全文获取类型
收费全文 | 269189篇 |
免费 | 10042篇 |
国内免费 | 2044篇 |
专业分类
化学 | 161481篇 |
晶体学 | 3842篇 |
力学 | 10322篇 |
综合类 | 5篇 |
数学 | 29129篇 |
物理学 | 76496篇 |
出版年
2021年 | 2280篇 |
2020年 | 3508篇 |
2019年 | 5020篇 |
2018年 | 4314篇 |
2017年 | 3808篇 |
2016年 | 8001篇 |
2015年 | 6428篇 |
2014年 | 7699篇 |
2013年 | 14784篇 |
2012年 | 12056篇 |
2011年 | 13098篇 |
2010年 | 9998篇 |
2009年 | 9640篇 |
2008年 | 12116篇 |
2007年 | 11695篇 |
2006年 | 10796篇 |
2005年 | 9977篇 |
2004年 | 9022篇 |
2003年 | 7818篇 |
2002年 | 8273篇 |
2001年 | 8289篇 |
2000年 | 6650篇 |
1999年 | 4543篇 |
1998年 | 3372篇 |
1997年 | 3314篇 |
1996年 | 3172篇 |
1995年 | 2861篇 |
1994年 | 2717篇 |
1993年 | 2619篇 |
1992年 | 2950篇 |
1991年 | 2854篇 |
1990年 | 2771篇 |
1989年 | 2534篇 |
1988年 | 2577篇 |
1987年 | 2581篇 |
1986年 | 2412篇 |
1985年 | 3163篇 |
1984年 | 3381篇 |
1983年 | 2763篇 |
1982年 | 2932篇 |
1981年 | 2887篇 |
1980年 | 2720篇 |
1979年 | 2826篇 |
1978年 | 2907篇 |
1977年 | 2896篇 |
1976年 | 2960篇 |
1975年 | 2747篇 |
1974年 | 2708篇 |
1973年 | 2861篇 |
1972年 | 1804篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
The influence of different referencing methods on the accuracy of δ13C value measurement of ethanol fuel by gas chromatography/combustion/isotope ratio mass spectrometry 下载免费PDF全文
3.
Chemical versus Electrochemical Synthesis of Carbon Nano‐onion/Polypyrrole Composites for Supercapacitor Electrodes 下载免费PDF全文
Olena Mykhailiv Monika Imierska Martyna Petelczyc Prof. Dr. Luis Echegoyen Dr. Marta E. Plonska‐Brzezinska 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(15):5783-5793
The development of high‐surface‐area carbon electrodes with a defined pore size distribution and the incorporation of pseudo‐active materials to optimize the overall capacitance and conductivity without destroying the stability are at present important research areas. Composite electrodes of carbon nano‐onions (CNOs) and polypyrrole (Ppy) were fabricated to improve the specific capacitance of a supercapacitor. The carbon nanostructures were uniformly coated with Ppy by chemical polymerization or by electrochemical potentiostatic deposition to form homogenous composites or bilayers. The materials were characterized by transmission‐ and scanning electron microscopy, differential thermogravimetric analyses, FTIR spectroscopy, piezoelectric microgravimetry, and cyclic voltammetry. The composites show higher mechanical and electrochemical stabilities, with high specific capacitances of up to about 800 F g?1 for the CNOs/SDS/Ppy composites (chemical synthesis) and about 1300 F g?1 for the CNOs/Ppy bilayer (electrochemical deposition). 相似文献
4.
Dr. Sabin Llona‐Minguez Dr. Matthieu Desroses Artin Ghassemian Dr. Sylvain A. Jacques Dr. Lars Eriksson Rebecka Isacksson Tobias Koolmeister Dr. Pål Stenmark Dr. Martin Scobie Prof. Thomas Helleday 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(20):7394-7398
A two‐step synthesis of structurally diverse pyrrole‐containing bicyclic systems is reported. ortho‐Nitro‐haloarenes coupled with vinylic N‐methyliminodiacetic acid (MIDA) boronates generate ortho‐vinyl‐nitroarenes, which undergo a “metal‐free” nitrene insertion, resulting in a new pyrrole ring. This novel synthetic approach has a wide substrate tolerance and it is applicable in the preparation of more complex “drug‐like” molecules. Interestingly, an ortho‐nitro‐allylarene derivative furnished a cyclic β‐aminophosphonate motif. 相似文献
5.
Interactions of Pt‐ttpy with G‐Quadruplexes Originating from Promoter Region of the c‐myc Gene Deciphered by NMR and Gel Electrophoresis Analysis 下载免费PDF全文
6.
7.
8.
9.
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
10.
Synthesis,spectral investigation and development of tetrahedral copper(II) complexes as artificial metallonucleases and antimalarial agents 下载免费PDF全文
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