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171.
Valdés A Prosmiti R Villarreal P Delgado-Barrio G 《The Journal of chemical physics》2005,122(4):44305
An intermolecular potential energy surface for He(2)Br(2) complex in the ground state is calculated at the levels of fourth-order (MP4) Moller-Plesset and coupled-cluster [CCSD(T)] approximations, using large-core pseudopotential for Br atoms and the aug-cc-pV5Z basis set for He. The surface is characterized by three minima and the minimum energy pathways through them. The global minimum corresponds to a linear He-Br(2)-He configuration, while the two other ones to "police-nightstick" and tetrahedral structures. The corresponding well depths are -90.39/-89.18, -81.23/-80.78 and -74.40/-74.02 cm(-1), respectively, at MP4/CCSD(T) levels of theory. It is found that results obtained by summing three-body parametrized HeBr(2) interactions and the He-He interaction are in very good accord with the corresponding MP4/CSSD(T) configuration energies of the He(2)Br(2). Variational calculations using a sum of three-body interactions are presented to study the bound states of the vdW He(2)Br(2) complex. The binding energy D(0) and the corresponding vibrationally averaged structure are determined for different isomers of the cluster and their comparison with the available experimental data is discussed. 相似文献
172.
Francia F Giachini L Palazzo G Mallardi A Boscherini F Venturoli G 《Bioelectrochemistry (Amsterdam, Netherlands)》2004,63(1-2):73-77
The coupling between electron transfer and protein dynamics has been studied at room temperature in isolated reaction centers (RCs) from the photosynthetic bacterium Rhodobacter sphaeroides by incorporating the protein in polyvinyl alcohol (PVA) films of different water/RC ratios. The kinetic analysis of charge recombination shows that dehydration of RC-containing PVA films causes reversible, inhomogeneous inhibition of electron transfer from the reduced primary quinone acceptor (Q(A)(-)) to the secondary quinone Q(B). A more extensive dehydration of solid PVA matrices accelerates electron transfer from Q(A)(-) to the primary photooxidized electron donor P(+). These effects indicate that incorporation of RCs into dehydrated PVA films hinders the conformational dynamics gating Q(A)(-) to Q(B) electron transfer at room temperature and slows down protein relaxation which stabilizes the primary charge-separated state P(+)Q(A)(-). A comparison with analogous effects observed in trehalose-coated RCs suggests that protein motions are less severely reduced in PVA films than in trehalose matrices at comparable water/RC ratios. 相似文献
173.
Elvia Becerra-Martínez Francisco Ayala-Mata Pedro Velázquez-Ponce Manuel E. Medina Hugo A. Jiménez-Vazquez Pedro Joseph-Nathan L. Gerardo Zepeda 《Tetrahedron: Asymmetry》2017,28(10):1350-1358
The synthesis of acetyldioxanes 4 and 9a starting from (?)-(1R)-myrtenal is described. The products were treated with a representative series of nucleophilic reagents (RMgX, RLi, NaBH4 and LiAlH4) to assess the effect of the substituent at C-3 on the stereochemical outcome. It was observed that the nucleophiles preferred the re-face of the CO group when the equatorial substituent at C-3 was a methyl group, whereas a phenyl group at the same position induced the addition through the si-face, thus allowing access to either desired stereochemistry of a final product. This behavior suggests that the formation of the expected Cram-chelated coordination complex takes a coplanar orientation with the C-3 equatorial substituent. Moreover, Grignard reagents were the most stereoselective nucleophiles. The stereochemistry of the addition was established by X-ray diffraction and chemical correlation. 相似文献
174.
Berencie Yahuaca-Juárez Gerardo González Marco A. Ramírez-Morales Calara Alba-Betancourt Martha A. Deveze-Álvarez Claudia L. Mendoza-Macías 《合成通讯》2020,50(4):539-548
AbstractThe first iodine(III)-based procedure for the benzylic oxidation of different arenes is described by using the (PhIO)n/Al(NO3)3 system under catalytic conditions leading to the formation of the corresponding carbonyl derivatives. The method proceeds under mild, operationally simple, room temperature, short reaction times, and open flask conditions. In light of the organocatalysis relevance and the novelty of our protocol, we wish to communicate our initial results of this novel oxidation. 相似文献
175.
Cabrera Pérez Laura C. Padilla-Martínez Itzia I. Cruz Alejandro Correa Basurto José Miliar García Ángel Hernández Zavala Argelia A. Gómez López Modesto Rosales Hernández Martha C. 《Molecular diversity》2020,24(4):1-14
Molecular Diversity - 11-Beta hydroxysteroid dehydrogenase type 1 (11β-HSD1) regulates cortisol levels mainly in adipose, hepatic and brain tissues. There is a relationship between the high... 相似文献
176.
Estrella Ramos Patricia Guadarrama Gerardo Terán Serguei Fomine 《Journal of Physical Organic Chemistry》2009,22(1):9-16
The electronic properties of the ground state, unrelaxed and relaxed first excited states of push–pull hyperbranched molecules bearing amino and nitro terminal groups have been studied at BB1K/cc‐pvdz//HF/6‐31g(d), TD‐BB1K/cc‐pvdz//HF/6‐31g(d) and TD‐BB1K/cc‐pvdz//CIS/6‐31g(d) levels of theory, respectively. It was demonstrated that dendritic architecture of push–pull molecules favours the charge transfer in the excited state compared to linear molecules. The possibility of adopting a plane conformation is an important condition for the charge transfer in an excited state. According to the calculations 1:1 ratio of donor and acceptor groups is another important precondition for the manifestation of strong charge separation in the excited state. In case of excess of nitro groups over the amino, some of the excitations participating in the S0 → S1 transition favour the charge transfer in the excited state in the opposite directions, thus decreasing the charge separation. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
177.
