全文获取类型
收费全文 | 468篇 |
免费 | 7篇 |
专业分类
化学 | 307篇 |
晶体学 | 4篇 |
力学 | 8篇 |
数学 | 23篇 |
物理学 | 133篇 |
出版年
2023年 | 3篇 |
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 10篇 |
2018年 | 6篇 |
2017年 | 2篇 |
2016年 | 7篇 |
2015年 | 11篇 |
2014年 | 10篇 |
2013年 | 22篇 |
2012年 | 26篇 |
2011年 | 28篇 |
2010年 | 20篇 |
2009年 | 13篇 |
2008年 | 34篇 |
2007年 | 31篇 |
2006年 | 27篇 |
2005年 | 32篇 |
2004年 | 19篇 |
2003年 | 13篇 |
2002年 | 13篇 |
2001年 | 11篇 |
2000年 | 15篇 |
1999年 | 2篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1993年 | 7篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1969年 | 3篇 |
1968年 | 3篇 |
1967年 | 5篇 |
1965年 | 1篇 |
1961年 | 2篇 |
1928年 | 2篇 |
排序方式: 共有475条查询结果,搜索用时 15 毫秒
111.
In glassy materials, aging proceeds at large times via thermal activation. We show that this can lead to negative dynamical response functions and novel and well-defined violations of the fluctuation-dissipation theorem, in particular, negative fluctuation-dissipation ratios. Our analysis is based on detailed theoretical and numerical results for the activated aging regime of simple kinetically constrained models. The results are relevant to a variety of physical situations, such as aging in glass formers, thermally activated domain growth, and granular compaction. 相似文献
112.
Fabienne Chouraqui 《代数通讯》2018,46(11):4710-4723
The structure group G of a non-degenerate symmetric set (X,S) is a Bieberbach and a Garside group. We describe a combinatorial method to compute explicitly a group of automorphisms of G and show this group admits a subgroup that preserves the Garside structure. In some special cases, we could also prove the group of automorphisms found is an outer automorphism group. 相似文献
113.
We prove large deviations principles in large time, for the Brownian occupation time in random scenery . The random field is constant on the elements of a partition of d into unit cubes. These random constants, say consist of i.i.d. bounded variables, independent of the Brownian motion {Bs,s0}. This model is a time-continuous version of Kesten and Spitzer's random walk in random scenery. We prove large deviations principles in ``quenched' and ``annealed' settings.Mathematics Subject Classification (2000):60F10, 60J55, 60K37 相似文献
114.
Laurent N Lafont D Dumoulin F Boullanger P Mackenzie G Kouwer PH Goodby JW 《Journal of the American Chemical Society》2003,125(50):15499-15506
Several 4-(4'-N,N-didodecylaminophenylazo)phenyl 1,2-trans glycosides 5a-e with various carbohydrate heads (beta-D-gluco, beta-D-galacto, beta-lacto, beta-D-xylo, and alpha-D-manno) have been synthesized. The key step was the formation of phenyldiazonium tetrafluoroborates 2a-e from the per-O-acetylated 4-aminophenyl glycosides 1a-e. These salts were condensed with N,N-didodecylaniline under phase transfer conditions and the per-O-acetylated 4-(4'-N,N-didodecylaminophenylazo)phenyl 1,2-trans glycosides 4a-e were fully de-O-acetylated by the Zemplén method. The self-organizing liquid crystal properties of the compounds were investigated by a variety of techniques, including polarized light microscopy, differential scanning calorimetry, and X-ray diffraction. All but one of the materials exhibited smectic A, lamellar phases. Remarkably, the glucose derivative exhibited a rectangular disordered columnar phase. This result has implications with respect to the induced curvature created by the recognition processes of the glucose headgroup relative to the other sugar moieties and to the prevalence of various glycolipids in cell membranes 相似文献
115.
A value for the nuclear magnetic moment of theI=2 (80.56 keV) level of166Er has been obtained by comparing measurements made by the Mössbauer effect on166Er with NMR measurements on the ground state of167Er in the same matrix. From measurements on ErFe2, ErAl2 and ErZn we obtain the value N (166Er; 80.56 keV)=0.650±0.010 n.m. This result is slightly higher than previously proposed values. 相似文献
116.
117.
