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711.
712.
Débora Bellini Machado Ivone M. Sato Flávia R. O. Silva Vera Lúcia R. Salvador Júlio Takehiro Marumo Nestor Schor Maria Helena Bellini 《Journal of Radioanalytical and Nuclear Chemistry》2014,302(1):97-102
Following physical examination and radiography analysis, cystotomy was performed to remove a rabbit’s single bladder stone. This rabbit urolith was analyzed by X-ray fluorescence spectrometry (EDXRF) and scanning electron microscopy (SEM). The EDXRF technique was successful for the determination of major elements (Ca, Mg, P, K and S) and presented sufficient sensitivity to also trace elements (Sr, Fe, Cu, V, Cr, Mn, Zn and Pb) determination. The results showed significant quantitative and structural variations among the urolith regions. The EDXRF technique using the fundamental parameters method and SEM attend as complementary techniques that can be useful in the management of urinary stone analysis. 相似文献
713.
Carbon Nanotubes: Controllable and Predictable Viscoelastic Behavior of 3D Boron‐Doped Multiwalled Carbon Nanotube Sponges (Part. Part. Syst. Charact. 1/2016)
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714.
Lacerda V da Silva GV Constantino MG Dos Santos RB de Castro EV Silva RC 《Magnetic resonance in chemistry : MRC》2008,46(3):268-273
The (2,3)J(CH) dependence on dihedral angle (theta H--C--C--X) for cyclopentane derivatives was investigated. We observed that the combined use of experimentally obtained (2,3)J(CH) values and the theoretically determined dihedral angles between the corresponding nuclei can be used to infer the relative stereochemistry of the ring substituents in cyclopentane derivatives. There is a good correlation between the magnitude of (3)J(CH) and the dihedral angle between the hydrogen and the coupled carbon (R2 = 0.88). 相似文献
715.
716.
Geronés M Downs AJ Erben MF Ge M Romano RM Yao L Della Védova CO 《The journal of physical chemistry. A》2008,112(26):5947-5953
One of the simplest thioester molecules, S-methyl thioacetate, CH 3C(O)SCH 3, has been investigated by HeI photoelectron spectroscopy (PES) and valence photoionization studies using synchrotron radiation in the same energy range. In the second series of experiments, total ion yield (TIY), photoelectron photoion coincidence (PEPICO), and partial ion yield (PIY) spectra were recorded. It was found that the photodissociation behavior of CH 3C(O)SCH 3 can be divided into three well-defined energy regions. Vibronic structure was observed in the valence synchrotron photoionization process, being associated with wavenumbers of 912, 671, 1288, 1690, and 1409 cm (-1) for the bands at 12.82, 13.27, 15.66, 15.72, and 17.42 eV, respectively. Evaluation of the PE spectrum in concert with the synchrotron photoionization measurements and complemented by high-level ab initio calculations thus provides unusually detailed insights into the valence ionization processes of this molecule. 相似文献
717.
In this work we introduce and analyze a mixed virtual element method(mixed-VEM)for the two-dimensional stationary Boussinesq problem.The continuous formulation is based on the introduction of a pseudostress tensor depending nonlinearly on the velocity,which allows to obtain an equivalent model in which the main unknowns are given by the aforementioned pseudostress tensor,the velocity and the temperature,whereas the pressure is computed via a postprocessing formula.In addition,an augmented approach together with a fixed point strategy is used to analyze the well-posedness of the resulting continuous formulation.Regarding the discrete problem,we follow the approach employed in a previous work dealing with the Navier-Stokes equations,and couple it with a VEM for the convection-diffusion equation modelling the temperature.More precisely,we use a mixed-VEM for the scheme associated with the fluid equations in such a way that the pseudostress and the velocity are approximated on virtual element subspaces of H(div)and H1,respectively,whereas a VEM is proposed to approximate the temperature on a virtual element subspace of H1.In this way,we make use of the L2-orthogonal projectors onto suitable polynomial spaces,which allows the explicit integration of the terms that appear in the bilinear and trilinear forms involved in the scheme for the fluid equations.On the other hand,in order to manipulate the bilinear form associated to the heat equations,we define a suitable projector onto a space of polynomials to deal with the fact that the diffusion tensor,which represents the thermal conductivity,is variable.Next,the corresponding solvability analysis is performed using again appropriate fixed-point arguments.Further,Strang-type estimates are applied to derive the a priori error estimates for the components of the virtual element solution as well as for the fully computable projections of them and the postprocessed pressure.The corresponding rates of convergence are also established.Finally,several numerical examples illustrating the performance of the mixed-VEM scheme and confirming these theoretical rates are presented. 相似文献
718.
