全文获取类型
收费全文 | 401篇 |
免费 | 13篇 |
国内免费 | 2篇 |
专业分类
化学 | 214篇 |
晶体学 | 4篇 |
力学 | 37篇 |
数学 | 76篇 |
物理学 | 85篇 |
出版年
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 9篇 |
2020年 | 10篇 |
2019年 | 16篇 |
2018年 | 24篇 |
2017年 | 16篇 |
2016年 | 36篇 |
2015年 | 12篇 |
2014年 | 31篇 |
2013年 | 46篇 |
2012年 | 31篇 |
2011年 | 34篇 |
2010年 | 26篇 |
2009年 | 24篇 |
2008年 | 15篇 |
2007年 | 19篇 |
2006年 | 12篇 |
2005年 | 10篇 |
2004年 | 7篇 |
2003年 | 4篇 |
2002年 | 5篇 |
2001年 | 6篇 |
1998年 | 1篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1988年 | 1篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
排序方式: 共有416条查询结果,搜索用时 31 毫秒
21.
A novel scheme for pressure fluctuations in turbulent flows is developed. The pressure fluctuations are sensitive parameter in some of the fluid phenomena. In the computational methods and modeling turbulence flow, the pressure fluctuations are eliminated after averaging of the Navier-Stokes equations, and only average pressure could be calculated. In this research, the Reynolds-averaged Navier-Stokes equations are computed using SIMPLE method. The Reynolds stress transport model (RSTM) is used to determine the Reynolds stresses and the flow details. The velocity fluctuations are simulated using the Kraichnan model. The Poisson equation for the pressure fluctuations is obtained by taking the divergence of the incompressible momentum equation and algebraic operations, and this equation is numerically solved by finite difference method. The effects of Reynolds number on the pressure fluctuations are studied. 相似文献
22.
Mahsa Taghavi Sirous Ebrahimi Jafarsadegh Moghaddas 《Journal of Dispersion Science and Technology》2014,35(8):1097-1105
The recently developed centrifugal impeller is examined to investigate the solid–liquid mixing in a mechanically agitated contactor. Using the sample withdrawal method, the effects of impeller geometrical parameters, impeller rotational speed (200–700 rpm), solid particle size (500–1100 µm), and solid loading (2–10 vol%) on the degree of homogeneity are studied. The axial and the radial solid concentration profiles and the minimum impeller speed for the complete homogenization are also determined. In comparison with a widely used propeller impeller, considerably higher homogeneity values in lower impeller speeds are obtained (90% homogeneity against 16% homogeneity at 200 rpm at the same conditions). Having also lower power consumption makes this a superior impeller in solid–liquid mixing processes especially in shear-sensitive systems. 相似文献
23.
Hamideh Sharifi Noghabi Gholam Hossein Rounaghi Mohammad Hossein ArbabZavar Javad Ebrahimi 《Russian Journal of General Chemistry》2014,84(7):1429-1433
We report on conductometric study of complexation between benzylbisthiosemicarbazone [(2E,2′E)-2,2′-(1,2-diphenylethane-1,2-diylidene)bis(hydrazine-1-carbothioamide)] with Zn2+, Cr3+, Co2+, and Ni2+ cations at different temperatures in acetonitrile-dimethylformamide binary solvents of varied composition. The equilibrium constant and standard thermodynamic parameters (Δc H 0 and Δc S 0) of the complexes formation have been determined and found to be dependent on the binary solvent composition, the metal ion nature, and temperature. 相似文献
24.
Mitra Ebrahimi Shahrzad Abdolmohammadi Reza Kia-Kojoori 《Journal of heterocyclic chemistry》2020,57(4):1875-1881
Ag2Cr2O7 nanoparticles were found to be an exceedingly effective catalyst for the mild and green synthesis of aminobenzochromenes. The reaction was performed under ultrasonic irradiation as an innocuous tool and in water as a green solvent at room temperature. This method encompasses several sustainable and economic benefits. 相似文献
25.
