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   477979篇
  免费   3968篇
  国内免费   1346篇
化学   227405篇
晶体学   7700篇
力学   24477篇
综合类   5篇
数学   67328篇
物理学   156378篇
  2020年   3274篇
  2019年   3706篇
  2018年   11910篇
  2017年   12520篇
  2016年   10239篇
  2015年   5024篇
  2014年   7102篇
  2013年   17782篇
  2012年   17020篇
  2011年   26564篇
  2010年   17469篇
  2009年   17355篇
  2008年   23619篇
  2007年   26625篇
  2006年   14534篇
  2005年   18449篇
  2004年   14716篇
  2003年   13479篇
  2002年   11680篇
  2001年   12155篇
  2000年   9535篇
  1999年   7343篇
  1998年   6015篇
  1997年   5914篇
  1996年   5713篇
  1995年   5183篇
  1994年   5033篇
  1993年   4997篇
  1992年   5395篇
  1991年   5499篇
  1990年   5238篇
  1989年   5031篇
  1988年   5189篇
  1987年   5033篇
  1986年   4715篇
  1985年   6324篇
  1984年   6704篇
  1983年   5464篇
  1982年   5824篇
  1981年   5725篇
  1980年   5460篇
  1979年   5666篇
  1978年   5844篇
  1977年   5744篇
  1976年   5879篇
  1975年   5415篇
  1974年   5383篇
  1973年   5622篇
  1972年   3771篇
  1971年   3062篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
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   
72.
73.
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   
74.
75.
76.
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   
77.
78.
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   
79.
Russian Journal of General Chemistry - Some new fluoro-heterocyclic compounds containing thiazole and pyridine moities have been synthesized and studied for their antiproliferative activity....  相似文献   
80.
Sybachin  A. V.  Stepanova  D. A. 《Colloid Journal》2021,83(4):531-531
Colloid Journal - An Erratum to this paper has been published: https://doi.org/10.1134/S1061933X21330024  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