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61.
Toward resolving the current controversy regarding the validity of the α-effect, we have examined the reactions of Y-substituted phenyl methanesulfonates 1a-1l with HOO(-), OH(-), and Z-substituted phenoxides in the gas phase versus solution (H(2)O). Criteria examined in this work are the following: (1) Br?nsted-type and Hammett plots for reactions with HOO(-)and OH(-), (2) comparison of β(lg) values reported previously for the reactions of Y-substituted phenyl benzenesulfonates 2a-2k with HOO(-) (β(lg) = -0.73) and OH(-) (β(lg) = -0.55), and for those of 1a-1l with HOO(-) (β(lg) = -0.69) and OH(-) (β(lg) = -1.35), and (3) Br?nsted-type plot showing extreme deviation of OH(-) for reactions of 2,4-dintrophenyl methanesulfonate 1a with aryloxides, HOO(-), and OH(-), signifying extreme solvation vs different mechanisms. The results reveal significant pitfalls in assessing the validity of current interpretations of the α-effect. The extreme negative deviation by OH(-) must be due, in part, to the difference in their reaction mechanisms. Thus, the apparent dependence of the α-effect on leaving-group basicity found in this study has no significant meaning due to the difference in operating mechanisms. The current results argue in favor of a further criterion, i.e., a consistency in mechanism for the α-nucleophiles and normal nucleophiles. 相似文献
62.
We constructed a mesh-grid integrated microwell array which enables easy trapping and consistent addition of droplets. The grid acts as a microchannel structure to guide droplets into the microwells underneath, and also provides open access for additional manipulation in a high-throughput manner. Each droplet in the array forms a stable environment of pico-litre volume to implement a single-cell-based assay. 相似文献
63.
Han OH Han KS Shin CW Lee J Kim SS Um MS Joh HI Kim SK Ha HY 《Angewandte Chemie (International ed. in English)》2012,51(16):3842-3845
The chemical conversion of methanol in direct methanol fuel cells was followed in situ by NMR spectroscopy. Comparing data of the methanol oxidation on Pt and PtRu anode catalysts allowed the role of Ru in both Faradaic and non-Faradaic reactions to be investigated. The spatial distributions of chemicals could also be determined. (Picture: T1-T4=inlet and outlet tubes.). 相似文献
64.
We report the influence of composition and very high transverse field annealing on the magnetic properties and structure of four FeCo-based amorphous and nanocrystalline alloys. The compositions (Fe50Co50)89Zr7B4 and (Fe65Co35)89Zr7B4 were investigated changing the Fe:Co ratio from 50:50 to 65:35. (Fe50Co50)85Zr2Nb4B8.5 was chosen to investigate Nb substitution for Zr in an FeCo-based alloy. This substitution is shown to increase the magnetostrictive constant, λS, of the nanocrystalline alloy from 36×10−6 to 54×10−6. The composition (Fe65Co35)84Cr5Zr7B4 was studied to investigate the influence of Cr on intergranular coupling across the amorphous matrix. Samples of each composition were annealed in the amorphous state at 300 °C and in the nanocrystalline state at 600 °C. Field annealing was performed in 17 T transverse field in an inert atmosphere. Frequency-dependent magnetic properties were measured with an automatic recording hysteresisgraph. Static magnetic properties were measured with a vibrating sample magnetometer. The mass-specific power loss of the alloys decreased with field annealing in both the nanocrystalline and amorphous states for some frequency and induction combinations. Furthermore, the hysteresis loops are sheared after field annealing, indicating a transverse magnetic anisotropy. The nanocrystalline (Fe50Co50)85Zr2Nb4B8.5 composition has a lower relative permeability than the other compositions. 相似文献
65.
66.
Hyung Jong Kim Ik Rang Choe Tae Ryang Hong Ju Sik Kang Hyun Ah Um Min Ju Cho 《Molecular Crystals and Liquid Crystals》2015,621(1):31-39
A series of bipolar host materials containing dibenzo[b,d]thiophene (DBT) or dibenzo[b,d]thiophene 5,5-dioxide core were successfully synthesized, and their physical, photophysical, and electrochemical properties were investigated. The three host materials showed well-localized electron distribution at the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) states, as evidenced by theoretical calculations. Triplet energies of the new host materials are higher than 2.6 eV, and the blend film with bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic) as a blue phosphorescent dopant showed highly efficient energy transfer between the host material and dopant. 相似文献
67.
68.
Gyeongtaek Gong Sun-Mi Lee Han Min Woo Tai Hyun Park Youngsoon Um 《Applied biochemistry and biotechnology》2017,183(3):931-942
Efficient isolation of lignocellulolytic bacteria is essential for the utilization of lignocellulosic biomass. In this study, bacteria with cellulolytic, xylanolytic, and lignolytic activities were isolated from environmental sites such as mountain, wetland, and mudflat using isolation media containing the combination of lignocellulose components (cellulose, xylan, and lignin). Eighty-nine isolates from the isolation media were characterized by analyzing taxonomic ranks and cellulolytic, xylanolytic, and lignolytic activities. Most of the cellulolytic bacteria showed multienzymatic activities including xylanolytic activity. The isolation media without lignin were efficient in isolating bacteria exhibiting multienzymatic activities even including lignolytic activity, whereas a lignin-containing medium was effective to isolate bacteria exhibiting lignolytic activity only. Multienzymatic activities were mainly observed in Bacillus and Streptomyces, while Burkholderia was the most abundant genus with lignolytic activity only. This study provides insight into isolation medium for efficient isolation of lignocellulose-degrading microorganisms. 相似文献
69.
70.
Second-order rate constants (k(N)) were measured for aminolyses of Y-substituted-phenyl 2-methoxybenzoates 2a-i and 4-nitrophenyl X-substituted-benzoates 3a-j in MeCN at 25.0 °C. The Br?nsted-type plot for the reactions of 2a-i with piperidine curves downward, indicating that a change in rate-determining step (RDS) occurs. The Hammett plot for the reactions of 3a-j with piperidine consists of two intersecting straight lines, which might be taken as evidence for a change in RDS. However, the nonlinear Hammett plot has been suggested not to be due to a change in RDS but rather to the stabilization of the ground state of substrates possessing an electron-donating group (EDG) (e.g., 3a-c) through a resonance interaction, since the corresponding Yukawa-Tsuno plot exhibits an excellent linear correlation with ρ = 0.54 and r = 1.54. The ρ value found for the reactions of 3a-j in MeCN is much smaller than that reported previously for the corresponding reactions in H(2)O (i.e., ρ = 0.75). It is proposed that the reactions of 3a-j in MeCN proceed through a forced concerted mechanism due to instability of T(±) in the aprotic solvent, while the reactions of 2a-i proceed through a stepwise pathway with a stabilized T(±) through an intramolecular H-bonding interaction. 相似文献