全文获取类型
收费全文 | 419篇 |
免费 | 10篇 |
专业分类
化学 | 276篇 |
晶体学 | 2篇 |
力学 | 7篇 |
数学 | 28篇 |
物理学 | 116篇 |
出版年
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 8篇 |
2015年 | 5篇 |
2014年 | 6篇 |
2013年 | 15篇 |
2012年 | 12篇 |
2011年 | 18篇 |
2010年 | 11篇 |
2009年 | 5篇 |
2008年 | 19篇 |
2007年 | 10篇 |
2006年 | 9篇 |
2005年 | 18篇 |
2004年 | 11篇 |
2003年 | 12篇 |
2002年 | 15篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 10篇 |
1981年 | 4篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 14篇 |
1977年 | 6篇 |
1976年 | 11篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1972年 | 4篇 |
1971年 | 5篇 |
1968年 | 7篇 |
1967年 | 4篇 |
1966年 | 4篇 |
1965年 | 6篇 |
1962年 | 6篇 |
排序方式: 共有429条查询结果,搜索用时 15 毫秒
101.
Tony W. J. Cooper Ian B. Campbell Dr. Simon J. F. Macdonald 《Angewandte Chemie (International ed. in English)》2010,49(44):8082-8091
Synthetic organic reactions are a fundamental enabler of small‐molecule drug discovery, and the vast majority of medicinal chemists are initially trained—either at universities or within industry—as synthetic organic chemists. The sheer breadth of synthetic methodology available to the medicinal chemist represents an almost endless source of innovation. But what reactions do medicinal chemists use in drug discovery? And what criteria do they use in selecting synthetic methodology? Why are arrays (small focused libraries) so powerful in the lead‐optimization process? In this Minireview, we suggest some answers to these questions and also describe how we have tried to expand the number of robust reactions available to the medicinal chemist. 相似文献
102.
103.
Yang J Cyr PW Wang Y Soong R Macdonald PM Chen L Manners I Winnik MA 《Photochemistry and photobiology》2006,82(1):262-267
We describe experiments that determine the quenching kinetics by poly(ferrocenylsilane) (PFS) for platinum octaethylporphine (PtOEP) phosphorescence in toluene solution. The phosphorescence quenching process was interpreted in terms of diffusion-controlled kinetics. Pulsed-gradient spin-echo nuclear magnetic resonance (PGSE NMR) and dynamic light scattering (DLS) were used to characterize the diffusion behavior of PFS and PtOEP in toluene solution. We found that the ferrocene group present in the repeat unit of polymer backbone is a good quencher for PtOEP phosphorescence. Quenching by the polymer involves the entire PFS polymer chain instead of individual ferrocene groups. The intrinsic quenching ability of PFS was found to be higher than that of a model compound, Bu-FS, that contains a single ferrocene group. 相似文献
104.
Atiya MS Chiang IH Frank JS Haggerty JS Ito MM Kycia TF Li KK Littenberg LS Stevens A Strand RC Louis WC Akerib DS Hildreth M Marlow DR Meyers PD Selen MA Shoemaker FC Smith AJ Azuelos G Blackmore EW Bryman DA Felawka L Kitching P Kuno Y Macdonald JA Numao T Padley P Poutissou JM Poutissou R Roy J 《Physical review letters》1989,63(20):2177-2180
105.
Thermal activation and deactivation of grown‐in defects limiting the lifetime of float‐zone silicon 下载免费PDF全文
Nicholas E. Grant Vladimir P. Markevich Jack Mullins Anthony R. Peaker Fiacre Rougieux Daniel Macdonald 《固体物理学:研究快报》2016,10(6):443-447
By studying the minority carrier lifetime in recently manufactured commercially available n‐ and p‐type float‐zone (FZ) silicon from five leading suppliers, we observe a very large reduction in the bulk lifetime when FZ silicon is heat‐treated in the range 450–700 °C. Photoluminescence imaging of these samples at the wafer scale revealed concentric circular patterns, with higher recombination occurring in the centre, and far less around the periphery. Deep level transient spectroscopy measurements indicate the presence of recombination active defects, including a dominant center with an energy level at ~Ev + 0.5 eV. Upon annealing FZ silicon at temperatures >1000 °C in oxygen, the lifetime is completely recovered, whereby the defects vanish and do not reappear upon subsequent annealing at 500 °C. We conclude that the heat‐treatments at >1000 °C result in total annihilation of the recombination active defects. Without such high temperature treatments, the minority carrier lifetime in FZ silicon is unstable and will affect the development of high efficiency (>24%) solar cells and surface passivation studies. 相似文献
106.
