全文获取类型
收费全文 | 259658篇 |
免费 | 3697篇 |
国内免费 | 751篇 |
专业分类
化学 | 136816篇 |
晶体学 | 3680篇 |
力学 | 10198篇 |
综合类 | 10篇 |
数学 | 33211篇 |
物理学 | 80191篇 |
出版年
2021年 | 2425篇 |
2020年 | 2602篇 |
2019年 | 2844篇 |
2018年 | 3755篇 |
2017年 | 3590篇 |
2016年 | 5667篇 |
2015年 | 3891篇 |
2014年 | 5225篇 |
2013年 | 12575篇 |
2012年 | 10552篇 |
2011年 | 12041篇 |
2010年 | 8271篇 |
2009年 | 7903篇 |
2008年 | 10833篇 |
2007年 | 10819篇 |
2006年 | 10181篇 |
2005年 | 9326篇 |
2004年 | 8467篇 |
2003年 | 7371篇 |
2002年 | 6989篇 |
2001年 | 7518篇 |
2000年 | 6013篇 |
1999年 | 4598篇 |
1998年 | 3681篇 |
1997年 | 3629篇 |
1996年 | 3534篇 |
1995年 | 3148篇 |
1994年 | 3073篇 |
1993年 | 2896篇 |
1992年 | 3271篇 |
1991年 | 3166篇 |
1990年 | 3097篇 |
1989年 | 2816篇 |
1988年 | 2859篇 |
1987年 | 2846篇 |
1986年 | 2653篇 |
1985年 | 3464篇 |
1984年 | 3695篇 |
1983年 | 2998篇 |
1982年 | 3168篇 |
1981年 | 3147篇 |
1980年 | 2965篇 |
1979年 | 3041篇 |
1978年 | 3113篇 |
1977年 | 3115篇 |
1976年 | 3189篇 |
1975年 | 2922篇 |
1974年 | 2909篇 |
1973年 | 3056篇 |
1972年 | 1931篇 |
排序方式: 共有10000条查询结果,搜索用时 484 毫秒
951.
D. Kast A. Jungclaus K.P. Lieb M. Górska G. de Angelis P.G. Bizzeti A. Dewald C. Fahlander H. Grawe R. Peusquens M. De Poli H. Tiesler 《The European Physical Journal A - Hadrons and Nuclei》1998,3(2):115-128
In the neutron deficient isotopes 104,105In lifetimes of high spin states in the range from 0.5 ps to 600 ps have been measured in a coincidence recoil distance Doppler
shift (RDDS) experiment. By combining the Doppler shift attenuation (DSA) and RDDS methods at few μm flight distances, the
problem of delayed feeding has been avoided and very short lifetimes in the range 0.5–0.8 ps have been determined. Shell model
calculations with strong restrictions for the neutron orbitals reveal good agreement with experimental level energies and
still fair agreement for most measured B(M1) and B(E2) values.
Received: 30 June 1998 相似文献
952.
953.
J. M. Pico C. P. Menaut J. Fernández J. L. Legido M. I. Paz Andrade 《Journal of solution chemistry》1991,20(1):115-124
Excess molar enthalpies hE at 25 and 35° C and atmospheric pressure, are reported for the binary mixtures formed by a 2-butanone and 2-pentanone with 1-chlorobutane, 1-chloropentane, 1-chlorohexane, or 1-chlorooctane. The hE values for all the mixtures are positive, increasing as the 1-chloroalkane length increases and as the ketone length decreases. Excess molar enthalpies depend slightly on the temperature. The experimental values together with those from the literature were used to calculate the interaction parameters for the Dang-Tassios version of the UNIFAC model.Communicated at the Festsymposium celebrating Dr. Henry V. Kehiaian's 60th birthday, Clermont-Ferrand, France, 17–18 May 1990. 相似文献
954.
955.
