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排序方式: 共有198条查询结果,搜索用时 406 毫秒
81.
BICENTRALPOLYMERSUPPORTEDPHASETRANSFERCATALYSTPOLYSTYRENE-SUPPORTEDPOLYETHYLENEGLYCOLANDPYRIDINIUMSALTYangJianwen(Instituteof... 相似文献
82.
Lothar Weber 《Angewandte Chemie (International ed. in English)》1983,22(7):516-528
In recent years both acyclic and cyclic sulfur ylides have proved to be interesting and versatile ligands in preparative organometallic chemistry. In addition to paralleling the coordination chemistry of their phosphorus analogues, sulfur ylide complexes show specific structural and chemical features; they are becoming more important in preparative inorganic and organic chemistry, and may also be biochemically relevant as methylene transfer agents. Recent studies of the complexes of the ylidic λ4-thiabenzenes and λ6-thiabenzene 1-oxides have frequently demonstrated unexpected and novel reactions, and thereby enriched the chemistry both of ylides and of carbonylmetals. 相似文献
83.
Ulrich Schllkopf 《Angewandte Chemie (International ed. in English)》1970,9(10):763-773
The Wittig rearrangement of ethers metalated in the alpha position with alkali metals is a 1,2-shift to an atom with a lone pair of electrons. The alkyl shift proceeds with racemization (and partial retention) at the migrating carbon atom. The experimental observations suggest a cleavage-recombination mechanism involving a radical pair, as must also be assumed for the ylide rearrangements. In the allyl migration, the double bond is displaced within the migrating residue (allyl inversion). This is readily explained by a one-step S′ mechanism, the transition state of which is allowed on symmetry grounds. In the case of benzyl 2-butynyl ether metalated on the butynyl residue, the ortho isomerization (corresponding to the Sommelet rearrangement) predominates. – α-Metalated alkyl isocyanides can react with carbonyl compounds to form olefins and metal cyanate (carbonyl olefination). Isocyanoacetic esters occupy a special place; they react with aldehydes and ketones to form β-substituted α-formylaminoacrylates (formylaminoalkoxycarbonylmethylenation), which can enter into a wide range of reactions. β-Hydroxyalkyl isocyanides or 2-oxazolines can be isolated as intermediates in the carbonyl olefination. α-Metalated isocyanides react with acylating agents to form β-ketoalkyl isocyanides, which cyclize to give oxazoles. 相似文献
84.
Shengxian Zhao 《Tetrahedron letters》2005,46(33):5487-5490
Porphyrinic pyridinium ylides react with 1,4-benzoquinone and 1,4-naphthoquinone to afford novel meso-substituted indolizine porphyrins. 相似文献
85.
The reaction between an α-pyridinium acetamide bearing an 8-phenylmenthyl group as the chiral auxiliary and β-substituted methylidenemalononitriles gave rise to trans-cyclopropanes with diastereomeric ratios of up to 98:2. For most of the reactions, the absolute stereochemistry of the major product was found to be opposite of that of the major products of the reaction of the corresponding ester series, which also utilized the 8-phenylmenthyl group. 相似文献
86.
吡啶阳离子表面活性剂的示波极谱测定方法研究 总被引:21,自引:2,他引:21
在 0 .0 4mol·L- 1Na2 HPO4 KH2 PO4 (pH 8.0 )底液中 ,氯化十六烷基吡啶在汞电极上峰电位 - 1.35V(vs .SCE)处产生灵敏的还原波 ,其浓度在 0~ 0 .6mg·L- 1范围内与极谱波二阶导数的峰高 (H)呈正比 ,检出限 (3S/k)为 0 .0 1mg·L- 1。该极谱波具有吡啶阳离子表面活性剂的典型特征 ,特异性强 ,多种共存物质无干扰。用于生活饮用水中吡啶阳离子表面活性剂总量的测定 ,获得了满意的结果 相似文献
87.
Thomas Kappe Mehdi Hariri Erik Pongratz 《Monatshefte für Chemie / Chemical Monthly》1981,112(10):1211-1219
Reaction of isatoic anhydride with the betaine esters2 or3 represents a new synthesis of pyridinium ylides of type5, which have been previously obtained by several other ways. Treatment of the ylide5 with inorganic acids results in the formation of their pyridinium salts5 a–d. Hydrogenation or dehydrogenation of5 with Pd/C give the piperidylquinoline9 or the betaine10, respectively. Both of them can be prepared by an alternative way. ThepK values of some pyridinium ylides were determined.