Samaneh Zarei Golzar Komeili Saeed Bahadorikhalili Azadeh Yahya-Meymandi Morteza Karami-Zarandi Bagher Larijani Mahmood Biglar Seyed Esmaeil Sadat Ebrahimi Mohammad Mahdavi 《Journal of heterocyclic chemistry》2020,57(12):4254-4261
In this paper, a novel series of 2-(4-((1-aryl-1H-1,2,3-triazol-4-yl)methoxy)phenyl)2-(2-oxoazetidin-1-yl)acetamide derivatives are synthesized in two steps. The first step involved Ugi multicomponent reaction of β-alanine, o-(propargyl)benzaldehyde and isocyanide derivatives. The product of this step, underwent a click 1,3-dipolar cycloaddition reaction with benzyl azide derivatives. The 2-(4-((1-aryl-1H-1,2,3-triazol-4-yl)methoxy)phenyl)2-(2-oxoazetidin-1-yl)acetamide product was characterized and their antibacterial activities were evaluated against various G-positive (Staphylococcus aureus and Bacillus subtilis) and G-negative (Pseudomonas aeruginosa and Escherichia coli) bacteria, using minimal inhibition concentration. The compounds showed very good antimicrobial activity and a number of products have been more active than ciprofloxacin. 相似文献
26.
T.?VazifehshenasEmail author F.?Ebrahimi 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,46(1):9-14
We investigate the band-gap renormalization due to electron-electron interaction in the n-type doped GaAs-based
double-quantum-wire systems. Electron self-energy is calculated using the leading-order perturbation theory
(GW) within the full random-phase-approximation (RPA). We include the impurity effects through Mermin
expression and show that decreasing the spacing in double-wire system can compensate partly the undesirable
effect of impurities on the band-gap renormalization. Therefore, it is possible to offset the effect of
impurity in related devices and to adjust the band-gap. We also, apply a constant electric field to one of the
wires. It is shown that the change of the band-gap renormalization in the other wire will be insignificant if
the drift velocity does not exceed Fermi velocity. 相似文献
27.
A -frame is a lattice in which countable joins exist and binary meets distribute over countable joins. In this paper, the category MFrm, of metric -frames, is introduced, and it is shown to be equivalent to the category MLFrm
u, of metric Lindelöf frames.Finally, it is shown that the complete metric -frames are exactly the cozero parts of complete metric Lindelöf frames. 相似文献
28.
Purity and equational compactness play a role at least in the Theories of Modules, Acts, Model, and Category. Adámek and Rosický have studied them categorically, Rothmaler model-theoretically, and some authors, including Banaschewski, Gould, and Normak have studied these notions on G-acts. We take both the group G and the set A in the definition of a G-act to be sheaves and study equationally compact G-sheaves. We get different kinds of equationally compact G-sheaves, study them and their interrelations, give some conditions for their proper behavior, and generalize some of the existing results. 相似文献
29.
30.
Leila Hejazi Diako Ebrahimi D. Brynn Hibbert Michael Guilhaus 《Rapid communications in mass spectrometry : RCM》2009,23(14):2181-2189
Orthogonal acceleration time‐of‐flight (oa‐TOF) mass spectrometry (MS) was coupled to gas chromatography (GC) to measure ion yields (ratio of ion counts to number of neutrals entering the ion source) and signal‐to‐noise (S/N) in the electron ionization (EI) mode (hard ionization) as well as in the soft ionization modes of chemical ionization (CI), electron capture negative ion chemical ionization (NICI) and field ionization (FI). Mass accuracies of the EI and FI modes were also investigated. Sixteen structurally diverse volatile organic compounds were chosen for this study. The oa‐TOF mass analyzer is highly suited for FI MS and provided an opportunity to compare the sensitivity of this ionization method to the more conventional ionization methods. Compared to the widely used quadrupole mass filter, the oa‐TOF platform offers significantly greater mass accuracy and therefore the possibility of determining the empirical formula of analytes. The findings of this study showed that, for the instrument used, EI generated the most ions with the exception of compounds able to form negative ions readily. Lower ion yields in the FI mode were generally observed but the chromatograms displayed greater S/N and in many cases gave spectra dominated by a molecular ion. Ion counts in CI are limited by the very small apertures required to maintain sufficiently high pressures in the ionization chamber. Mass accuracy for molecular and fragment ions was attainable at close to manufacturer's specifications, thus providing useful information on molecular ions and neutral losses. The data presented also suggests a potentially useful instrumental combination would result if EI and FI spectra could be collected simultaneously or in alternate scans during GC/MS. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献