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881.
Segregation of alloying and impurity elements to grain boundaries in ferritic steels and alloys is known to modify the mechanical properties. This paper considers segregation of such elements, in particular phosphorus and carbon, that occur in ferritic nuclear pressure vessel steels subject to neutron irradiation and temperature typical of that encountered in service. Models are presented that allow the prediction of equilibrium and non-equilibrium segregation of phosphorus to grain boundaries and also take into account synergistic interaction with carbon under various combinations of neutron-irradiation temperature. These are related to a wide range of experimental observations compiled from data in the literature for mainly phosphorus and carbon measured at grain boundaries in neutron-irradiated ferritic vessel steels and alloys. The predictions from the segregation models are compared with these experimental data. The discussion provides a rationalization for the apparent variability in the measured grain boundary phosphorus compositions and thereby fracture susceptibility for various nuclear pressure vessel ferritic steels. 相似文献
882.
Derry W. Jones 《Contemporary Physics》2013,54(6):613-614
This article reviews experimental and theoretical work on the spectrum of ice. Its features in the radiofrequency region arise from the reorientation of water molecules at lattice sites where strong thermal excitations of a molecular vibration produce a defect. The large permittivity and relaxation time in ice are consistent with our knowledge of its structure. The microwave region has been less extensively studied, but enough information is available to determine how the molecular polarizability of a water molecule in ice depends upon temperature and volume. In the infrared region, two features, arising from the translational lattice vibrations and symmetric O-H stretching, have received much attention, and progress is being made towards understanding them theoretically. The visible and ultraviolet regions show no distinctive features, and the absorptivity in this region is small. The entire spectrum of ice is, of course, useful for studies of many natural phenomena, but the features in the radiohquency and microwave regions are of particular value in field-work in the polar regions. 相似文献
883.
This paper proposes and investigates the use of several factors for portfolio selection of international mutual funds. Three of the selected factors are specific to mutual funds, additional three factors are taken from Macroeconomics and one factor represents regional and country preferences. Each factor is treated as an objective in the multiple objective approach of goal programming. Three variants of goal programming are utilized. 相似文献
884.
Cletus A D'Souza Vikramjit Chopra Richard Varhol Yuan-Yun Xie Slavita Bohacec Yongjun Zhao Lisa LC Lee Mikhail Bilenky Elodie Portales-Casamar An He Wyeth W Wasserman Daniel Goldowitz Marco A Marra Robert A Holt Elizabeth M Simpson Steven JM Jones 《BMC neuroscience》2008,9(1):1-14
Background
We have recorded responses from single neurons in murine visual cortex to determine the effectiveness of the input from the two murine cone photoreceptor mechanisms and whether there is any unique selectivity for cone inputs at this higher region of the visual system that would support the possibility of colour vision in mice. Each eye was stimulated by diffuse light, either 370 (strong stimulus for the ultra-violet (UV) cone opsin) or 505 nm (exclusively stimulating the middle wavelength sensitive (M) cone opsin), obtained from light emitting diodes (LEDs) in the presence of a strong adapting light that suppressed the responses of rods.Results
Single cells responded to these diffuse stimuli in all areas of striate cortex. Two types of responsive cells were encountered. One type (135/323 – 42%) had little to no spontaneous activity and responded at either the on and/or the off phase of the light stimulus with a few impulses often of relatively large amplitude. A second type (166/323 – 51%) had spontaneous activity and responded tonically to light stimuli with impulses often of small amplitude. Most of the cells responded similarly to both spectral stimuli. A few (18/323 – 6%) responded strongly or exclusively to one or the other spectral stimulus and rarely in a spectrally opponent manner.Conclusion
Most cells in murine striate cortex receive excitatory inputs from both UV- and M-cones. A small fraction shows either strong selectivity for one or the other cone mechanism and occasionally cone opponent responses. Cells that could underlie chromatic contrast detection are present but extremely rare in murine striate cortex. 相似文献885.
“A series of novel spirobiisoxazoline dibenzoquinone derivatives were synthesized starting from 2,5-dimethoxybenzaldehyde in a six-step synthetic sequence”. The key step [3?+?2] double 1,3-dipolar cycloaddition of oxime chloride with allenoate was performed under mild reaction conditions using sodium carbonate at ambient temperature. This is the first innovative synthesis of Spirobiisoxazoline Dibenzoquinone system where quinone ring is alkylated to isoxazoline moiety. 相似文献
886.
Marc F. Tesch Shannon A. Bonke Travis E. Jones Maryam N. Shaker Jie Xiao Katarzyna Skorupska Rik Mom Jens Melder Philipp Kurz Axel Knop‐Gericke Robert Schlgl Rosalie K. Hocking Alexandr N. Simonov 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(11):3464-3470
Manganese oxide (MnOx) electrocatalysts are examined herein by in situ soft X‐ray absorption spectroscopy (XAS) and resonant inelastic X‐ray scattering (RIXS) during the oxidation of water buffered by borate (pH 9.2) at potentials from 0.75 to 2.25 V vs. the reversible hydrogen electrode. Correlation of L‐edge XAS data with previous mechanistic studies indicates MnIV is the highest oxidation state involved in the catalytic mechanism. MnOx is transformed into birnessite at 1.45 V and does not undergo further structural phase changes. At potentials beyond this transformation, RIXS spectra show progressive enhancement of charge transfer transitions from oxygen to manganese. Theoretical analysis of these data indicates increased hybridization of the Mn?O orbitals and withdrawal of electron density from the O ligand shell. In situ XAS experiments at the O K‐edge provide complementary evidence for such a transition. This step is crucial for the formation of O2 from water. 相似文献
887.