II. Mitteilung:Kappe Th., Korbuly G., Stadlbauer W., Chem. Ber.111, 3857 (1978). 相似文献
88.
The first cryptand/monopyridinium [2]pseudorotaxanes were prepared from five bis(m-phenylene)-32-crown-10- and one bis(m-phenylene)-26-crown-8-based cryptand hosts and three monopyridinium guests. These pseudorotaxanes were studied by proton NMR spectroscopy, mass spectrometry, and X-ray crystallography. Association constants ranged from 141 M−1 to 1.86×104 M−1 in 1:1 acetone: chloroform at 22 °C. 相似文献
89.
Ljiljana T. Milovanović Katarina D. Karljiković-Rajić Branislava S. Stanković 《Monatshefte für Chemie / Chemical Monthly》1988,119(10):1069-1078
The UV absorption spectra of 1-(1-hydroxyimino-2-oxo-2-phenyl) pyridinium chloride (compound I) and 1-(1-hydroxyimino-2-oxo-2-phenyl)-4-hydroxyiminomethyl pyridinium chloride (compound II) in water solution at differentpH values have been measured. The spectral changes, with changingpH, in aqueous solutions are attributed to the dissociation of individual functional groups of the compounds. The mixed acidic constants (pKa) of the investigated monoxime and dioxime, have been determined spectrophotometrically in the series ofBritton-Robinson's buffer solutions in thepH range 3.0–5.19 and 7.70–9.90 (t=25±0.5°C,I=0.2). The followingpKa values have been obtained for monoximepKa
1=4.30 and for dioximepKa
1=4.28,pKa
2=8.36.Thermodynamic acidic constants (pKa) have been determined on the basis of potentiometric titrations and they have been found to bepKa
1=4.32 for compound I andpKa
1=4.27,pKa
2=8.51 for compound II. The values obtained by transferringpKa intopKa are in good agreement with the values obtained potentiometrically.
Spektrophotometrische und potentiometrische Bestimmung der Aciditätskonstanten von Oxo-Phenyl-Pyridinium-Monooxim und -Dioxim
Zusammenfassung Die UV-Absorptionsspektren von 1-(1-Hydroxyimino-2-oxo-2-phenyl)-pyridiniumchlorid (Verbindung I) und 1-(1-Hydroxyimino-2-oxo-2-phenyl)-4-hydroxyiminomethylpyridiniumchlorid (Verbindung II) wurden in wäßrigen Lösungen bei verschiedenenpH-Werten aufgenommen. Die Änderungen in den Spektren, die in wäßrigen Lösungen mit derpH-Änderung entstehen, können der Dissoziation der einzelnen funktionellen Gruppen der untersuchten Verbindungen zugeschrieben werden. Die Mischaciditätskonstanten (pKa) des untersuchten Monooxims und Dioxims wurden spektrophotometrisch in einer Reihe vonBritton-Robinson-Pufferlösungen inpH-Intervallen 3.0–5.19 und 7.70–9.90 (t=25±0.5°C;I=0.2) bestimmt: für das MonooximpKa 1=4.30 und für DioximpKa 1=4.28 undpKa 2=8.36. Die thermodynamischen Aciditätskonstanten (pKa) wurden aufgrund der potentiometrischen Titration berechnet:pKa 1=4.32 für die Verbindung I undpKa 1=4.27 undpKa 2=8.51 für die Verbindung II. Die durch ÜbertragungpKa inpKa erhaltenen Werte sind mit den über die potentiometrische Methode erhaltenen Werten in guter Übereinstimmung.相似文献
90.
Tsukasa Tawatari Ritsuki Kato Riku Kudo Prof. Dr. Kiyosei Takasu Prof. Dr. Hiroshi Takikawa 《Angewandte Chemie (International ed. in English)》2023,62(19):e202300907
We report herein intramolecular (3+2) cycloaddition reactions between ynamides as three-atom components and benzyne. In these intramolecular reactions, the two-bond formation is realized by exploiting benzyne precursors that contain a chlorosilyl group as a linking functionality. This method thus highlights the ambivalent character of the intermediate indolium ylide, which exhibits both nucleophilic and electrophilic properties at its C2 atom. 相似文献