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21.
Suspensions of cellulose nanocrystals form colloidal chiral nematic phases. The liquid crystalline order in these suspensions can be captured in solid films by slow evaporation of the liquid. Studies of the microstructure of such chiral nematic solid films revealed parabolic focal conic (PFC) defects, a symmetric form of focal conic defects in which the line defects form a pair of perpendicular, antiparallel, and confocal parabolas. The cellulose films with PFC defects were characterized by polarized-light and atomic force microscopy. The film surface showed a regular array of large and small elevations resulting from the displacement of the structural layers. Film fracture lines showed a series of layered half-cones. The microstructure of the films was modeled by computer. The model revealed that many structural layers terminate at the film surface. 相似文献
22.
Alkyl radicals, derived from decarboxylation of carboxylic acids, add readily to phenyl vinyl sulphone and vinyl phosphonium bromide. The adducts may be further converted into a variety of useful synthetic intermediates. 相似文献
23.
The reaction of 4, 7-phenanthroline (1) with aqueous transitionmetal complexes [Mn(H2O)6][NO3]2, [Co(H2O)6][NO3]2, [Ni(H2O)6[NO3]2, [Mn(H2O)6][ClO4]2, and [Co(H2O)6][ClO4]2 does not produce coordination complexes between these metal cations and the N-donor ligand as expected. Instead, supramolecular hydrogenbonded networks are formed between the nitrogen donor atoms of 4, 7-phenanthroline and the OH groups of coordinated water molecules: M-O-H...N interactions. This motif of second-sphere coordination for 1 can be exploited as a tool for crystal engineering. As a demonstration of the generality of this new interaction as a supramolecular building block, five X-ray crystal structures are reported that utilise this hydrogen bonding scheme; [Co(H2O)4(NO3)2].(1)2 (2a), [Co(MeCN)2(H2O)4][ClO4]2.(1)2 (2b), [Ni(H2O)4(NO3)2].(1)2 (3a), [Mn(H2O)4(NO3)2].(1)2 (4a), and [Mn(H2O)6][ClO4]2.(1)(4).4H2O (4b). Each network involves complete saturation of the hydrogen-bond donor sets between the aqua complex and 1 using primarily M-O-H...N(1) and M-O-H...O(anion), interactions. Thermogravimteric analysis shows these materials to have stabililities similar to coordination polymers involving metal-ligand bonds; this demonstrates that second-sphere hydrogen bonding has potential for the construction of polymeric metal-containing materials. 相似文献
24.
N-Unsubstituted diaryl, alkyl aryl and dialkyl ketimines are prepared in good yield at ambient temperature by the reaction of KOBut on oxaziridines having an α-hydrogen atom on the N-alkyl substituent; the mechanism and stereochemistry of the reaction are discussed. 相似文献
25.
Richard H. Boyd 《Journal of polymer science. Part A, Polymer chemistry》1967,5(7):1573-1583
The effect of volatilization of molecules larger than monomer has been introduced into the solution of the Simha, Wall, and Blatz kinetic equations for the degradation of a high polymer with an initial “most probable” distribution. Equations describing the rate of sample weight and average molecular weight change result. They differ from the previous “most probable” equations primarily in the presence of an additive term representing the random splitting near the chain ends due to bond scission or transfer attack. Equations are also obtained for the rate of formation of each volatile species and hence the product distribution. The effect of volatilization of larger fragments is discussed in detail for the special case of random scission initiation. The product distribution is discussed for two special cases. 相似文献
26.
SCF MO calculations at the 6-31G** level of approximation are reported for 2H and 14N electric field gradients in HCN?HCN, HCN?HF, and CH3CN?HF dimers, with emphasis on the configurational dependence of these quantities in (HCN)2. In comparison with available experimental nuclear quadrupolar coupling constants, the calculated values for the monomers and dimers exhibit an accuracy of ≈ 10%, which is comparable to that of other spectroscopic parameters. The implications of hydrogen bonding for quadrupolar spin-lattice relaxation rates are briefly discussed. 相似文献
27.
The nickel(1) complex, Ni(teta)+, formed by cathodic reduction of the corresponding nickel(11) complex, reacts rapidly with alkyl bromides to form an unstable intermediate containing a nickelcarbon bond. When the electrolysis medium also contains an activated olefin an insertion reaction occurs. The new metalcarbon bond is cleaved by further reduction and overall the reduction of Ni(teta)2+ in the presence of RBr and CH2CHY leads to high yiels of RCH2CH2Y. 相似文献
28.
A Taylor dispersion tube has been used to measure mutual diffusion in aqueous solutions of glycine hydrochloride at 25°C and concentrations from 0.0005 to 0.5 M. Analysis of the dispersion profiles shows that the diffusion of glycine hydrochloride (GlyHCl) produces a subtantial additional flow of hydrochloric acid that is liberated by the dissociation: GlyH+ + Cl- Gly + H+ + Cl-. Diffusion in this system is, therefore, a ternary process described by the equations J
1(GlyHCl) = – D
11C
1 – D
12C
2 and J
2(HCl) = –D
21C
1 – D
22C
2 for the coupled fluxes of total glycine hydrochloride (1) and hydrochloric acid (2) components. The ratio D
21/D
11 of measured diffusion coefficients indicates that up to two moles of HCl are cotransported per mole of GlyHCl. Although protonated glycine diffuses with relatively mobile Cl– counterions, the main diffusion coefficient of glycine hydrochloride, D
11, is lower than or nearly identical to the diffusion coefficient of aqueous glycine. A model for the diffusion of protonated solutes is developed to interpret this result and the large coupled flows of HCl. Diffusion coefficients are also reported for the aqueous hydrochlorides of 3- and 4-aminobenzoic acids. 相似文献
29.
Boyd DR Sharma ND King AW Shepherd SD Allen CC Holt RA Luckarift HR Dalton H 《Organic & biomolecular chemistry》2004,2(4):554-561
Direct and indirect evidence, of unexpected stereoselective reductase-catalysed deoxygenations of sulfoxides, was found. The deoxygenations proceeded simultaneously, with the expected dioxygenase-catalysed asymmetric sulfoxidation of sulfides, during some biotransformations with the aerobic bacterium Pseudomonas putida UV4. Stereoselective reductase-catalysed asymmetric deoxygenation of racemic alkylaryl, dialkyl and phenolic sulfoxides was observed, without evidence of the reverse sulfoxidation reaction, using anaerobic bacterial strains. A purified dimethyl sulfoxide reductase, obtained from the intact cells of the anaerobic bacterium Citrobacter braakii DMSO 11, yielded, from the corresponding racemates, enantiopure alkylaryl sulfoxide and thiosulfinate samples. 相似文献
30.
The thermal and photochemical decomposition of a typical thiohydroxamic ester (mixed anhydride) doubly labelled with deuterium has shown the photochemical reaction to be a radical chain process, whereas about 20% of the thermal reaction involves a cage mechanism. An improved route to 1-hydroxy-5-phenylthiazolin- -2-thione is reported. 相似文献