全文获取类型
收费全文 | 390912篇 |
免费 | 2277篇 |
国内免费 | 554篇 |
专业分类
化学 | 182491篇 |
晶体学 | 5845篇 |
力学 | 22405篇 |
综合类 | 9篇 |
数学 | 56094篇 |
物理学 | 126899篇 |
出版年
2020年 | 4163篇 |
2019年 | 5059篇 |
2018年 | 7452篇 |
2017年 | 7613篇 |
2016年 | 9532篇 |
2015年 | 4428篇 |
2014年 | 8437篇 |
2013年 | 15852篇 |
2012年 | 12905篇 |
2011年 | 15135篇 |
2010年 | 12618篇 |
2009年 | 12815篇 |
2008年 | 14589篇 |
2007年 | 14384篇 |
2006年 | 12886篇 |
2005年 | 11212篇 |
2004年 | 10841篇 |
2003年 | 10030篇 |
2002年 | 10340篇 |
2001年 | 10481篇 |
2000年 | 8123篇 |
1999年 | 6192篇 |
1998年 | 5692篇 |
1997年 | 5480篇 |
1996年 | 5016篇 |
1995年 | 4471篇 |
1994年 | 4511篇 |
1993年 | 4508篇 |
1992年 | 4590篇 |
1991年 | 5079篇 |
1990年 | 5006篇 |
1989年 | 5049篇 |
1988年 | 4695篇 |
1987年 | 4774篇 |
1986年 | 4463篇 |
1985年 | 5354篇 |
1984年 | 5550篇 |
1983年 | 4724篇 |
1982年 | 4972篇 |
1981年 | 4635篇 |
1980年 | 4287篇 |
1979年 | 4926篇 |
1978年 | 5105篇 |
1977年 | 5298篇 |
1976年 | 5451篇 |
1975年 | 5060篇 |
1974年 | 4891篇 |
1973年 | 5133篇 |
1972年 | 4306篇 |
1971年 | 3946篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
64.
Dr. Antonio M. Rodríguez Dr. Pilar Prieto Prof. Antonio de la Hoz Prof. Ángel Díaz-Ortiz D. Raúl Martín Prof. José I. García 《ChemistryOpen》2015,4(3):308-317
The aim of this work was to determine the parameters that have decisive roles in microwave-assisted reactions and to develop a model, using computational chemistry, to predict a priori the type of reactions that can be improved under microwaves. For this purpose, a computational study was carried out on a variety of reactions, which have been reported to be improved under microwave irradiation. This comprises six types of reactions. The outcomes obtained in this study indicate that the most influential parameters are activation energy, enthalpy, and the polarity of all the species that participate. In addition to this, in most cases, slower reacting systems observe a much greater improvement under microwave irradiation. Furthermore, for these reactions, the presence of a polar component in the reaction (solvent, reagent, susceptor, etc.) is necessary for strong coupling with the electromagnetic radiation. We also quantified that an activation energy of 20–30 kcal mol−1 and a polarity (μ) between 7–20 D of the species involved in the process is required to obtain significant improvements under microwave irradiation. 相似文献
65.
Synthesis,spectral investigation and development of tetrahedral copper(II) complexes as artificial metallonucleases and antimalarial agents
下载免费PDF全文
![点击此处可从《应用有机金属化学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Seven new copper(II) complexes of type [Cu(A)(L)]?H2O (A = sparfloxacin, ciprofloxacin, levofloxacin, gatifloxacin, pefloxacin, ofloxacin, norfloxacin; L = 5‐[(3‐chlorophenyl)diazenyl]‐4‐hydroxy‐1,3‐thiazole‐2(3H)‐thione) were synthesized and characterized using elemental and thermogravimetric analyses, and electronic, electron paramagnetic resonance (EPR), Fourier transform infrared and liquid chromatography–mass spectroscopies. Tetrahedral geometry around copper is assigned in all complexes using EPR and electronic spectral analyses. All complexes were investigated for their interaction with herring sperm DNA utilizing absorption titration (Kb = 1.27–3.13 × 105 M?1) and hydrodynamic volume measurement studies. The studies suggest the classical intercalative mode of DNA binding. The cleavage reaction on pUC19 DNA was monitored by agarose gel electrophoresis. The results indicate that the Cu(II) complexes can more effectively promote the cleavage of plasmid DNA. The superoxide dismutase mimic activity of the complexes was evaluated by nitroblue tetrazolium assay, and the complexes catalysed the dismutation of superoxide at pH = 7.8 with IC50 values in the range 0.597–0.900 μM. The complexes were screened for their in vitro antibacterial activity against five pathogenic bacteria. All the complexes are good cytotoxic agents and show LC50 values ranging from 5.559 to 11.912 µg ml?1. All newly synthesized Cu(II) complexes were also evaluated for their in vitro antimalarial activity against Plasmodium falciparum strain (IC50 = 0.62–2.0 µg ml?1). Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
66.
67.
K.V. Stepurska О.О. Soldatkin I.S. Kucherenko V.M. Arkhypova S.V. Dzyadevych A.P. Soldatkin 《Analytica chimica acta》2015
This study was aimed at the development of a conductometric biosensor based on acetylcholinesterase considering the feasibility of its application for the inhibitory analysis of various toxicants. In this paper, the optimum conditions for enzyme immobilization on the transducer surface are selected as well as the optimum concentration of substrate for inhibitory analysis. Sensitivity of the developed biosensor to different classes of toxic compounds (organophosphorus pesticides, heavy metal ions, surfactants, aflatoxin, glycoalkaloids) was tested. It is shown that the developed biosensor can be successfully used for the analysis of pesticides and mycotoxins, as well as for determination of total toxicity of the samples. A new method of biosensor analysis of toxic substances of different classes in complex multicomponent aqueous samples is proposed. 相似文献
68.
69.
70.