全文获取类型
收费全文 | 542篇 |
免费 | 21篇 |
国内免费 | 1篇 |
专业分类
化学 | 372篇 |
晶体学 | 6篇 |
力学 | 18篇 |
数学 | 33篇 |
物理学 | 135篇 |
出版年
2023年 | 9篇 |
2022年 | 7篇 |
2021年 | 21篇 |
2020年 | 17篇 |
2019年 | 12篇 |
2018年 | 9篇 |
2017年 | 7篇 |
2016年 | 19篇 |
2015年 | 12篇 |
2014年 | 19篇 |
2013年 | 33篇 |
2012年 | 44篇 |
2011年 | 47篇 |
2010年 | 30篇 |
2009年 | 22篇 |
2008年 | 46篇 |
2007年 | 37篇 |
2006年 | 27篇 |
2005年 | 24篇 |
2004年 | 31篇 |
2003年 | 22篇 |
2002年 | 21篇 |
2001年 | 10篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有564条查询结果,搜索用时 500 毫秒
101.
Motivated by the recent work on Escherichia coli bacteria clustering [Park, S., Wolanin, P.M., Yuzbashyan, E.A., Lin, H., Darnton, N.C., Stock, J.B., Silberzan, P., Austin, R., 2003. Proc. Natl. Acad. Sci. U.S.A. 100 (24), 13910], we have conducted a computer simulation of E. coli chemotaxis induced by a self-excreted attractant and investigated how bacteria clusters interact through a self-excreted attractant. By modeling the variation of tumbling frequency in the context of phosphorylation rate change, we have investigated the dependency of clustering behavior on the sensitivity of cells to the attractant. We have found that there exists an optimal sensitivity leading to bigger clusters and that the geometry surrounding the cells also plays an important role in localizing the cluster formation. This result suggests that bacterial cluster formation can be reduced by making bacteria more sensitive to attractants, which is opposite to an instinctive way (making them retarded to attractants). In addition, we have studied the effect of an initial cell distribution on clustering. 相似文献
102.
The potential ability of atomic force microscopy (AFM) as a quantitative bioanalysis tool is demonstrated by using gold nanoparticles
as a size enhancer in a DNA hybridization reaction. Two sets of probe DNA were functionalized on gold nanoparticles and sandwich
hybridization occurred between two probe DNAs and target DNA, resulting in aggregation of the nanoparticles. At high concentrations
of target DNA in the range from 100 nM to 10 μM, the aggregation of gold nanoparticles was determined by monitoring the color
change with UV-vis spectroscopy. The absorption spectra broadened after the exposure of DNA–gold nanoparticles to target DNA
and a new absorption band at wavelengths >600 nm was observed. However, no differences were observed in the absorption spectra
of the gold nanoparticles at low concentrations of target DNA (10 pM to 10 nM) due to insufficient aggregation. AFM was used
as a biosensing tool over this range of target DNA concentrations in order to monitor the aggregation of gold nanoparticles
and to quantify the concentration of target DNA. Based on the AFM images, we successfully evaluated particle number and size
at low concentrations of target DNA. The calibration curve obtained when mean particle aggregate diameter was plotted against
concentration of target DNA showed good linearity over the range 10 pM to 10 nM, the working range for quantitative target
DNA analysis. This AFM-based DNA detection technique was three orders of magnitude more sensitive than a DNA detection method
based on UV-vis spectroscopy. 相似文献
103.
2-Bromobenzaldehyde reacts with phenols in acetonitrile under carbon monoxide pressure in the presence of a catalytic amount of bis(triphenylphosphine)palladium(II) chloride to afford the corresponding 3-phenoxy-1,3-dihydro-1-isobenzofuranones in high yields. 相似文献
104.
