全文获取类型
收费全文 | 128篇 |
免费 | 6篇 |
国内免费 | 2篇 |
专业分类
化学 | 82篇 |
晶体学 | 2篇 |
力学 | 8篇 |
数学 | 17篇 |
物理学 | 27篇 |
出版年
2024年 | 2篇 |
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 1篇 |
2019年 | 3篇 |
2018年 | 12篇 |
2017年 | 2篇 |
2016年 | 6篇 |
2015年 | 3篇 |
2014年 | 6篇 |
2013年 | 8篇 |
2012年 | 11篇 |
2011年 | 12篇 |
2010年 | 4篇 |
2009年 | 5篇 |
2008年 | 6篇 |
2007年 | 4篇 |
2006年 | 4篇 |
2005年 | 10篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2002年 | 1篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1997年 | 1篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1990年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有136条查询结果,搜索用时 0 毫秒
1.
2.
A new bis-andrographolide ether from Andrographis paniculata nees and evaluation of anti-HIV activity 总被引:3,自引:0,他引:3
Reddy VL Reddy SM Ravikanth V Krishnaiah P Goud TV Rao TP Ram TS Gonnade RG Bhadbhade M Venkateswarlu Y 《Natural product research》2005,19(3):223-230
Novel bis-andrographolide ether (1) and six known compounds andrographolide, 14-deoxy-11,12-didehydroandrographolide, andrograpanin, 14-deoxyandrographolide, (+/-)-5-hydroxy-7,8-dimethoxyflavanone, and 5-hydroxy-7,8-dimethoxyflavone have been isolated from the aerial parts of Andrographis paniculata and their structures were established by spectral data. All the isolates were tested for the anti-HIV and cytotoxic activity. 相似文献
3.
袁勤勤 杨正 李仁忠 Wesley J. Transue 李志鹏 江凌 Niranjan Govin Christopher C. Cummins 王学斌 《化学物理学报》2018,31(4):463-470
Gaseous dibenzo-7-phosphanorbornadiene P-sulfide anions APS-(A=C14H10 or anthracene) were generated via electrospray ionization, and characterized by magnetic-bottle photoelectron spectroscopy, velocity-map imaging (VMI) photoelectron spectroscopy, and quantum chemical calculations. The electron affinity (EA) and spin-orbit (SO) splitting of the APS· radical are determined from the photoelectron spectra and Franck-Condon factor simulations to be EA=(2.62±0.05) eV and SO splitting=(43±7) meV. VMI photoelectron images show strong and sharp peaks near the detachment threshold with an identical electron kinetic energy (eKE) of 17.9 meV at three different detachment wavelengths, which are therefore assigned to autodetachment from dipole-bound anion states. The B3LYP/6-31++G(d,p) calculations indicate APS· has a dipole moment of 3.31 Debye, large enough to support a dipole-bound electron. 相似文献
4.
Haritha Rajaram N. Harshitha Shweta A. Ram Swarna M. Patra Vidya Niranjan K.A. Vishnumurthy 《印度化学会志》2022,99(6):100488
In the present study, the main protease 3CLpro and non-structural protein (NSP-12 with co-factors 7 and 8) trimer complex are used to study the protein-drug interactions with the phytochemicals from Ocimum Sanctum, Tinospora Cordifolia, Glycyrrhiza Glabra, and Azadirachta Indica. Which can give insight to be used as potent antiviral drugs against SARS-CoV-2. Twenty phytochemicals, five from each plant species, known for their wide range of biological activities were chosen from the literature. The in-silico study was carried out using virtual screening tools and the top five, which showed the least binding energies, were selected. Molecular docking tools revealed that gedunin and epoxy azadiradione proved to be excellent inhibitors for 3CLpro and so did Tinosporide for non-structural-protein complex. Further, the best-hit phytochemicals with respect to structure similarities with FDA drugs and investigatory drugs, were considered for comparative study. Molecular docking was done to check the drug-protein interactions and to check the inhibitory responses of these drugs against the viral protein. The analyses showed that the phytochemicals had similar responses on the protein complex but with exceptionally higher inhibitory responses hence which may be taken for further clinical study. 相似文献
5.
Because Nitrosomonas europaea contains ammonia-oxidizing enzyme, nitrite reductase, and nitrous oxide reductase, the conversion of ammonia to dinitrogen
was tried with different reaction conditions. In aerobic reaction conditions, ammonium was converted to nitrite (NO
2
−
), while under oxygen-limiting or oxygen-free conditions, NO
2
−
-N formed from ammonia oxidation by N. europaea was reduced to N2O and dinitrogen with 22% conversion. During denitrification, optimal pH for the production of N2O and dinitrogen was found to be 7.0–8.0. Dinitrogen was not produced in acidic pH<7.0. A low partial oxygen pressure as well
as oxygen-free conditions are favorable for high production of dinitrogen. 相似文献
6.