Gilberto Gonzalez Avalos Gerardo Ayala Noe Barrera Gallegos Aaron Padilla Jose 《Mathematical and Computer Modelling of Dynamical Systems: Methods, Tools and Applications in Engineering and Related Sciences》2019,25(3):284-332
Based on non-linear systems described by multibond graphs, a procedure designed to present symbolic linearization of these multibond graphs, is presented in this paper. Firstly, a junction structure of a multibond graph with multiport gyrators that represent Eulerian junction structures is proposed. In addition, non-linear multiport resistors are considered. By knowing the non-linear causal paths and loops of the non-linear multibond graph, the linearization is obtained by two steps: (1) The original multibond graph on the nominal operating point is evaluated; (2) New and additional paths based on the non-linear causal paths and loops are included. The state space representation of the linearized multibond graph using the corresponding junction structure is presented. An advantage of this methodology is its ability to allow the user to define a nominal operating point in which the linearization will be carried out.
In order to apply the proposed methodology, two physical systems are modelled and linearized by multibond graphs: a synchronous generator and a two degrees of freedom PUMA. Simulation results of these non-linear and linearized systems are shown. 相似文献
178.
Renovato J Gutiérrez-Sánchez G Rodríguez-Durán LV Bergman C Rodríguez R Aguilar CN 《Applied biochemistry and biotechnology》2011,165(1):382-395
Significant differences on structure, stability, and catalytic properties of tannase were found when this enzyme was produced
under solid-state and submerged fermentations (SSF and SmF) by Aspergillus niger. The specific activity was 5.5 times higher on SSF than in SmF. Significant differences in isoelectric points of tannases
were found. The pH optima for both types of enzyme was found at 6 and the pH stability of SSF and SmF tannase were at 6 and
5–8, respectively. The optimal temperature range was from 50 to 60 °C for SmF tannase and 60 °C for SSF tannase, and both
enzyme types showed tolerance to high temperatures (60–70 °C). The SSF tannase showed a major specificity for methyl gallate
substrate while SmF tannase for tannic acid. All metal ions tested, had an activity inhibition from 30–46% on SSF tannase.
SDS-PAGE analysis as well as gel localization studies of both SSF and SmF purified tannases showed a single band with a molecular
weight of 102 and 105 kDa, respectively. Different levels of glycosylation were found among SSF and SmF purified tannases.
This is the first report about structural differences among tannase produced under SSF and SmF and this study provides basis
for explanation of the stability and catalytic differences observed previously for this two tannase types. 相似文献
179.
In this work we present an investigation of viscoelastic flow in a planar sudden expansion with expansion ratio D/d = 4. We apply the modified FENE–CR constitutive model based on the non-linear finite extensibility dumbbells (FENE) model. The governing equations were solved using a finite volume method with the high-resolution CUBISTA scheme utilised for the discretisation of the convective terms in the stress and momentum equations. Our interest here is to investigate two-dimensional steady-state solutions where, above a critical Reynolds number, stable asymmetric flow states are known to occur. We report a systematic parametric investigation, clarifying the roles of Reynolds number (0.01 < Re < 100), Weissenberg number (0 < We < 100) and the solvent viscosity ratio (0.3 < β < 1). For most simulations the extensibility parameter of the FENE model was kept constant, at a value L2 = 100, but some exploration of its effect in the range 100–500 shows a rather minor influence. The results given comprise flow patterns, streamlines and vortex sizes and intensities, and pressure and velocity distributions along the centreline (i.e. y = 0). For the Newtonian case, in agreement with previous studies, a bifurcation to asymmetric flow was observed for Reynolds numbers greater than about 36. In contrast viscoelasticity was found to stabilise the flow; setting β = 0.5 and We = 2 as typical values, resulted in symmetric flow up to a Reynolds number of about 46. We analyse these two cases in particular detail. 相似文献
180.
Simon A. Mathias Gerardo J. González Martínez de Miguel Kate E. Thatcher Robert W. Zimmerman 《Transport in Porous Media》2011,89(3):383-397
CO2 injected into porous formations is accommodated by reduction in the volume of the formation fluid and enlargement of the
pore space, through compression of the formation fluids and rock material, respectively. A critical issue is how the resulting
pressure buildup will affect the mechanical integrity of the host formation and caprock. Building on an existing approximate
solution for formations of infinite radial extent, this article presents an explicit approximate solution for estimating pressure
buildup due to injection of CO2 into closed brine aquifers of finite radial extent. The analysis is also applicable for injection into a formation containing
multiple wells, in which each well acts as if it were in a quasi-circular closed region. The approximate solution is validated
by comparison with vertically averaged results obtained using TOUGH2 with ECO2N (where many of the simplifying assumptions
are relaxed), and is shown to be very accurate over wide ranges of the relevant parameter space. The resulting equations for
the pressure distribution are explicit, and can be easily implemented within spreadsheet software for estimating CO2 injection capacity. 相似文献