全文获取类型
收费全文 | 9830篇 |
免费 | 161篇 |
国内免费 | 40篇 |
专业分类
化学 | 6224篇 |
晶体学 | 132篇 |
力学 | 293篇 |
数学 | 1074篇 |
物理学 | 2308篇 |
出版年
2021年 | 58篇 |
2020年 | 89篇 |
2019年 | 92篇 |
2018年 | 55篇 |
2016年 | 119篇 |
2015年 | 113篇 |
2014年 | 144篇 |
2013年 | 441篇 |
2012年 | 383篇 |
2011年 | 449篇 |
2010年 | 226篇 |
2009年 | 253篇 |
2008年 | 428篇 |
2007年 | 454篇 |
2006年 | 456篇 |
2005年 | 434篇 |
2004年 | 399篇 |
2003年 | 333篇 |
2002年 | 317篇 |
2001年 | 200篇 |
2000年 | 214篇 |
1999年 | 113篇 |
1998年 | 98篇 |
1997年 | 106篇 |
1996年 | 145篇 |
1995年 | 117篇 |
1994年 | 170篇 |
1993年 | 183篇 |
1992年 | 166篇 |
1991年 | 123篇 |
1990年 | 122篇 |
1989年 | 129篇 |
1988年 | 101篇 |
1987年 | 121篇 |
1986年 | 111篇 |
1985年 | 190篇 |
1984年 | 155篇 |
1983年 | 102篇 |
1982年 | 130篇 |
1981年 | 123篇 |
1980年 | 137篇 |
1979年 | 133篇 |
1978年 | 132篇 |
1977年 | 117篇 |
1976年 | 131篇 |
1975年 | 115篇 |
1974年 | 133篇 |
1973年 | 131篇 |
1972年 | 55篇 |
1971年 | 64篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
J. D. Lamb F. R. Nordmeyer R. G. Smith A. Van Orden R. Allison R. P. Lash 《Journal of Radioanalytical and Nuclear Chemistry》1992,159(2):285-292
Ion chromatography (IC) can be used to separate radioiodine from fission products and other ionic species in complex reprocessing solution matrices. A preliminary concentration and separation of the radioiodine is performed using a column filled with a platinum-coated copper bed which converts all forms of iodine to iodide and selectively adsorbs the iodide. The separation is completed by employing an anion chromatographic system. The iodide peak aliquot is collected for subsequent radioanalysis by low energy photon spectroscopy. Results indicate quantitative separation and recovery of iodine. The entire system is automated under computer control and is able to handle small (l) and large (500 ml) sample sizes. 相似文献
42.
43.
44.
45.
46.
Shaw NM Blanis D Bodek A Budd H Coombes R Eno S Fry CA Harada H Ho YH Kim YK Kumita T Mori T Olsen SL Sill A Thorndike EH Ueno K Zheng HW Imlay R Kirk P Lim J McNeil RR Metcalf W Myung SS Cheng CP Gu P Li J Li YK Mao ZP Xu YT Zhu YC Abashian A Gotow K Hu K Low EH Mattson ME Naito F Piilonen L Sterner KL Lusin S Rosenfeld C Wang AT Wilson S Frautschi M Kagan H Kass R Trahern CG Breedon RE Kim GN Ko W Lander RL Maeshima K Malchow RL Smith JR Sparks K Williams MC Abe K Fujii Y Higashi Y Kim SK 《Physical review letters》1989,63(13):1342-1345
47.
48.
Mishra SR Bachmann KT Bernstein RH Blair RE Foudas C Lefmann WC Leung WC Oltman E Quintas PZ Sciulli FJ Shaevitz MH Smith WH Merritt FS Oreglia MJ Schellman H Schumm BA Borcherding F Fisk HE Lamm MJ Marsh W Merritt KW Yovanovitch DD Bodek A Budd HS Sakumoto WK 《Physical review letters》1989,63(2):132-135
49.
Stephen G. Davies Ian A. Hunter Rebecca L. Nicholson Paul.M. Roberts Edward D. Savory Andrew D. Smith 《Tetrahedron》2004,60(35):7553-7577
α-Dibenzylamino- and α-benzyloxy- derivatives of N-acetyl-(S)-4-benzyl-5,5-dimethyloxazolidin-2-one readily undergo highly stereoselective boron mediated syn-aldol reactions with a range of aromatic and aliphatic aldehydes, generating the syn-aldol products in good to excellent yields as single diastereoisomers after purification. In the α-dibenzylamino series, deprotection of the functionalised aldol fragments to the corresponding α-amino-β-hydroxy methyl ester or α-amino-β-hydroxyaldehyde proved problematic, with a range of N- and O-protecting groups giving mixtures of products arising from endocyclic and exocyclic cleavage pathways. However, in the α-benzyloxy series, O-silyl protection of the aldol products, and subsequent DIBAL reduction gives stereoselectively the corresponding N-1′-hydroxyalkyloxazolidin-2-ones, which undergo base promoted fragmentation to the desired highly functionalised and differentially protected α,β-dihydroxyaldehydes in good yields and without loss of stereochemical integrity. 相似文献
50.
Gerald J. Smith Kenneth R. Markham W. Hugh Melhuish 《Photochemistry and photobiology》1994,60(3):196-198
Abstract Solvent-cleaned Merino wool, which was enzymatically digested with protease K, displayed a fluorescence maximum at 500 nm when excited at 430 nm. The yield of this emission was approximately 15 times greater for a fiber tips digest than for a digest of the mid-length region of the same fibers.
Separation of the components in the wool tip digest by silica gel thin-layer chromatography revealed the presence of several fluorescent species. The chromatographic mobility of these species was similar to the behavior observed in a preparation of authentic 1-methyltetrahydro-P-carboline, 1,3-dicarboxylic acid.
Mass spectroscopy of the fluorescent compounds in the wool tip digest displayed molecular ions, [M + H]+ with m/z = 273.0890 and 257.0560, and molecular weights that define the formulae C14 H12 N2 O4 and C11 H8 O4 N2 , respectively, which correspond to β-carboline 1,3-dicarboxylic acids. Mass spectral evidence also indicates the presence of two other β-carbolines. 相似文献
Separation of the components in the wool tip digest by silica gel thin-layer chromatography revealed the presence of several fluorescent species. The chromatographic mobility of these species was similar to the behavior observed in a preparation of authentic 1-methyltetrahydro-P-carboline, 1,3-dicarboxylic acid.
Mass spectroscopy of the fluorescent compounds in the wool tip digest displayed molecular ions, [M + H]