全文获取类型
收费全文 | 381693篇 |
免费 | 2576篇 |
国内免费 | 1177篇 |
专业分类
化学 | 163064篇 |
晶体学 | 5723篇 |
力学 | 22201篇 |
综合类 | 1篇 |
数学 | 74865篇 |
物理学 | 119592篇 |
出版年
2020年 | 1787篇 |
2019年 | 2048篇 |
2018年 | 18847篇 |
2017年 | 19318篇 |
2016年 | 12267篇 |
2015年 | 3843篇 |
2014年 | 4334篇 |
2013年 | 10445篇 |
2012年 | 14224篇 |
2011年 | 28493篇 |
2010年 | 17497篇 |
2009年 | 17883篇 |
2008年 | 23252篇 |
2007年 | 28075篇 |
2006年 | 8606篇 |
2005年 | 14707篇 |
2004年 | 11213篇 |
2003年 | 10879篇 |
2002年 | 8205篇 |
2001年 | 7435篇 |
2000年 | 5896篇 |
1999年 | 4402篇 |
1998年 | 3773篇 |
1997年 | 3614篇 |
1996年 | 3589篇 |
1995年 | 3196篇 |
1994年 | 3093篇 |
1993年 | 3192篇 |
1992年 | 3262篇 |
1991年 | 3453篇 |
1990年 | 3189篇 |
1989年 | 3143篇 |
1988年 | 3203篇 |
1987年 | 3083篇 |
1986年 | 2918篇 |
1985年 | 3932篇 |
1984年 | 4136篇 |
1983年 | 3319篇 |
1982年 | 3530篇 |
1981年 | 3448篇 |
1980年 | 3350篇 |
1979年 | 3468篇 |
1978年 | 3560篇 |
1977年 | 3401篇 |
1976年 | 3519篇 |
1975年 | 3201篇 |
1974年 | 3202篇 |
1973年 | 3295篇 |
1972年 | 2289篇 |
1971年 | 1878篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Pd0‐Catalyzed Intramolecular α‐Arylation of Sulfones: Domino Reactions in the Synthesis of Functionalized Tetrahydroisoquinolines
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Prof.Dr. Daniel Solé Ferran Pérez‐Janer Dr. Raffaella Mancuso 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4580-4584
A new strategy for the synthesis of tetrahydroisoquinolines based on the Pd0‐catalyzed intramolecular α‐arylation of sulfones is reported. The combination of this Pd‐catalyzed reaction with intermolecular Michael and aza‐Michael reactions allows the development of two‐ and three‐step domino processes to synthesize diversely functionalized scaffolds from readily available starting materials. 相似文献
42.
43.
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
44.
45.
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
46.
47.
Iodine(III)‐Catalyzed Rearrangements of Imides: A Versatile Route to α,α‐Dialkylated α‐Hydroxy Carboxylamides
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Anna Ulmer Dr. Maciej Stodulski Stefanie V. Kohlhepp Christoph Patzelt Dr. Alexander Pöthig Dr. Wolfgang Bettray Dr. Tanja Gulder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(4):1444-1448
A tertiary hydroxy group α to a carboxyl moiety comprises a key structural motif in many bioactive substances. With the herein presented metal‐free rearrangement of imides triggered by hypervalent λ3‐iodane, an easy and selective way to gain access to such a compound class, namely α,α‐disubstituted‐α‐hydroxy carboxylamides, was established. Their additional methylene bromide side chain constitutes a useful handle for rapid diversification, as demonstrated by a series of further functionalizations. Moreover, the in situ formation of an iodine(III) species under the reaction conditions was proven. Our findings clearly corroborate that hypervalent λ3‐benziodoxolones are involved in these organocatalytic reactions. 相似文献
48.
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
49.
Applied Magnetic Resonance - The suggested approach allowed us to derive analytical expressions for modeling the shape of solid-echo signal and its time evolution for a system of three-spin groups... 相似文献
50.