全文获取类型
收费全文 | 173篇 |
免费 | 1篇 |
国内免费 | 1篇 |
专业分类
化学 | 144篇 |
晶体学 | 5篇 |
力学 | 5篇 |
数学 | 11篇 |
物理学 | 10篇 |
出版年
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 1篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 14篇 |
2015年 | 4篇 |
2014年 | 5篇 |
2013年 | 4篇 |
2012年 | 7篇 |
2011年 | 8篇 |
2010年 | 3篇 |
2009年 | 4篇 |
2008年 | 7篇 |
2007年 | 9篇 |
2006年 | 8篇 |
2005年 | 8篇 |
2004年 | 4篇 |
2003年 | 6篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1989年 | 12篇 |
1988年 | 11篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1980年 | 1篇 |
1975年 | 1篇 |
1973年 | 3篇 |
1970年 | 1篇 |
1965年 | 3篇 |
1964年 | 2篇 |
1934年 | 1篇 |
排序方式: 共有175条查询结果,搜索用时 15 毫秒
111.
Gloria Zlati Anamarija Arapovi Ivana Martinovi Anita Martinovi Bevanda Perica Bokovi Ante Prki Andrea Paut Tina Vukui 《Molecules (Basel, Switzerland)》2022,27(17)
Considering the vast cultural and traditional heritage of the use of aromatic herbs and wildflowers for the treatment of light medical conditions in the Balkans, a comparison of the antioxidant capacity of wildflowers extracts from Herzegovina was studied using both cyclic voltammetry and spectrophotometry. The cyclic voltammograms taken in the potential range between 0 V and 800 mV and scan rate of 100 mV s−1 were used for the quantification of the electrochemical properties of polyphenols present in four aqueous plant extracts. Antioxidant capacity expressed as mmoL of gallic acid equivalents per gram of dried weight of the sample (mmoL GAE g−1 dw) was deduced from the area below the major anodic peaks (Q400 pH 6.0, Q500 pH 4.7, Q600 pH 3.6). The results of electrochemical measurements suggest that the major contributors of antioxidant properties of examined plants are polyphenolic compounds that contain ortho-dihydroxy-phenol or gallate groups. Using Ferric reducing-antioxidant power (FRAP) and 2,2′-azino-bis spectrophotometric methods (3-ethylbenzthiazoline-6-sulphonic acid) radical cation-scavenging activity (ABTS) additionally determined antioxidant capacity. The FRAP results ranged from 2.9702–9.9418 mmoL Fe/g dw, while the results for ABTS assays expressed as Trolox equivalents (TE) ranged from 14.1842–42.6217 mmoL TE/g dw. The Folin–Ciocalteu procedure was applied to determine the total phenolics content (TP). The TP content expressed as Gallic acid equivalents (GAE) ranged from 6.0343–9.472 mmoL GAE/g dw. The measurements of total flavonoid (TF) and total condensed tannin (TT) contents were also performed to obtain a broader polyphenolic profile of tested plant materials. Origanum vulgare L. scored the highest on each test, with the exception of TT content, followed by the Mentha × piperita L., Artemisia annua L., and Artemisia absinthium L., respectively. The highest TT content, expressed as mg of (−)catechin equivalents per gram of dried weight of sample (mg CE/g dw), was achieved with A. absinthium extract (119.230 mg CE/g dw) followed by O. vulgare (90.384 mg CE/g dw), A. annua (86.538 mg CE/g dw) and M. piperita (69.231 mg CE/g dw), respectively. In addition, a very good correlation between electrochemical and spectroscopic methods was achieved. 相似文献
112.
Zapilko C Widenmeyer M Nagl I Estler F Anwander R Raudaschl-Sieber G Groeger O Engelhardt G 《Journal of the American Chemical Society》2006,128(50):16266-16276
The surface reactions of mesoporous silica MCM-41 with a series of new trisilylamines (trisilazanes) (SiHMe2)2NSiMe2R and (SiMe2Vin)2NSiMe2R (R = indenyl, norpinanyl, chloropropyl, 3-(N-morpholin)propyl; Vin = vinyl), disilylalkylamine (SiHMe2)iPrNSiMe2(CH2)3Cl, and monosilyldialkylamines Me2NSiMe2R (R = indenyl, chloropropyl, 3-(N-morpholin)propyl) were investigated. 1H, 13C, and 29Si MAS NMR spectroscopy, nitrogen adsorption/desorption, infrared spectroscopy, and model reactions with calix[4]arene as a mimic for an oxo surface were used to clarify the chemical nature of surface-bonded silyl groups. The trisilylamines exhibited a comparatively slow surface reaction, which allowed for the adjustment of the amount of silylated and nonreacted SiOH groups and led to a stoichiometric distribution of surface functionalities. The 2:1 integral ratio of SiHMe2 and SiMe2R moieties of such trisilazanes was found to be preserved on the silica surface as indicated by microanalytical as well as 13C and 29Si MAS NMR spectroscopic data of the hybrid materials. For example, the reaction of MCM-41 with (SiHMe2)2NSiMe2(CH2)3Cl, (SiHMe2)iPrNSiMe2(CH2)3Cl, and Me2NSiMe2(CH2)3Cl provided bi- and monofunctional hybrid materials with one-third, one-half, or all chemically accessible silanol groups derivatized by chloropropyl groups, respectively. Thus, a molecular precursor strategy was developed to efficiently control the relative amount of three different surface species, SiHMe2 (or SiVinMe2), SiMe2R, and SiOH, in a single reaction step. The reaction behavior of indenyl-substituted monosilazanes and trisilazanes (R = Ind) with calix[4]arene proved that the indenyl substituent can act as a leaving group forming a dimethylsilyl species, which is anchored bipodally on the silica surface, that is, via two Si-O bonds. 相似文献
113.
