全文获取类型
收费全文 | 278136篇 |
免费 | 2306篇 |
国内免费 | 876篇 |
专业分类
化学 | 134162篇 |
晶体学 | 4401篇 |
力学 | 14545篇 |
综合类 | 11篇 |
数学 | 50361篇 |
物理学 | 77838篇 |
出版年
2020年 | 1738篇 |
2019年 | 1931篇 |
2018年 | 12381篇 |
2017年 | 12312篇 |
2016年 | 9426篇 |
2015年 | 3013篇 |
2014年 | 3832篇 |
2013年 | 9399篇 |
2012年 | 10132篇 |
2011年 | 18114篇 |
2010年 | 11133篇 |
2009年 | 11509篇 |
2008年 | 13516篇 |
2007年 | 15548篇 |
2006年 | 6934篇 |
2005年 | 7339篇 |
2004年 | 7005篇 |
2003年 | 7005篇 |
2002年 | 5863篇 |
2001年 | 6392篇 |
2000年 | 4908篇 |
1999年 | 3661篇 |
1998年 | 2928篇 |
1997年 | 2841篇 |
1996年 | 2798篇 |
1995年 | 2560篇 |
1994年 | 2420篇 |
1993年 | 2263篇 |
1992年 | 2889篇 |
1991年 | 2804篇 |
1990年 | 2729篇 |
1989年 | 2756篇 |
1988年 | 2779篇 |
1987年 | 2780篇 |
1986年 | 2659篇 |
1985年 | 3366篇 |
1984年 | 3369篇 |
1983年 | 2645篇 |
1982年 | 2756篇 |
1981年 | 2818篇 |
1980年 | 2593篇 |
1979年 | 2931篇 |
1978年 | 2912篇 |
1977年 | 3015篇 |
1976年 | 2842篇 |
1975年 | 2572篇 |
1974年 | 2523篇 |
1973年 | 2495篇 |
1972年 | 1723篇 |
1968年 | 1715篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
Kanitskaya L. V. Elokhina V. N. Fedorov S. V. Shulunova A. M. Nakhmanovich A. S. Turchaninov V. K. Lopyrev V. A. 《Russian Journal of General Chemistry》2002,72(5):778-784
Pyridine was reacted with propargyl bromide to obtain the dibromide [C5H5NCH = CHCH = CHCH = CHC5H5N]2
+ 2Br-. The effect of the vinyl group on its UV spectrum is qualitatively interpreted using the results of nonempirical quantum-chemical calculations (basis HF/6-31G*). 相似文献
995.
Yamada K Harada Y Miyamoto T Isobe R Higuchi R 《Chemical & pharmaceutical bulletin》2000,48(1):157-159
A new ganglioside molecular species, HPG-7 (1) was obtained from the polar fraction of the chloroform/methanol extract of the sea cucumber, Holothuria pervicax. On the basis of chemical and spectroscopic evidence, the structure of 1 was determined, and the major component was 1-O-[alpha-L-fucopyranosyl-(1-->4)-(N-acetyl-alpha-D-neuraminosyl) - (2-->11)-(N-glycolyl-alpha-D-neuraminosyl)-(2-->4)-(N-acetyl -alpha-D- neuraminosyl)-(2-->6)-beta-D-glucopyranosyl]-(2S,3S,4R)-2-[(2R)-2- hydroxytetracosanoylamino]-14-methyl-hexadecane-1,3,4-triol. This is the first report on the isolation and structure elucidation of trisialo-ganglioside from sea cucumber. 1 showed neuritogenic activity toward the rat pheochromocytoma cell line, PC-12 cell. 相似文献
996.
The amount of alcohol required to produce a microemulsion in a quaternary water-in-oil system was evaluated for a series of alcohols and hydrocarbon solvents of different size or topology. It was observed that the amount of n-hexanol and n-decanol required was similar in all the solvents considered. On the other hand, considerably higher concentrations of the branched alcohols (2,4-dimethyl-3-pentanol and 3-ethyl-3-pentanol) were required to produce the microemulsion, irrespective of the solvent topology (n-hexane or 2,2,4-trimethylpentane). From an analysis of the change in the analytical alcohol concentration with the surfactant concentration the amounts of alcohol present at the microaggregates' surface at the point of microemulsion formation were obtained. It is concluded that the high amounts of branched alcohols required are due to both less efficient incorporation at the interface and the larger number of alcohol molecules per surfactant required to stabilize the microemulsion. 相似文献
997.
Catalytic condensation of cyclopentanone with arylmethylene(6-quinolyl)amines gave previously unknown 8-aryl-10,11-dihydro-9H-cyclopenta[a]-4,7-phenanthrolines. 相似文献
998.
Betaines are formed in good yields in the reaction of N-heteroaromatic compounds with 2-dicyanomethyleneindane-1,3-dione oxide and its 4- and 5-halo derivatives in dioxane. The corresponding oxides were obtained by oxidation of 2-dicyanomethyleneindane-1,3-dione and its 4- and 5-substituted derivatives with hydrogen peroxide in dioxane. Data from the IR spectra of the compounds are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 889–892, July, 1978. 相似文献
999.
1000.