首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   479908篇
  免费   5291篇
  国内免费   1487篇
化学   252608篇
晶体学   7529篇
力学   21469篇
综合类   12篇
数学   58176篇
物理学   146892篇
  2020年   3968篇
  2019年   4511篇
  2018年   5841篇
  2017年   5695篇
  2016年   8678篇
  2015年   5445篇
  2014年   8351篇
  2013年   20824篇
  2012年   15910篇
  2011年   19324篇
  2010年   13603篇
  2009年   13422篇
  2008年   17959篇
  2007年   17995篇
  2006年   16916篇
  2005年   15286篇
  2004年   14023篇
  2003年   12490篇
  2002年   12229篇
  2001年   13311篇
  2000年   10331篇
  1999年   8076篇
  1998年   7028篇
  1997年   6866篇
  1996年   6636篇
  1995年   6017篇
  1994年   6138篇
  1993年   5930篇
  1992年   6385篇
  1991年   6505篇
  1990年   6230篇
  1989年   5994篇
  1988年   6101篇
  1987年   5876篇
  1986年   5580篇
  1985年   7584篇
  1984年   7890篇
  1983年   6534篇
  1982年   6795篇
  1981年   6697篇
  1980年   6596篇
  1979年   6622篇
  1978年   6993篇
  1977年   6800篇
  1976年   6944篇
  1975年   6412篇
  1974年   6417篇
  1973年   6617篇
  1972年   4625篇
  1971年   3887篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
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   
82.
Experimental Techniques - The analysis of residual stress in glass is usually carried out by means of photoelastic methods. This article considers the automation of the white light photoelastic...  相似文献   
83.
84.
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   
85.
86.
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   
87.
Russian Chemical Bulletin - Quantum chemical calculations and a comparative analysis of Raman spectra of 3,4,5-triphenyl-1-propyl-1,2-diphosphole (1),...  相似文献   
88.
89.
90.
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   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号