全文获取类型
收费全文 | 6622篇 |
免费 | 103篇 |
国内免费 | 30篇 |
专业分类
化学 | 4086篇 |
晶体学 | 29篇 |
力学 | 178篇 |
数学 | 1349篇 |
物理学 | 1113篇 |
出版年
2022年 | 48篇 |
2020年 | 62篇 |
2016年 | 90篇 |
2015年 | 83篇 |
2014年 | 89篇 |
2013年 | 221篇 |
2012年 | 196篇 |
2011年 | 215篇 |
2010年 | 142篇 |
2009年 | 138篇 |
2008年 | 225篇 |
2007年 | 258篇 |
2006年 | 219篇 |
2005年 | 242篇 |
2004年 | 208篇 |
2003年 | 164篇 |
2002年 | 174篇 |
2001年 | 81篇 |
2000年 | 107篇 |
1999年 | 82篇 |
1998年 | 61篇 |
1997年 | 86篇 |
1996年 | 89篇 |
1995年 | 88篇 |
1994年 | 89篇 |
1993年 | 85篇 |
1992年 | 100篇 |
1991年 | 70篇 |
1990年 | 79篇 |
1989年 | 78篇 |
1988年 | 94篇 |
1987年 | 75篇 |
1986年 | 94篇 |
1985年 | 130篇 |
1984年 | 121篇 |
1983年 | 88篇 |
1982年 | 127篇 |
1981年 | 131篇 |
1980年 | 113篇 |
1979年 | 128篇 |
1978年 | 109篇 |
1977年 | 106篇 |
1976年 | 97篇 |
1975年 | 111篇 |
1974年 | 87篇 |
1973年 | 87篇 |
1972年 | 57篇 |
1971年 | 64篇 |
1970年 | 66篇 |
1966年 | 47篇 |
排序方式: 共有6755条查询结果,搜索用时 15 毫秒
51.
Anton Meller Walter Maringgele Rainer Oesterle 《Monatshefte für Chemie / Chemical Monthly》1980,111(5):1087-1096
The reaction of galliumtrichloride and galliumtribomide resp. with 2,6-dimethyl- and 2,4,6-trimethyl-N-trimethylsilyl-trifluoroacetanilide leads to the trifluoracetanilidodihalogenogallanes1–3. The 2,6,9-trioxa-4,8-diaza-1,5-digalla-bicyclo-[3.3.1]-nonadiene derivatives1 a–3 a are formed probably as by products.N-Trimethylsilyltrifluoroacetamide reacts with galliumtrichloride to yield the trifluoroacetamido-dichlorogallane4.N-Trimethylsilyl-N,N,N-triorganyl-thioureas react with galliumtrichloride under elimination of chlorotrimethylsilane to give the thio-ureido-gallanes5 and6. IfN,N-diorganylureas andN,N-diorganyl-thio-ureas resp. are reacted with galliumtrichloride and methyl-gallium-dichloride resp., the thio-ureido- and ureido-gallanes7–9 are obtained by elimination of hydrogenchloride. The compounds are characterized by analysis and spectral data (NMR:1H,19F; MS; IR). The substances are monomeric in the gas phase, obviously due to internal coordination.
30. Mitt.:W. Maringgele undA. Meller, J. Organomet. Chem., im Druck. 相似文献
52.
The synthesis of endo- and exo-13-oxo-4b, 5, 12, 12a-tetrahydro-5, 12-ethanoindeno[2,3-b]anthracene ( 23 ; Schemes 1 and 2), exo- and endo-11-oxo-4b, 5, 10, 10a-tetrahydro-5, 10-ethano-indeno[2,3-b]naphthalene ( 31 ; Scheme 3), 1,2,3,4,4a,9a-hexahydro?1,4-(peri-naphthaleno)-fluoren-9-one (36; Scheme 4), and the corresponding hydrocarbons of the stereoisomeric ketone pairs 23 and 36 , is described. 相似文献
53.
