全文获取类型
收费全文 | 179篇 |
免费 | 3篇 |
国内免费 | 1篇 |
专业分类
化学 | 84篇 |
晶体学 | 2篇 |
力学 | 1篇 |
数学 | 21篇 |
物理学 | 75篇 |
出版年
2022年 | 2篇 |
2020年 | 2篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2014年 | 2篇 |
2013年 | 7篇 |
2012年 | 3篇 |
2011年 | 6篇 |
2010年 | 2篇 |
2009年 | 10篇 |
2008年 | 9篇 |
2007年 | 8篇 |
2006年 | 9篇 |
2005年 | 11篇 |
2004年 | 5篇 |
2003年 | 6篇 |
2002年 | 2篇 |
2000年 | 12篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1970年 | 3篇 |
1968年 | 3篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1965年 | 1篇 |
1963年 | 1篇 |
1943年 | 2篇 |
1936年 | 4篇 |
1935年 | 2篇 |
1934年 | 1篇 |
1931年 | 1篇 |
排序方式: 共有183条查询结果,搜索用时 15 毫秒
1.
2.
Garcia Ruano JL Alcudia A del Prado M Barros D Maestro MC Fernandez I 《The Journal of organic chemistry》2000,65(10):2856-2862
The addition of the lithium anions derived from (R)- and (S)-methyl and -ethyl p-tolyl sulfoxides to (S)-N-benzylidene-p-toluenesulfinamide provides an easy access route to enantiomerically pure beta-(N-sulfinyl)amino sulfoxides. Stereoselectivity can be achieved when the configurations at the sulfur atoms of the two reagents are opposite (matched pair), thus resulting in only one diastereoisomer, even for the case in which two new chiral centers are created. The N-sulfinyl group primarily controls the configuration of the carbon bonded to the nitrogen, whereas the configuration of the alpha-sulfinyl carbanion seems to be responsible for the level of asymmetric induction, as well as for the configuration of the new stereogenic C-SO carbon in the reactions with ethyl p-tolyl sulfoxides. An efficient method for transforming the obtained beta-(N-sulfinyl)amino sulfoxides into optically pure beta-amino alcohols, based on the stereoselective non-oxidative Pummerer reaction, is also reported. 相似文献
3.
4.
John A. Montgomery James R. Piper Robert D. Elliott Eugene C. Roberts Carroll Temple Y. Fulmer Shealy 《Journal of heterocyclic chemistry》1979,16(3):537-539
Eighteen derivatives of 2,4-diamino-6-methylpteridine related to methotrexate and aminopterin have been prepared from 6-(bromomethyl)-2,4-pteridinediamine by nucleophilic displacement reactions. None of these compounds showed any antileukemic acitivity. 相似文献
5.
Deborah L. Buhrman Piper I. Price Patrick J. Rudewiczcor 《Journal of the American Society for Mass Spectrometry》1996,7(11):1099-1105
The effect of coeluting matrix compounds on the quantitation of SR 27417 in human plasma using electrospray liquid chromatography-tandem mass spectrometry has been examined. During the method development stage of this assay, plasma samples spiked with the analyte at 100 pg/mL were extracted using three different procedures: a hexane liquid-liquid extraction, an ethyl acetate back-extraction, and a solid phase extraction. Ion intensity of the analyte was found to be related inversely to the percent ionization of coeluting matrix components as evidenced by full scan spectra. The ethyl acetate back-extraction, which contained the fewest coeluting components, resulted in the highest ion intensity for the analyte. An assay comparison was done by using the liquid-liquid hexane and the ethyl acetate back-extractions for sample preparation. Replicate 1-mL samples (n=5) at 11 concentrations from 5 to 2000 pg/mL were extracted and analyzed. The results for the ethyl acetate back-extracted samples were acceptable from 2000 to 5 pg/mL with accuracy ranging from ?11.6 to 2.61% of the nominal concentrations. In contrast, the hexane liquid-liquid method had poor accuracy and precision below 20 pg/mL. The difference is explained by suppression of analyte ion intensity. These results are consistent with the current theory of electrospray ionization. 相似文献
6.
