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761.
Sugar vinyl ethers and vinyl glycosides are conveniently synthesized by catalytic transfer vinylation with butyl vinyl ether, which serves as both the solvent and source of vinyl. The air‐stable catalyst (4,7‐diphenyl‐1,10‐phenanthroline)Pd(OOCCF3)2 is prepared in situ from commercially available components. 相似文献
762.
Phenylglycinol-derived, unsaturated oxazolopiperidone lactams are extremely useful building blocks that undergo stereoselective conjugate addition reactions with organocuprates, enolates, and sulfur-stabilized anions, allowing the stereocontrolled introduction of substituents at the piperidine 4-position. The factors governing the exo- or endo-facial selectivity are discussed. The methodology can be used for the preparation of a variety of enantiopure piperidines, including pharmaceuticals, alkaloids precursors, piperidine-fused derivatives, as well as complex piperidine-containing natural products. 相似文献
763.
Layered double hydroxides (LDHs), hydrotalcite‐like compounds, or hydrotalcites are porous materials, which may be used in catalysis, biomedicine, or adsorption as they may work as anion exchangers or drug deliverers. The morphology of hydrotalcites determines their use: in catalysis or in adsorption, reagents and gases have to reach as much surface as possible; in biomedicine, drugs have to be encapsulated and delivered later on. In this work, we synthesize hydrotalcites in presence of protein templates (egg white and yolk) and under two crystallization conditions (conventional and microwave). The obtained materials are hydrotalcites whose morphologies correspond to platelets organized as sand roses. Depending on the template and the preparation procedure, the amount of platelets can be increased. This feature is explained through the template effect of egg components. The resulting materials are promising adsorbers. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
764.
Luis S. Yagüe Bosch Tim Ehret Francesco Petiziol Ennio Arimondo Sandro Wimberger 《Annalen der Physik》2023,535(12):2300275
A shortcut-to-adiabatic protocol for the realization of a fast and high-fidelity controlled-phase gate in Rydberg atoms is developed. The adiabatic state transfer, driven in the high-blockade limit, is sped up by compensating nonadiabatic transitions via oscillating fields that mimic a counterdiabatic Hamiltonian. High fidelities are obtained in wide parameter regions. The implementation of the bare effective counterdiabatic field, without original adiabatic pulses, enables to bypass gate errors produced by the accumulation of blockade-dependent dynamical phases, making the protocol efficient also at low blockade values. As an application toward quantum algorithms, how the fidelity of the gate impacts the efficiency of a minimal quantum-error correction circuit is analyzed. 相似文献
765.
The hyperfine quenching mechanism of metastable states in polarized heliumlike heavy ions is considered. The lifetime dependence of these states on the ion polarization in an external magnetic field is established. This dependence is presented for the 23P0 state of the europium (Z=63) ion and is proposed as a method for the measurement of the ion polarization in experiments for the search of parity violating effects. 相似文献
766.
We consider in this paper the problem of automatic detection of ultrasonic echo pulses in a grain noise background. We start by assuming a reference model for grain noise: multivariate correlated Gaussian model having, in general, different variances under every hypothesis. We show that, even for this simple model, there is not practical optimum solution, except if the variances are equal under every hypothesis and the echo pulse satisfies a spectral constraint. Then we consider split-spectrum (SS) suboptimum solutions. Firstly, SS algorithms are formulated following an algebraic approach which is appropriate in an automatic detection framework. Popular minimization and polarity thresholding algorithms are considered under this framework. Then a new detector called normalized SS (NSS) is proposed. The underlying idea is to actually exploit the tuning frequency sensitivity (i.e., variability of the output magnitudes from one SS channel to another), making this measurement independent of the absolute magnitudes. Different experiments with simulated and real data show evidences of the interest of the new method in an automatic detection framework. Derivations of the formulas for fitting the probability of false alarm in every detector are included in the paper. 相似文献
767.
Water effect on the combustion preparation of MgO is presented. The obtained materials are characterized through their specific surface area, morphology, particle shape, fractal dimension and Co2+ sorption. The surface fractal dimension of the combustion prepared sample was 2.0 but in those where water was included it decreased to 1.8. In the sample prepared by calcination it was 2.3. A linear correlation between the fractal dimension and Co2+ sorption was found. 相似文献
768.
C. Brandau C. Kozhuharov A. Müller D. Bernhardt F. Bosch D. Boutin F. J. Currell C. Dimopoulou B. Franzke S. Fritzsche A. Gumberidze Z. Harman U. D. Jentschura C. H. Keitel Y. S. Kozhedub R. Krücken Yu. A. Litvinov F. Nolden B. O’Rourke R. Reuschl S. Schippers V. M. Shabaev U. Spillmann Z. Stachura M. Steck Th. St?hlker I. I. Tupitsyn D. F. A. Winters A. Wolf 《Hyperfine Interactions》2010,196(1-3):115-127
Sharp resonant structures in the cross section of the atomic electron-ion collision process of dielectronic recombination are exploited to study isotope shifts and hyperfine interaction of heavy highly-charged ions. This novel approach provides a conceptual alternative to existing methods. In this contribution, we present a series of measurements, which we performed at the heavy ion storage ring ESR of the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany. In a first experiment the stable isotopes A = 142 and A = 150 of three-electron neodymium ANd57?+? were studied. Isotope shifts of dielectronic resonances associated with 2s???2p j (j?=?1/2, 3/2) transitions were extracted from the measured data. The evaluation of the energy shift was performed within a full QED framework and yielded a change in the mean-square charge radius of $^{142,150}\delta \langle r^2 \rangle = -1.36(1)(3)$ fm2. At GSI, in addition to the investigation of stable isotopes unstable species can be artificially synthesized and studied. Radioisotopes produced in-flight from fragmentation of a 238U primary beam were injected into the ESR and were subsequently separated by their mass-to-charge ratio. This enabled us to perform first DR experiments with the exotic nuclei 237U89?+? (Z = 92 )and 234Pa88?+? (Z = 91). 相似文献
769.
Megan L. Rammer Emily R. Gonnering Zakarias L. Driscoll Herh G. Vang Prof. Eric Bosch Prof. Nathan P. Bowling 《European journal of organic chemistry》2023,26(36):e202300716
A molecular rotor is created when a 2,1,3-benzothiadiazole rotator is incorporated into a rigid arylene ethynylene framework supported by pyridine coordination to a metal (Ag+ or PdCl2) guest. Comparisons to a similarly sized naphthyl rotator via 1H NMR spectroscopy provide insights into the movement of these bicyclic rotators relative to the rigid stator framework. Chemical shift increases of 0.3 ppm, or more, upon metal complexation are consistent with through-space interaction of the central arene with a bound PdCl2 guest. Further study via X-ray crystallography illustrates that rotation of the 2,1,3-benzothiadiazole unit in the solid state is likely hampered by relatively strong chalcogen bonding (N⋅⋅⋅S distance of 2.93 Å), forming 2S-2N squares between benzothiadiazoles of neighboring complexes. Strong π–π interactions (3.29–3.36 Å) between neighboring complexes likewise restrict solid-state rotation of the potential benzothiadiazole rotator. Modest changes to UV–vis spectra upon metal coordination suggest that electronic properties are mostly independent of stator configuration. 相似文献
770.