全文获取类型
收费全文 | 213篇 |
免费 | 10篇 |
国内免费 | 1篇 |
专业分类
化学 | 118篇 |
晶体学 | 6篇 |
力学 | 3篇 |
数学 | 22篇 |
物理学 | 75篇 |
出版年
2021年 | 1篇 |
2020年 | 3篇 |
2019年 | 1篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2015年 | 4篇 |
2014年 | 2篇 |
2013年 | 7篇 |
2012年 | 15篇 |
2011年 | 10篇 |
2010年 | 10篇 |
2009年 | 20篇 |
2008年 | 10篇 |
2007年 | 8篇 |
2006年 | 19篇 |
2005年 | 6篇 |
2004年 | 11篇 |
2003年 | 6篇 |
2002年 | 12篇 |
2001年 | 4篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 8篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
排序方式: 共有224条查询结果,搜索用时 640 毫秒
1.
2.
Craft JL Horng YC Ragsdale SW Brunold TC 《Journal of the American Chemical Society》2004,126(13):4068-4069
Magnetic circular dichroism (MCD) spectroscopy and variable-temperature variable-field MCD are used in combination with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to characterize the so-called ox1-silent, red1, and ox1 forms of the Ni-containing cofactor F430 in methyl-coenzyme M reductase (MCR). Previous studies concluded that the ox1 state, which is the precursor of the key reactive red1 state of MCR, is a Ni(I) species that derives from one-electron reduction of the Ni(II)-containing ox1-silent state. However, our absorption and MCD data provide compelling evidence that ox1 is actually a Ni(II) species. In support of this proposal, our DFT and TD-DFT calculations indicate that addition of an electron to the ox1-silent state leads to formation of a hydrocorphin anion radical rather than a Ni(I) center. These results and biochemical evidence suggest that ox1 is more oxidized than red1, which prompted us to test a new model for ox1 in which the ox1-silent species is oxidized by one electron to form a thiyl radical derived from coenzyme M that couples antiferromagnetically to the Ni(II) ion. This alternative ox1 model, formally corresponding to a Ni(III)/thiolate resonance form but with predicted S = 1/2 EPR parameters reminiscent of a Ni(I) (3dx2-y2)1 species, rationalizes the requirement for reduction of ox1 to yield the red1 species and the seemingly incongruent EPR and electronic spectra of the ox1 state. 相似文献
3.
4.
LoSecco JM Bionta RM Biewitt G Bratton CB Casper D Chrysicopoulou P Claus R Cortez BG Errede S Foster GW Gajewski W Ganezer KS Goldhaber M Haines TJ Jones TW Kielczewska D Kropp WR Learned JG Lehmann E Park HS Reines F Schultz J Seidel S Shumard E Sinclair D Sobel HW Stone JL Sulak L Svoboda R van der Velde JC Wuest C 《Physical review letters》1985,54(21):2299-2301
5.
Aqueous two-phase extraction as an effective tool for isolation of geniposide from gardenia fruit 总被引:5,自引:0,他引:5
Natural products are normally obtained by organic solvent extraction and many subsequent chromatographic separations. Compounds of interest are often isolated with very low yield and limited purity. An aqueous two-phase extraction process combined with a simple ethanol treatment, for removing excess inorganic salt, has been developed for preparation of geniposide from gardenia. The system was comprised of PE62, a random copolymer composed of 20% ethylene oxide and 80% propylene oxide, KH2PO4 and ethanol. To find optimal conditions, the partition behavior of geniposide under an aqueous two-phase system was investigated. Various factors were considered, including the concentration of salt, the concentration of polymer, the sample loading, and the addition of ethanol. The experimental results demonstrated that increasing salt concentration or decreasing PE62 concentration results in enhancement of the geniposide partition in the salt-rich phase. The addition of ethanol and higher sample loading also promoted the partition efficiency of geniposide. Based on this study, an optimized system containing 5% PE62, 7.5% KH2PO4, and 10% ethanol was tested on a large-scale extraction. A 39.0-g aliquot of final product (in powder form) with 77% purity of geniposide can be effectively extracted from 500 g of gardenia fruit. This process is proved to be useful for industrial application of geniposide preparation. 相似文献
6.
