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排序方式: 共有297条查询结果,搜索用时 15 毫秒
21.
Dr. Jérôme Fortage Dr. Fabien Tuyèras Dr. Philippe Ochsenbein Dr. Fausto Puntoriero Dr. Francesco Nastasi Prof. Dr. Sebastiano Campagna Dr. Sophie Griveau Dr. Fethi Bedioui Dr. Ilaria Ciofini Dr. Philippe P. Lainé 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(36):11047-11063
This study evaluates the impact of the extension of the π‐conjugated system of pyridiniums on their various properties. The molecular scaffold of aryl‐substituted expanded pyridiniums (referred to as branched species) can be photochemically bis‐cyclized into the corresponding fused polycyclic derivatives (referred to as pericondensed species). The representative 1,2,4,6‐tetraphenylpyridinium ( 1H ) and 1,2,3,5,6‐pentaphenyl‐4‐(p‐tolyl)pyridinium ( 2Me ) tetra‐ and hexa‐branched pyridiniums are herein compared with their corresponding pericondensed derivatives, the fully fused 9‐phenylbenzo[1,2]quinolizino[3,4,5,6‐def]phenanthridinium ( 1H f ) and the hitherto unknown hemifused 9‐methyl‐1,2,3‐triphenylbenzo[h]phenanthro[9,10,1‐def]isoquinolinium ( 2Me f ). Combined solid‐state X‐ray crystallography and solution NMR experiments showed that stacking interactions are barely efficient when the pericondensed pyridiniums are not appropriately substituted. The electrochemical study revealed that the first reduction process of all the expanded pyridiniums occurs at around ?1 V vs. SCE, which indicates that the lowest unoccupied molecular orbital (LUMO) remains essentially localized on the pyridinium core regardless of pericondensation. In contrast, the electronic and photophysical properties are significantly affected on going from branched to pericondensed pyridiniums. Typically, the number of absorption bands increases with extended activity towards the visible region (down to ca. 450 nm in MeCN), whereas emission quantum yields are increased by three orders of magnitude (at ca. 0.25 on average). A relationship is established between the observed differential impact of the pericondensation and the importance of the localized LUMO on the properties considered: predominant for the first reduction process compared with secondary for the optical and photophysical properties. 相似文献
22.
We present a new approach that combines electronic structure methods and molecular dynamics simulations to investigate the infrared spectroscopy of condensed phase systems. This approach is applied to the OH stretch band of dilute HOD in liquid D2O and the OD stretch band of dilute HOD in liquid H2O for two commonly employed models of water, TIP4P and SPC/E. Ab initio OH and OD anharmonic transition frequencies are calculated for 100 HOD x (D2O)n and HOD x(H2O)n (n = 4-9) clusters randomly selected from liquid water simulations. A linear empirical relationship between the ab initio frequencies and the component of the electric field from the solvent along the bond of interest is developed. This relationship is used in a molecular dynamics simulation to compute frequency fluctuation time-correlation functions and infrared absorption line shapes. The normalized frequency fluctuation time-correlation functions are in good agreement with the results of previous theoretical approaches. Their long-time decay times are 0.5 ps for the TIP4P model and 0.9 ps for the SPC/E model, both of which appear to be somewhat too fast compared to recent experiments. The calculated line shapes are in good agreement with experiment, and improve upon the results of previous theoretical approaches. The methods presented are simple, and transferable to more complicated systems. 相似文献
23.
24.
B Kintses C Hein MF Mohamed M Fischlechner F Courtois C Lainé F Hollfelder 《Chemistry & biology》2012,19(8):1001-1009
Highlights? Microfluidic droplet compartments miniaturize cell lysate screening assays ? Picoliter single-cell lysate assays comparable in sensitivity to macroscale ? Directed evolution results in improved clones validating this experimental set-up ? Precision of droplet sorting enables enrichment of clones with slight improvements 相似文献
25.
