全文获取类型
收费全文 | 481篇 |
免费 | 14篇 |
国内免费 | 2篇 |
专业分类
化学 | 278篇 |
晶体学 | 4篇 |
力学 | 29篇 |
数学 | 75篇 |
物理学 | 111篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 20篇 |
2021年 | 20篇 |
2020年 | 17篇 |
2019年 | 18篇 |
2018年 | 14篇 |
2017年 | 12篇 |
2016年 | 41篇 |
2015年 | 15篇 |
2014年 | 29篇 |
2013年 | 60篇 |
2012年 | 29篇 |
2011年 | 47篇 |
2010年 | 30篇 |
2009年 | 26篇 |
2008年 | 23篇 |
2007年 | 19篇 |
2006年 | 11篇 |
2005年 | 11篇 |
2004年 | 7篇 |
2003年 | 15篇 |
2002年 | 9篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有497条查询结果,搜索用时 125 毫秒
1.
Soltani Rad Mohammad Navid Behrouz Somayeh Mohammad-Javadi Mehdi Zarenezhad Elham 《Molecular diversity》2022,26(5):2503-2521
Molecular Diversity - The preparation, characterization and application of hydroxyapatite silica propyl bis aminoethoxy ethane cuprous complex (HASPBAEECC) as a novel hybrid nano-catalyst for... 相似文献
2.
Rachida M’chaar Abdelaziz Sabbar Mouloud El Moudane Noureddine Ouerfelli 《哲学杂志》2020,100(11):1415-1438
ABSTRACT By applying the geometric models and the theoretical equation, the surface tension, the molar volume and the density were studied. The empirical calculations were carried out in temperature range 623?K?≤?T?≤?1123?K. Only few thermophysical properties were estimated for eight quinary alloys: Sn3.55Ag0.5Cu3Bi3Sb, Sn3.48Ag0.5Cu3Bi5Sb, Sn3.48 Ag0.5Cu5Bi3Sb, Sn3.40 Ag0.5Cu5Bi5Sb, Sn3.53Ag1Cu3Bi3Sb, Sn3.46Ag1Cu3Bi5Sb, Sn3.46Ag1Cu5Bi3Sb, Sn3.38Ag1Cu5Bi5Sb. The results show that surface tension and density have a linear appearance for all temperatures. We have also studied the influence of the composition and temperature in the studied alloys. The obtained theoretical results are compared with the experimental ones and with the conventional Pb–Sn welds. 相似文献
3.
Noureddine Berrahou 《Comptes Rendus Mathematique》2006,343(9):595-600
In this Note, we obtain a large deviations principle for the uniform deviation of the delta-sequence density estimator. A general result is stated for any regular delta-sequence and a discussion of hypotheses for the most usual methods is given. Implications of our results in the study of the inaccuracy rate of these estimates with the comparisons of performances of various methods are given. The estimation is based upon sequences of i.i.d. random variables. To cite this article: N. Berrahou, C. R. Acad. Sci. Paris, Ser. I 343 (2006). 相似文献
4.
Noureddine Igbida 《Journal of Mathematical Analysis and Applications》2007,335(2):1061-1078
In this paper, we study the nonlinear evolution equation of Hele-Shaw type with dynamical boundary conditions. That is, the equation ut=Δw+f where u∈H(w) and H is the Heaviside function, with boundary condition μ(x,w)t∂w+k∇w⋅ν=g, where ν denotes the outward normal vector of the fixed boundary of the domain. We prove existence, uniqueness and some qualitative properties of the solution. 相似文献
5.
Shayesteh S. Farjami B. Soltani M. A. Solimany 《International Journal of Infrared and Millimeter Waves》2002,23(12):1691-1697
We present and discuss infrared magnetoplasma reflectivity and surface polariton modes in Ga1–xNxAs. It assumed that the sample is characterized by a magnetoplasma dielectric tensor. Surface polariton dispersion for two component magnetoplasma was calculated from reflectivity spectra data. We detect transverse optic phonon of GaN sublattice in 470 cm-1. The origin of sharp feature in p-polarization reflectivity about 300 cm–1 as well as LO phonon frequency of GaAs sublattice is due to Brewster mode. An interesting feature of surface modes in Voigt geometry is nonreciprocalicity, which means that the frequency changes when the direction of propagation is reversed. Also, the infrared magnetoplasma reflectivity of GaNAs should be providing determination of the electrons and heavy holes effective mass and carrier's concentration. 相似文献
6.
