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121.
Experimental data on the activation energies of reactions of H-abstraction from oxygencontaining compounds by oxygen atoms and hydroxyl and alkoxyl radicals in the gas and liquid phases have been analyzed by means of the parabolic model of the transition state. The contribution of polar interaction to the activation energies of the reactions has been calculated. The contribution of solvation to the activation energy has been calculated by comparison of the reaction parameters of the respective reaction in the liquid and gas phases.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 38–42, January, 1994. 相似文献
122.
Teresa Corona Lídia Ribas Mireia Rovira Dr. Erik R. Farquhar Dr. Xavi Ribas Prof. Dr. Kallol Ray Dr. Anna Company 《Angewandte Chemie (International ed. in English)》2016,55(45):14005-14008
High‐valent terminal copper–nitrene species have been postulated as key intermediates in copper‐catalyzed aziridination and amination reactions. The high reactivity of these intermediates has prevented their characterization for decades, thereby making the mechanisms ambiguous. Very recently, the Lewis acid adduct of a copper–nitrene intermediate was trapped at ?90 °C and shown to be active in various oxidation reactions. Herein, we describe for the first time the synthesis and spectroscopic characterization of a terminal copper(II)–nitrene radical species that is stable at room temperature in the absence of any Lewis acid. The azide derivative of a triazamacrocyclic ligand that had previously been utilized in the stabilization of aryl–CuIII intermediates was employed as an ancillary ligand in the study. The terminal copper(II)–nitrene radical species is able to transfer a nitrene moiety to phosphines and abstract a hydrogen atom from weak C?H bonds, leading to the formation of oxidized products in modest yields. 相似文献
123.
Sebastian Litters Dr. Elisabeth Kaifer Prof. Hans‐Jörg Himmel 《Angewandte Chemie (International ed. in English)》2016,55(13):4345-4347
The red‐colored tetraborane(4) [B4(hpp)4]3+. ( 3 ; hpp=1,3,4,6,7,8‐hexahydro‐2H‐pyrimido[1,2‐a]pyrimidinate) with a rhomboid B4 skeleton stabilized by four N donors, was synthesized by the reaction of the strong hydride abstraction reagent [(acridine)BCl2][AlCl4] with the electron‐rich diborane(4) [HB(hpp)]2 ( 1 ). The salt 3 [AlCl4]3 was structurally characterized and the presence of unpaired electrons proven by EPR measurements. The unprecedented radical tricationic 3 is distinguished by a high positive charge and boron atoms in a low oxidation state (less than two). 相似文献
124.
Masumi Takamura Tomoyuki Nakamura Kiyohito Koyama 《Polymer Degradation and Stability》2008,93(10):1909-1916
Poly(l-lactide) (PLLA) was cross-linked with various types of peroxides under constant mole ratios of peroxide-derived radicals to PLLA during reactive extrusion. Peroxides were classified into three groups according to their decomposition rates (Group I: fast, Group II: moderate and Group III: slow) and comparisons were performed within each group. Cross-linking behavior was readily understood in terms of free radical efficiency and hydrogen abstraction ability of radicals. In the case of Groups II and III, the weight-average molecular weight (Mw) of cross-linked PLLA increased with overall hydrogen abstraction ability, because slow decomposition caused uniform cross-linking in molten PLLA. In Group I, Mw and gel fraction were higher than other groups despite Group I's lower hydrogen abstraction ability, leading to the conclusion that peroxide decomposition localized in solid PLLA caused partial cross-linking because of rapid decomposition. Furthermore, the efficiency of peroxide-induced cross-linking was investigated using the Charlesby-Pinner equation. 相似文献
125.
本文利用G3B3 和CBS-Q高精度理论方法检验了一系列胺类有机化合物中α-碳氢键离解能的实验测量值,在此基础上筛选出(U)BHandH/6-311++G(2df, 2p)//(U)B3LYP/6-31G(d)方法,发现其可以准确快速的预测氮α-碳氢键离解能。运用该方法研究了若干含氮药物分子,发现氮α-碳氢键离解能随药物分子结构发生明显变化。为了阐明其变化规律,系统研究单取代和双取代基效应,并解释了不同取代基效应的来源。 相似文献
126.
