全文获取类型
收费全文 | 574篇 |
免费 | 18篇 |
国内免费 | 1篇 |
专业分类
化学 | 364篇 |
晶体学 | 10篇 |
力学 | 11篇 |
数学 | 22篇 |
物理学 | 186篇 |
出版年
2021年 | 3篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 11篇 |
2014年 | 9篇 |
2013年 | 18篇 |
2012年 | 23篇 |
2011年 | 18篇 |
2010年 | 21篇 |
2009年 | 21篇 |
2008年 | 27篇 |
2007年 | 31篇 |
2006年 | 29篇 |
2005年 | 30篇 |
2004年 | 28篇 |
2003年 | 18篇 |
2002年 | 14篇 |
2001年 | 6篇 |
2000年 | 9篇 |
1999年 | 13篇 |
1998年 | 6篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 10篇 |
1992年 | 15篇 |
1991年 | 16篇 |
1990年 | 12篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 14篇 |
1986年 | 11篇 |
1985年 | 23篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 7篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1968年 | 2篇 |
排序方式: 共有593条查询结果,搜索用时 0 毫秒
81.
L-Threonine was transformed, stereospecifically, to a versatile β-lactam (5a) in 3 steps. This β-lactam was further converted to a key intermediate (25) for the synthesis of thienamycin and its biologically active analogues. Furthermore, the compound 5a was changed to iodides (18 and 23), cyanides (19 and 24), chloromethylketone (26) and aldehydes (30 and 31) which appear to have a latent potential as precursors for the syntheses of the carbapenems. 相似文献
82.
4-Diazomethyl-substituted coumarins, 1-methyl-2(1H)-quinolinones, 1 -thiocoumarin and their tricyclic analogs were found to be easily cyclized into the corresponding pyrazole isomers condensed with heteroaromatics. Thermodependent feature of these conversions and the remarkably accelerating effect of the alkyl substituent peri to the diazomethyl group were realized. Some other diazomethyl compounds connected with 2-pyridinone, 3-pyrazolone, chromone and 1-thiochromone were prepared, and their stability and thermal properties were compared. 相似文献
83.
K Osawa H Yasuda T Maruyama H Morita K Takeya H Itokawa 《Chemical & pharmaceutical bulletin》1992,40(11):2970-2974
The methanolic extract of Swartzia polyphylla DC. heartwood had antibacterial activity against cariogenic bacteria, the mutans Streptococci. The chromatographic purification of the extract afforded seven flavonoids. Among them, three known isoflavanones, dihydrobiochanin A, ferreirin and darbergioidin, and one new isoflavanone, 5,2',4'-trihydroxy-7-methoxyisoflavanone (dihydrocajanin) had potent antibacterial activity against cariogenic bacteria. This effect was not detected on isoflavone derivatives. A comparative antibacterial study of various flavonoids was further performed, and their structure-activity relationship was discussed. 相似文献
84.
85.
Y. Harada K. Murano I. Shirotani T. Takahashi Y. Maruyama 《Solid State Communications》1982,44(6):877-879
The X-ray photoelectron spectrum of black phosphorus has been measured for the first time. The features in the valence band spectrum are found to be in good agreement with those of the valence state density recently calculated on the basis of a pseudopotential method. The 2s and 2p core spectrum of black phosphorus is also discussed. 相似文献
86.
Sadao Nakajima Kyoko Kosasa Yoshio Maruyama Seichi Kawai 《Spectrochimica Acta Part B: Atomic Spectroscopy》1982,37(8):685-690
The behavior of powdered samples in the region behind the incident and reflected shock wave were investigated. When the particle size is less than 8 μm, the powdered samples are effectively vaporized and excited to emit spectral lines. It was shown that the sample particles are scattered behind the incident wave and concentrated again in a narrow portion near the observation window by the use of a reflector so that intense emission can be attained. As an excitation source, the shock tube was used for the determination of trace metals contained in copper oxide. 相似文献
87.
The electrochemical behavior of ten nitrogen heterocycles was investigated in DMF-water and aqueous buffer solution. On the basis of these data, the effect of proton on the reduction behavior in DMF-water media and the reduction pathway in aqueous buffer solution ware phenomenologically classified. The adsorption phenomena in aqueous buffer solution and the correlation of reduction behavior with structure and reactivity were discussed. The structure of electrolytic products was also estimated and identified by negative electron density distributions of radical anion, GC-MS and spectrophotometry. 相似文献
88.
89.
Toshikazu Shimada Yoshifumi Katayama Kiyokazu Nakagawa Hirokazu Matsubara Masatoshi Migitaka Eiichi Maruyama 《Journal of Non》1983
The structural properties of microcrystalline silicon (μc-Si) are studied by Raman scattering. It is found that the intensity of each Raman band closely correlates with the absorption coefficient in the interband region and that the Raman band at ca. 150 cm?1 is a sensitive probe to randomness of Si-Si bonding structure in μc-Si. 相似文献
90.