Thin films of polystyrene (PS), poly(methyl methacrylate) (PMMA) and polystyrene-polyacrylonitrile copolymer (PS-AN), containing various embedded transition-metal complexes, have been studied by FTIR microscopy. The spatial distributions of the transition-metal carbonyl complexes throughout the thin organic polymer films have been determined by a two-dimensional IR mapping procedure. The spectral variations observed in the distribution of the metal carbonyls throughout the different polymer films are discussed. The IR data show that the technique used to prepare the organometallic-embedded thin films (viz. freeze-drying of solutions followed by hot mechanical pressing of the residues) does in general lead to homogeneous films which may eventually find industrial application, e.g. as membrane sensors for small molecules. 相似文献
956.
The possible types of ordering diagrams of ternary substutional alloys with an fcc lattice are analyzed, taking account of interactions in two coordination spheres.Ural Polytechnic Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 38–41, December, 1992. 相似文献
957.
Dr.-Ing. M. Millies Dipl.-Ing. St. v. Bose Dipl.-Ing. A. Tokarz Univ.-Prof.Dr.-Ing. D. Mewes 《Heat and Mass Transfer》1994,30(1):17-25
The common methods for calculating the mass transfer across liquid-liquid interfaces in technical applications take into account the mass transfer resistances within the bulk phases. The transfer resistance of the interface and a possible coupling between the momentum and the mass transport is not taken into account. In the present paper a survey is given of theoretical approaches which can describe this coupling and the additional mass transfer resistance. A theory is proposed by Hampe which can be used to explain the coupling between momentum and mass transport employing thermodynamics of irreversible processes. On the basis of this work, the influence of the dilatation of a flat interface on the mass transfer is deduced. It is also concluded from this theory that the diffusion coefficients within the bulk phases are coupled near the thermodynamic equilibrium. 相似文献
958.
Novel 3-phenyloxy substituted propane-1,2-diol derivatives, 4-(4-n-hexyloxyphenyl)-butane-1,2-diol and 4-(trans-4-n-pyropylcyclohexyl)-butane-1,2-diol have been synthesized and their thermal behaviour has been studied. These compounds exhibit thermotropic and, after addition of water, also lyotropic liquid-crystalline behaviour. The clearing temperatures of the smectic mesophases were found to be strongly dependent on the alkyl chain length and on the structural units that link the aromatic ring to the alkyl chain and to the diol unit. The behaviour of the aromatic compounds is compared with that of the cyclohexane derivative. Thereby it has been realized that the mesophase stability of the amphiphilic diols incorporating a rigid unit is largely determined by both, the molecular geometry (molecular shape and intramolecular flexibility) and the amphiphilic structural pattern. 相似文献
959.
Jesús M. Velásquez Bermúdez 《Annals of Operations Research》2002,117(1-4):21-31
This document presents theoretical considerations about the solution of dynamic optimization problems integrating the Benders Theory, the Dynamic Programming approach and the concepts of Control Theory. The so called Generalized Dual Dynamic Programming Theory (GDDP) can be considered as an extension of two previous approaches known as Dual Dynamic Programming (DDP): The first is the work developed by Pereira and Pinto [3–5], which was revised by Velásquez and others [8,9]. The second is the work developed by Read and others [2,6,7]. 相似文献
960.
The pion cloud renormalises the light-cone wavefunction of the nucleon which is measured in hard, exclusive photon-nucleon reactions. We discuss the leading twist contributions to high-energy exclusive reactions taking into account both the pion cloud and perturbative QCD physics. The nucleon’s electromagnetic form-factor at high Q2 is proportional to the bare nucleon probability Z and the cross-sections for hard (real at large angle or deeply virtual) Compton scattering are proportional to Z2. Our present knowledge of the pion-nucleon system is consistent with Z = 0.7 ± 0.2. If we apply just perturbative QCD to extract a light-cone wavefunction directly from these hard exclusive cross-sections, then the light-cone wavefunction that we extract measures the three valence quarks partially screened by the pion cloud of the nucleon. We discuss how this pion cloud renormalisation effect might be understood at the quark level in terms of the (in-)stability of the perturbative Dirac vacuum in low energy QCD. 相似文献