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   2084篇
  免费   213篇
  国内免费   173篇
化学   924篇
晶体学   29篇
力学   41篇
综合类   1篇
数学   28篇
物理学   1447篇
  2024年   2篇
  2023年   57篇
  2022年   21篇
  2021年   22篇
  2020年   50篇
  2019年   34篇
  2018年   46篇
  2017年   61篇
  2016年   54篇
  2015年   65篇
  2014年   136篇
  2013年   136篇
  2012年   96篇
  2011年   170篇
  2010年   106篇
  2009年   116篇
  2008年   138篇
  2007年   154篇
  2006年   136篇
  2005年   71篇
  2004年   78篇
  2003年   71篇
  2002年   70篇
  2001年   80篇
  2000年   55篇
  1999年   67篇
  1998年   108篇
  1997年   42篇
  1996年   30篇
  1995年   21篇
  1994年   22篇
  1993年   15篇
  1992年   24篇
  1991年   16篇
  1990年   14篇
  1989年   11篇
  1988年   9篇
  1987年   11篇
  1986年   10篇
  1985年   4篇
  1984年   10篇
  1983年   3篇
  1982年   9篇
  1981年   2篇
  1979年   4篇
  1978年   2篇
  1977年   2篇
  1976年   3篇
  1973年   4篇
  1972年   1篇
排序方式: 共有2470条查询结果,搜索用时 218 毫秒
41.
A series of new light emitting subphthalocyanines, lower homologues of phthalocyanines, were synthesized having color points covering the red-orange region of the visible spectrum. Additionally, they were found to be of potential use as narrow band emitters for red-light emitting diodes.  相似文献   
42.
Sono-induced cold vapor generation (SI-CVG) has been used for the first time in combination with a graphite furnace atomizer for determination of Hg in natural waters by electrothermal-atomic absorption spectrometry after in situ trapping onto a noble metal-pretreated platform (Pd, Pt or Rh) inserted into a graphite tube. The system allows ‘in-atomizer trapping’ of Hg without the use of conventional reduction reactions based on sodium borohydride or tin chloride in acid medium for cold vapor generation. The sono-induced reaction is accomplished by applying ultrasound irradiation to the sample solution containing Hg(II) in the presence of an organic compound such as formic acid. As this organic acid is partly degraded upon ultrasound irradiation to yield CO, CO2, H2 and H2O, the amount of lab wastes is minimized and a green methodology is achieved.  相似文献   
43.
44.
本文用自旋捕捉-ESR技术研究了二茂戊铁、环二烯和胺甲基类取代二茂铁的紫外光解过程中的活泼自由基。结果表明,二茂铁光解初级过程中生成的自由基为(C_5H_5Fe)·和C_5H_5·,其衍生物光解则生成(C_5H_5Fe)·和RC_5H_4·,而(C_5H_5Fe)·还可以进一步分解给出C_5H_5和Fe。  相似文献   
45.
在文中所述条件下,镍的原子捕集灵敏度较常规法高320倍,即在离子交换法浓缩仅40倍的情况下,可使镍的测定灵敏度提高12800倍,从而成功实现了ppt级超痕量镍的测定。  相似文献   
46.
An evaluation of the most commonly used HPLC system (reversed phase octadecyl sillica gel) was undertaken in order to determine the level of certain carbohydrates in molasses produced in the refining of sugar beet. Chromatographic parameters and purification operations prior to analysis are discussed in order to develop an analytical method permitting automation of sugar determination. A Zorbax ODS column (250 × 9.4 mm), water elution, and light scattering detection allow easy determination of glucose + fructose, sucrose, and raffinose in molasses using an internal standard (maltose).  相似文献   
47.
Aspects of intramolecular light energy and electron transfer are discussed for three protein cofactor complexes whose three-dimensional structures have been elucidated by X-ray crystallography: the light harvesting phycobilisomes of cyanobacteria, the reaction center of purple bacteria, and the blue multi-copper oxidases. A wealth of functional data is available for these systems which allows specific correlations to be made between structure and function and general conclusions to be drawn about light energy and electron transfer in biological materials.  相似文献   
48.
The vanadium trapping effect of Mg and La containing additives in cracking catalyst contaminated with 2300 ppm Ni and 4700 ppm V has been analyzed by microactivity test (MAT) and imaging secondary ion mass spectrometry (SIMS). The results of SIMS imaging are consistent with cracking activity data and show that the La/spinel is a superior vanadium trap for the fluid catalytic cracking of hydrocarbons (FCC) operation. La/spinel serves as a dual function additive for both vanadium trap and SOx removal. The optimum amount of La/spinel added to the cracking catalyst is about 15% by weight. This results in an increased catalytic activity, an increase in gasoline yield, and a decrease in coke and gas factors. The MgAl2O4 phase of Mg/Al2O3 additive is found capable of trapping vanadium while its MgO of Mg/Al2O3 phase can migrate to zeolite particles (the active component of the FCC catalyst) that, in turn, causes a decline in the activity of that catalyst.  相似文献   
49.
阻抑动力学光度法测定痕量铜   总被引:5,自引:0,他引:5  
在pH 4.5的HAc-NaAc缓冲溶液中, 痕量铜对KBrO3氧化亮绿SF的褪色反应有明显的阻抑作用, 据此建立了测定痕量铜的新方法. 方法的线性范围为0.004~0.048 μg/mL, 检出限为8.63×10-4 μg/mL, 已用于人发中铜的测定.  相似文献   
50.
Mhatre  R.  Qian  R.  Krull  I. S.  Gadam  S.  Cramer  S. M. 《Chromatographia》1994,38(5-6):349-354
Summary -Lactoglobulin A and B (-LACT) were separated by displacement chromatography (DSC) on an ionexchange column using dextran sulfate as the displacer. A LALLS photometer and a UV detector, in series, were used to determine the molecular weight (MW) of the proteins, on-line. The results indicate that both, -LACT A and B, were present as dimers in the buffer used for the mobile phase. The MWs of the proteins were about 6–8% higher than the theoretical MW of a dimer (37,000). Additional control studies have shown the presence of a high molecular weight species in both the proteins, which could possibly be an aggregate. This species was observed in the LALLS signal but was nearly absent in the UV signal. Our work has demonstrated the feasibility of interfacing LALLS with displacement chromatography for detecting impurities or aggregates which may be difficult to detect by conventional detectors used for chromatography.  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