全文获取类型
收费全文 | 534013篇 |
免费 | 5797篇 |
国内免费 | 1539篇 |
专业分类
化学 | 287481篇 |
晶体学 | 8049篇 |
力学 | 23285篇 |
综合类 | 16篇 |
数学 | 61279篇 |
物理学 | 161239篇 |
出版年
2021年 | 4447篇 |
2020年 | 4970篇 |
2019年 | 5349篇 |
2018年 | 6898篇 |
2017年 | 6829篇 |
2016年 | 10502篇 |
2015年 | 6629篇 |
2014年 | 10115篇 |
2013年 | 24503篇 |
2012年 | 18876篇 |
2011年 | 23106篇 |
2010年 | 16232篇 |
2009年 | 16169篇 |
2008年 | 21321篇 |
2007年 | 21065篇 |
2006年 | 19762篇 |
2005年 | 17714篇 |
2004年 | 16350篇 |
2003年 | 14568篇 |
2002年 | 14347篇 |
2001年 | 16694篇 |
2000年 | 12533篇 |
1999年 | 9808篇 |
1998年 | 7942篇 |
1997年 | 7740篇 |
1996年 | 7490篇 |
1995年 | 6775篇 |
1994年 | 6674篇 |
1993年 | 6331篇 |
1992年 | 7268篇 |
1991年 | 7433篇 |
1990年 | 7066篇 |
1989年 | 6874篇 |
1988年 | 6891篇 |
1987年 | 6756篇 |
1986年 | 6304篇 |
1985年 | 8154篇 |
1984年 | 8337篇 |
1983年 | 6603篇 |
1982年 | 6730篇 |
1981年 | 6579篇 |
1980年 | 6172篇 |
1979年 | 6788篇 |
1978年 | 6981篇 |
1977年 | 6855篇 |
1976年 | 6750篇 |
1975年 | 6217篇 |
1974年 | 6212篇 |
1973年 | 6288篇 |
1972年 | 4377篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
962.
An apparatus for the deuteration of solid samples and for recording their IR spectra in a current of D2O vapor, and an IR-spectroscopic method of determining the degree of deuteration (q) of the hydroxy groups of pectin substances (PSs) are described. It has been established that there are no zones of structurally different nature in films of derivatives of PSs at the carboxy group. The rate of deuterium-exchange of the water of hydration of PSs is higher than for the hydroxy groups of the pyranose rings. The rate of deuterium exchange depends on the density of packing of the polymer chains of the pectin derivatives.Center for the Automation of Scientific Investigations and Metrology, Academy of Sciences of the Moldavian SSR, Kishinev. Translated from Khimiya Priorodnykh Soedinenii, No. 3, pp. 343–348, May–June, 1987. 相似文献
963.
M. V. Priyutov M. A. Kovner I. E. Krainova P. V. Kosterin 《Journal of Structural Chemistry》1983,24(5):653-658
964.
965.
G. T. Pilyugin Ya. O. Gorichok B. M. Gutsulyak S. I. Gorichok 《Chemistry of Heterocyclic Compounds》1966,1(6):603-608
Reaction of phenyl-ß-naphthylamines with formaldehyde and acetone in the presence of HCl and nitrobenzene in butanol solution leads to cyclization involving the naphthalene and phenyl rings, and formation of N-aryllepidine salts. 15 lepidine and 5, 6-benzoepidine salts are synthesized and characterized by their UV absorption spectra, as well as by their picrates.For Part LIII see [3]. 相似文献
966.
967.
Topochemical investigations of peptide systems 总被引:4,自引:0,他引:4
M M Shemyakin Y A Ovchinnikov V T Ivanov 《Angewandte Chemie (International ed. in English)》1969,8(7):492-499
The basic principles of the topochemical approach to the investigation of the structure-function relation in peptide systems are formulated. This approach makes use of the new possibility of transforming natural peptides, consisting in the modification of the molecule as a whole and utilization of the resultant analogs to elucidate the boundaries of the stereoelectronic complementarity of the biologically active peptide to the corresponding receptor. In particular, on the example of depsipeptide antibiotics and their topochemical analogs the fruitfulness of using such compounds as tools in elucidating the physicochemical basis of functioning of biological membranes is shown. The topochemical principle has also been applied in preparing specific competitive inhibitors of proteolytic enzymes, whose study may shed light on the nature of the forces binding the substrate to the contact site of the corresponding enzyme. 相似文献
968.
969.
I Kitagawa A Matsuda T Nishimura S Hirai I Yoshioka 《Chemical & pharmaceutical bulletin》1967,15(9):1435-1437
970.
A new pyridine synthesis has been found by refluxing certain simple secondary car☐amides in HMPA. Thus 2,6-dimethylpyridine, 2-ethyl-6-methylpyridine, 2,3,6-trimethylpyridine, 2-ethyl-3,6-dimethylpyridine, 2-benzyl-6-methyl-3-phenylpyridine, 2-ethyl-3-methyl-5,6,7,8-tetrahydroquinoline and 2-t-butyl-6-methylpyridine were prepared in 15–40% yield. 相似文献