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   2126篇
  免费   42篇
化学   1143篇
晶体学   41篇
力学   77篇
数学   534篇
物理学   373篇
  2023年   12篇
  2022年   22篇
  2021年   32篇
  2020年   39篇
  2019年   55篇
  2018年   95篇
  2017年   95篇
  2016年   95篇
  2015年   74篇
  2014年   115篇
  2013年   318篇
  2012年   115篇
  2011年   130篇
  2010年   143篇
  2009年   89篇
  2008年   126篇
  2007年   110篇
  2006年   74篇
  2005年   44篇
  2004年   43篇
  2003年   30篇
  2002年   31篇
  2001年   21篇
  2000年   20篇
  1999年   17篇
  1998年   15篇
  1997年   11篇
  1996年   11篇
  1995年   9篇
  1992年   3篇
  1991年   3篇
  1990年   5篇
  1989年   7篇
  1988年   6篇
  1987年   8篇
  1986年   9篇
  1985年   15篇
  1984年   9篇
  1983年   9篇
  1982年   10篇
  1981年   16篇
  1980年   5篇
  1979年   9篇
  1978年   3篇
  1977年   7篇
  1976年   11篇
  1975年   5篇
  1974年   9篇
  1973年   9篇
  1968年   9篇
排序方式: 共有2168条查询结果,搜索用时 15 毫秒
991.
Cereal varieties are normally identified using time-consuming methods such as visual examination of either the intact grain or one-dimensional electrophoretic patterns of the grain storage proteins. A fast method for identification of wheat (Triticum aestivum L.) varieties has previously been developed, which combines analysis of alcohol-soluble wheat proteins (gliadins) using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry with neural networks. Here we have applied the same method for the identification of both barley (Hordeum vulgare L.) and rye (Secale cereale L.) varieties. For barley, 95% of the mass spectra were correctly classified. This is an encouraging result, since in earlier experiments only a grouping into subsets of varieties was possible. However, the method was not useful in the classification of rye, due to the strong similarity between mass spectra of different varieties.  相似文献   
992.
Nano Fe3O4 particles were obtained in microvawe oven using closed system. Oxovanadium(IV) complexes of Fe3O4@SiO2@(aminomethylphosphine) type ligands were synthesized and characterized using SEM, EDX, TEM, UV‐Visible, XRD, FT‐IR and TG/DTA techniques. Catalytic properties of the synthesized pincer type oxovanadium(IV)‐aminomethylphosphine complexes supported on magnetic nano structure were investigated in the synthesis of 2‐methyl‐1, 4‐naphthoquinone (Vitamin K3, menadione, 2MNQ) from 2‐methyl naphthalene (2MN) in hydrogen peroxide, acetic acid and sulfuric acid. Magnetic‐nano particle supported oxovanadium(IV)‐aminomethylphosphine type complexes were very efficient catalysts with the 51.36‐55.20 % selectivities in conversions of 89.78‐95.01 %. Besides, the hetergeneous complexes were very active in five cycling tests on avarage evaluated in the reusability.  相似文献   
993.
A rapid and novel method combining dispersive liquid–liquid microextraction and high-performance liquid chromatography coupled with fluorescence detection was developed for the determination of donepezil in human urine. Parameters affecting extraction efficiency and chromatographic determination, such as the type and volume of the extraction and disperser solvent, pH of sample for dispersive liquid–liquid microextraction, mobile-phase composition, pH, column oven temperature, and flow rate for chromatographic determination, were evaluated and optimized. Using a C18 core–shell column (7.5 × 4.6?mm, 2.7?μm), the determination of donepezil was accomplished within 5?min. Under optimum conditions, developed method was linear in the range of 0.5–25?ng?mL?1 with the correlation coefficient >0.99. Limit of detection was 0.15?ng?mL?1. The relative standard deviation at three concentration levels (2, 12.5, and 20?ng?mL?1) was less than 11% with accuracy in the range of 96.9–102.8%. The results of this study demonstrate that the use of dispersive liquid–liquid microextraction and core–shell column can be considered as a powerful tool for the analysis of donepezil in human urine.  相似文献   
994.
Journal of Solid State Electrochemistry - We report the synthesis of non-peripheral metallophthalocyanines which carry four 4-(4-methoxyphenyl)-2-thiazole-2-thio units. 1H-NMR, FT-IR, UV–Vis,...  相似文献   
995.
Green chemistry (GC) was developed to maximise resource efficiency and minimise hazards in chemical processes and products. Over time, the approach evolved into green and sustainable chemistry (GSC), which aims at promoting the development of an ecologically friendly society. GSC encourages society's reliance on sustainable materials and technologies/processes and supports the ambitious sustainability targets set by international organisations. It also steers public attention to the provision of sustainable solutions for producers, consumers and investors. Since GSC implementation requires significant financial investment, this paper describes a broad range of approaches and tools to assess the sustainability of potential investments and shows, although with a primary focus on environmental sustainability, how life cycle approaches could be used to define enhanced key performance indicators. Thus, the paper may serve as a useful reference for: (i) chemical companies interested in evaluating the sustainability performance of activities requiring financial investment, and (ii) investors interested in evaluating the sustainability of potential financial investments.  相似文献   
996.
Explosive detection technologies play a critical role in maintaining national security, remain an active research field with many devices and analytical/electroanalytical techniques. Analytical chemistry needs for homeland defense against terrorism make it clear that real-time and on-site detection of explosives and chemical warfare agents (CWAs) are in urgent demand. Thus, current detection techniques for explosives have to be improved in terms of sensitivity and selectivity, opening the way to electrochemical devices suitable to obtain the targeted analytical information in a simpler, cheaper and faster way. For the electrochemical determination of energetic substances, a large number of sensor electrodes have been presented in literature using different modification materials, especially displaying higher selectivity with molecularly imprinted polymers (MIPs). MIPs have already been utilized for the detection of hazardous materials due to their mechanical strength, flexibility, long-time storage and low cost. The sensitivity of MIP-based electrosensors can be enhanced by coupling with nanomaterials such as graphene oxide (GOx), carbon nanotubes (CNTs), or nanoparticles (NPs). Specific characteristics of involved nanomaterials, their modification, detection mechanism, and other analytical aspects are discussed in detail. Non-MIP electrosensors are generally functionalized with materials capable of charge transfer, H-bonding or electrostatic interactions with analytes for pre-concentration and electrocatalysis on their surface, whereas nanobio-electrosensors use analyte-selective aptamers having specific sequences of DNA, peptides or proteins to change the potential or current. This review intends to provide a combination of information related to MIPs and nanomaterial-based electrochemical sensors, limited to the most significant and illustrative work recently published.  相似文献   
997.
Journal of Solid State Electrochemistry - A powder-free solid oxide cell electrode fabrication route is demonstrated, in which a polymeric precursor, containing the cations of electrocatalyst and...  相似文献   
998.
In this Letter the baker’s yeast-mediated biotransformation of variously substituted α-hydroxy- and α-acetoxymethyl-5-phenylfuran-2-yl-ethanones is described. The stereochemical outcome of the reactions was strongly influenced by the nature of the substituents on the phenyl ring.  相似文献   
999.
1000.
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