全文获取类型
收费全文 | 737篇 |
免费 | 15篇 |
国内免费 | 2篇 |
专业分类
化学 | 575篇 |
晶体学 | 10篇 |
力学 | 6篇 |
数学 | 27篇 |
物理学 | 136篇 |
出版年
2022年 | 5篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 5篇 |
2016年 | 4篇 |
2015年 | 9篇 |
2014年 | 15篇 |
2013年 | 33篇 |
2012年 | 35篇 |
2011年 | 55篇 |
2010年 | 18篇 |
2009年 | 16篇 |
2008年 | 47篇 |
2007年 | 53篇 |
2006年 | 46篇 |
2005年 | 50篇 |
2004年 | 36篇 |
2003年 | 30篇 |
2002年 | 18篇 |
2001年 | 16篇 |
2000年 | 18篇 |
1999年 | 16篇 |
1998年 | 12篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 11篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 7篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1974年 | 4篇 |
1972年 | 6篇 |
1970年 | 5篇 |
1969年 | 5篇 |
排序方式: 共有754条查询结果,搜索用时 0 毫秒
41.
42.
Hiromichi Takagi 《Proceedings of the American Mathematical Society》1999,127(2):315-321
We investigate divisorial contractions of extremal rays from
smooth fourfolds. When the exceptional divisor is contracted to a curve, we prove that the divisor is a -bundle or quadric bundle over a smooth curve and the contraction is the blowing up along the curve. Furthermore we determine the local analytic structure of the contraction.
smooth fourfolds. When the exceptional divisor is contracted to a curve, we prove that the divisor is a -bundle or quadric bundle over a smooth curve and the contraction is the blowing up along the curve. Furthermore we determine the local analytic structure of the contraction.
43.
44.
K.J.L. Paciorek T.I. Ito J.H. Nakahara R.H. Kratzer 《Journal of fluorine chemistry》1980,16(5):431-440
A series of novel eight-membered heterocycles containing 1,3 and 1,5 phosphorus arrangements were synthesized. The 1,5-diphosphatetraazacyclooctatetraenes were obtained from the interaction of perfluoroalkyletheramidines and trichlorophosphoranes; the 1,3-isomers were prepared from perfluoroalkyletherimidoylamidines and imido-tetraphenyl-diphosphinic acid trichloride. The two series of cyclooctatetraenes exhibited infrared spectral absorptions characteristic for the given positional arrangement. However, electron impact fragmentation patterns of the two ring systems were closely comparable. 相似文献
45.
46.
The vibration-rotation transitions for a fundamental band of SeO (X3Σ?) were studied by means of the infrared laser magnetic resonance (LMR) method employing a CO2 laser. The LMR spectra arising from five SeO isotopic species except 74SeO were detected and analyzed. Band origins for these species were determined. Molecular parameters ωe, ωeχe, Be, and αe, were obtained with the aid of the reduced mass relations. For 77SeO the axial component of magnetic hyperfine interaction was obtained. 相似文献
47.
Determination of optical isomers for left-handed or right-handed chiral double-wall carbon nanotubes
The handedness relationship between adjacent layers in nested double-wall carbon nanotubes (DWNTs) has been investigated for the first time. Our high-resolution electron microscopy analysis on a series of specimen tilts can successfully tell the handedness of each constituent nanotube in a DWNT, and therefore the chiral indices (n, m) including their optical isomers [(n, m) or (m, n)] of inner and outer nanotubes can be uniquely determined. It is shown that right-handed and left-handed nanotubes are equally distributed for both the inner and outer nanotubes in the examined specimens and a preferable handedness relationship between the adjacent layers in DWNT may exist. 相似文献
48.
Haraguchi K Shiina N Yoshimura Y Shimada H Hashimoto K Tanaka H 《Organic letters》2004,6(16):2645-2648
2'-Beta-methyl- and 2'-beta-hydroxymethyl-2'-deoxy-4'-thionucleosides have been synthesized through PhSeCl-mediated electrophilic glycosidation using 4-thiofuranoid glycals having carbon substituents at the C2-position as a glycosyl donor. Preparation of these glycals were carried out by means of the C2 lithiation of 1-chloro-4-thiofuranoid glycal with LTMP followed by the Birch reduction of the chlorine atom. [reaction: see text] 相似文献
49.
Tunneling chemical reactions between deuterated methyl radicals and the hydrogen molecule in a parahydrogen crystal have been studied by Fourier transform infrared spectroscopy. The tunneling rates of the reactions R + H2 --> RH + H (R = CD3,CD2H,CDH2) in the vibrational ground state were determined directly from the temporal change in the intensity of the rovibrational absorption bands of the reactants and products in each reaction in solid parahydrogen observed at 5 K. The tunneling rate of each reaction was found to differ definitely depending upon the degree of deuteration in the methyl radicals. The tunneling rates were determined to be 3.3 x 10(-6) s(-1), 2.0 x 10(-6) s(-1), and 1.0 x 10(-6) s(-1) for the systems of CD3, CD2H, and CDH2, respectively. Conversely, the tunneling reaction between a CH3 radical and the hydrogen molecule did not proceed within a week's time. The upper limit of the tunneling rate of the reaction of the CH3 radical was estimated to be 8 x 10(-8) s(-1). 相似文献
50.
Machida S Mineta S Fujimori A Nakahara H 《Journal of colloid and interface science》2003,260(1):135-141
From AFM observation of transferred films on mica, it has been found that mixed monolayers of hexadecanol with poly(vinyl stearate) give a film with a less-defective and flat surface by spreading from bulk solids of those mixtures onto a water surface without using any organic solvent. As a result, those mixed monolayers have a considerably larger effect on retardation of water evaporation in comparison with those spread from the solution of the mixtures. After the saturated surface pressure of the mixed monolayer spread from the bulk solids, an enhanced effect on retardation of water evaporation was found, accompanied by the preferential spreading of hexadecanol and the gradual reduction of defects in the mixed monolayer. 相似文献