全文获取类型
收费全文 | 1106篇 |
免费 | 38篇 |
国内免费 | 4篇 |
专业分类
化学 | 840篇 |
晶体学 | 12篇 |
力学 | 13篇 |
综合类 | 1篇 |
数学 | 64篇 |
物理学 | 218篇 |
出版年
2023年 | 11篇 |
2022年 | 6篇 |
2021年 | 16篇 |
2020年 | 13篇 |
2019年 | 21篇 |
2018年 | 16篇 |
2017年 | 10篇 |
2016年 | 20篇 |
2015年 | 27篇 |
2014年 | 27篇 |
2013年 | 51篇 |
2012年 | 64篇 |
2011年 | 67篇 |
2010年 | 37篇 |
2009年 | 42篇 |
2008年 | 64篇 |
2007年 | 73篇 |
2006年 | 108篇 |
2005年 | 77篇 |
2004年 | 63篇 |
2003年 | 65篇 |
2002年 | 43篇 |
2001年 | 17篇 |
2000年 | 24篇 |
1999年 | 13篇 |
1998年 | 13篇 |
1997年 | 17篇 |
1996年 | 9篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 8篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 13篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1970年 | 3篇 |
1966年 | 3篇 |
1935年 | 2篇 |
排序方式: 共有1148条查询结果,搜索用时 312 毫秒
11.
12.
13.
14.
T Takamura T Kato E Arakawa S Ogawa Y Suzumura T Kato 《Chemical & pharmaceutical bulletin》1989,37(10):2828-2831
Several analogues substituted with fatty acid at the 2'-, 3'-, or 5'-position of the ribose moiety of N6,N6-dimethyladenosine were synthesized and tested for antitumor activity against cultured cells of L1210 leukemia and/or Ehrlich ascites. The cytotoxicity and increase of life span obtained with congeners in the N6,N6-dimethyladenosine 3'- or 5'-substituted series were comparable to in vitro or several times better in vivo than those of the mother compound. 相似文献
15.
The electronic effect on the regioselectivity in the alkynylation of phenyloxiranes was investigated using three kinds of metal acetylides. BF3 mediated lithium acetylide provided either the α- or β-alkynylated products by controlling the effect of the para-substituents of the phenyloxiranes. LiClO4 mediated lithium acetylide and titanium acetylide, on the other hand, afforded predominantly the β- and α-products, respectively. 相似文献
16.
Arakawa Y Ohnishi M Yoshimura N Yoshifuji S 《Chemical & pharmaceutical bulletin》2003,51(8):1015-1020
Synthesis of (1R,2S,5S,6R,8S)-3-azabicyclo[3.3.0]octane-2,6,8-tricarboxylic acid (2) from trans-4-hydroxy-L-proline (5) was attempted. A Diels-Alder reaction of 3,4-dehydroproline derivative 9 and cyclopentadiene afforded a single stereoisomer 11. The Diels-Alder adduct was smoothly converted to the hydrochloride of 2 (24) via RuO(4) oxidation. Although some racemization of the material or product was observed during the synthetic processes, the amino acid 24 proved to be optically pure. 相似文献
17.
Shin-ichi Hirano Toshinobu Yogo Wataru Sakamoto Seiji Yamada Tomoyuki Nakamura Tomoe Yamammto Hiroyuki Ukai Kouichi Banno Tomoko Nakafuku Yukari Ando 《Journal of Sol-Gel Science and Technology》2003,26(1-3):35-41
Nano sized crystalline particles/polymer hybrids were synthesized form designed metal-organic precursors. The newly developed method is composed of the synthesis of organic matrix by polymerization and the in situ nucleation and growth of crystalline oxide particles in the organic matrix below 100°C. The design of metal-organic precursor modified with polymerizable ligand and the selection of reaction conditions does influence the size and crystallinity of ceramic particles in organic matrix. The nano-sized magnetic particle/polymer hybrid exhibits the interesting feature of superparamagnetism and quantum size effect. The crystalline particles of BaTiO3/, PbTiO3/, and KNbO3/polymer hybrids behave to be dielectric and show the typical electro-rheological behavior. 相似文献
18.
Mizooku Y Yoshikawa M Tsuneyoshi T Arakawa R 《Rapid communications in mass spectrometry : RCM》2003,17(16):1915-1918
(-)-Epigallocatechin gallate (EGCG) of catechins changes from non-colored at around neutral pH to yellow at higher pH region in aqueous solution. The pH-dependent oxidation of EGCG was analyzed by liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS). LC/MS/MS analysis of EGCG and its related compounds, (-)-epicatechin gallate (ECG) and (-)-epigallocatechin (EGC), successfully elucidated the structure relationship of EGCG solution involving the color change reaction at different pH conditions. The oxidation species produced at alkaline pH was detected at a different retention time from EGCG in the chromatograms of the EGCG sample. The oxidation species was found to correspond to M+14 (where M is the molecular weight of EGCG), which has two hydrogen atoms removed and addition of one oxygen atom to the gallyl moiety in the B-ring of EGCG. 相似文献
19.
Fumiyo Saito Ryo Takeuchi Tomoyuki Kamino Kouji Kuramochi Kengo Sakaguchi Susumu Kobayashi Masashi Tsuda 《Tetrahedron letters》2004,45(43):8069-8071
A total synthesis of the proposed structure of plakevulin A was accomplished. However, the NMR spectral data of the synthetic plakevulin A were not identical of those of the reported compound. We next converted the synthetic plakevulin A into 1-dihydrountenone A. The 1H and 13C NMR spectral data of 1-dihydrountenone A were identical with those of reported plakevulin A except for the peaks derived from levulinic acid. Thus, we repurified sample of the natural product and confirmed that the natural sample contained 1-dihydrountenone A and levulinic acid in the ratio of one to one. We also found that not plakevulin A but 1-dihydountenone A possessed the inhibitory activity against mammalian DNA polymerases α and β. 相似文献
20.
Tomoyuki Yoshimura 《Tetrahedron letters》2004,45(50):9241-9244
Diastereoselective construction of the 19-epi-C18-C25 segment of (−)-lasonolide A was achieved using a 5-exo-trigonal mode of radical cyclization for the creation of the contiguous quaternary and tertiary stereogenic centers at C22 and C23 as the key reaction step. During the dehydration stage, it was found that an unusual inversion of configuration took place. 相似文献