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   515932篇
  免费   4659篇
  国内免费   1526篇
化学   251754篇
晶体学   6279篇
力学   26202篇
综合类   16篇
数学   86258篇
物理学   151608篇
  2019年   3053篇
  2018年   19368篇
  2017年   19922篇
  2016年   13907篇
  2015年   5241篇
  2014年   6193篇
  2013年   16639篇
  2012年   17957篇
  2011年   32796篇
  2010年   20278篇
  2009年   20600篇
  2008年   26939篇
  2007年   31555篇
  2006年   12409篇
  2005年   18347篇
  2004年   14382篇
  2003年   13595篇
  2002年   10795篇
  2001年   10904篇
  2000年   8628篇
  1999年   6529篇
  1998年   5318篇
  1997年   5102篇
  1996年   4826篇
  1995年   4598篇
  1994年   4411篇
  1993年   4190篇
  1992年   5095篇
  1991年   4893篇
  1990年   4803篇
  1989年   4815篇
  1988年   4803篇
  1987年   4815篇
  1986年   4533篇
  1985年   6100篇
  1984年   6156篇
  1983年   4929篇
  1982年   5279篇
  1981年   5301篇
  1980年   4971篇
  1979年   5388篇
  1978年   5657篇
  1977年   5535篇
  1976年   5355篇
  1975年   4964篇
  1974年   4906篇
  1973年   4920篇
  1972年   3276篇
  1968年   3528篇
  1967年   3524篇
排序方式: 共有10000条查询结果,搜索用时 307 毫秒
61.
62.
63.
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   
64.
Su  X. F.  Zhang  Y. L.  Maximov  A. L.  Zhang  K.  Xin  Q.  Feng  C. Q.  Bai  X. F.  Wu  W. 《Russian Journal of Applied Chemistry》2020,93(1):127-136
Russian Journal of Applied Chemistry - Nanoscale ZSM-5 (AlZ5-D) and Ga-substituted ZSM-5 zeolites ((Al,Ga)Z5-D and GaZ5-D) were synthesized by a green dry-gel conversion strategy. For comparison,...  相似文献   
65.
In this communication, we report the synthesis of small‐sized (<10 nm), water‐soluble, magnetic nanoparticles (MNPs) coated with polyhedral oligomeric silsesquioxanes (POSS), which contain either polyethylene glycol (PEG) or octa(tetramethylammonium) (OctaTMA) as functional groups. The POSS‐coated MNPs exhibit superparamagnetic behavior with saturation magnetic moments (51–53 emu g?1) comparable to silica‐coated MNPs. They also provide good colloidal stability at different pH and salt concentrations, and low cytotoxicity to MCF‐7 human breast epithelial cells. The relaxivity data and magnetic resonance (MR) phantom images demonstrate the potential application of these MNPs in bioimaging.  相似文献   
66.
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   
67.
68.
69.
70.
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