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471.
472.
Unsteady Natural Convection Flow in a Square Cavity Filled with a Porous Medium Due to Impulsive Change in Wall Temperature 总被引:1,自引:0,他引:1
Unsteady natural convection flow in a two-dimensional square cavity filled with a porous material has been studied. The flow
is initially steady where the left-hand vertical wall has temperature T
h and the right-hand vertical wall is maintained at temperature T
c (T
h > T
c) and the horizontal walls are insulated. At time t > 0, the left-hand vertical wall temperature is suddenly raised to which introduces unsteadiness in the flow field. The partial differential equations governing the unsteady natural convection
flow have been solved numerically using a finite control volume method. The computation has been carried out until the final
steady state is reached. It is found that the average Nusselt number attains a minimum during the transient period and that
the time required to reach the final steady state is longer for low Rayleigh number and shorter for high Rayleigh number. 相似文献
473.
An efficient, simple, and environmentally friendly synthesis of a series of chromeno[2,3-d]pyrimidine-trione derivatives has been accomplished via the three-component reaction of a barbituric acid, dimedone/cyclohexane-1,3-dione, and aromatic aldehydes using Sc(OTf)3 as a recyclable catalyst under solvent-free condition. This method exploits the use of Sc(OTf)3 as a Lewis acid catalyst in organic synthesis and offers many rewards such as excellent product yield and easy work-up procedure. Harmless reaction conditions, as well as the absence of side-products, are another green aspects of this protocol. 相似文献
474.
Guda Mallikarjuna Reddy Jarem Raul Garcia Vemulapati Hanuman Reddy Avula Krishna Kumari Grigory V. Zyryanov Gutha Yuvaraja 《Journal of Saudi Chemical Society》2019,23(3):263-273
An ecofriendly itinerary for the synthesis of pyranopyrazole derivatives having thioether link has been established via reusable, green catalyst, green solvent and multicomponent domino approach. To avoid impurities, usage of toxic solvents, toxic catalyst, simple workup and quantitative yields were strategies of this method. In addition, all the reported compounds were tested for their antioxidant and antibacterial properties. Some compounds displayed higher antioxidant activity than the standard drug (6a and 6j), while some other active compounds showed prominent antibacterial activity (6e and 6n). The results demonstrated that these active compounds may be used to support as a decent stand for further investigation in a way to ascertain innovative antioxidant and antibacterial medicines. 相似文献
475.
Archana Kumari Devendra Deo Pathak Sanchita Chakravarty Jae-chun Lee 《Separation & Purification Reviews》2019,48(2):91-121
Europium (Eu), one of the most significant rare earth (RE) elements, has wide applications as functional material in phosphor production, majorly used in fluorescent lamps, computer monitors, televisions etc. Eu is one of the three divalent lanthanides (along with Yb and Sm) having a reduction potential higher than ?2 V. This possibility of Eu reduction is attributed to a relatively stable half-filled 4f7 electronic configuration, thus providing a high stabilization energy and selective recovery. But the Eu recuperation from natural minerals is either accompanied with other REs or Eu is recovered as a group of light REs. Selective recovery of Eu has sparked the progress for its reutilization through recycling of secondary resources. The perspectives of reclaiming Eu as a value added product from various sources using different pyro-hydro or hybrid techniques are discussed. The systematic research and salient findings on methods, viz., reduction, leaching, solvent extraction, as well as combined methods scaled-up to commercial scale to recover Eu, are also reported with recommendations. Thus, this comparative as well as summarized review hopes to help researchers to develop feasible processes for Eu recovery. 相似文献
476.
Ratnamala A Kumari VD Subrahmanyam M Archana N 《Chemical communications (Cambridge, England)》2004,(23):2710-2711
High activity of cyclohexanone, formaldehyde and ammonia to form 1,2,3,4,5,6,7,8-octahydroacridine (OHA) is observed over different classes of zeolites and molecular modeling studies confirm the suitability of HZSM-5 catalyst for selective synthesis of OHA. 相似文献
477.
The relaxational dynamics of a classical planar Heisenberg spin system is studied using the Fokker-Planck equation. A new
approach is introduced in which we attempt to directly calculate the eigenvalues of the Fokker-Planck operator. In this connection
a number space representation is introduced, which enables us to visualize the eigenvalue structure of the Fokker-Planck operator.
The mean field approximation is derived and a systematic method to improve the mean field approximation is presented. 相似文献
478.
Vinod Kumari R. C. Sharma Dr. G. K. Chaturvedi 《Monatshefte für Chemie / Chemical Monthly》1974,105(3):629-636
Potentiometric evidences have been cited for the formation of 1∶1∶1 ternary complexes in the systems: Cu(II)/Ni(II)-glycine-diamines [where diamines = ethylenediamine (en), propylenediamine (pn), o-phenylenediamine (phenen) and 1.8-naphthalenediamine (naphen)]. 相似文献
479.
ESR investigations on exchange coupled pairs of Cu ions in single crystals of Cu(dtc)2, isomorphously diluted with the corresponding diamagnetic zinc salt, are reported. The spin Hamiltonian parameters for the
coupled species (S=1) are:g
‖=2.1025,g
+=2.031,A=75.1×10−4 cm−1,B=14.8×10−4,D=276.0×10−4 cm−1 andE=46.7×10−4 cm−1. While theg andA tensors show tetragonal symmetry, the zeor-field splitting tensor is rhombic and has principal axes different from those
of theg andA tensors. Intensity measurements made down to 4.2 K indicate that the exchange is ferromagnetic with |FFF| ∼ 10 cm−1. Direct dipole-dipole interaction appears to be the major contribution to the zero-field splitting. A calculation on the
distributed point dipole model shows that dipolar interaction is considerably modified by the high covalency of the Cu-S bond
and accounts for the rhombic nature of the tensor. The possible exchange mechanisms in Cu(dtc)2—direct exchange and superexchange through the bridging sulphurs—are discussed. 相似文献
480.
P. Venkataiah Y. Laxmi Kumari M. Srinivas Mohan Harinath B. Bathina 《Journal of Chemical Sciences》1994,106(4):813-818
Interaction of adenosine-5′-triphosphate (ATP) with a series of binary Cu(II) complexes (ML) (where L =o-phenanthroline (Phen), 5-nitrophenanthroline (NPhen), 5-methyl phenanthroline (MPhen), 2,9-dimethylphenanthroline (DPhen),
2,9-dimethyl-4,7-diphenylphenanthroline (DPhPhen), 2,2′-bipyridyl (Bipy), bis(imidazol-2-yl) methane (BIM), oxalic acid (Ox),
glycine (Gly), alanine (Ala), valine (Val), phenylalanine (Phe), tryptophan (Trp), methionine (Met), histidine (His) or aspartic
acid (Asp) to form ternary complexes (MLA) was investigated by a pH-metric technique and the formation constants were evaluated
at 35.0°C and μ = 0.2 M (KNO3). The influence exerted by ligand L on the binding of ATP to Cu(II) was quantitatively assessed and ATP was found to bind
more strongly when L = bidentate nitrogen donors, relatively less strongly when L = amino acids and least strongly when L
= a bidentate oxygen donor. With respect to the nitrogen donor ligands the stability of the ternary complexes decreases in
the order NPhen > Phen > Bipy > MPhen > DPhen > BIM ≈ DPhPhen, whereas in ternary complexes containing amino acids the stability
decreases in the order: Phe ≈ Trp > Ala > Gly ≈ Val ≈ Met > His > Asp. The trends in the stability of the various complexes
are discussed in terms of the nature of the metal ion and the two ligands in its coordination sphere. 相似文献