全文获取类型
收费全文 | 3614篇 |
免费 | 317篇 |
国内免费 | 439篇 |
专业分类
化学 | 4165篇 |
晶体学 | 13篇 |
力学 | 4篇 |
综合类 | 17篇 |
物理学 | 171篇 |
出版年
2024年 | 5篇 |
2023年 | 26篇 |
2022年 | 66篇 |
2021年 | 105篇 |
2020年 | 165篇 |
2019年 | 128篇 |
2018年 | 110篇 |
2017年 | 124篇 |
2016年 | 138篇 |
2015年 | 162篇 |
2014年 | 182篇 |
2013年 | 388篇 |
2012年 | 210篇 |
2011年 | 210篇 |
2010年 | 171篇 |
2009年 | 188篇 |
2008年 | 201篇 |
2007年 | 186篇 |
2006年 | 169篇 |
2005年 | 157篇 |
2004年 | 167篇 |
2003年 | 175篇 |
2002年 | 130篇 |
2001年 | 74篇 |
2000年 | 76篇 |
1999年 | 75篇 |
1998年 | 84篇 |
1997年 | 52篇 |
1996年 | 68篇 |
1995年 | 53篇 |
1994年 | 51篇 |
1993年 | 55篇 |
1992年 | 50篇 |
1991年 | 29篇 |
1990年 | 21篇 |
1989年 | 16篇 |
1988年 | 15篇 |
1987年 | 10篇 |
1986年 | 15篇 |
1985年 | 10篇 |
1984年 | 15篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有4370条查询结果,搜索用时 578 毫秒
991.
Young Ho Kim Bong Seok Moon F. W. Harris S. Z. D. Cheng 《Journal of Thermal Analysis and Calorimetry》1996,46(3-4):921-933
A new high molecular weight polyimide based on 4,4-oxidiphthalic anhydride (ODPA) dianhydride and 2,2-dimethyl-4,4-diaminobiphenyl (DMB) diamine has been synthesizedvia a one-step polymerization method. This polyimide is soluble in phenolic solvents. Films from 7 to 30 m thick were cast from the polymer solution and show in-plane orientation on a molecular scale detected by Fourier transform infrared spectroscopy experiments. This anisotropic structure leads to anisotropic optical properties arising from two different refractive indices along the inplane and out-of-plane directions. ODPA DMB possesses high thermal and thermo-oxidative stability. The glass transition temperature has been determined to be 298 °C. Dynamic mechanical analyses show two relaxation processes appearing above room temperature: the - and the -relaxation processes. The -relaxation corresponds to the glass transition while the -relaxation is a secondary relaxation process associated with the non-cooperative subsegmental motion.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayYHK acknowledges the support from the Yonam Foundation, Korea. This work was also supported by the Center of Molecular and Microstructure of Composites (CMMC) of NSF/EPIC/Industry, SZDC gratefully acknowledges the support from his PYI Award (DMR-9157738) from the National Science Foundation. 相似文献
992.
Veselovsky V. V. Lozanova A. V. Maltsev S. D. Danilov L. L. Shibaev V. N. Jedrzejas M. J. 《Russian Chemical Bulletin》2001,50(11):2221-2226
A series of fluorescent dolichyl phosphates containing the (1-naphthyl)amino group in the -fragment of the chain and possessing a definite distance between fluorophoric and phosphate groups were synthesized for studying the interactions of dolichyl phosphates with enzymes and biological membranes. The corresponding terminal 2,3-dihydrohexadeca-, 2,3-dihydroundeca-, and 2,3-dihydrooctaprenol epoxides were obtained from racemic dolichols (prepared from natural polyprenol mixtures) by van Tamelen epoxidation of their -isoprene unit and separated by preparative HPLC. These epoxides were converted to aldehydes, which were subjected to reductive amination with 1-aminonaphthalene and NaBH4 with subsequent phosphorylation of the resulting amino alcohols. 相似文献
993.
994.
995.
The condensation reaction rates of 7,9‐dioxo‐6,10‐dioxaspiro[4.5]decane with aromatic aldehydes in chloroform in the presence of piperidine has been investigated spectrophotometrically at 25–50 °C. The reaction follows overall second order kinetics, first order in each of the reactants and zero order with respect to piperidine. The rate of condensation increases with the presence of electron withdrawing groups on the aromatic ring of the aldehyde. From the dependence of the rate constants on temperature, activation parameters have been calculated. Plot of ΔH# versus ΔS# for the reaction gave a good straight line with an isokinetic temperature of 367.55 K. Based on this reaction, determination often aromatic aldehydes in a concentration range of 2.65–69.2 μg/mL is proposed. 相似文献
996.
Kenji Miyatake Mitsutoshi Jikei Kimihisa Yamamoto Hiroyuki Nishide Eishun Tsuchida 《先进技术聚合物》1992,3(7):401-405
The electrophilic reaction of sulfur dichloride with diphenyl sulfide proceeds efficiently at room temperature to yield oligo(phenylene sulfide) in the presence of a catalytic amount of Fe powder. Sulfur dichloride shows higher reactivity than sulfur monochloride. The reaction is promoted through the activation of sulfur dichloride by Fe powder. The polymeric product contains a linear structure linked by disulfide and sulfide bonds. 相似文献
997.
I. I. Oleynik I. V. Oleynik S. S. Ivanchev G. A. Tolstikov 《Russian Chemical Bulletin》2007,56(6):1174-1177
A formic acid-catalyzed reaction of substituted cycloalkylanilines with 4,6-dibenzofuran-and 4,6-dibenzothiophenedicarboxaldehydes
in methanol-dichloromethane mixture afforded a number of the corresponding diimines, which can be of interest as components
of catalytic systems for polymerization of olefins.
Dedicated to the memory of Academician N. N. Vorozhtsov on the 100th anniversary of his birth.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1131–1134, June, 2007. 相似文献
998.
G. V. Kryshtal G. M. Zhdankina I. V. Astakhova S. G. Zlotin 《Russian Chemical Bulletin》2004,53(3):647-651
Metal carbonate-catalyzed reactions of CH-acids (diethyl malonate, ethyl acetoacetate, ethyl cyanoacetate, and ethyl 2-acetyl- and 2-ethoxycarbonyl-5,9-dimethyldeca-4,8-dienoates) with ,-unsaturated aldehydes (acrolein, crotonaldehyde, citral) were studied in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6], and in a 1-butyl-3-methylimidazolium bromide ([bmim][Br]) — benzene system. The reactions with acrolein and crotonaldehyde afforded Michael addition products, those with citral resulted in Knoevenagel addition products. Sonication increased the yields of the Michael adducts. The ionic liquid [bmim][PF6] can be recovered and repeatedly used in the reactions. 相似文献
999.
1000.