全文获取类型
收费全文 | 180017篇 |
免费 | 902篇 |
国内免费 | 265篇 |
专业分类
化学 | 89946篇 |
晶体学 | 2637篇 |
力学 | 9391篇 |
综合类 | 7篇 |
数学 | 20964篇 |
物理学 | 58239篇 |
出版年
2020年 | 1865篇 |
2019年 | 2311篇 |
2018年 | 3409篇 |
2017年 | 3537篇 |
2016年 | 4176篇 |
2015年 | 1868篇 |
2014年 | 3610篇 |
2013年 | 7073篇 |
2012年 | 5580篇 |
2011年 | 6613篇 |
2010年 | 5532篇 |
2009年 | 5662篇 |
2008年 | 6382篇 |
2007年 | 6337篇 |
2006年 | 5626篇 |
2005年 | 4991篇 |
2004年 | 4826篇 |
2003年 | 4374篇 |
2002年 | 4530篇 |
2001年 | 5005篇 |
2000年 | 3693篇 |
1999年 | 2823篇 |
1998年 | 2606篇 |
1997年 | 2460篇 |
1996年 | 2253篇 |
1995年 | 2049篇 |
1994年 | 2006篇 |
1993年 | 2039篇 |
1992年 | 2075篇 |
1991年 | 2383篇 |
1990年 | 2317篇 |
1989年 | 2385篇 |
1988年 | 2266篇 |
1987年 | 2296篇 |
1986年 | 2130篇 |
1985年 | 2658篇 |
1984年 | 2670篇 |
1983年 | 2317篇 |
1982年 | 2373篇 |
1981年 | 2277篇 |
1980年 | 2079篇 |
1979年 | 2393篇 |
1978年 | 2549篇 |
1977年 | 2640篇 |
1976年 | 2729篇 |
1975年 | 2537篇 |
1974年 | 2469篇 |
1973年 | 2637篇 |
1972年 | 2152篇 |
1971年 | 1973篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
831.
C. Oproiu S. Marghitu S. Jipa I. Mihalcea 《Journal of Radioanalytical and Nuclear Chemistry》1994,181(1):109-116
This paper presents the results of an experimental study undertaken on the irradiation process of polyethylene tubing in an electron beam. Isodoses of distribution through material thickness in case of irradiation in one or two irradiation directions have been analyzed. 相似文献
832.
Classical methods of structural analysis cannot be applied to liquid crystals because higher order reflections disappear during the transition from crystal to liquid crystal due to the reduction in long range orientational and translational correlations. However, in order to relate physical properties to the molecular architecture, it is essential to have information about molecular positions and orientations in the crystalline state as well as in the liquid crystalline state. In this work, the transition from crystalline to liquid crystalline phase is carefully monitored and the relationship between the original lattice and the new molecular positions found using electron diffraction. In addition to this, a new high resolution electron-microscopic technique is described in which the positions of molecules in the crystalline and the quenched discotic phase are directly imaged and the defects observed in the crystalline and LC phase compared and quantitatively analysed. 相似文献
833.
Di[2-(4-substituted-phenyl)-3-mercapto-propenato]-nickel(II) complexes have been synthesized and investigated. All of them are mesomorphic; they have nematic phases with wide ranges and typical Schlieren textures. 相似文献
834.
V. I. Saloutin I. T. Bazyl' Z. E. Skryabina P. N. Kondrat'ev O. N. Chupakhin 《Russian Chemical Bulletin》1994,43(2):279-282
Reactions of pentafluorobenzoylpyruvic acid with amines afford the respective enamines. The intramolecular cyclization of the latter results inN-substituted 4-quinolone-2-carboxylic acids. Ammonia and triethylamine favor the cyclization of pentafluorobenzoylpyruvic acid to 2-carboxychromone.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 299–302, February, 1994. 相似文献
835.
Reactions of acetone, cyclohexanone, and adamantanone oximes withN,N-dibromo-tert-butylamine result in the correspondingC-bromo-diazene-N-oxides. In the case of benzophenone oxime,O, O'-(diphenylmethylene)-bis-benzophenone oxime has been obtained.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 176–177, January, 1994. 相似文献
836.
837.
V. E. Kirichenko E. P. Promyshlennikova K. I. Pashkevich 《Russian Chemical Bulletin》1994,43(5):812-815
The dependence of the variations in the differential molar free energy of sorption of polyfluorocarboxamides RFC(O)NR2 (RF = CF3(CF2)
i
,i=0 to 5, R=H or Me) on capillary columns on the molecular structure of the amides, the temperature of analysis, and the nature of the stationary phases (OV-101, XE-60, and PEG-40M) were investigated by GLC. The peculiarities of the variation of the sorption characteristics of amides in XE-60 and PEG-40M polar phases, which cause the inversion of the order of retention of the members of pseudohomologous series, were found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 868–871, May, 1994.We are grateful to R. V. Golovnya and D. N. Grigor'eva (Institute of Food Substances of the RAS, Moscow) for their participation in the discussion of the results obtained. 相似文献
838.
V. P. Bubnov I. S. Krainskii E. E. Laukhina E. B. Yagubskii 《Russian Chemical Bulletin》1994,43(5):746-750
The effect of the parameters of the electric arc (helium pressure, current and voltage, clearance between electrodes) and of the peculiarities of the setup design (arrangement of electrodes, distance between the arc and the cooling surface, temperature of the soot condensation surface) on the yield of fullerenes has been studied. Conditions for producing soot with a C60 and C70 content up to 43% (toluene extract) have been found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 805–809, May, 1994.The authors are grateful to N. G. Spitsyna and A. V. Dubovitskii for the determination of the content of C60 and C70 fullerenes in the extract.The work was financially supported by the Russian Foundation for Basic Research (Project 93-03-18705). 相似文献
839.
Sokolova T. N. Grishin Yu. K. Timofeev I. V. Kartashov V. R. 《Russian Chemical Bulletin》1994,43(6):1044-1047
Regiochemistry and stereochemistry of the addition of mercury salts to benzobarrelene and tetrafluorobenzobarrelene have been studied in acetic acid and methanol. The effect of the substrate structure on the regiochemistry of the reaction is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1105–1108, June, 1994. 相似文献
840.
Potassium salts of O-substitutedN-nitrohydroxylamines were synthesized by nitration of O-substituted.N-acetylhydroxylamines followed by treatment of the reaction products with potassium methoxide.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 178–179, January, 1994. 相似文献