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91.
G. Cocco S. Enzo C. Antonione G. Riontino G. Venturello 《Solid State Communications》1984,51(10):777-780
A SAXS study was undertaken on Fe75TM5B20 amorphous alloys (TM Ti, V, Cr, Mn, Fe, Co, Ni) to prove the effects of the substituting metals on structural homogeneity of the systems. A density-density correlation extending up to 20 Å belongs to Fe-, Ni- and Co-containing alloys whereas the absence of a medium-range order characterizes the texture of the remaining alloys. A net correspondence was found between these structural conditions and the isothermal behavior of the resistivity. 相似文献
92.
We discuss the theory of non-critical strings with extrinsic curvature embedded in a target space dimensiond greater than one. We emphasize the analogy between 2d gravity coupled to matter and non self-avoiding liquid-like membranes with bending rigidity. We first outline the exact solution
for strings in dimensionsd<1 via the double scaling limit of matrix models and then discuss the difficulties of an extension tod>1. Evidence from recent and ongoing numerical simulations of dynamically triangulated random surfaces indicate that there
is a non-trivial crossover from a crumpled to an extended surface as the bending rigidity is increased. If the cross-over
is a true second order phase transition corresponding to a critical point there is the exciting possibility of obtaining a
well defined continuum string theory ford>1.
This essay received the third award from the Gravity Research Foundation, 1992-Ed. 相似文献
93.
Let H be a real Hilbert space, :H [0, + ] a proper l.s.c., convex function with Lk:={u H; u2 + (u) k} compact for every k > 0, let > 0 be a given constant and
. We prove an existence result for strong solutions to a class of functional differential equations of the form
相似文献
94.
Enzo Maria Li Marzi 《Rendiconti del Circolo Matematico di Palermo》1992,41(3):466-478
We consider, on the euclidean planeE 2, a lattice of fundamental regions that are regular polygons, triangles or parallelograms. We determin the probabilityp in order that a vertex of the latticeR belongs to a circle of the random center and any radius. 相似文献
95.
96.
97.
Iengo E Zangrando E Minatel R Alessio E 《Journal of the American Chemical Society》2002,124(6):1003-1013
Treatment of the octahedral Ru(II)-dimethyl sulfoxide complexes trans-RuCl(2)(dmso-S)(4) (1), trans-RuCl(2)(dmso-O)(2)(CO)(2) (2), and trans-RuCl(2)(dmso)(3)(CO) (3) with a stoichiometric amount of 5,10-bis(4'-pyridyl)-15,20-diphenylporphyrin (4'-cis-DPyP) yields, after chromatographic purification, the novel 2+2 molecular squares of formula [trans,cis,cis-RuCl(2)(dmso-S)(2)(4'-cis-DPyP)](2) (4), [trans,cis,cis-RuCl(2)(CO)(2)(4'-cis-DPyP)](2) (5), and [trans,cis,cis-RuCl(2)(dmso-S)(CO)(4'-cis-DPyP)](2) (6), respectively. Compound 6 exists as an equimolar mixture of the isomeric metallacycles 6a and 6b, depending on whether the 4'-N(py) rings of 4'-cis-DPyP's are trans to CO or to dmso-S. Compounds 4-6 were fully characterized by NMR and IR spectroscopy and by FAB mass spectrometry. Treatment of 5 with excess zinc acetate in chloroform/methanol mixtures led to the isolation of the corresponding zinc adduct [trans,cis,cis-RuCl(2)(CO)(2)(Zn x 4'-cis-DPyP)](2) (5Zn). Treatment of 5Zn with 1 equiv of a trans ditopic N-donor ligand L (L = 4,4'-bipy, 5,15-bis(4'-pyridyl)-2,8,12,18-tetra-n-propyl-3,7,13,17-tetramethylporphyrin (4'-trans-DPyP-npm), or 5,15-bis(4'-pyridyl)-10,20-diphenylporphyrin (4'-trans-DPyP)) leads readily and selectively, according to (1)H NMR spectroscopy, to the quantitative assembling of 2:2 supramolecular adducts of stacked metallacycles of formula [(5Zn)(2)(mu-L)(2)] (7-9), which were thoroughly characterized in solution by NMR spectroscopy. NMR features indicate that, at ambient temperature, the equilibrium between 5Zn and L to yield [(5Zn)(2)(mu-L)(2)] has an intermediate to slow rate on the NMR time scale (relatively broad signals for L) and is totally shifted toward the 2:2 product (all or nothing process). Single-crystal X-ray investigations showed that, depending on the nature of the bridging ligand, in the solid state these sandwich structures can either be maintained or originate polymeric chains formulated as [(5Zn)(mu-L)](infinity). When L = 4'-trans-DPyP, both solution- and solid-state data indicate that [(5Zn)(2)(mu-4'-trans-DPyP)(2)] (9) is a discrete supramolecular assembly of two molecular squares of metalloporphyrins axially connected through other porphyrins. In this molecular box, the two bridging porphyrins are coplanar at a distance of about 11.4 A. When L = 4,4'-bipy, the corresponding adduct 7 has the anticipated sandwich-like discrete architecture [(5Zn)(2)(mu-4,4'-bipy)(2)] in solution, but it assumes a stair-like polymeric wire structure in the solid state. The polymer [(5Zn)(mu-4,4'-bipy)](infinity) is made by 5Zn squares bridged by 4,4'-bipy ligands which are axially coordinated alternatively on the two opposite sides of each square. Our work clearly established that relatively simple supramolecular adducts of porphyrins, such as molecular squares, are suitable building blocks for the construction of more elaborate assemblies of higher order by axial coordination of bridging ligands. 相似文献
98.
A frequency-dependent lineshape analysis of the ESR spectra of ternary systems in solution has been carried out. The 5′-ATP—Mn(II)—Trp complex has been chosen as a model system. The analysis points out the presence of inverted spectra at both X- and Q-bands. The lineshape is described by a distribution of configurational sites, Yl(ω) = ΣkPkYk(H). The temperature dependence of the ESR linewidth has also been investigated and is discussed in terms of chemical equilibria and correlation times. 相似文献
99.
Freek Brinkmann Niels Ebbe Dam Eva Deák Francesca Durbiano Enzo Ferrara Judit Fűkő Hans D. Jensen Michal Máriássy Rubina H. Shreiner Petra Spitzer Uwe Sudmeier Michael Surdu Leoš Vyskočil 《Accreditation and quality assurance》2003,8(7-8):346-353
This paper surveys the state of the art for primary methods for the evaluation of electrolytic conductivity in aqueous solutions as they are currently carried out in several national metrological institutes (NMIs). The theoretical and practical basic knowledge of this measurement is described. Analysis of and comments on the different approaches are offered to give emphasis to technical difficulties and possible solutions. Further development is foreseeable, ensuring a common effort for the sharing of expertise that has been undertaken at the NMIs. In particular, improvements are expected towards traceable measurements of solutions with conductivity values lower than those actually standardized, down to the level of ultrapure water. 相似文献
100.
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