全文获取类型
收费全文 | 1423篇 |
免费 | 26篇 |
国内免费 | 3篇 |
专业分类
化学 | 1029篇 |
晶体学 | 4篇 |
力学 | 17篇 |
数学 | 222篇 |
物理学 | 180篇 |
出版年
2021年 | 11篇 |
2020年 | 18篇 |
2019年 | 9篇 |
2016年 | 33篇 |
2015年 | 26篇 |
2014年 | 25篇 |
2013年 | 38篇 |
2012年 | 61篇 |
2011年 | 69篇 |
2010年 | 39篇 |
2009年 | 38篇 |
2008年 | 49篇 |
2007年 | 61篇 |
2006年 | 46篇 |
2005年 | 57篇 |
2004年 | 50篇 |
2003年 | 36篇 |
2002年 | 39篇 |
2001年 | 26篇 |
2000年 | 32篇 |
1999年 | 26篇 |
1998年 | 21篇 |
1997年 | 25篇 |
1996年 | 27篇 |
1995年 | 24篇 |
1994年 | 40篇 |
1993年 | 20篇 |
1992年 | 23篇 |
1991年 | 27篇 |
1990年 | 9篇 |
1989年 | 27篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 19篇 |
1985年 | 29篇 |
1984年 | 32篇 |
1983年 | 12篇 |
1982年 | 28篇 |
1981年 | 29篇 |
1980年 | 30篇 |
1979年 | 26篇 |
1978年 | 23篇 |
1977年 | 16篇 |
1976年 | 21篇 |
1975年 | 18篇 |
1974年 | 15篇 |
1973年 | 12篇 |
1972年 | 10篇 |
1971年 | 12篇 |
1970年 | 8篇 |
排序方式: 共有1452条查询结果,搜索用时 31 毫秒
61.
Zinad DS Shaaban KA Abdalla MA Islam MT Schüffler A Laatsch H 《Natural product communications》2011,6(1):45-48
Four isocoumarins have been isolated from the terrestrial Streptomyces sp. ANK302, namely 6,8-dimethoxy-3-methylisocoumarin (1), 6,8-dihydroxy-3-methylisocoumarin (2), 6,8-dihydroxy-7-methoxy-3-methylisocoumarin (3), and 6,7,8-trimethoxy-3-methylisocoumarin (4). Compound 1 is a new naturally-occurring isocoumarin, and 2 was isolated as a new bacterial product. The structures 1-4 were deduced from high resolution mass, 1D and 2D NMR spectra and by comparison with related compounds from the literature. Compound 2 showed a strong zoosporicidal activity at a concentration of 5 microg/mL against a phytopathogenic oomycete, Plasmopara viticola, and 1 was active against 相似文献
62.
Boca R Gembický M Herchel R Haase W Jäger L Wagner C Ehrenberg H Fuess H 《Inorganic chemistry》2003,42(22):6965-6967
Triethylenetetramine (L(4)) was used as a tetradentate blocking ligand that, after complexation with Ni(II), leaves two sites ready for ligation with tricyanomethanide. The formed binuclear complex [L(4)Ni(NCC(CN)CN)(2)NiL(4)](ClO(4))(2) exhibits a ferromagnetic coupling with J/hc = +0.15 cm(-1) and g(Ni) = 2.126; below 16 K, a ferromagnetic ordering is evidenced by ac magnetic susceptibility (both in-phase and out-of-phase), magnetization, field-cooled magnetization, and zero-field-cooled magnetization measurements. 相似文献
63.
64.
The reaction of titanocene dichloride,Cp
2TiCl2 (Cp=5-C5H5), with one or two equivalents of sodium cyanodithioformate affords the new mono- or bis(dithiocarboxylato) derivativesCp
2TiCl(S2CCN) (1) andCp
2Ti(S2CCN)2 (2). Elimination of sulfur converts2 into the metallacyclicCp
2TiS2C2(CN)2 (3), which does not react with the diene isoprene, but can be reconverted into the appropriate titanocene dihalides by chlorine or bromine. 相似文献
65.
