全文获取类型
收费全文 | 310篇 |
免费 | 21篇 |
国内免费 | 3篇 |
专业分类
化学 | 262篇 |
晶体学 | 3篇 |
力学 | 7篇 |
数学 | 26篇 |
物理学 | 36篇 |
出版年
2023年 | 3篇 |
2022年 | 1篇 |
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 8篇 |
2018年 | 17篇 |
2017年 | 17篇 |
2016年 | 14篇 |
2015年 | 19篇 |
2014年 | 16篇 |
2013年 | 65篇 |
2012年 | 23篇 |
2011年 | 23篇 |
2010年 | 20篇 |
2009年 | 17篇 |
2008年 | 18篇 |
2007年 | 16篇 |
2006年 | 11篇 |
2005年 | 5篇 |
2004年 | 10篇 |
2003年 | 6篇 |
2002年 | 3篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有334条查询结果,搜索用时 15 毫秒
111.
In this paper, we present the result of TiN nanocrystalline deposition on SS316L, using a 4 kJ plasma focus (PF) device for 10, 20, and 30 focus shots. The effect of different number of focus shots on micro-structural changes of thin film is characterized by field emission scanning electron microscope. Existence of grains in different size confirms the formation of TiN nanocrystals on the surface of SS316L substrate. X-ray diffraction (XRD) reveals the formation of a nanocrystalline titanium nitride coating on the surface of SS316L samples. The crystalline size of TiN obtained from XRD data is strongly dependent on the number of focus shots. Thickness of the elements found on the surface of the treated sample that obtain by Rutherford backscattering spectroscopy (RBS) analysis is in the range of 150×1015?200×1015 atoms/cm2. All the existence elements in the coated samples are identified by Particle Induced X-ray Emission (PIXE) spectra. Investigation on the corrosion resistance of TiN coatings was performed using an electrochemical potentiodynamic polarization. Our results suggest that TiN nanocrystalline implantation with proper ion fluences using PF can significantly improve the corrosion resistance of SS316L. 相似文献
112.
A. Ebrahimi S. M. Habibi‐Khorassani M. Doosti 《International journal of quantum chemistry》2011,111(5):1013-1024
Nucleophilic substitution reaction between some substituted benzyl chlorides and chloride ion has been investigated by ab initio and DFT methods. New calculated energy data are in better agreement with experimental data. The electron‐withdrawing groups increase the energy barriers and the electron‐donating groups decrease them. The changes of geometrical parameters and energy data are in good agreement with the results of atoms in molecules and natural bond orbital analyses. The relationship between Hammett coefficients and energy data (and geometry parameters) has been established and the ρ constant has been calculated for this reaction. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
113.
Novel sulfur-modified niobium(V) oxide nanoparticles (SNON) that firstly exhibited good visible light sensitization were fabricated
by a modified sol–gel technique using a very stable sol containing niobium(V) chloride, oxalic acid, isopropanol as chelating
agent and thiourea as sulfur source. The resulting S-doped Nb2O5 nanomaterials were characterized by cyclic voltammetry (CV), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy
(EDAX), scanning electron microscope (SEM), ultra-violet diffuse reflectance (UV-DRS) and thermogravimetry thermal Analysis
(TG-DTA). As against the response of unmodified niobium(V) oxide nanoparticles (UNON), the doped samples show different electrochemical
response indicating an induced charge transfer across the niobium pentoxide/solution interface, thus forming two anodic peaks
and a cathodic peak. This important observation was confirmed by UV-DRS in terms of band bending due to sulfur doping. Upon
sulfur-modification, the absorption edge extends into the visible light region. The SEM observation shows that the SNPN existed
in the mode of polycrystalline structure and the average grain size 63 nm. The EDAX analysis of undoped Nb2O5 and sulfur doped Nb2O5 shows the Nb2O5 (98%) and S (2%) content of nanopowder. These SNON nanoparticles are expected to be suitable candidates as visible light
niobium(V) oxide nanoparticles sensitization. 相似文献
114.
A. R Hajipour S. Habibi A. E. Ruoho 《Journal of inclusion phenomena and macrocyclic chemistry》2011,69(1-2):107-117
The novel chiral polymeric compounds containing more than one calix[4]arene have been synthesized by reacting a new calix[4]arene diamine derivative with two chiral monomers. These newly prepared compounds were studied by extraction of toxic heavy metal (Cu2+, Co2+, Cd2+, Hg2+), silver and alkali metal (Na+, K+) cations from aqueous phase. It was observed that the resulting calixarene-based polymers have a good complexing ability towards silver, alkali metal and toxic heavy metal cations. 相似文献
115.
