全文获取类型
收费全文 | 1379篇 |
免费 | 21篇 |
国内免费 | 5篇 |
专业分类
化学 | 972篇 |
晶体学 | 11篇 |
力学 | 16篇 |
数学 | 54篇 |
物理学 | 352篇 |
出版年
2023年 | 7篇 |
2022年 | 10篇 |
2021年 | 15篇 |
2020年 | 11篇 |
2019年 | 22篇 |
2017年 | 11篇 |
2016年 | 15篇 |
2015年 | 12篇 |
2014年 | 22篇 |
2013年 | 85篇 |
2012年 | 40篇 |
2011年 | 52篇 |
2010年 | 27篇 |
2009年 | 39篇 |
2008年 | 67篇 |
2007年 | 63篇 |
2006年 | 55篇 |
2005年 | 49篇 |
2004年 | 47篇 |
2003年 | 65篇 |
2002年 | 51篇 |
2001年 | 32篇 |
2000年 | 46篇 |
1999年 | 31篇 |
1998年 | 21篇 |
1997年 | 21篇 |
1996年 | 16篇 |
1995年 | 10篇 |
1994年 | 21篇 |
1993年 | 15篇 |
1992年 | 41篇 |
1991年 | 20篇 |
1990年 | 19篇 |
1989年 | 21篇 |
1988年 | 25篇 |
1987年 | 26篇 |
1986年 | 18篇 |
1985年 | 28篇 |
1984年 | 22篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 19篇 |
1980年 | 14篇 |
1979年 | 28篇 |
1978年 | 22篇 |
1977年 | 13篇 |
1976年 | 11篇 |
1975年 | 12篇 |
1974年 | 13篇 |
1973年 | 20篇 |
排序方式: 共有1405条查询结果,搜索用时 15 毫秒
11.
12.
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
13.
(Styrene-p-chlorostyrene) triblock copolymers of the ABA and BAB types (A—polystyrene; B—poly-p-chlorostyrene) were prepared by anionic polymerization and their conformational behaviours in solutions were studied from measurements of the dipole moments. Two solvents, toluene and cumene, were used for the study; toluene is a good solvent for both polystyrene and poly-p-chlorostyrene whereas cumene is a selective solvent, good for polystyrene but poor for poly-p-chlorostyrene. It was found that the dipole moments of the block copolymers measured in toluene are the same for the ABA and BAB copolymers; in cumene however the dipole moment of the BAB copolymer is smaller than that of the ABA copolymer. The results give an additional support to our previous conclusion that the conformation of the block copolymers in a good solvent such as toluene could be approximated with a pseudo-random coil form; in a selective solvent, however, some anomalies take place in the conformation of the block copolymers, as deduced from intrinsic viscosity, osmotic pressure and light scattering measurements. 相似文献
14.
M Ogawa H Matsuda H Eto T Asaoka T Kuraishi A Iwasa T Nakashima K Yamaguchi 《Chemical & pharmaceutical bulletin》1991,39(9):2301-2307
A series of vinylimidazoles containing a hetero atom such as sulfur or oxygen at a beta-position of the vinyl group was prepared and the antifungal activities were tested. It was found that sulfur-substituted derivatives such as (E)-1-[2-(methylthio)-1-[2-(pentyloxy)phenyl]ethenyl]-1H-imidazole (5a-5) and (E)-1-[1-[2-(hexyloxy)phenyl]-2-(methylthio)ethenyl]-1H-imidazole (5a-6) showed excellent antifungal activities against dermatophytes and yeast cells. The stereochemistry of the hydrochloride salt of 5a-5 was determined by X-ray crystallography. The structure-activity relationships were discussed. 相似文献
15.
Kawasaki T Nonaka Y Watanabe K Ogawa A Higuchi K Terashima R Masuda K Sakamoto M 《The Journal of organic chemistry》2001,66(4):1200-1204
The reverse aromatic Cope rearrangement of 2-allyl-3-alkylideneindolines obtained by Horner-Wadsworth-Emmons olefination of 2-allylindolin-3-ones was performed. When 2-allylindolin-3-ones were treated with phosphonium ylides in refluxing toluene, domino Wittig reaction and reverse aromatic Cope rearrangement took place to give alpha-allyl-3-indole acetate derivatives in good yields. The aromatization as a new driving force in the Cope rearrangement is preferable to the conjugation with the carbonyl and cyano groups and also to the alkyl substitution pattern, which are well-known driving forces. 相似文献
16.
