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81.
Racemic 1-methyl-2-oxocycloalkanecarbonitriles have been subjected to bioreduction by the fungus Mortierella isabellina NRRL 1757 through a parallel kinetic-resolution process. The u and l alcohols thus obtained (up to >99% ee) were easily separated and oxidized to the R and S ketones, respectively. The process can be then repeated so that both enantiomers of the ketone and two epimers of the alcohol can be obtained in their enantiopure forms. 相似文献
82.
Maderna A Huertas R Hawthorne MF Luguya R Vicente MG 《Chemical communications (Cambridge, England)》2002,(16):1784-1785
A boron-rich, water-soluble porphyrin conjugate was synthesized by coupling of two carboranyl alcohols with 2-chlorophenoxyphosphorus dichloride, followed by conjugation to an amine-functionalized tetraphenyl-porphyrin via an amide linkage. 相似文献
83.
Escuer A Vicente R Mautner FA Goher MA Abu-Youssef MA 《Chemical communications (Cambridge, England)》2002,(1):64-65
Novel 3D topologies combining diazine and azido bridges between MnII magnetic centres have been obtained and characterised by low-temperature magnetic measurements. 相似文献
84.
Adam W García H Diedering M Martí V Olivucci M Palomares E 《Journal of the American Chemical Society》2002,124(41):12192-12199
The photochemical denitrogenation of the cyclopentene-annelated DBH-type azoalkanes 1 has been examined in solution as a function of bridgehead substitution and temperature. For all derivatives, namely, the unsubstituted 1a(H/H), monomethyl 1b(Me/H) dimethyl 1c(Me/Me), monophenyl 1d(Ph/H), and diphenyl 1e(Ph/Ph), the temperature-dependent ratio of syn and anti housanes 2 provides experimental support for a competition between the singlet (high temperature) and triplet (low temperature) reaction channels in the direct photolysis. The syn/anti ratio of the housanes 2 depends on the extent and type of bridgehead substitution; the amount of the anti diastereomer (retention) follows the order Ph > Me > H, and double substitution is more effective than single. This stereochemical memory is interpreted in terms of the mass effect (inertia) of the substituents and steric interaction (size) between the substituents at the bridgehead and the methylene bridge during the deazetation step of the transient diazenyl diradical conformations (1)DZ (exo-ax) and (1)DZ (exo-eq). These conformers are impulsively generated upon decay of the (1)(n,pi)-excited azoalkane, a trajectory assessed through computational work. The new mechanistic feature disclosed by the unprecedented anti stereoselectivity (retention) is the intervention of a puckered 1,3-cyclopentanediyl singlet diradical (1)DR as product bifurcation step, whose conformational relaxation to the planar species (loss of stereochemical memory) is encumbered by bridgehead substitution. 相似文献
85.
86.
García-Jareño JJ Giménez-Romero D Keddam M Vicente F 《The journal of physical chemistry. B》2005,109(10):4593-4598
The graphical analysis of the impedance plots is used in the study of the electrodic systems that take place through two consecutive single electron transfers. The zinc anodic dissolution is studied by using this procedure. The characteristic points easily allow us to explain and to simulate the impedance behavior of this electrodic system according to the steady-state potential and the roughness of the working electrode. The direct procedure for parametrical identification from the graphical analysis allows us to reduce the time needed for an impedance experiment. This graphical analysis is suggested for studying thin coated galvanized steels. 相似文献
87.
Effect of the platinum content on the microstructure and micropore size distribution of Pt/alumina-pillared clays 总被引:1,自引:0,他引:1
Barrera-Vargas M Valencia-Rios J Vicente MA Korili SA Gil A 《The journal of physical chemistry. B》2005,109(49):23461-23465
The aim of this work is to study the effect of the platinum content (0-1.8 wt % Pt) on the microstructure of an alumina-pillared clay. For this purpose, the nitrogen physisorption data at -196 degrees C, the micropore size distributions of the supported platinum catalysts, and the hydrogen chemisorption results at 30 degrees C have been analyzed and compared. The preparation of the catalysts has modified the textural properties of the Al-pillared clay support, giving rise to a loss of surface area and micropore volume. After reduction at 420 degrees C, the presence of dispersed metallic platinum with mean crystallite size in the 22-55 A range has been found by hydrogen adsorption. Comparison of all results reveals that the platinum species block the micropore entrances by steric hindrance to nitrogen access as the platinum content increases. 相似文献
88.
Zúñiga-Pérez J Muñoz-Sanjosé V Palacios-Lidón E Colchero J 《Physical review letters》2005,95(22):226105
The surface electrical properties of ZnO thin films grown along the nonpolar [1120] direction have been investigated by Kelvin probe microscopy on a nanometer scale. Two different charge domains, with a 75 meV work function difference, coexist within the ZnO surface, which is covered by rhombohedral pyramids whose sidewalls are shown to be {1011}-type planes. The presence and relative orientation of the two kinds of charge domains are explained in terms of the atomic arrangement at the {1011} polar surfaces. 相似文献
89.
Xia JS Pan W Vicente CL Adams ED Sullivan NS Stormer HL Tsui DC Pfeiffer LN Baldwin KW West KW 《Physical review letters》2004,93(17):176809
At a very low-temperature of 9 mK, electrons in the second Landau level of an extremely high-mobility two-dimensional electron system exhibit a very complex electronic behavior. With a varying filling factor, quantum liquids of different origins compete with several insulating phases leading to an irregular pattern in the transport parameters. We observe a fully developed nu=2+2/5 state separated from the even-denominator nu=2+1/2 state by an insulating phase and a nu=2+2/7 and nu=2+1/5 state surrounded by such phases. A developing plateau at nu=2+3/8 points to the existence of other even-denominator states. 相似文献
90.
R. Jimnez M. Villar M. Cueto E. Grueso J. Illanes J. I. Cobrian F. Cantn I. Villa J. M. Snchez S. Maza J. M. Muoz C. Muoz R. Prado‐Gotor 《国际化学动力学杂志》2004,36(7):410-415
The base‐catalyzed linkage isomerization of [Co(NH3)5‐ONO]2+ to the nitro [(NH3)5Co‐NO2]2+ form is studied in various isodielectric water–cosolvent mixtures (methanol, ethanol, tert‐butyl alcohol, and 2‐propanol) at 298 K. In all cases, except for methanol–water mixtures, the rate constants increase with the proportion of cosolvent. Medium effects have been rationalized by using a multiparameter regression of solvent parameters which rationalizes the results obtained, including water–methanol mixtures. The experimental data, k2, in fact, are well correlated through the following equation: where A, B, and Gexc are the acidity parameter, the basicity parameter, and the excess Gibbs free energy of the mixture, respectively. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 410–415, 2004 相似文献