全文获取类型
收费全文 | 353篇 |
免费 | 18篇 |
专业分类
化学 | 305篇 |
晶体学 | 1篇 |
力学 | 2篇 |
数学 | 38篇 |
物理学 | 25篇 |
出版年
2023年 | 10篇 |
2022年 | 50篇 |
2021年 | 44篇 |
2020年 | 12篇 |
2019年 | 7篇 |
2018年 | 9篇 |
2017年 | 15篇 |
2016年 | 33篇 |
2015年 | 15篇 |
2014年 | 10篇 |
2013年 | 28篇 |
2012年 | 27篇 |
2011年 | 17篇 |
2010年 | 15篇 |
2009年 | 14篇 |
2008年 | 21篇 |
2007年 | 8篇 |
2006年 | 11篇 |
2005年 | 9篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2002年 | 2篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1992年 | 1篇 |
排序方式: 共有371条查询结果,搜索用时 15 毫秒
91.
92.
Let E be a Euclidean space,
dim E 2. We say that
f : E
E preserves equilateral triangles if for all triples of
points x, y, z E
we have
We show that if E is a finite-dimensional Euclidean space,
dim E 2,
f:E
E is measurable and preserves
equilateral triangles, then it is a similarity transformation (an isometry
multiplied by a positive constant). Moreover, in spaces at least
three-dimensional we get a similarity transformation without any
regularity assumption. Some generalizations as well as some interesting examples are also
presented in the paper. 相似文献
93.
94.
Pawe Szczeblewski Witold Andraoj Justyna Polit Aneta abka Konrad Winnicki Tomasz Laskowski 《Molecules (Basel, Switzerland)》2021,26(18)
Being a methyl ester of partricin, the mepartricin complex is the active substance of a drug called Ipertrofan (Tricandil), which was proven to be useful in treatment of benign prostatic hyperplasia and chronic nonbacterial prostatitis/chronic pelvic pain syndrome. Nevertheless, no direct structural evidence on the stereochemistry of its components has been presented to date. In this contribution, we have conducted detailed, NMR-driven stereochemical studies on mepartricins A and B, aided by molecular dynamics simulations. The absolute configuration of all the stereogenic centers of mepartricin A and B was defined as 3R, 7R, 9R, 11S, 13S, 15R, 17S, 18R, 19S, 21R, 36S, 37R, and 38S, and proposed as 41R. The geometry of the heptaenic chromophore of both compounds has been established as 22E, 24E, 26E, 28Z, 30Z, 32E, and 34E. Our studies on mepartricin ultimately proved that partricins A and B are structurally identical to the previously described main components of the aureofacin complex: gedamycin and vacidin, respectively. The knowledge of the stereochemistry of this drug is a fundamental matter not only in terms of studies on its molecular mode of action, but also for potential derivatization, aiming at improvement of its pharmacological properties. 相似文献
95.
96.
Dr. Marta K. Dudek Dr. Justyna Śniechowska Dr. Aneta Wróblewska Dr. Sławomir Kaźmierski Prof. Marek J. Potrzebowski 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(58):13264-13273
A well-defined and stable “AB” binary system in the presence of “C” a crystalline synthon ground in a ball mill undergoes selective transformation in the solid state according to the equation AB+C→AC+B. When the amount of C is increased two times then the equation AB+2C→AC+BC is valid. The other variants are more complex. The pathway BC+A is allowed and leads to the AC and B products. The pathway AC+B is not preferred, and no transformation is observed. These non-obvious correlations were observed for cocrystal of barbituric acid (BA):thiobarbituric acid (TBA) recently reported by Shemchuk et al. (Chem. Commun. 2016 , 52, 11815–11818) in the presence of 1-hydroxy-4,5-dimethyl-imidazole 3-oxide (HIMO). This synthon shows high affinity for the BA0.5TBA0.5 cocrystal as well for its individual components, BA and TBA. Single-quantum, double-quantum (SQ-DQ) 2D 1H very fast MAS NMR with a spinning rate of 60 kHz was employed as a basic and most diagnostic tool for the study of cocrystals transformations. Analysis of the experimental data was supported by theoretical calculations, including computation of the stabilization energy, Estab, defined as the energy difference between the energy of a co-crystal and the sum of the energies of particular components in the respective stoichiometric ratios. Two mechanisms of synthon replacement have been proposed. Pathway 1 assumes a concerted mechanism of substitution. In this approach, synthon attack is synchronized in time with the departure of one of the components of the binary system. Pathway 2 implies a non-concerted process, with an intermediate stage in which three separate components are present. Evidence suggesting a preference for Pathway 2 is shown. 相似文献
97.
98.
Rafał Ślusarz Magdalena J. Ślusarz Justyna Samaszko Janusz Madaj 《Central European Journal of Chemistry》2011,9(3):422-431
Six complexes of vancomycin and peptidoglycan precursors were studied via molecular dynamics simulations. The interactions
between the antibiotic and peptidoglycan fragments were identified and described in detail. All six studied modifications
of the peptidoglycan precursor resulted in a weakening of the interaction with vancomycin when comparing to the native D-Ala-D-Ala-terminated
fragment. It was confirmed that the N-terminus of the vancomycin is directly responsible for peptidoglycan recognition and
antimicrobial activity. In simulated systems, the saccharide part of the antibiotic interacts with peptide precursors, thus
it could also be important for antimicrobial activity. The complex terminated with D-Lac is the only one in which there is
a weak interaction with the sugar moiety in the simulated systems. Analysis of conformational changes is a major scope of
this work. The lack of interactions resulting from modification of the peptidoglycan precursors (D-Lac, D-Ser or other substitution)
would be counterbalanced by proper modifications of the vancomycin moiety, especially the saccharide part of vancomycin. 相似文献
99.
100.
Zbigniew Grobelny Marek Matlengiewicz Kinga Skrzeczyna Sylwia Golba Justyna Jurek-Suliga 《International Journal of Polymer Analysis and Characterization》2015,20(5):457-468
Anhydrous alkali metal hydroxide (KOH, NaOH, and LiOH)-activated macrocyclic ligand complexing metal cations, i.e., coronands 12C4, 15C5, 18C6, DCH24C8, and cryptand C222, were selected for initiation of β-butyrolactone (β-BL) and ε-caprolactone (ε-CL) polymerization. It was found that β-BL polymerizes in the presence of KOH/18C6, KOH/C222, and NaOH/C222 systems. The real initiators in this case are two salts, potassium 3-hydroxybutyrate and potassium trans-crotonate, which are responsible for the formation of two fractions of the obtained polymer. ε-CL underwent polymerization with KOH or NaOH activated by all ligands used or without the ligand but with LiOH/12C4. Using KOH-activated strong ligands, i.e., 15C5, 18C6, or C222, two polymer fractions were generated containing linear and, unexpectedly, also cyclic macromolecules. The mechanism of the studied processes is discussed. 相似文献