Sano S Takehisa T Ogawa S Yokoyama K Nagao Y 《Chemical & pharmaceutical bulletin》2002,50(9):1300-1302
Tetrasubstituted (Z)-alkenes were readily prepared through the Horner-Wadsworth-Emmons reactions of methyl 2-[bis(2,2,2-trifluoroethyl)phosphono]propionate with aryl alkyl ketones by employing Sn(OSO(2)CF(3))(2) and N-ethylpiperidine. 相似文献
17.
Tomomi KawasakiAtsuyo Ogawa Yasuyuki TakashimaMasanori Sakamoto 《Tetrahedron letters》2003,44(8):1591-1593
A new and efficient total synthesis of (−)-pseudophrynaminol, the pyrrolo[2,3-b]indole alkaloid bearing the allylic moiety at the 3a-position, has been achieved by a sequence involving 3-allylindol-2-one 8 as a key intermediate. The enantioselective construction of the quaternary carbon in 8 was performed through a tandem cascade reaction of 2-allyloxyindolin-3-one 4, olefination, isomerization, and asymmetric Claisen rearrangement. 相似文献
18.
The degradation of acenaphthylene, acenaphthene, 2-methylnaphthalene, 2-methylindene, 3-methylindene and indene in water solutions was studied. These compounds at the 25-150 mug/l. level were almost totally degraded at ambient temperature within three days. The microbial population responsible for the degradation occurs naturally in ground-water taken from an aquifer in Ames, Iowa, which is contaminated with coal-tar products. These unidentified micro-organisms adapt readily to other waters when used as an inoculant for the degradation of aromatic compounds. The preservation of water to prevent such degradation was also investigated. Filtration through a 0.45-mum filter was found the most effective procedure for preserving the hydrocarbons in these waters. 相似文献
19.
Ogawa T Araki M Miyamae T Okayama T Hagiwara M Sakurada S Morikawa T 《Chemical & pharmaceutical bulletin》2003,51(7):759-771
To improve the oral bioavailability of a dermorphin tetrapeptide analog, N(alpha)-1-iminoethyl-Tyr-D-MetO-Phe-MebetaAla-OH (III), which has a potent analgesic activity after oral administration, various derivatives were synthesized to increase lipophilicity by esterification of the C-terminal carboxyl group and/or acylation of the phenolic hydroxyl group on Tyr1. Antinociceptive activity was evaluated after subcutaneous or oral administration using the mouse tail pressure test. As a result, increased antinociceptive activity after oral administration as well as an improved ED50(p.o.)/ED50(s.c.) ratio, which is an indicator of oral bioavailability, were found for some compounds. With regard to the improvement of bioavailability, derivatives with acylation of the phenolic hydroxyl group on Tyr1 showed better results than derivatives with esterification of the C-terminal carboxyl group. In particular, an ED50(p.o.)/ED50(s.c.) ratio equivalent to that of morphine was found for an acetylated derivative, N(alpha)-1-iminoethyl-Tyr(COMe)-D-MetO-Phe-MebetaAla-OH (7a), as well as for a methoxycarbonylated derivative, N(alpha)-1-iminoethyl-Tyr(CO2Me)-D-MetO-Phe-MebetaAla-OH (7l). 相似文献
20.
Jun-ichi KawakamiMitsuhiro Takeba Ikuyo KamiyaNoboru Sonoda Akiya Ogawa 《Tetrahedron》2003,59(34):6559-6567
Highly regioselective thioformylation of terminal acetylenes with thiols and carbon monoxide has been developed by the use of rhodium(I) complexes as the catalyst: formyl and thio groups are introduced into the terminal and inner positions of acetylenes, respectively. The thioformylation is performed in the presence of a catalytic amount of rhodium(I) complexes, such as RhH(CO)(PPh3)3, RhCl(PPh3)3, and RhCl(CO)(PPh3)2, under the pressure of CO (3 MPa) at 120°C in CH3CN to provide β-thio-α,β-unsaturated aldehydes in good yields. This thioformylation can be applied to a variety of terminal acetylenes and aromatic thiols. A mechanistic proposal includes the formation of the rhodium sulfide complex as the key species. 相似文献