Narayani Ramakrishnan Nancy L. Oleinick Marian E. Clay Min-Fen Horng Antonio R. Antunez Helen H. Evans 《Photochemistry and photobiology》1989,50(3):373-378
Two closely related strains of mouse lymphoma L5178Y cells, LY-R and LY-S, have been found to differ in their sensitivity to the cytotoxic effects of photodynamic treatment (PDT) with chloroaluminum phthalocyanine (CAPC) and red light. Strain LY-R is more sensitive to photodynamic cell killing than strain LY-S. Differences in uptake of CAPC could not account for the differences in cytotoxic effects. There was no marked difference between the two strains in the induction of single-strand breaks (which includes frank single-strand breaks and alkali-labile lesions), but substantially more DNA-protein cross-links were formed in strain LY-R by CAPC and light. Repair of single-strand breaks proceeded with similar kinetics in both strains for the first 30 min post-irradiation, suggesting that these lesions are not responsible for the differential sensitivity of the two strains to the lethal effects of photodynamic treatment. Thereafter, alkaline elution revealed the presence of increasing DNA strand breakage in strain LY-R. DNA degradation, as measured by the conversion of prelabeled [14C] DNA to acid-soluble radioactivity, was more rapid and extensive in strain LY-R. 相似文献
7.
The self‐assembly of NiCl2·6H2O with a diaminodiamide ligand 4,8‐diazaundecanediamide (L‐2,3,2) gave a [Ni(C9H20N4O2)(Cl)(H2O)] Cl·2H2O ( 1 ). The structure of 1 was characterized by single‐crystal X‐ray diffraction analysis. Structural data for 1 indicate that the Ni(II) is coordinated to two tertiary N atoms, two O atoms, one water and one chloride in a distorted octahedral geometry. Crystal data for 1: orthorhombic, space group P 21nb, a = 9.5796(3) Å, b = 12.3463(4) Å, c = 14.6305(5) Å, Z = 4. Through NH···Cl–Ni (H···Cl 2.42 Å, N···Cl 3.24 Å, NH···Cl 158°) and OH···Cl–Ni contacts (H···Cl 2.36 Å, O···Cl 3.08 Å, OH···Cl 143°), each cationic moiety [Ni(C9H20N4O2) (Cl)(H2O)]+ in 1 is linked to neighboring ones, producing a charged hydrogen‐bonded 1D chainlike structure. Thermogrametric analysis of compound 1 is consistent with the crystallographic observations. The electronic absorption spectrum of Ni(L‐2,3,2)2+ in aqueous solution shows four absorption bands, which are assigned to the 3A2g → 3T2g, 3T2g → 1Eg, 3T2g → 3T1g, and 3A2g → 3T1g transitions of triplet‐ground state, distorted octahedral nickel(II) complex. The cyclic volammetric measurement shows that Ni2+ is more easily reduced than Ni(L‐2,3,2)2+ in aqueous solution. 相似文献
8.
9.
10.
Yeoung-Sheng Wang Jyun-Hong Shen Jhan-Ping Lin Jao-Jia Horng 《Journal of Thermal Analysis and Calorimetry》2013,111(2):1443-1448
The porous, stable zeolite materials impregnated with 1 wt% silver (AgZ) were used as anti-bacterial filters to reduce the bio-aerosols as bacterial counts in the indoor air quality of a medical facility to fulfill the regulation of the Taiwan environmental protection administration. The anti-bacterial efficacies of AgZ reach 99 % after 2 h of air circulation in rooms, and its capacity could be re-generated through heated air at 160 °C. The stability and characteristics of AgZ were analyzed by the transmission electron microscopy, X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, and zeta-potential. Heat of the endothermic reaction of AgZ was evaluated to be 377–388 J g?1 and was discovered as stable below 300 °C. The analysis results also showed the recovery of second isoelectric points at pH 8.5 of AgZ could represent the ability to adsorb negative charged bio-aerosols as well as anti-bacterial capacity. 相似文献