalism is employed and the equation of motion is solved by second order perturbation to evaluate the nonlinear susceptibility for SHG. It is found that the system shows large resonance-enhanced second order susceptibilities for color center concentration of 1023 m−3. A scheme of phase matching in terms of anomalous dispersion of the centers is discussed. 相似文献
109.
A radiation-temperature coupling model of the optical fiber attenuation spectrum in the Ge/P co-doped fiber
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A radiation-temperature coupling model of optical fiber attenuation spectrum has been developed. The spectrum in Ge/P co-doped fiber ranging from 800 nm-1600 nm at different temperatures and doses was measured and decomposed according to the configurational coordinate model based on which the power-law model was employed to predict the intensity of the color center absorption band at different doses. And the fiber loss in space was predicted by the model. This work will benefit the application of fibers in a complicated radiation environment. 相似文献
110.
Itai Massad Heiko Sommer Ilan Marek 《Angewandte Chemie (International ed. in English)》2020,59(36):15549-15553
An in situ generated cationic Ir‐catalyst isomerizes simple allylic silyl ethers into valuable, fully substituted aldehyde‐derived silyl enol ethers. Importantly, by judicious choice of substrate, either of the two possible stereoisomers of a given enolate derivative is accessible with complete stereoselectivity. One‐pot isomerization‐aldol and isomerization‐allylation processes illustrate the synthetic utility of this method. 相似文献