The matrix elements of the total Hamiltonian between a multiconfigurational SCF wave function and some well-defined linear combinations of excited Slater determinants are equal to zero. By means of this generalized Brillouin theorem it is possible to estimate the improvements to be expected from a subsequent configuration-interaction treatment. The expression of the effective potential for the orbitals can be also derived in the frame of a given multiconfigurational theory. As an example, the case of the CMC-SCF method recently suggested [9] is examined. 相似文献
118.
From chiral counterions to twisted membranes 总被引:1,自引:0,他引:1
Berthier D Buffeteau T Léger JM Oda R Huc I 《Journal of the American Chemical Society》2002,124(45):13486-13494
In membranes, the chirality of the amphiphile constituents is sometimes expressed at a supramolecular scale of nanometers or micrometers. We have recently reported that membranes of nonchiral dicationic n-2-n amphiphiles can also be chirally twisted upon interacting with chiral tartrate counterions. Here, we demonstrate that the mechanism of the chiral induction by counterions involves specific anion-cation recognition and the induction of conformationally labile chirality in the cations. Single-crystal X-ray diffraction shows that the amphiphilic cations exist as a mixture of chiral conformers. (1)H NMR data establish a specific recognition between tartrate and n-2-n cations and show that chiral conformers also exist in solution. Circular dichroism (CD) in the UV-vis shows a sharp conformational change of tartrate ions from anti to gauche when bound to the chiral cationic membranes. This is confirmed by CD in the infrared region which also shows concomitant induced CD bands in the vibrations of the n-2-n amphiphiles. These results represent the first example of the so-called Pfeiffer effect in a membrane. They provide a general framework for designing new tunable membrane systems. Our work also includes the first application of vibrational circular dichroism in the study of chiral conformations of amphiphiles in membranes and demonstrates the very high potential of this technique. 相似文献
119.
Sergiy S. Mikhailichenko Vadim M. Timoshenko Yuriy G. Shermolovich Fabienne Grellepois 《Journal of fluorine chemistry》2007,128(7):703-709
Reactions of N-alkyl- or N-aryl(perfluoroalkyl)thiocarboxamides with alkyl lithium reagents are described. Trifluorothioacetamides are converted into the corresponding lithium salts. Compounds bearing a long polyfluorinated chain terminated by a CHF2 group and compounds containing an N-alkyl substituent with a proton adjacent to nitrogen react further via a multi-step reaction sequence involving HF elimination and then vinylic fluorine substitution and/or SN′ type fluorine substitution. These transformations led to unsaturated N-monosubstituted polyfluorinated thioamides. 相似文献
120.
Résumé On a calculé la structure électronique de l'état initial et de l'état de transition de la réaction de substitution F–+CH3FFCH3+F– par la méthode des orbitales moléculaires SCF dans l'approximation gaussienne. On trouve que l'énergie de l'état de transition est inférieure à la somme des énergies des produits séparés CH3F et F–. Cependant, cette contribution négative à l'énergie d'activation est contrebalancée par la variation des énergies de solvatation.
Remerciements. Nous remercions bien sincèrement M. A. Rassat (CEN, Grenoble) de nous avoir suggéré ce problème et M. Ph. Millie (ENS, Paris) de nous avoir apporté des éléments de discussion constructifs. 相似文献
Ab initio calculations on a typical SN2 ReactionElectronic structure of methyl fluoride and of the transition state (FCH3F)–
The electronic structure of the initial and transition states of the substitution reaction F–+CH3F FCH3+F– have been calculated by the SCF molecular orbital method in the Gaussian approximation. It is found that the energy of the transition state is lower than the sum of the energies of the separated systems CH3F and C–. However, this negative contribution to the activation energy is balanced by the variation of solvatation energies.
Zusammenfassung Die Elektronenstruktur des Ausgangs- und des Übergangszustandes der Substitutionsreaktion F–+CH3FFCH3+F– wurden mit einer SCF-MO-Methode mit Gaußfunktionen berechnet. Die Energie des Übergangszustandes ist niedriger als die Summe der Energien der separierten Systeme CH3F und F–. Dieser negative Beitrag zu der Aktivierungsenergie wird allerdings ausgeglichen durch eine Änderung der Solvatationsenergie.
Remerciements. Nous remercions bien sincèrement M. A. Rassat (CEN, Grenoble) de nous avoir suggéré ce problème et M. Ph. Millie (ENS, Paris) de nous avoir apporté des éléments de discussion constructifs. 相似文献