7.
Niranjan Das 《Pramana》2004,62(1):135-142
In the present paper, a study of the deep-sea water wave caused by an oscillatory wind stress due to the atmospheric depression,
resulting in spiral cyclonic wind pressure on the surface of the sea is made. It has been observed that the motion of the
water wave in the case of wind stress exhibits a greater elevation on the sea surface asg the acceleration due to gravity decreases and maintains the oscillatory nature with the increase of time. For the case of
spiral cyclonic motion for which the sea surface experiences the elliptical pressure on the surface, the motion diminishes
asg diminishes and oscillates with the variation of time. The motion also diminishes asymptotically as the radius vector of the
elliptical pressure approaches unity. 相似文献
8.
A series of hyperbranched polyamines have been prepared by the reported method. All these polyamines exhibit fluorescence at about 350-650 nm with maximum intensity at about 450 nm. The study shows that the fluorescence intensity and the range of wavelength of fluorescence are strongly influenced by the structure of the hyperbranched polyamines. The effect of concentration of the polymer, pH of the medium and metal ion has also been investigated on the fluorescence characteristics of sulfone containing hyperbranched polyamine (Ps), as it shows the best result among the studied polymers. The results show that the intensity of fluorescence increases with the decrease of concentration (5-0.1 g/L in N,N′-dimethyl sulfoxide) of polymer and with the increase of pH (3.1-11.6) of the medium. The quenching of fluorescence increases with the increase of concentration of Cu2+ ions (0.01-0.04%). The hyperbranched polyamine (Ps) has also been end capped with benzoyl chloride and 4-hydroxybenzaldehyde to study the influence of end groups. The results showed that the structure of end capped compounds has prominent role to influence fluorescence characteristics of this hyperbranched polyamine. 相似文献
9.
A novel palladium catalyzed protocol for the synthesis of benzoxazolidine by the reaction sulfamidophenol and terminal alkene was developed. This oxamidation process is simple and does not require any ligand, base or inert atmosphere for the overall transformation. From control experiments, it is apparent that the cross-coupling reaction proceeds with initial formation of enesulfonamide which undergoes nucleopalladation by the intramolecular annulation and subsequent protodepalladation by TsOH to afford the benzoxazolidine. 相似文献
10.
Bhatti BS Strachan JP Breining SR Miller CH Tahiri P Crooks PA Deo N Day CS Caldwell WS 《The Journal of organic chemistry》2008,73(9):3497-3507
In an attempt to generate nicotinic acetylcholine receptor (nAChR) ligands selective for the alpha4beta2 and alpha7 subtype receptors we designed and synthesized constrained versions of anabasine, a naturally occurring nAChR ligand. 2-(Pyridin-3-yl)-1-azabicyclo[2.2.2]octane, 2-(pyridin-3-yl)-1-azabicyclo[3.2.2]nonane, and several of their derivatives have been synthesized in both an enantioselective and a racemic manner utilizing the same basic synthetic approach. For the racemic synthesis, alkylation of N-(diphenylmethylene)-1-(pyridin-3-yl)methanamine with the appropriate bromoalkyltetrahydropyran gave intermediates which were readily elaborated into 2-(pyridin-3-yl)-1-azabicyclo[2.2.2]octane and 2-(pyridin-3-yl)-1-azabicyclo[3.2.2]nonane via a ring opening/aminocyclization sequence. An alternate synthesis of 2-(pyridin-3-yl)-1-azabicyclo[3.2.2]nonane via the alkylation of N-(1-(pyridin-3-ylethylidene)propan-2-amine has also been achieved. The enantioselective syntheses followed the same general scheme, but utilized imines derived from (+)- and (-)-2-hydroxy-3-pinanone. Chiral HPLC shows that the desired compounds were synthesized in >99.5% ee. X-ray crystallography was subsequently used to unambiguously characterize these stereochemically pure nAChR ligands. All compounds synthesized exhibited high affinity for the alpha4beta2 nAChR subtype ( K i < or = 0.5-15 nM), a subset bound with high affinity for the alpha7 receptor subtype ( K i < or = 110 nM), selectivity over the alpha3beta4 (ganglion) receptor subtype was seen within the 2-(pyridin-3-yl)-1-azabicyclo[2.2.2]octane series and for the muscle (alpha1betagammadelta) subtype in the 2-(pyridin-3-yl)-1-azabicyclo[3.2.2]nonane series. 相似文献