全文获取类型
收费全文 | 94篇 |
免费 | 2篇 |
国内免费 | 15篇 |
专业分类
化学 | 97篇 |
数学 | 2篇 |
物理学 | 12篇 |
出版年
2022年 | 4篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2017年 | 1篇 |
2016年 | 1篇 |
2015年 | 6篇 |
2014年 | 1篇 |
2013年 | 6篇 |
2012年 | 9篇 |
2011年 | 9篇 |
2010年 | 6篇 |
2009年 | 2篇 |
2008年 | 10篇 |
2007年 | 7篇 |
2006年 | 8篇 |
2005年 | 5篇 |
2004年 | 11篇 |
2003年 | 6篇 |
2002年 | 2篇 |
2001年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有111条查询结果,搜索用时 15 毫秒
1.
In view of the attributed medicinal properties of beta-carboline alkaloids, some new O-acyl derivatives of beta-carboline alkaloid--harmol, were prepared and tested for possible antimycobacterial activity against Mycobacterium tuberculosis H37Rv. 相似文献
2.
Gury Zvilichovsky 《Journal of heterocyclic chemistry》1987,24(2):465-470
The crystal structure of 4-phenyl-3-hydroxyisoxazol-5-one semihydrate exhibits an exceptional hydrogen bonded polymeric structure with a unit cell of 8 molecules. The hydrogen bonds stretch out, using the oxohydroxy groups in positions 3 and 5 in the direction of one axis and along a perpendicular direction the layers are stitched together by water molecules. The layers are stitched by using four hydrogen bridges of water molecules, the heterocyclic ring nitrogen as well as the oxygen at position 5. Tautomerism of this moiety in solution is discussed, in light of some new dialkylation products. The state in which these products exist in solution depends on the solvent. A zwitterionic tautomer is present in ether. In some alkylation conditions, the predominant dialkylation product is the N,N-disubstituted betaine (Anhydro-2,2-dialkyl-3(5)-oxo-5(3)hydroxy-4-phenylisoxazolonium hydroxide). Study of tautomerism in polar and protic solvent is unreliable owing to associations and dissociation phenomena. 相似文献
3.
C.?Korah Bina K.?G.?Kannan K.?N.?NinanEmail author 《Journal of Thermal Analysis and Calorimetry》2004,78(3):753-760
The urethane forming cure reactions of hydroxyl terminated polybutadiene (HTPB) binder with three different isocyanate curatives, viz., toluene diisocyanate (TDI), isophorone diisocyanate (IPDI) and 4,4-methylene bis(cyclohexyl isocyanate) (MCHI), were investigated by differential scanning calorimetry (DSC). The effect of two cure catalysts, viz., dibutyl tin dilaurate (DBTDL) and ferrric tris-acetylacetonate (FeAA) on the cure reactions was also studied. Cure kinetics was evaluated using the multiple heating rate Ozawa method. The reactivities of the three isocyanates and catalytic efficiencies were compared based on the DSC reaction temperatures, activation energies and rate constants. Viscosity build-up in these systems at isothermal temperature was also studied and compared with the results from DSC. 相似文献
4.
A new insecticidal amide piptigrine (1) possessing highly extended conjugation was isolated from the dried ground seeds of Piper nigrum Linn. along with the known amides piperine and wisanine (hitherto unreported from this plant). The structure of 1 has been elucidated as 1-[9-(3',4'-methylenedioxyphenyl)-4E,6E,8E-nonatrienoyl]piperidine through extensive 1D- and 2D-NMR (COSY-45, NOESY, J-resolved, HMQC, HMBC and NOESY studies. The known compounds have been identified through comparison of their spectral data with those reported in literature. 1 exhibited toxicity of 15.0 ppm against fourth instar larvae of Aedes aegypti Liston. 相似文献
5.
Allylic alcohols can be successfully oxidized into the corresponding α, β-unsaturated aldehydes by two new types polymer-supported oxidizing reagents which do not oxidize saturated alcohols under similar condition. 相似文献
6.
L. F. Rojas M. Bina G. Cerchiari M. A. Escobedo-Sánchez F. Ferri F. Scheffold 《The European physical journal. Special topics》2011,199(1):167-180
We show that the spectral speckle intensity correlation (SSIC) technique can be profitably exploited to recover the path length
distribution of photons scattered in a random turbid medium. We applied SSIC to the study of Teflon slabs of different thicknesses
and were able to recover, via the use of the photon diffusion approximation theory, the characteristic transport mean free
path ℓ∗ and absorption length s
a
of the medium. These results were compared and validated by means of complementary measurements performed on the same samples
with standard pulsed laser time of flight techniques. 相似文献
7.
8.
The methanolic extract of the aerial parts of Datura innoxia afforded a new withanolide, daturacin, the structure of which was elucidated as (20R, 22S)-21,24-epoxy-1,6-dioxo-14alpha-methoxy-5beta-witha-2,25(27)-dienolide (1) by an analysis of the spectroscopic data, including extensive NMR experiments. 相似文献
9.
Rasheed M Afshan F Tariq RM Siddiqui BS Gulzar T Mahmood A Begum S Khan B 《Natural product research》2005,19(7):703-712
The petroleum ether extract of dried ground seeds of Piper nigrum Linn. and some column fractions of this extract were subjected to GC and GC-MS analysis, resulting in the identification of fourteen compounds (1-14) by using NIST Mass spectral search program 1998 and the Kovat's retention indices. Ten of the compounds (1, 2, 4-12) are reported for the first time from this plant. All the fractions showed insecticidal activity against the fourth instar larvae of Aedes aegypti and against the fourth instar larvae of Anopheles stephensi Liston, determined by the WHO method. 相似文献
10.
Siddiqui BS Gulzar T Mahmood A Begum S Khan B Afshan F 《Chemical & pharmaceutical bulletin》2004,52(11):1349-1352
The petroleum ether extract of dried ground whole fruits of Piper nigrum L. afforded 20 compounds (1-20) including two new insecticidal amides named as pipnoohine (1), and pipyahyine (2), seven reported for the first time from this plant (12, 13, 15-17, 19, 20), and eleven known compounds (3-11, 14, 18). The structure of 1 has been elucidated as (2E,4E,12Z)-N-(4-methylpentyl)octadeca-2,4,12-trienamide and that of 2 as (2E,4E,11E)-12-(benzo[1,3]dioxol-5-yl)-N-(3-methylbutyl)dodeca-2,4,11-trien-amide through extensive ID-, 2D-NMR spectral studies and chemical reactions. The known compounds have been identified through comparison of their spectral data with those reported in literature. 1 and 2 exhibited toxicity at 35.0 and 30.0 ppm respectively against fourth instar larvae of Aedes aegypti L. by WHO method. 相似文献