Hans Günther Wahl Silke-Yvonne Habel Norbert Schmieder Hartmut M. Liebich 《Journal of separation science》1994,17(7):543-548
Identification of cis/trans isomers of unsaturated fatty acids cannot usually be achieved by GC-MS (gas chromatography-mass spectrometry) without reference substances. In this study a GC-FTIR-MS system (gas chromatography-Fourier transform-mass spectrometry) was used to identify fatty acid methyl esters (FAMEs) and differentiate between the cis/trans isomers. Besides methyl esters, 2-alkenyl-4,4-dimethyloxazoline derivatives (DMOX), which have been used to locate double bond positions of unsaturated fatty acids, were examined with respect to their suitability for cis/trans differentiation. A combined GC-FTIR-MS system with a wide band (4000–550 cm?1) mercury cadmium telluride (MCT) detector was used in series and parallel to identify 31 reference unsaturated fatty acids, including 7 pairs of cis/trans isomers. Serum samples of healthy persons and commercially available fish oil were analyzed as examples of complex mixtures. Using splitless injection the detection limit for the less sensitive IR detector was 25 ng/μl in case of the weak cis and trans bands. In the FTIR spectra cis/trans isomers were identified by analysis of bands arising from C? H out-of-plane (oop) bending: for both the FAME and DMOX derivatives cis-1,2-disubstituted double bonds give a strong band near 720 cm?1 and the corresponding trans isomers near 967 cm?1. cis Isomers could be identified further by a band at 3012 cm?1. With the combined data of the GC-FTIR-MS system it is now possible to identify polyunsaturated fatty acids with regard to the discrimination of cis/trans isomers. 相似文献
66.
Abstract The phosphonium salts have been prepared by the reaction of triphenylphosphine with the corresponding halomethanes (eq. (1)) and bromine (eq.(2)), respectively. 相似文献
67.
Tuija Jokinen Dr. Mikko Sipilä Stefanie Richters Prof. Veli‐Matti Kerminen Dr. Pauli Paasonen Dr. Frank Stratmann Dr. Douglas Worsnop Prof. Markku Kulmala Dr. Mikael Ehn Prof. Hartmut Herrmann Dr. Torsten Berndt 《Angewandte Chemie (International ed. in English)》2014,53(52):14596-14600
Gas‐phase oxidation routes of biogenic emissions, mainly isoprene and monoterpenes, in the atmosphere are still the subject of intensive research with special attention being paid to the formation of aerosol constituents. This laboratory study shows that the most abundant monoterpenes (limonene and α‐pinene) form highly oxidized RO2 radicals with up to 12 O atoms, along with related closed‐shell products, within a few seconds after the initial attack of ozone or OH radicals. The overall process, an intramolecular ROO→QOOH reaction and subsequent O2 addition generating a next R′OO radical, is similar to the well‐known autoxidation processes in the liquid phase (QOOH stands for a hydroperoxyalkyl radical). Field measurements show the relevance of this process to atmospheric chemistry. Thus, the well‐known reaction principle of autoxidation is also applicable to the atmospheric gas‐phase oxidation of hydrocarbons leading to extremely low‐volatility products which contribute to organic aerosol mass and hence influence the aerosol–cloud–climate system. 相似文献
68.
Hartmut Frommert 《International Journal of Theoretical Physics》1996,35(12):2631-2643
The orbits of a relativistic charged body in a static, spherically symmetric electric field are calculated and classified in the classical theory. Contrary to the nonrelativistic problem, we find that there is a limiting minimal value for the angular momentumL
c
. Should the actual angular momentum of a charged test body be lower than this limit, the test particle will spiral into the central point charge instead of having (precessing) Keplerian orbits. 相似文献
69.
Minhhuy H Robin P. Sagar Hartmut Schmider Donald F. Weaver Vedene H. Smith 《International journal of quantum chemistry》1995,53(6):627-633
Atomic charge and momentum densities of 91 atoms (He? U) are classified in terms of their L1, L2, and entropic measures of distance from the densities of the preceding atoms. The relationship between these distances and the first ionization energies is also considered. © 1995 John Wiley & Sons, Inc. 相似文献
70.