全文获取类型
收费全文 | 2891篇 |
免费 | 34篇 |
国内免费 | 38篇 |
专业分类
化学 | 707篇 |
晶体学 | 6篇 |
力学 | 49篇 |
综合类 | 10篇 |
数学 | 219篇 |
物理学 | 283篇 |
综合类 | 1689篇 |
出版年
2023年 | 13篇 |
2022年 | 28篇 |
2021年 | 15篇 |
2020年 | 27篇 |
2019年 | 213篇 |
2018年 | 48篇 |
2017年 | 31篇 |
2016年 | 27篇 |
2015年 | 49篇 |
2014年 | 131篇 |
2013年 | 122篇 |
2012年 | 145篇 |
2011年 | 234篇 |
2010年 | 200篇 |
2009年 | 175篇 |
2008年 | 171篇 |
2007年 | 132篇 |
2006年 | 122篇 |
2005年 | 97篇 |
2004年 | 68篇 |
2003年 | 67篇 |
2002年 | 53篇 |
2001年 | 28篇 |
2000年 | 34篇 |
1999年 | 27篇 |
1998年 | 20篇 |
1997年 | 18篇 |
1996年 | 16篇 |
1995年 | 16篇 |
1994年 | 17篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 13篇 |
1986年 | 5篇 |
1985年 | 41篇 |
1984年 | 32篇 |
1983年 | 26篇 |
1982年 | 28篇 |
1981年 | 86篇 |
1980年 | 81篇 |
1979年 | 28篇 |
1978年 | 43篇 |
1977年 | 49篇 |
1976年 | 38篇 |
1975年 | 40篇 |
1974年 | 33篇 |
1973年 | 31篇 |
1968年 | 6篇 |
排序方式: 共有2963条查询结果,搜索用时 10 毫秒
121.
The effects of the inorganic matrix of the oil shale on the oxidation of the kerogen at temperatures up to 1000°C in an air atmosphere were investigated Kerogen was isolated by successive HCl, HF and LiAlH4 treatments. The initial shale and each product of every demineralization process were oxidized in a thermogravimetric system in an air atmosphere. The oxidation products were analyzed by Fourier transform infrared spectroscopy. Changes in the chemical structure of the organic material of the shale were correlated with the separated constituents of the inorganic matrix. Oxidation of the kerogen occurred in two stages. The first stage was complete at about 400°C. The oxidized product after the first stage contained a char of an aromatic ring system substituted with some aliphatic material and carbonyl groups. Calcium minerals increased the reactivity of the aromatic part of the organic material towards the oxidation reactions. Where calcium minerals were absent, mainly the aliphatic and the carbonyl groups decomposed. Silicates and pyrites did not affect the reactivity of the organic material in oxidation reactions. 相似文献
122.
123.
Thioacids and thioamino acids were synthesized in excellent yields from readily available acyl benzotriazoles and sodium hydrosulfide in water at room temperature. The new methodology features mild reaction conditions, high yields, short reaction times, and does not involve the use of organic solvents or bases. The reaction is eco-friendly, and the workup procedure is simple and does not require chromatographic separation. 相似文献
124.
Kelly R. Morrison Ryan A. Allen Kevin P.C. Minbiole William M. Wuest 《Tetrahedron letters》2019,60(37):150935
Quaternary ammonium compounds (QACs) are a class of antimicrobials that have been around for over a century; nevertheless, they have found continued renewal in the structures to which they can be appended. Ranging from antimicrobial polymers to adding novel modes of action to existing antibiotics, QACs have found ongoing use due to their potent properties. However, resistance against QACs has begun to emerge, and the mechanism of resistance is still only partially understood. In this review, we aim to summarize the current state of the field and what is known about the mechanisms of resistance so that the QACs of the future can be designed to be evermore efficacious and utilized to unearth the remaining mysteries that surround bacteria’s resistance to them. 相似文献
125.
The antibiotic pipeline has failed to keep pace with the rise of multidrug resistant tuberculosis and extensively drug-resistant tuberculosis pathogens. Naturally occurring peptides provide a rich source of lead compounds for developing novel pharmaceuticals with high selectivity and potency. Given the vast number of naturally-occurring bioactive cyclic peptides identified so far, the following digest highlights several cyclic peptides, discovered in the preceding decade, that exhibit promising activity against Mycobacterium tuberculosis. 相似文献
126.
