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991.
Cai-Dian Lü Yue-long Shen Jin Zhu 《The European Physical Journal C - Particles and Fields》2005,41(3):311-317
The rare decay
can occur only via the penguin annihilation topology in the standard model. We calculate this channel in the perturbative QCD approach. The predicted branching ratio is very small: around 10-8. We also give the polarization fractions, which show that the transverse polarization contribution is comparable to the longitudinal one, due to a big transverse contribution from factorizable diagrams. The small branching ratio in SM makes it sensitive to any new physics contributions.Received: 29 January 2005, Published online: 28 April 2005 相似文献
992.
Liu Z Xu D Liang J Shen J Zhang S Qian Y 《The journal of physical chemistry. B》2005,109(21):10699-10704
We demonstrate a facile solution-phase method for the synthesis of single-crystal, high aspect ratio, and ultrathin nanowires of hexagonal-phase Cu2S by thermal decomposition of CuS2CNEt2 in a mixed surfactant solvent of dodecanethiol and oleic acid at 160 degrees C. Cu2S nanowires can be controllably synthesized with a diameter as thin as 1.7 nm and length up to tens of micrometers; they are usually aligned in the form of bundles with a thickness of hundreds of nanometers. Based on the experimental results, the formation mechanism of the ultrathin nanowires has been properly proposed. Some key synthetic parameters, which have a significant effect on the sizes and shapes of the products, have also been investigated in detail. UV-vis spectroscopy measurement reveals that the resultant ultrathin nanowires show a strong quantum size effect. 相似文献
993.
The significance of kinetics on the development of microstructures in connection with sintering of ceramics is well recognized. In practice, however, it still remains a challenge to prepare designed microstructures via engineering the sintering kinetics because of an insufficient understanding of the different operative mechanisms that are in many cases overlapping. In this article the kinetic issues involved in sintering are described and discussed with respect to their potential for prototyping microstructures that yield desired properties. By exploiting and mastering the differences present in the kinetics of grain sliding, densification, chemical reactions, and grain growth, respectively, we have established processing principles for producing bulk ceramics with microstructures consisting of nano-sized grains, aligned grains, and/or non-equilibrium-phase constitutions, and for achieving radically improved superplasticity in brittle ceramics. Although the studies quoted in this article were mainly carried out by spark plasma sintering, more general implications of them are expected, including efficient particle sliding, deformation-induced dynamic ripening, superplastic deformation-induced dynamic ripening, and non-equilibrium integration. 相似文献
994.
995.
Rösch O Gunnarsson O Zhou XJ Yoshida T Sasagawa T Fujimori A Hussain Z Shen ZX Uchida S 《Physical review letters》2005,95(22):227002
We present angle-resolved photoemission spectroscopy (ARPES) data on undoped La2CuO4, indicating polaronic coupling between bosons and charge carriers. Using a shell model, we calculate the electron-phonon coupling and find that it is strong enough to give self-trapped polarons. We develop an efficient method for calculating ARPES spectra in undoped systems. Using the calculated couplings, we find the width of the phonon sideband in good agreement with experiment. We analyze reasons for the observed dependence of the width on the binding energy. 相似文献
996.
Adaptive optics is used to compensate for modal dispersion in digital transmission through multimode fiber (MMF). At the transmitter, a spatial light modulator (SLM) controls the launched field pattern. An estimate of intersymbol interference (ISI) caused by modal dispersion is formed at the receiver and fed back to the transmitter, where the SLM is adjusted to minimize ISI. Error-free transmission of 10 Gbit/s non-return-to-zero signals through standard 50 microm graded-index MMFs up to 11.1 km long is demonstrated. It is shown that a single SLM can compensate for modal dispersion across a 600 GHz bandwidth. 相似文献
997.
Brouet V Yang WL Zhou XJ Choi HJ Louie SG Cohen ML Goldoni A Parmigiani F Hussain Z Shen ZX 《Physical review letters》2004,93(19):197601
We observe, with angle-resolved photoemission, a dramatic change in the electronic structure of two C60 monolayers, deposited, respectively, on Ag (111) and (100) substrates, and similarly doped with potassium to half filling of the C60 lowest unoccupied molecular orbital. The Fermi surface symmetry, the bandwidth, and the curvature of the dispersion at Gamma point are different. Orientations of the C60 molecules on the two substrates are known to be the main structural difference between the two monolayers, and we present new band-structure calculations for some of these orientations. We conclude that orientations play a key role in the electronic structure of fullerides. 相似文献
998.
Fifty different carbon–hydrogen distances have been predicted from ab initio MP2/6-311+G(d,p) calculations, which range from a short value of 1.0611 Å for HCNO to a long value of 1.1044 Å for H2CO. The values include those predicted for a series of methyl (CH3) moieties where the two different C–H distances vary by as much as 0.005 Å. These predicted values are compared to r
0(C–H) distances obtained from the isolated carbon–hydrogen stretching frequencies, as well as to r
0 or r
s
parameters obtained from microwave data. Except for the very short C–H bonds, the ab initio values from the MP2/6–311+G(d,p) calculations can be used for the carbon–hydrogen distances with error limits of ± 0.003 Å. By utilizing the spectral data from CD3CClO, it is shown that combination bands in the C–H stretching region could cause problems in the identification of the isolated C–H stretching frequency from the CD2HCClO isotopomer. The value of the ab initio predicted C–H distances for checking unusually long or short r
s
(C–H) or r
0 values is demonstrated. 相似文献
999.
Using FT-Raman spectroscopy, column wicking technique and the equations of Washburn as well as van Oss et al., the surface properties of xylan, the main component in hemicelluloses, has been characterized and estimated. Raman spectrum showed that xylan has been structured by acetyl group and methyl-bonded glucurono group. Obtained results show that the surface free energy of xylan is higher in comparison with literature reported values for cellulose because the former has a larger Lifshitz–van der Waals component than the latter. However, xylan has been found to have very smaller polarity and orientation data than that of cellulose. 相似文献
1000.
Fabrication of alternating polycation and albumin multilayer coating onto stainless steel by electrostatic layer-by-layer adsorption 总被引:1,自引:0,他引:1
Ji J Tan Q Fan DZ Sun FY Barbosa MA Shen J 《Colloids and surfaces. B, Biointerfaces》2004,34(3):185-190
Multilayer films consisting of polyethylenimine (PEI) and albumin were successfully prepared on biomedical 316L stainless steel surface via electrostatic self-assembly of the PEI and albumin. The process of electrostatic self-assembly of PEI/albumin was monitored by125I radiolabeling, electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM). The EIS data revealed that the multilayer coating was stable in Tris-HCl (pH 7.35) buffer solution for 21 days. 125I radiolabeling experiments indicated that less than 10% albumin was eluted by PBS in 45 days. Static platelet adhesion experiments indicated that the PEI/albumin deposited on stainless steel could resist platelet adhesion effectively. Such an easy processing and shape-independent method may have good potential for surface modification of cardiovascular devices. 相似文献