Coordination studies on supramolecular chiral ligands and application in asymmetric hydroformylation
In this study we introduce a series of monodentate pyridine-based ligands for which the phosphorus coordination mode to rhodium can be controlled by the binding of Zn(II)-templates to the pyridyl group. A series of monodentate phosphoroamidite and phosphite ligands have been prepared and studied under hydroformylation conditions by in situ high-pressure NMR and IR techniques. These studies reveal the exclusive formation of rhodium hydride complexes in which the phosphorus atom of the ligand resides in an axial position, trans to the hydride, but only after addition of Zn(II)-template. In the absence of these templates the usual mono-coordinated rhodium hydrido complexes are formed, with the phosphorus ligated in the equatorial plane, cis to the hydride. The catalytic performance of these complexes is evaluated in asymmetric hydroformylation of unfunctionalised internal alkenes in which the supramolecular change is reflected in higher activity and selectivity. 相似文献
719.
Talita M. Lacerda Mauricio P. de Paula Márcia D. Zambon Elisabete Frollini 《Cellulose (London, England)》2012,19(2):351-362
Cultivation of sisal, a plant with a short growth cycle, is highly productive in Brazil. This work is part of extensive research
in which sisal is valued. In these studies, sisal fibers are used in the preparation of bio-based composites and in the derivatization
of the pulp, including posterior preparation of films. This study aimed to examine the use of sisal pulp in the production
of bioethanol, which can potentially be a high efficiency process because of the cellulose content of this fiber. A previous
paper addressed the hydrolysis of sisal pulp using sulfuric acid as a catalyst. In the present study, the influence of the
mercerization process on the acid hydrolysis of sisal pulp was evaluated. Mercerization was achieved in a 20% wt NaOH solution,
and the cellulosic pulp was suspended and vigorously mixed for 1, 2 and 3 h, at 50 °C. The previously characterized mercerized
pulps were hydrolyzed (100 °C, 30% H2SO4, v/v), and the results are compared with those obtained for unmercerized pulp (described in a companion paper). The starting
sample was characterized by viscometry, α-cellulose content, crystallinity index and scanning electron microscopy. During
the reactions, aliquots were withdrawn, and the liquor was analyzed by HPLC. The residual pulps (non-hydrolyzed) were also
characterized by the techniques described for the initial sample. The results revealed that pretreatment decreases the polyoses
content as well as causes a decrease of up to 23% in the crystallinity and up to 21% in the average molar mass of cellulose
after 3 h of mercerization. The mercerization process proved to be very important to achieve the final target. Under the same
reaction conditions (30% and 100 °C, 6 h), the hydrolysis of mercerized pulp generated yields of up to 50% more glucose. The
results of this paper will be compared with the results of subsequent studies obtained using other acids, and enzymes, as
catalysts. 相似文献
720.
Carbajal-Tinoco MD 《The Journal of chemical physics》2012,136(9):094504
We present a new closure relation that is an extension of the Percus-Yevick approximation. In the proposed closure, we introduce an additional term and a mixing coefficient that can be determined by imposing a condition of thermodynamic self-consistency. Moreover, the mixing coefficient is calculated analytically within a linear approximation. In the case of a monodisperse system of hard spheres, we compare the results of our model to well-established thermodynamic expressions and also to the structural properties of fairly known closure approximations. In the second case, and using an equivalent scheme, the new closure relation is extended to the depletion potential between two large hard spheres immersed in a liquid of small hard spheres. In both cases, the results of our model are in good agreement with numerical simulations performed at intermediate concentrations. 相似文献