全文获取类型
收费全文 | 1571篇 |
免费 | 94篇 |
国内免费 | 3篇 |
专业分类
化学 | 1214篇 |
晶体学 | 19篇 |
力学 | 21篇 |
数学 | 57篇 |
物理学 | 357篇 |
出版年
2023年 | 17篇 |
2022年 | 18篇 |
2021年 | 35篇 |
2020年 | 27篇 |
2019年 | 40篇 |
2018年 | 27篇 |
2017年 | 28篇 |
2016年 | 38篇 |
2015年 | 43篇 |
2014年 | 53篇 |
2013年 | 76篇 |
2012年 | 89篇 |
2011年 | 98篇 |
2010年 | 58篇 |
2009年 | 45篇 |
2008年 | 98篇 |
2007年 | 91篇 |
2006年 | 70篇 |
2005年 | 78篇 |
2004年 | 56篇 |
2003年 | 44篇 |
2002年 | 42篇 |
2001年 | 44篇 |
2000年 | 32篇 |
1999年 | 26篇 |
1998年 | 25篇 |
1997年 | 13篇 |
1996年 | 19篇 |
1995年 | 15篇 |
1994年 | 14篇 |
1993年 | 21篇 |
1992年 | 25篇 |
1991年 | 22篇 |
1990年 | 16篇 |
1989年 | 26篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 17篇 |
1985年 | 16篇 |
1984年 | 17篇 |
1983年 | 11篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1979年 | 15篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1976年 | 10篇 |
1975年 | 9篇 |
1974年 | 12篇 |
1973年 | 9篇 |
排序方式: 共有1668条查询结果,搜索用时 15 毫秒
11.
N Murakami T Tanase S Nagai Y Sato T Ueda J Sakakibara H Ando Y Hotta K Takeya 《Chemical & pharmaceutical bulletin》1991,39(8):1962-1966
The Diels-Alder reactions of a cardiac glycoside, proscillaridin (1), with some dienophiles were investigated. The reaction of 1 with alkenes such as methyl vinyl ketone and methyl acrylate afforded 3-oxo-2-oxabicyclo[2.2.2]oct-7-enes (2-5) and para-substituted benzene derivatives (6 and 7), while 1 reacted with alkynes (3-butyn-2-one, methyl propiolate) to yield para- or meta-substituted benzene derivatives (6-9). The biological activities of the resulting derivatives were evaluated by the use of isolated guinea-pig papillary muscle preparations and Na+,K(+)-adenosine triphosphatase (ATPase) preparation from dog kidney. Among the proscillaridin derivatives, compounds 4 and 7 moderately inhibited Na+,K(+)-ATPase activity. Furthermore, the concentration range of 7 over which its positive inotropic effect on guinea-pig papillary muscle preparations, increased from 5% to 95% of maximum was broader than that of 1, i.e., concentration dependency was maintained over a greater range of concentration. 相似文献
12.
M. Sugawara H. Kusakari T. Murakami T. Kohno 《The European Physical Journal A - Hadrons and Nuclei》1998,1(3):237-239
A new rotational band has been observed in 167Lu by 152Sm (19F,4n)reaction at the HI-13 tandem accelerator of CIAE in Beijing. The high spin transition energies of the new band are almost
identical to the triaxial superdeformed bands recently discovered in 163Lu and 165Lu. This new band is predicted as a triaxial superdeformed band by total routhian surface calculations.
Received: 6 October 1997 相似文献
13.
14.
Bond IA Budding E Conway MJ Fenton KB Fujii H Fujii Z Fujimoto M Hasegawa H Hayashida N Honda M Hotta N Humble JE Kabe S Kasahara K Kifune T Masaike A Matsubara Y Mitsui K Miura Y Mori M Murakami K Muraki Y Nagano M Nakamura K Nakamura T Norris PM Ohashi Y Okada A Saito T Sakata M Sato H Shibata S Shima M Storey JR Tanimori T Teshima M Torii S Uchino K Watase Y Woodhams MD Yamamoto Y Yock PC Yuda T 《Physical review letters》1988,61(20):2292-2295
15.
Anionic cycloaddition of methyl isocyanoacetate to diethoxyacetonitrile afforded methyl 5-diethoxymethylimidazole-4-carboxylate, a useful imidazole nucleus with two different functional groups. 相似文献
16.
17.
Masafumi Unno Hiroyuki Murakami Satoshi Kagawa Hideyuki Matsumoto 《Silicon Chemistry》2007,3(3-4):195-198
Two new silanols bearing very bulky silyl groups, (i-Pr3
Si)3SiOH and (t − BuMe2Si)3SiOH were prepared by peracidoxidation of their respective silanes. The X − ray crystallographic analysis revealed that (t − BuMe2Si)3 SiOH forms a dimeric structure with hydrogen bonding, while (i − Pr3 Si)3 SiOH exists as a monomer in the crystal. The effects of the size of the substituents as well as the reactivity of these silanols
are discussed. 相似文献
18.
1,6-Enynes reacted with arylboronic acids in the presence of a catalytic amount of a rhodium(I) complex under mild conditions to give (Z)-1-(1-arylethylidene)-2-vinylcyclopentanes. The regioselective addition of an arylrhodium(I) species across the carbon-carbon triple bond triggered the cyclization process. Intramolecular carborhodation onto the pendent alkene in a 5-exo mode furnished a five-membered ring. Finally, the rhodium(I) methoxide generated by beta-methoxy elimination reacted with the arylboronic acid to promote the next catalytic cycle. 相似文献
19.
A highly selective and sensitive method of fluorometry is described for determination of the fluoride ion at the parts per billion level via the ion-pair complex formation of the fluoride ion with an expanded prophyrin [2,23-diethyl-8,17-bis(2-ethoxycarbonylethyl)-3,7,12,13,18,22-hexamethylsapphyrin (H3sap)]. The ion-pair complex gives out an enhanced fluorescence intensity at 680 nm on excitation at 450 nm. Since the present method is based on a direct reaction of the fluoride ion with the sappyrin, a 200-fold amount of the aluminum (III) ion [10−4M (M = mol dm−3)] and a 2000-fold amount of the iron(III) ion (10−3M) over the fluoride ion did not interfere with determination of the fluoride ion at concentrations as low as 5 × 10−7M in the presence of 1,2-diaminocyclohexane-N,N,N′,N′-teraacetic acid. The proposed method was applied to determination of the fluoride ion in various water samples (tap water, river water, rain water, underground water, and hot spring water) and satisfactory results were obtained. 相似文献
20.