A. S. Levchenko A. N. Khotjantsev A. P. Ivashkin M. Abe M. A. Aliev V. V. Anisimovsky M. Aoki I. Arai Y. Asano T. Baker M. Blecher P. Depommier M. Hasinoff K. Horie H. C. Huang Y. Igarashi T. Ikeda J. Imazato M. M. Khabibullin Yu. G. Kudenko Y. Kuno L. S. Lee G. Y. Lim J. A. Macdonald D. R. Marlow C. R. Mindas O. V. Mineev C. Rangacharyulu S. Shimizu Y. -M. Shin A. Suzuki A. Watanabe N. V. Yershov T. Yokoi 《Physics of Atomic Nuclei》2002,65(12):2232-2237
The form factors of the decay K + → π 0 e + ν e (K e3) have been determined from the comparison of the experimental and Monte Carlo Dalitz distributions containing about 105 K e3 events. The following values of the parameters were obtained: λ +=0.0278±0.0017 (stat.)±0.0015 (syst.), |f S/f +(0)|=0.0040±0.0160 (stat.)±0.0067 (syst.), and |f T/f +(0)|=0.019±0.080 (stat.)±0.038 (syst.). Both scalar f S and tensor f T form factors are consistent with the Standard Model predictions of zero values. 相似文献
107.
Peter A. Macdonald Dr. Sumanta Banerjee Dr. Alan R. Kennedy Dr. Alexander van Teijlingen Dr. Stuart D. Robertson Prof. Tell Tuttle Prof. Robert E. Mulvey 《Angewandte Chemie (International ed. in English)》2023,62(27):e202304966
Catalytic reduction of a representative set of imines, both aldimines and ketimines, to amines has been studied using transfer hydrogenation from 1,4-dicyclohexadiene. Unusually, this has been achieved using s-block pre-catalysts, namely 1-metallo-2-tert-butyl-1,2-dihydropyridines, 2-tBuC5H5NM, M(tBuDHP), where M=Li–Cs. Reactions have been monitored in C6D6 and tetrahydrofuran-d8 (THF-d8). A definite trend is observed in catalyst efficiency with the heavier alkali metal tBuDHPs outperforming the lighter congeners. In general, Cs(tBuDHP) is the optimal pre-catalyst with, in the best cases, reactions producing quantitative yields of amines in minutes at room temperature using 5 mol % catalyst. Supporting the experimental study, Density Functional Theory (DFT) calculations have also been carried out which reveal that Cs has a pathway with a significantly lower rate determining step than the Li congener. In the postulated initiation pathways DHP can act as either a base or as a surrogate hydride. 相似文献
108.
The coupling between bound modes of a corrugated dielectric-slab waveguide and modes of the radiation continuum is analysed by a perturbation method. Loss coefficients that account for the power coupled into radiation modes by any Bragg order of corrugations with an arbitrary profile are determined for the bound modes. Agreement is found with published results for sinusoidal profiles. The proportion of power coupled out through each dielectric interface of the slab waveguide is also determined. When the corrugation has an asymmetric (blazed) profile and coupling to radiation modes is by the first Bragg order, more power can be coupled out through one interface than the other, even if the refractive indices of the cladding regions are equal. If the coupling is by a higher Bragg order, then the division of power can be considerably more unequal than for first-order coupling, with the greater proportion leaving the side of the waveguide opposite to that for first-order coupling. The ratio of the power coupled out the two sides varies cyclically with radiation wavelength. 相似文献
109.
