全文获取类型
收费全文 | 256篇 |
免费 | 13篇 |
专业分类
化学 | 226篇 |
晶体学 | 3篇 |
数学 | 19篇 |
物理学 | 21篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 15篇 |
2020年 | 4篇 |
2019年 | 11篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 7篇 |
2015年 | 11篇 |
2014年 | 15篇 |
2013年 | 34篇 |
2012年 | 17篇 |
2011年 | 17篇 |
2010年 | 10篇 |
2009年 | 16篇 |
2008年 | 13篇 |
2007年 | 16篇 |
2006年 | 5篇 |
2005年 | 15篇 |
2004年 | 9篇 |
2003年 | 3篇 |
2002年 | 5篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1990年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1973年 | 2篇 |
1968年 | 1篇 |
排序方式: 共有269条查询结果,搜索用时 15 毫秒
61.
The paper proposes a new method for amino acid determination which can be applied for amino acid profiling in solutions for parenteral nutrition. The MEKC method based on a mixed micellar system was developed for the separation of 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) derivatized amino acids. Background electrolyte was based on tris-borate buffer with high alkaline pH. Sodium dodecyl sulfate micelles were modified using 1,2-hexanediol as a co-surfactant. The effect of the modifier on amino acid migration was studied with respect to hydrophobicity of the analytes. The modifier appeared to be suitable to improve the separation of AQC-tagged amino acids without an adverse effect on buffer ionic strength or EOF velocity. The method was successfully validated and applied for amino acid profiling in medicinal preparations for parenteral nutrition. The results obtained were compared with a reference chromatographic method (amino acid analyser). 相似文献
62.
63.
Quantitative structure-activity relationship (QSAR) analysis of H1-antihistamine activity was carried out and chromatographic data of 2-[2-(phenylamino)thiazol-4-yl]ethanamine, 2-(2-benzyl-4-thiazolyl)ethanamine, 2-(2-benzhydrylthiazol-4-yl)ethylamine derivative, and 2-(1-piperazinyl- and 2-(hexahydro-1H-1,4-diazepin-1-yl)benzothiazole derivatives were obtained. Normal-phase (NP) TLC plates (silica gel 60F254), impregnated with solutions of selected amino acid mixtures (L-Asp, L-Asn, L-Thr and L-Lys) were used in two developing solvents as human histamine H1-receptor (hH1R) antagonistic interaction models. The lipophilicity data of the examined compounds were obtained and used in the QSAR assay. Using regression analysis, relationships between chromatographic and biological activity data were found. The correlations obtained in the present experiment with NP-TLC are more significant that those obtained in the experiment with RP2 TLC, because of the optimal fitting of the chromatographic system conditions to the lipophilicity of solutes. All proposed chromatographic models should facilitate pre-selection of the new drug candidates. The correlations of calculated pA2(H1) values of the tested compounds predicted by the use of the best equations versus their pA2(H1) obtained from the biological tests were significant (R2 = 0.91-0.94). 相似文献
64.
Alicja Smoktunowicz 《BIT Numerical Mathematics》2002,42(3):600-610
We study numerical properties of Clenshaw's algorithm for summing the series w =
n = 0
N
b
n
p
n
where p
n
satisfy the linear three-term recurrence relation. We prove that under natural assumptions Clenshaw's algorithm is backward stable with respect to the data b
n, n = 0,N. 相似文献
65.
Guzow K Rzeska A Mrozek J Karolczak J Majewski R Szabelski M Ossowski T Wiczk W 《Photochemistry and photobiology》2005,81(3):697-704
Photophysical properties of tyrosine and its derivatives with free and blocked functional groups were studied by steady state and time-resolved fluorescence spectroscopy and global analysis in organic solvents, such as methanol, 2-propanol, tetrahydrofuran (THF), and dimethylsulfoxide (DMSO). The mono-exponential fluorescence intensity decays were observed for all tyrosine derivatives in THF and DMSO solutions, whereas in alcohols some derivatives have bi-exponential decays. The rotamer population calculated from 1H nuclear magnetic resonance spectroscopy in DMSO does not correspond to the pre-exponential factors obtained from fluorescence spectroscopy. Moreover in the case of DMSO, the strong interaction of this solvent with the hydroxyl group of the fluorophore's phenol ring causes substantial changes in the fluorescence and nonradiative rate constants of tyrosine derivatives compared with those of tyrosine with a blocked hydroxyl group, Tyr(Me). The steady state and time-resolved fluorescence measurements in pure organic solvents and water-organic solvent mixtures indicate that the fluorescence quenching of the phenol chromophore of tyrosine by an acetyl or amide group or both depends on the polarity of the solvent used as well as the ability of the solvent to form hydrogen bonds with functional groups of tyrosine. 相似文献
66.