Christopher N. MunningsRuth Sayers Paul A. StuartStephen J. Skinner 《Solid State Sciences》2012,14(1):48-53
The oxidation of the n = 1 Ruddlesden-Popper phase, Sr2MnO3.5+x, where 0 ≤ x ≤ 0.5 has been investigated using a combination of in-situ diffraction techniques. In agreement with previous reports the room temperature structure of Sr2MnO3.5+x was determined to be monoclinic crystallising in space group P21/c. On heating in air the material undergoes rapid oxidation at a relatively modest temperature, ∼275 °C. The oxidation process is coincident with a significant change in the structure, with the material now adopting a tetragonal I4/mmm structure. In the oxygen deficient phase where x > 0 the Mn coordination is square pyramidal, with a sixth partially occupied oxygen position giving rise to octahedral coordination. Oxidation of Sr2MnO3.5+x results in the filling of the partially occupied O4 positions and a resulting increase in symmetry, with the Mn coordination now adopting solely a distorted octahedral environment. 相似文献
26.
Joseph A. Connor Jose A. Martinho-Simoes Henry A. Skinner Mohammad T. Zafarani-Moattar 《Journal of organometallic chemistry》1979,179(3):331-356
Microcalorimetric measurements at elevated temperatures of the heats of thermal decomposition and iodination have led to values of the standard enthalpies of formation of the following crystalline compounds (values given in kJ mol?1) at 298K: [Cr(η6-1,3,5-C6H3(CH3)3)2] = (63±12); [Cr(η6-C6(CH3)6)2] : -(88±12); [Cr(1,2,3,4,4a,8a-η-C10H8)2] = (407±11); [Cr(CO)3(1,2,3,4,4a,8a-η-C10H8)] = -(258±8). Separate measurements by the vacuum sublimation microcalorimetric technique gave the following values for the enthalpy of sublimation at 298K (kJ mol?1) : [Cr(η6-1,3,5-C6H3(CH3)3)2] = (104±1); [Cr(η6-C6(CH3)6)2] = (119±4); [Cr(CO)3(1,2,3,4,4a,8a-η-C10H8)] = (107±3). From these and other data, the bond enthalpy contributions of the metal-ligand bonds in the gaseous metal complexes were evaluated as follows: [(η6-C6(CH3)6)-Cr] (155±7); [(η6-C6H3(CH3)3)-Cr] (151±6); [(1,2,3,4,4a, 8a-η-C10H8)-Cr](145±6) kJ mol?1]The question of the transferability of the enthalpy contributions of chromium—ligand bonds between organochronium complexes is discussed with aid of information from structural and spectroscopic investigation. The limitations of the procedure are defined.The thermodynamic data are used to discuss various substitution, redistribution and exchange reaction of Cr(η-arene)2 and [Cr(CO)3(η-arene)] compounds. 相似文献
27.
C. Chevennement-Roux T. Dreher P. Alliot E. Aubry J.-P. Lainé L. Jézéquel 《Experimental Mechanics》2007,47(2):201-210
The optimization of wiper systems under various conditions and the creation of a product which is as robust as possible are
the main objectives for an equipment supplier. However, in certain conditions, instabilities can appear and generate wiping
defects due to the rubber-glass contact. To improve wiping quality and to reduce the number of test stages for design, this
study proposes a wiper system modeling method. The wiper system is represented by a rigid blade holder on which a rubber blade
is fitted. This rigid blade system is used on a flat test bench at constant wiping velocity. The model is based on modal synthesis
methods and will be validated through comparison with experimental tests under various conditions. The right correlation obtained
allows the same modelling method to be applied to the new generation of flexible wiper blades which take account of the degree
of freedom of the wiper blade flexions. So, a new computation tool will be developed and validated through experimentation
on a specific test bench. 相似文献
28.
Oscillatory rheological experiments at different temperatures and over a wide range of frequencies have been used to investigate
the gelation process and, more particularly, the sol–gel transition of various poly(vinyl chloride) (PVC) plastisols. The
sol–gel transition process was found to be universal with respect to the temperature and solid volume fraction according to
the similarity of the fractal structure in PVC plastisols. The variation of the gel time (t
gel) with temperature for any composition of PVC plastisols was predicted from the Dickinson’s model (E. Dickinson, J Chem Soc
Faraday Trans, 93:111–114, 1997). Dynamic viscoelastic properties of PVC plastisols have also been studied as a function of
temperature that allowed us to follow the gelation process of various plastisols. Thus, the influence of the type and concentration
of PVC resins in gelation process was investigated. The variation of the complex shear modulus at a constant frequency was
depicted by a master curve regarding the dependence of the moduli on PVC concentrations. 相似文献
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