Samuel Barabé 《International Journal of Mathematical Education in Science & Technology》2013,44(8):1051-1064
Synthetic division is viewed as a change of basis for polynomials written under the Newton form. Then, the transition matrices obtained from a sequence of changes of basis are used to factorize the inverse of a bidiagonal matrix or a block bidiagonal matrix. 相似文献
127.
The hydrogen abstraction reactions from hydrazine and its methyl derivatives by the H atom have been investigated theoretically by using CBS-QB3//DSD-BLYP-D3(BJ)/Def2-TZVP quantum chemical calculations and transition state theory calculations coupled with various tunneling correction methods. Both the products and transition state energies of the hydrogen abstraction from the amino group were stabilized by the methyl group substitution. The substitution effect on the αN site was two times larger than that on the βN site. On the other hand, the substitution effect was negligible on the hydrogen abstraction from the methyl group. The overall rate coefficients of N2H4 + H reaction calculated by canonical variational transition state theory with the small-curvature tunneling correction agreed well with previously reported values, but those of CH3NHNH2/(CH3)2NNH2 + H were slightly lower than a previous experimental value. The product-specific rate coefficients have been proposed for the kinetics modeling of these fuels’ combustion. 相似文献
128.
《Electroanalysis》2018,30(8):1706-1713
The radical redox mediator tetrachloro‐phthalimido‐N‐oxyl (Cl4PINO) is generated at a glassy carbon electrode and investigated for the model oxidation of primary and secondary alcohols with particular attention to reaction rates and mechanism. The two‐electron oxidation reactions of a range of primary, secondary, and cyclic alcohols are dissected into an initial step based on C−H hydrogen abstraction (rate constant k1, confirmed by kinetic isotope effect) and a fast radical‐radical coupling of the resulting alcohol radical with Cl4PINO to give a ketal that only slowly releases the aldehyde/ketone and redox mediator precursor back into solution (rate constant k2). In situ electrochemical EPR reveals Cl4PINO sensitivity towards moisture. DFT methods are applied to confirm and predict C−H hydrogen abstraction reactivity. 相似文献
129.
William H. Watson Srikanth Kandala Michael G. Richmond 《Journal of chemical crystallography》2006,36(1):71-75
Treatment of the activated trirhenium cluster H3Re3(CO)10(MeCN)2 with the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) in CH2Cl2 does not afford the expected cluster product H3Re3(CO)10(bpcd) but rather the mononuclear complex fac-ClRe(CO)3(bpcd). The identity of fac-ClRe(CO)3(bpcd) was determined in solution by IR and NMR (1H and 31P) spectroscopies and the solid-state structure was established by X-ray diffraction analysis. fac-ClRe(CO)3(bpcd) crystallizes in the triclinic space P-1, a = 9.958(2) Å, b = 11.991(3) Å, c = 13.676(3) Å, α = 73.230(4)°, β = 73.806(4)°, γ = 77.409(4)°, V = 1484.6(6) Å3, Z = 2, and d
calc = 1.723 Mg/m3; R = 0.0367, R
w
= 0.0857 for 4253 reflections with I > 2σ(l). 相似文献
130.
The photochemical reaction between three A5‐steroids (1–3) and a series of substituted 1,4‐benzoquinones and their mechanistic study were reported. The reaction in nitrogen atmosphere led to the formation of three products including the steroid‐quinone coupling compound (A), 7‐hydroxy derivatives of Δ5‐steroids (B) and substituted 1, 4‐hydroquinone (C). Both chemical and spectrometric evidences such as UV‐Visible spectra, ESR, chemically induced dynamic nuclear polarization (CIDNP) and cyclic voltammetry (CV) verified that the title reaction underwent a predominant photoinduced electron transfer pathway via the triplet quinone. 相似文献