Morteza Ziyaadini Malek Taher Maghsoodlou Nourollah Hazeri Sayyed Mostafa Habibi‐Khorassani 《Heteroatom Chemistry》2012,23(2):131-137
New and stable phosphorous ylides are obtained from a simple and efficient one‐pot three‐component reaction between hexamethyl phosphorous triamide and dimethyl acetylenedicarboxylate in the presence of NH‐heterocyclic compounds in excellent yields at an ambient temperature. These stable ylides exist in solution as a mixture of two geometrical isomers as a result of the restricted rotation around the carbon–carbon partial double bond resulting from the conjugation of the ylide moiety with the adjacent carbonyl group. Dynamic effects are observed in the 1H NMR spectra that are attributed to the restricted rotation around the carbon–carbon double bond. The experimental rotational energy barrier (Δ G#) and other activation parameters on the basis of the 1H NMR study for the rotational interchangeable process of major and minor isomers in ylides 4a–d are reported. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 23:131–137, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20761 相似文献
116.
Three-component reactions of 3-substituted pyridines, dimethyl acetylenedicarboxylate (DMAD), and α-halo ketones led to regioselective and stereoselective synthesis of pyrido[2,1-b][1,3]oxazines in high to excellent yields under mild conditions. All the reactions gave the pyrido[2,1-b][1,3]oxazine derivatives without formation of any indolizine products. 相似文献
117.
M. Giahi H. Taghavi S. Habibi 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2012,86(13):2003-2007
The photocatalytic degradation of betamethasone sodium phosphate has been investigated in aqueous phase by using ultraviolet (UV) light and ZnO nanopowder. The effect of catalyst loading, irradiation time, pH, addition of oxidizers, effect of alcohol and anion presence on the reaction rate was ascertained and optimum conditions for maximum degradation were determined. The photocatalytic degradation of betamethasone sodium phosphate was strongly influenced by these parameters. The optimum amount of the photocatalyst used is 0.44 g/L. The efficiency of betamethasone sodium phosphate increases with the photo-degradation increase of the irradiation time. 相似文献
118.
Saeed Balalaie Mohammad Ali Bigdeli Enayatollah Sheikhhosseini Azizollah Habibi Hamed Piri Moghadam Mehrnoush Naderi 《Helvetica chimica acta》2012,95(3):528-535
The novel coumarin‐3‐carboxamides (=2‐oxo‐2H‐1‐benzopyran‐3‐carboxamides) 5a – 5g containing lipophilic spacers were synthesized through the Ugi‐four‐component reaction (Scheme 1). The reactions of aromatic aldehydes 1 , 4,4′‐oxybis[benzenamine] or 4,4′‐methylenebis[benzenamine] as diamine 2 , coumarin‐3‐carboxylic acid (=2‐oxo‐2H‐benzopyran‐3‐carboxylic acid; 3 ), and alkyl isocyanides 4 lead to the desired substituted coumarin‐3‐carboxamides 5a – 5g at room temperature with high bond‐forming efficiency. These novel coumarin derivatives exhibit brilliant fluorescence at 544 nm in CHCl3. 相似文献
119.
Mohsen Rostamizadeh Malek Taher Maghsoodlou Sayyed Mostafa Habibi‐Khorassani Nourallah Hazeri Seyed Sajad Sajadikhah Faramarz Rostami Charati Mohammad Amin Kazemian Brian W. Skelton Mohamed Makha 《Heteroatom Chemistry》2011,22(1):36-43
The reaction between dialkyl acetylenedicarboxylates and NH heterocyclic compounds in the presence of trialkyl phosphite leads to stable phosphorus ylide derivatives in good yields. The x‐ray crystallographic data and theoretical study show that there is a resonance between two bonds of C9P1 and C91O91 in phosphorous ylide 4c . This compound crystallizes in the triclinic system, space group ( ), with the following unit cell parameters: a = 8.7522(3)Å, b = 8.8513(5)Å, c = 18.3469(5)Å, α = 99.1220(10)°, β = 90.954(2)°, γ = 118.792(2)°, Z = 2, and V = 1222.72(9)Å3. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 22:36–43, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20653 相似文献
120.
Mojtaba Lashkari Nourallah Hazeri Malek Taher Maghsoodlou Sayyed Mostafa Habibi Khorassani Niloufar Akbarzadeh Torbati Asghar Hosseinian Santiago García‐Granda Laura Torre‐Fernndez 《Heteroatom Chemistry》2013,24(1):58-65
A three‐component synthesis of α‐aminophosphonate is described from a reaction between aldehydes, 2‐aminobenzothiazole, and triethyl phosphite in the presence of InCl3 as a catalyst under solvent‐free conditions for the generation of the particular α‐aminophosphonates. These products have two potentially biologically active parts, aminophosphonate and benzothiazole. This method offers advantages such as short reaction times, good yields, solvent‐free conditions, and easy workup with the green aspects by avoiding toxic catalysts and solvents. The crystal structure of 4b has been determined by X‐ray crystallography. This compound crystallizes in the monoclinic space group C2/c with cell parameters a = 21.9285(5) Å, b = 10.3221(2) Å, c = 18.5979(5) Å, β = 108.759(3)°, V = 3985.99(18) Å3, Dcalc = 1.301 mg m−3, and Z = 8. The final R value is 0.0501 for 3741 reflections. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 24:58–65, 2013; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21063 相似文献