全文获取类型
收费全文 | 237篇 |
免费 | 21篇 |
专业分类
化学 | 212篇 |
晶体学 | 1篇 |
力学 | 3篇 |
数学 | 18篇 |
物理学 | 24篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 9篇 |
2020年 | 4篇 |
2019年 | 14篇 |
2018年 | 10篇 |
2017年 | 5篇 |
2016年 | 13篇 |
2015年 | 16篇 |
2014年 | 17篇 |
2013年 | 17篇 |
2012年 | 20篇 |
2011年 | 14篇 |
2010年 | 6篇 |
2009年 | 8篇 |
2008年 | 15篇 |
2007年 | 14篇 |
2006年 | 11篇 |
2005年 | 12篇 |
2004年 | 9篇 |
2003年 | 7篇 |
2002年 | 7篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1994年 | 4篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有258条查询结果,搜索用时 15 毫秒
101.
Benzimidazole Annulated New Heterocyclic Compounds: Synthesis of Polycyclic Pyrrole Derivatives
下载免费PDF全文
![点击此处可从《Journal of heterocyclic chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Mohamed A. Raslan Mohamed A. Khalil Samia M. Sayed 《Journal of heterocyclic chemistry》2015,52(6):1834-1838
Several benzimidazolo[1,2‐a]pyrrole derivative s were obtained by reaction of benzimidazolo[1,2‐a]indeno[2,1‐d]pyrrole derivative with different reactants such as p‐toluenesulfonyl chloride, phenylthiocyanate, phenyl‐isothiocyanate, dimethylsulfate, and active methylene such as malononitrile, ethyl cyanoacetate, benzoyl acetonitrile, ethyl acetoacetate, and diethyl malonate. The newly synthesized products have been deduced on the basis of spectral and analytical data. 相似文献
102.
Samia Oueslati Ahlem Ellili Jean Legault Andre Pichette Riadh Ksouri Mokhtar Lachaal 《Natural product research》2015,29(12):1189-1191
This study investigates the polyphenol content of Diplotaxis simplex extract and the biological activities of the main organ. The analysed extracts showed that polyphenol contents varied considerably as a function of organs. Furthermore, novel biological activities of this species were assessed. Flower extracts exhibit a potent in vitro antioxidant capacity using oxygen radical absorbance capacity and displayed a strong anti-inflammatory activity, inhibiting nitric oxide release, by 79.3% at 160 μg/mL. Our findings suggested that the Diplotaxis flower is a valuable source of antioxidants and anti-inflammatory agents. 相似文献
103.
Amri I Lamia H Gargouri S Hanana M Mahfoudhia M Fezzani T Ezzeddine F Jamoussi B 《Natural product communications》2011,6(10):1531-1536
Essential oils isolated from needles of Pinus patula by hydrodistillation were analyzed by gas chromatography-flame ionization detection (GC-FID) and gas chromatography mass spectrometry (GC-MS). Thirty-eight compounds were identified, representing 98.3% of the total oil. The oil was rich in monoterpene hydrocarbons (62.4%), particularly alpha-pinene (35.2%) and beta-phellandrene (19.5%). The in vitro antifungal assay showed that P. patula oil significantly inhibited the growth of 9 plant pathogenic fungi. The oil, when tested on Sinapis arvensis, Lolium rigidum, Phalaris canariensis and Trifolium campestre, completely inhibited seed germination and seedling growth of all species. Our preliminary results showed that P. patula essential oil could be valorized for the control of weeds and fungal plant diseases. 相似文献
104.
Perruchas S Tard C Le Goff XF Fargues A Garcia A Kahlal S Saillard JY Gacoin T Boilot JP 《Inorganic chemistry》2011,50(21):10682-10692
Three copper(I) iodide clusters coordinated by different phosphine ligands formulated [Cu(4)I(4)(PPh(3))(4)] (1), [Cu(4)I(4)(Pcpent(3))(4)] (2), and [Cu(4)I(4)(PPh(2)Pr)(4)] (3) (PPh(3) = triphenylphosphine, Pcpent(3) = tricyclopentylphosphine, and PPh(2)Pr = diphenylpropylphosphine) have been synthesized and characterized by (1)H and (31)P NMR, elemental analysis and single crystal X-ray diffraction analysis. They crystallize in different space groups, namely, monoclinic P21/c, cubic Pa ?3, and tetragonal I ?42m for 1, 2, and 3, respectively. The photoluminescence properties of clusters 1 and 3 show reversible luminescence thermochromism with two highly intense emission bands whose intensities are temperature dependent. In accordance to Density Functional Theory (DFT) calculations, these two emission bands have been attributed to two different transitions, a cluster centered (CC) one and a mixed XMCT/XLCT one. Cluster 2 does not exhibit luminescence variation in temperature because of the lack of the latter transition. The absorption spectra of the three clusters have been also rationalized by time dependent DFT (TDDFT) calculations. A simplified model is suggested to represent the luminescence thermochromism attributed to the two different excited states in thermal equilibrium. In contrast with the pyridine derivatives, similar excitation profiles and low activation energy for these phosphine-based clusters reflect high coupling of the two emissive states. The effect of the Cu-Cu interactions on the emission properties of these clusters is also discussed. Especially, cluster 3 with long Cu-Cu contacts exhibits a controlled thermochromic luminescence which is to our knowledge, unknown for this family of copper iodide clusters. These phosphine-based clusters appear particularly interesting for the synthesis of original emissive materials. 相似文献
105.
