全文获取类型
收费全文 | 3669篇 |
免费 | 90篇 |
国内免费 | 9篇 |
专业分类
化学 | 2120篇 |
晶体学 | 26篇 |
力学 | 99篇 |
数学 | 513篇 |
物理学 | 1010篇 |
出版年
2022年 | 25篇 |
2021年 | 81篇 |
2020年 | 77篇 |
2019年 | 89篇 |
2018年 | 96篇 |
2017年 | 60篇 |
2016年 | 130篇 |
2015年 | 67篇 |
2014年 | 118篇 |
2013年 | 173篇 |
2012年 | 209篇 |
2011年 | 204篇 |
2010年 | 144篇 |
2009年 | 133篇 |
2008年 | 144篇 |
2007年 | 145篇 |
2006年 | 140篇 |
2005年 | 127篇 |
2004年 | 93篇 |
2003年 | 82篇 |
2002年 | 99篇 |
2001年 | 50篇 |
2000年 | 42篇 |
1999年 | 51篇 |
1998年 | 30篇 |
1997年 | 35篇 |
1996年 | 32篇 |
1995年 | 46篇 |
1994年 | 31篇 |
1993年 | 28篇 |
1992年 | 31篇 |
1991年 | 33篇 |
1990年 | 25篇 |
1989年 | 26篇 |
1985年 | 26篇 |
1984年 | 38篇 |
1983年 | 29篇 |
1982年 | 24篇 |
1981年 | 24篇 |
1980年 | 20篇 |
1979年 | 46篇 |
1978年 | 28篇 |
1977年 | 31篇 |
1976年 | 36篇 |
1975年 | 38篇 |
1974年 | 19篇 |
1973年 | 22篇 |
1972年 | 19篇 |
1971年 | 20篇 |
1969年 | 21篇 |
排序方式: 共有3768条查询结果,搜索用时 15 毫秒
71.
P. Abreu W. Adam T. Adye E. Agasi R. Aleksan G. D. Alekseev A. Algeri S. Almehed S. J. Alvsvaag U. Amaldi et al. 《Zeitschrift fur Physik C Particles and Fields》1994,61(3):407-419
The study of the properties of inclusive production ofD
s
mesons and of events in which a and a muon are present in the same jet provides two independent measurements of the probability,f
s
w
, for a heavy quark to hadronize into a strangeB orD meson. The data sample analysed corresponds to 243,000 hadronicZ
0 decays. The combined value of these measurements isf
s
w
=0.19±0.06±0.08. From the flight distance distributions ofD
s and of (-lepton) secondary vertices, with the lepton emitted at high transverse momentum relative to the jet axis, two values are obtained for theB
s
0
meson lifetime. Combining these measurements with a previous result based on the study ofD
s- events, theB
s
0
meson lifetime is measured to be: 0.96±0.37 ps. 相似文献
72.
We study the Hopfield model of an autoassociative memory on a random graph onN vertices where the probability of two vertices being joined by a link isp(N). Assuming thatp(N) goes to zero more slowly thanO(1/N), we prove the following results: (1) If the number of stored patternsm(N) is small enough such thatm(N)/Np(N) 0, asN, then the free energy of this model converges, upon proper rescaling, to that of the standard Curie-Weiss model, for almost all choices of the random graph and the random patterns. (2) If in additionm(N) < ln N/ln 2, we prove that there exists, forT< 1, a Gibbs measure associated to each original pattern, whereas for higher temperatures the Gibbs measure is unique. The basic technical result in the proofs is a uniform bound on the difference between the Hamiltonian on a random graph and its mean value. 相似文献
73.
Summary The international motions of a single cyclohexane molecule are studied by molecular dynamics calculations. Classical trajectories are calculated by integrating Newton's equation of motion. The potential functions used are essentially the same as in Allinger's MM2 program which is widely applied for calculations on conformational energies of organic molecules.Geometries and relative energies are reported for all stable low energy conformers and some transition states of cyclohexane. Vibrational frequencies of classical oscillations of individual bonds — computed for ethane as reference system — are close to the experimental values.Two trajectories of the molecular dynamics of cyclohexane were simulated. In the first we were able to follow the process of ring inversion: chair twisted forms inverted chair. The reaction path is analysed in detail and compared with static approaches. The second trajectory shows the correlated reorientation of the possible twisted forms alone. This process is known as pseudorotation.Dedicated to Prof. Dr. Karl Schlögl 相似文献
74.
