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81.
Nancy M. Edwards Donatella Peressini James E. Dexter Steven J. Mulvaney 《Rheologica Acta》2001,40(2):142-153
Linear viscoelastic properties (LVP) were determined for five durum wheat doughs and five common wheat doughs (representing
four different classes of Canadian common wheat) of different strength using creep testing. A creep time of 10,000 s was sufficient
to reach a state of steady state flow for all of the doughs. Creep compliances were analyzed in terms of a Burgers model.
For the durum doughs, the entire elastic compliance curve was shifted to higher values as the strength of the dough (as measured
by extensigraph) decreased, while the steady state viscosity increased with strength. For common wheat doughs, the elastic
compliance curves were steeper and the steady state viscosities were lower than for durum doughs of comparable extensigraph
strength. The retardation strengths associated with a maximum in the retardation spectra were lower for the stronger durum
doughs than for common wheat doughs of comparable strength. Differences in the LVP between durum and common wheat doughs of
similar extensigraph strength were interpreted in the context of physical gels with crosslinks and entanglements, whose contributions
to material properties are difficult to distinguish in short-time creep or dynamic measurements. The increased extensibility
of common wheat doughs relative to durum doughs of comparable extensigraph strength was attributed to a higher molecular weight
fraction in the polypeptide chains, similar in some respects to end-linked bimodal polymer networks. The idea of considering
these doughs as physical gels was supported by their stress relaxation behavior.
Received: 6 February 2000 Accepted: 22 August 2000 相似文献
82.
Herbert L. Holland Peter R. Andreana Reza Salehzadeh-Asl Aaron van Vliet Nancy J. Ihasz Frances M. Brown 《Monatshefte für Chemie / Chemical Monthly》2000,40(5):667-672
Biotransformation of a series of racemic N-benzoyl α-amino acids by the fungus Beauveria bassiana ATCC 7159 results in isolation of the corresponding D-amino acid benzamides in high enantiomeric purity and yield. 相似文献
83.
84.
NirmlaDevi Thakur Vilas G. Gaikar Debasis Sen Subhasish Mazumder Nancy S. Pandita 《Analytical letters》2017,50(4):690-711
A green method using Juglans regia bark extract was used to synthesize silver nanoparticles at room temperature with monitoring by absorption spectroscopy. The size and shape of the synthesized nanoparticles were characterized by infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, high-resolution transmission electron microscopy, and small-angle X-ray scattering. The average particle size was from 10 to 30?nm. Gas chromatography–mass spectrometry (GC–MS) was used for the separation, identification, and quantification of components of the plant extracts. A possible mechanism for the synthesis of nanoparticles was elucidated based on the GC–MS results. The synthesized silver nanoparticles showed effective inhibition against Streptococcus mutans, which is the main causative agent for dental caries. The nanoparticles also showed promising antibiofilm activity by inhibiting the glucosyltransferase enzyme. 相似文献
85.
Sara Luisa Rodríguez De Luna Luis Ángel GarzaSylvain Bernès Perla ElizondoBlanca Nájera Nancy Pérez 《Polyhedron》2010
A series of mononuclear complexes based on lanthanide ions has been synthesized and X-ray characterized. The compounds [LnIIIL2(NO3)3(H2O)2] (Ln = La, Ce, Pr, Nd, Sm, Gd and Tm; L = 2,6-bis(2-formylphenoxymethyl)pyridine) are found to be isomorphous and isostructural. Ligand L systematically coordinates through one carbonyl functionality, and the resulting complexes are placed on a twofold axis in crystals belonging to C2/c space-group. Emission spectra for Ln = La, Pr, Nd revealed a correlation between the Ln–O coordination bond length and the photoluminescent properties of the complexes, in line with a Förster–Dexter mechanism for intramolecular energy transfer. Ligand L is therefore a suitable sensitizer for lanthanide ions. 相似文献
86.
Brodie-Linder N Le Caër S Alam MS Renault JP Alba-Simionesco C 《Physical chemistry chemical physics : PCCP》2010,12(42):14188-14195
Measurement of H(2) production from electron irradiation (10 MeV) on SBA-15 materials has shown that adsorbed water is attacked preferentially. Silanol groups are only attacked when they are in the majority with respect to adsorbed water, however they are much less efficient at producing H(2). The comparison between water content before and after electron irradiation and the corresponding H(2) production indicates that water desorption is the main route to adsorbed water loss for SBA-15 materials. On the other hand, surface silanol groups are more susceptible to attack, leading to H(2) production when SBA-15 samples have undergone extensive thermal treatment. Electron irradiation of SBA-15-Cu materials has shown that the presence of Cu(II) on the surface reduces and inhibits the production of H(2.) This inhibiting power affects adsorbed water bonded to grafted copper but not surface silanol groups. 相似文献
87.