SangNyon Kim SangChul Shim DoYoung Kim YoungHa Rhee YoungBaek Kim 《Macromolecular rapid communications》2001,22(13):1066-1071
Biodegradable poly(3‐hydroxyundecenoate) (PHU) films on silicon wafers were crosslinked with UV light under patterned masks. The films were crosslinked most efficiently when irradiated in the presence of diphenyl(2,4,6‐trimethylbenzoylphosphane oxide) as the initiator. Crosslinked patterns were developed with depolymerase solution because crosslinked PHU was degraded much more slowly than natural PHU. Patterned images with thicknesses of as low as 2.5 μm were obtained showing the potential application of PHU in microlithography as a photosensitive material, which is friendly to the environment. 相似文献
105.
Hyoung-Geun Kim Seon Min Oh Na Woo Kim Ji Heon Shim Youn Hee Nam Trong Nguyen Nguyen Min-Ho Lee Dae Young Lee Tong Ho Kang Nam-In Baek 《Molecules (Basel, Switzerland)》2021,26(22)
The extract from Cnidium officinale rhizomes was shown in a prior experiment to markedly recover otic hair cells in zebrafish damaged by neomycin. The current study was brought about to identify the principal metabolite. Column chromatography using octadecyl SiO2 and SiO2 was performed to isolate the major metabolites from the active fraction. The chemical structures were resolved on the basis of spectroscopic data, including NMR, IR, MS, and circular dichroism (CD) data. The isolated phthalide glycosides were assessed for their recovery effect on damaged otic hair cells in neomycin-treated zebrafish. Three new phthalide glycosides were isolated, and their chemical structures, including stereochemical characteristics, were determined. Two glycosides (0.1 μM) showed a recovery effect (p < 0.01) on otic hair cells in zebrafish affected by neomycin ototoxicity. Repeated column chromatography led to the isolation of three new phthalide glycosides, named ligusticosides C (1), D (2), and E (3). Ligusticoside C and ligusticoside E recovered damaged otic hair cells in zebrafish. 相似文献
106.
Novel silicon-based alternating copolymers: synthesis,photophysical properties,and tunable EL colors
Hwan Kyu Kim Kyung Lim Paik Nam Seob Baek Youngil Lee Katsumi Yoshino 《Macromolecular Symposia》2003,192(1):135-150
We synthesized novel silicon-based alternating copolymers for tunable electroluminescent (EL) colors by Heck synthetic method. Their thermal, photophysical and electroluminescent properties were studied. Most of them exhibited a blue-green EL color at the operating voltage of lower than 12 V. Unusually, we observed the white EL color from a EL device based on SiPhPVK. From photophysical studies and the time-resolved PL spectroscopies, it might be attributed to the formation of stabilized excited state in SiPhPVK. Furthermore, in order to reduce the operating voltage of their LED with increasing the electron affinity of the main chain in silicon-based alternating copolymers, we synthesized the silicon-based copolymers containing electron transporting oxadiazole units in main chain. We also studied their photophysical and electroluminescent properties. 相似文献
107.
Hyoung-Geun Kim Youn Hee Nam Young Sung Jung Seon Min Oh Trong Nguyen Nguyen Min-Ho Lee Dae-Ok Kim Tong Ho Kang Dae Young Lee Nam-In Baek 《Molecules (Basel, Switzerland)》2021,26(20)
(1) Background: Many flavonoids have been reported to exhibit pharmacological activity; a preparatory study confirmed that Coreopsis lanceolata flowers (CLFs) contained high flavonoid structure content; (2) Methods: CLFs were extracted in aqueous methanol (MeOH:H2O = 4:1) and fractionated into acetic ester (EtOAc), normal butanol (n-BuOH), and H2O fractions. Repeated column chromatographies for two fractions led to the isolation of two aurones and two flavonols; (3) Results: Four flavonoids were identified based on a variety of spectroscopic data analyses to be leptosidin (1), leptosin (2), isoquercetin (3), and astragalin (4), respectively. This is the first report for isolation of 2–4 from CLFs. High-performance liquid chromatography (HPLC) analysis determined the content levels of compounds 1–4 in the MeOH extract to be 2.8 ± 0.3 mg/g (1), 17.9 ± 0.9 mg/g (2), 3.0 ± 0.2 mg/g (3), and 10.9 ± 0.9 mg/g (4), respectively. All isolated compounds showed radical scavenging activities and recovery activities in Caco-2, RAW264.7, PC-12, and HepG2 cells against reactive oxygen species. MeOH extract, EtOAc fraction, and 1–3 suppressed NO formation in LPS-stimulated RAW 264.7 cells and decreased iNOS and COX-2 expression. Furthermore, all compounds recovered the pancreatic islets damaged by alloxan treatment in zebrafish; (4) Conclusions: The outcome proposes 1–4 to serve as components of CLFs in standardizing anti-oxidant, pro-inflammatory inhibition, and potential anti-diabetic agents. 相似文献
108.