Hinchley SL Morrison CA Rankin DW Macdonald CL Wiacek RJ Voigt A Cowley AH Lappert MF Gundersen G Clyburne JA Power PP 《Journal of the American Chemical Society》2001,123(37):9045-9053
The molecular structures of the stable phosphinyl and arsinyl radicals, .PnR(2) [Pn = P (2); As (4); R = CH(SiMe(3))(2)], have been determined by gas-phase electron diffraction (GED) in conjunction with ab initio molecular orbital calculations. The X-ray crystal structures of the corresponding dipnictines, the "dimers", R(2)PnPnR(2) [Pn = P (1), As (3)], and the chloro derivatives R(2)PnCl [Pn = P (5), As (6)] have also been determined. Collectively, these structural investigations demonstrate that large distortions of the ligands attached to Pn occur when the pnictinyl radicals unite to form the corresponding dipnictine dimers. Principally, it is the shape and flexibility of the CH(SiMe(3))(2) ligands that permit the formation of the P-P and As-As bonds in 1and 3, respectively. However, theoretical studies indicate that in the process of pnictinyl radical dimerization to form 1 and 3, both molecules accumulate substantial amounts of potential energy and are thus primed to spring apart upon release from the solid state by melting, dissolution, or evaporation. The insights gleaned from these unusual systems have permitted a deeper understanding of the functioning of sterically demanding substituents. 相似文献
110.
The recombination rate constants for the reactions NH2(X2B1) + NH2(X2B1) + M → N2H4 + M and NH2(X2B1) + H + M → NH3 + M, where M was CH4, C2H6, CO2, CF4, or SF6, were measured in the same experiment over presseure ranges of 1-20 and 7-20 Torr, respectively, at 296 ± 2 K. The NH2 radical was produced by the 193 nm laser photolysis of NH3. Both NH2 and NH3 were monitored simultaneously following the photolysis laser pulse. High-resolution time-resolved absorption spectroscopy was used to monitor the temporal dependence of both species: NH2 on the (1)2(21) ← (1)3(31) rotational transition of the (0,7,0)A2A1 ← (0,0,0)X2B1 electronic transition near 675 nm and NH3 in the IR on either of the inversion doublets of the qQ3(3) rotational transition of the ν1 fundamental near 2999 nm. The NH2 self-recombination clearly exhibited falloff behavior for the third-body collision partners used in this work. The pressure dependences of the NH2 self-recombination rate constants were fit using Troe’s parametrization scheme, k(inf), k(0), and F(cent), with k(inf) = 7.9 × 10(-11) cm3 molecule(-1) s(-1), the theoretical value calculated by Klippenstein et al. (J. Phys. Chem. A113, 113, 10241). The individual Troe parameters were CH4, k(0)(CH4) = 9.4 × 10(-29) and F(cent)(CH4) = 0.61; C2H6, k(0)(C2H6) = 1.5 × 10(-28) and F(cent)(C2H6) = 0.80; CO2, k(0)(CO2) = 8.6 × 10(-29) and F(cent)(CO2) = 0.66; CF4, k(0)(CF4) = 1.1 × 10(-28) and F(cent)(CF4) = 0.55; and SF6, k(0)(SF6) = 1.9 × 10(-28) and F(cent)(SF6) = 0.52, where the units of k0 are cm6 molecule(-2) s(-1). The NH2 + H + M reaction rate constant was assumed to be in the three-body pressure regime, and the association rate constants were CH4, (6.0 ± 1.8) × 10(-30); C2H6, (1.1 ± 0.41) × 10(-29); CO2, (6.5 ± 1.8) × 10(-30); CF4, (8.3 ± 1.7) × 10(-30); and SF6, (1.4 ± 0.30) × 10(-29), with units cm6 molecule(-1) s,(-1) and the systematic and experimental errors are given at the 2σ confidence level. 相似文献