全文获取类型
收费全文 | 699篇 |
免费 | 16篇 |
国内免费 | 2篇 |
专业分类
化学 | 498篇 |
晶体学 | 12篇 |
力学 | 25篇 |
数学 | 102篇 |
物理学 | 80篇 |
出版年
2019年 | 6篇 |
2016年 | 15篇 |
2015年 | 14篇 |
2014年 | 15篇 |
2013年 | 40篇 |
2012年 | 32篇 |
2011年 | 52篇 |
2010年 | 25篇 |
2009年 | 28篇 |
2008年 | 26篇 |
2007年 | 17篇 |
2006年 | 30篇 |
2005年 | 19篇 |
2004年 | 12篇 |
2003年 | 12篇 |
2002年 | 15篇 |
2001年 | 11篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1998年 | 12篇 |
1996年 | 17篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1989年 | 7篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1975年 | 5篇 |
1972年 | 4篇 |
1970年 | 4篇 |
1968年 | 7篇 |
1966年 | 11篇 |
1931年 | 4篇 |
1930年 | 6篇 |
1929年 | 8篇 |
1928年 | 14篇 |
1927年 | 11篇 |
1925年 | 5篇 |
1908年 | 4篇 |
1893年 | 6篇 |
1890年 | 4篇 |
1888年 | 5篇 |
1887年 | 4篇 |
1884年 | 5篇 |
1883年 | 8篇 |
1882年 | 4篇 |
排序方式: 共有717条查询结果,搜索用时 15 毫秒
1.
2.
3.
Stulz E Scott SM Ng YF Bond AD Teat SJ Darling SL Feeder N Sanders JK 《Inorganic chemistry》2003,42(20):6564-6574
The synthesis of linear multiporphyrin arrays with mono- and bisphosphine-substituted porphyrins as ligand donors and ruthenium(II) or rhodium(III) porphyrins as ligand acceptors is described. With appropriate amounts of the building blocks mixed, linear dimeric and trimeric arrays have been synthesized and analyzed by (1)H NMR and (31)P NMR spectroscopy. The Ru/Rh acceptor porphyrins can be located either at the periphery or in the center of the array. Likewise, the monophosphine porphyrins can be positioned at the periphery, thus allowing a high degree of freedom in the overall composition of the arrays. This way, both donor and acceptor porphyrins can act as chain extenders or terminators. One of the trimeric complexes with two nickel and one ruthenium porphyrin has also been analyzed by X-ray crystallography. Attempts have also been made to synthesize higher order arrays by mixing appropriate amounts of the porphyrins; however, from the NMR data it cannot be concluded if monodisperse five, seven, or nine porphyrin arrays are present or if the solutions are composed of a statistical mixture of smaller and larger arrays. 相似文献
4.
S. G. Wang Y.X. Qiu E. Neumann H. J. Deiseroth W. H. Eugen Schwarz 《无机化学与普通化学杂志》2003,629(10):1718-1730
About 60 molecular species composed of up to 10 mercury atoms and of oxygen atoms and/or of some other elements or groups (such as halogen, OH2, OH, H, alkali, NO3) have been investigated quantum chemically. Different density functional approaches and the ab initio SCF‐MP2 method were applied, comparing different basis sets and different atomic core sizes. It is important not to treat the Hg 5s, p, d as inactive core shells, and to use sufficiently many polarization functions. The shape of the 〉O‐Hg‐Hg‐O〈 units is not favorable concerning the formation of lattices composed of HgI, O and OH only. Despite its bulkiness, the OHgHgO units can easily come into contact with each other and then disproportionate. This is prevented in the so‐called ternary M‐HgI oxides by the embedded oxometallate (oxoacidic) anions. Furthermore, the HgI and HgII oxide bond energies are less favorable towards the stability of HgI oxo compounds, as compared to Hg halidic or oxoacidic compounds. Both points are not promising concerning the search for HgI oxides/hydroxides, although the preparation of such compounds, including spacer groups, by topochemical reactions can still not be excluded. So far, experimental efforts towards the synthesis of such a new class of compounds have only demonstrated that HgII is strictly preferred over HgI in the formation of solids of binary Hg‐O or ternary A‐Hg‐O composition (A = electropositive metal such as alkali, in contrast to M = transition or semi‐metal). This is so even if compounds containing ‘electron rich Hgδ— atoms’ (i.e. A‐Hg amalgams) are oxidized under mild conditions. 相似文献
5.
Fenesan I Popescu R Supuran CT Nicoara S Culea M Palibroda N Moldovan Z Cozar O 《Rapid communications in mass spectrometry : RCM》2001,15(9):721-729
This work discusses the synthesis and the fragmentation patterns for 2-(p-acetylaminosulfonamido)-2-thiono-(5,5-dimethyl-1,3,2-dioxaphosphorinane)(1) and for the p-acetylaminosulfonylamides of O,O-diethylthiophosphoric acid (2), O,O-diphenylthiophosphoric acid (3), dimethylaminocyclohexylthiophosphoric acid (4), and diethylaminophenylthiophosphoric acid (5). A thionamidic-thiolimidic structure was attributed to compounds 1-5, consistent with their IR and NMR spectra. EI mass spectra at 70 eV, high resolution (HR) mass measurements and metastable ion spectra were used to elucidate the fragmentation processes and to determine the kinetic energy release values associated with the metastable ion dissociations. HR accurate mass measurements were used to confirm the compositions of the more abundant ions. 相似文献
6.
