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271.
Usselman RJ Walter ED Willits D Douglas T Young M Singel DJ 《Journal of the American Chemical Society》2011,133(12):4156-4159
This work describes an approach for calculating and measuring dipolar interactions in multispin systems to monitor conformational changes in icosahedral protein cages using site-directed spin labeling. Cowpea chlorotic mottle virus (CCMV) is used as a template that undergoes a pH-dependent reversible capsid expansion wherein the protein cage swells by 10%. The sequence-position-dependent geometric presentation of attached spin-label groups provides a strategy for targeting amino acid residues most probative of structural change. The labeled protein cage residues and structural transition were found to affect the local mobility and dipolar interactions of the spin label, respectively. Line-shape changes provided a spectral signature that could be used to follow the conformational change in CCMV coat dynamics. The results provide evidence for a concerted swelling process in which the cages exist in only two structural forms, with essentially no intermediates. This methodology can be generalized for all symmetry types of icosahedral protein architectures to monitor protein cage dynamics. 相似文献
272.
Changfei He Peter R. Christensen Trevor J. Seguin Eric A. Dailing Brandon M. Wood Rebecca K. Walde Kristin A. Persson Thomas P. Russell Brett A. Helms 《Angewandte Chemie (International ed. in English)》2020,59(2):735-739
Control of equilibrium and non‐equilibrium thermomechanical behavior of poly(diketoenamine) vitrimers is shown by incorporating linear polymer segments varying in molecular weight (MW) and conformational degrees of freedom into the dynamic covalent network. While increasing MW of linear segments yields a lower storage modulus at the rubbery plateau after softening above the glass transition (Tg), both Tg and the characteristic time of stress relaxation are independently governed by the conformational entropy of the embodied linear segments. Activation energies for bond exchange in the solid state are lower for networks incorporating flexible chains; the network topology freezing temperature decreases with increasing MW of flexible linear segments but increases with increasing MW of stiff segments. Vitrimer reconfigurability is therefore influenced not only by the energetics of bond exchange for a given network density, but also the entropy of polymer chains within the network. 相似文献
273.
Trevor A. Shear Fuding Lin Lev N. Zakharov Darren W. Johnson 《Angewandte Chemie (International ed. in English)》2020,59(4):1496-1500
Cyclophanes are a venerable class of macrocyclic and cage compounds that often contain unusual conformations, high strain, and unusual properties. However, synthesis of complex, functional derivatives remains difficult due to low functional group tolerance, high dilution, extreme reaction conditions, and sometimes low yields using traditional stepwise synthetic methods. “Design of experiments” (DOE) is a method employed for the optimization of reaction conditions, and we showcase this approach to generate a dramatic increase in the yield of specific targets from two different self‐assembling systems. These examples demonstrate that DOE provides an additional tool in tuning self‐assembling, dynamic covalent systems. 相似文献
274.
Pascal Vermeeren Trevor A. Hamlin Israel Fernndez F. Matthias Bickelhaupt 《Angewandte Chemie (International ed. in English)》2020,59(15):6201-6206
The Lewis acid(LA)‐catalyzed Diels–Alder reaction between isoprene and methyl acrylate was investigated quantum chemically using a combined density functional theory and coupled‐cluster theory approach. Computed activation energies systematically decrease as the strength of the LA increases along the series I2<SnCl4<TiCl4<ZnCl2<BF3<AlCl3. Emerging from our activation strain and Kohn–Sham molecular orbital bonding analysis was an unprecedented finding, namely that the LAs accelerate the Diels–Alder reaction by a diminished Pauli repulsion between the π‐electron systems of the diene and dienophile. Our results oppose the widely accepted view that LAs catalyze the Diels–Alder reaction by enhancing the donor–acceptor [HOMOdiene–LUMOdienophile] interaction and constitute a novel physical mechanism for this indispensable textbook organic reaction. 相似文献
275.
Miguel . Baeza Cinco Guang Wu Nikolas Kaltsoyannis Trevor W. Hayton 《Angewandte Chemie (International ed. in English)》2020,59(23):8947-8951
The “masked” terminal Zn sulfide, [K(2.2.2‐cryptand)][MeLZn(S)] ( 2 ) (MeL={(2,6‐iPr2C6H3)NC(Me)}2CH), was isolated via reaction of [MeLZnSCPh3] ( 1 ) with 2.3 equivalents of KC8 in THF, in the presence of 2.2.2‐cryptand, at ?78 °C. Complex 2 reacts readily with PhCCH and N2O to form [K(2.2.2‐cryptand)][MeLZn(SH)(CCPh)] ( 4 ) and [K(2.2.2‐cryptand)][MeLZn(SNNO)] ( 5 ), respectively, displaying both Brønsted and Lewis basicity. In addition, the electronic structure of 2 was examined computationally and compared with the previously reported Ni congener, [K(2.2.2‐cryptand)][tBuLNi(S)] (tBuL={(2,6‐iPr2C6H3)NC(tBu)}2CH). 相似文献
276.
277.
Trevor J Davies A Christopher Garner Stephen G Davies Richard G Compton 《Chemphyschem》2005,6(12):2633-2639
Electrocatalytic processes can take place either homogeneously in a single liquid phase or heterogeneously at the liquid-liquid interface formed in emulsions. This Article addresses the question as to whether a change in rate and/or mechanism can occur between the two possibilities. Specifically, cyclic voltammetry and electrosynthetic experiments are used to demonstrate that for the vitamin B12 mediated reduction of vicinal dibromides producing olefins, electric field effects likely operate at the liquid-liquid interface which can change the populations of different conformers relative to the single homogeneous-phase experiment, leading to significant changes in rate. 相似文献
278.
Trevor J Davies Eleanor R Lowe Shelley J Wilkins Richard G Compton 《Chemphyschem》2005,6(7):1340-1347
The average size of inert particles is determined using a simple electrochemical procedure. Alumina particles are deposited on an edge-plane graphite electrode, and a cyclic voltammogram is recorded. The scan rate employed varies between 0.2 and 2 V s(-1). At these scan rates the diffusion layer thickness is greater than the size of the alumina particles, minimizing the influence of the particles' height on the observed voltammetry. The average size of the particles is determined via comparison of the experimental voltammograms with simulations. 相似文献
279.
280.
El-Mohamady E. Eid The Late Trevor G. Bonner David Lewis 《Journal of heterocyclic chemistry》1983,20(6):1501-1503
3-Methyl or 3-phenyl-5-chloro-1-phenyl-4-phenylazopyrazole with primary amines, sodium polysulfide and sodium azide yielded amines, disulfides and 2,4-dihydropyrazolo[3,4-d]-1,2,3-triazoles respectively. 4-Amino-5-anilino-1,3-diphenylpyrazole was also prepared and characterized. 相似文献