全文获取类型
收费全文 | 1551篇 |
免费 | 89篇 |
国内免费 | 47篇 |
专业分类
化学 | 880篇 |
晶体学 | 23篇 |
力学 | 62篇 |
综合类 | 3篇 |
数学 | 272篇 |
物理学 | 447篇 |
出版年
2023年 | 10篇 |
2022年 | 23篇 |
2021年 | 21篇 |
2020年 | 34篇 |
2019年 | 49篇 |
2018年 | 44篇 |
2017年 | 41篇 |
2016年 | 62篇 |
2015年 | 39篇 |
2014年 | 50篇 |
2013年 | 149篇 |
2012年 | 104篇 |
2011年 | 96篇 |
2010年 | 103篇 |
2009年 | 88篇 |
2008年 | 123篇 |
2007年 | 88篇 |
2006年 | 62篇 |
2005年 | 64篇 |
2004年 | 64篇 |
2003年 | 75篇 |
2002年 | 44篇 |
2001年 | 46篇 |
2000年 | 34篇 |
1999年 | 15篇 |
1998年 | 15篇 |
1997年 | 9篇 |
1996年 | 13篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1991年 | 4篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 13篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1970年 | 2篇 |
排序方式: 共有1687条查询结果,搜索用时 296 毫秒
61.
62.
A simple porogen containing only DMF and aqueous buffer was used for synthesis of monolithic stationary media for CEC). Butyl methacrylate (BMA)‐based capillary monoliths were obtained using proposed porogen together with acrylic/methacrylic cross‐linking agents with different alkyl chain lengths. For this purpose, ethylene glycol dimethacrylate, butanediol dimethacrylate and hexanediol diacrylate (HDDA) were used. The monoliths with better electrochromatographic separation performance were obtained when the acrylic cross‐linking agent with the longest alkyl chain length (i.e. HDDA) was used with the proposed porogen. The electrochromatographic separation of alkylbenzenes, phenols and benzoic acids were sucessfully performed in CEC particularly using poly(BMA‐co‐HDDA) monolithic stationary phase with the column efficiency up to 270 000 plates/m. 相似文献
63.
Gülşah Kalaycı Murat Belivermiş Önder Kılıç Sayhan Topcuoğlu Yavuz Çotuk 《Journal of Radioanalytical and Nuclear Chemistry》2013,295(1):239-244
This study was carried out to better understand the biokinetics of radiocesium in clams living in sediment. The accumulation and depuration kinetics of 134Cs were investigated in the Manila clam (Ruditapes philippinarum) under controlled laboratory conditions. The concentration factor was found to be 3.0 for 134Cs in the whole body; however, the concentration factor in the soft part of the clams (12) was significantly higher than those in the whole body and shell (0.80). The depuration kinetics of the radionuclide were described by a two-component exponential model for the whole body. The biological half-lives in the fast and slow components were found to be 0.63 and 22.1 days, respectively. The depuration kinetics for 134Cs in the soft parts were described by a single-component exponential model with a resultant the biological half-life of 18.0 days. 相似文献
64.
Hüseyin Ovalıoğlu 《Journal of Dispersion Science and Technology》2013,34(10):1470-1476
Nuclear magnetic resonance and the Overhauser effect type dynamic nuclear polarization experiments were performed to study suspensions of asphaltene in the xylene isomers at a low magnetic field of 1.44 mT at room temperature. Intermolecular spin-spin interactions occur between nuclear spins of hydrogen in the solvent medium and the free electron spins in the asphaltene micelles. The samples were prepared in three different asphaltene concentrations at vacuum. The samples were waited for four years and dynamic nuclear polarization parameters were found via dynamic nuclear polarization experiments performed again. Thus, it was investigated the effect of sample age to dynamic nuclear polarization parameters. In addition, the medium concentrations of each sample were exposed to radiation for 48 hours and neutron radiation effects to the dynamic nuclear polarization parameters were investigated. The results are discussed. 相似文献
65.
