全文获取类型
收费全文 | 516632篇 |
免费 | 19754篇 |
国内免费 | 10287篇 |
专业分类
化学 | 283782篇 |
晶体学 | 7522篇 |
力学 | 25396篇 |
综合类 | 525篇 |
数学 | 59817篇 |
物理学 | 169631篇 |
出版年
2022年 | 5385篇 |
2021年 | 6560篇 |
2020年 | 7376篇 |
2019年 | 7326篇 |
2018年 | 8407篇 |
2017年 | 7954篇 |
2016年 | 11986篇 |
2015年 | 8822篇 |
2014年 | 12436篇 |
2013年 | 24677篇 |
2012年 | 21865篇 |
2011年 | 24925篇 |
2010年 | 17280篇 |
2009年 | 16828篇 |
2008年 | 21133篇 |
2007年 | 20721篇 |
2006年 | 19548篇 |
2005年 | 17132篇 |
2004年 | 15229篇 |
2003年 | 13403篇 |
2002年 | 12996篇 |
2001年 | 13883篇 |
2000年 | 10960篇 |
1999年 | 9071篇 |
1998年 | 7806篇 |
1997年 | 7717篇 |
1996年 | 7300篇 |
1995年 | 6701篇 |
1994年 | 6543篇 |
1993年 | 6041篇 |
1992年 | 6572篇 |
1991年 | 6583篇 |
1990年 | 6252篇 |
1989年 | 5805篇 |
1988年 | 5813篇 |
1987年 | 5697篇 |
1986年 | 5402篇 |
1985年 | 7013篇 |
1984年 | 7303篇 |
1983年 | 6058篇 |
1982年 | 6343篇 |
1981年 | 6192篇 |
1980年 | 6043篇 |
1979年 | 6072篇 |
1978年 | 6406篇 |
1977年 | 6349篇 |
1976年 | 6436篇 |
1975年 | 5940篇 |
1974年 | 6007篇 |
1973年 | 6252篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Conclusions Polyfluorinated tetrahydro-1,3,5-oxadiazine derivatives were obtained by the condensation of urea and thiourea with polyfluoro ketones.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2168–2169, September, 1977. 相似文献
992.
993.
994.
Sources of error in the fast neutron activation analysis determination of oxygen have been investigated and minimised. The oxygen contents of eighteen international rock standards and a sulphide ore standard have been determined, and compared with the values calculated by difference using the reported full analyses. Accuracies of 0.3% average deviation and reproducibilities of ±0.2% standard deviation have been obtained, where oxygen contents exceeded 1.0 g. 相似文献
995.
N. A. Klyuev R. A. Khmel'nitskii G. A. Mal'tseva L. N. Zhukauskaite A. N. Kost 《Chemistry of Heterocyclic Compounds》1973,9(7):895-900
The mass spectra of the following methyl-substituted hydroxyquinolines have been studied in the range of energies of the ionizing electrons of 15–50 eV: 2-hydroxy-4-methylquinoline, 6-hydroxy-2-methylquinoline, 6-hydroxy-4-methylquinoline, 8-hydroxy-2-methylquinoline, 8-hydroxy-4-methylquinoline, 2,6-dihydroxy-4-methylquinoline, and 4,6-dihydroxy-2-methylquinoline. It has been shown that the processes of dissociative ionization for the series of compounds investigated take place exclusively from the keto forms of the molecular ions. The stability to electron impact is determined largely by the degree of enolization of the structures considered. The values of the selective decomposition are given and a scheme is proposed for the identification of the isomeric methyl-substituted hydroxyquinolines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 972–978, July, 1973. 相似文献
996.
THE SYNERGISTIC ACTION OF ULTRAVIOLET AND X RADIATION ON MUTANTS OF ESCHERICHIA COLI K-12 总被引:1,自引:0,他引:1
Abstract— Prior UV irradiation increased the X-ray sensitivity of wild-type E. coli K-12. This synergistic effect of combined UV and X irradiation was also observed, but to a reduced extent, in uvrA, uvrB, uvrC , and polA mutants, but was absent in exrA, recA, recB , or recC mutants of E. coli K-12. Alkaline sucrose gradient studies demonstrated that the wand err gene-controlled, growth-medium-dependent (Type III) repair of X-ray-induced DNA single-strand breaks was inhibited by prior UV irradiation. This inhibition probably explains the synergistic effect of these two radiations on survival. 相似文献
997.
998.
Prokof'ev A. I. Solodovnikov S. P. Rasuleva D. Kh. Volod'kin A. A. Ershov V. V. 《Russian Chemical Bulletin》1970,19(7):1566-1568
Conclusions The polarographic reduction of certain methylenequinones was studied, and the mechanism of the reduction was investigated by the method of EPR spectroscopy.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1656–1658, July, 1970. 相似文献
999.
1000.
The behavior of epimanool (1), epimanool oil, larixol (2), cis-abienol (3) and methyl dehydroabietate (4) on alumina impregnated with oxidants (H2CrO4 and KMnO4) has been studied. This has led to the methyl ketone (5) and norambrenolide (8) - precursors of the perfume substances 14,15,17-trinorlabdane-8,13-dione (6), 8-hydroxy-14,15-bisnorlabd-II-en-13-one (7), and methyl 7-oxodehydroabietate (14). -Levantenolide (11) has been synthesized in one stage from cis-abienol (3)for the first time.Novosibirsk Insitute of Organic Chemistry, Siberian Division of the Russian Academy of Sciences. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 229–234, March-April, 1995. Original article submitted July 25, 1994. 相似文献