Li YJ Latouche C Kahlal S Liao JH Dhayal RS Saillard JY Liu CW 《Inorganic chemistry》2012,51(14):7439-7441
Two luminescent, undecanuclear silver complexes [Ag(11)(μ(9)-I)(μ(3)-I)(3){E(2)P(O(i)Pr)(2)}(6)](PF(6)) [E = S (yellow), 1; Se (orange), 2], containing the first μ(9)-iodine inscribed at the center of a pentacapped trigonal-prismatic silver skeleton, were reported. 相似文献
106.
The crystal structure of copper sulfate templated by 2-methylpiperazine, (C5H14N2)[Cu(SO4)2(H2O)4] · H2O, was investigated using single crystal X-ray diffraction data. At room temperature, it crystallises in the monoclinic P21/n space group with the following unit-cell parameters: a = 6.9153(1), b = 23.1295(3), c = 10.4472(1) Å, β = 104.227(1)°, V = 1619.75(4) Å3 and Z = 4. The CuII cation adopts a slightly distorted octahedral geometry, arising from four water molecules and two sulfate tetrahedra leading to the formation of [Cu(SO4)2(H2O)4] units. The structure consists of isolated [Cu(SO4)2(H2O)4]2− anions, 2-methylpiperazinediium cations (C5H14N2)2+ and water molecules connected by a three-dimensional hydrogen-bond network. The thermal decomposition of the precursor, studied by thermogravimetry and temperature-dependent X-ray powder diffraction, proceeds through four stages giving rise to the copper oxide. 相似文献
107.
Ahmed Salah A. S. Abdel-Rady Abdel-Nasser A. Osman Samia S. A. Hassan 《Journal of Russian Laser Research》2018,39(1):28-36
We present a two-level atomic Bose–Einstein condensate (BEC) with dispersion, which is coupled to a high-finesse optical cavity. We call this model the extended Jaynes–Cummings–Dicke (JC-Dicke) model and introduce an effective Hamiltonian for this system. From the direct product of Heisenberg–Weyl (HW) coherent states for the field and U(2) coherent states for the matter, we obtain the potential energy surface of the system. Within the framework of the mean-field approach, we evaluate the variational energy as the expectation value of the Hamiltonian for the considered state. We investigate numerically the quantum phase transition and the Berry phase for this system. We find the influence of the atom–atom interactions on the quantum phase transition point and obtain a new phase transition occurring when the microwave amplitude changes. Furthermore, we observe that the coherent atoms not only shift the phase transition point but also affect the macroscopic excitations in the superradiant phase. 相似文献
108.
Thin layer chromatography–densitometric determination of some non‐sedating antihistamines in combination with pseudoephedrine or acetaminophen in synthetic mixtures and in pharmaceutical formulations
下载免费PDF全文
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Michael E. El‐Kommos Samia M. El‐Gizawy Noha N. Atia Noha M. Hosny 《Biomedical chromatography : BMC》2014,28(3):391-400
The combination of certain non‐sedating antihistamines (NSA) such as fexofenadine (FXD), ketotifen (KET) and loratadine (LOR) with pseudoephedrine (PSE) or acetaminophen (ACE) is widely used in the treatment of allergic rhinitis, conjunctivitis and chronic urticaria. A rapid, simple, selective and precise densitometric method was developed and validated for simultaneous estimation of six synthetic binary mixtures and their pharmaceutical dosage forms. The method employed thin layer chromatography aluminum plates precoated with silica gel G 60 F254 as the stationary phase. The mobile phases chosen for development gave compact bands for the mixtures FXD–PSE (I), KET–PSE (II), LOR–PSE (III), FXD–ACE (IV), KET–ACE (V) and LOR–ACE (VI) [Retardation factor (Rf) values were (0.20, 0.32), (0.69, 0.34), (0.79, 0.13), (0.36, 0.70), (0.51, 0.30) and (0.76, 0.26), respectively]. Spectrodensitometric scanning integration was performed at 217, 218, 218, 233, 272 and 251 nm for the mixtures I–VI, respectively. The linear regression data for the calibration plots showed an excellent linear relationship. The method was validated for precision, accuracy, robustness and recovery. Limits of detection and quantitation were calculated. Statistical analysis proved that the method is reproducible and selective for the simultaneous estimation of these binary mixtures. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
109.
Hung Banh Katharina Dilchert Christine Schulz Dr. Christian Gemel Dr. Rüdiger W. Seidel Dr. Régis Gautier Dr. Samia Kahlal Prof. Dr. Jean‐Yves Saillard Prof. Dr. Roland A. Fischer 《Angewandte Chemie (International ed. in English)》2016,55(10):3285-3289
The bottom‐up synthesis of organometallic zinc clusters is described. The cation {[Zn10](Cp*)6Me}+ ( 1 ) is obtained by reacting [Zn2Cp*2] with [FeCp2][BAr4F] in the presence of ZnMe2. In the presence of suitable ligands, the high reactivity of 1 enables the controlled abstraction of single Zn units, providing access to the lower‐nuclearity clusters {[Zn9](Cp*)6} ( 2 ) and {[Zn8](Cp*)5(tBuNC)3}+ ( 3 ). According to DFT calculations, 1 and 2 can be described as closed‐shell species that are electron‐deficient in terms of the Wade–Mingos rules because the apical ZnCp* units that constitute the cluster cage do not have three, but only one, frontier orbitals available for cluster bonding. Zinc behaves flexibly in building the skeletal metal–metal bonds, sometimes providing one major frontier orbital (like Group 11 metals) and sometimes providing three frontier orbitals (like Group 13 elements). 相似文献
110.
Edgar Ocando Samia Majid Jean Pierre Majoral Antoine Baceiredo Guy Bertrand 《Polyhedron》1985,4(9):1667-1668
Under thermolytic or photolytic conditions, phosphine azide complexes Ph2PN3M(CO)5 (M = W, Cr) gave rise to the corresponding isocyanato complexes and not to the expected iminophosphane complexes. 相似文献