全文获取类型
收费全文 | 265篇 |
免费 | 11篇 |
国内免费 | 6篇 |
专业分类
化学 | 169篇 |
晶体学 | 1篇 |
力学 | 12篇 |
数学 | 46篇 |
物理学 | 54篇 |
出版年
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 2篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2016年 | 14篇 |
2015年 | 12篇 |
2014年 | 11篇 |
2013年 | 23篇 |
2012年 | 24篇 |
2011年 | 19篇 |
2010年 | 15篇 |
2009年 | 20篇 |
2008年 | 15篇 |
2007年 | 19篇 |
2006年 | 16篇 |
2005年 | 7篇 |
2004年 | 13篇 |
2003年 | 7篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有282条查询结果,搜索用时 15 毫秒
101.
Separation and fragmentation study of isocoproporphyrin derivatives by UHPLC‐ESI‐exact mass MS/MS and identification of a new isocoproporphyrin sulfonic acid metabolite 下载免费PDF全文
Christopher M. Benton Chang Kee Lim Caje Moniz Sinéad L. Baxter Donald J. L. Jones 《Journal of mass spectrometry : JMS》2014,49(1):80-85
Isocoproporphyrin and its derivatives are commonly used as biomarkers of porphyria cutanea tarda, heavy metal toxicity and hexachlorobenzene (HCB) intoxication in humans and animals. However, most are isobaric with other porphyrins and reference materials are unavailable commercially. The structural characterisation of these porphyrins is important but very little data is available. We report here the separation and characterisation of isocoproporphyrin, deethylisocoproporphyrin, hydroxyisocoproporphyrin and ketoisocoproporphyrin, isolated in the faeces of rats fed with a diet containing HCB, by ultra high performance liquid chromatography‐exact mass tandem mass spectrometry (UHPLC‐MS/MS). Furthermore, we report the identification and characterisation of a previously unreported porphyrin metabolite, isocoproporphyrin sulfonic acid isolated in the rat faeces. The measured mass‐to‐charge ratio (m/z) of the precursor ion was m/z 735.2338, corresponding to a molecular formula of C36H39N4O11S with an error of 0.3 ppm from the calculated m/z 735.2336. The MS/MS data was consistent with an isocoproporphyrin sulfonic acid structure, derived from dehydroisocoproporphyrinogen by sulfonation of the vinyl group. The metabolite was present in a greater abundance than other isocoproporphyrin derivatives and may be a more useful biomarker for HCB intoxication. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
102.
This paper investigates the Rouquier blocks of the Hecke algebras of the symmetric groups and the Rouquier blocks of the q-Schur algebras. We first give an algorithm for computing the decomposition numbers of these blocks in the ``abelian defect
group case' and then use this algorithm to explicitly compute the decomposition numbers in a Rouquier block. For fields of
characteristic zero, or when q=1 these results are known; significantly, our results also hold for fields of positive characteristic with q≠1. We also discuss the Rouquier blocks in the ``non–abelian defect group' case. Finally, we apply these results to show
that certain Specht modules are irreducible. 相似文献
103.
104.
Chi‐Ming Che Prof. Hai‐Feng Xiang Dr. Stephen Sin‐Yin Chui Dr. Zong‐Xiang Xu V. A. L. Roy Dr. Jessie Jing Yan Wen‐Fu Fu Prof. P. T. Lai Prof. Ian D. Williams Prof. 《化学:亚洲杂志》2008,3(7):1092-1103
Organic field‐effect transistors incorporating planar π‐conjugated metal‐free macrocycles and their metal derivatives are fabricated by vacuum deposition. The crystal structures of [H2(OX)] (H2OX=etioporphyrin‐I), [Cu(OX)], [Pt(OX)], and [Pt(TBP)] (H2TBP=tetra‐(n‐butyl)porphyrin) as determined by single crystal X‐ray diffraction (XRD), reveal the absence of occluded solvent molecules. The field‐effect transistors (FETs) made from thin films of all these metal‐free macrocycles and their metal derivatives show a p‐type semiconductor behavior with a charge mobility (μ) ranging from 10?6 to 10?1 cm2 V?1 s?1. Annealing the as‐deposited Pt(OX) film leads to the formation of a polycrystalline film that exhibits excellent overall charge transport properties with a charge mobility of up to 3.2×10?1 cm2 V?1 s?1, which is the best value reported for a metalloporphyrin. Compared with their metal derivatives, the field‐effect transistors made from thin films of metal‐free macrocycles (except tetra‐(n‐propyl)porphycene) have significantly lower μ values (3.0×10?6–3.7×10?5 cm2 V?1 s?1). 相似文献
105.
Copper indium disulfide (CuInS2; CIS) films were deposited on various substrates by two-stage metal-organic chemical vapor deposition (MOCVD) at relatively mild conditions, using Cu- and In/S-containing precursors without toxic H2S gas: first, a pure Cu thin film was prepared on glass or indium/tin oxide glass substrates by using a single-source precursor, bis(ethylbutyrylacetato)copper(II) or bis(ethylisobutyrylacetato)copper(II); second, on the resulting Cu film, tris(N,N-ethylbutyldithiocarbamato)indium(III) was treated to produce CIS films by a MOCVD method at 430 degrees C. In this process, their thicknesses and stoichiometries were found to be elaborately controlled on demand by adjusting the process conditions. The optical band gap of the stoichiometric CIS film was about 1.41 eV, which is in the near-optimal range for harvesting solar radiation energy. 相似文献
106.
107.
