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   3166篇
  免费   571篇
  国内免费   361篇
化学   2312篇
晶体学   37篇
力学   196篇
综合类   29篇
数学   311篇
物理学   1213篇
  2024年   12篇
  2023年   93篇
  2022年   115篇
  2021年   142篇
  2020年   168篇
  2019年   145篇
  2018年   143篇
  2017年   91篇
  2016年   191篇
  2015年   152篇
  2014年   198篇
  2013年   210篇
  2012年   294篇
  2011年   324篇
  2010年   187篇
  2009年   220篇
  2008年   209篇
  2007年   164篇
  2006年   154篇
  2005年   123篇
  2004年   95篇
  2003年   77篇
  2002年   75篇
  2001年   56篇
  2000年   53篇
  1999年   57篇
  1998年   47篇
  1997年   41篇
  1996年   59篇
  1995年   31篇
  1994年   40篇
  1993年   21篇
  1992年   22篇
  1991年   17篇
  1990年   17篇
  1989年   13篇
  1988年   10篇
  1987年   7篇
  1986年   11篇
  1985年   4篇
  1984年   3篇
  1983年   2篇
  1982年   1篇
  1974年   1篇
  1957年   3篇
排序方式: 共有4098条查询结果,搜索用时 62 毫秒
111.
112.
Circular dichroism is known to be the feature of a chiral agent which has inspired scientist to study the interesting phenomena of circularly polarized light (CPL) modulated molecular chirality. Although several organic molecules or assemblies have been found to be CPL‐responsive, the influence of CPL on the assembly of chiral coordination compounds remains unknown. Herein, a chiral coordination polymer, which is constructed from achiral agents, was used to study the CPL‐induced enantioselective synthesis. By irradiation with either left‐handed or right‐handed CPL during the reaction and crystallization, enantiomeric excesses of the crystalline product were obtained. Left‐handed CPL resulted in crystals with a left‐handed helical structure, and right‐handed CPL led to crystals with a right‐handed helical structure. It is exciting that the absolute asymmetric synthesis of a chiral coordination polymer could be enantioselective when using CPL, and provides a strategy for the control of the chirality of chiral coordination polymers.  相似文献   
113.
114.
115.
116.

In order to deliver reliable results for a multitude of different scenarios, e.g. emergency preparedness, environmental monitoring, nuclear decommissioning and waste management, there is a constant process of method development in the field of radioanalytical chemistry. This work presents the results of a method comparison exercise aimed at quantifying 90Sr and 239,240Pu in environmental soil samples, with the intention of evaluating the performance and applicability of different methods. From the methods examined in this work, recommendations are given in order to find a radioanalytical measurement procedure, for 90Sr and 239,240Pu analysis, which is fit-for-purpose for a particular scenario.

  相似文献   
117.
We performed a systematic study of soft X-ray absorption spectroscopy in various manganese oxides and fluorides. Both Mn L-edges and ligand (O and F) K-edges are presented and compared with each other. Despite the distinct crystal structure and covalent/ionic nature in different systems, the Mn-L spectra fingerprint the Mn valence and spin states through spectral lineshape and energy position consistently and evidently. The clear O- and F-K pre-edge features in our high resolution spectra enable a quantitative definition of the molecular orbital diagram with different Mn valence. In addition, while the binding energy difference of the O-1s core electrons leads to a small shift of the O-K leading edges between trivalent and quadrivalent manganese oxides, a significant edge shift, with an order of magnitude larger in energy, was found between divalent and trivalent compounds, which is attributed to the spin exchange stabilization of half-filled 3d system. This shift is much enhanced in the ionic fluoride system. This work provides the spectroscopic foundation for further studies of complicated Mn compounds.  相似文献   
118.
Lu  Yuchan  He  Qiao  Peng  Qiao  Chen  Wenhai  Cheng  Qunpeng  Song  Guangsen  Fan  Guozhi 《Cellulose (London, England)》2021,28(13):8343-8354
Cellulose - The coproduction of 5-hydroxymethylfurfural (5-HMF) and furfural (FUR) via the direct hydrolysis of holocellulose analogue composed of cellulose and hemicellulose was investigated. The...  相似文献   
119.
Supramolecular polymers and materials are attracting more and more attention nowadays due to their dynamic properties such as reversibility, stimuli-responsiveness and self-healing. Conventionally, bifunctional or multi-functional monomers are first covalently synthesized, followed by the supramolecular complexation to form supramolecular polymers and materials. Recently, we have proposed the supramonomer concept to construct supramolecular polymers and materials in a different way. Supramonomers are bifunctional or multi-functional monomers fabricated by noncovalent synthesis, but can undergo traditional covalent polymerization. In this highlight article, we will summarize and discuss the fabrication of supramonomer and covalent polymerization methods of supramonomers; fabrication of multi-responsive supramolecular polymers from supramonomers; and fabrication of supramolecular materials from supramonomers. It is highly anticipated that the supramonomer concept will enrich the methodology towards supramolecular polymers and materials. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 604–609  相似文献   
120.
The thermal behaviors of glycidyl methacrylate (GMA)-grafted polypropylene (PP) (PP-g-GMA) with two different grafting degrees, namely, GPP1 and GPP2, were investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide-angle X-ray diffraction (WAXD), dynamic mechanical analysis (DMA), and thermogravimetrical analysis (TGA). DSC results suggested that the GMA grafted PP exhibited higher crystallization temperature Tc, higher melting temperature Tm, and higher crystallinity compared with the neat PP. The isothermal crystallization kinetics was analyzed with the Avrami equation and the total crystallization activation energy was calculated. It was concluded that the crystallization processes of PP and the grafted PP were controlled by nucleation and the values of the crystallization activation energy of PP and the grafted PP were almost identical. POM results suggested that the GMA grafted PP exhibited smaller spherulites size compared with the neat PP. WAXD patterns indicated that the neat PP encouraged the formation of γ phase, compared with the grafted PP, during the crystallization process. DMA results showed that melt grafting did not induce a clear effect on the γ-transition and β-transition of the amorphous phase but resulted in a decrease in mobility of the PP chains in the crystals. TGA curves suggested that the melt grafting slightly improved the thermal stability of PP.  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