全文获取类型
收费全文 | 475篇 |
免费 | 16篇 |
国内免费 | 4篇 |
专业分类
化学 | 285篇 |
晶体学 | 12篇 |
力学 | 22篇 |
数学 | 115篇 |
物理学 | 61篇 |
出版年
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 9篇 |
2020年 | 13篇 |
2019年 | 20篇 |
2018年 | 20篇 |
2017年 | 10篇 |
2016年 | 38篇 |
2015年 | 16篇 |
2014年 | 23篇 |
2013年 | 90篇 |
2012年 | 25篇 |
2011年 | 50篇 |
2010年 | 38篇 |
2009年 | 25篇 |
2008年 | 24篇 |
2007年 | 23篇 |
2006年 | 15篇 |
2005年 | 9篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2002年 | 8篇 |
2001年 | 5篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1995年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有495条查询结果,搜索用时 18 毫秒
121.
122.
We propose a new globalization strategy that can be used in unconstrained optimization algorithms to support rapid convergence from remote starting points. Our approach is based on using multiple points at each iteration to build a sequence of representative models of the objective function. Using the new information gathered from those multiple points, a local step is gradually improved by updating its direction as well as its length. We give a global convergence result and also provide the parallel implementation details accompanied with a numerical study. Our numerical study shows that the proposed algorithm is a promising alternative as a globalization strategy. 相似文献
123.
Aysel Kantürk Figen Osman İsmail Sabriye Pişkin 《Journal of Thermal Analysis and Calorimetry》2012,107(3):1177-1189
Devolatilization behavior of several types of agricultural stalks (sunflower, rice, corn, and wheat) was studied using thermogravimetric
system (TG) under nitrogen atmosphere at different heating rates (10, 15, and 20 °C min-1). Coats&Redfern, Horowitz&Metzger, and Arrhenius non-isothermal kinetic models were applied to calculate the devolatilization
kinetic parameters and the devolatilization rate equations have been established. In addition, the kinetic compensation effect
(KCE) has also been used to correlate pre-exponential factor (k
o) with activation energy (E
a) and an existence of the KCE is accepted. TG-FT/IR analyses were applied of the different stalks and FT/IR stack plot used
to analyze the devolatilization gas products (CO2, CH4, HCOOH, CH3OH). Infrared vibrational frequencies, micro structure and crystallinity of stalks were investigated by Fourier transform
infrared spectroscopy (FT/IR), scanning electron microscope (SEM), and X-ray diffraction analysis (XRD), respectively. 相似文献
124.
Numerical solution of the Korteweg-de Vries equation is obtained by using the meshless method based on the collocation with radial basis functions. Five standard radial basis functions are used in the method of the collocation. The results are compared for the numerical experiments of the propagation of solitons, interaction of two solitary waves and breakdown of initial conditions into a train of solitons. 相似文献
125.
Karaböcek Serdar Değirmencioğlu İsmail Karaböcek Nevin Serbest Kerim 《Transition Metal Chemistry》2003,28(5):529-533
1,9-Dioxa-3,6-dithiacyclotridecane-10,12-dione (L1), and 1,4-dioxa-7,10-dithiacyclododecane-2,3-dione, (L2), two novel ligands, and their mono- and di-nuclear copper(II) and/or nickel(II) complexes have been prepared and characterized by elemental analyses, 1H- and 13C-n.m.r., i.r., magnetic moments and mass spectral studies. Elemental analyses, stochiometric and spectroscopic data on the complexes indicate that the metal ions are coordinated to the nitrogen, oxygen and sulphur atoms and the data support the proposed structure for the diones and their mono–dinuclear copper(II) complexes. Moreover, copper(II) complexes of the dione ligands have a 1:1 metal:ligand ratio. 相似文献
126.
This study investigates the adsorption kinetics of CTAB (cethyltrimethylammonium bromide), a cationic surfactant, onto PAC from aqueous solution with respect to the initial CTAB concentration at 20C. The pseudo-first-order, second-order kinetic models and intraparticle diffusion model were used to describe the kinetic data and the rate constants were calculated. The rate parameter, ki, of intraparticle diffusion, the rate parameter, k2, of the pseudo-second-order and k1, the rate parameter for the pseudo-first-order mechanism were compared. It was found that the pseudo-second-order adsorption mechanism is predominant and the overall rate of the CTAB adsorption process appears to be controlled by more than one step, namely both the external mass transfer and intraparticle diffusion mechanisms. 相似文献
127.
Hamdi Temel Hüseyin Alp Salih İlhan Berrin Ziyadanoğulları İsmail Yılmaz 《Monatshefte für Chemie / Chemical Monthly》2007,138(12):1199-1209
Summary. La(III), Cu(II), Ni(II), and Zn(II) metal complexes with a novel quadridentate Schiff base derived from 1,7-bis(2-formylphenyl)-1,4,7-trioxaheptane and 2-aminothiophenol were synthesized and characterized by
microanalytical data, elemental analysis, magnetic measurements, 1H NMR, 13C NMR, UV-Vis, IR, mass spectra, cyclic voltammetric and conductance measurements. The extractability of divalent cations
was evaluated as a function of relationship between distribution ratio of the metal and pH or ligand concentration. The highest extraction percentage of Cu2+ and Ni2+ showed pH 7.0 and 6.4. It was concluded that the ligand can effectively be used in solvent extraction of copper(II) and nickel(II)
from the aqueous phase to the organic phase. 相似文献
128.
Mahmure ü. ?zgür Abdürrezzak Bozdo?an Ay?e Er?a? ?kbal Koyuncu 《Monatshefte für Chemie / Chemical Monthly》2001,1(3):669-673
Two methods for the simultaneous determination of anthocyanin and ponceau 4R in drink powders by second derivative spectrophotometry and by partial least-squares multivariate spectrophotometric calibration are described. The procedures do not require any separation step. The methods were applied to determine both colorants in commercial gelatin powders; the results obtained are compared. 相似文献
129.
Musa Özil Fatih İslamoğlu Emre Menteşe Bahittin Kahveci 《Helvetica chimica acta》2010,93(10):1967-1974
The novel 4‐amino‐ or 4‐aryl‐substituted 2,4‐dihydro‐5‐[(4‐trifluoromethyl)phenyl]‐3H‐1,2,4‐triazol‐3‐ones 3a – 3g were synthesized by reaction of N‐(ethoxycarbonyl)‐4‐(trifluoromethyl)benzenehydrazonic acid ethyl ester ( 2 ) and primary amines or hydrazine by microwave irradiation. Compounds 3a – 3g were potentiometrically titrated with tetrabutylammonium hydroxide (Bu4NOH) in four nonaqueous solvents, i.e., iPrOH, tBuOH, MeCN, and N,N‐dimethylformamide (DMF). Also half‐neutralization potential values and the corresponding pKa values were determined in all cases. 相似文献
130.