Exercise type and muscle fiber specific induction of caveolin-1 expression for insulin sensitivity of skeletal muscle 总被引:1,自引:0,他引:1
Oh YS Kim HJ Ryu SJ Cho KA Park YS Park H Kim M Kim CK Park SC 《Experimental & molecular medicine》2007,39(3):395-401
It is well known that exercise can have beneficial effects on insulin resistance by activation of glucose transporter. Following up our previous report that caveolin-1 plays an important role in glucose uptake in L6 skeletal muscle cells, we examined whether exercise alters the expression of caveolin-1, and whether exercise-caused changes are muscle fiber and exercise type specific. Fifty week-old Sprague Dawley (SD) rats were trained to climb a ladder and treadmill for 8 weeks and their soleus muscles (SOL) and extensor digitorum longus muscles (EDL) were removed after the last bout of exercise and compared with those from non-exercised animals. We found that the expression of insulin related proteins and caveolins did not change in SOL muscles after exercise. However, in EDL muscles, the expression of insulin receptor beta (IR beta) and glucose transporter-4 (GLUT-4) as well as phosphorylation of AKT and AMPK increased with resistance exercise but not with aerobic exercise. Also, caveolin-1 and caveolin-3 increased along with insulin related proteins only in EDL muscles by resistance exercise. These results suggest that upregulation of caveolin-1 in the skeletal muscle is fiber specific and exercise type specific, implicating the requirement of the specific mode of exercise to improve insulin sensitivity. 相似文献
108.
M.H. Jeon A.K. Mishra S.-K. Kang K.N. Kim I.J. Kim S.B. Lee T.H. Sin G.Y. Yeom 《Current Applied Physics》2013,13(8):1830-1836
60 MHz pulsed radio frequency (rf) source power and 2 MHz continuous wave rf bias power, were used for SiO2 etching masked with an amorphous carbon layer (ACL) in an Ar/C4F8/O2 gas mixture, and the effects of the frequency and duty ratio of the 60 MHz pulse rf power on the SiO2 etch characteristics were investigated. With decreasing duty ratio of the 60 MHz pulse rf power, not only the etch rate of SiO2 but also the etch rate of ACL was decreased, however, the etch selectivity of SiO2 over ACL was improved with decreasing the duty ratio. On the other hand, when the pulse frequency was varied at a constant duty ratio, no significant change in the etch rate and etch selectivity of both materials could be observed. The variation of the etch characteristics was believed to be related to the change in the gas dissociation characteristics caused by the change in the average electron temperature for different pulsing conditions. The improvement in the etch selectivity with the decrease of duty ratio, therefore, was related to the decreased gas dissociation of C4F8 by the decrease of average electron temperature and, which resulted in a change in composition of the fluorocarbon polymer on the etched materials surface from C–C rich to CF2 rich. With decreasing the duty ratio, not only the etch selectivity but also the improvement in the SiO2 etch profile could be observed. 相似文献
109.
Davis C Gordon N Murphy S Singh I Kavanagh K Carberry S Doyle S 《Analytical and bioanalytical chemistry》2011,401(8):2519-2529
Gliotoxin is produced by non-ribosomal peptide synthesis and secreted from certain fungi, including Aspergillus fumigatus. It is an epipolythiodioxopiperazine that contains an intact disulphide bridge and is the focus of intense research as a
consequence of its negative immunomodulatory properties. Gliotoxin detection is generally enabled by reversed-phase–high-performance
liquid chromatography (RP-HPLC), with absorbance detection (220–280 nm), or liquid chromatography-mass spectrometry, yet detection
is not readily achievable by matrix-assisted laser desorption ionisation–time-of-flight mass spectrometry (MALDI-ToF MS).
We have developed a single-pot derivatisation strategy which uses sodium borohydride-mediated reduction of gliotoxin followed
by immediate alkylation of exposed thiols by 5′-iodoacetamidofluorescein to yield a stable product, diacetamidofluorescein-gliotoxin
(GT-(AF)2), of molecular mass 1103.931 Da ((M + H)+). This product is readily detectable by RP-HPLC and exhibits a 6.8-fold increase
in molar absorptivity compared with gliotoxin, which results in a higher sensitivity of detection (40 ng; 125 pmoL). GT-(AF)2 also fluoresces (excitation/emission, 492:518 nm). Unlike free gliotoxin, the product (>800 fmol) is detectable by MALDI-ToF
MS. Sporidesmin A can also be detected by RP-HPLC and MALDI-ToF MS (>530 fmol) using this strategy. We also demonstrate that
the strategy facilitates detection of gliotoxin (mean ± SD = 3.55 ± 0.07 μg 100 μL−1; n = 2) produced by A. fumigatus, without the requirement for organic extraction of culture supernatants and associated solvent removal. GT-(AF)2 is also detectable (150 ng; 460 pmol) by thin-layer chromatography. 相似文献
110.
In this work, polyester polyols with high weight average molecular weight (Mw) (Mw?10000–15000) were prepared from epoxidized palm olein (EPOo) and a series of dicarboxylic acids (C6–C12) at elevated temperature under non‐catalyzed condition. The optimal reaction conditions were determined as 180°C for 4 h. Longer carbon chain length of dicarboxylic acids was more reactive when reacted with EPOo. The physical appearance of the product was observed as liquid at room temperature. This palm oil‐based polyester polyol is proposed as starting material for flexible polyurethane. For reaction monitoring purposes, FTIR was used while 1H NMR analysis was carried out to characterize the important functional groups of the products. The effects of reaction time and temperature on the Mw of the reaction mixture were also studied by GPC. 相似文献