全文获取类型
收费全文 | 3804篇 |
免费 | 79篇 |
国内免费 | 20篇 |
专业分类
化学 | 2492篇 |
晶体学 | 50篇 |
力学 | 62篇 |
数学 | 239篇 |
物理学 | 1060篇 |
出版年
2022年 | 24篇 |
2021年 | 23篇 |
2020年 | 41篇 |
2019年 | 47篇 |
2018年 | 32篇 |
2017年 | 30篇 |
2016年 | 51篇 |
2015年 | 66篇 |
2014年 | 62篇 |
2013年 | 209篇 |
2012年 | 169篇 |
2011年 | 199篇 |
2010年 | 115篇 |
2009年 | 131篇 |
2008年 | 200篇 |
2007年 | 219篇 |
2006年 | 214篇 |
2005年 | 176篇 |
2004年 | 129篇 |
2003年 | 132篇 |
2002年 | 149篇 |
2001年 | 98篇 |
2000年 | 110篇 |
1999年 | 70篇 |
1998年 | 41篇 |
1997年 | 43篇 |
1996年 | 66篇 |
1995年 | 46篇 |
1994年 | 34篇 |
1993年 | 45篇 |
1992年 | 67篇 |
1991年 | 43篇 |
1990年 | 43篇 |
1989年 | 41篇 |
1988年 | 61篇 |
1987年 | 45篇 |
1986年 | 51篇 |
1985年 | 62篇 |
1984年 | 62篇 |
1983年 | 28篇 |
1982年 | 42篇 |
1981年 | 37篇 |
1980年 | 40篇 |
1979年 | 41篇 |
1978年 | 36篇 |
1977年 | 43篇 |
1976年 | 22篇 |
1975年 | 31篇 |
1974年 | 31篇 |
1973年 | 24篇 |
排序方式: 共有3903条查询结果,搜索用时 15 毫秒
41.
42.
43.
T. Takahashi S. Uchida H. Hayashi S. Matsuoka K. Tomita N. Kurosawa 《Journal of Radioanalytical and Nuclear Chemistry》2007,272(3):451-454
For the assessment of a public impact caused by radionuclides released from nuclear facilities, a dynamic compartment model
was developed for prediction of behavior of radioiodine in air, paddy field and rice plant system. The transfer coefficients
among compartments were determined by some experimental data and assumptions for each chemical form of iodine. A verification
of the model was carried out by some case studies. 相似文献
44.
Kazufumi Takahashi Raymond N. Castle Milton L. Lee 《Journal of heterocyclic chemistry》1987,24(4):977-979
The four acridinecarbaldehydes, namely, acridine-1-carbaldehyde, acridine-2-carbaldehyde, acridine-3-carbaldehyde, and acridine-4-carbaldehyde have been synthesized for the first time. 相似文献
45.
Yoshihiro Itoh Masamitsu Inoue Tomoko Takahashi Akira Hachimori Satoshi Suzuki 《Journal of polymer science. Part A, Polymer chemistry》1995,33(7):1069-1074
Alternating and random copolymers of 9-phenanthrylmethyl methacrylate or 2-(9-carbazolyl)ethyl methacrylate with styrene were synthesized and their fluorescence properties were examined. There was no noticeable difference in the spectral features of the alternating and random copolymers in tetrahydrofuran (THF), demonstrating that this type of polymers have no quenching sites in the polymer chains. The fluorescence quenching studies indicated that the alternating copolymers permitted singlet-state energy migration as efficiently as the corresponding random copolymers but less efficiently than the random copolymers with higher chromophore contents. These results strongly suggest that to be chromophores close to each other is most important for facilitation of an intramolecular energy migration. © 1995 John Wiley & Sons, Inc. 相似文献
46.
47.
Nishimoto A Narita K Ohmoto S Takahashi Y Yoshizumi S Yoshida T Kado N Okezaki E Kato H 《Chemical & pharmaceutical bulletin》2001,49(9):1120-1127
A series of erythromycin A 9-O-substituted oxime ether derivatives have been synthesized and evaluated for antibacterial activity against Mycobacterium avium complex (MAC) and Staphylococcus aureus. These compounds possessed stronger in vitro activity against MAC including macrolide-resistant strains than clarithromycin (2), although in vitro antibacterial activities of these compounds were less than that of 2 against Staphylococcus aureus. Our studies found that several factors contribute to the antibacterial activity against MAC. The length and spatial orientation of the substituent at 9-position were found to significantly influenced the anti-MAC activity, especially against macrolide-resistant strains. Of all the compounds prepared, erythromycin A 9-[O-(4-phenylbutyl)oxime] (12q) and erythromycin A 9-[O-(3-phenoxypropyl)oxime] (12t) possessed 16 times stronger antibacterial activity than 2 against clarithromycin-resistant strains. Surprisingly, the minimum inhibitory concentrations (MICs) of 12q and 12t against the resistant strains were almost same as those against the susceptible strains. These results suggest that the erythromycin A 9-O-substituted oxime ether derivatives would be promising macrolide antibiotics. 相似文献
48.
Antioxidant activity of a series of hydroxybenzalacetones was determined against peroxynitrite-induced lipid peroxidation in red blood cell membrane and SOS response through DNA damage in bacterial cells. Hydroxybenzalacetone derivatives with hydroxy, methoxy, ethoxy or methyl substitution were analyzed and found to be more effective than the water-soluble vitamin E analogue Trolox. The inhibitory effect against lipid peroxidation correlated well to that against the SOS response, which is dependent on decomposition of peroxynitrite by hydroxybenzalacetones outside of the cell membrane. The antioxidant activity was shown to correlate well with the electric parameter sigma+. Electron-donating substituents with more negative sigma+ values increased the potencies. The result suggests that hydroxybenzalacetones with more electron-donating substituents will protect tissue more effectively against oxidative stress. 相似文献
49.
Stereocontrolled alkynylzirconation of unactivated alkynes was achieved by the reaction of an alkyne with Cp2ZrEt2 and alkynyl halide in this order. After hydrolysis of the alkynylzirconation product, trisubstituted enyne derivatives were obtained in good yields. Functionalized enynes were also prepared by the reaction of the alkynylzirconation products with a variety of electrophiles. Subsequent addition of the second alkynyl halide to the alkynylzirconation products provided an in situ protocol for bisalkynylation of alkynes into (Z)-enediynes in good yields. 相似文献
50.
Y Fukuyama M Kodama I Miura Z Kinzyo M Kido H Mori Y Nakayama M Takahashi 《Chemical & pharmaceutical bulletin》1989,37(2):349-353
Eckol (1), a novel phlorotannin with a dibenzo-1,4-dioxin skeleton, has been isolated from the brown alga Ecklonia kurome Okamura as a potent and specific anti-plasmin inhibitor. Its structure has been elucidated based on the spectral data, in particular, by means of negative nuclear Overhauser effect (NOE), and finally established as 1-(3,5-dihydroxyphenoxy)-2,4,7,9-tetrahydroxydibenzo-1,4-dio xin by X-ray analysis. Some partially methoxylated derivatives of eckol were prepared by methylation with diazomethane and also by selective dimethylation of eckol permethylate (1b) to establish the structural requirements for inhibitory activities on alpha 2-macroglobulin and alpha 2-plasmin inhibitor, the main plasmin inhibitors in plasma. 相似文献