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441.
442.
Reduction of aldehydes using decaborane (B10H14) in an aqueous solution gave the corresponding alcohol chemoselectively in good to high yields. 相似文献
443.
444.
Yeong-Jae Seok Seong-Tae Kim Kap-Seok Yang Won-Ki Huh Sa-Ouk Kang 《Journal of carbohydrate chemistry》2013,32(9):1073-1083
ABSTRACT Two interconvertible enediol group-containing reductones were produced nonenzymatically from L-xylosone in citrate-phosphate buffer (pH 6.0). These compounds were oxidized by ascorbate oxidase (E.C. 1.10.3.3.) and had ability to reduce 2.6-dichloroindophenol. GLC-MS analysis of trimethylsilylated L-xylosone indicates that it exists in several tautomeric forms including the enediol group-containing reductones which are L-glycero-2-pentenopyranose and L-glycero-2-pentenofuranose. The production rates of both reductones from L-xylosone were proportional to pH within a pH range 4 to 7, and above that pH range further degradation of the reductones occurred. 相似文献
445.
Young June Yoon Stephen C. Cowin 《International Journal of Solids and Structures》2009,46(3-4):527-533
Conceptually, the undrained elastic constants estimated by the poroelasticity theory should be identical to the effective moduli of the two-phase composite of a porous material saturated with pore water. Here we show numerically that the undrained elastic constants determined by an effective moduli estimate are almost identical with those calculated by poroelasticity theory, and if pore shapes are not exactly known and the porosity is around 50%, estimating the elastic constant as the average value of its Voigt and Reuss bounds is reasonably accurate. This is the situation in bone and dentin, the materials that are our primary intended application. This result will hold for situations in which the totally enclosed water phase is constrained to small deformations by virtue of its confinement. Importantly, in this work we assume that water is an isotropic elastic solid with a shear modulus that is 10?4 times the bulk modulus of the water. Note that it is compressible, but almost incompressible with a Poisson’s ratio of 0.4999. 相似文献
446.
447.
Two basic disadvantages of the symmetric rank one (SR1) update are that the SR1 update may not preserve positive definiteness
when starting with a positive definite approximation and the SR1 update can be undefined. A simple remedy to these problems
is to restart the update with the initial approximation, mostly the identity matrix, whenever these difficulties arise. However,
numerical experience shows that restart with the identity matrix is not a good choice. Instead of using the identity matrix
we used a positive multiple of the identity matrix. The used positive scaling factor is the optimal solution of the measure
defined by the problem—maximize the determinant of the update subject to a bound of one on the largest eigenvalue. This measure
is motivated by considering the volume of the symmetric difference of the two ellipsoids, which arise from the current and
updated quadratic models in quasi-Newton methods. A replacement in the form of a positive multiple of the identity matrix
is provided for the SR1 update when it is not positive definite or undefined. Our experiments indicate that with such simple
initial scaling the possibility of an undefined update or the loss of positive definiteness for the SR1 method is avoided
on all iterations. 相似文献
448.
Hyun Shin Lee So Youn Ahn Hyun Sue Huh Yunkyoung Ha 《Journal of organometallic chemistry》2009,694(20):3325-3330
We investigated the effect of an ancillary ligand (AL) on the emission color and luminous efficiencies of its complex, Ir(4-Me-2,3-dpq)2(AL), where 4-Me-2,3-dpq represents 4-methyl-2,3-diphenylquinolinato ligand. We expected that ancillary ligand modification by introduction of the bulky substituent to the complexes might allow luminous efficiency increase by reduction of T–T annihilation. Furthermore, some ancillary ligands may contribute to fine-tuning of their complex emission colors by influencing the energy level of Ir d-orbitals upon the orbital mixing. As new ancillary ligands substituting for acac which is a typical AL in the iridium complexes, pyrazolone-based ligands, 4-R-5-methyl-2-phenyl-2,4-dihydro-pyrazol-3-one series (przl-R), were prepared, where R represents C6H5, C6H4CH3 and C6H4Cl. These ligands were chelated to the iridium center to yield a new series of the iridium complexes, Ir(4-Me-2,3-dpq)2(przl-R). The X-ray crystal structure of Ir(4-Me-2,3-dpq)2(przl-C6H4Cl) was determined. The electrochemical and luminescence properties of the iridium complexes were investigated. The effect of the przl-substituents on the emission colors of the complexes was not significant. On the other hand, the luminous efficiencies of Ir(4-Me-2,3-dpq)2(przl-C6H5) and Ir(4-Me-2,3-dpq)2(przl-C6H4CH3) were higher than that of Ir(4-Me-2,3-dpq)2(acac). 相似文献
449.
Kwon S Shin HS Gong J Eom JH Jeon A Yoo SH Chung IS Cho SJ Lee HS 《Journal of the American Chemical Society》2011,133(44):17618-17621
Molecular self-assembly is the spontaneous association of molecules into structured aggregates by which nature builds complex functional systems. While numerous examples have focused on 2D self-assembly to understand the underlying mechanism and mimic this process to create artificial nano- and microstructures, limited progress has been made toward 3D self-assembly on the molecular level. Here we show that a helical β-peptide foldamer, an artificial protein fragment, with well-defined secondary structure self-assembles to form an unprecedented 3D molecular architecture with a molar tooth shape in a controlled manner in aqueous solution. Powder X-ray diffraction analysis, combined with global optimization and Rietveld refinement, allowed us to propose its molecular arrangement. We found that four individual left-handed helical monomers constitute a right-handed superhelix in a unit cell of the assembly, similar to that found in the supercoiled structure of collagen. 相似文献
450.
Tzy-Jiun M. Luo Ching-Chang Ko Chi-Kai Chiu Jacob Llyod Uk Huh 《Journal of Sol-Gel Science and Technology》2010,53(2):459-465
Aminosilane has been explored as an alternative chemical linker to facilitate the binding and solidification of hydroxyapatite-gelatin
nanocomposite at room temperature, which was synthesized using co-precipitation method in the presence of gelatin. This aminosilane
treatment was found effective at low concentration (~25 μL/mL) and the solidification and dehydration of hydroxyapatite-gelatin
slurry completes within hours depending on the amount of aminosilane. The resulting sample exhibits compressive strength of
133 MPa, about 40% higher than glutaraldehyde treated samples, and shows good biocompatibility based on cell adhesion, proliferation,
alkaline phosphate synthesis, and mineralization studies. 相似文献