全文获取类型
收费全文 | 2706篇 |
免费 | 41篇 |
国内免费 | 9篇 |
专业分类
化学 | 1882篇 |
晶体学 | 11篇 |
力学 | 42篇 |
数学 | 575篇 |
物理学 | 246篇 |
出版年
2016年 | 34篇 |
2015年 | 34篇 |
2014年 | 35篇 |
2013年 | 105篇 |
2012年 | 56篇 |
2011年 | 76篇 |
2010年 | 43篇 |
2009年 | 70篇 |
2008年 | 88篇 |
2007年 | 65篇 |
2006年 | 77篇 |
2005年 | 86篇 |
2004年 | 79篇 |
2003年 | 67篇 |
2002年 | 70篇 |
2001年 | 61篇 |
2000年 | 49篇 |
1999年 | 25篇 |
1998年 | 38篇 |
1997年 | 48篇 |
1996年 | 45篇 |
1995年 | 34篇 |
1994年 | 50篇 |
1993年 | 44篇 |
1992年 | 46篇 |
1991年 | 36篇 |
1990年 | 42篇 |
1989年 | 59篇 |
1988年 | 65篇 |
1987年 | 64篇 |
1986年 | 30篇 |
1985年 | 47篇 |
1984年 | 49篇 |
1983年 | 25篇 |
1982年 | 45篇 |
1981年 | 48篇 |
1980年 | 67篇 |
1979年 | 49篇 |
1978年 | 49篇 |
1977年 | 32篇 |
1976年 | 32篇 |
1975年 | 49篇 |
1974年 | 40篇 |
1973年 | 45篇 |
1972年 | 33篇 |
1971年 | 35篇 |
1970年 | 32篇 |
1969年 | 19篇 |
1967年 | 27篇 |
1966年 | 23篇 |
排序方式: 共有2756条查询结果,搜索用时 15 毫秒
61.
62.
Horst Weitkamp und Friedhelm Korte 《Fresenius' Journal of Analytical Chemistry》1964,204(4):245-263
Zusammenfassung Die Spin-Spin-Kopplungskonstanten der olefinischen Protonen mit dem 31P sowie die Feinstruktur der 1H-NMR-Spektren sind charakteristisch für die Lage der Doppelbindung. Vielfach kann auch die Intensität der
C=C-Schwingung im IR zur Bestimmung der Doppelbindungslage benutzt werden. Massenspektren geben nur in Ausnahmefällen Hinweise, können jedoch zur exakten Bestimmung des Molekulargewichts dienen.
Die Ausführung der Untersuchungen erfolgte unter Mitarbeit von Herrn F. Dlugosch, Herrn H. Au und Fräulein R. Barth.
Herrn Dr. C. A. Reilly, Shell-Development Company, Emeryville, USA, danken wir für die Überlassung getesteter Programmkartensätze zur Berechnung der NMR-Spektren. 相似文献
Summary The spin-spin coupling constants of the olefinic protons with the phosphorus-31 as well as the fine structure of the nmr-spectra are characteristic for the position of the double bond. In the infrared, the intensity of the C=C-frequency may often serve as indication of the position of the double bond. The applicability of mass spectra is limited to a small number of compounds. They may be used, however, for an accurate determination of the molecular weight.
Die Ausführung der Untersuchungen erfolgte unter Mitarbeit von Herrn F. Dlugosch, Herrn H. Au und Fräulein R. Barth.
Herrn Dr. C. A. Reilly, Shell-Development Company, Emeryville, USA, danken wir für die Überlassung getesteter Programmkartensätze zur Berechnung der NMR-Spektren. 相似文献
63.
Fluorescence resonance energy transfer has been studied between lanthanide(III) chelates as donors and protein-coupled CdTe semiconductor nanoparticles as acceptors. Wide excitation spectra and large Stokes shift of semiconductor nanoparticles and timeresolved fluorescence detection were shown to provide a combination for successful energy transfer assay. Different intrinsically fluorescent europium(III) and terbium(III) chelates coupled to single biotin molecules were studied for optimal energy transfer with streptavidin labeled semiconductor nanoparticles. No significant differences between the studied chelates were observed. The strength of the methodology was demonstrated in a clinically relevant competitive and separation-free immunoassay of estradiol, where subnanomolar limit of detection was achieved with the coefficient of variation 2-11%. The data suggested that relatively short distance was needed to obtain adequate energy transfer. Therefore, biomolecules were coupled onto the semiconductor nanoparticles without any spacers. 相似文献
64.
