全文获取类型
收费全文 | 365298篇 |
免费 | 12331篇 |
国内免费 | 7150篇 |
专业分类
化学 | 188454篇 |
晶体学 | 5631篇 |
力学 | 19258篇 |
综合类 | 526篇 |
数学 | 51483篇 |
物理学 | 119427篇 |
出版年
2022年 | 3356篇 |
2021年 | 3811篇 |
2020年 | 4198篇 |
2019年 | 4305篇 |
2018年 | 12933篇 |
2017年 | 13598篇 |
2016年 | 10372篇 |
2015年 | 6085篇 |
2014年 | 7288篇 |
2013年 | 13972篇 |
2012年 | 16450篇 |
2011年 | 26032篇 |
2010年 | 16612篇 |
2009年 | 16643篇 |
2008年 | 21485篇 |
2007年 | 24554篇 |
2006年 | 10287篇 |
2005年 | 15702篇 |
2004年 | 11241篇 |
2003年 | 10211篇 |
2002年 | 7833篇 |
2001年 | 7701篇 |
2000年 | 6265篇 |
1999年 | 5064篇 |
1998年 | 4094篇 |
1997年 | 3864篇 |
1996年 | 3943篇 |
1995年 | 3587篇 |
1994年 | 3404篇 |
1993年 | 3087篇 |
1992年 | 3649篇 |
1991年 | 3450篇 |
1990年 | 3286篇 |
1989年 | 3237篇 |
1988年 | 3147篇 |
1987年 | 3140篇 |
1986年 | 2951篇 |
1985年 | 3681篇 |
1984年 | 3599篇 |
1983年 | 2856篇 |
1982年 | 2922篇 |
1981年 | 2948篇 |
1980年 | 2694篇 |
1979年 | 3021篇 |
1978年 | 3025篇 |
1977年 | 3053篇 |
1976年 | 2923篇 |
1975年 | 2656篇 |
1974年 | 2605篇 |
1973年 | 2595篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
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
12.
V. A. Bespalov V. M. Glazov E. A. Il’ichev Yu. A. Klimov S. V. Kuklev A. E. Kuleshov R. M. Nabiev G. N. Petrukhin B. G. Potapov G. S. Rychkov D. S. Sokolov V. V. Fandeev E. A. Fetisov S. S. Yakushov 《Technical Physics》2015,60(4):553-560
The results of investigation of optical image detectors designed for the largest problem, near-VUV, range of the spectrum are presented. The possibility of using a dual-stage image detection system to appreciably lower the sensitivity threshold and make computer data processing feasible is considered. The integration of a UV module into a wideband image detector is studied. 相似文献
13.
A. Lashgari S. Ghammamy R. Ramirez-Tagle G. Salgado-Moran 《Journal of Structural Chemistry》2015,56(8):1505-1513
Two new compounds of fluorine: (C2H5)4N[I2F] and (C2H5)4N[Br2F], have been easily synthesized in a nearly quantitative by a direct reaction of (C2H5)4NF, I2 and Br2. The products were isolated and characterized by elemental analysis and spectroscopic methods such as: Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy (UV-Vis). These compounds have been studied computationally with the Scalar ZORA relativistic level of theory using the ADF program package. The molecular parameters, and vibrational spectra were calculated. The excitation energies were found by timedependent perturbation density functional theory (TD-DFT). Molecule optimization, frequencies and excitation energies were calculated with standard Slatertype-orbital (STO) basis sets with triple-zeta quality double plus polarization functions (TZ2P) for all atoms. The FTIR, UV-Vis spectra and assignment of principal transitions and total density of state (TDOS) were extracted using the GaussSum 2.2 program. The comparison between experimental and calculated values showes that the experimental results correlate well with the predicted data. 相似文献
14.
15.
16.
17.
18.
19.
Recyclable and reusable Pd(OAc)2/PPh3/PEG‐2000 system for homocoupling reaction of arylboronic acids under air without base 下载免费PDF全文
A stable and efficient Pd(OAc)2/PPh3/PEG‐2000 catalytic system for homocoupling of arylboronic acids has been developed. In the presence of Pd(OAc)2 and PPh3, the homocoupling reaction of arylboronic acids was carried out smoothly in PEG‐2000 at 70 °C under air without base to afford a variety of symmetric biaryls in good to excellent yields. The isolation of the products was readily performed by extraction with diethyl ether, and the Pd(OAc)2/PPh3/PEG‐2000 system could be easily recycled and reused six times without significant loss of catalytic activity. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
20.
In this work, the effect of various properties of materials on vacuum breakdown initiated by laser radiation is considered. Estimating calculations are performed which show that the material of the target electrode distinctly affects the minimum energy of laser radiation needed for igniting a vacuum spark. The experimental studies carried out confirm the estimating calculations, and a number of materials are revealed which can be arranged in order of increase in the energy needed for the formation of breakdown in vacuum by the impact of a laser pulse. 相似文献