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   2341篇
  免费   95篇
  国内免费   69篇
化学   2178篇
晶体学   2篇
力学   18篇
综合类   8篇
数学   87篇
物理学   212篇
  2024年   6篇
  2023年   57篇
  2022年   54篇
  2021年   51篇
  2020年   56篇
  2019年   59篇
  2018年   58篇
  2017年   81篇
  2016年   84篇
  2015年   93篇
  2014年   67篇
  2013年   198篇
  2012年   143篇
  2011年   134篇
  2010年   105篇
  2009年   140篇
  2008年   113篇
  2007年   151篇
  2006年   101篇
  2005年   113篇
  2004年   95篇
  2003年   64篇
  2002年   58篇
  2001年   48篇
  2000年   48篇
  1999年   40篇
  1998年   34篇
  1997年   37篇
  1996年   24篇
  1995年   20篇
  1994年   13篇
  1993年   20篇
  1992年   21篇
  1991年   25篇
  1990年   27篇
  1989年   6篇
  1988年   18篇
  1987年   11篇
  1986年   6篇
  1985年   4篇
  1984年   6篇
  1983年   4篇
  1982年   1篇
  1981年   2篇
  1980年   4篇
  1979年   3篇
  1978年   2篇
排序方式: 共有2505条查询结果,搜索用时 32 毫秒
11.
Surimi from silver carp with different salt contents (0–5%) was obtained treated by high intensity ultrasound (HIU, 100 kHz 91 W·cm−2). The gelation properties of samples were evaluated by puncture properties, microstructures, water-holding capacity, dynamic rheological properties and intermolecular interactions. As the salt content increased from 0 to 5%, gel properties of surimi without HIU significantly improved. For samples with low-salt (0–2% NaCl) content, HIU induced obvious enhancement in breaking force and deformation. HIU promoted the protein aggregation linked by SS bonds, hydrophobic interactions and non-disulfide covalent bonds in surimi gels with low-salt content. Moreover, microstructures of HIU surimi gels with low-salt content were more compact than those of the corresponding control samples. HIU also improved the gelation properties of surimi with 3% NaCl to an extent. However, for high-salt (4–5% NaCl) samples, HIU decreased the breaking force and deformation of surimi gels due to the degradation of proteins suggested by increased TCA-soluble peptides. In conclusion, HIU effectively improved the gelation properties of surimi with low-salt content (0–2% NaCl), but was harmful for high-salt (4–5% NaCl) surimi. This might provide the theoretical basis for the production of low-salt surimi gels.  相似文献   
12.
Abstract

Exhaustive extraction of analytes in their original chemical forms from samples with complex matrices is a pivotal step for speciation analysis. Herein we propose a pretreatment method for extracting and preconcentrating methylmercury and ethylmercury from coal samples by using KBr–H2SO4/CuSO4–C6H5CH3–Na2S2O3 system. The extraction conditions, including the volume of the organic phase and the extraction time, were optimized in detail. Speciation analysis of alkylmercuries was carried out by high‐performance liquid chromatography online coupled with UV‐digestion and cold vapor atomic fluorescence spectrometry. The detection limits were 0.6 ng mL?1 for methylmercury and 1 ng mL?1 for ethylmercury, respectively. The recoveries of methylmercury and ethylmercury spiked in a sample were 84% and 82%, respectively. The method was applied successfully to analysis of alkylmercuries in four coal samples collected from northeast China.  相似文献   
13.
The direct introduction of solid samples (air filters) to the inductively coupled plasma source of an atomic emission spectrometer using a furnace atomizer has been studied. Conditions have been found for the analysis of elements which volatilize with varyling degrees of difficulty. Lead, copper and vandaium compounds retained on glass fibre filters from air pollution studies have been determined. The results are in good agreement with those obtained by means of established sample dissolution/atomic emision methods.  相似文献   
14.
Abstract

The present article gives an overview of recent publications and modern techniques of sample preparation for food analysis employing atomic and inorganic mass spectrometric techniques, such as flame atomic absorption spectrometry, chemical vapor generation atomic absorption and atomic fluorescence spectrometry, graphite furnace atomic absorption spectrometry, inductively coupled plasma optical emission spectrometry, and inductively coupled plasma mass spectrometry. Among the most frequently applied sample preparation techniques for food analysis are dry ashing, usually with the addition of an ashing aid, and acid digestion, preferably with the assistance of microwave energy. Slurry preparation, particularly with the assistance of ultrasound, is increasingly used to reduce acid consumption and sample preparation time. Direct analysis of solid samples is gaining importance in the field of food analysis as it offers the highest sensitivity, avoids the use of acids and other aggressive reagents, makes possible the analysis of micro‐samples, and can be applied for fast screening analysis, e.g., of fresh meat.  相似文献   
15.
