全文获取类型
收费全文 | 298637篇 |
免费 | 1970篇 |
国内免费 | 523篇 |
专业分类
化学 | 142667篇 |
晶体学 | 5008篇 |
力学 | 14788篇 |
综合类 | 11篇 |
数学 | 43274篇 |
物理学 | 95382篇 |
出版年
2020年 | 1725篇 |
2019年 | 1918篇 |
2018年 | 10842篇 |
2017年 | 11726篇 |
2016年 | 7480篇 |
2015年 | 3042篇 |
2014年 | 3674篇 |
2013年 | 9200篇 |
2012年 | 10767篇 |
2011年 | 20318篇 |
2010年 | 12680篇 |
2009年 | 12768篇 |
2008年 | 17528篇 |
2007年 | 21026篇 |
2006年 | 6886篇 |
2005年 | 12779篇 |
2004年 | 8901篇 |
2003年 | 8440篇 |
2002年 | 6266篇 |
2001年 | 6298篇 |
2000年 | 4933篇 |
1999年 | 3559篇 |
1998年 | 2791篇 |
1997年 | 2720篇 |
1996年 | 2755篇 |
1995年 | 2533篇 |
1994年 | 2415篇 |
1993年 | 2239篇 |
1992年 | 2894篇 |
1991年 | 2798篇 |
1990年 | 2743篇 |
1989年 | 2769篇 |
1988年 | 2798篇 |
1987年 | 2802篇 |
1986年 | 2665篇 |
1985年 | 3387篇 |
1984年 | 3413篇 |
1983年 | 2693篇 |
1982年 | 2794篇 |
1981年 | 2851篇 |
1980年 | 2620篇 |
1979年 | 2976篇 |
1978年 | 2976篇 |
1977年 | 3009篇 |
1976年 | 2878篇 |
1975年 | 2605篇 |
1974年 | 2559篇 |
1973年 | 2552篇 |
1972年 | 1740篇 |
1968年 | 1799篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Synthesis of Highly Substituted γ‐Butyrolactones by a Gold‐Catalyzed Cascade Reaction of Benzyl Esters 下载免费PDF全文
Maria Camila Blanco Jaimes Alexander Ahrens Daniel Pflästerer Dr. Matthias Rudolph Prof. Dr. A. Stephen K. Hashmi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):427-433
Easily accessible benzylic esters of 3‐butynoic acids in a gold‐catalyzed cyclization/rearrangement cascade reaction provided 3‐propargyl γ‐butyrolactones with the alkene and the carbonyl group not being conjugated. Crossover experiments showed that the formation of the new C?C bond is an intermolecular process. Initially propargylic–benzylic esters were used, but alkyl‐substituted benzylic esters worked equally well. In the case of the propargylic–benzylic products, a simple treatment of the products with aluminum oxide initiated a twofold tautomerization to the allenyl‐substituted γ‐butyrolactones with conjugation of the carbonyl group, the olefin, and the allene. The synthetic sequence can be conducted stepwise or as a one‐pot cascade reaction with similar yields. Even in the presence of the gold catalyst the new allene remains intact. 相似文献
3.
4.
5.
6.
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
7.
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
8.
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
9.
10.