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   1029篇
  免费   25篇
  国内免费   9篇
化学   649篇
晶体学   4篇
力学   27篇
数学   204篇
物理学   179篇
  2025年   1篇
  2024年   6篇
  2023年   17篇
  2022年   29篇
  2021年   45篇
  2020年   32篇
  2019年   27篇
  2018年   26篇
  2017年   27篇
  2016年   47篇
  2015年   45篇
  2014年   48篇
  2013年   83篇
  2012年   75篇
  2011年   79篇
  2010年   55篇
  2009年   47篇
  2008年   55篇
  2007年   72篇
  2006年   48篇
  2005年   59篇
  2004年   40篇
  2003年   18篇
  2002年   18篇
  2001年   7篇
  2000年   12篇
  1999年   6篇
  1998年   2篇
  1997年   9篇
  1996年   5篇
  1995年   6篇
  1994年   3篇
  1993年   2篇
  1992年   3篇
  1991年   1篇
  1990年   2篇
  1987年   1篇
  1983年   1篇
  1981年   1篇
  1979年   2篇
  1976年   1篇
排序方式: 共有1063条查询结果,搜索用时 0 毫秒
111.
We developed a constituent quark-diquark model for the nucleon and its resonances using a harmonic oscillator potential for the interaction. The effects due to relativistic kinetic energy correction are studied. Finally, charge form factor of the model is calculated and compared with experimental data.   相似文献   
112.
The aim of this work is to apply the complex interpolation method to norms of n-tuples of operators in a symmetrically-normed ideal J?B(H) defined by a ? symmetric norming function (s.n.f.). The norms considered define Finsler metrics in a certain manifold of positive operators, and can be regarded as weighted ?-norms, the weight being a positive invertible operator.  相似文献   
113.
114.
115.
In the present study, a whole heat exchanger with a hydraulic diameter of 2.3 mm is tested, which is a minichannel heat exchanger according to the Kandlikar classification. This is a louvered fin and flat tube heat exchanger currently used in car cooling systems, also known as radiator. A glycol-water mixture (60/40 in volume) circulates through the tubes at flows ranging from 100 to 7800 l/h and at a supply temperature of 90 °C. This fluid is cooled with ambient air at a temperature of 20 °C and at frontal air velocities varying between 0.5 and 7 m/s. The thermohydraulic performance of the heat exchanger is compared with the classical correlations given in the literature for the heat transfer and the friction factor calculation. On the glycol-water side the heat exchanger is characterized for Reynolds numbers from 30 to 8000. A first comparison is carried out with the correlations available in the literature with a purely predictive model by obtaining a predictive value with a systematic under prediction lower than 10%. In a second step a semi-empirical model is considered to identify the experimental heat transfer coefficients for this application.  相似文献   
116.
    
Cyclobis(paraquat-p-phenylene), also known as “blue box”, is a highly electron-deficient macrocycle, widely used as a molecular receptor for small electron-rich molecules. Inserting a reactive functional group onto the molecular structure of this cyclophane is paramount for its inclusion into complex architectures. To this aim, including an alkyne moiety would be ideal, because it can participate in click reactions. However, the synthesis of such alkyne-functionalized cyclophane suffers from several drawbacks: the use of toxic and expensive CCl4, the need for high-pressure reactors, and overall low yield. We have revised the existing synthesis of this cyclophane derivative bearing an alkyne moiety, to overcome all these limitations. In particular, photochemical radical bromination is adopted to obtain a sensitive intermediate. We demonstrated that the synthesized host molecule can be functionalized via click reactions and take part in radical-radical interactions. Our work makes a key functionalized paraquat macrocycle more accessible, facilitating the development of novel redox-responsive systems.  相似文献   
117.
118.
    
The use of amine-rich N-doped carbon nanodots (NCNDs) for the photochemical radical perfluoroalkylation of organic compounds is reported. This operationally simple approach occurs under mild conditions producing valuable new C−C bonds. The chemistry is driven by the ability of NCNDs to directly reach an electronically excited state upon light absorption, thereby successively triggering the formation of reactive radical species from simple perfluoroalkyl iodides. Preliminary mechanistic studies are also reported.  相似文献   
119.
    
Cross‐coupling reactions mediated by dual nickel/photocatalysis are synthetically attractive but rely mainly on expensive, non‐recyclable noble‐metal complexes as photocatalysts. Heterogeneous semiconductors, which are commonly used for artificial photosynthesis and wastewater treatment, are a sustainable alternative. Graphitic carbon nitrides, a class of metal‐free polymers that can be easily prepared from bulk chemicals, are heterogeneous semiconductors with high potential for photocatalytic organic transformations. Here, we demonstrate that graphitic carbon nitrides in combination with nickel catalysis can induce selective C?O cross‐couplings of carboxylic acids with aryl halides, yielding the respective aryl esters in excellent yield and selectivity. The heterogeneous organic photocatalyst exhibits a broad substrate scope, is able to harvest green light, and can be recycled multiple times. In situ FTIR was used to track the reaction progress to study this transformation at different irradiation wavelengths and reaction scales.  相似文献   
120.
    
Biocatalysis is an environmentally friendly strategy widely used in the chemical and pharmaceutical industries. One of its approaches consists in utilizing whole cells, which usually involves the consumption of large quantities of water. Oceans cover a large part of the Earth's surface, and constitute an important reservoir that can be used as an alternative to freshwater in chemical reactors. This work analyzed the behavior of several yeast halotolerant species belonging to genera Debaryomyces and Schwanniomyces in both freshwater and seawater. It concluded that these microorganisms were more resistant to organic solvents/compounds in the second medium. Their metabolic activity was also greater, which made the reduction reaction of several prochiral ketones more effective. Besides, yeasts cells displayed better performance in subsequent recycling steps, which could help reduce the costs of the process.  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