全文获取类型
收费全文 | 33215篇 |
免费 | 1880篇 |
国内免费 | 4971篇 |
专业分类
化学 | 33263篇 |
晶体学 | 621篇 |
力学 | 179篇 |
综合类 | 167篇 |
数学 | 1200篇 |
物理学 | 4636篇 |
出版年
2024年 | 36篇 |
2023年 | 300篇 |
2022年 | 510篇 |
2021年 | 670篇 |
2020年 | 805篇 |
2019年 | 1709篇 |
2018年 | 848篇 |
2017年 | 1704篇 |
2016年 | 1111篇 |
2015年 | 992篇 |
2014年 | 1394篇 |
2013年 | 3034篇 |
2012年 | 1963篇 |
2011年 | 2076篇 |
2010年 | 1522篇 |
2009年 | 1802篇 |
2008年 | 2051篇 |
2007年 | 2158篇 |
2006年 | 2029篇 |
2005年 | 1887篇 |
2004年 | 1824篇 |
2003年 | 1478篇 |
2002年 | 1172篇 |
2001年 | 977篇 |
2000年 | 964篇 |
1999年 | 742篇 |
1998年 | 680篇 |
1997年 | 543篇 |
1996年 | 465篇 |
1995年 | 474篇 |
1994年 | 383篇 |
1993年 | 333篇 |
1992年 | 307篇 |
1991年 | 222篇 |
1990年 | 132篇 |
1989年 | 124篇 |
1988年 | 101篇 |
1987年 | 64篇 |
1986年 | 54篇 |
1985年 | 62篇 |
1984年 | 54篇 |
1983年 | 24篇 |
1982年 | 55篇 |
1981年 | 53篇 |
1980年 | 29篇 |
1979年 | 55篇 |
1978年 | 20篇 |
1977年 | 19篇 |
1976年 | 16篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
151.
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
152.
Maria Carmelita Kasuya 《Journal of fluorine chemistry》2007,128(5):562-565
A series of fluorinated galactosides, dodecyl 2-deoxy-2-fluoro-β-d-galactopyranoside (2F Gal), dodecyl 4-deoxy-4-fluoro-β-d-galactopyranoside (4F Gal) and dodecyl 6-deoxy-6-fluoro-β-d-galactopyranoside (6F Gal), was chemically synthesized and introduced to B16 cells to serve as scaffolds for cellular enzyme glycosylation. Results showed that the presence of fluorine exercised significant effects on cell viability. Among the fluorinated galactosides used, 2F Gal was glycosylated to afford a GM4 analogue. 相似文献
153.
R. Souzy B. Ameduri B. Boutevin 《Journal of polymer science. Part A, Polymer chemistry》2004,42(20):5077-5097
The radical co‐ and terpolymerization of 4‐[(α,β,β‐trifluorovinyl)oxy]bromo benzene (TFVOBB) with 1,1‐difluoroethylene (or vinylidene fluoride, VDF, or VF2), hexafluoropropene (HFP), perfluoromethyl vinyl ether (PMVE), and chlorotrifluroroethylene (CTFE) is presented. Although TFVOBB could be thermocyclodimerized, it could not homopolymerize under radical initiation. TFVOBB could be copolymerized in solution under a radical initiator with VDF or CTFE comonomers, while its copolymerization with HFP or PMVE were unsuccessful. The terpolymerization of TFVOBB with VDF and HFP, or VDF and PMVE, or VDF and CTFE also led to original fluorinated terpolymers bearing bromoaromatic side‐groups. The conditions of co‐ and terpolymerization were optimized in terms of the nature of the radical initiators, and of the nature of solvents (fluorinated or nonhalogenated). Various monomer concentrations in the co‐ and terpolymers were assessed by 19F and 1H‐NMR spectroscopy. The thermal and physico chemical properties were also studied. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5077–5097, 2004 相似文献
154.
155.
156.
A. S. Peregudov L. N. Usatova E. I. Smyslova E. I. Fedin D. N. Kravtsov 《Russian Chemical Bulletin》1995,44(8):1513-1519
It has been shown by the19F NMR method that the relative polarities of nitrogenelement bonds in 2-(4-fluorophenyl)benzimidazole and its PhHg and PPh3Au derivatives increase in the order N-H19F NMR. It has been found that these reactions occur by a bimolecular associative mechanism and that the N-H bond is substantially less reactive than the N-Hg and N-Au bonds, which have identical reactivities within the limits of sensitivity of the method used.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1574–1580, August, 1995.This work was carried out with financial support from the Russian Foundation for Basic Research (Project No. 93-03-5528). 相似文献
157.
Ajay K. Saini Clifford M. Carlin Howard H. Patterson 《Journal of polymer science. Part A, Polymer chemistry》1992,30(3):419-427
New model compounds for poly[N,N′-bis(phenoxyphenyl)pyromellitimide] have been synthesized in order to investigate the formation of imine bonds which are proposed to form during the curing process and lead to crosslinking in the bulk polymer. Raman studies show that terminal amines can react with imide carbonyls during curing to form C?N bonds. The Raman band due to C?N appears at 1656 cm?1 and the band due to C?O closest to the imine bond is observed at 1742 cm?1. These results are in agreement with previously published results on vapor deposited polyimide films. 相似文献
158.
Trichloroethylene has been found to act as a rate enhancing co-factor in the liquid phase, tantalum (V) halide catalyzed, fluorine-for-chlorine exchange reaction of 1,2-dichloro-1,1-difluoroethane (R-132b) to 2-chloro-1,1,1-trifluorethane (R-133a). Several trifluoromethyl substituted benzenes have also been found to be rate-enhancing solvents. 相似文献
159.
160.
利用内径为57 mm的压缩气炮,在撞击速度为0.2~1.2 km/s(相应的靶中压力为3~15 GPa)范围内进行对称碰撞实验,以研究TC4(Ti-Al6-V4)钛合金在一维应变冲击压缩条件下的绝热剪切现象。对回收得到的受冲击样品,在扫描电镜(SEM)下进行细观金相分析。结果指出,一维应变冲击压缩条件下,TC4钛合金中绝热剪切带产生的对称碰撞速度阈值为500 m/s(相当于样品中的压力为5.87 GPa);主剪切带与冲击方向约为45°角,带上有圆形和椭圆形两种孔洞且随碰撞速度的增大而增多和长大,这是典型的韧性损伤特征。随碰撞速度增大,产生与主剪切带成15°角的支剪切带。这些与理论预言相符。X射线能谱分析结果指出,剪切带内材料发生了(α+β)→β相的转变,是典型的相变带。剪切带的温度估算与实验提供的信息吻合。 相似文献