Synthesis and Absolute Configuration of Clemastine and its Isomers. Condensation of 4-chloro-α-methylbenzhydrylalkohol ( 1 ) with 2-(2-chloroethyl)-1-methylpyrrolidine ( 2 ) gave an isomeric mixture of 2-[2-(p-chloro-α-methyl-=-phenylbenzyloxy)ethyl]-1-methylpyrrolidine ( 3 ) and 4-(p-chloro-=-phenylbenzyloxy)-1-methyl-hexahydroazepin ( 4 ). The separation of the four possible optically active isomers of 3 is described and their absolute configuration established by degradation to (R)- and (S)-1-methyl-2-pyrrolidineethanol ( 6 ), respectively, and by an X-ray cristallographic analysis of the quarternary methiodide of the isomer 3-A . Clemastine (3-A) is (+)-(2R)-2-[2-((αR)-(p-chloro-α-methyl-α-phenylbenzyloxy)ethyl)]-1-methylpyrrolidine. 相似文献
75.
In spite of the higher reactivity of styrene with respect to ethene for the alternating copolymerization with carbon monoxide, catalyzed by chiral (dihydrooxazole)(phosphino)palladium complexes, ethene is preferentially (and randomly) enchained in terpolymerization experiments; enantioface selection for styrene is comparably high in both copolymerization and terpolymerization processes. 相似文献
76.
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 565–566, April, 1992. 相似文献
77.
Kolen'ko YV Kovnir KA Gavrilov AI Garshev AV Meskin PE Churagulov BR Bouchard M Colbeau-Justin C Lebedev OI Van Tendeloo G Yoshimura M 《The journal of physical chemistry. B》2005,109(43):20303-20309
Mesoporous nanosized TiO2 and Zn(x)Ti(1-x)O(2-x) solid solution having a Zn content below 10 mol % with a particles size between 13 and 17 nm are prepared by a template-free sol-gel method followed by high-temperature supercritical drying in 2-propanol. The structural, textural, and electronic properties of the obtained nanomaterials are methodically investigated by using XRD, SEM, TEM, ED, HREM, EDX, ICP-OES, N(2) adsorption-desorption, Raman spectroscopy, and diffuse reflectance UV-vis spectroscopy. It is shown that the proposed synthesis technique leads to the formation of a Zn(x)Ti(1-x)O(2-x) solid solution based on the anatase crystal structure rather than a two-phase sample. High-resolution electron microscopy and electron diffraction indicate that the distribution of zinc atoms over the anatase structure does not lead to a considerable deformation of the crystal structure. 相似文献
78.
S. F. Solodovnikov O. A. Man'kova Z. A. Solodovnikova N. V. Ivannikova V. I. Alekseev 《Journal of Structural Chemistry》1996,37(4):645-650
The crystal structure of Cs2W3O10 (a=16.103, c=10.169 Å, $I\bar 4$ , Z=120/11) was determined from three-dimensional X-ray diffraction data (CAD-4 automatic diffractometer, 1612 reflections, R=0.044). The structure has an AB2O6 defective pyrochlore motif in which some of the groups consisting of four WO6 octahedra have been subtracted from the tungsten-oxygen framework and substituted by Cs+. The crystal has no vacancies in the substitution site (as confirmed by the occupancy refinement), and the composition of the crystal is strictly stoichiometric with a fractional number of atoms in the unit cell. A similar composition is suggested for the isostructural rubidium compound, which was earlier considered nonstoichiometric. 相似文献
79.
Alex Berlin Neil Gilkes Douglas Kilburn Vera Maximenko Renata Bura Alexander Markov Anton Skomarovsky Alexander Gusakov Arkady Sinitsyn Oleg Okunev Irina Solovieva John N. Saddler 《Applied biochemistry and biotechnology》2006,130(1-3):528-545
Seven cellulase preparations from Penicillium and Trichoderma spp. were evaluated for their ability to hydrolyze the cellulose fraction of hardwoods (yellow poplar and red maple) pretreated by organosolv extraction, as well as model cellulosic substrates such as filter paper. There was no significant correlation among hydrolytic performance on pretreated hardwood, based on glucose release, and filter paper activity. However, performance on pretreated hardwood showed significant correlations to the levels of endogenous β-glucosidase and xylanase activities in the cellulase preparation. Accordingly, differences in performance were reduced or eliminated following supplementation with a crude β-glucosidase preparation containing both activities. These results complement a previous investigation using softwoods pretreated by either organosolv extraction or steam explosion. Cellulase preparations that performed best on hardwood also showed superior performance on the softwood substrates. 相似文献
80.
Yu. M. Shafran V. A. Bakulev V. S. Mokrushin S. G. Alekseev A. T. Lebedev P. A. Sharbatyan 《Chemistry of Heterocyclic Compounds》1986,22(7):740-745
1,2,3-Triazol-5-olates are formed in the reaction of diazomalonodiamide and 2-diazo-2-cyanoacetic acid amide and N-methylamide with sodium ethoxide, triethylamine, and ammonia. The products of the reaction of 2-diazo-2-cyanoacetamide with primary amines are mixtures of 4-cyano-1,2,3-triazol-5-olates and 5-amino-1-alkyl-1,2,3-triazole-4-carboxamides.See [1] for communication 2.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 926–931, July, 1986. 相似文献