Max Ziegler und Walter Rittner 《Fresenius' Journal of Analytical Chemistry》1958,164(3):310-313
Zusammenfassung Die Trennung der Thioglykolsäurekomplexe des Molybdäns von dem des Vanadiums verläuft mit einer Molybdänausbeute von 99%. Das Vanadium kann im Durchlauf in bequemer Weise mittels Thioglykolsäure im pH-Bereich 4,5–8 bei guter Genauigkeit photometriert werden.Herrn Prof. Dr. O. Glemser, Direktor des Anorganisch-Chem.-Instituts, danken wir sehr für das stete Interesse und die Unterstützung, die er uns zuteil werden ließ.Dem Herrn Bundesminster für Atomkernenergie und Wasserwirtschaft sowie der Deutschen Forschungsgemeinschaft danken wir für apparative und finanzielle Hilfe. 相似文献
54.
Saalfrank RW Deutscher C Maid H Ako AM Sperner S Nakajima T Bauer W Hampel F Hess BA van Eikema Hommes NJ Puchta R Heinemann FW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(8):1899-1905
In the reaction of the N-substituted diethanolamines (H(2)L(1-3)) (1-3) with calcium hydride followed by addition of iron(III) or indium(III) chloride, the iron wheels [Fe(6)Cl(6)(L(1))(6)] (4) and [Fe(6)Cl(6)(L(2))(6)] (6) or indium wheels [In(6)Cl(6)(L(1))(6)] (5), [In(6)Cl(6)(L(2))(6)] (8) and [In(6)Cl(6)(L(3))(6)] (9) were formed in excellent yields. Exchange of the chloride ions of 6 by thiocyanate ions afforded [Fe(6)(SCN)(6)(L(2))(6)] (7). Whereas the structures of 4, 5 and 7 were determined unequivocally by single-crystal X-ray analyses, complexes 8 and 9 were characterised by NMR spectroscopy. Contrary to what is normally presumed, the scaffolds of six-membered metallic wheels are not generally rigid, but rather undergo nondissociative topomerisation processes. This was shown by variable temperature (VT) (1)H NMR spectroscopy for the indium wheel [In(6)Cl(6)(L(1))(6)] (5) and is highlighted for the enantiotopomerisation of one indium centre [ 1/6[S(6)-5]<==>[1/6[S(6)-5']]. The self-assembly of metallic wheels, starting from diethanolamine dendrons, is an efficient strategy for the convergent synthesis of metallodendrimers. 相似文献
55.
Cayuela E Jalón FA Manzano BR Espino G Weissensteiner W Mereiter K 《Journal of the American Chemical Society》2004,126(22):7049-7062
Diastereomerically pure complexes of formula CpRuCl(PP) and CpRuH(PP) with chiral ferrocenyl diphosphines were prepared and the selectivity of proton-transfer processes over the monohydride compounds with different acids was studied. With 1 equiv of HBF(4) the cis-dihydrogen and trans-dihydride complexes were formed while with 3 equiv of CF(3)CO(2)H the trans-dihydride derivative was the only product. However, the use of 1 equiv of CF(3)CO(2)H led to a dihydrogen bonded complex with an extremely short RuH...HO(2)CF(3) interaction that exhibits proton-hydride exchange. Using the labeled acid CF(3)CO(2)D, a stereoselective transference of the deuteron was demonstrated that implies the previous epimerization of the monohydride and the subsequent attack of the acid in the position previously occupied by the hydride. 相似文献
56.
Tilson JL Naleway C Seth M Shepard R Wagner AF Ermler WC 《The Journal of chemical physics》2004,121(12):5661-5675
A valence full configuration interaction study with a polarized double-zeta quality basis set has been carried out for the lowest 49 electronic states of AmCl(+). The calculations use a pseudopotential treatment for the core electrons and incorporate a one-electron spin-orbit interaction operator. Electrons in the valence s, p, d, and f subshells were included in the active space. The resulting electronic potential energy curves are largely repulsive. The chemical bonding is ionic in character with negligible participation of 5f electrons. The molecular f-f spectroscopy of AmCl(+) arises essentially from an in situ Am(2+) core with states slightly redshifted by the presence of chloride ion. Am(+)+Cl asymptotes which give rise to the few attractive potential energy curves can be predicted by analysis of the f-f spectroscopy of isolated Am(+) and Am(2+). The attractive curves have substantial binding energies, on the order of 75-80 kcal/mol, and are noticeably lower than recent indirect measurements on the isovalent EuCl(+). An independent empirical correlation supports the predicted reduction in AmCl(+) binding energy. The energies of the repulsive curves are strongly dependent on the selection of the underlying atomic orbitals while the energies of the attractive curves do not display this sensitivity. The calculations were carried out using our recently developed parallel spin-orbit configuration interaction software. 相似文献
57.
