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251.
Cosolvents added to aqueous solutions of biomolecules profoundly affect protein stability, as well as biochemical equilibria. Some cosolvents, such as urea and guanidine hydrochloride, denature proteins, whereas others, such as osmolytes and crowders, stabilize the native structures of proteins. The way cosolvents interact with biomolecules is crucial information required to understand the cosolvent effect at a molecular level. We present a statistical mechanical framework based upon Kirkwood-Buff theory, which enables one to extract this picture from experimental data. The combination of two experimental results, namely, the cosolvent-induced equilibrium shift and the partial molar volume change upon the reaction, supplimented by the structural change, is shown to yield the number of water and cosolvent molecules bound or released during a reaction. Previously, denaturation experiments (e.g., m-value analysis) were analyzed by empirical and stoichiometric solvent-binding models, while the effects of osmolytes and crowders were analyzed by the approximate molecular crowding approach for low cosolvent concentration. Here we synthesize these previous approaches in a rigorous statistical mechanical treatment, which is applicable at any cosolvent concentration. The usefulness and accuracy of previous approaches was also evaluated. 相似文献
252.
Shimizu S 《The Journal of chemical physics》2004,120(10):4989-4990
To elucidate, at a molecular level, how cosolvents influence protein stability, it is indispensable to understand the distribution of water and cosolvent molecules around proteins. Calculation of excess solvation numbers of water and cosolvents serves this purpose, and I show that they can be extracted from preferential interaction parameter and volumeric data via the Kirkwood-Buff theory. This scheme was applied to trehalose and glycerol (stabilizers) and urea (denaturant). Important insights from the application include stabilizer-induced enhancement of protein hydration, which, together with the stabilizer's exclusion from protein surfaces, may contribute to protein stabilization at high osmolyte concentrations. 相似文献
253.
Kenji Yajima 《Communications in Mathematical Physics》1979,69(2):101-129
We study the quasi-classical limit of the quantum mechanical scattering operator for non-relativistic simple scattering system. The connection between the quantum mechanical and classical mechanical scattering theories is obtained by considering the asymptotic behavior as 0 of the quantum mechanical scattering operator on the state exp(—ip·a/)f(p) in the momentum representation.Partially supported by Fûjû-kai Foundation and Sakkô-kai Foundation 相似文献
254.
K. Yajima 《Communications in Mathematical Physics》2016,347(1):103-126
We consider Schrödinger equations for N number of particles in (classical) electro-magnetic fields that are interacting with each other via time dependent inter-particle potentials. We prove that they uniquely generate unitary propagators \({\{U(t,s), t,s \in \mathbb{R}\}}\) on the state space \({\mathcal{H}}\) under the conditions that fields are spatially smooth and do not grow too rapidly at infinity so that propagators for single particles satisfy Strichartz estimates locally in time, and that local singularities of inter-particle potentials are not too strong that time frozen Hamiltonians define natural selfadjoint realizations in \({\mathcal{H}}\). We also show, under very mild additional assumptions on the time derivative of inter-particle potentials, that propagators possess the domain of definition of the quantum harmonic oscillator \({\Sigma(2)}\) as an invariant subspace such that, for initial states in \({\Sigma(2)}\), solutions are C1 functions of the time variable with values in \({\mathcal{H}}\). New estimates of Strichartz type for propagators for N independent particles in the field will be proved and used in the proof. 相似文献
255.
The stereoselective synthesis of the maitotoxin C'D'E'F'-ring system having a side chain has been accomplished through a convergent strategy. The key reactions include Horner-Wadsworth-Emmons coupling of the C'D'E'-ring and the side chain and subsequent construction of the F'-ring by silane reduction of dihydropyran. 相似文献
256.
