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71.
T Courant VG Roullin C Cadiou M Callewaert MC Andry C Portefaix C Hoeffel MC de Goltstein M Port S Laurent LV Elst R Muller M Molinari F Chuburu 《Angewandte Chemie (International ed. in English)》2012,51(36):9119-9122
Do not tumble dry: Gadolinium-DOTA encapsulated into polysaccharide nanoparticles (GdDOTA?NPs) exhibited high relaxivity (r(1) =101.7?s(-1) mM(-1) per Gd(3+) ion at 37?°C and 20?MHz). This high relaxation rate is due to efficient Gd loading, reduced tumbling of the Gd complex, and the hydrogel nature of the nanoparticles. The efficacy of the nanoparticles as a T(1) /T(2) dual-mode contrast agent was studied in C6 cells. 相似文献
72.
We have measured fragmentation cross sections of protonated water cluster cations (H(2)O)(n=30-50)H(+) by collision with water molecules. The clusters have well-defined sizes and internal energies. The collision energy has been varied from 0.5 to 300 eV. We also performed the same measurements on deuterated water clusters (D(2)O)(n=5-45)D(+) colliding with deuterated water molecules. The main fragmentation channel is shown to be a sequential thermal evaporation of single molecules following an initial transfer of relative kinetic energy into internal energy of the cluster. Unexpectedly, that initial transfer is very low on average, of the order of 1% of collision energy. We evaluate that for direct collisions (i.e., within the hard sphere radius), the probability for observing no fragmentation at all is more than 35%, independently of cluster size and collision energy, over our range of study. Such an effect is well known at higher energies, where it is attributed to electronic effects, but has been reported only in a theoretical study of the collision of helium atoms with sodium clusters in that energy range, where only vibrational excitation occurs. 相似文献
73.
74.
Sergei V. Levchik Giovanni Camino Maria Paola Luda Luigi Costa Bruno Costes Yves Henry Emile Morel George Muller 《先进技术聚合物》1995,6(2):53-62
Tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) undergoes homopolymerization on heating. Intramolecular reactions which compete with crosslinking favor the formation of cyclic structures with increasing thermal and fire resistance of the resin, whereas physical mechanical properties tend to decrease. The mechanism of thermal decomposition of TGDDM is studied by thermogravimetry, differential scanning calorimetry and thermal volatilization analysis with characterization of volatiles evolved and residue left. Thermal degradation of poly-(TGDDM) starts at 260°C with elimination of water from secondary alcoholic groups which is a typical pathway for epoxy resin degradation. Resulting unsaturations weaken bonds in the β-position and provoke the first chain breaking at allyl–amine and allyl–either bonds. With increasing temperature, saturated alkyl–ether bonds and alkyl carbon–carbon bonds are broken first, followed by the most stable alkyl–aryl bonds at T>365°C. The combustion performance of TGDDM is discussed on the basis of the thermal degradation behavior. 相似文献
75.
76.
Susperregui N Miqueu K Sotiropoulos JM Le Callonnec F Fouquet E Felpin FX 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(23):7210-7218
The palladium-catalyzed Heck-Matsuda reaction with a catalytic amount of an in-situ-generated diazonium salt proceeded under mild and sustainable conditions. The reaction proceeded at room temperature, under base-free conditions, and only generated tBuOH, H(2)O, and N(2) as by-products. Ortho-substituted diazonium salts were more-efficiently coupled to methyl acrylate than their corresponding para isomers, which required the addition of anisole as an additive. In support of these experimental data, we carried out theoretical studies to gain a deeper understanding of these reaction outcomes. 相似文献
77.
The site occupancies of the Mo-Ni-Re σ phase have been studied as a function of the composition in the ternary homogeneity domain by both experimental measurements and calculations. Because of the possible simultaneous occupancy of three elements on the five sites of the crystal structure, the experimental determination of the site occupancies was achieved by using combined Rietveld refinement of X-ray and neutron diffraction data, whereas calculation of the site occupancies was carried out by using the density functional theory results of every ordered (i.e., 3(5) = 243) configuration appearing in the ternary system. A comparison of the experimental and calculation results showed good agreement, which suggests that the topologically close-packed phases, such as the σ phase, could be described by the Bragg-Williams approximation (i.e., ignoring the short-range-order contributions). On the other hand, the atomic distribution on different crystallographic sites of the Mo-Ni-Re σ phase was found to be governed by the atomic sizes. Ni, having the smallest atomic size, showed a preference for low-coordination-number (CN) sites, whereas Mo, being the largest in atomic size, preferred occupying high-CN sites. However, the preference of Re, having intermediate atomic size, varied depending on the composition, and a clear reversal in the preference of Re as a function of the composition was evidenced in both the calculated and experimental site-occupancy results. 相似文献
78.