自制固相微萃取探头用于分析大白菜中有机磷农药   总被引:5,自引:0,他引:5  
采用溶胶-凝胶方法制备的聚甲基苯基乙烯基硅氧烷/羟基硅油(PMPVS/OH-TSO)固相微革取探头与气相色谱(GC)联用对大白菜样品中的有机磷农药(敌敌鼹、二嗪农、甲摹对硫磷、马拉硫磷和乙基对硫磷)进行了分析,同时优化了固相微革取的实验条件.该探头较商用探头萃取能力更强,方法的检出限低(1.01~2.56ng/g),重现性好(3.5%~9.9%),线性范围宽(2个数量级),对市售的大白菜样品进行了标准加入回收实验,5种有机磷农药的同收率分别为80.2%,90.3%,85.4%,81.9%和91.8%,  相似文献   
16.
报道一种快速测定人体尿液中4'-羟基黄烷酮和6-甲氧基黄烷酮的HPLC方法.采用自制的大蒜新素键合硅胶填充柱(DTSP,4.6 mm i.d.×15 mm,10 μm),以乙腈/1.5%三乙胺-甲酸(65:35,v/v,pH=3.0) 为流动相,流速设定为1.0 mL·minn~(-1),检测波长为 257 nm时,实现了人体尿样品中上述黄烷酮化合物的良好分离.4'-羟基黄烷酮的线性范围为5~100 mg·L~(-1),r=0.992 0;6-甲氧基黄烷酮线性范围为5~100 mg·L~(-1),r=0.999 1,它们的最低检出限分别为1.03 ng和1.56 ng,平均回收率分别为99.02%~99.26%和98.21%~98.62%,相应的RSD分别小于0.354%和0.605%(n=5).该方法快速、简便、可靠,适用于人体尿液样品中上述黄烷酮分离分析.  相似文献   
17.
We have carried out some photon interaction measurements using 59.54 keV γ-rays from a 241Am source. These include γ attenuation studies as well as photoelectric absorption studies in various samples. The attenuation studies have been made using leaf and wood samples, samples like sand, sugar etc., which contain particles of varying sizes as well as pellets and aqueous solutions of rare earth compounds. In the case of the leaf and wood samples, we have used the γ-ray attenuation technique for the determination of the water content in fresh and dried samples. The variation of the attenuation coefficient with particle size has been investigated for sand and sugar samples. The attenuation studies as well as the photoelectric studies in the case of rare earth elements have been carried out on samples containing such elements whose K-absorption edge energies lie below and close to the γ-energy used. Suitable compounds of the rare earth elements have been chosen as mixture absorbers in these investigations. A narrow beam good geometry set-up was used for the attenuation measurements. A well-shielded scattering geometry was used for the photoelectric measurements. The mixture rule was invoked to extract the values of the mass attenuation coefficients for the elements from those of the corresponding compounds. The results are consistent with theoretical values derived from the XCOM package.  相似文献   
18.
研究了平台石墨炉原子吸收测定磷的方法,表明以氯化钯和硝酸钙的混合液作为基体改进剂测定生物样品中的磷效果最好,方法特征量为8×10~(-9)g,工作曲线线性范围为0~0.400吸光度,精密度好,抗干扰能力强,方法简单,利用标准曲线即可测定生物样品中磷。  相似文献   
19.
基于宽带多通道的光谱反射率重建方法研究   总被引:7,自引:0,他引:7  
复制的多光谱数据获取要求图像数据具有设备无关、场景无关特性,能够真实客观表征物体颜色信息。针对获取系统扰动、噪声误差以及光谱重建中训练样本典型代表性与相关性要求,提出了基于正交回归的光谱重建算法,并通过子空间跟踪的训练样本选择算法,选择重建样本与训练样本集中相关性与代表性最好的样本参与光谱重建。实验通过改造后的仙娜宽带多通道成像系统进行验证,数据表明本文提出的方法,所选训练样本能较好的表征样本空间并具有较好的正交性,在宽带多光谱成像方面,重建光谱平均色度误差为3.6,其光谱精度与色度精度较其他方法具有明显提高。  相似文献   
20.
该文建立了新的流动注射-化学发光快速测定莱克多巴胺的分析方法。基于碱性介质中莱克多巴胺对鲁米诺-铁氰化钾体系化学发光的增敏作用,研究了各因素对化学发光的影响。结果表明,在最佳发光条件下,相对发光强度与莱克多巴胺浓度在4.0×10-9~8.0×10-7 g.mL-1范围内呈良好的线性关系,检出限为2.5×10-9 g.mL-1,相对标准偏差为5.6%。应用该方法成功分析了猪肉和尿样中莱克多巴胺的含量,回收率为69.3%~101.3%,结果令人满意。  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