全文获取类型
收费全文 | 947篇 |
免费 | 9篇 |
专业分类
化学 | 507篇 |
晶体学 | 10篇 |
力学 | 39篇 |
数学 | 89篇 |
物理学 | 311篇 |
出版年
2022年 | 12篇 |
2021年 | 9篇 |
2020年 | 16篇 |
2019年 | 22篇 |
2018年 | 19篇 |
2017年 | 20篇 |
2016年 | 24篇 |
2015年 | 12篇 |
2014年 | 28篇 |
2013年 | 32篇 |
2012年 | 29篇 |
2011年 | 40篇 |
2010年 | 30篇 |
2009年 | 34篇 |
2008年 | 31篇 |
2007年 | 27篇 |
2006年 | 25篇 |
2005年 | 13篇 |
2004年 | 24篇 |
2003年 | 15篇 |
2002年 | 11篇 |
2001年 | 19篇 |
2000年 | 16篇 |
1999年 | 11篇 |
1998年 | 13篇 |
1997年 | 14篇 |
1996年 | 16篇 |
1995年 | 13篇 |
1994年 | 26篇 |
1993年 | 21篇 |
1992年 | 18篇 |
1991年 | 20篇 |
1990年 | 22篇 |
1989年 | 18篇 |
1988年 | 14篇 |
1987年 | 24篇 |
1986年 | 11篇 |
1985年 | 16篇 |
1984年 | 11篇 |
1983年 | 18篇 |
1982年 | 11篇 |
1980年 | 12篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1977年 | 10篇 |
1976年 | 7篇 |
1972年 | 13篇 |
1971年 | 11篇 |
1970年 | 9篇 |
1968年 | 9篇 |
排序方式: 共有956条查询结果,搜索用时 15 毫秒
71.
Zhao Y Zhang J Wang B Kim SH Fang A Bogdanov B Zhou Z McClain C Zhang X 《Journal of chromatography. A》2011,1218(18):2577-2583
A method was developed to calculate the second dimension retention index of comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC/TOF-MS) data using n-alkanes as reference compounds. The retention times of the C(7)-C(31) alkanes acquired during 24 isothermal experiments cover the 0-6s retention time area in the second dimension retention time space, which makes it possible to calculate the retention indices of target compounds from the corresponding retention time values without the extension of the retention space of the reference compounds. An empirical function was proposed to show the relationship among the second dimension retention time, the temperature of the second dimension column, and the carbon number of the n-alkanes. The proposed function is able to extend the second dimension retention time beyond the reference n-alkanes by increasing the carbon number. The extension of carbon numbers in reference n-alkanes up to two more carbon atoms introduces <10 retention index units (iu) of deviation. The effectiveness of using the proposed method was demonstrated by analyzing a mixture of compound standards in temperature programmed experiments using 6 different initial column temperatures. The standard deviation of the calculated retention index values of the compound standards fluctuated from 1 to 12 iu with a mean standard deviation of 5 iu. 相似文献
72.
A new representative of hetarylketene aminals, ethyl 3,3-diamino-2-(2-p-tolylpyrimidin-4-yl)acrylate, was synthesized by the reaction ofp-toluamidine with the condensation product of dimethylformamide dimethyl acetal and the difluoroboron chelate of acetyl(ethoxycarbonyl)ketene (N-benzoyl)aminal. This synthesis is an example of pyrimidine ring assembly using the methodology based on transformations of chelate complexes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1638–1640, September, 1994.This research was partially supported by the International Science Foundation (Grant No. M5QOOO). 相似文献
73.
Milen G. Bogdanov Mariana D. Palamareva Blagovesta T. Gocheva Darina B. Dimitrova 《Journal of heterocyclic chemistry》2007,44(3):673-677
The reaction between homophthalic anhydride and cyclohexanone was examined both in the presence of DMAP or BF3·Et2O complex as a catalyst. The latter yielded (±)‐1‐oxo‐1H‐spiro[benzo[c]pyran‐3(4H), 1′‐cyclohexane]‐4‐carboxylic acid ( 3 ) in a higher yield (82 %). A series of new (±)‐4‐(N,N‐disubstituted‐1‐carbamoyl)‐1H‐spiro[benzo[c]pyran‐3(4H),1′‐cyclohexane]‐1‐ones ( 5a‐h ) were synthesized from the parent acid 3 by a two‐step reaction. Differentiating microbial screening was performed for most of the synthesized compounds against twelve microorganisms belonging to different taxonomic groups. The spiro acid 3 was active against all bacterial strains with MIC ≥ 20 μg/ml against B. subtillis and P. vulgaris. E. coli was the most sensitive strain to the antibacterial effect of the tested compounds. 相似文献
74.
V. F. Mironov A. V. Bogdanov A. V. Nemtarev A. A. Shtyrlina E. N. Varaksina V. K. Cherkasov A. B. Dobrynin D. B. Krivolapov R. Z. Musin I. A. Litvinov A. I. Konovalov 《Russian Chemical Bulletin》2007,56(9):1900-1910
The reactions of 3,5-di(tert-butyl)-1,2-benzoquinone with aryl-and alkylacetylenes in the presence of phosphorus trichloride afford 4-aryl(alkyl)-8-tert-butyl-2,6-dichloro-2-oxo-2H-benzo[e][1,2]oxaphosphinines as the major ipso-substitution products of the tert-butyl group by the chlorine atom. 4-Aryl(alkyl)-6,8-di(tert-butyl)-2,5-dichloro-2-oxo-and 4-aryl(alkyl)-6-tert-butyl-2,8-dichloro-2-oxo-2H-benzo[e][1,2]oxaphosphinines were obtained as the minor products. The structures of the stable representatives of this series were
confirmed by X-ray diffraction.
Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1836–1845, September, 2007. 相似文献
75.
A. A. Bogdanov Yu. V. Kosmotynskaya K. I. Yakovlev N. A. Kas’yanenko 《Journal of Structural Chemistry》2006,47(1):178-185
A comparison has been made of conformational changes in the DNA molecule during its interaction in solution with different binuclear coordination compounds of platinum [Pt(NH3)2Cl-R-Pt(NH3)2Cl]Cl2 in cis and trans conformations, which contain cytosine, pyrazine, and carboxypyrazine as the common ligand (R). The influence of concentration of the components, and in particular, of ionic strength of the solution on the complexation process was studied. The influence of the nature of the common ligand, and of cis and trans conformations of coordination compounds on the character of their interaction with DNA was considered. A comparison was made between the structures of DNA complexes with mono-and binuclear compounds with the same set of ligands in the platinum coordination sphere. 相似文献
76.
77.
78.
79.
A modified equation, which refines the model of unsteady transonic flow with axial symmetry, is proposed, and the following problems are considered: the determination of the wave front when a weak perturbation propagates and the formation of a shock wave from a perturbation with a continuous profile. 相似文献
80.