全文获取类型
收费全文 | 202篇 |
免费 | 6篇 |
国内免费 | 1篇 |
专业分类
化学 | 152篇 |
晶体学 | 1篇 |
力学 | 2篇 |
数学 | 24篇 |
物理学 | 30篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 11篇 |
2020年 | 9篇 |
2019年 | 12篇 |
2018年 | 7篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 9篇 |
2014年 | 7篇 |
2013年 | 17篇 |
2012年 | 10篇 |
2011年 | 13篇 |
2010年 | 5篇 |
2009年 | 4篇 |
2008年 | 13篇 |
2007年 | 9篇 |
2006年 | 13篇 |
2005年 | 13篇 |
2004年 | 14篇 |
2003年 | 6篇 |
2002年 | 6篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1978年 | 2篇 |
排序方式: 共有209条查询结果,搜索用时 15 毫秒
1.
Chetan Bhadaliya Bala Krishna Panigrahy Dipanjan Goswami Sovan Maiti Sanjay Jagannath Gurule Arshad H. Khuroo 《Biomedical chromatography : BMC》2022,36(4):e5337
A selective, highly sensitive, precise, and novel bioanalytical method has been developed and validated to quantify sinococuline, an active constituent present in the phytopharmaceutical drug product containing Cocculus hirsutus plant extract, in vivo. Chromatographic separation was achieved on a Luna Omega Polar-C18 bonded analytical column maintained at 45°C. The isocratic mobile phase consisted of methanol and ammonium formate buffer (60:40, v/v) at acidic pH with a low flow rate of 0.250 mL/min. Detection was performed on an API 4000 mass spectrometer using electrospray ionization in positive polarity and multiple reaction monitoring mode to achieve a lower limit of quantification of 1.50 ng/mL. Excellent accuracy and precision were obtained after extracting the analyte from plasma samples using a chemical analogue as an internal standard in the absence of an isotope-labeled compound. The extraction efficacy was evidenced from recovery study, and the analyte was found to be stable in plasma. Validation study demonstrated linearity with coefficient of correlation, r ≥ 0.99, and minimal matrix effect. This bioanalytical method was successfully applied to evaluate pharmacokinetic parameters of sinococuline from a phase I clinical trial of an aqueous extract of C. hirsutus in healthy human volunteers. 相似文献
2.
A horizontal translation of a function is the focus of this study. We examine the explanations provided by secondary school students and secondary school teachers to a translation of a function, focusing on the example of the parabola y=(x−3)2 and its relationship to y=x2. The participants’ explanations focused on attending to patterns, locating the zero of the function, and the point-wise calculation of function values. The results confirm that the horizontal shift of the parabola is, at least initially, inconsistent with expectations and counterintuitive to most participants. We articulate possible sources of this perceived inconsistency and describe a pedagogical approach aimed at resolving it. 相似文献
3.
Aldopyranose peracetates react with thionyl chloride and BiCl3, generated in situ from a substoichiometric amount of the procatalyst BiOCl, producing the corresponding peracylated aldopyranosyl chlorides in very good to excellent yields (82–97%) with exclusive α-anomeric selectivity. 相似文献
4.
Meijler MM Arad-Yellin R Cabantchik ZI Shanzer A 《Journal of the American Chemical Society》2002,124(43):12666-12667
Synthetic iron chelators based on the natural siderophore ferrichrome have previously been shown to bind Fe(III) with high affinity (pKf > 27) and have shown no toxicity to mammalian cell cultures in vitro. A new class of lipophilic ferrichrome analogues carrying acetoxymethyl ester moieties has been synthesized. We have shown that these molecules penetrate rapidly through cell membranes and turn highly hydrophilic while inside the cells, upon esterase mediated hydrolysis of the lipophilic termini. The intracellular retention was visualized by labeling these analogues with a fluorescent naphthalic diimide probe. The prohydrophilic iron chelators have been shown to inhibit the metal-catalyzed intracellular formation of reactive oxygen species with high effectivity, and preliminary results suggest these molecules to be potent antimalarial agents. 相似文献
5.
Several enones are converted into their alpha-iodo derivatives in excellent yields and carbonylated with palladium catalysis in the presence of alcohol or amines to the alpha-carbonyl enones in satisfactory yields. 相似文献
6.
Gil Markovich Stuart Pollack Rina Giniger Ori Cheshnovsky 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,26(1):98-100
We have measured the photoelectron-spectra of I? (H2O)n clusters in the size range n=1–60. We have found that the first six water molecules form a solvation layer with an average 0.35 eV electrostatic stabilization of the anion. At larger cluster sizes the electrostatic stabilization of water does not fit a continuous dielectric solvent. The most stable structures of the clusters consist of internally solvated anions. In the size range n=34–40 we have found evidence for existence of cluster structures with surface solvated anions. 相似文献
7.
Lesaicherre ML Lue RY Chen GY Zhu Q Yao SQ 《Journal of the American Chemical Society》2002,124(30):8768-8769
We report here the first example using an intein-mediated expression system to generate biotinylated proteins suitable for immobilization onto avidin-functionalized glass slides. With this novel array, proteins are site-specifically immobilized on the glass surface and are able to retain their native activity. The advantage of the avidin/biotin linkage over his-tag/Ni-NTA strategies for protein immobilization is highlighted by its ability to withstand a variety of chemical conditions, which makes this new protein array compatible with most biological assays. 相似文献
8.
Acylation of heteroatoms (O, N and S) with acetyl chloride based on the use of a catalytic amount of the moisture stable, inexpensive ZrOCl2·8H2O, proceeds efficiently producing the corresponding acylated products in excellent yields. 相似文献
9.
Oxidations of alkanes, alkenes, and aromatic rings with pyridine N-oxides are efficiently catalyzed by ruthenium porphyrins under mild conditions. We show here that the oxidation of N-acyl cyclic amines with RuIVtetraarylporphyrin dichloride-2,6-substituted pyridine N-oxides directly gives N-acyl amino acids in modest to good yield via oxidative C-N bond cleavage. N-Acylpyrrolidines and N-acylpiperidines were converted to N-acyl-gamma-aminobutyric acids and N-acyl-delta-aminovaleric acids, respectively. This type of reaction is a novel one in which the C-N bond is cleaved selectively at the less substituted carbon. Notably, the proline residue in proline-containing peptides was selectively converted to glutamate. A large intramolecular kinetic isotope effect (kH/kD = 9.8) was observed in the oxidation of N-benzoyl[2,2,-d2]pyrrolidine, indicating that the reaction should involve an alpha-hydrogen atom abstraction process as the rate-determining step. N-Acylcarbaldehyde, the putative intermediate ring-opened form of alpha-hydroxylated N-acyl cyclic amine, was readily oxidized with the oxidizing system to afford the corresponding N-acylamino acid in good yield. Further, lactams (1-methyl-2-pyrrolidone and 1-methyl- 2-piperidone) were also oxidized to give the corresponding imides (1-methylsuccinimide and 1-methylpiperidine-2,6-dione). 相似文献
10.
Rina Chun Saegun Kim Sang Hoon Han Ashok Kumar Pandey Neeraj Kumar Mishra In Su Kim 《Tetrahedron letters》2018,59(43):3848-3852
The site-selective C–H nitration reaction of 7-azaindoles with t-butyl nitrite under palladium catalysis is described. This protocol provides an efficient method for the construction of ortho-nitrated N-aryl-7-azaindoles with excellent site-selectivity and functional group compatibility. The formed 7-azaindole derivatives can be readily transformed into 7-azaindoles containing an aniline functional group under palladium-catalyzed hydrogenation conditions. 相似文献