Donald Hill Peter J. Holliman Eurig W. Jones James McGettrick David A. Worsley Marco Appleman Pranesh Chatterjee 《Surface and interface analysis : SIA》2019,51(9):934-942
This paper studies the removal of chemisorbed carboxylates and phosphonates from TiO2-coated galvanized steel using NaOH(aq). XPS and FTIR data show that NaOH(aq) is effective at desorbing these species and so is an alternative to gas phase processes (eg, plasma cleaning). Tribological investigations show that NaOH(aq)-treated surfaces show reduced friction and wear, relative to the “as-received” galvanized steel. This is ascribed to carbonate (present as an impurity in NaOH) that adsorbs to the surface of the substrate during NaOH(aq) immersion. Carbonate removal through sonication in water generates surfaces that show friction similar to “as-received” galvanized steel. This work is useful in areas (eg, automotive manufacturing), where the effective removal of lubricants following tribological contact is key to subsequent paint adhesion. 相似文献
888.
Walker M. Jones Aaron G. Davis R. Hunter Wilson Katherine L. Elliott Isaiah Sumner 《Journal of computational chemistry》2019,40(22):1969-1977
The mechanism used by the ubiquitin-conjugating enzyme, Ubc13, to catalyze ubiquitination is probed with three computational techniques: Born–Oppenheimer molecular dynamics, single point quantum mechanics/molecular mechanics energies, and classical molecular dynamics. These simulations support a long-held hypothesis and show that Ubc13-catalyzed ubiquitination uses a stepwise, nucleophilic attack mechanism. Furthermore, they show that the first step—the formation of a tetrahedral, zwitterionic intermediate—is rate limiting. However, these simulations contradict another popular hypothesis that supposes that the negative charge on the intermediate is stabilized by a highly conserved asparagine (Asn79 in Ubc13). Instead, calculated reaction profiles of the N79A mutant illustrate how charge stabilization actually increases the barrier to product formation. Finally, an alternate role for Asn79 is suggested by simulations of wild-type, N79A, N79D, and H77A Ubc13: it stabilizes the motion of the electrophile prior to the reaction, positioning it for nucleophilic attack. © 2019 Wiley Periodicals, Inc. 相似文献
889.
Ludwig Hackl Dr. Alex R. Petrov Dr. Thomas Bannenberg Dr. Matthias Freytag Prof. Dr. Peter G. Jones Prof. Dr. Matthias Tamm 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(70):16148-16155
The reaction of 1,2-dipiperidinoacetylene ( 1 ) with 0.5 equivalents of SnCl2 or GeCl2⋅dioxane afforded the 1,2,3,4-tetrapiperidino-1,3-cyclobutadiene tin and germanium dichloride complexes 2 a and 2 b , respectively. A competing redox reaction was observed with excess amounts of SnCl2, which produced a tetrapiperidinocyclobutadiene dication with two trichlorostannate(II) counterions. Heating neat 1 to 110 °C for 16 h cleanly produced the dimer 1,3,4,4-tetrapiperidino-3-buten-1-yne ( 3 ); its reaction with stoichiometric amounts of SnCl2 or GeCl2⋅dioxane furnished the 1,3,4,4-tetrapiperidino-1,2-cyclobutadiene tin and germanium dichloride complexes 4 a and 4 b , respectively. Transition-metal complexes containing this novel four-membered cyclic bent allene (CBA) ligand were prepared by reaction of 3 with [(tht)AuCl], [RhCl(CO)2]2, and [(Me3N)W(CO)5] to form [(CBA)AuCl] ( 5 ), [(CBA)RhCl(CO)2] ( 6 ), and [(CBA)W(CO)5] ( 7 ). The molecular structures of all compounds 2 – 7 were determined by X-ray diffraction analyses, and density functional theory (DFT) calculations were carried out to rationalise the formation of 3 and 4 a . 相似文献
890.
André U. Augustin Prof. Dr. Peter G. Jones Prof. Dr. Daniel B. Werz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(50):11620-11624
A 1,3-aminothiolation was realized by reacting 2-substituted cyclopropane 1,1-dicarboxylates with sulfonamides and N-(arylthio)succinimides. Under Sn(OTf)2 catalysis the transformation proceeded smoothly to the corresponding ring-opened products bearing the sulfonamide in the 1-position next to the donor and the arylthio residue in the 3-position next to the acceptor. The procedure was extended to the corresponding selenium analogues by employing N-(phenylseleno)succinimides as an electrophilic selenium source. 相似文献