全文获取类型
收费全文 | 2671篇 |
免费 | 71篇 |
国内免费 | 9篇 |
专业分类
化学 | 1734篇 |
晶体学 | 5篇 |
力学 | 41篇 |
数学 | 417篇 |
物理学 | 554篇 |
出版年
2023年 | 19篇 |
2022年 | 39篇 |
2021年 | 70篇 |
2020年 | 62篇 |
2019年 | 73篇 |
2018年 | 71篇 |
2017年 | 41篇 |
2016年 | 90篇 |
2015年 | 58篇 |
2014年 | 92篇 |
2013年 | 122篇 |
2012年 | 152篇 |
2011年 | 165篇 |
2010年 | 98篇 |
2009年 | 106篇 |
2008年 | 112篇 |
2007年 | 106篇 |
2006年 | 98篇 |
2005年 | 98篇 |
2004年 | 71篇 |
2003年 | 63篇 |
2002年 | 65篇 |
2001年 | 24篇 |
2000年 | 26篇 |
1999年 | 37篇 |
1998年 | 20篇 |
1997年 | 21篇 |
1996年 | 16篇 |
1995年 | 28篇 |
1994年 | 16篇 |
1993年 | 24篇 |
1992年 | 21篇 |
1991年 | 20篇 |
1989年 | 18篇 |
1984年 | 16篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1979年 | 22篇 |
1978年 | 19篇 |
1977年 | 19篇 |
1976年 | 21篇 |
1975年 | 20篇 |
1974年 | 12篇 |
1967年 | 12篇 |
1957年 | 13篇 |
1956年 | 18篇 |
1955年 | 11篇 |
1954年 | 14篇 |
1927年 | 11篇 |
1907年 | 11篇 |
排序方式: 共有2751条查询结果,搜索用时 15 毫秒
11.
Zusammenfassung Bei der Chlorierung von 2,4,6-Trimethylborazin konnten unter anderen Reaktionsprodukten 2,4,6-Tris(dichlormethyl)-und 2,4,6-Tris(trichlormethyl)borazin erhalten werden. Weitergehende Chlorierung führt zum 2,4,6-Trichlorborazin. Bei der Chlorierung von 2,4,4,6,6-Pentamethyl-biborazinyl-(1,2) verläuft der Abbau der Verbindung rasch bis zum 2,4,6-Trichlorborazin. Bei der Chlorierung von 1,3,5-Trimethyl-2,4,6-trichlorborazin konnte eines der Reaktionsprodukte als 1,3-Bis(dichlorcarbo)-2,4-bis(dichlor)cyclodiborazan charakterisiert werden.
Chlorination of 2,4,6-trimethylborazine leads to 2,4,6-tris-(dichloromethyl)-and 2,4,6-tris(trichloromethyl)borazine and finally to 2,4,6-trichloroborazine. Several other intermediates have been identified by mass spectrometry. Chlorination of 2,4,4,6,6-pentamethyl-biborazinyl-1,2 readily yields 2,4,6-trichloroborazine. Amongst the chlorination products of 1,3,5-trimethyl-2,4,6-trichloroborazine 1,3-bis(dichlorcarbo)-2,4-bis (dichlor)cyclodiborazane has been identified.相似文献
12.
Uwe Klingebiel Peter Werner Anton Meller 《Monatshefte für Chemie / Chemical Monthly》1976,30(6):939-943
The reaction of RSiCl3 (R=CH3, C2H5, C6H5) and R2SiCl2 (R=CH3) with one mole of the phosphenimidous amides R2N–P=NR [R=R=Si(CH3)3; R=Si(CH3)3, R=C(CH3)3] yieds a four membered PN2Si-ring system under elimination of (CH3)3SiCl. 相似文献
13.
Eugen Jóna Marian Koman Anton Sirota 《Journal of inclusion phenomena and macrocyclic chemistry》1998,30(1):1-12
The stoichiometry and spectral properties of [Ni(4-Etpy)4(NCS)2]nG clathrates have been studied where n = 2 for G = 1-BrN (N = naphthalene), n = 1 or 2 for G = 1-MeN, and n = 0.5 for 2-MeN and 2-BrN. The complexes under study show electronic absorption spectra typical of an octahedral environment of the Ni(II) central atom. The differences found in IR spectra for the (CN) and (Ni–-NNCS) vibrations are discussed. The crystal structure of [Ni(4-Etpy)4(NCS)2]1-MeN was determined by X-ray diffraction and refined to R = 0.0586. Discrete non-centrosymmetric [Ni(4-Etpy)4(NCS)2] molecules form layers of a host structure and the space between the layers is occupied by 1-MeN. The relationship between interatomic distances in the host complex of similar clathrates are discussed. 相似文献
14.
