全文获取类型
收费全文 | 403篇 |
免费 | 40篇 |
国内免费 | 109篇 |
专业分类
化学 | 376篇 |
力学 | 10篇 |
数学 | 47篇 |
物理学 | 119篇 |
出版年
2023年 | 3篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 8篇 |
2016年 | 11篇 |
2015年 | 15篇 |
2014年 | 26篇 |
2013年 | 34篇 |
2012年 | 29篇 |
2011年 | 35篇 |
2010年 | 23篇 |
2009年 | 35篇 |
2008年 | 32篇 |
2007年 | 22篇 |
2006年 | 20篇 |
2005年 | 19篇 |
2004年 | 25篇 |
2003年 | 26篇 |
2002年 | 35篇 |
2001年 | 37篇 |
2000年 | 16篇 |
1999年 | 27篇 |
1998年 | 24篇 |
1997年 | 12篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有552条查询结果,搜索用时 31 毫秒
41.
42.
A new gelator of urea‐containing triazine derivatives was synthesized and tested in order to explore the gelation potential in different organic solvents. This compound has been found to form organogels with a variety of organic solvents such as decalin and other solvents. The resulting thermo‐reversible gel was characterized by using the dropping ball method and a number of other instruments. The melting temperature of the gel increased with the gel concentration. The intermolecular hydrogen bonding of gelation was demonstrated through an FT‐IR spectrometer. UV‐Vis and fluorescence analysis showed that the gel displayed various optical effects in different organic solvents. The blue fluorescence of the gel in decalin and the quenched effect of gel in CHCl3 were displayed, respectively. Morphological features in decalin and CHCl3 were studied by applying atomic force microscopy (AFM), and the morphological features demonstrated that there were different aggregations in different solvents. In conductivity electrolyte experiments, the organogel electrolytes indicated high conductivity (σ) comparable to the corresponding NaClO4/THF solution. The conductivity of gel electrolytes was increased with electrolyte salt. 相似文献
43.
Tércio de Freitas Paulo Solange de Oliveira Pinheiro Maria Aparecida S. Da Silva Luiz Gonzaga de França Lopes Lucidalva S. Pinheiro Gil F. A. Aquino Márcia Laudelina Arruda Temperini Pedro de Lima Neto Izaura Cirino Nogueira Diógenes 《Electroanalysis》2009,21(9):1081-1089
STM and impedance results of the self‐assembled monolayer (SAM) formed with thionicotinamide (TNA) on gold indicate the presence of defects that increase with the immersion time of the electrode in the TNA solution affecting the SAM electroactivity toward the electron transfer reaction of the cytochrome c metalloprotein and [Fe(CN)6]4? and [Ru(NH3)6]3+ complexes. It was observed that this electroactivity was also affected by the pH of the electrolyte solution. SERS and STM data indicate sulfur coordination to the surface with contribution of the NH2 group. From the dependence of the TNA surface coverage on the temperature and concentration in solution, thermodynamic parameters of adsorption were determined. 相似文献
44.
Bisphenol A polycarbonate degrades due to sunlight, humidity and oxygen. In this study two possible techniques to stabilize the polymer were compared, i.e. blending of UV-absorbers (UVAs) into the polymer or using block copolymers based on resorcinol polyarylates. Combination of different analysis techniques shows that the protection by UVAs is not as good as by the resorcinol polyarylate block copolymers. The block copolymer rearranges itself through a photo-Fries rearrangement within hours into a UV-absorbing top layer. Two different block compositions were studied, and the copolymer with the highest concentration of resorcinol polyarylate groups shows the best protection. 相似文献
45.
《中国化学会会志》2017,64(1):94-102
Treatment of known complex [Cp2Fe2 (μ‐SEt )2(CH3CN )2](BF4 )2 ( 1 (BF4 )2) with 2 equiv of 1,4‐bis(isocyanomethyl)benzene (1,4‐CNCH2C6H4CH2NC ; L1 ) or 4,4′‐diisocyanophenyl ether (4,4′‐CNC6H4OC6H4NC ; L2 ) result in the formation of two new‐type diisocyanide complexes [Cp2Fe2 (μ‐SEt )2(1,4‐CNCH2C6H4CH2NC )2](BF4 )2 ( 2a (BF4 )2) or [Cp2Fe2 (μ‐SEt )2(4,4′‐CNC6H4OC6H4NC )2](BF4 )2 ( 2b (BF4 )2), respectively. The new‐type 24‐membered ring tetranuclear iron–thiolate–aryldiisocyanide metallocyclophane complex [Cp4Fe4 (μ‐SEt )4(μ‐1,4‐CNCH2C6H4CH2NC )2](BF4 )4 ( 3a (BF4 )4) has been synthesized by using a self‐assembly reaction between equimolar amounts of 1 (BF4 )2 and 1,4‐bis(isocyanomethyl)benzene or by a stepwise route involving mixing a 1:1 molar ratio of complexes 1 (BF4 )2 and 2a (BF4 )2. A similar approach was used through the application of equal molar ratio of complexes 1 (BF4 )2 and 2b (BF4 )2 to give a 30‐membered ring tetranuclear iron–thiolate–aryldiisocyanide metallocyclophane complex [Cp4Fe4 (μ‐SEt )4(4,4′‐CNC6H4OC6H4NC )2][BF4 ]4 ( 3b (BF4 )4). The spectroscopic and electrochemical properties of four iron–sulfur core complexes were determined. 相似文献
46.
