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排序方式: 共有898条查询结果,搜索用时 31 毫秒
891.
Chad J. PickensKyle R. Gee 《Tetrahedron letters》2011,52(39):4989-4991
The synthesis and characterization of a novel 3′ p-hydroxyphenacyl-caged thymidine bearing a 5′ N,N-diisopropylcyanoethylphosphoramidite is presented representing a new methodology for the photoregulation of PCR and gene expression. Solid phase oligonucleotide synthesis affords a primer blocked at the 3′ position, which could function as a phototrigger for polymerase activity. The caging group exhibits quantitative photolysis in 15 s using a 532 nm green hand laser. 相似文献
892.
Hydrocarbon radical stabilization energy (RSE) estimates based on the differences in R-H vs CH(3)-H bond dissociation energies have inherent advantages over RSEs based on R-CH(3) vs CH(3)-CH(3), as well as R-R vs CH(3)-CH(3) comparisons, since the R-CH(3) and R-R reference systems are prone to unbalanced contaminating intramolecular interactions involving the R groups. When the effects of steric crowding, branching, protobranching, conjugation, and hyperconjugation are taken into account, R-CH(3) and R-R based RSE values are nearly identical to R-H RSEs. Corrections for electronegativity differences between H and R are not needed to achieve agreement. 相似文献
893.
Personick ML Langille MR Zhang J Harris N Schatz GC Mirkin CA 《Journal of the American Chemical Society》2011,133(16):6170-6173
Two {110}-faceted gold nanostructures--rhombic dodecahedra and obtuse triangular bipyramids--have been synthesized via a Ag-assisted, seed-mediated growth method. The combination of a Cl(-)-containing surfactant with a low concentration of Ag(+) plays a role in the stabilization of the {110} facets. To the best of our knowledge, this is the first reported synthesis of a {110}-faceted bipyramid structure. 相似文献
894.
The paper examines the progress made in nanotechnology development since 2000, achievements at ten years, and opportunities
in research, education, innovation and societal outcomes by 2020 worldwide. 相似文献
895.
Chad J. Unrau Richard L. Axelbaum Phil Fraundorf 《Journal of nanoparticle research》2010,12(6):2125-2133
Single-walled carbon nanotubes (SWCNTs) are shown to grow rapidly on iron oxide catalysts on the fuel side of an inverse ethylene diffusion flame. The pathway of carbon in the flame is controlled by the flame structure, leading to formation of SWCNTs free of polycyclic aromatic hydrocarbons (PAH) or soot. By using a combination of oxygen-enrichment and fuel dilution, fuel oxidation is favored over pyrolysis, PAH growth, and subsequent soot formation. The inverse configuration of the flame prevents burnout of the SWCNTs while providing a long carbon-rich region for nanotube formation. Furthermore, flame structure is used to control oxidation of the catalyst particles. Iron sub-oxide catalysts are highly active toward SWCNT formation while Fe and Fe2O3 catalysts are less active. This can be understood by considering the effects of particle oxidation on the dissociative adsorption of gas-phase hydrocarbons. The optimum catalyst particle composition and flame conditions were determined in near real-time using a scanning mobility particle sizer (SMPS) to measure the catalyst and SWCNT size distributions. In addition, SMPS results were combined with flame velocity measurement to measure SWCNT growth rates. SWCNTs were found to grow at rates of over 100 μm/s. 相似文献
896.
Mark A. Hempenius Neil S. Robins Rob G. H. Lammertink G. Julius Vancso 《Macromolecular rapid communications》2001,22(1):30-33
The water soluble poly(ferrocenylsilane) polycation, poly(ferrocenyl(3‐ammoniumpropyl)methylsilane), was synthesized by transition metal‐catalyzed ring‐opening polymerization of the novel [1]ferrocenophane Fe(η‐C5H4)2SiCH3(CH2)3Cl and by subsequent side group modification. Amination of the chloropropyl moieties using potassium 1,1,3,3‐tetramethyldisilazide followed by acidic hydrolysis produced the polycation. The polycation was employed together with poly(sodium vinylsulfonate) in the electrostatic layer‐by‐layer self‐assembly process to form organometallic multilayers on quartz. The multilayer fabrication process was monitored using UV/Vis absorption spectroscopy and XPS. 相似文献
897.
Vamshikrishna Reddy Sammeta Brian M. Anderson John D. Norris Chad D. Torrice Carstyn Joiner Shubin Liu Haoxi Li Konstantin I. Popov Sean W. Fanning Donald P. McDonnell Timothy M. Willson 《Helvetica chimica acta》2023,106(9):e202300097
Synthetic, structural, and computational approaches were used to solve the puzzle as to how a phenolic nonsteroidal estrogen 1 with only a single H-bond to its receptor was more potent than an isomer 2 which formed an intricate network of H-bonds. Synthesis of a series of substituted phenols revealed that pKa was not a determinant of estrogenic activity. First-principles calculation also failed to explain the difference in activity of 1 and 2 . Molecular dynamics revealed that 1 formed a more stable receptor complex compared to 2 , which may explain its increased activity despite forming fewer apparent H-bonds with the protein. 相似文献
898.
A theory is presented for the flow-induced fiber orientation and stress in fiber-reinforced polymer composites with planar fiber orientation. The rate of change of fiber orientation is given as a function of the strain rate in the continuum and the probabilistic effects of physical inter-fiber contacts. The continuum stress is calculated from the stress in the fluid and fibers, where fiber stress is a result of the local disturbance in the fluid velocity field and of the inter-fiber contact forces. Fiber orientation is described via a probability density function whose transport equation has the form of a standard advection-diffusion equation with an orientation-dependent rotary diffusion. This equation is solved using a finite difference scheme and the results are presented. 相似文献