全文获取类型
收费全文 | 212篇 |
免费 | 4篇 |
专业分类
化学 | 168篇 |
晶体学 | 2篇 |
力学 | 1篇 |
数学 | 35篇 |
物理学 | 10篇 |
出版年
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 10篇 |
2015年 | 4篇 |
2014年 | 4篇 |
2013年 | 14篇 |
2012年 | 11篇 |
2011年 | 18篇 |
2010年 | 7篇 |
2009年 | 17篇 |
2008年 | 10篇 |
2007年 | 15篇 |
2006年 | 22篇 |
2005年 | 12篇 |
2004年 | 7篇 |
2003年 | 4篇 |
2002年 | 4篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有216条查询结果,搜索用时 31 毫秒
81.
Using a one-pot Sharpless asymmetric epoxidation/regioselective epoxide ring-opening as a key step, the protecting-group-free total synthesis of goniothalesdiol A was accomplished in only three steps starting from commercially available trans-cinnamaldehyde in 55.1% overall yield. In 6 previously reported total syntheses, 6–11 steps were required. 相似文献
82.
Ghezzi Lisa Duce Celia Bernazzani Luca Bramanti Emilia Colombini Maria Perla Tiné Maria Rosaria Bonaduce Ilaria 《Journal of Thermal Analysis and Calorimetry》2015,122(1):315-322
Journal of Thermal Analysis and Calorimetry - The thermal degradation of rabbit skin glue, a collagen-based proteinaceous material used as a paint binder in paintings, was investigated in this... 相似文献
83.
Kumari R Meyyappan A Nandi D Agrawalla BK Chowdhury AA Selvamani P Latha S Giri VS Mukherjee J Bandyopadhyay S Jaisankar P 《Natural product research》2011,25(15):1454-1462
This study investigates the in vitro antioxidant and antimicrobial activities of eight extracts obtained from the dried barks of Commiphora berryi and Commiphora caudata (Burseraceae). The radical scavenging activity was assessed by 1,1-diphenyl-2-picryl hydrazyl (DPPH) and nitric oxide assays. The methanolic extracts of C. berryi and C. caudata showed significant DPPH radical scavenging activity, with IC?? values of 26.92 and 21.16?μg?mL?1, respectively, and low radical scavenging activity against the nitric oxide assay. The antimicrobial activity of the plants was tested against the Gram-positive and Gram-negative bacteria. The ethyl acetate, chloroform and petroleum ether extracts of C. berryi showed good antibacterial activity against Pseudomonas aeruginosa, with a minimum inhibitory concentration (MIC) of 0.26?mg?mL?1, whereas the ethyl acetate and methanol extracts of C. caudata showed moderate antimicrobial activity with an MIC of more than 2.0?mg?mL?1 against P. aeruginosa compared to the petroleum ether and chloroform extracts, which showed an MIC of 1.1?mg?mL?1. The methanolic extracts of C. berryi and C. caudata also showed moderate cytotoxic activity against a human mammary carcinoma cell line (MCF-7), with values IC?? of 82.6 and 88.4?μg?mL?1, respectively. 相似文献
84.
Saliu F Modugno F Orlandi M Colombini MP 《Analytical and bioanalytical chemistry》2011,401(6):1785-1800
The lipid fractions of residues from historical pharmaceutical ointments were analysed by reversed-phase liquid chromatography
coupled with atmospheric pressure chemical ionization and mass spectrometer detection. The residues were contained in a series
of historical apothecary jars, dating from the eighteenth century and conserved at the “Aboca Museum” in Sansepolcro (Arezzo,
Italy) and at the pharmacy of the “Real Cartuja de Valldemossa” in Palma de Majorca (Spain). The analytical protocol was set
up using a comparative study based on the evaluation of triacylglycerol (TAG) compositions in raw natural lipid materials
and in laboratory-reproduced ointments. These ointments were prepared following pharmaceutical recipes reported in historical
treatises and used as reference materials. The reference materials were also subjected to stress treatments in order to evaluate
the modification occurring in the TAG profiles as an effect of ageing. TAGs were successfully detected in the reproduced formulations
even in mixtures of up to ten ingredients and after harsh degradative treatments, and also in real historical samples. No
particular interferences were detected from other non-lipid ingredients of the formulations. The TAG compositions detected
in the historical ointments indicated a predominant use of olive oil and pig adipose material as lipid ingredients. The detection
of a high level of tristearine and myristyl-palmitoyl-stearyl glycerol in two of the samples suggested the presence of a fatty
material of a different origin (maybe a ruminant). On the basis of the positional isomer ratio, sn-PPO/sn-POP, it was possible to hypothesize an exclusive use of pig fat in one sample. We also evaluated the application of principal
component analysis of TAG profiles as an approach for the multivariate statistical comparison of the reference and historical
ointments. 相似文献
85.
Gas chromatography/mass spectrometry (GC/MS) after alkaline hydrolysis, solvent extraction and trimethylsilylation, and analytical pyrolysis using hexamethyldisilazane (HMDS) for in situ derivatisation followed by gas chromatographic/mass spectrometric analysis (Pyrolysis-silylation-GC/MS) were used to investigate the hydrolysable and soluble constituents, and the polymerised macromolecules of an archaeological fig (Ficus carica) recovered in Zaragoza (Spain), as well as of modern figs. The main aim was to study the compositional alterations undergone by the fig tissues in a particular archaeological environment: the fig was in a vessel and covered by a layer of a mixture of orpiment and gypsum. A comparison between the GC/MS results from modern and archaeological figs revealed that degradative reactions took place, leading to the disappearance/depletion of reactive (unsaturated fatty acids) and sensitive compounds (phytosterols and triterpenes). Py-silylation-GC/MS data provided evidence of a significant degradation of the saccharide and lipid components of the fig tissue, which left a residue enriched in polyphenols and polyesters. 相似文献
86.