Ante Mimica 《Potential Analysis》2010,32(3):275-303
In this paper we prove Harnack inequality for nonnegative functions which are harmonic with respect to random walks in ℝ
d
. We give several examples when the scale invariant Harnack inequality does not hold. For any α ∈ (0,2) we also prove the Harnack inequality for nonnegative harmonic functions with respect to a symmetric Lévy process
in ℝ
d
with a Lévy density given by $c|x|^{-d-\alpha}1_{\{|x|\leq 1\}}+j(|x|)1_{\{|x|>1\}}$c|x|^{-d-\alpha}1_{\{|x|\leq 1\}}+j(|x|)1_{\{|x|>1\}}, where 0 ≤ j(r) ≤ cr
− d − α
, ∀ r > 1, for some constant c. Finally, we establish the Harnack inequality for nonnegative harmonic functions with respect to a subordinate Brownian motion
with subordinator with Laplace exponent ϕ(λ) = λ
α/2ℓ(λ), λ > 0, where ℓ is a slowly varying function at infinity and α ∈ (0,2). 相似文献
114.
Gupta A Ali A Bilic A Gao M Hegedus K Singh B Watkins SE Wilson GJ Bach U Evans RA 《Chemical communications (Cambridge, England)》2012,48(13):1889-1891
Improvements in the performance of small molecule-based organic solar cells have been reported through the use of a cyanopyridone acceptor group. This acceptor fragment enhances the absorbance of an oligothiophene-based dye and enables the addition of a solubilising alkyl chain that facilitates simple device fabrication from solution. 相似文献
115.
Mario Cetina Ante Nagl Svjetlana Prekupec Silvana Rai‐Mali Mladen Mintas 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(3):o158-o160
In the title compound, C10H14N2O3, a pyrimidine ring is fused with a piperidine ring. The pyrimidine ring is planar, whereas the piperidine ring adopts a half‐chair conformation. The molecules of the title compound are connected via O—H⋯O intermolecular hydrogen bonds into infinite zigzag chains. The pyrimidine ring is involved in three C—H⋯π interactions, which link the hydrogen‐bonded chains into a three‐dimensional framework. 相似文献
116.
117.
Završnik D Muratović S Makuc D Plavec J Cetina M Nagl A Clercq ED Balzarini J Mintas M 《Molecules (Basel, Switzerland)》2011,16(7):6023-6040
We report on the synthesis of 4-hydroxycoumarin dimers 1-15 bearing an aryl substituent on the central linker and fused benzopyranocoumarin derivatives 16-20 and on their in vitro broad anti-DNA and RNA virus activity evaluations. The chemical identities and structure of compounds 1-20 were deduced from their homo- and heteronuclear NMR measurements whereas the conformational properties of 5, 14 and 20 were assessed by the use of 1D difference NOE enhancements. Unequivocal proof of the stereostructure of compounds 7, 9, 16 and 18 was obtained by single crystal X-ray diffraction method. The X-ray crystal structure analysis revealed that two 4-hydroxycoumarin moieties in the 4-trifluoromethylphenyl- and 2-nitrophenyl derivatives (compounds 7 and 9, respectively) are intramolecularly hydrogen-bonded between hydroxyl and carbonyl oxygen atoms. Consequently, the compounds 7 and 9 adopt conformations in which two 4-hydroxy-coumarin moieties are anti-disposed. Antiviral activity evaluation results indicated that the 4-bromobenzylidene derivative of bis-(4-hydroxycoumarin) (compound 3) possesses inhibitory activity against HSV-1 (KOS), HSV-2 (G), vaccinia virus and HSV-1 TK? KOS (ACVr) at a concentration of 9-12 μM and at a minimum cytotoxic concentration (MCC) greater than 20 μM. Compounds 4-6, 8, and 20 were active against feline herpes virus (50% effective concentration, EC?? = 5-8.1 μM), that is at a 4-7-fold lower concentration than the MCC. 相似文献
118.
We describe a new method using flow-injection analysis with spectro-photometric detection, suitable for the determination of N-acetyl-L-cysteine (NAC). The proposed method is appropriate for the determination of NAC in reaction with Pd(2+) ions in the concentration range from 1.0 × 10(-5) mol L(-1) to 6.0 × 10(-5) mol L(-1). The detection limit NAC was 5.84 × 10(-6) mol L(-1) and the recorded relative standard deviation of the method is in the range from 1.67 to 4.11%. NAC and Pd(2+) form complexes of Pd(2+):NAC molar ratios of 1:1 and 1:2, depending on the ratio of their analytical concentrations. The cumulative conditional stability constant for the Pd(NAC)(2)(2+) complex is β(12)' = 2.69 × 10(9) L(2) mol(-2). The proposed method was compared with the classic spectrophotometric determination of NAC, using the same reagent, PdCl(2), and had shown certain advantages: a) shorter analysis time; b) the use of smaller volumes of sample and reagents, which make the proposed method cheaper and faster for NAC determination in real samples without sample pretreatment. 相似文献
119.
Stefan Jezierski Anke S. Klein Christian Benz Michael Schaefer Stefan Nagl Detlev Belder 《Analytical and bioanalytical chemistry》2013,405(16):5381-5386
We immobilized adherent human embryonic kidney (HEK) cells—which are able to trace adenosine triphosphate (ATP) —inside a microfluidic free-flow electrophoresis (μFFE) chip in order to develop an integrated device combining separation and biosensing capabilities. HEK 293 cells loaded with fluorescent calcium indicators were used as a model system to enable the spatially and temporally resolved detection of ATP. The local position of a 20 μM ATP stream was successfully visualized by these cells during free-flow electrophoresis, demonstrating the on-line detection capability of this technique towards native, unlabeled compounds. 相似文献
120.