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231.
This paper investigates finite-stretching corrections
to the classical Milner-Witten-Cates theory for semi-dilute
polymer brushes in a good solvent. The dominant correction to the
free energy originates from an entropic repulsion caused by the
impenetrability of the grafting surface, which produces a
depletion of segments extending a distance μ∝L-1
from the substrate, where L is the classical brush height. The
next most important correction is associated with the
translational entropy of the chain ends, which creates the
well-known tail where a small population of chains extend beyond
the classical brush height by a distance ξ∝L-1/3.
The validity of these corrections is confirmed by quantitative
comparison with numerical self-consistent field theory. 相似文献
232.
L. Ye 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(2):413-416
We propose two schemes for generating a four-atom cluster state in a thermal
cavity. With the assistant of a strong classical field the
photon-number-dependent parts in the effective Hamiltonian are canceled.
Thus the schemes are insensitive to the thermal field. The schemes can also
be used to generate the cluster state for the trapped ions in thermal
motion. 相似文献
233.
N. Vujičić S. Vdović D. Aumiler T. Ban H. Skenderović G. Pichler 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(3):447-454
We present direct observation of the velocity-selective optical pumping of
the Cs ground state hyperfine levels induced by the femtosecond (fs) laser
oscillator centered at either D2 (6 2S1/2↦6 2P3/2,
852 nm) or D1 (6
P1/2, 894 nm) cesium
line. We utilized previously developed modified direct frequency comb
spectroscopy (DFCS) which uses a fixed frequency comb for the excitation and
a weak cw scanning probe laser centered at the 133Cs 6
2S1/2↦6 2P3/2 transition (D2 line) for ground
levels population monitoring. The frequency comb excitation changes the
usual Doppler absorption profile into a specific periodic, comblike
structure. The mechanism of the velocity selective population transfer
between the Cs ground state hyperfine levels induced by fs pulse train
excitation is verified in a theoretical treatment of the multilevel atomic
system subjected to a pulse train resonant field interaction. 相似文献
234.
We study well-posedness of a class of nonlocal interaction equations with spatially dependent mobility. We also allow for the presence of boundaries and external potentials. Such systems lead to the study of nonlocal interaction equations on subsets ? of ? d endowed with a Riemannian metric g. We obtain conditions, relating the interaction potential and the geometry, which imply existence, uniqueness and stability of solutions. We study the equations in the setting of gradient flows in the space of probability measures on ? endowed with Riemannian 2-Wasserstein metric. 相似文献
235.
Investigation of laterally single-diffused metal oxide semiconductor (LSMOS) field effect transistor
《Current Applied Physics》2015,15(10):1130-1133
We propose a distinct approach to implement a laterally single diffused metal-oxide-semiconductor (LSMOS) FET with only one impurity doped p-n junction. In the LSMOS, a single p-n junction is first created using lateral dopant diffusion. The channel is formed in the p region of the p-n junction and the n region acts as the drift region. Two distinct metals of different work function are used to form the “n+” source/drain regions and “p+” body contact using the charge plasma concept. We demonstrate that the LSMOS is similar in performance to a laterally double diffused metal-oxide-semiconductor (LDMOS) although it has only one impurity doped p-n junction. The LSMOS exhibits a breakdown voltage of ∼50.0 V, an average ON-resistance of 48.7 mΩ-mm2 and a peak transconductance of 53.6 μS/μm similar to that of a comparable LDMOS. 相似文献
236.
Chemically synthesized single‐crystalline gold microplates have been attracting increasing interest because of their potential as high‐quality gold films for nanotechnology. We present the growth of tens of nanometers thick and tens of micrometers large single‐crystalline gold plates directly on solid substrates by solution‐phase synthesis. Compared to microplates deposited on substrates from dispersion phase, substrate‐grown plates exhibit significantly higher quality by avoiding severe small‐particle contamination and aggregation. Substrate‐grown gold plates also open new perspectives to study the growth mechanism via step‐growth and observation cycles of a large number of individual plates. Growth models are proposed to interpret the evolution of thickness, area and shape of the plates. It is found that the plate surface remains smooth after regrowth, implying the applicability of regrowth for producing giant plates as well as unique single‐crystalline nano‐structures. 相似文献
237.
238.
239.
On‐Line Monitoring of Chemical Reactions by using Bench‐Top Nuclear Magnetic Resonance Spectroscopy
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Dr. E. Danieli Dr. J. Perlo Dr. A. L. L. Duchateau G. K. M. Verzijl Dr. V. M. Litvinov Prof. Dr. B. Blümich Dr. F. Casanova 《Chemphyschem》2014,15(14):3060-3066
Real‐time nuclear magnetic resonance (NMR) spectroscopy measurements carried out with a bench‐top system installed next to the reactor inside the fume hood of the chemistry laboratory are presented. To test the system for on‐line monitoring, a transfer hydrogenation reaction was studied by continuously pumping the reaction mixture from the reactor to the magnet and back in a closed loop. In addition to improving the time resolution provided by standard sampling methods, the use of such a flow setup eliminates the need for sample preparation. Owing to the progress in terms of field homogeneity and sensitivity now available with compact NMR spectrometers, small molecules dissolved at concentrations on the order of 1 mmol L?1 can be characterized in single‐scan measurements with 1 Hz resolution. Owing to the reduced field strength of compact low‐field systems compared to that of conventional high‐field magnets, the overlap in the spectrum of different NMR signals is a typical situation. The data processing required to obtain concentrations in the presence of signal overlap are discussed in detail, methods such as plain integration and line‐fitting approaches are compared, and the accuracy of each method is determined. The kinetic rates measured for different catalytic concentrations show good agreement with those obtained with gas chromatography as a reference analytical method. Finally, as the measurements are performed under continuous flow conditions, the experimental setup and the flow parameters are optimized to maximize time resolution and signal‐to‐noise ratio. 相似文献
240.
Dr. Carles Acosta-Silva Prof. Joan Bertran Prof. Vicenç Branchadell Prof. Antoni Oliva 《Chemphyschem》2020,21(22):2594-2604
The effect of solvent reaction fields and oriented electric fields on the Kemp elimination reaction between methylamine or imidazole and 5-nitrobenzisoxazole has been theoretically studied. The Kemp reaction is the most widely used for the design of new enzymes. Our results, using the SMD continuous model for solvents, are in quite good agreement with the experimental fact that the rate of the analogous reaction with butylamine is one order of magnitude smaller in water than in acetonitrile. In the case of external electric fields, our results show that they can increase or decrease the energy barrier depending on the magnitude and orientation of the field. A duly oriented electric field may have a notable catalytic effect on the reaction. So, external electric fields and reaction fields due to the medium can contribute to the design of new enzymes. Several factors that must be taken into account to increase the catalytic effect are discussed. 相似文献