Johan van den Bergh Weidong Zhu Freek Kapteijn Jacob A. Moulijn Kenji Yajima Kunio Nakayama Toshihiro Tomita Shuichi Yoshida 《Research on Chemical Intermediates》2008,34(5-7):467-474
The permeation of CO2 and CH4 and their binary mixtures through a DDR membrane has been investigated over a wide range of temperatures and pressures. The synthesized DDR membrane exhibits a high permeance and maintains a very high selectivity for CO2. At a total pressure of 101 kPa, the highest selectivity for CO2 in a 50∶50 feed mixture was found to be over 4000 at 225 K. This is ascribed to the higher adsorption affinity, as well as to the higher mobility for the smaller CO2 molecules in the zeolite, preventing the bypassing of the CH4 through the membrane. An engineering model, based on the generalized Maxwell-Stefan equations, has been used to interpret the transport phenomena in the membrane. The feasibility of DDR membranes as applied to CO2 removal from natural gas or biogas is anticipated. 相似文献
257.
Ryoda A Yajima N Haga T Kumamoto T Nakanishi W Kawahata M Yamaguchi K Ishikawa T 《The Journal of organic chemistry》2008,73(1):133-141
(+/-)-1,2-Bis(2-methylphenyl)ethylene-1,2-diamine, prepared from benzil and ammonium acetate, was optically resolved as a chiral framework for 2-(1-benzyl-2-hydroxyethyl)imino-1,3-dimethylimidazolidine with 2-methylphenyl pendants at the 4,5-positions. Catalysis ability of the 1,3-dimethyl-4,5-bis(2-methylphenyl)imidazolidine and the related 1,3-dibenzyl-4,5-diphenylimidazolidine was examined in the asymmetric Michael reaction of t-butyl diphenyliminoacetate and ethyl acrylate. 相似文献
258.
Fluorinated organic compounds have attracted significant attention over the past few decades owing to their unique properties and versatility. An established method for the synthesis of fluorinated organic compounds involves radical perfluoroalkylation reactions towards double bonds. In this radical pathway, electrophilic perfluoroalkyl radicals exhibit excellent reactivity towards electron-rich olefins. Therefore, several splendid perfluoroalkylation reactions of electron-rich olefins have been reported. However, there are only a few examples of reaction involving electron-deficient olefins because of their poor electronic compatibility with perfluoroalkyl radicals. This review focuses on the reports that challenge this long-standing issue. Radical perfluoroalkylation/bifunctionalization reactions of electron-deficient olefins are described according to the radical generation methods. 相似文献
259.
Hyperfine Interactions - Experimental results of “time-delayed interferometry” with nuclear resonances at KEK are reported. Mössbauer nuclei were used as a cavity for X-rays in... 相似文献
260.
Setsuko Yajima Tsuyoshi Yahata Yasuyuki Takeda 《Journal of inclusion phenomena and macrocyclic chemistry》2000,38(1-4):305-322
In order to quantitatively investigate effects of the size, the structuralrigidity, and the lipophilicity of dibenzo-18-crown-6 (DB18C6) on itsextraction-ability and -selectivity for alkali metal ions, constants of theoverall extraction (Kex), the distribution for various diluents of lowdielectric constants (KD,MLA), and the aqueous ion-pairformation (KMLA) of DB18C6-alkali metal (Na-—Cs) picrate 1:1:1 complexes were determined at 25°C; the partition constants of DB18C6 itself were also measured at 25°C. The log KMLA of Na, K, Rb, and Cs are -0.14 ± 0.11, 1.30 ± 0.10, 1.00 ± 0.09, and 0.24 ± 0.11, respectively. The partition behavior of DB18C6 and its1:1:1 complexes with the alkali metal picrates can be clearly explained byregular solution theory, except for chloroform. The molar volumes andsolubility parameters of DB18C6 and the 1:1:1 complexes were determined.A relation between molar volumes of the complexes and KMLAis discussed. The magnitude of Kex is largely determined by that ofKD,MLA. For every diluent, the extraction selectivity of DB18C6increases in the order Na > Cs > Rb > K. The K extraction-selectivity of DB18C6 over Na is the highest among all the combinations of the two neighboring alkali metals in the periodic table. The extraction-ability and -selectivity for the alkalimetal picrates and their change with the diluent of DB18C6 were completely elucidated by the four fundamental equilibria and regular solution theory. 相似文献