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61.
Pure aluminium containing about 200?at.ppm Fe in solution is shown to creep about 106 times slower at 200°C than the same aluminium containing a negligible amount of iron in solution. The high creep resistance of the Al–200?at.ppm?Fe alloy is attributed to the presence of subgrain boundaries containing iron solute atoms. It is proposed that the opposing stress fields from subgrain boundaries and from the piled-up dislocations during creep are cyclically relaxed, by iron solute diffusion, to allow climb of the lead dislocation in the pile-up. The mechanism is a form of mechanical ratcheting. The model is applied to Al–Fe alloys and correctly predicts that the creep rate is controlled by the rate of iron solute diffusion and by a temperature dependence equal to the activation energy for iron diffusion, namely Q c?=?221?kJ?mol?1. Basic creep studies on solid-solution alloying with solute atoms that diffuse slowly in the lattice of aluminium (e.g. manganese, chromium, titanium and vanadium) appear worthy of study as a way of enhancing creep strength and of understanding creep mechanisms involving solute-atom-containing subgrain boundaries. 相似文献
62.
Let f:X→Y be an algebraic fiber space with general fiber F. If Y is of maximal Albanese dimension, we show that κ(X)≥κ(Y)+κ(F). 相似文献
63.
Clemens Nothegger Alfred Mayer Andreas Chwatal Günther R. Raidl 《Annals of Operations Research》2012,194(1):325-339
In this work we present a new approach to tackle the problem of Post Enrolment Course Timetabling as specified for the International Timetabling Competition 2007 (ITC2007), competition track 2. The heuristic procedure is
based on Ant Colony Optimization (ACO) where artificial ants successively construct solutions based on pheromones (stigmergy) and local information. The key feature of our algorithm is the use of two distinct but simplified pheromone matrices
in order to improve convergence but still provide enough flexibility for effectively guiding the solution construction process.
We show that by parallelizing the algorithm we can improve the solution quality significantly. We applied our algorithm to
the instances used for the ITC2007. The results document that our approach is among the leading algorithms for this problem;
in all cases the optimal solution could be found. Furthermore we discuss the characteristics of the instances where the algorithm
performs especially well. 相似文献
64.
Alfred Inselberg 《Journal of Mathematical Analysis and Applications》1982,90(2):440-455
A problem of Lighthill and Levich, where convective heat (mass) transfer occurs through a boundary layer, is considered. This gives rise to a certain integral equation. The unique L2 solution of a generalized version of this integral equation is obtained providing the solution, in closed form, of the original problem. 相似文献
65.
Let (X,B) be a complex projective klt pair, and let f:X→Z be a surjective morphism onto a normal projective variety with maximal albanese dimension such that KX+B is relatively big over Z. We show that such pairs have good log minimal models. 相似文献
66.
We study classes of mappings which do not belong to the QRT family. We obtain several integrable non-autonomous forms of these mappings extending previous results where only linearisable cases were found. Using our recently introduced method of singularity confinement with full deautonomisation, we analyse a mapping which, while non-integrable, does possess confined singularities and show that our method makes it possible to obtain the exact value of its algebraic entropy. 相似文献
67.
68.
Dr. Jiawei Zhang Dr. Daisuke Ishikawa Dr. Michael M. Koza Prof. Dr. Eiji Nishibori Dr. Lirong Song Dr. Alfred Q. R. Baron Prof. Dr. Bo B. Iversen 《Angewandte Chemie (International ed. in English)》2023,62(13):e202218458
Loosely bonded (“rattling”) atoms with s2 lone pair electrons are usually associated with strong anharmonicity and unexpectedly low thermal conductivity, yet their detailed correlation remains largely unknown. Here we resolve this correlation in thermoelectric InTe by combining chemical bonding analysis, inelastic X-ray and neutron scattering, and first principles phonon calculations. We successfully probe soft low-lying transverse phonons dominated by large In1+ z-axis motions, and their giant anharmonicity. We show that the highly anharmonic phonons arise from the dynamic lone pair expression with unstable occupied antibonding states induced by the covalency between delocalized In1+ 5s2 lone pair electrons and Te 5p states. This work pinpoints the microscopic origin of strong anharmonicity driven by rattling atoms with stereochemical lone pair activity, important for designing efficient materials for thermoelectric energy conversion. 相似文献
69.
Wooten A Carroll PJ Maestri AG Walsh PJ 《Journal of the American Chemical Society》2006,128(14):4624-4631
This report describes the solid-state structures of a series of divinylzinc complexes, one of which represents the only structurally characterized zinc(II) pi-complex. Vinylzinc reagents, Zn[C(Me)=CH2]2 (1) and Zn[C(H)=CMe2]2 (2), have been synthesized and isolated as white crystalline solids in 66 and 72% yield, respectively. Each compound exhibits an infinite polymeric architecture in the solid state via a series of zinc-pi (1) and zinc-sigma-bonded (2) bridging interactions. Addition of chelating ligands to these divinylzinc compounds allowed isolation of the monomeric adducts (bipy)Zn[C(Me)=CH2]2 (1.bipy), (tmeda)Zn[C(Me)=CH2]2 (1*tmeda), (bipy)Zn[C(H)=CMe2]2 (2*bipy), and (tmeda)Zn[C(H)=CMe2]2 (2*tmeda), of which 1*bipy, 2*bipy, and 2*tmeda have been characterized crystallographically. 相似文献
70.