全文获取类型
收费全文 | 972篇 |
免费 | 36篇 |
国内免费 | 23篇 |
专业分类
化学 | 862篇 |
晶体学 | 4篇 |
力学 | 20篇 |
数学 | 64篇 |
物理学 | 81篇 |
出版年
2024年 | 4篇 |
2023年 | 7篇 |
2022年 | 30篇 |
2021年 | 37篇 |
2020年 | 64篇 |
2019年 | 56篇 |
2018年 | 83篇 |
2017年 | 40篇 |
2016年 | 73篇 |
2015年 | 56篇 |
2014年 | 73篇 |
2013年 | 127篇 |
2012年 | 68篇 |
2011年 | 79篇 |
2010年 | 55篇 |
2009年 | 50篇 |
2008年 | 45篇 |
2007年 | 30篇 |
2006年 | 10篇 |
2005年 | 13篇 |
2004年 | 6篇 |
2003年 | 7篇 |
2002年 | 6篇 |
2001年 | 3篇 |
1999年 | 1篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1976年 | 2篇 |
排序方式: 共有1031条查询结果,搜索用时 15 毫秒
51.
Mina Neghabi Abbas Behjat Bi Bi Fatemeh Mirjalili Leila Zamani 《Current Applied Physics》2013,13(1):302-306
One of the porphyrin derivatives, meso-tetraphenylporphyrin (TPP), has been synthesized and examined as an emitter material (EM) for efficient fluorescent red organic light-emitting diodes (OLEDs). By inserting a tungsten oxide (WO3) layer into the interface of anode (ITO) and hole transport layer N,N′-Di-[(1-napthyl)-N,N′-diphenyl]-(1,1′-biphenyl)-4,4′-diamine (NPB) and by using fullerene (C60) in contact with a LiF/Al cathode, the performance of devices was markedly improved. The current density–voltage–luminance (J–V–L) characterizations of the samples show that red OLEDs with both WO3 and C60 as buffer layers have a lower driving voltage and higher luminance compared with the devices without buffer layers. The red OLED with the configuration ITO/WO3 (3 nm)/NPB (50 nm)/TPP (60 nm)/BPhen (30 nm)/C60 (5 nm)/LiF (0.8 nm)/Al (100 nm) achieved the high luminance of 6359 cd/m2 at the low driving voltage of 8 V. At a current density of 20 mA/cm2, a pure red emission with CIE coordinates of (0.65; 0.35) is observed for this device. Moreover, a power efficiency of 2.07 lm/W and a current efficiency of 5.17 cd/A at 20 mA/cm2 were obtained for the fabricated devices. The study of the energy level diagram of the devices revealed that the improvement in performance of the devices with buffer layers could be attributed to lowering of carrier-injecting barrier and more balanced charge injection and transport properties. 相似文献
52.
In this paper via a novel method of discretized continuous-time Kalman filter, the problem of synchronization and cryptography in fractional-order systems has been investigated in presence of noisy environment for process and output signals. The fractional-order Kalman filter equation, applicable for linear systems, and its extension called the extended Kalman filter, which can be used for nonlinear systems, are derived. The result is utilized for chaos synchronization with the aim of cryptography while the transmitter system is fractional-order, and both the transmitter and transmission channel are noisy. The fractional-order stochastic chaotic Chen system is then presented to apply the proposed method for chaotic signal cryptography. The results show the effectiveness of the proposed method. 相似文献
53.
Fatemeh Fattahi 《佛山科学技术学院》2013,5(3):327-333
At the present paper, the new concepts of fuzzy quasi norm, fuzzy Banach space, fuzzy quasi continuity and fuzzy quasi boundedness is introduced. Furthermore, we define the fuzzy quasi operator norm and also it is shown that the set all of fuzzy quasi bounded operator from X to Y is fuzzy quasi Banach space. Finally, we have introduced and investigated some notions and some results on *-algebra theory. 相似文献
54.
Seyyed Javad Sabounchei Khadijeh Badpa Mehdi Bayat Roya Karamian Fatemeh Ghasemlou Robert W. Gable Parviz Gohari Derakhshandeh Kristof Van Hecke 《应用有机金属化学》2019,33(3)
The reaction of α‐keto‐stabilized diphosphine ylides [Ph2P(CH2)nPPh2═C(H)C(O)C6H4‐p‐CN] (n = 1 (Y1); n = 2 (Y2)) with dibromo(1,5‐cyclooctadiene) palladium(II)/platinum(II) complexes, [Pd/PtBr2(cod)], in equimolar ratio gave the new cyclometalated Pd(II) and Pt(II) complexes [Br2Pd(κ2‐Y1)] ( 1 ), [Br2Pt(κ2‐Y1)] ( 2 ), [Br2Pd(κ2‐Y2)] ( 3 ) and [Br2Pt(κ2‐Y2)] ( 4 ). These compounds were screened in a search for novel antibacterial agents and characterized successfully using Fourier transfer infrared and NMR (1H, 13C and 31P) spectroscopic methods. Also, the structures of complexes 1 and 2 were characterized using X‐ray crystallography. The results showed that the P,C‐chelated complexes 1 and 2 have structures consisting of five‐membered rings, while 3 and 4 have six‐membered rings, formed by coordination of the ligand through the phosphine group and the ylidic carbon atom to the metal centre. Also, a theoretical study of the structures of complexes 1 – 4 was conducted at the BP86/def2‐SVP level of theory. The nature of metal–ligand bonds in the complexes was investigated using energy decomposition analyses (EDA) and extended transition state combined with natural orbitals for chemical valence analyses. The results of EDA confirmed that the main portions of ΔEint, about 57–58%, in the complexes are allocated to ΔEelstat. 相似文献
55.
