全文获取类型
收费全文 | 328篇 |
免费 | 12篇 |
国内免费 | 1篇 |
专业分类
化学 | 267篇 |
晶体学 | 5篇 |
力学 | 4篇 |
数学 | 13篇 |
物理学 | 52篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 11篇 |
2021年 | 19篇 |
2020年 | 17篇 |
2019年 | 15篇 |
2018年 | 16篇 |
2017年 | 11篇 |
2016年 | 6篇 |
2015年 | 7篇 |
2014年 | 20篇 |
2013年 | 44篇 |
2012年 | 6篇 |
2011年 | 18篇 |
2010年 | 17篇 |
2009年 | 12篇 |
2008年 | 9篇 |
2007年 | 6篇 |
2006年 | 7篇 |
2005年 | 3篇 |
2004年 | 6篇 |
2003年 | 9篇 |
2002年 | 12篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1967年 | 1篇 |
1960年 | 3篇 |
1959年 | 1篇 |
排序方式: 共有341条查询结果,搜索用时 31 毫秒
31.
32.
A novel series of pyrazolo[1,5-a]pyrimidines 14a–j and pyrazolo[1,5-a]quinazolines 18a, b were synthesized via condensation of 5-amino-1H-pyrazoles 10a, b with 3-(dimethylamino)-1-aryl-prop-2-en-1-ones 11a–e and 2-((dimethylamino)methylene)-5,5-dimethylcyclohexane-1,3-dione (15), respectively, in glacial acetic acid. Finally, treatment of 10a, b with sodium nitrite (NaNO2) afforded pyrazolo[3,4-d]triazines 20a, b. Structures of compounds were confirmed by their spectral data. These compounds were screened for their in vitro cytotoxic activities against human cancer cell lines (HepG-2 and MCF-7) using 3-[4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. The results reveal that, the compounds 14b and 14h were the most potent in comparison with doxorubicin. The structure–activity relationship was discussed. 相似文献
33.
Moustafa A. Gouda 《合成通讯》2017,47(17):1527-1558
The biological and medicinal properties of oxicams and its analogues have prompted enormous research aimed at developing synthetic routes to these heterocycles. This review focuses on the chemical properties associated with this system. 相似文献
34.
<正>Two new eudesmane derivatives were isolated from the leaves and flowers of Verbesina virginica,along with the known 6-O-β-E -p-coumaroyl-4α-hydroxyeudesmane(1).Their structures were determined as 6-O-β-Z-p-coumaroyl-4α-hydroxyeudesmane(2) and 6-O-α-E-p-coumaroyl-1β-4α-dihydroxyeudesmane(3) by spectroscopic methods. 相似文献
35.
36.
Ha?ja Moustafa 《Communications in Mathematical Physics》2010,298(2):369-405
In this paper, we first remind how we can see the “hull” of the pinwheel tiling as an inverse limit of simplicial complexes
(Anderson and Putnam in Ergod Th Dynam Sys 18:509–537, 1998) and we then adapt the PV cohomology introduced in Savinien and
Bellissard (Ergod Th Dynam Sys 29:997–1031, 2009) to define it for pinwheel tilings. We then prove that this cohomology is
isomorphic to the integer Čech cohomology of the quotient of the hull by S
1 which let us prove that the top integer Čech cohomology of the hull is in fact the integer group of coinvariants of the canonical
transversal Ξ of the hull. The gap-labeling for pinwheel tilings is then proved and we end this article by an explicit computation
of this gap-labeling, showing that
mt ( C(X,\mathbb Z) ) = \frac1264\mathbb Z [ \frac15]{\mu^t \left( C(\Xi,\mathbb {Z}) \right) = \frac{1}{264}\mathbb {Z} \left [ \frac{1}{5}\right ]}. 相似文献
37.
A series of S-glycosyl and S-alkyl derivatives of 4-amino-3-mercapto-6-(2-(2-thienyl)vinyl)-1,2,4-triazin-5(4H)-one (1) were synthesized using different halo compounds such as preacetylated sugar bromide, 4-bromobutylacetate, 2-acetoxyethoxy-methyl bromide, 3-chloropropanol, 1,3-dichloro-2-propanol, epichlorohydrin, allyl bromide, propargyl bromide, phthalic and succinic acids in POCl3. The structures of the synthesized compounds have been deduced from their elemental analysis and spectral (IR, 1H-NMR, and 13C-NMR) data. Some of the synthesized compounds were screened as anticancer agents. Significant anticancer activities were observed in vitro for some members of the series, and compounds 4-Amino-3-(3-hydroxypropylthio)-6-(2-(2-thienyl)vinyl)-1,2,4-triazin-5(4H)-one (12) and 3-(4-Oxo-3-(2-(2-thienyl)vinyl)-4H-[1,3,4]thiadiazolo-[2,3-c][1,2,4]tr-iazin-7-yl)propanoic acid (18) are active cytotoxic agents against different cancer cell lines. 相似文献
38.
The reactivity of the product believed to be 2-(1-phenyl-2-thiocyanato-ethylidene)malononitrile toward a variety of electrophilic and nucleophilic reagents is reported. 相似文献
39.
Moustafa A. Gouda 《Journal of heterocyclic chemistry》2011,48(1):1-10
This review describe the synthesis and reactions of 3‐amino‐4,6‐dimethyl‐1H‐pyrazolo[3,4‐b]pyridine as building block for the synthesis of polyfunctionalized heterocyclic compounds with pharmacological interest. J. Heterocyclic Chem., 2011. 相似文献
40.
Rabie UM Abou-El-Wafa MH Nassar H 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,78(1):512-517
Thiazolidine-2-thione (T2T) has been studied spectrophotometrically by UV–visible and IR spectra. The spectral studies have indicated that T2T has two tautomeric forms, namely thione and thiole forms, in addition to the dimeric thioamide complex existing as a hydrogen-bonded dimer of two thione forms. Interaction of the T2T as an electron donor with iodine as a typical σ-type acceptor has been studied spectrophotometrically. Electronic absorption spectra of the system T2T–I2 in several organic solvents of different polarities have performed a clear charge transfer (CT) band in each spectrum. Formation constants (KCT) and molar absorption coefficients (?CT) and thermodynamic properties, ΔH, ΔS, and ΔG, of this system in various organic solvents were determined and discussed. The stoichiometric ratio of the T2T–I2 system in solutions was found to be 1:1 T2T:I2, whereas the elemental analysis of the prepared solid CT complex has illustrated the same stoichiometry. The obtained KCT and ?CT values have indicated that T2T is a donor of moderately strength capable of interacting with the iodine just to form the corresponding CT complex with an iodine molecule without further reducing of the iodine to either of the corresponding poly-iodide ions viz. I3?, I5?, etc. This action of spongy trapping of iodine simulates in vitro the chemical scenario of the anti-thyroid action of this compound. 相似文献