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271.
The photooxygenation of three homoallylic substrates, the γ,δ-unsaturated ketone 1a, nitrile 2a, and the γ,δ-unsaturated ester 3a was investigated in homogeneous solution and in microemulsion (for 1a). Two secondary reaction pathways were detected for the allylic hydroperoxides of type b and c, respectively. The cyclization reactions of 1b and 2b to the 1,2-dioxanes 1d and 2d followed well-known reaction patterns, whereas the base-catalyzed epoxide (1e-3e) formation from the tertiary allylic hydroperoxides 1c-3c is a unprecedented reaction type. 相似文献
272.
Mohammad Kamal Hossain Yasutaka Kitahama Genin Gary Huang Xiaoxia Han Yukihiro Ozaki 《Analytical and bioanalytical chemistry》2009,394(7):1747-1760
Surface-enhanced Raman scattering (SERS) enhancement and the reproducibility of the SERS signal strongly reflect the quality
and nature of the SERS substrates because of diverse localized surface plasmon resonance (LSPR) excitations excited at interstitials
or sharp edges. LSPR excitations are the most important ingredients for achieving huge enhancements in the SERS process. In
this report, we introduce several gold and silver nanoparticle-based SERS-active substrates developed solely by us and use
these substrates to investigate the influence of LSPR excitations on SERS. SERS-active gold substrates were fabricated by
immobilizing colloidal gold nanoparticles on glass slides without using any surfactants or electrolytes, whereas most of the
SERS-active substrates that use colloidal gold/silver nanoparticles are not free of surfactant. Isolated aggregates, chain-like
elongated aggregates and two-dimensional (2D) nanostructures were found to consist mostly of monolayers rather than agglomerations.
With reference to correlated LSPR and SERS, combined experiments were carried out on a single platform at the same spatial
position. The isolated aggregates mostly show a broadened and shifted SPR peak, whereas a weak blue-shifted peak is observed
near 430 nm in addition to broadened peaks centered at 635 and 720 nm in the red spectral region in the chain-like elongated
aggregates. In the case of 2D nanostructures, several SPR peaks are observed in diverse frequency regions. The characteristics
of LSPR and SERS for the same gold nanoaggregates lead to a good correlation between SPR and SERS images. The elongated gold
nanostructures show a higher enhancement of the Raman signal than the the isolated and 2D samples. In the case of SERS-active
silver substrates for protein detection, a new approach has been adopted, in contrast to the conventional fabrication method.
Colloidal silver nanoparticles are immobilized on the protein functionalized glass slides, and further SERS measurements are
carried out based on LSPR excitations. A new strategy for the detection of biomolecules, particularly glutathione, under aqueous
conditions is proposed. Finally, supramolecular J-aggregates of ionic dyes incorporated with silver colloidal aggregates are
characterized by SERS measurements and correlated to finite-difference time-domain analysis with reference to LSPR excitations.
Figure SPR and SERS images for isolated, elongated and two-dimensional gold nanostructures 相似文献
273.
Anqi Li Xiaoli Xin Tingting Zhang Tao Xu Luo Li Chang Liu Weihua Li Jiansheng Li Yi Li Rui Lu 《Surface and interface analysis : SIA》2023,55(1):71-81
In this study, the surface of polyamide (PA) films are electrostatically deposited with the carbon-coated silver (Ag@C) nanoparticles, resulting in a two-dimensional (2D) PA-Ag@C film substrate. The TEM images demonstrate that the nanoparticles were successful synthesized. By adjusting the pH of the system, the core–shell structure and the 2D SERS substrate work together to improve the sensitivity, stability, and repeatability of the substrate to be used in complex real-world water samples. The SERS enhancement effect and substrate uniformity were determined using rhodamine 6G (R6G), crystal violet (CV), and malachite green (MG). The results indicate that the 2D PA-Ag@C film substrate in this study has the optimal Raman effect at a system pH of 6. Under ideal pH conditions, the R6G detection limit (LOD) is as low as 10−10 M (D2 attenuation), and the Raman signal intensity deviation of the same substrate is maintained within 9.49%. Overall, the Raman signal of probe molecule on the fabricated PA-Ag@C film possesses excellent sensitivity, repeatability, and stability. 相似文献
274.
275.
Hao Zhang Min Lu Hui Jiang Xu Wang Feng‐Qing Yang 《Journal of separation science》2020,43(15):3136-3145
In this study, a capillary electrophoresis‐based online immobilized enzyme microreactor was developed for evaluating the inhibitory activity of green tea catechins and tea polyphenol extracts on trypsin. The immobilized trypsin activity and other kinetic parameters were evaluated by measuring the peak area of the hydrolyzate of chromogenic substrate S‐2765. The results indicated that the activity of the immobilized trypsin remained approximately 90.0% of the initial immobilized enzyme activity after 30 runs. The value of Michaelis–Menten constant (Km) was (0.47 ± 0.08) mM, and the half‐maximal inhibitory concentration (IC50) and inhibition constant (Ki) of benzamidine were measured as 3.34 and 3.00 mM, respectively. Then, the inhibitory activity of four main catechins (epicatechin, epigallocatechin, epicatechin gallate, and epigallocatechin gallate) and three tea polyphenol extracts (green tea, white tea, and black tea) on trypsin were investigated. The results showed that four catechins and three tea polyphenol extracts had potential trypsin inhibitory activity. In addition, molecular docking results illustrated that epigallocatechin gallate, epicatechin gallate, epicatechin, and epigallocatechin were all located not only in the catalytic cavity, but also in the substrate‐binding pocket of trypsin. These results indicated that the developed method is an effective tool for evaluating inhibitory activity of catechins on trypsin. 相似文献
276.