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1.
2.
Photocycloaddition reactions of 3-phenyl-1,2-benzisothiazole alkenes yield derivatives of 2,3-dihydro-1,4-benzothiazepine in one step reactions. The photoadditions are both regio and stereospecific. 相似文献
3.
The S-configuration of the alkaloids cryptostylines I, II, and III was assigned on the basis of a single crystal X-ray analysis of unnatural cryptostyline II hydrobromide (5.HBr: orthorhombic, P212121a = 10·162, b = 12·352, c = 16·456 Å) and confirmed by application of the aromatic chirality method. Further evidence for the configurational assignment was provided by the CD spectra of the monophenolic derivatives of unnatural cryptostyline II (14). 相似文献
4.
The synthesis and X-ray structural determination of 3-O-[(bis-morpholino)phosphinyl]-5,6-O-isopropylidene-l-ascorbate (9) are described. Acid-catalyzed hydrolysis of 9 afforded the 2-O-phosphate 6. Definitive structural proof of 6 is based on a study of the pH profile of its UV spectra as compared with those of ascorbic esters, 2 and 9 (Figs. 1–3). 相似文献
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6.
Abstract SV40-transformed weanling Syrian hamster kidney cells were exposed to long wavelength ultraviolet radiation in the presence of 8-methoxypsoralen or angelicin. The number of viruses induced as a result of this treatment was quantitated on CV-1P cells. The results indicate that angelicin, which is generally believed to form only monoadducts, is a potent viral inducing agent even when compared with 8-methoxypsoralen (8-MOP), which forms both monoadducts and crosslinks. At low radiation exposures 8-MOP is more effective than angelicin; as the radiation exposure is increased angelicin is capable of inducing the same peak level of virus expression as was 8-MOP. It appears that the induction of SV40 is a phenomenon possibly related to the repair of monoadducts. 相似文献
7.
A study of the static stereochemistry of 1,1,2,2-tetraphenyldisilane (1) and 1,1,2,2-tetramesityldisilane (2) by empirical force field calculations, X-ray diffraction, and 1H NMR reveals that the preference for the anti conformation, exhibited by the unclamped 1,1,2,2-tetraarylethanes, is sustained in the analogous disilanes, although in somewhat attenuated form. This anti preference stands in contrast to the gauche preference of 1,1,2,2-tetraalkyldisilanes. Examination of 3JHH coupling constants for R2HSiSiHR2; (R = phenyl, mesityl, 2,6-dimethyl-phenyl, t-butyl, cyclohexyl) suggests the existence of a Karplus relation for H-Si-Si-H systems. 相似文献
8.
9.
John F. Blount Glenna D. Gray Karnail S. Atwal Thomas Y.R. Tsai Karel Wiesner 《Tetrahedron letters》1980,21(46):4413-4416
The α,β-unsaturated ketone yields with allene the photocycloadduct predicted by our empirical photoaddition rule and the byproduct 7. The formation of this material may be rationalized by the sequence → → → → . The isomeric ketone is unreactive under the same conditions, since α addition is prohibited by the rule and β addition is severely blocked. 相似文献
10.
Cardinali FL Ashley DL Morrow JC Moll DM Blount BC 《Journal of chromatographic science》2004,42(4):200-206
The prevalence of water disinfection byproducts in drinking water supplies has raised concerns about possible health effects from chronic exposure to these compounds. To support studies exploring the relation between exposure to trihalomethanes (THMs) and health effects, we have developed an automated analytical method using headspace solid-phase microextraction coupled with capillary gas chromatography and mass spectrometry. This method quantitates trace levels of THMs (chloroform, bromodichloromethane, dibromochloromethane, and bromoform) and methyl tertiary-butyl ether in tap water. Detection limits of less than 100 ng/L for all analytes and linear ranges of three orders of magnitude are adequate for measuring the THMs in tap water samples tested from across the United States. THMs are stable for extended periods in tap water samples after quenching of residual chlorine and buffering to pH 6.5, thus enabling larger epidemiologic field studies with simplified sample collection protocols. 相似文献