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81.
Candice Botuha Fabrice Chemla Franck Ferreira Julien Louvel Alejandro Pérez-Luna 《Tetrahedron: Asymmetry》2010,21(9-10):1147-1153
The stereoselective synthesis of alkynyl 1,2-amino alcohols by the addition of 3-chloro- and 3-methoxymethoxy- allenylzincs to chiral tert-butylsulfinylimines is described. The methodology is applicable to the preparation of alkynyl 2-amino-1,3-diols (O,N,O stereotriads) using α-alkoxy tert-butylsulfinylimines as chiral starting materials. The scope and limitations of the methodology along with recent applications to the efficient asymmetric syntheses of natural and/or bioactive alkaloids and polyhydroxylated alkaloids are presented. 相似文献
82.
83.
Franck Pastor Malorie Trillat Joseph Pastor Etienne Loute 《Comptes Rendus Mecanique》2006,334(4):213-219
A nonlinear interior point method associated with the kinematic theorem of limit analysis is proposed. Associating these two tools enables one to determine an upper bound of the limit loading of a Gurson material structure from the knowledge of the sole yield criterion. We present the main features of the interior point algorithm and an original method providing a rigorous kinematic bound from a stress formulation of the problem. This method is tested by solving in plane strain the problem of a Gurson infinite bar compressed between rough rigid plates. To cite this article: F. Pastor et al., C. R. Mecanique 334 (2006). 相似文献
84.
In this Note we describe a preconditionner for iteratively solving the linear system arising from the discretization of a general nonseparable elliptic problem by spectral element method. This preconditionner is constructed from approximating the original problem with the closest (in some sense) separable elliptic problem. A direct method is then used to invert the preconditionner. To cite this article: M. Azaïez et al., C. R. Mecanique 331 (2003). 相似文献
85.
Gerber I Oubenali M Bacsa R Durand J Gonçalves A Pereira MF Jolibois F Perrin L Poteau R Serp P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(41):11467-11477
The nitric acid oxidation of multiwalled carbon nanotubes leading to surface carboxylic groups has been investigated both experimentally and theoretically. The experimental results show that such a reaction involves the initial rapid formation of carbonyl groups, which are then transformed into phenol or carboxylic groups. At room temperature, this reaction takes place on the most reactive carbon atoms. At higher temperatures a different mechanism would operate, as evidenced by the difference in activation energies. Experimental data can be partially related to first-principles calculations, showing a multistep functionalization mechanism. The theoretical aspects of the present article have led us to propose the most efficient pathway leading to carboxylic acid functional groups on the surface. Starting from mono-vacancies, it ends up with the synergistic formation of dangling -COOH groups and the enlargement of the vacancies. 相似文献
86.
Bilé EG Sassine R Denicourt-Nowicki A Launay F Roucoux A 《Dalton transactions (Cambridge, England : 2003)》2011,40(24):6524-6531
Novel anionic species, such as hydrogen carbonate (HCO(3)(?)), fluoride (F(?)), triflate (CF(3)SO(3)(?)), tetrafluoroborate (BF(4)(?)) and chloride (Cl(?)) were investigated as new partners of water soluble N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl) ammonium salts, used as a protective agent of rhodium colloids. The effect of the surfactant polar head on the micellar behavior, size and morphology of the nanospecies was studied by adapted physico-chemical experiments (surface tension measurements, dynamic light scattering, thermogravimetric and TEM analyses) and discussed in terms of strong or weak stabilization of the growing nanoparticles surface. Finally, the influence of the nanoenvironment generated by the surfactant with various counter-anions was evaluated via the hydrogenation of aromatics. 相似文献
87.
Bonnel D Longuespee R Franck J Roudbaraki M Gosset P Day R Salzet M Fournier I 《Analytical and bioanalytical chemistry》2011,401(1):149-165
The large amount of data generated using matrix-assisted laser desorption/ionization mass spectrometric imaging (MALDI-MSI)
poses a challenge for data analysis. In fact, generally about 1.108–1.109 values (m/z, I) are stored after a single MALDI-MSI experiment. This imposes processing techniques using dedicated informatics tools
to be used since manual data interpretation is excluded. This work proposes and summarizes an approach that utilizes a multivariable
analysis of MSI data. The multivariate analysis, such as principal component analysis–symbolic discriminant analysis, can
remove and highlight specific m/z from the spectra in a specific region of interest. This approach facilitates data processing and provides better reproducibility,
and thus, broadband acquisition for MALDI-MSI should be considered an effective tool to highlight biomarkers of interest.
Additionally, we demonstrate the importance of the hierarchical classification of biomarkers by analyzing studies of clusters
obtained either from digested or undigested tissues and using bottom-up and in-source decay strategies for in-tissue protein
identification. This provides the possibility for the rapid identification of specific markers from different histological
samples and their direct localization in tissues. We present an example from a prostate cancer study using formalin-fixed
paraffin-embedded tissue. 相似文献
88.
Martineau C Fayon F Suchomel MR Allix M Massiot D Taulelle F 《Inorganic chemistry》2011,50(6):2644-2653
The room temperature structure of Ba(5)Al(3)F(19) has been solved using electron microscopy and synchrotron powder diffraction data. One-dimensional (1D) (27)Al and ultrafast magic-angle-spinning (MAS) (19)F NMR spectra have been recorded and are in agreement with the proposed structural model for Ba(5)Al(3)F(19). The (19)F isotropic chemical shift and (27)Al quadrupolar parameters have been calculated using the CASTEP code from the experimental and density functional theory geometry-optimized structures. After optimization, the calculated NMR parameters of both the (19)F and (27)Al nuclei show improved consistency with the experimental values, demonstrating that the geometry optimization step is necessary to obtain more accurate and reliable structural data. This also enables a complete and unambiguous assignment of the (19)F MAS NMR spectrum of Ba(5)Al(3)F(19). Variable-temperature 1D MAS (19)F NMR experiments have been carried out, showing the occurrence of fluorine ion mobility. Complementary insights were obtained from both two-dimensional (2D) exchange and 2D double-quantum dipolar recoupling NMR experiments, and a detailed analysis of the anionic motion in Ba(5)Al(3)F(19) is proposed, including the distinction between reorientational processes and chemical exchange involving bond breaking and re-formation. 相似文献
89.
90.
Deschamps M Fayon F Cadars S Rollet AL Massiot D 《Physical chemistry chemical physics : PCCP》2011,13(17):8024-8030
Measuring internuclear distances through dipolar interaction is a major challenge for solid-state nuclear magnetic resonance (NMR) spectroscopy. Obtaining reliable interatomic distances provides an access to the local structure in ordered or disordered solids. We show that at magic angle spinning (MAS) frequencies larger than ca. 50 kHz, some of the three-spin terms of the homogeneous homonuclear dipolar Hamiltonian can be used to promote the creation of double-quantum coherences between neighbouring (1)H or (19)F spins without using dipolar recoupling pulse sequences in the Dipolar Homonuclear Homogeneous Hamiltonian (DH(3)) double-quantum/single-quantum correlation experiment. This makes it possible to probe inter-nuclear spatial proximity with limited risk of probe or sample damage from radio-frequency (RF) irradiation, and is fully appropriate for fast repetition rate offering sensitivity gains in favourable cases. Experimental demonstrations are supported by multi-spin numerical simulations, which points to new possibilities for the characterization of spin-system geometries. 相似文献