Reza Karimi Shervedani Saied Mohsen Siadat‐Barzoki Mojtaba Bagherzadeh 《Electroanalysis》2010,22(9):969-977
A new sensor, gold‐6‐amino‐2‐mercaptobenzothiazole (6A2MBT), was fabricated via a self‐assembly procedure. Electrochemical properties of the monolayer were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The modified electrode showed excellent antifouling property against the oxidation products of DA, allowed us to construct a dynamic calibration curve with two linear parts, 1.00×10?6 to 3.72×10?4 and 3.72×10?4 to 6.42×10?4 M DA, with correlation coefficients of 0.997 and 0.992 and a detection limit of 1.57×10?7 M DA by using differential pulse voltammetry (DPV), respectively. Finally, the performance of the Au‐6A2MBT modified electrode was successfully tested for electrochemical detection of DA in a pharmaceutical sample. 相似文献
47.
Regina Luschtinetz Augusto F. Oliveira Hélio A. Duarte Gotthard Seifert 《无机化学与普通化学杂志》2010,636(8):1506-1512
Density‐functional based calculations were used to investigate self‐assembled monolayers of different alkylphosphonic acids on corundum α‐Al2O3 (0001), bayerite β‐Al(OH)3 (001) and boehmite γ‐AlOOH (010) surface models. Mono‐, bi‐, and tridentate adsorption modes were considered. In addition, the organization of single adsorbed molecules was compared to the organization at full surface coverage. The height (thickness) of the self‐assembled monolayers is always shorter than the length of the phosphonic acid molecules due to tilting of the alkyl chains. Tilt angles at full surface coverage are very similar to the tilt angle of a single adsorbed molecule, which indicates that the density of the self‐assembled monolayers is limited by the density of adsorption sites. The lateral interactions between alkyl chains are evidenced by small torsions of the adsorbed molecules, which may serve to minimize the repulsion forces between interchain hydrogen atoms. Similar tilt angles were obtained for mono‐, bi‐, and tridentate adsorptions. Hence, the coordination mode cannot be characterized by the molecule tilting. 相似文献
48.
Wen Wu Sun Shi Rong Li Hong Zhou Dr. Zhi Quan Pan Dr. Qi Mao Huang Xue Lei Hu 《无机化学与普通化学杂志》2010,636(7):1386-1391
A new dumbbell‐type 4,4′‐bipy‐bridged dinuclear copper(II) complex, [Cu2(4,4′‐bipy)L2(H2O)2](ClO4)4 · 8CH3OH · 10H2O, where L = 1‐[bis(3‐aminopropyl)amino]‐2‐ propanol and bipy = bipyridine, has been synthesized and characterized, X‐ray crystallographic analysis shows that the [Cu2(4,4′‐bipy)L2(H2O)2]4+ cations and water molecules generate layer structures extending parallel to bc planes through hydrogen bonding interactions of O–H ··· O and C–H ··· O. The layers are also connected by hydrogen bonding interactions involving methanol, water, and perchlorate anions. These interactions lead to the formation of rectangular channels of 12.3 Å × 6.0 Å along the crystallographic c axis. Perchlorate anions fill in each channel in a sandwich‐like packing mode, they are joined with the adjacent layers by water heptamers. Magnetic susceptibility measurements show that the magnetic exchange interaction is weak although it has a regular π‐type electron transfer pathway. Furthermore, the electrochemical and thermogravimetric properties of the complex were also investigated. 相似文献
49.
In the present paper, self‐focusing of laser beams in relativistic plasmas is studied by the moment theory approach. The equilibrium beam radius of the self‐trapped laser beams is also derived. Results are compared with the paraxial ray theory. It is observed from the analysis that at higher intensities, the equilibrium beam radius increases in case of the paraxial ray theory, whereas it becomes independent of the beam intensity in case of the moment theory. Analysis also confirms the role of relativistic electrons travelling with the light pulse in (3D PIC) simulation studies (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
50.
Andrea Posilicano 《Mathematische Nachrichten》2014,287(16):1848-1885
Let be bounded with a smooth boundary Γ and let S be the symmetric operator in given by the minimal realization of a second order elliptic differential operator. We give a complete classification of the Markovian self‐adjoint extensions of S by providing an explicit one‐to‐one correspondence between such extensions and the class of Dirichlet forms in which are additively decomposable by the bilinear form of the Dirichlet‐to‐Neumann operator plus a Markovian form. By such a result two further equivalent classifications are provided: the first one is expressed in terms of an additive decomposition of the bilinear forms associated to the extensions, the second one uses the additive decomposition of the resolvents provided by Kre?n's formula. The Markovian part of the decomposition allows to characterize the operator domain of the corresponding extension in terms of Wentzell‐type boundary conditions. Some properties of the extensions, and of the corresponding Dirichlet forms, semigroups and heat kernels, like locality, regularity, irreducibility, recurrence, transience, ultracontractivity and Gaussian bounds are also discussed. 相似文献