Hubert A Popp P Wenzel KD Engewald W Schüürmann G 《Analytical and bioanalytical chemistry》2003,376(1):53-60
A new one-step cleanup procedure, based on size-exclusion chromatography (SEC), usable for the extracts from accelerated solvent extraction (ASE), Soxhlet extraction, or ultrasonic extraction (USE), is described. The method is suitable for the determination of polycyclic aromatic hydrocarbons (PAHs), especially from very complicated plant matrices (e.g. pine needles, deciduous leaves, mosses). The main improvement compared with previous conventional procedures is that analyte peaks barely overlap with matrix peaks in the chromatograms and that it is a very rapid and simple one-step procedure with clearly improved analytical performance. Essential advantages of this SEC procedure are the sharper GC-MS chromatograms for the PAH fraction at retention times between 9.2 and 12.0 min, distinctly separated substance peaks resulting in better analysis, shorter running times, and lower solvent consumption. 相似文献
58.
59.
Bhattarai KM Davis AP Perry JJ Walter CJ Menzer S Williams DJ 《The Journal of organic chemistry》1997,62(24):8463-8473
The macrocyclic "cholaphanes" 3a-c were synthesized from the inexpensive steroid cholic acid. Like earlier relatives they feature substantial cavities with inward-directed hydroxyl groups, suitable for binding polar molecules such as carbohydrates in nonpolar media. New features are the externally directed alkyl chains, promoting solubility in organic solvents, and (in the case of 3b/c) reduced conformational freedom resulting from truncation of the steroidal side-chain. In particular, modeling shows that the smallest macrocycle 3c possesses very little flexibility, preferring an open conformation which is also revealed in the X-ray crystal structure of its pentahydrate. NMR studies indicated that all three cholaphanes form 1:1 complexes with octyl beta-D-glucoside in CDCl(3), with K(a) = 600-1560 M(-)(1). Cholaphanes 3b/c proved able to extract methyl beta-D-glucoside from aqueous solutions into CHCl(3). The transport of methyl beta-D-glucoside across a chloroform barrier was also demonstrated for 3c. 相似文献
60.
Marius Rebek Josef Schurz Walter Stöger Wolfgang Popp 《Monatshefte für Chemie / Chemical Monthly》1969,100(2):532-539
Zusammenfassung Die vorliegende Arbeit stellt eine Beschreibung von Experimenten dar, die die Erhöhung der Pfropfbereitschaft von trägen Komponenten durch Beimischung von aktiveren zum Ziele hatten.Das Trägermolekül war in allen Fällen Cellulose in Form von hochgradig gereinigtem Zellstoff. Durch die Verwendung von Mischsystemen aus Styrol und Methylmethacrylat gelang es, das trägere Styrol in bedeutend größerer Menge auf die Cellulose aufzupfropfen, als es bei Abwesenheit des aktiven Methylmethacrylats der Fall war.
Nach einem Vortrag, den der erstgenannte der Autoren im Rahmen der Arbeitstagung des Vereins Österreichischer Chemiker am 27. September 1968 in Wien gehalten hat. 相似文献
Grafting Polymerization of Cellulose with Two Vinyl Monomers
This paper describes experiments to increase the grafting of cellulose with components of poor reactivity by mixing them with highly reactive ones. A highly purified wood pulp was used as backbone. Using combinations of styrene and methyl methacrylate it was possible to graft considerably higher amounts of the poorly reacting styrene than in the absence of the highly reactive methyl methacrylate.
Nach einem Vortrag, den der erstgenannte der Autoren im Rahmen der Arbeitstagung des Vereins Österreichischer Chemiker am 27. September 1968 in Wien gehalten hat. 相似文献