Begüm Akduman Murat Uygun Esin Poyrazoğlu Çoban Deniz Aktaş Uygun Halil Bıyık Sinan Akgöl 《Applied biochemistry and biotechnology》2013,171(8):2285-2294
In this work, bacterial cellulose nanofibers were produced by using the Gluconacetobacter hansenii HE1 strain. These nanofibers were derivatized with dye affinity ligand Reactive Green 5, and these newly synthesized dye-attached nanofibers were used for affinity adsorption of urease. Reactive Green 5-attached nanofibers were characterized by Fourier transform infrared spectroscopy, SEM, and energy-dispersive x-ray spectroscopy analysis. Some adsorption conditions which significantly affect the adsorption efficiency were investigated. The maximum urease adsorption capacity was found to be 240 mg/g nanofiber in pH 6.0 and at room temperature. Dye-free plain nanofibers also used for studying nonspecific urease adsorption onto plain nanofibers and nonspecific adsorption were found to be negligible (3.5 mg/g nanofiber). Prepared dye-attached nanofibers can be used in five successive adsorption/desorption steps without any decrease in their urease adsorption capacity. The desorption rate of the adsorbed urease was found to be 98.9 %. The activity of the urease was also investigated, and it was found that free and desorbed urease from the dye-attached nanofibers showed similar specific activity. 相似文献
66.
Nuray Şatıroğlu İlknur Tokgöz 《International journal of environmental analytical chemistry》2013,93(7):560-572
Cloud point extraction was applied as a preconcentration step for the determination of trace level of Al(III) in water samples with electrothermal atomic absorption spectrometry (ETAAS), flame atomic absorption spectrometry (FAAS) and UV-visible spectrophotometry. The aluminum was extracted as aluminum-Eriochrome Cyanine R (ECR) complex, at pH 6 by micelles of the non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114). The investigations showed that the same CPE procedure can be used for different detection techniques. The results obtained from these techniques were evaluated. Under the optimal conditions, limit of detection obtained with ETAAS, FAAS and UV-visible spectrophotometry were 0.03 ng mL?1, 0.06 µg mL?1 and 0.01 µg mL?1, respectively. The accuracy of the procedure was tested by analysing certified reference material. The method was successfully applied to determination of aluminum in water samples and dialysis fluid. 相似文献
67.
2-(2-Aminoethylamino)ethanol (L) reacts with cupric bromide in dimethylformamide to give a mononuclear complex of Cu(II) [L2Cu]Br2, with six-coordinate distorted octahedral geometry, in which two molecules of tridentate (N,N,O) ligand are involved. The structure was confirmed by spectroscopic methods, elemental and thermogravimetric analyses, and magnetic measurements. Optimization of possible configurations indicated the formation of the trans structure of the complex. Experimental results indicate that the investigated complex, bis[2-(2-aminoethylamino)ethanol] copper(II) bromide, behaves as a semiconductor in the studied temperature range of 298–388 K. Gas sensing properties of the film for the volatile organic compounds (VOCs): acetone, tetra-chloromethane, chloroform, ethanol, and methanol, were also investigated as a function of vapor concentration and temperature in dark. The film showed maximum sensitivity to tetrachloromethane and ethanol vapors at room temperature. Responses of the film to the tested gases are reversible. 相似文献
68.
S. Sönmezoğlu T. A. Termeli S. Akın İ. Askeroğlu 《Journal of Sol-Gel Science and Technology》2013,67(1):97-104
In this work, tellurium (Te) doped CdO nanoparticles thin films with different Te concentrations (1, 3, 5, 7 and 10 %) were prepared by sol–gel method. The effects of Te doping on the structural, morphological and optical properties of the CdO thin films were systematically studied. From X-ray diffraction spectra, it has seen that all of thin films were formed polycrystalline and cubic structure having (111), (200) and (311) orientations. The structure of CdO thin films with Te-dopant was formed the unstable CdTeO3 monoclinic structure crystal plane ( $ {\bar{\text{1}}\text{22}} $ 1 ¯ 22 ), however, the intensity of this unstable peak of the crystalline phase decreased with the increase of Te-doping ratio. The strain in the structure is also studied by using Williamson-Hall method. From FE-SEM images, it has seen that particles have homogeneously distributed and well hold onto the substrate surface. Additionally, grain size increases from 27 to 121 nm with the increase of Te-doping ratio. Optical results indicate that 1 % Te-doped CdO thin film has the maximum transmittance of about 87 %, and the values of optical energy band gap increases from 2.50 to 2.64 eV with the increase of Te-doping ratio. These results make Te-doped CdO thin films an attractive candidate for thin film material applications. 相似文献
69.
70.