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   2773篇
  免费   57篇
  国内免费   263篇
化学   1460篇
晶体学   5篇
力学   182篇
综合类   2篇
数学   255篇
物理学   1189篇
  2024年   7篇
  2023年   62篇
  2022年   43篇
  2021年   43篇
  2020年   51篇
  2019年   59篇
  2018年   47篇
  2017年   57篇
  2016年   81篇
  2015年   76篇
  2014年   95篇
  2013年   171篇
  2012年   204篇
  2011年   253篇
  2010年   188篇
  2009年   194篇
  2008年   179篇
  2007年   190篇
  2006年   163篇
  2005年   151篇
  2004年   138篇
  2003年   80篇
  2002年   68篇
  2001年   61篇
  2000年   46篇
  1999年   42篇
  1998年   50篇
  1997年   39篇
  1996年   29篇
  1995年   39篇
  1994年   23篇
  1993年   27篇
  1992年   20篇
  1991年   21篇
  1990年   10篇
  1989年   14篇
  1988年   9篇
  1987年   7篇
  1986年   5篇
  1985年   8篇
  1984年   10篇
  1983年   3篇
  1982年   3篇
  1981年   6篇
  1980年   2篇
  1979年   6篇
  1978年   4篇
  1977年   4篇
  1976年   3篇
  1974年   2篇
排序方式: 共有3093条查询结果,搜索用时 390 毫秒
101.
常温直接沉淀法制备ZnO纳米棒   总被引:11,自引:1,他引:11  
在常温下, 以PEG-400(聚乙二醇400)为表面活性剂, 采用直接沉淀法合成了ZnO纳米棒. 产物用XRD, TEM, SAED和 HRTEM等进行了表征. 结果表明, 所得ZnO为一维的纳米棒, 属于六方纤维矿的单晶结构. ZnO纳米棒的直径在20~40 nm之间, 长度在300~800 nm范围. (0001)面为ZnO纳米棒的生长方向. 讨论了ZnO相的生成和ZnO纳米棒的形成机理以及PEG-400在其形成过程中的作用.  相似文献   
102.
在自制的仪器上,以脉冲激光束在高真空中溅射适当的样品,产生了一系列合有1个VA族原子(N、P、As)或ⅢA族原子(B、Al)及13个以下碳原子的原子簇负离子。在实验记录的飞行时间质谱中,这些簇离子的信号强度均因其碳原子数的奇偶而发生交替变化.对实验结果的分析研究显示:这些簇离子均为直链构型.VA或ⅢA族原子位于链的一端,所有成簇原子的价键均得到满足.  相似文献   
103.

Heating a suspension of Bisphenol A diglycidyl ether (BADGE) in 20 : 80 tetrahydrofuran/water at 70°C and subsequent passage of the resulting solution through C18 columns allowed isolation and purification to > 97% of each of the two hydrolysis products 2-[4-(2,3-dihydroxypropoxy) phenyl]-2-[4-(2,3-epoxypropoxy)phenyl]propane (1HP) and 2,2-bis[4-(2,3-dihydroxypropoxy)phenyl] propane (2HP), which were characterized by UV, IR, 1H and I3C NMR spectroscopy and mass spectrometry.  相似文献   
104.
A fast procedure has been developed for the direct determination of paint solvents. The method is based on the injection of small volumes of untreated solvent mixtures into a heated Pyrex glass reactor in which the sample is volatilized and introduced by means of a flow of nitrogen into an IR multiple pass gas cell and the spectrum in the mid-IR region is registered as a function of time. Data found for samples are interpolated in calibration graphs obtained by injecting different volumes of pure compounds which constitute the solvent mixture. A methylisobutylketone (MIBK) toluene mixture was used as test system to develop the proposed procedure. The method provides a limit of detection of the order of 1–4 μg, a relative standard deviation of the order of 0.4 to 2% for five independent measurements, and recovery percentage values from 99.8 till 103.6 %. A commercial sample of polyurethane paint solvent has been analysed by the developed procedure.  相似文献   
105.
