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排序方式: 共有538条查询结果,搜索用时 8 毫秒
1.
The deformation surrounding Vickers indentations on InGaAsP/InP epilayers have been studied in detail. The surface topography was characterized by using atomic force microscopy (AFM). The material pile-up and sink-in regions around the indentation impression was observed for the quaternary InGaAsP/InP epilayers. The sectional analysis mode of the AFM shows the depth profile at the indented region. Microindentation studies were carried out for different atomic fraction of the quaternary InGaAsP/InP compound semiconductor alloys. The microhardness values of InGaAsP/InP epilayers were found to be in the range of 5.08 and 5.73 GPa. These results show that the hardness value of the quaternary alloy drastically increases as the composition of As was increased by 0.01 atomic fraction and when the phosphorous concentration decreases from 0.4 to 0.38. The reason may be that the increase in As concentration hardens the lattice when phosphorous concentration was less and hardness decreases when phosphorous was increased. 相似文献
2.
N. Ponpandian A. Narayanasamy D. Prabhu K. Ganesan M. Manivel Raja K. Chattopadhyay 《Journal of magnetism and magnetic materials》2006
The Fe73.5Cu1Nb3Si13.5B9 FINEMET alloy has been prepared by the rapid solidification technique. The critical behaviour of this alloy in the amorphous as well as in its nanocrystalline states has been studied near their respective Curie temperatures. From the values of the critical exponents one can conclude that the alloy behaves like a 3D Heisenberg ferromagnet in the amorphous and nanocrystalline states. But there exists a slight increase in the value of β for the alloy annealed at 823 K (the nanocrystalline state) as observed in most of the amorphous alloys. 相似文献
3.
Solid solutions of CsCl-Br in five different concentrations were prepared in sealed quartz tubes by heating the mixture to
1123°K for 6–8 hr and quenching to room temperature. X-ray diffractograms were taken at eight different temperatures between
room temperature and 90°K for these solid solutions using the YPC50NM powder diffractometer and a continuous flow cryostat.
The observed lattice parameters for each sample at each temperature obtained from the powder diffractograms were then extrapolated
to give the true lattice parameters using the least square method with Nelson-Riley extrapolation scheme. The values of the
true lattice parameters at each concentration and at each temperature were tabulated and the results discussed. It is shown
that the lattice parameters vs temperature for some concentrations exhibit an anomalous behaviour.
Contribution No. 691 相似文献
4.
We achieved the total synthesis of the histone deacetylase inhibitor spiruchostatin A, as the prelude to the preparation of a combinatorial library of its analogues. Two key reactions were an asymmetric acetate aldol reaction using a Zr-enolate and macrolactonization using the Shiina method. 相似文献
5.
A simple method for the separation of hemoglobin chains from hemolysate or globin, by sodium dodecyl sulfate polyacrylamide gel electrophoresis, is described. The alpha, beta, and gamma chains can be clearly separated from each other. The alpha chain has the highest mobility, the beta chain has a slower mobility than the gamma chain, while the delta chain has about the same mobility as the beta chain. Hemoglobins with elongated chains can easily be detected by this method. Tak-beta, elongated by 11 residues, moves much more slowly than betaA but is much faster than alpha Constant Spring which is elongated by 31 residues. Screening of several individuals with slow-moving hemoglobins using this method led to the finding of a case with Hb Tak-beta thalassemia and other carriers of Hb Tak. 相似文献
6.
Rupture of thin stagnant films on a solid surface due to random thermal and mechanical perturbations
Narsimhan G 《Journal of colloid and interface science》2005,287(2):624-633
A generalized formalism for the rupture of a nondraining thin film on a solid support due to imposed random thermal and mechanical perturbations, modeled as a Gaussian white noise, is presented. The evolution of amplitude of perturbation is described by a stochastic differential equation. The average film rupture time is the average time for the amplitude of perturbation to equal to the film thickness and is calculated by employing a first passage time analysis for different amplitudes of imposed perturbations, wavenumbers, film thickness, van der Waals and electrostatic interactions and surface tensions. The results indicate the existence of an optimum wavenumber at which the rupture time is minimum. A critical film thickness is identified based on the sign of the disjoining pressure gradient, below which the film is unstable in that the rupture time is very small. The calculated values of rupture time as well as the optimum wavenumber in the present analysis agree well with the results of linear stability analysis for immobile as well as completely mobile gas-liquid film interfaces. For stable films, the rupture time is found to increase dramatically with film thickness near the critical film thickness. As expected, the average rupture time was found to be higher for smaller amplitudes of imposed perturbations, larger surface potentials, larger surface tensions and smaller Hamaker constants. 相似文献
7.
D. Indumathi 《Pramana》1995,45(1):155-171
This talk discusses the current understanding in some aspects of polarised lepton-nucleon deep inelastic scattering. The first section focuses on the non-singlet part of available spin dependent structure function data. The results, though consistent with theoretical predictions in this sector, are extremely sensitive to extrapolation of the data to thex→1 region and seem to indicate that the quarksdo carry a very small fraction of the nucleon spin. We then review the formalism of DIS processes with emphasis on the gluon sector. 相似文献
8.
Zinc triflate was found to be an effective reagent for the C3-alkylation of indoles by alkyl halides in the presence of Hünig's base and tetrabutylammonium iodide. This new method for indole alkylation proceeds by a S(N)1-like pathway, and is general for allylic, benzylic, and tertiary halides. 相似文献
9.
[reaction: see text] The convergent total synthesis of (+)-okaramine J was achieved in a longest linear sequence of 12 steps from l-tryptophan tert-butyl ester. A key reaction was the acid-catalyzed room-temperature aza-Claisen rearrangement of a N-reverse-prenylated hexahydro[2,3-b]pyrroloindole to a C-prenylated derivative. 相似文献
10.
Mani Ganesan 《Journal of organometallic chemistry》2005,690(23):5145-5149
Treatment of [Cp*CrCl(C6F5)]2 with BnMgCl (Bn = benzyl) in Et2O/THF affords [Cp*Cr(C6F5)(Bn)(THF)] (1) which has been isolated in 72% yield. This compound whose magnetic moment is equal to of 4.037 μB has been characterized by NMR and single crystal X-ray analysis. Compound 1 alone does not polymerize ethylene when dissolved in toluene. However, addition of excess AlEt3 to a solution of 1 in toluene leads to a catalytically active system which readily oligomerizes ethylene under standard conditions. Oligomerization experiments carried out with [1] = 10−3 M and [AlEt3] = 9 × 10−2 M for 15 min lead to the production of ethylene oligomers with an activity of 280 kg mol Cr−1 h−1. The experimental molecular weight distribution observed at intermediate times during the reaction is satisfactorily accounted for by the Poisson distribution formula, which is indicative of a living polymerization system. These observations are in agreement with a catalytic cycle in which the growing alkyl chain is transferred from chromium to aluminum via a bimetallic complex in which the chromium and aluminum centers are bridged by an alkyl group and the growing polymer chain. 相似文献