Jean-Marc Tornare Pierre Vogel A. Alan Pinkerton Dieter Schwarzenbach 《Helvetica chimica acta》1985,68(8):2195-2215
Stereoselective synthesis of 2-methylidene-3-[(Z)-(2-nitrophenylsulfenyl)methylidene]-7-oxabicyclo[2.2.1]-heptane ( 16 ), 1,4-epoxy-1,2,3,4-tetrahydro-5,8-dimethoxy-2-methylidene-3-[(Z)-(2-nitrophenylsulfenyl)methylidene]anthracene ( 18 ), and 1,4-epoxy-1,2,3,4-tetrahydro-5,8-dimethyoxy-2-methylidene-3-[(Z)-(phenylsulfenyl)-methylidene]anthracene ( 19 ) are presented. The Diels-Alder additions of these S-substituted dienes and those of 2,5-dimethylidene-3,6-bis{[(Z)-(2-nitrophenyl)sulfenyl]methylidene}-7-oxabicyclo[2.2.1]heptane ( 17 ) have been found to be face selective and ‘ortho’ regiospecific. The face selectivity depends on the nature of the dienophile. It is exo-face selective with bulky dienophiles such as ethylene-tetracarbonitrile (TCNE) and 2-nitro-1-butene and endo-face selective with methyl vinyl ketone, methyl acrylate, and 3-butyn-2-one. In the presence of a Lewis acid, the face selectivity of the Diels-Alder reaction can be reversed. The addition of the first equivalent of a dienophile to tetraene 17 is at least 100 times faster than the addition of the second equivalent of the same dienophile to the corresponding mono-adduct. The X-ray structure of the crystalline bis-adduct 43 , a 7-oxabicyclo[2.2.1]hepta-2,5-diene system annellated to two cyclohexene rings, resulting from the successive additions of methyl acrylate and methyl vinyl ketone to tetraene 17 is presented. Only one of the two endocyclic double bonds of the 7-oxabicyclo[2.2.1]hepta-2,5-diene deviates from planarity, the substituents bending towards the endo face by 5.7°. 相似文献
79.
Dipl. Chem. Keven Muller Dr. Yu Sun Andreas Heimermann Fabian Menges Gereon Niedner‐Schatteburg Christoph van Wüllen Prof. Dr. Werner R. Thiel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(24):7825-7834
Pyridinylazolato (N–N′) ruthenium(II) complexes of the type [(N–N′)RuCl(PMe3)3] have been obtained in high yields by treating the corresponding functionalised azolylpyridines with [RuCl2(PMe3)4] in the presence of a base. 15N NMR spectroscopy was used to elucidate the electronic influence of the substituents attached to the azolyl ring. The findings are in agreement with slight differences in the bond lengths of the ruthenium complexes. Furthermore, the electronic nature of the azolate moiety modulates the catalytic activity of the ruthenium complexes in the hydrogenation of carbon dioxide under supercritical conditions and in the transfer hydrogenation of acetophenone. DFT calculations were performed to shed light on the mechanism of the hydrogenation of carbon dioxide and to clarify the impact of the electronic nature of the pyridinylazolate ligands. 相似文献
80.
Capillary isoelectric focusing (CIEF) separations are usually performed with neutral coated fused-silica capillaries in aqueous anticonvective media. Glycerol, a very viscous solvent (eta = 945 mPa x s at 25 degrees C), known to help stabilize any kind of proteins and solubilize hydrophobic ones, was tested as an alternative to using commercial gels. Viscosity and electroosmotic mobility were measured as a function of gel or glycerol content in water, and a 30:70 v/v glycerol-water medium appeared as a good compromise for performing CIEF in a bare fused-silica capillary without imposing too high a viscosity. To demonstrate the feasibility of this new CIEF system, a standard mixture of nine model proteins was separated according to their pI with a good agreement between experimental and literature aqueous pIs. Moreover, better resolution was achieved with this system than with the conventional aqueous CIEF system, as two of the model proteins could not be separated in the latter system. Glycerol-water CIEF in bare silica capillary was next applied to the separation of horse radish peroxidase, a complex mixture of protein isoforms. The good concordance with the separation obtained by the conventional CIEF system indicated the adequacy of this new system. Finally, as anticipated from the results obtained for the separation of bacteriorhodopsin, a membrane protein, glycerol-water CIEF performed in bare silica capillary appears to be a promising alternative to conventional aqueous CIEF for hydrophobic protein characterization, under their native form. 相似文献