Garcia Ruano JL Alemparte C Martin Castro AM Adams H Rodriguez Ramos JH 《The Journal of organic chemistry》2000,65(23):7938-7943
The behavior of (Z)-3-p-tolylsulfinylacrylonitrile (1) as a chiral dienophile has been evaluated from its reactions with furan and acyclic dienes. Electrostatic interactions of the cyano group with the sulfinyl one restrict the conformational mobility around the C-S bond, thus controlling the pi-facial selectivity, which is almost complete in all cases, the approach of the diene from the less-hindered face of the dienophile (that bearing the lone electron pair) in the predominant rotamer being the favored one. The regioselectivity is also completely controlled by the cyano group. Additionally, the reactivity of compound 1 as well as its endo-selectivity are both higher than those observed for the corresponding (Z)-3-sulfinylacrylates, thus proving the potential of sulfinylnitriles as chiral dienophiles. 相似文献
7.
Zhou D Piper JD Abell C Klenerman D Kang DJ Ying L 《Chemical communications (Cambridge, England)》2005,(38):4807-4809
We show that direct coupling of a dye-labelled DNA (acceptor) to a quantum dot (QD) donor significantly reduces the donor-acceptor distance and improves the FRET efficiency: a highly efficient FRET (approximately 88%) at a low acceptor-to-donor ratio of 2 has been achieved at the single-molecule level. 相似文献
8.
(1R)- and (1S) [1-3H, 2H, 1H]-octanes and mixed with [1-14C]-octane, were synthesized. The mixed samples were incubated with homogenats of P. oleovorans strain TF4-1L and the biosynthesized mixtures of octanols isolated. It was shown that mainly the achiral termini [-C1H3] were hydroxylated and that chiral methyls were oxygenated to the extent of 20–30%. In all instances the products derived from hydroxylation at the chiral methyls [-C-3H, 2H, 1H] were mixtures of (1R)- and (1S)-octanols, the major component of which was the alcohol obtained by displacement of 1H. The results indicate that hydroxylation proceeded with a normal isotope effect kh>kd>kt. The amount of (1R)-octanol in the mixtures of octanols derived from (1R)- and (1S)-octane was determined. It was found that the C-1 hydroxylation of octane proceeded with retention, i.e. the incoming hydroxyl assumed the orientation of the displaced hydrogen (or isotopic hydrogen) atom. 相似文献
9.
Andreas Thomas Matthias Vogel Thomas Piper Oliver Krug Simon Beuck Wilhelm Schänzer Mario Thevis 《Analytical and bioanalytical chemistry》2013,405(30):9703-9709
AICAR (5-amino-4-imidazolecarboxyamide ribonucleoside) arguably provides performance-enhancing properties even in the absence of physical exercise and, therefore, the substance is banned in elite sports since 2009. Due to the natural presence of AICAR in human blood and urine, uncovering the misuse by direct qualitative analysis is not possible. Entering the circulation, the riboside is immediately incorporated into red blood cells (RBCs) and transformed into the corresponding ribotide (5′-monophosphate) form. Within the present study, an analytical method was developed to determine AICAR-ribotide concentrations in RBC concentrates by means of liquid chromatography-tandem mass spectrometry. The method was validated enabling quantitative result interpretation considering the parameters specificity, precision (intra- and interday), linearity, recovery, accuracy (LOD/LOQ), stability and ion suppression. By analysing 99 RBC samples of young athletes, normal physiological levels of AICAR-ribotide were determined (10–500 ng/mL), and individual levels were found to be stable for several days. Employing in vitro incubation experiments with AICAR riboside in fresh whole blood samples, the ribotide concentrations were observed to increase significantly within 30 min from baseline to 1–10 μg/mL. These levels are considered conserved for the lifetime of the erythrocyte and, thus, the results of the in vitro model strongly support the hypothesis that measuring abnormally high AICAR-ribotide concentrations in RBC of elite athletes has the potential to uncover the misuse of this substance for a long period of time. 相似文献
10.
We report the measurement of the surface conductivity of biological macromolecules by dielectrophoretic trapping at the tip of a glass nanopipet. We find that the threshold voltage for trapping is a function of salt concentration and can be directly linked to the effective conductivity of the biomolecule and its solvation shell. The surface conductivities obtained for 20-mer single-stranded DNA, 40-mer double-stranded DNA, and yellow fluorescent protein are 7.9+/-1.9 nS, 5.3+/-0.7 nS, and 21.5+/-1.6 nS, respectively. 相似文献