In this work, for the first time, Solanum melongena plant extract was used for the green synthesis of Pd/MnO2 nanocomposite via reduction osf Pd(II) ions to Pd(0) and their immobilization on the surface of manganese dioxide (MnO2) nanoparticles (NPs) as an effective support. The synthesized nanocomposite were characterized by various analytical techniques such as Fourier transform infrared (FT‐IR), X‐ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X‐ray spectroscopy (EDS) and UV–Vis spectroscopy. The catalytic activity of Pd/MnO2 nanocomposite was used as a heterogeneous catalyst for the one‐pot synthesis of 5‐substituted 1H‐tetrazoles from aryl halides containing various electron‐donating or electron‐withdrawing groups in the presence of K 4 [Fe (CN) 6 ] as non‐toxic cyanide source and sodium azide. The products were obtained in good yields via a simple methodology and easy work‐up. The nanocatalyst can be recycled and reused several times with no remarkable loss of activity. 相似文献
56.
Majid M. Heravi Fatemeh Derikvand Masoumeh Haghighi 《Monatshefte für Chemie / Chemical Monthly》2008,14(4):31-33
An efficient and improved procedure for the synthesis of tetrasubstituted imidazoles by FeCl3 · 6H2O catalyzed four-component one-pot synthesis in refluxing ethanol is described. 相似文献
57.
Babak Mokhtarani Ali Sharifi Hamid Reza Mortaheb Mojtaba Mirzaei Morteza Mafi Fatemeh Sadeghian 《The Journal of chemical thermodynamics》2009,41(12):1432-1438
Densities and viscosities of 1-butyl-3-methylimidazolium nitrate [Bmim][NO3], and its binaries with alcohol (ethanol, 1-propanol, or 1-butanol) were measured at different temperatures. The densities and viscosities of pure ionic liquid were correlated successfully by empirical equations. The Vogel–Fulcher–Tammann equations can fit the experimental data of viscosities for pure IL. Excess molar volume and viscosity deviations were calculated for the binaries. The excess molar volumes have negative deviations from the ideal solution. 相似文献
58.
Wilkes JG Rafii F Sutherland JB Rushing LG Buzatu DA 《Rapid communications in mass spectrometry : RCM》2006,20(16):2383-2386
Pyrolysis mass spectrometry (PyMS) was investigated as a rapid tool to distinguish potential bioterror hoax materials from samples containing pathogenic bacteria. A pyrolysis time-of-flight (TOF) mass spectrometer equipped with an alternative ionization technique, metastable atom bombardment (MAB), was used to produce sample spectra. These spectra were analyzed by principal component and discriminant analysis for pattern recognition. Materials investigated were two strains of Vibrio parahaemolyticus, one of which produced the tdh toxin, two Salmonella enterica serotypes, a biological mosquito control product containing spores of Bacillus thuringiensis, and several white to off-white powders (which could be used as hoax materials), such as flour, corn starch, methyl cellulose, and xanthan gum. PyMS distinguished bacterial samples from hoax materials. Furthermore, pattern analysis differentiated Vibrios from Salmonellae, Salmonella enterica Anatum from S. enterica Heidelberg, and the two V. parahaemolyticus strains from each other. The B. thuringiensis mixture was distinguished from other bacteria and powders, suggesting that PyMS with pattern recognition may differentiate samples containing pathogens, including Bacillus spp., from nonbiological agents and that it can be a rapid method for detection of bacteria. MS data acquisition took only 7 min for each sample. 相似文献
59.
The present study reports the preparation and characterization of PbO nanocrystals obtained via a thermal decomposition route. The PbO nanocrystals were synthesized using lead oxalate powder as a precursor. Nanostructured products were investigated by means of XRD, TEM, FT-IR and XPS. The XRD results indicate that tetragonal phase β-PbO with a particle size of about 30–45 nm was obtained when the intermediate precipitate was calcined at 500 °C. 相似文献
60.
In this work we use the vapor-sorption equilibrium data to show the degree of solvent upturn in each solvent-polymer system. For this purpose, 23 isothermal data sets for four polymer + solvent binaries, one block copolymer + solvent binary and for the corresponding polymer pairs have been used in the temperature range of 25-70 °C. Solvents studied are benzene, carbon tetrachloride, chloroform and pentane. Homopolymers studied are polyisobutylene, poly(ε-caprolactone), poly(ethylene oxide), n-heptadecane, polystyrene, poly(vinyl chloride), poly(vinyl methyl ether), and n-tetracosane.According to these data sets, solvent weight fraction in the polymer is plotted against solvent-vapor activity that is calculated assuming an ideal gas phase of pure solvent vapor neglecting the vapor pressure of the polymer. We use the Flory-Huggins theory to obtain dimensionless interaction parameter, χ. Also the Zimm-Lundberg clustering theory and non-ideality thermodynamic factor, Γ are used to interpret the equilibrium data. 相似文献