全文获取类型
收费全文 | 3315篇 |
免费 | 146篇 |
国内免费 | 15篇 |
专业分类
化学 | 2280篇 |
晶体学 | 13篇 |
力学 | 128篇 |
数学 | 501篇 |
物理学 | 554篇 |
出版年
2023年 | 45篇 |
2022年 | 34篇 |
2021年 | 87篇 |
2020年 | 84篇 |
2019年 | 85篇 |
2018年 | 51篇 |
2017年 | 41篇 |
2016年 | 109篇 |
2015年 | 99篇 |
2014年 | 99篇 |
2013年 | 165篇 |
2012年 | 211篇 |
2011年 | 236篇 |
2010年 | 119篇 |
2009年 | 113篇 |
2008年 | 191篇 |
2007年 | 190篇 |
2006年 | 184篇 |
2005年 | 171篇 |
2004年 | 104篇 |
2003年 | 100篇 |
2002年 | 73篇 |
2001年 | 51篇 |
2000年 | 27篇 |
1999年 | 36篇 |
1998年 | 42篇 |
1997年 | 32篇 |
1996年 | 35篇 |
1995年 | 27篇 |
1994年 | 25篇 |
1993年 | 26篇 |
1992年 | 27篇 |
1991年 | 23篇 |
1990年 | 16篇 |
1989年 | 15篇 |
1988年 | 15篇 |
1987年 | 23篇 |
1986年 | 37篇 |
1985年 | 23篇 |
1984年 | 26篇 |
1983年 | 21篇 |
1982年 | 26篇 |
1981年 | 29篇 |
1980年 | 39篇 |
1978年 | 26篇 |
1977年 | 28篇 |
1976年 | 28篇 |
1975年 | 21篇 |
1974年 | 18篇 |
1972年 | 17篇 |
排序方式: 共有3476条查询结果,搜索用时 296 毫秒
991.
Optical absorption spectrum of VO2+ ion in sodium zinc sulphate tetrahydrate single crystal has been reported at room and liquid nitrogen temperatures. From the nature and position of the observed bands, they have been attributed to VO2+ ion in C4v symmetry. The crystal field and molecular orbital coefficients have been evaluated. 相似文献
992.
H. -J. Jacob 《Mathematical Methods of Operations Research》1981,25(8):B265-B269
Zusammenfassung Durch Minimierung der Zahl der verzögerten Anstellungen bzw. der Variation der Planstellenanzahl kommt man zu konstanten jährlichen Einstellungen für jede Unterteilung des Planungszeitraumes. Ziel dieser Untersuchung ist die formale Beschreibung der Einstellungsraten.
Summary In order to cover a strongly varying demand for personnel with constant recruiting rates it will be permitted to defer the moment of the acceptance respectively to vary the quantity of the established positions. We get two solutions of this problem minimizing the number of acceptances, which will be deferred, respectively the change of the quantity of established positions.相似文献
993.
For euclidean functional integrals, the relevance of configurations beyond the set of classical solutions is investigated. We propose an equation to select the important configurations and derive general expressions for their contribution to the integral. Employing a pseudoparticle picture, we perform a dilute-gas approximation and estimate finite-density corrections through a virial expansion. The methods are exemplified for the anharmonic oscillator and the double well potential. 相似文献
994.
(Selectivity of the bromine—methanol dissolution in the determination of oxygen in aluminium.) The chemical determination of oxygen in aluminium by the classical bromine—methanol method is compared with the 14-MeV neutron activation technique. It is shown that the bromine dissolution method is affected by compounds such as AlN or MgAl2O4. A mode of operation which limits the resulting error is proposed. 相似文献
995.
Bonding criteria for molecular orbitals in diatomic molecules are discussed. An orbital force criterion is shown to have several conceptual and practical advantages, providing a basis for the investigation of inter-relations among many of the commonly employed criteria.It is found that interconsistency among those criteria is guaranteed, within the framework of Koopmans' Theorem, if the orbital energies are monotonic in the range (R
e, ).The application of the orbital force criterion to the second row homonuclear diatomics exhibits reasonable chemical trends concerning the valence-shell orbitals, as well as indications of a slightly antibonding nature of the inner orbitals.Based on a section of a thesis to be submitted by Y.T. to the Senate of the Technion-Israel Institute of Technology, in partial fulfilment of the requirements for the D.Sc. degree 相似文献
996.
997.
Sum rules for inelastic reactions are derived from boundary dispersion relations. If sufficient data or a model is available for the amplitude in the direct channel, then these sum rules provide a means of studying the dynamics in the cross channel. The convergence of these sum rules is investigated, assuming they can be saturated with narrow-width resonances, and rough estimates of the coupling constants of cross-channel exchanges for the photoproduction of pseudoscalar mesons are obtained. 相似文献
998.
Lawrence P. Giver Robert W. Boese Jacob H. Miller 《Journal of Quantitative Spectroscopy & Radiative Transfer》1974,14(8):793-802
Quantitative measurements of intensities and half-widths were made for individual rotational lines of the atmospheric oxygen B band. The total band intensity, as derived from the line intensity measurements, is 40·8±0·6 cm?1km?1atm?1 STP. As had been previously found in this laboratory for the oxygen A band, the relative line intensities conform closely to the rotational distribution calculated by either Schlapp or by Watson. The line half-widths at half-intensity were determined for oxygen self-broadening for the and branch lines and for a few and branch lines near the band origin, and were found to vary from 0·064 cm?1atm?1 at J′ = 1 to 0·042 cm?1atm?1 at J′ = 25. 相似文献
999.
Jacob Feldman 《Israel Journal of Mathematics》1980,36(3-4):321-345
A new approach is given to the entropy of a probability-preserving group action (in the context ofZ and ofR
n
), by defining an approximate “r-entropy”, 0<r<1, and lettingr → 0. If the usual entropy may be described as the growth rate of the number of essential names, then ther-entropy is the growth rate of the number of essential “groups of names” of width≦r, in an appropriate sense. The approach is especially useful for actions of continuous groups. We apply these techniques to
state and prove a “second order” equipartition theorem forZ
m
×R
n
and to give a “natural” proof of Ornstein’s isomorphism theorem for Bernoulli actions ofZ
m
×R
n
, as well as a characterization of such actions which seems to be the appropriate generalization of “finitely determined”. 相似文献
1000.
A simple model to predict the relative occupation numbers of various interstitial sites in intermetallic hydrides is proposed. The model assumes that the occupation numbers are determined by Boltzmann distribution function as well as by the heat of formation of the “imaginary binary hydrides” formed between the hydrogen atoms and the host metallic atoms forming the interstitial sites. Comparison of our calculations with recent neutron scattering data on various hydrides indicate good agreement at T=300 K. 相似文献