《Electroanalysis》2018,30(2):345-352
We reported here three simple, low cost and easy to accomplish strategies for the fabrication of microelectrodes and other conductive patterns using ordinary office laser‐printers. In this work, toner patterns were directly printed onto the flexible substrate, acting as a mask to create the intended conductive design. To highlight the versatility of such technology, toner‐printed patterns were employed in two diverse ways: one in which the patterned toner had the exact design of the electrode and other employing a reverse toner‐printed pattern. The first one was used for the adaptation of the well‐known printed circuit board (PCB) fabrication technique, but using direct toner printing (DTP) in an already conductive flexible substrate. The second was employed for the two remaining strategies: one based on the deposition of conductive film, followed by lift‐off process; and another based on drop‐casting of a conductive ink into the formed toner cavities, followed by thermal cure. As proof‐of‐concept, all three DTP strategies were used for the fabrication of miniaturized gold electrodes in polyimide substrate, and electrochemical performance of each obtained electrode was evaluated by cyclic voltammetry. Insights about DTP technology, alignment issues, advantages, limitations and resolution of each presented approach were provided. Finally, direct toner printing showed to be a simple, affordable and quite promising technology for the fabrication of low cost point‐of‐care electrochemical devices using flexible platforms.  相似文献   
106.
《Analytical letters》2012,45(9):671-687
Abstract

Methods were investigated to measure exhaust emission rates of individual low-molecular-weight phenols from gasoline and diesel vehicles driven on a chassis dynamometer using the FTP driving cycle. An extraction procedure to isolate the phenols from exhaust scrubs was evaluated. Separation of individual phenols was done by gas chromatography, with detection by a flame ionization detector. Phenol identifications were confirmed by mass spectroscopy. Results of a limited survey of gasoline and diesel vehicles are reported.  相似文献   
107.
108.
阎波 《光谱实验室》2012,29(4):2477-2483
研究了冷冻-解冻处理对A1CI3溶液团簇结构和AICl3与血清白蛋白相互作用的影响。测定了AICl3溶液冷冻-解冻处理前后电导率的变化,发现AICI3溶液经冷冻处理后,电导率有明显增加。采用紫外分光光度法和荧光光谱法对冷冻前后AICI3溶液与血清白蛋白相互作用的研究表明,A1C13溶液经冷冻-解冻处理后,与血清白蛋白的相互作用变弱,配位诱导作用降低,静态猝灭作用变小,这种相互作用变弱的效应是由于水的分子团簇结构变化引起的。  相似文献   
109.
The diffuse reflectance infrared spectra of TiO2 thin films deposited on different base materials and formed under different experimental conditions(temperature, ratio of tetrabutyl titanate to water and adulteration of different metallic elements) were determined and the structure of the films were discussed.  相似文献   
110.
Ring-opening (ROP) and enzymatic copolymerization (ECP) are among the most widely used approaches for synthesizing copolymers of polycaprolactone (PCL). It involves multiple-step reactions and the utilization of enzymes that make the process a lot more complicated, time consuming, and expensive. Atom transfer radical polymerization (ATRP) has been adopted to synthesize a novel amphiphilic copolymer in our study. The study presents a method to eliminate the ROP/ECP multiple steps in monomer polymerization thus making the process simpler and smoother. The synthesis of cationic polymer micelles copolymer of PCL-PGMA (polycaprolactone grafted poly glycidyl methacrylate) was carried out using direct functionalization of hydroxy group in crude PCL to achieve a higher degree of functionalization, i.e., 12.8% for macroinitiator. FTIR and 1H-NMR confirmed the successful synthesis of the copolymer with better control over the molecular weight with a PDI (1.84). DSC and XRD results showed the reduction of crystallinity by 86.81%, making copolymer more compatible for drug delivery application. The synthesized copolymer was further converted to nano-micelles drug carrier having an average size of 96.08 ± 21.22 nm. The drug encapsulation efficiency achieved was 60.0 ± 1.7%, and nano-micelles rendered a slow and controlled release of naproxen with long-term storage stability.  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