Horst Schneider Gerd T. Puchta Franz A. R. Kaul Gabriele Raudaschl-Sieber Frdric Lefebvre Guillaume Saggio Dimitrios Mihalios Wolfgang A. Herrmann Jean Marie Basset 《Journal of molecular catalysis. A, Chemical》2001,170(1-2):127-141
The modification of a mesoporous silica surface with Si(Ind)(CH3)2Cl and the immobilization of CpZr(NMe2)3 on this surface was studied via IR-spectroscopy. To reduce side reactions, the indenyl-modified silica was reacted with hexamethyldisilazane (HMDS) under IR-control before the CpZr(NMe2)3-immobilization. The role of the hydroxyl group protection with HMDS is discussed. The surface modifications have been repeated via Schlenk technique at the same conditions and the surface modifications were studied with 13C CP MAS–NMR, 1H MAS–NMR, elemental-, SEM- and BET-analysis. The surface species of the resulting catalysts are discussed. The precatalysts have been treated with methylaluminoxane (MAO) (Al:Zr (mol:mol)=500:1) and the resulting Zr contents (leaching-effect) are discussed. All catalysts have been tested in ethylene and propylene polymerization. 相似文献
65.
Rusina O Eremenko A Frank G Strunk HP Kisch H 《Angewandte Chemie (International ed. in English)》2001,40(21):3993-3995
66.
Terrettaz S Ulrich WP Guerrini R Verdini A Vogel H 《Angewandte Chemie (International ed. in English)》2001,40(9):1740-1743
67.
LiSr2[ReN4] and LiBa2[ReN4] – isotypic Nitridorhenates(VII) The quaternary nitridorhenates(VII) LiAE2[ReN4] (AE = Sr, Ba) were synthesized by reaction of the metals with molecular nitrogen at 850–900 °C. The plate‐like, nearly colourless crystals were investigated by X‐ray single crystal methods and were identified as isotypic phases: LiSr2[ReN4] (LiBa2[ReN4]); monoclinic, P21/m; a = 614.64(8) pm (651.04(12) pm), b = 585.97(6) pm (b = 598.86(9) pm), c = 689.70(17) pm (737.43(5) pm), β = 106.375(4)° (108.535(2)°); Z = 2. Crystals of the strontium compound were systematically twinned along [001]. In the crystal structures of the quaternary compounds the alkaline earth‐ and nitride‐ ions are arranged in the motif of the InNi2‐type structure. Strontium and barium are in a trigonal prismatic coordination by nitrogen (Sr–N: 261.0(7)–284.3(4) pm; Ba–N: 278.0(7)–303.0(6) pm). One half of the tetrahedral voids within the partial structure formed by stacking of trigonal prismatic rod layers is occupied by rhenium (formation of [ReVIIN4]5–‐tetrahedra; Re–N: 181.0(6)–184.5(8) pm), lithium takes the positions of the remaining tetrahedral sites (Li–N: 2 × 198(1) pm, 224(2) pm and 228(2) pm for the strontium phase). In the barium compound the lithium positions show a larger shift from the tetrahedral centres towards a tetrahedral plane (Li–N: 2 × 195(1) pm, 213(2) pm and 304(2) pm). 相似文献
68.
69.
70.
Na5AlF2(PO4)2: Synthesis, Crystal Structure and Ionic Conductivity Two different procedures (precipitation from aqueous solution and solid state reaction) for the synthesis of hitherto unknown Na5AlF2(PO4)2 were optimized. The crystal structure was determined using diffractometer data (P3 , a = b = 10.483(1), c = 6.607(1) Å, MoKα, 1080 independent reflections, Rw = 0.025). PO4-tetrahedra and AlO4F2-“octahedra” are connected via common vertices forming a twodimensionally extended heteropolyanion. Sodium is located in interconnected spacings of the [AlF2(PO4)2]-part of the structure. Ionic conductivity as expected because of these structural features was affirmed experimentally. 相似文献