Breanna M. Wong Greg Collinge Alyssa J.R. Hensley Yong Wang Jean-Sabin McEwen 《Progress in Surface Science》2019,94(2):100538
Bimetallic catalysts have demonstrated properties favorable for upgrading biofuel through catalytic hydrodeoxygenation. However, the design and optimization of such bimetallic catalysts requires the ability to construct accurate, predictive models of these systems. To generate a model that predicts the kinetic behavior of benzene adsorbed on Pt (1 1 1) and a Pt3Sn (1 1 1) surface alloy (Pt3Sn (1 1 1)), the adsorption of benzene was studied for a wide range of benzene coverages on both surfaces using density functional theory (DFT) calculations. The adsorption energy of benzene was found to correlate linearly with benzene coverage on Pt (1 1 1) and Pt3Sn (1 1 1); both surfaces exhibited net repulsive lateral interactions. Through an analysis of the d-band properties of the metal surface, it was determined that the coverage dependence is a consequence of the electronic interactions between benzene and the surface. The linear coverage dependence of the adsorption energy allowed us to quantify the influence of the lateral interactions on the heat of adsorption and temperature programmed desorption (TPD) spectra using a mean-field model. A comparison of our simulated TPD to experiment showed that this mean-field model adequately reproduces the desorption behavior of benzene on Pt (1 1 1) and Pt3Sn (1 1 1). In particular, the TPD correctly exhibits a broadening desorption peak as the initial coverage of benzene increases on Pt (1 1 1) and a low temperature desorption peak on Pt3Sn (1 1 1). However, due to the sensitivity of the TPD peak temperature to the desorption energy, precise alignment of experimental and theoretical TPD spectra demands an accurate calculation of the adsorption energy. Therefore, an analysis of the effect of the exchange-correlation functional on TPD modeling is presented. Through this work, we show the necessity of incorporating lateral interactions into theoretical models in order to correctly predict experimental behavior. 相似文献
127.
Qiang Xue Yajie Zhang Ruoning Li Chao Li Na Li Chenyang Yuan Shimin Hou Yongfeng Wang 《中国化学快报》2019,30(12):2355-2358
The self-assembly of l-tryptophan on Cu(111) is investigated by an ultrahigh vacuum scanning tunneling microscope (STM) at 4.4 K. When deposited onto the substrate at around 120 K with a coverage of 0.1 monolayer, molecular trimers, tetramers, hexamers, and chains coexist on Cu(111). Then almost all molecules self-assemble into chiral hexamers after being annealed at room temperature. When increasing molecular coverage to the full layer, a new type of chain is observed on the surface. Based on the high-resolution STM images at sub-molecular level, we suggest that the l-tryptophan molecules are present in neutral, zwitterionic or anionic states in these structures. 相似文献
128.
The acidic gases such as SO2, NOx, H2S and CO2 are typical harmful pollutants and greenhouse gases in the atmosphere, which are also the main sources of PM2.5. The most widely used method of treating these gas molecules is to capture them with different adsorption materials, i.e., metal and nonmetallic materials such as MnO2, MoS2 and carbon-based materials. And doping transition metal atoms in adsorption materials are beneficial to the gas adsorption process. The first-principles calculation is a powerful tool for studying the adsorption properties of contaminant molecules on different materials at the molecular and atomic levels to understand surface adsorption reactions, adsorption reactivity, and structure-activity relationships which can provide theoretical guidance for laboratory researches and industrial applications. This review introduces the adsorption models and surface properties of these gas molecules on metal and nonmetallic surfaces by first-principles calculation in recent years. The purpose of this review is to provide the theoretical guidance for experimental research and industrial application, and to inspire scientists to benefit from first-principles calculation for applying similar methods in future work. 相似文献
129.
The electrochemical behavior of austenitic stainless steel (Type 304) in 3 M sulfuric acid with 3.5% recrystallized sodium chloride at specific concentrations of butan-1-ol was investigated with the aid of potentiodynamic polarization, open circuit measurement and weight loss technique. Butan-1-ol effectively inhibited the steel corrosion with a maximum inhibition efficiency of 78.7% from weight-loss analysis and 80.9% from potentiodynamic polarization test at highest concentration studied. Adsorption of the compound obeyed the Freundlich isotherm. Thermodynamic calculations reveal physiochemical interactions and spontaneous adsorption mechanism. Surface characterizations showed the absence of corrosion products and topographic modifications of the steel. Statistical analysis depicts the overwhelming influence and statistical significance of inhibitor concentration on the inhibition performance. 相似文献
130.
Manuel Palencia Alexander Córdoba Manuel F. Melendrez 《Arabian Journal of Chemistry》2019,12(6):825-834
The objective of this work was to synthesize nanocomposites based on cationic polyelectrolytes and silver nanoparticles using poly(N-vinylbenzyl-N-triethylammonium chloride) as polymer phase. For that, a nanostructured crosslinker was synthesized from silver nanoparticles (AgNPs) and acrylic acid. Molybdate retention properties of nanocomposites were studied in function of pH and ionic strength. In addition, their antimicrobial properties were evaluated against E. coli and S. aureus. It was evidenced that AgNPs can be stabilized using acrylic acid and that this material can be incorporated to the polymer phase during polymerization by free radical of cationic monomers. The effect of pH on retention of molybdate, by the nanostructured polymer, was significant only to low ionic strength (the order seen was pH 5.0 > pH 7.0 > pH 9.0 for 0.0% NaCl). Results suggest that the main interaction influencing the molybdate retention is electrostatic in nature. Finally, antimicrobial activity was enhanced by incorporation of polymerizable nanostructured crosslinker based on AgNPs. 相似文献