全文获取类型
收费全文 | 8634篇 |
免费 | 257篇 |
国内免费 | 62篇 |
专业分类
化学 | 5721篇 |
晶体学 | 80篇 |
力学 | 249篇 |
综合类 | 1篇 |
数学 | 1425篇 |
物理学 | 1477篇 |
出版年
2023年 | 42篇 |
2021年 | 78篇 |
2020年 | 157篇 |
2019年 | 113篇 |
2018年 | 90篇 |
2017年 | 96篇 |
2016年 | 203篇 |
2015年 | 155篇 |
2014年 | 197篇 |
2013年 | 418篇 |
2012年 | 467篇 |
2011年 | 569篇 |
2010年 | 290篇 |
2009年 | 231篇 |
2008年 | 505篇 |
2007年 | 468篇 |
2006年 | 451篇 |
2005年 | 466篇 |
2004年 | 441篇 |
2003年 | 296篇 |
2002年 | 310篇 |
2001年 | 84篇 |
2000年 | 67篇 |
1999年 | 55篇 |
1998年 | 65篇 |
1997年 | 90篇 |
1996年 | 133篇 |
1995年 | 81篇 |
1994年 | 67篇 |
1993年 | 93篇 |
1992年 | 65篇 |
1991年 | 77篇 |
1990年 | 72篇 |
1989年 | 64篇 |
1988年 | 75篇 |
1987年 | 65篇 |
1986年 | 58篇 |
1985年 | 118篇 |
1984年 | 134篇 |
1983年 | 92篇 |
1982年 | 114篇 |
1981年 | 114篇 |
1980年 | 92篇 |
1979年 | 84篇 |
1978年 | 112篇 |
1977年 | 98篇 |
1976年 | 83篇 |
1975年 | 71篇 |
1974年 | 70篇 |
1973年 | 60篇 |
排序方式: 共有8953条查询结果,搜索用时 15 毫秒
991.
992.
993.
Edward M. Suzuki Joseph W. Nibler Kent A. Oakes David Eggers 《Journal of Molecular Spectroscopy》1975,58(2):201-215
Infrared and visible absorption spectra of the low pressure heated products of S2O6F2 trapped in inert gas matrices at 14 K are presented. The following have been identified as major infrared-absorbing species: SO3F, SO3, HSO3F, and S2O6F2, with matrix spectra of the latter three unequivocally confirming their presence. Reasonable reactions accounting for the production of these species are proposed, and a reassignment of the fundamental vibrations of monomeric HSO3F is offered. The infrared absorptions of the SO8F radical have been observed for the first time, and the six fundamental vibrations determined. These frequencies are in good accord with earlier values deduced indirectly by King and Warren from hot band transitions in the visible absorption spectrum of the vapor. This same visible system () has also been observed here for the matrix isolated species. 相似文献
994.
Elastic scattering angular distributions for 10, 11B + 40Ca at Elab = 46.6 and 51.5 MeV and12C+39K at Elab = 54 and 63 MeV have been measured and compared with Woods-Saxon and double-folding optical models. The oscillatory structure observed previously for 12C + 40Ca disappears when the projectile is changed to 10,11B or the target is changed to 39K. The angular distributions are adequately reproduced by a double-folding analysis, which employs the nucleon-nucleon potential of Bertsch et al., with a range of real normalizations NR = 1.0–1.38. This same range of real normalizations was also able to describe previously measured 10,11B, 12C + 27A1 data. The double-folding analysis of 12C + 40Ca scattering indicates that this system behaves differently from neighboring systems. 相似文献
995.
Philip DeShong Subban Ramesh Joseph J. Perez Cynthia Bodish 《Tetrahedron letters》1982,23(22):2243-2246
An efficient synthesis of a 2,9-dioxabicyclo[3.3.1]nonane system, similar to that of tirandamycin, is accomplished from 2,3-dimethylfuran. 相似文献
996.
997.
998.
A method for the use of natural orbital iterations in limited CI calculations is discussed. This method is then applied to the ground X2II state of the nitric oxide molecule at its experimental equilibrium internuclear separation to yield the total energy, dipole moment, spin densities at each nucleus, and approximate natural spin orbitals for this molecule. 相似文献
999.
1000.
Laurine L. Graham Garret Vanderkooi Joseph A. Getz 《Magnetic resonance in chemistry : MRC》1977,9(2):80-89
A new method of conformational analysis has been developed, in which energy minimization calculations are combined with lanthanide-induced shift data. First, exhaustive energy calculations are carried out on the free molecules in order to determine the conformations of lowest energy. Then, the coordinates of all low energy conformations or pairs of conformations are used in the pseudocontact shift equation for lanthanide-induced shifts in order to find which of the theoretically obtained conformation(s) gives the best agreement with experiment. The molecules complexed to the lanthanide shift reagent were N,N-diisopropylformamide (DIPF) and N,N-diisopropylacetamide (DIPA). Two different lanthanide shift reagents were used, Eu(fod)3 1 Fod is the anion of 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione-d27. and Pr(fod)3, in order to check the validity of the method. Proton magnetic resonance spectra were taken at 6 °C in carbon tetrachloride solution. The principal conformation found was different for each amide. DIPF was found to exist as a mixture of I (39 mol%) and II (61 mol%) with Eu(fod)3, and a mixture of I (37%) and II (63%) with Pr(fod)3. DIPA was found to exist as a mixture of I (79%) and IV (21%) with Eu(fod)3 and a mixture of I (87%) and IV (13%) with Pr(fod)3. For both molecules, the two conformations of lowest computed energy were also the pair which gave the best fit to the lanthanide shift reagent data. The location of the principal magnetic axis of the complex was found to lie between 0° and 14° from the lanthanide atom–oxygen atom bond axis. The technique of combining lanthanide shift reagent data with energy calculations shows great promise in conformational analysis. 相似文献