Jeng-Hao Pai Wei Xu Christopher E. Sims Nancy L. Allbritton 《Analytical and bioanalytical chemistry》2010,398(6):2595-2604
Cell microarrays with culture sites composed of individually removable microstructures or micropallets have proven benefits
for isolation of cells from a mixed population. The laser energy required to selectively remove these micropallets with attached
cells from the array depends on the microstructure surface area in contact with the substrate. Laser energies sufficient to
release micropallets greater than 100 μm resulted in loss of cell viability. A new three-dimensional culture site similar
in appearance to a table was designed and fabricated using a simple process that relied on a differential sensitivity of two
photoresists to UV-mediated photopolymerization. With this design, the larger culture area rests on four small supports to
minimize the surface area in contact with the substrate. Microtables up to 250 × 250 μm were consistently released with single
10-μJ pulses to each of the four support structures. In contrast, microstructures with a 150 × 150-μm surface area in contact
with the substrate could not be reliably released at pulse energies up to 212 μJ. Cassie–Baxter wetting is required to provide
a barrier of air to localize and sequester cells to the culture sites. A second asset of the design was an increased retention
of this air barrier under conditions of decreased surface tension and after prolonged culture of cells. The improved air retention
was due to the hydrophobic cavity created beneath the table and above the substrate which entrapped air when an aqueous solution
was added to the array. The microtables proved an efficient method for isolating colonies from the array with 100% of selected
colonies competent to expand following release from the array. 相似文献
88.
Wei Xu Alicia M. Luikart Christopher E. Sims Nancy L. Allbritton 《Analytical and bioanalytical chemistry》2010,397(8):3377-3385
A novel contact printing method utilizing a sacrificial layer of polyacrylic acid (PAA) was developed to selectively modify
the upper surfaces of arrayed microstructures. The method was characterized by printing polystyrene onto SU-8 microstructures
to create an improved substrate for a cell-based microarray platform. Experiments measuring cell growth on SU-8 arrays modified
with polystyrene and fibronectin demonstrated improved growth of NIH 3T3 (93% vs. 38%), HeLa (97% vs. 77%), and HT1080 (76%
vs. 20%) cells relative to that for the previously used coating method. In addition, use of the PAA sacrificial layer permitted
the printing of functionalized polystyrene, carboxylate polystyrene nanospheres, and silica nanospheres onto the arrays in
a facile manner. Finally, a high concentration of extracellular matrix materials (ECM), such as collagen (5 mg/mL) and gelatin
(0.1%), was contact-printed onto the array structures using as little as 5 μL of the ECM reagent and without the formation
of a continuous film bridge across the microstructures. Murine embryonic stem cells cultured on arrays printed with this gelatin
hydrogel remained in an undifferentiated state indicating an adequate surface gelatin layer to maintain these cells over time. 相似文献
89.
The structural evolution of orthorhombic CaTiO3 perovskite has been studied using high-pressure single-crystal x-ray diffraction under hydrostatic conditions up to 8.1 GPa and under a non-hydrostatic stress field formed in a diamond anvil cell (DAC) up to 4.7 GPa. Under hydrostatic conditions, the TiO6 octahedra become more tilted and distorted with increasing pressure, similar to other 2:4 perovskites. Under non-hydrostatic conditions, the experiments do not show any apparent difference in the internal structural variation from hydrostatic conditions and no additional tilts and distortions in the TiO6 octahedra are observed, even though the lattice itself becomes distorted due to the non-hydrostatic stress. The similarity between the hydrostatic and non-hydrostatic cases can be ascribed to the fact that CaTiO3 perovskite is nearly elastically isotropic and, as a consequence, its deviatoric unit-cell volume strain produced by the non-hydrostatic stress is very small; in other words, the additional octahedral tilts relevant to the extra unit-cell volume associated with the deviatoric unit-cell volume strain may be totally neglected. This study further addresses the role that three factors--the elastic properties, the crystal orientation and the pressure medium--have on the structural evolution of an orthorhombic perovskite loaded in a DAC under non-hydrostatic conditions. The influence of these factors can be clearly visualized by plotting the three-dimensional distribution of the deviatoric unit-cell volume strain in relation to the cylindrical axis of the DAC and indicates that, if the elasticity of a perovskite is nearly isotropic as it is for CaTiO3, the other two factors become relatively insignificant. 相似文献
90.
Andrews and Paule introduced broken k-diamond partitions by using MacMahon’s partition analysis. Later, Fu found a generalization which he called k dots bracelet partitions. In this paper, with the aid of Farkas and Kra’s partition theorem and a p-dissection identity of f(?q), we derive many congruences for broken 3-diamond partitions and 7 dots bracelet partitions. 相似文献