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51.
E. K. Squire P. A. Snow P. St. J. Russell L. T. Canham A. J. Simons C. L. Reeves 《Journal of luminescence》1998,80(1-4):125-128
Experimental and theoretical techniques are used to examine the effects of microstructuring on the optical properties of multilayer, single and multiple microcavity structures fabricated from porous silicon. Measurements of the reflectivity and photoluminescence spectra of three multilayer samples are presented. The results are modelled using a transfer matrix technique including a negative absorption term to represent the effect of spontaneous emission which gives luminescence. The emitted light is strongly controlled by the optical modes of the structures and very good agreement is observed between theory and experiment. 相似文献
52.
Thin films of CaF2 co-doped with low concentrations of Eu and Sm ions were grown by pulsed laser deposition (PLD) using a KrF (λ=248 nm) as the ablation source. To the best of our knowledge, the work presented here is the first report of rare-earth-doped CaF2 films grown by PLD with this source. Combined laser excitation-emission spectroscopy was used to map out electronic transitions of Eu3+ with 7F0→5D1 excitation and the 5D0→7F1 emission. At the low concentrations used here the crystal field center of cubic symmetry is dominant in the films that are same for laser targets. However, charge compensated centers are present in the bulk crystal precursor. The removal of the charge compensated centers in the films and the target is likely caused by the target preparation where high pressure and temperature were applied. 相似文献
53.
Jinhua J. Song Zhulin Tan Jonathan T. Reeves Daniel R. Fandrick Heewon Lee Nathan K. Yee Chris H. Senanayake 《Tetrahedron letters》2009,50(27):3952-1877
Treatment of unprotected 5-amino-4-methylpyrimidine (2) with n-BuLi gave dianion 3. Direct condensation of the dianion with various carboxylic acid derivatives furnished a range of 2-substituted-4,6-diazaindoles in good yields in one step without the need for protecting groups or oxidation-state adjustment. 相似文献
54.
Song JJ Gallou F Reeves JT Tan Z Yee NK Senanayake CH 《The Journal of organic chemistry》2006,71(3):1273-1276
N-Heterocyclic carbenes were found to be highly effective organocatalysts in activating TMSCN for facile cyanosilylation of carbonyl compounds. Cyano transfer from TMSCN to aldehydes and ketones proceeds at room temperature in the presence of only 0.01-0.5 mol % of N-heterocyclic carbene (1), leading to a range of trimethylsilylated cyanohydrins in very good to excellent yields. These conditions are extremely mild and simple and tolerate various functional groups. 相似文献
55.
Computer simulations based on Discrete Element Method have been performed in order to investigate the influence of interparticle interactions on the kinetics of self-assembly and the mechanical strength of nanoparticle aggregates.Three different systems have been considered.In the first system the interaction between particles has been simulated using the JKR (Johnson,Kendall and Roberts) contact theory,while in the second and third systems the interaction between particles has been simulated using van der Waals and electrostatic forces respectively.In order to compare the mechanical behaviour of the three systems,the magnitude of the maximum attractive force between particles has been kept the same in all cases.However,the relationship between force and separation distance differs from case to case and thus,the range of the interparticle force.The results clearly indicate that as the range of the interparticle force increases,the self-assembly process is faster and the work required to produce the mechanical failure of the assemblies increases by more than one order of magnitude. 相似文献
56.
An importance issue concerning the practical application of chance-constrained programming is the lack of a rational method for choosing risk levels or tolerances on the chance constraints. While there has also been much recent debate on the relationship, equivalence, usefulness, and other characteristics of chance-constrained programming relative to stochastic programming with recourse, this paper focuses on the problem of improving the selection of tolerances within the chance-constrained framework. An approach is presented, based on multiple objective linear programming, which allows the decision maker to be more involved in the tolerance selection process, but does not demand a priori decisions on appropriate tolerances. An example is presented which illustrates the approach. 相似文献
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Metallic nanoparticles bridge the length scale between atoms and crystals, exhibiting mesoscopic properties unique to their size. Thus, they have generated much interest for their potential applications as chemical or biological sensors and particularly as waveguides for light in nanoscale structures. [Y. W. C. Cao, R. C. Jin, and C. A. Mirkin, Science 297, 1536 (2002); H. J. Lezec et al., Science 297, 820 (2002); S. A. Maier, P. G. Kik, and H. A. Atwater, Appl. Phys. Lett. 81, 1714 (2002); J. M. Oliva and S. K. Gray, Chem. Phys. Lett. 379, 325 (2003)]. One important direction of research into the properties of individual metal nanoparticles involves the controlled variation of their geometry, which can yield new and tunable optical properties that simple spherical configurations do not possess. [T. S. Ahmadi, Z. L. Wang, T. C. Green, A. Henglein, and M. A. Ei-Sayed, Science 272, 1924 (1996)]. A prime example of this is the core-shell nanostructure that has a central material surrounded by differing cladding layer. 相似文献
60.
Titrimetric assays for phytic acid by titration with iron(III) or thorium are described. Stannous chloride interferes in both systems, causing negative errors directly proportional to the amount of stannous chloride. The thorium:phytate ratio in the complex formed is 2:1, which is interpreted as resulting from the possession of two chelating centres by phytic acid. 相似文献