首页 | 官方网站   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   1527篇
  免费   67篇
  国内免费   46篇
数理化   1640篇
  2024年   2篇
  2023年   9篇
  2022年   42篇
  2021年   53篇
  2020年   62篇
  2019年   64篇
  2018年   88篇
  2017年   56篇
  2016年   92篇
  2015年   76篇
  2014年   101篇
  2013年   219篇
  2012年   108篇
  2011年   115篇
  2010年   82篇
  2009年   74篇
  2008年   81篇
  2007年   68篇
  2006年   45篇
  2005年   27篇
  2004年   26篇
  2003年   12篇
  2002年   29篇
  2001年   15篇
  2000年   13篇
  1999年   14篇
  1998年   10篇
  1997年   8篇
  1996年   2篇
  1995年   2篇
  1994年   5篇
  1993年   4篇
  1992年   2篇
  1991年   3篇
  1990年   3篇
  1988年   4篇
  1987年   1篇
  1986年   1篇
  1985年   5篇
  1984年   3篇
  1983年   3篇
  1982年   4篇
  1981年   1篇
  1978年   3篇
  1974年   1篇
  1973年   1篇
  1964年   1篇
排序方式: 共有1640条查询结果,搜索用时 0 毫秒
31.
A series of thioamides are transformed to their corresponding oxo analogues in good to excellent yields with acidified, wet, silica-supported tetrabutylammonium periodate under solvent-free conditions.  相似文献   
32.
An environmentally friendly procedure for the preparation of dihydropyrimidinone derivatives or their sulfur analogues under thermal solvent-free conditions in the presence of aluminium hydrogen sulfate [Al(HSO4)3] and alumina sulfuric acid (Al2O3-SO3H) as heterogeneous catalysts was developed.  相似文献   
33.
34.
A novel, diastereoselective, one-pot synthesis of new bis-Betti bases via condensation of dihydroxynaphthalene, two equivalents of aryl aldehydes, and two equivalents of 3-amino-5-methylisoxazole is reported. Conversion into the adducts was almost quantitative without the use of solvent or catalyst. The reaction conditions are very simple and enable easy isolation of the product.  相似文献   
35.
Herein, we describe a green procedure for the one-pot preparation of 1,8-dioxo-octahydroxanthene derivatives by condensation of dimedone and substituted benzaldehydes in the presence of FeCl 3 -SiO 2 as an efficient and heterogeneous catalyst under microwave irradiation and thermal conditions. This method has the advantages of high yields, cleaner reactions, efficient and cost-effective method, simple methodology, short reaction times, easy workup, and greener conditions.  相似文献   
36.
Reduction of aromatic nitro compounds to amine with hydroiodic acid was revisited. Under microwave irradiation on solid support the reduction proceeded efficiently and rapidly.  相似文献   
37.
Cerium ammonium nitrate (CAN) adsorbed on HNO 3 /silica gel is a mild reagent for selective oxidation of benzylic alcohols to the corresponding aldehydes under microwave irradiation in solventless system.  相似文献   
38.
This study reports on the synthesis of Cu2S nanoparticles via an ultrasonic method by employing Na2SO3 as a reducing agent. Morphology, structure, and composition of the obtained products were characterized by X-ray diffraction, energy dispersive X-ray analysis, scanning electron microscope and photoluminescence spectroscopy. The effects of time and power of irradiation were studied.  相似文献   
39.
Owing to the versatile applications in different areas including biology, natural compounds, dyes, and fluorescent materials, the synthesis of 2-pyridone compounds is an important research field and has attracted a great deal of attention. In this review, 2-pyridones new synthetic methods are classified to tree classes including reactions based on pyridine rings, cyclization, and cycloaddition reactions.  相似文献   
40.
A new composite electrode has been fabricated based on coating multi‐walled carbon nanotubes (MWCNTs) and n‐octylpyridinum hexafluorophosphate (OPPF6) ionic liquid composite on a glassy carbon (GC) electrode (OPPF6‐MWCNTs/GCE). This electrode shows very attractive electrochemical performances for electrooxidation of risperidone (RIS) compared to conventional electrodes using carbon and mineral oil, notably improved sensitivity and stability. The oxidation peak potentials in cyclic voltammogram of RIS on the OPPF6‐MWCNTs/GCE was occurred around 230 mV vs. SCE at Britton–Robinson (B–R) buffer (pH 4.0) at scan rate of 100 mV s?1. The electrochemical parameters such as diffusion coefficient (D), charge transfer coefficient (α) and the electron transfer rate constant (k/s) were determined using cyclic voltammetry. Under the optimized conditions, the peak current was linear to risperidone concentration over the concentration range of 10–200 nM with sensitivity of 0.016 μA/nM?1 using differential pulse voltammetry. The detection limit was 6.54 nM (S/N = 3). The electrode also displayed good selectivity and repeatability. In the presence of clozapine (CLZ) the response of RIS kept almost unchanged. Thus this electrode could find application in the determination of RIS in some real samples. The analytical performance of the OPPF6‐MWCNTs/GCE was demonstrated for the determination of RIS in human serum and pharmaceutical samples.  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-23

京公网安备 11010802026262号