全文获取类型
收费全文 | 201篇 |
免费 | 2篇 |
国内免费 | 2篇 |
专业分类
化学 | 113篇 |
力学 | 1篇 |
数学 | 30篇 |
物理学 | 61篇 |
出版年
2017年 | 1篇 |
2016年 | 2篇 |
2015年 | 1篇 |
2014年 | 2篇 |
2013年 | 5篇 |
2012年 | 1篇 |
2011年 | 5篇 |
2010年 | 8篇 |
2009年 | 3篇 |
2008年 | 6篇 |
2007年 | 4篇 |
2006年 | 11篇 |
2005年 | 7篇 |
2004年 | 6篇 |
2003年 | 7篇 |
2002年 | 7篇 |
2001年 | 4篇 |
2000年 | 12篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 2篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1970年 | 2篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1887年 | 1篇 |
排序方式: 共有205条查询结果,搜索用时 15 毫秒
121.
122.
Arthur W. Snow 《Journal of polymer science. Part A, Polymer chemistry》2017,55(1):93-106
Bulk free radical polymerization of the monomer series CH2 = C(CH3)C(O)OCH2CH3‐n Cln , n = 1, 2, 3, yields an unexpectedly crosslinked product with a crosslink density that increases with decreasing chlorine content of the respective monomer (n = 3 < n = 2 < n = 1). This chlorine substituent effect is investigated by correlation with chain transfer constant measurements for four homologous series of chloroalkyl compounds (chloroethyl acetates (CH3C(O)OCH2CH3‐n Cln , n = 1,2,3); chloromethanes (CH4‐n Cln , n = 2,3,4) and CD2Cl2 and CDCl3 analogs; butyl chloride isomers (n‐ , iso‐ , sec‐, tert‐) and tert‐C4D9Cl analog; and nine chloroethanes (C2Hn ?6Cln , n = 1–6)) in a methyl methacrylate polymerization. The pattern conveyed by the magnitude of chain transfer constants and deuterium isotope effects is consistent with a vicinal chlorine effect (i.e., chlorine activation of a vicinal hydrogen for abstraction) to account for the relative activities of the four series of model compounds and for the propensity of the chloroethyl methacrylates to crosslink in a bulk free radical polymerization. The chloroalkyl moiety's contribution to chain transfer is relatively modest (≤10?4), but, when incorporated as a monomer pendant group in free radical polymerizations, it is effective in broadening molecular weight to the extent of resulting in a crosslinked polymer. Published 2016.? J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 93–106 相似文献
123.
Five different hydrogen-bonded conformers of the dimer of 2-propanol have been characterized by Fourier transform microwave spectroscopy. In all observed species, the proton donor moiety adopts a gauche conformation. While in the gauche monomer a transient chirality takes place, all dimers are classical chiral systems. The Ubbelohde effect has been observed upon OH → OD isotopic substitution and its structural effects--a 5 m? reduction of the O---O distance--have been quantitatively defined. 相似文献
124.
Daniel D. Snow Teyona Damon-Powell Sathaporn Onanong David A. Cassada 《Analytical and bioanalytical chemistry》2013,405(5):1759-1771
Analytical methods for the determination of several natural and synthetic steroids in water and solid samples were developed using liquid chromatography tandem mass spectrometry. Atmospheric pressure photoionization (APPI) in positive mode was used as the source which appeared to reduce background and interferences as compared to electrospray ionization. Toluene was identified as the most appropriate dopant and its concentration optimized to enhance ionization efficiency. Method detection limits were in the low-nanogram-per-liter range for water samples using on-line solid-phase extraction and near 0.2 ng/g using microwave-assisted solvent extraction for solid samples. This on-line method, using APPI as a source and toluene as a dopant, is beneficial as it saves time due to on-line extraction and reduces interference and matrix effects using gas-phase photoionization. Groundwater, wastewater, runoff, and soil samples were collected and analyzed using the method indicating that traces of several androgens, estrogens, and other steroid-like compounds do occur in samples impacted by animal waste. Figure
Sensitive and simplified analysis of natural and synthetic steroids in water and solids using on-line solid phase extraction and microwave-assisted solvent extraction coupled to liquid chromatography tandem mass spectrometry atmospheric pressure photoionization 相似文献
125.
MR Eskildsen AB Abrahamsen PL Gammel DJ Bishop NH Andersen K Mortensen PC Canfield 《Pramana》2002,58(5-6):903-905
We compare the results of small angle neutron scattering on the flux line lattice (FLL) obtained in the borocarbide superconductor
LuNi2B2C with the applied field along the c- and a-axes. For H‖c the temperature dependence of the FLL structural phase transition from square to hexagonal symmetry was investigated. Above
10 K the transition onset field. H
2(T), rises sharply, bending away from H
c2(T) in contradiction to theoretical predictions of the two merging. For H‖a a first order FLL reorientation transition is observed at H
tr=3–3.5 kOe. Below H
tr the FLL nearest neighbor direction is parallel to the b-axis, and above H
tr to the c-axis. This transition cannot be explained using nonlocal corrections to the London model. 相似文献
126.
127.
128.
129.
P.A. Snow D.J. Westland J.F. Ryan T. Kerr H. Munekata L.L. Chang 《Superlattices and Microstructures》1989,5(4)
We have investigated hot carrier dynamics in GaSb structures, bulk and quantum wells, using picosecond time-resolved photoluminescence. Bulk samples show remarkably little carrier heating which we attribute to rapid electron relaxation within the L valleys. Quantum wells show slower cooling than the bulk, which is consistent with similar measurements of other III–V systems. Strong Auger recombination heating of the plasma is found to be responsible for maintaining relatively high temperatures at times 25 ps. 相似文献
130.
Steven D. Bull Stephen G. Davies A. Christopher Garner Edward D. Savory Emma J. Snow Andrew D. Smith 《Tetrahedron: Asymmetry》2004,15(24):3989-4001
A range of (2S,5S)-5-isopropyl-2-halo-N,N′-bis-(p-methoxybenzyl)-piperazine-3,6-diones 8 (Cl), 11, 12 (F) and 13 (Br) have been prepared, either via electrophilic halogenation of the corresponding lithiated diketopiperazine, or via transhalogenation from fluoro-11 and 12. The product distribution and stereoselectivity of additions of allyltrimethylsilane, sodium thiophenolate and a range of organomagnesium reagents to chloro 8 are reported. In the reactions with Grignard reagents the observed stereo- and regioselectivities are dependent on the reagent employed, with C-3 carbonyl addition products predominating upon addition of allyl or methylmagnesium chloride and stereodivergent formal C-2 addition predominating with benzyl or isopropylmagnesium chloride. A model to account for the different reactivity and stereoselectivity in these reactions is proposed. 相似文献