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   30206篇
  免费   5109篇
  国内免费   6928篇
化学   22530篇
晶体学   733篇
力学   2161篇
综合类   819篇
数学   3938篇
物理学   12062篇
  2024年   69篇
  2023年   420篇
  2022年   887篇
  2021年   963篇
  2020年   1037篇
  2019年   1023篇
  2018年   884篇
  2017年   1139篇
  2016年   1147篇
  2015年   1350篇
  2014年   1676篇
  2013年   2157篇
  2012年   2536篇
  2011年   2586篇
  2010年   2094篇
  2009年   2091篇
  2008年   2437篇
  2007年   2194篇
  2006年   2099篇
  2005年   1840篇
  2004年   1487篇
  2003年   1183篇
  2002年   1241篇
  2001年   1069篇
  2000年   1035篇
  1999年   841篇
  1998年   509篇
  1997年   444篇
  1996年   455篇
  1995年   382篇
  1994年   344篇
  1993年   314篇
  1992年   305篇
  1991年   268篇
  1990年   222篇
  1989年   245篇
  1988年   177篇
  1987年   147篇
  1986年   134篇
  1985年   102篇
  1984年   104篇
  1983年   80篇
  1982年   67篇
  1981年   63篇
  1980年   56篇
  1979年   36篇
  1978年   30篇
  1977年   27篇
  1974年   27篇
  1973年   29篇
排序方式: 共有10000条查询结果,搜索用时 505 毫秒
1.
2.
3.
Journal of Radioanalytical and Nuclear Chemistry - The simplified 8-oxide system (SiO2-B2O3-Na2O-Al2O3-CaO-TiO2-MoO3-La2O3) has been prepared under two types of cooling methods, and analyzed with...  相似文献   
4.
Given their superior penetration depths, photosensitizers with longer absorption wavelengths present broader application prospects in photodynamic therapy (PDT). Herein, Ag2S quantum dots were discovered, for the first time, to be capable of killing tumor cells through the photodynamic route by near-infrared light irradiation, which means relatively less excitation of the probe compared with traditional photosensitizers absorbing short wavelengths. On modification with polydopamine (PDA), PDA-Ag2S was obtained, which showed outstanding capacity for inducing reactive oxygen species (increased by 1.69 times). With the addition of PDA, Ag2S had more opportunities to react with surrounding O2, which was demonstrated by typical triplet electron spin resonance (ESR) analysis. Furthermore, the PDT effects of Ag2S and PDA-Ag2S achieved at longer wavelengths were almost identical to the effects produced at 660 nm, which was proved by studies in vitro. PDA-Ag2S showed distinctly better therapeutic effects than Ag2S in experiments in vivo, which further validated the enhanced regulatory effect of PDA. Altogether, a new photosensitizer with longer absorption wavelength was developed by using the hitherto-unexplored photodynamic function of Ag2S quantum dots, which extended and enhanced the regulatory effect originating from PDA.  相似文献   
5.
利用n维有限射影空间上的一些性质,构作了组合群验的数学模型de-析取矩阵,并研究了它的参数和Hamming距离.  相似文献   
6.
7.
A class of acceptor–donor–acceptor chromophoric small-molecule non-fullerene acceptors, 1–4, with difluoroboron(iii) β-diketonate (BF2bdk) as the electron-accepting moiety has been developed. Through the variation of the central donor unit and the modification on the peripheral substituents of the terminal BF2bdk acceptor unit, their photophysical and electrochemical properties have been systematically studied. Taking advantage of their low-lying lowest unoccupied molecular orbital energy levels (from −3.65 to −3.72 eV) and relatively high electron mobility (7.49 × 10−4 cm2 V−1 s−1), these BF2bdk-based compounds have been employed as non-fullerene acceptors in organic solar cells with maximum power conversion efficiencies of up to 4.31%. Moreover, bistable resistive memory characteristics with charge-trapping mechanisms have been demonstrated in these BF2bdk-based compounds. This work not only demonstrates for the first time the use of a boron(iii) β-diketonate unit in constructing non-fullerene acceptors, but also provides more insights into designing organic materials with multi-functional properties.

Boron(iii) β-diketonates have been demonstrated to serve as multi-functional materials in NFA-based OPVs and organic resistive memories.  相似文献   
8.
9.
A stable and efficient Pd(OAc)2/PPh3/PEG‐2000 catalytic system for homocoupling of arylboronic acids has been developed. In the presence of Pd(OAc)2 and PPh3, the homocoupling reaction of arylboronic acids was carried out smoothly in PEG‐2000 at 70 °C under air without base to afford a variety of symmetric biaryls in good to excellent yields. The isolation of the products was readily performed by extraction with diethyl ether, and the Pd(OAc)2/PPh3/PEG‐2000 system could be easily recycled and reused six times without significant loss of catalytic activity. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
10.
通过对盐酸伊达比星脱羟基杂质A的合成研究,为盐酸伊达比星的质控标准提供参考。以盐酸伊达比星为起始原料,经过4步反应得到脱羟基杂质A。本文提供了盐酸伊达比星杂质A的制备方法以及高效液相色谱分析方法,为杂质含量控制提供了依据。该工艺可以稳定、快速制备高纯度脱羟基杂质A,制备总收率为57.20%,纯度为57.20%,其结构经1H NMR, 13C NMR和MS(ESI)表征。  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