Aiguo Shen Benjian Zhang Jie Ping Wei Xie Patrice Donfack Seong‐Joon Baek Xiaodong Zhou Hui Wang Arnulf Materny Jiming Hu 《Journal of Raman spectroscopy : JRS》2009,40(5):550-555
Micro‐Raman spectroscopy (MRS) was utilized for the first time to evaluate the effect of indole‐3‐carbinol (I3C) on acute alcoholic liver injury in vivo. In situ Raman analysis of tissue sections provided distinct spectra that can be used to distinguish alcoholic liver injury as well as ethanol‐induced liver fibrosis from the normal state. Sixteen mice with liver diseases including acute liver injury and chronic liver fibrosis, and eight mice with normal liver tissues, and eight remedial mice were studied employing the Raman spectroscopic technique in conjunction with biomedical assays. The biochemical changes in mouse liver tissue when liver injury/fibrosis occurs such as the loss of reduced glutathione (GSH), and the increase of collagen (α‐helix protein) were observed by MRS. The intensity ratio of two Raman peaks (I1450/I666) and in combination with statistical analysis of the entire Raman spectrum was found capable of classifying liver tissues with different pathological features. Raman spectroscopy therefore is an important candidate for a nondestructive in vivo screening of the effect of drug treatment on liver disease, which potentially decreases the time‐consuming clinical trials. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
109.
Temperature-dependent photoluminescence (PL) measurements were carried out ZnSe/ZnS quantum dots (QDs) grown with post-growth interruption under a dimethylzinc (DMZn) flow. The PL spectra showed sigmoidal peak shifts and V-shaped full width at half maximum (FWHM) variations with increasing temperature, which strongly suggest that the QD structure of ZnSe/ZnS is quite similar to that of other material systems grown in the Stranski–Krastanov mode. Apparent differences are revealed as a consequence of DMZn treatment: (i) the PL spectra of ZnSe/ZnS QDs showed peaks at higher energies and persisted up to 300 K, and(ii) the minimum points of the V-shaped FWHM appear at a higher temperature compared to H2-purged ZnSe/ZnS QDs. Experimental results demonstrate the enhancement of localization energy. 相似文献
110.
New iron (III) complexes of S-methyl-βN-(5-methylpyrazole-3-yl)methylenedithiocarbazate, S-benzyl-β-N-β-(5-methylpyrazole-3-yl)methylenedithiocarbazate,
5-methyl-3-formylpyrazole-3-pyrrolidinylthiosemicarbazone, and 5-methyl-3-formylpyrazole-4N-benzylthiosemicarbazone have been synthesized and physicochemically characterized by elemental analyses, magnetic moment
measurements (polycrystalline state), electronic, IR, and EPR spectra, as well as conductance measurements, are used to confirm
the coordination geometry. The spectral studies reveal the low-spin distorted octahedral structure of the iron (III) complexes
containing two uninegative tridentate ligands with NNS donor sites, where the EPR data confirm the presence of a spin — paired
iron (III) with d
xz
2
d
yz
2
d
xy
1 configuration in the ground state.
The article is published in the original. 相似文献