全文获取类型
收费全文 | 689篇 |
免费 | 9篇 |
国内免费 | 7篇 |
专业分类
化学 | 474篇 |
晶体学 | 6篇 |
力学 | 9篇 |
数学 | 52篇 |
物理学 | 164篇 |
出版年
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 12篇 |
2015年 | 9篇 |
2014年 | 22篇 |
2013年 | 45篇 |
2012年 | 31篇 |
2011年 | 43篇 |
2010年 | 15篇 |
2009年 | 24篇 |
2008年 | 42篇 |
2007年 | 49篇 |
2006年 | 44篇 |
2005年 | 41篇 |
2004年 | 32篇 |
2003年 | 49篇 |
2002年 | 28篇 |
2001年 | 8篇 |
2000年 | 18篇 |
1999年 | 14篇 |
1998年 | 10篇 |
1997年 | 11篇 |
1996年 | 9篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1973年 | 4篇 |
1965年 | 2篇 |
1964年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有705条查询结果,搜索用时 15 毫秒
131.
132.
Toshiyuki Taniuchi Hiroshi Kumigashira Masato Kubota Takanori Wakita Takanori Yokoya Kanta Ono Masaharu Oshima Mikk Lippmaa Hideomi Koinuma 《Surface science》2007,601(20):4690-4693
We have used photoelectron emission microscopy (PEEM) and X-ray magnetic circular dichroism (XMCD) to study the effect of thin film thickness on the magnetic domain formation in La0.6Sr0.4MnO3 samples that were epitaxially grown on stepped SrTiO3 (0 0 1) substrates. The magnetic image exhibited a stripe structure elongated along the step direction, irrespective of film thickness, suggesting that uniaxial magnetic anisotropy induced by step-and-terrace structures plays an important role in the magnetic domain formation. Additional domains evolved gradually with increasing film thickness. In these domains, the direction of magnetization differed from the step direction due to biaxial magneto-crystalline anisotropy. The evolution of additional magnetic domains with increasing film thickness implies that a competition exists between the two anisotropies in LSMO films. 相似文献
133.
HBr+ (A2Σ+-X2Πi) and DBr+ (A2Σ+-X2Πi) emissions are found up to v′=1 and v′=2, respectively, from the thermal energy charge transfer reactions of Ar+ with HBr and DBr molecules in a flowing afterglow apparatus. Both A-state vibrational distributions have a peak at the lowest vibrational level, which are inconsistent with those expected from the energy resonance and/or Franck-Condon factors for ionization. This discrepancy is explained in terms of the distortion of target molecules by approach of reactant ions. Both A-state rotational distributions show that energies partitioned into rotation decrease with increasing vibrational levels, whereas the internal energy is nearly constant for all vibrational levels. The vibrational and rotational distributions obtained suggest that the reaction occurs at a relatively short distance and the product has a broad translational energy distribution. 相似文献
134.
135.
Susumu Ohira Hiroyuki Fujiwara Kiyomi Maeda Masaharu Habara Naomi Sakaedani Megumi Akiyama Atsuhito Kuboki 《Tetrahedron letters》2004,45(8):1639-1641
All diastereomers of pentenocin B, an inhibitor of interleukin-1β converting enzyme produced by Trichoderma hamatum FO-6903, were synthesized in chiral forms starting from l-threonine. Absolute configurations of natural pentenocin B were clarified to be 4S, 5R, and 6R. 相似文献
136.
Takehiko Nishio Megumi Tabata Hiroyuki Koyama Masami Sakamoto 《Helvetica chimica acta》2005,88(1):78-86
The photochemical reactions of various ‘N‐methacryloyl acylanilides’ (=N‐(acylphenyl)‐2‐methylprop‐2‐enamides) have been investigated. Under irradiation, the acyl‐substituted anilides 1a – 1c and 1o afforded exclusively the corresponding quinoline‐based cyclization products of type 2 (Table 1). In contrast, irradiation of the benzoyl (Bz)‐substituted anilides 1e – 1h afforded a mixture of the open‐chain amides 4e – 4h and the cyclization products 2e – 2h . Irradiation of the para‐acyl‐substituted anilides 6a – 6e and 6h afforded the corresponding quinoline‐based cyclization products of type 5 as the sole products (Table 2). The formation of the cyclization products 2a – 2c and 2o can be rationalized in terms of 6π‐electron cyclization, followed by thermal [1,5] acyl migration, and that of compounds 3p, 5a – 5e , and 5h can be explained by a 6π‐electron cyclization only. The formation of the open‐chain amides 4e – 4h probably follows a mechanism involving a 1,7‐diradical, C and a spirolactam of type D (Scheme). Long‐range ζ‐H abstraction by the excited carbonyl O‐atom of the benzoyl group on the aniline ring is expected to proceed via a nine‐membered cyclic transition state, as proposed on the basis of X‐ray crystallographic analyses (Fig. 2). 相似文献
137.
Kiitiro Utimoto Michio Obayashi Yuho Shishiyama Masaharu Inoue Hitosi Nozaki 《Tetrahedron letters》1980,21(35):3389-3392
Triethylaluminium-mediated reaction of cyanotrimethylsilane with 6-methylbicyclo[4.4.0]dec-1-en-3-one affords a mixture of diastereomeric 1,4-adducts. The reaction is kinetically controlled in toluene, whereas thermodynamically in refluxing THF. 4-Methyl-3-penten-2-one and carvone analogously give the respective 1,4-adducts and a conjugated dienone addords the 1,6-adduct in good yield. 相似文献
138.
Kazuhiko Ohashi Masaharu Nishiguchi Yoshiya Inokuchi Hiroshi Sekiya Nobuyuki Nishi 《Research on Chemical Intermediates》1998,24(7):755-764
Electronic spectra of a homo-molecular dimer cation, (C6H5CN)2
+, are measured by photodissociation spectroscopy in the gas phase. Broad features appeared in the 450–650 nm region are characteristic
of π3 → πCN transitions of the C6H5CN+ chromophore. No intense band is observed in the 650–1300 nm region, where other aromatic dimer cations usually show charge
resonance bands. Two component molecules of (C6H5CN)2
+ cannot take a parallel sandwich configuration suitable for the resonance interaction, because of geometrical constraints
due to other stronger interactions. 相似文献
139.
The photochemical synthesis of indole derivatives starting from the indoline-2-thiones 1 is described. Irradiation of indoline-2-thiones 1 in the presence of alkenes 3 gave 2-alkyl-3H-indoles 4 – 7 or 2-alkylindoles 8 – 22 through the ring cleavage of the intermediates, spirocyclic amino-thietanes, initially derived by [2 + 2] cycloaddition of the C?S bond of 1 and the C?C bond of 3 . Irradiation of 1 in the presence of trialkylamines 26 gave desulfurization products 27 – 32 and unexpected 3-alkylindoles 33 – 40 . N-Acylindoline-2-thiones 11 - p yielded the deacylated products, indoline-2-thiones 1a - b , and ethyl esters 43 through γ-H abstraction by the excited thioamide S-atom when irradiated in CDC13/EtOH or benzene/EtOH. Oxygen analogues 2a - d also underwent intramolecular H abstraction to give the indolin-2-ones 2e – f and ethyl esters 43 in a similar way. 相似文献
140.