Ayyasami Kathiresan Krishnan Srinivasan Selvaraj Brinda Munirathinam Nethaji Subbaiah Govindarajan 《Transition Metal Chemistry》2012,37(4):393-397
Divalent metal complexes of general formula [M(2-nb)2(mc)2].2(2-nbH), where M = Co(II), Ni(II), Cu(II) or Zn(II), 2-nbH = 2-nitrobenzoic acid and mc = methyl carbazate (NH2NHCOOCH3), have been prepared and characterized by physicochemical and spectroscopic methods. Single-crystal X-ray study of the Cu(II)
complex revealed that the molecule is centrosymmetric, with two N,O-chelating mc ligands in equatorial positions and a pair
of monodentate 2-nb anions in the axial positions. The lattice 2-nbH molecules help to establish the packing of monomers through
hydrogen-bonding interactions. Thermal stability and reactivity of the complexes were studied by TG–DTA. Emission studies
show that these complexes are fluorescent. 相似文献
87.
María de los ngeles Zermeo-Macías Marco Martín Gonzlez-Chvez Francisco Mndez Arlette Richaud Rodolfo Gonzlez-Chvez Luis Enrique Ojeda-Fuentes Perla del Carmen Nio-Moreno Roberto Martínez 《Molecules (Basel, Switzerland)》2021,26(16)
The assertion made by Wu et al. that aromaticity may have considerable implications for molecular design motivated us to use nucleus-independent chemical shifts (NICS) as an aromaticity criterion to evaluate the antifungal activity of two series of indol-4-ones. A linear regression analysis of NICS and antifungal activity showed that both tested variables were significantly related (p < 0.05); when aromaticity increased, the antifungal activity decreased for series I and increased for series II. To verify the validity of the obtained equations, a new set of 44 benzofuran-4-ones was designed by replacing the nitrogen atom of the five-membered ring with oxygen in indol-4-ones. The NICS(0) and NICS(1) of benzofuran-4-ones were calculated and used to predict their biological activities using the previous equations. A set of 10 benzofuran-4-ones was synthesized and tested in eight human pathogenic fungi, showing the validity of the equations. The minimum inhibitory concentration (MIC) in yeasts was 31.25 µg·mL–1 for Candida glabrata, Candida krusei and Candida guilliermondii with compounds 15-32, 15-15 and 15-1. The MIC for filamentous fungi was 1.95 µg·mL–1 for Aspergillus niger for compounds 15-1, 15-33 and 15-34. The results obtained support the use of NICS in the molecular design of compounds with antifungal activity. 相似文献
88.
Perla V. B. da Silva Marianne M. Ramiro Edna K. K. Iriguchi William A. Corrêa Jennifer Lowe Claudia A. L. Cardoso 《Natural product research》2019,33(16):2413-2416
This study evaluated the hypoglycemic effect of the oil extracted from the Acrocomia aculeata pulp (OPAC) in normoglycemic rats and streptozotocin (STZ), fructose-induced diabetic rat models and its in vitro antioxidant and cytotoxic potential. OPAC (3, 30 or 300 mg/kg, v.o.) significantly decreased (p < 0.05) the high glucose levels induced by a high fructose-diet in rats. Persistent treatment with OPAC for 24 days also reduced the high plasmatic glucose induced by STZ. In normoglycemic animals, OPAC significantly decreased glucose levels. While A. aculeata oil exhibited good in vitro antioxidant activity, no sign of cytotoxicity was observed in LLC-PK1 cells (5–500 μg/mL). OPAC has antidiabetic and antioxidant activities without causing in vitro cytotoxicity. 相似文献
89.
90.
Perla Cruz-Mondragón M. Concepción Lozada Benjamín Ortiz Raúl G. Enríquez Manuel Soriano-García 《Journal of chemical crystallography》2009,39(7):474-477
Abstract Grandiflorenic acid [(−)-kaura-9(11)-16-dien-19-oic acid] methyl ester (2), C21H30O2, was synthesized from grandiflorenic acid, isolated from the plant Montanoa tomentosa. Compound (2) was formerly described as an oily derivative. X-ray diffraction analysis of (2) demonstrated that it consists
of four rings, three six-membered rings (I, II and III) and one five-membered ring (IV). I, II and III rings occur in chair,
twist, and envelope conformations, respectively. Ring IV occurs in a conformation between envelope and half-chair. The crystal
of grandiflorenic acid methyl ester is in monoclinic crystal system with space group P21, lattice constants: a = 7.2170(10), b = 11.4170(10), c = 11.2850(10) ?, β = 98.700(10)°, V = 919.1(2) ?3 and Z = 2.
Index Abstract Grandiflorenic acid [(−)-kaura-9(11)-16-dien-19-oic acid] methyl ester (2) was synthesized. This compound was formerly considered as an oily derivative. The crystal structure of (2) was obtained by determination of X-ray diffraction from suitable single crystals.
相似文献