Alexander Meller 《Monatshefte für Chemie / Chemical Monthly》1956,87(4):491-497
Zusammenfassung Eine logarithmische Geschwindigkeitsgleichung für Chemisorption wird abgeleitet und ihre begrenzte Gültigkeit erläutert. Die umfangreiche Anwendbarkeit, dieTaylor undThon
1 der logarithmischen Gleichung zuschreiben, wird überprüft und es ergibt sich, daß diese Gleichung nur eine annähernde und begrenzte Gültigkeit und Anwendbarkeit im Gebiete der Chemisorption von Gasen an Festkörperoberflächen besitzt.Bei manchen Adsorptionsvorgängen dürfte sich der geschwindigkeitsbestimmende Mechanismus im Laufe des Versuchsgeschehens ändern. Diesem Einfluß müßte aber Rechnung getragen werden, wenn Geschwindigkeitsgleichungen abzuleiten sind.Mit 2 Abbildungen 相似文献
15.
Uwe Klingebiel Dieter Bentmann Anton Meller 《Journal of organometallic chemistry》1978,144(3):381-388
Aminofluorsilanes are obtained by the reaction of fluorosilanes with the lithium salts of the corresponding amines. The reaction of aminofluorosilanes with butyllithium in a (2 + 2)cyclo addition reaction leads to the formation of fourmembered silicon-nitrogen ring compounds. The mechanism of the reaction is discussed, the mass, 1H and 19F NMR spectra of the compounds are reported. 相似文献
16.
We establish a previously conjectured connection betweenp-adics and quantum groups. We find in Sklyanin's two parameter elliptic quantum algebra and its generalizations, the conceptual basis for the Macdonald polynomials, which interpolate between the zonal spherical functions of related real andp-adic symmetric spaces. The elliptic quantum algebras underlie theZ
n
-Baxter models. We show that in then limit, the Jost function for the scattering offirst level excitations in the 1+1 dimensional field theory model associated to theZ
n
-Baxter model coincides with the Harish-Chandra-likec-function constructed from the Macdonald polynomials associated to the root systemA
1. The partition function of theZ
2-Baxter model itself is also expressed in terms of this Macdonald-Harish-Chandrac-function, albeit in a less simple way. We relate the two parametersq andt of the Macdonald polynomials to the anisotropy and modular parameters of the Baxter model. In particular thep-adic regimes in the Macdonald polynomials correspond to a discrete sequence of XXZ models. We also discuss the possibility of q-deforming Euler products.Work supported in part by the NSF: PHY-9000386 相似文献
17.
18.
Abstract— Three covalently-linked porphyrin hybrid dimers were synthesized, each containing a metallotetraarylporphyrin [Zn(II), Cu(II), or Ni(II)], and a free base tetraarylporphyrin. Transfer of singlet excitation energy from the metalloporphyrin center to the free base porphyrin center was determined by measuring fluorescence properties. The Zn hybrid dimer displayed excellent intramolecular transfer of energy ( 85%) from the excited singlet state of the Zn(II) chromophore to the free base chromophore. No evidence for such transfer of the excited singlet state energy was found in the Ni(II) or Cu(II) analogues. From our experimental data, the fluorescence quantum yield of the Zn hybrid dimer was the same as for the free base monomer porphyrin (0.11; Seybold and Gouterman, 1969). Thus, the covalent attachment of another fluorescent porphyrin center effectively doubled the antenna size without decreasing the quantum yield even though the fluorescence quantum yield of the Zn(II) containing monomer was substantially less (0.03, according to Seybold and Gouterman, 1969) than that of the free base porphyrin. The donor-acceptor distance and the rate constant for energy transfer were calculated using the Forster equation. Assuming random orientation, a donor-acceptor distance of 15 Å was calculated with an associated rate constant (kci) for energy transfer of 1.9 ± 109 s–1. 相似文献
19.
Olga Bakulina Anton Bannykh Ekaterina Levashova Mikhail Krasavin 《Molecules (Basel, Switzerland)》2022,27(12)
Screening of a library of novel N-hydroxylactams amenable by the Castagnoli-Cushman reaction identified four lead compounds that facilitated 55Fe transport into P. aeruginosa cells (one of these synthetic siderophores was found to be as efficient at promoting iron uptake as the natural siderophores pyoverdine, pyochelin or enterobactin). Conjugates of the four lead siderophores with ciprofloxacin were tested for antibacterial activity against P. aeruginosa POA1 (wild type) and the ∆pvdF∆pchA mutant strain. The antibacterial activity was found to be pronounced against the ∆pvdF∆pchA mutant strain grown in CAA medium but not for the POA1 strain. This may be indicative of these compounds being ‘Trojan horse’ antibiotics. Further scrutiny of the mechanism of the antibacterial action of the newly developed conjugates is warranted. 相似文献
20.
We study the Hopfield model of an autoassociative memory on a random graph onN vertices where the probability of two vertices being joined by a link isp(N). Assuming thatp(N) goes to zero more slowly thanO(1/N), we prove the following results: (1) If the number of stored patternsm(N) is small enough such thatm(N)/Np(N) 0, asN, then the free energy of this model converges, upon proper rescaling, to that of the standard Curie-Weiss model, for almost all choices of the random graph and the random patterns. (2) If in additionm(N) < ln N/ln 2, we prove that there exists, forT< 1, a Gibbs measure associated to each original pattern, whereas for higher temperatures the Gibbs measure is unique. The basic technical result in the proofs is a uniform bound on the difference between the Hamiltonian on a random graph and its mean value. 相似文献