全文获取类型
收费全文 | 334篇 |
免费 | 33篇 |
国内免费 | 5篇 |
专业分类
化学 | 285篇 |
力学 | 18篇 |
数学 | 26篇 |
物理学 | 43篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 10篇 |
2020年 | 13篇 |
2019年 | 20篇 |
2018年 | 16篇 |
2017年 | 12篇 |
2016年 | 36篇 |
2015年 | 26篇 |
2014年 | 38篇 |
2013年 | 39篇 |
2012年 | 42篇 |
2011年 | 35篇 |
2010年 | 9篇 |
2009年 | 11篇 |
2008年 | 7篇 |
2007年 | 9篇 |
2006年 | 5篇 |
2005年 | 4篇 |
2004年 | 11篇 |
2003年 | 5篇 |
2002年 | 2篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有372条查询结果,搜索用时 15 毫秒
51.
A value space is a topological algebra B equipped with a non-empty family of continuous quantifiers :B∗→B. We will describe first-order logic on the basis of B. Operations of B are used as connectives and its relations are used to define statements. We prove under some normality conditions on the value space that any theory in the new setting can be represented by a classical first-order theory. 相似文献
52.
In this work, neat and supported H6P2W18O62 into nanocage of β‐zeolite were synthesized. However, H6P2W18O62 into nanocage of β‐zeolite was synthesized via template synthesis method. In addition, TiO2 was supported on H6P2W18O62/β zeolite by impregnation method. The obtained materials were characterized by XRD, FT‐IR, UV‐Vis, FESEM and EDS techniques. Also, W and Ti contents of the catalyst were determined by ICP and EDS technique. The results reveal that the photocatalyst performance depends on catalyst loading, pH effect, and methyl orange concentration. Photocatalytic degradation of methyl orange follows a pseudo‐first order kinetic. The chemical oxygen demand (COD) experimental proved mineralization of methyl orange. Another reason for degradation and mineralization of methyl orange is the absence of hydrazine at the end of reaction which is one of the photodecolorization products. The plausible mechanism for photodegradation of MO was proposed. 相似文献
53.
54.
55.
56.
甲醇制丙烯:最重要的催化剂及其性能 总被引:1,自引:0,他引:1
由于世界范围内原油缺乏和丙烯需求量增长,在甲醇转化制烃类的不同路线中,甲醇制丙烯(MTP)过程得到发展.本文讨论了催化剂结构对MTP工艺条件的影响以及分子筛酸性、晶粒尺寸、中孔特性和拓扑结构等因素对催化剂催化MTP反应活性和选择性的影响. 相似文献
57.
Surface properties for three binary mixtures containing a 1-butyl-3-methylimidazolium thiocyanate ([BMIM][SCN]) and a long-chain alcohol (1-butanol, 1-pentanol and 1-hexanol) were determined by surface tension data at the following temperatures: (298.15, 308.15, 318.15, 328.15 and 338.15) K. The surface tension data over the entire mole fraction range are correlated by the Fu et al.(FLW) and Myers-Scott (MS) models. There is good agreement between the experimental data and the results of correlations for 15 binary systems (the three systems at five temperatures) with an average relative error below 1.5%. In addition, the UNIFAC group contribution method is applied for calculation of activity coefficients of components in solution. Moreover, the relative adsorptions of alcohol at the air/liquid interface are determined using Gibbs adsorption isotherm. The obtained results show that the values of adsorption for mixtures of alcohols/[BMIM][SCN] increase with increasing the alkyl chain length of alcohol and decreasing temperature. 相似文献
58.
Refinement of the primary hydration shell model for molecular dynamics simulations of large proteins
A realistic representation of water molecules is important in molecular dynamics simulation of proteins. However, the standard method of solvating biomolecules, that is, immersing them in a box of water with periodic boundary conditions, is computationally expensive. The primary hydration shell (PHS) method, developed more than a decade ago and implemented in CHARMM, uses only a thin shell of water around the system of interest, and so greatly reduces the computational cost of simulations. Applying the PHS method, especially to larger proteins, revealed that further optimization and a partial reworking was required and here we present several improvements to its performance. The model is applied to systems with different sizes, and both water and protein behaviors are compared with those observed in standard simulations with periodic boundary conditions and, in some cases, with experimental data. The advantages of the modified PHS method over its original implementation are clearly apparent when it is applied to simulating the 82 kDa protein Malate Synthase G. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009 相似文献
59.
Mohammadreza Khanmohammadi Amir Bagheri Garmarudi Keyvan Ghasemi Miguel de la Guardia 《Microchemical Journal》2009,91(1):47-52
A method has been introduced for quantitative determination of protein content in yogurt samples based on the characteristic absorbance of protein in 1800-1500 cm− 1 spectral region by mid-FTIR spectroscopy and chemometrics. Successive Projection Algorithm (SPA) wavelength selection procedure, coupled with feed forward Back-Propagation Artificial Neural Network (BP-ANN) model was the benefited chemometric technique. Relative Error of Prediction (REP) in BP-ANN and SPA-BP-ANN methods for training set was 7.25 and 3.70 respectively. Considering the complexity of the sample, the ANN model was found to be reliable, while the proposed method is rapid and simple, without any sample preparation step. 相似文献
60.
Solid‐state synthesis of a new core–shell nanocomposite of polyaniline and silica via oxidation of aniline hydrochloride by FeCl3.6H2O 下载免费PDF全文
Among the different oxidants used for the preparation of polyaniline in the solid‐state, iron (III) chloride (FeCl3.6H2O) can act as both oxidant and dopant. This work reports the synthesis and characterization of novel composite of polyaniline/silica. The polymerization was performed by oxidative polymerization of aniline hydrochloride in the presence of silica and FeCl3.6H2O under solid‐state (solvent‐free) condition. The FeCl3.6H2O has been chemically supported on silica and generated silica‐supported FeCl3 ( SSFe ), which plays three important roles simultaneously (a) oxidant, (b) primary dopant, and (c) secondary dopant (Lewis acid). Furthermore, the existence of silica is important for proceeding of polymerization in solid state. In the other words, the surface polymerization and green chemistry in solid state have been coupled. The characterization and doping process are verified by ultraviolet‐visible, Fourier transform infrared, atomic absorption spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and elemental analysis (CHNS). From atomic absorption spectroscopy the ratio of Fe/N in the composite obtained about 1, which confirms the formation of delocalized polarons by SSFe in the composites. The conductivity is in the range of semi‐conductive. Furthermore, contact resistance was determined by circular‐transmission line measurement. According to scanning electron microscopy images silica particles have been thoroughly coated by polyaniline within the range of 0.2 to 1 µm. However, transition electron microscopy images depict the uniform solid nanospheres (no hollow spheres or fibers), and their mean diameters are under of 50 nm. It confirms nanocomposite of core–shell PANI‐SSFe. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献