M. Culea I. Fenesan S. Cobzac S. Gocan M. Chiriac N. Palibroda 《Fresenius' Journal of Analytical Chemistry》1996,355(5-6):748-749
A method for the determination of trace levels of triazines and organophosphorus pesticides in water is presented. The extraction method is based on a solid-phase extraction on C-18 bound silica SPE cartridges. A precolumn filled with Merck C-18 bound silica and home-made C-18 bound silica have been tested at a flow-rate of 3 ml/min with comparable preconcentration yields. A SIM-MS method using a 15N labelled internal standard has been developed for the organophosphorus pesticides. Detection limits lower than 1 g/L have been obtained. Separations have been carried out on a conventional GC column OV 17 (1 m) and a capillary column OV 17 (25 m) with a temperature program from 150° C (2 min) to 300° C (rate of 6° C/min). 相似文献
7.
Electron attachment spectroscopy is employed to study the formation of negative ions from the chloroethylenes. It is found that the resonances recently observed in the total electron scattering cross section are predominantly associated with the formation of Cl?. Only in tetrachloroethylene is a long-lived parent negative ion observed. 相似文献
8.
Gerald Kainz und Eugen Wachberger 《Fresenius' Journal of Analytical Chemistry》1966,222(2):278-282
Zusammenfassung Zur Bestimmung des Sauerstoffs wird die organische Probe in Helium-Atmosphäre gecrackt; die sauerstoffhaltigen Crackprodukte werden über Kohle zu Kohlenmonoxid konvertiert. Um das Kohlenmonoxid von den übrigen Crackprodukten, wie H2, N2 und CH4 abzutrennen, wird es zu Kohlendioxid oxydiert und danach an einem Molekularsieb bei 20° C durch Adsorption zurückgehalten; H2, N2 und CH4 werden aus der Apparatur gespült. Sobald in der Probeleitung reines Spülgas auftritt, wird das adsorbierte Kohlendioxid durch Erhitzen desorbiert und im Detektor gemessen.
Es ist uns eine angenehme Pflicht, der Shell Austria AG., Wien, insbesondere Herrn Direktor Dipl.-Ing. R. Wallner, für die Gewährung eines Forschungsstipendiums an den einen von uns (E. W.) ergebenst zu danken. 相似文献
Summary For the determination of oxygen the organic sample is cracked in helium atmosphere. Cracking products, containing oxygen, are converted to carbon monoxide by coal. For separation from the remaining cracking products (H2, N2, CH4) carbon monoxide is oxidized and then adsorbed on molecular sieve 5A at 20°C; H2, N2 and CH4 are flushed out. As soon as pure carrier gas flows through the sample pipe, carbon dioxide is desorbed by heating the molecular sieve and flushed to the detector.
Es ist uns eine angenehme Pflicht, der Shell Austria AG., Wien, insbesondere Herrn Direktor Dipl.-Ing. R. Wallner, für die Gewährung eines Forschungsstipendiums an den einen von uns (E. W.) ergebenst zu danken. 相似文献
9.
W. H. Eugen Schwarz 《Theoretical chemistry accounts》1968,11(5):377-384
Zusammenfassung Anionen der ersten und neutrale Atome der zweiten Familie des Periodensystems wurden nach dem Kombinierten Näherungsverfahren (KN) mit einem Hellmann-Potential behandelt. Die Fehler in der Hartree-Fock-Energie kompensieren sich auf unter 0.1 eV, ebenso genau wird die Intrahüllenkorrelationsenergie erhalten. Auf Grund der gewonnenen Rechenergebnisse sind als wahrscheinlichste Werte der Elektronenaffinitäten der einwertigen Metalle (in eV) anzusehen: Li 0.63, Na 0.54, K 0.52, Rb 0.50, Cu 1.0.
Die Arbeit wurde auf Wunsch des Autors erst jetzt veröffentlicht. 相似文献
Hellmann's pseudopotential method
Neutral atoms of the second and negative ions of the first family of the periodic system are treated by Hellmann's pseudopotential method (Kombiniertes Näherungsverfahren, KN). The various errors inherent in this method compensate to a large degree so that the errors in the Hartree-Fock and correlation energies will be below 0.1 eV. The electron affinities of the first family atoms are calculated as 0.63 eV for Li, 0.54 for Na, 0.52 for K, 0.50 for Rb, and 1.0 for Cu.
Résumé Des anions du premier groupe et des atoms neutres du deuxième groupe du système périodique sont traités à l'aide de la méthode Kombiniertes Näherungsverfahren (KN) avec une potential de Hellmann. Les erreurs dans l'énergie SCF se compensent au dessous 0,1 eV, de la même exactitude on obtient l'énergie de correlation de la couche de valence. D'aprés les resultats du calcul on peut accepter les valeurs suivantes comme les plus probables pour les affinités électroniques dans les metaux monovalents (en eV): Li 0,63, Na 0,54, K 0,52, Rb 0,50, Cu 1,0.
Die Arbeit wurde auf Wunsch des Autors erst jetzt veröffentlicht. 相似文献
10.
Design, synthesis, and binding affinities of pyrrolinone-based somatostatin mimetics 总被引:1,自引:0,他引:1
Smith AB Charnley AK Mesaros EF Kikuchi O Wang W Benowitz A Chu CL Feng JJ Chen KH Lin A Cheng FC Taylor L Hirschmann R 《Organic letters》2005,7(3):399-402
[structure: see text] Tetrapyrrolinone somatostatin (SRIF) mimetics (cf. 1), based on a heterochiral (D,L-mixed) pyrrolinone scaffold, were designed, synthesized, and evaluated for biological activity. The iterative synthetic sequence, incorporating the requisite functionalized coded and noncoded amino acid side chains, comprised a longest linear synthetic sequence of 23 steps. Binding affinities at two somatostatin receptor subtypes (hsst 4 and 5) reveal micromolar activity, demonstrating that the d,l-mixed pyrrolinone scaffold can be employed to generate functional mimetics of peptide beta-turns. 相似文献