This paper describes a new capacitive structure of pressure sensor to increase simultaneously the sensitivity and the linearity of the transducer. This structure contains two capacitors which change in response to pressure, but in opposite senses. To increase even more the sensitivity of each capacitor, the pressure sensitive diaphragm carries a central boss. The optimal position and the length of the boss are also calculated. To cite this article: A. Ettouhami et al., C. R. Mecanique 332 (2004). 相似文献
7.
Parasteh Pirasteh Ali Soltani Lazhar Haji Nicolas Errien 《Applied Surface Science》2006,253(4):1999-2002
In order to understand the optical loss mechanisms in porous silicon based waveguides, structural and optical studies have been performed. Scanning and transmission electron microscopic observations of porous silicon layers are obtained before and after an oxidation process at high temperature in wet O2. Pore size and shape of heavily p-type doped Si wafers are estimated and correlated to the optical properties of the material before and after oxidation. The refractive index was measured and compared to that determined by the Bruggeman model. 相似文献
8.
A simple one-pot procedure for the direct conversion of alcohols into azides using TsIm 总被引:1,自引:0,他引:1
A facile and efficient method for one-pot conversion of alcohols into azides using N-(p-toluenesulfonyl)imidazole (TsIm) is described. In this method, alcohols are refluxed with a mixture of NaN3, TsIm and triethylamine in the presence of catalytic amounts of tetra-n-butylammonium iodide (TBAI) in DMF affording the corresponding alkyl azides in good yields. This methodology is highly efficient for various structurally diverse alcohols with selectivity for ROH: 1° > 2° > 3°. 相似文献
9.
Abdelhak Benabra Ana Alcudia Noureddine Khiar Inmaculada Fernández Felipe Alcudia 《Tetrahedron: Asymmetry》1996,7(12):3353-3356
The stereochemical outcome of the reaction of chiral secondary alcohols with a phosphinyl chloride was found to be highly dependent on the achiral base used. Thus, the reaction of the readily available sugar derived carbinols, 1 and 2, with methylphenylphosphinyl chloride in the presence of triethylamine yields stereoselectively the corresponding Snp-phosphinates 3Sp and 5Sp in 94 and 92% diastereomeric excess (de). Simply changing the base from triethylamine to pyridine affords Rp-phosphinates 4Rp and 6Rp epimers to 3Sp and 5Sp at the phosphinyl phosphorus in 50 and 40% de respectively. These phosphinate esters were found to be good P-chiral transferring intermediates, they react with Grignard reagents under very mild conditions to give the corresponding phosphine oxides. Both enantiomers Sp- and Rp-o-anisylmethylphenylphosphine oxide (PAMPO) as well Sp- and Rp- methylphenylpropyl phosphine oxide were obained enantiomerically pure in high yields 相似文献
10.
Behpour M Attaran AM Ghoreishi SM Soltani N 《Analytical and bioanalytical chemistry》2005,382(2):444-447
A sensitive, selective and simple preconcentration method for ultra-trace gold determination has been developed that uses naphthalene–methyltrioctyl ammonium chloride (Aliquat 336s) as an adsorbent. Gold, in the form of AuCl4–, was retained by the adsorbent in the column at a flow rate of 1 ml min–1. After filtration, the solid mass consisting of the gold complex and naphthalene was dissolved out of the column with 5 ml of N,N-dimethylformamide (DMF), and the metal was then determined by atomic absorption spectrometry. In the initial solution, the calibration graph of absorbance versus gold concentration was found to be linear in the range 0.5–150 ng ml–1 Au(III) with r=0.997 (n =9), and the 3 s detection limit was 0.428 ng ml–1. The relative standard deviation for eight replicate measurements of 20 g of gold was 2.14%. Preconcentration factors of 390 and 650 were achieved using 5 ml and 3 ml of DMF, respectively. The proposed method was successfully applied to the determination of gold in wastewater, processed pool water, slurry pool water, and raw well-water from the Moteh gold mine, and synthetic samples. 相似文献