L. J. Haynes Alicja Kirkien-Konasiewicz A. G. Loudon Allan Maccoll 《Journal of mass spectrometry : JMS》1968,1(6):743-759
The mass spectra of tetronic acid and of a number of its derivatives are recorded and discussed. Where necessary, the composition of the fragment ions has been checked by high resolution mass measurements. Fragmentation of the molecular ion is explained in terms of the rupture of a bond attached to C-4, and the predominant routes for many of the compounds can be explained on the basis of two schemes, the first involving preliminary ketonisation of the molecular ion, followed by elimination of carbon monoxide, the second involving rupture of the C-4? R3 bond prior to elimination of carbon monoxide. Special structural features, however, provide alternative routes. 相似文献
67.
Anna epecka Anna Oko Piotr Szymaski Dorota Zieliska Katarzyna Kajak-Siemaszko Danuta Jaworska Katarzyna Neffe-Skociska Barbara Sionek Monika Trzskowska Danuta Kooyn-Krajewska Zbigniew J. Dolatowski 《Molecules (Basel, Switzerland)》2022,27(3)
The aim of this study was to use local LAB cultures for the production of organic acid-rennet cheeses from unpasteurized cow’s milk. Under industrial conditions, three types of cheese were produced, i.e., traditionally with acid whey (AW), with starter culture L. brevis B1, or with starter culture L. plantarum Os2. Strains were previously isolated from traditional Polish cheeses. Chemical composition, physico-chemical, microbiological, and sensory studies during 2 months of storage were carried out. As a result of this research, it was found that the basic composition was typical for semi-hard, partially skimmed cheeses. Mainly saturated fatty acids were detected. The cheeses were rich in omega-3, -6, and -9 fatty acids and conjugated linoleic acid (CLA), and were characterized by good lipid quality indices (LQI). All of the cheeses were characterized by a high number of lactic acid bacteria, with Enterobacteriaceae, yeast, molds, and staphylococci contaminants, which is typical microbiota for unpasteurized milk products. Water activity, pH, and total acidity were typical. A lower oxidation-reduction potential (ORP) of cheeses with the addition of strains and stability of the products during storage were observed. The B1 and Os2 cheeses were lighter, less yellow, had a more intense milk and creamy aroma, were softer, moister, and more elastic than AW cheese. The research results indicate the possibility of using environmental LAB strains in the production of high-quality acid-rennet cheeses, but special attention should be paid to the production process due to the microbiological quality of the cheeses. 相似文献
68.
Electroless deposition of Ni-P-nano-ZrO2 composite coatings in the presence of various types of surfactants 总被引:2,自引:0,他引:2
Ni-P-nano-ZrO(2) coatings were produced using the electroless deposition technique. To prevent agglomeration of zirconia nanoparticles in the plating bath, various surfactant additives (anionic, cationic, and nonionic) were used. The most stable bath was obtained with the addition of dodecyltrimethylammonium bromide (DTAB). The impact of this surfactant on the deposition rate, coating composition, and topography, as well as ζ potential of particles, was examined. Surface morphology and composition of the Ni-P-nano-ZrO(2) composite coatings was analyzed by various techniques including scanning electron microscopy (SEM) equipped with in situ energy-dispersive X-ray (EDX) spectroscopy. Coatings with a clearly greater amount of zirconia (21.88-22.10 wt.%) were obtained from baths containing DTAB in concentrations equal to or above its critical micelle concentration (cmc). For these surfactant concentrations, the reduction of Ni and P content was observed. 相似文献
69.
Alicja Smoktunowicz 《Linear algebra and its applications》2008,429(10):2628-2635
We prove that if A=[Aij]∈RN,N is a block symmetric matrix and y is a solution of a nearby linear system (A+E)y=b, then there exists F=FT such that y solves a nearby symmetric system (A+F)y=b, if A is symmetric positive definite or the matricial norm μ(A)=(‖Aij‖2) is diagonally dominant. Our blockwise analysis extends existing normwise and componentwise results on preserving symmetric perturbations (cf. [J.R. Bunch, J.W. Demmel, Ch. F. Van Loan, The strong stability of algorithms for solving symmetric linear systems, SIAM J.Matrix Anal. Appl. 10 (4) (1989) 494-499; D. Herceg, N. Kreji?, On the strong componentwise stability and H-matrices, Demonstratio Mathematica 30 (2) (1997) 373-378; A. Smoktunowicz, A note on the strong componentwise stability of algorithms for solving symmetric linear systems, Demonstratio Mathematica 28 (2) (1995) 443-448]). 相似文献
70.
Yunan Cui Henryk Hudzik Narin Petrot Suthep Suantai Alicja Szymaszkiewicz 《Proceedings Mathematical Sciences》2005,115(4):461-476
Necessary and sufficient conditions under which the Cesàro-Orlicz sequence spaceces
ϕ
is nontrivial are presented. It is proved that for the Luxemburg norm, Cesàro-Orlicz spacesces
ϕ
have the Fatou property. Consequently, the spaces are complete. It is also proved that the subspace of order continuous elements
inces
ϕ
can be defined in two ways. Finally, criteria for strict monotonicity, uniform monotonicity and rotundity (= strict convexity)
of the spacesces
ϕ
are given. 相似文献