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   2839篇
  免费   447篇
  国内免费   507篇
化学   2059篇
晶体学   57篇
力学   204篇
综合类   46篇
数学   368篇
物理学   1059篇
  2025年   3篇
  2024年   60篇
  2023年   61篇
  2022年   144篇
  2021年   121篇
  2020年   135篇
  2019年   166篇
  2018年   118篇
  2017年   136篇
  2016年   141篇
  2015年   177篇
  2014年   158篇
  2013年   221篇
  2012年   241篇
  2011年   280篇
  2010年   217篇
  2009年   191篇
  2008年   211篇
  2007年   149篇
  2006年   167篇
  2005年   150篇
  2004年   100篇
  2003年   56篇
  2002年   58篇
  2001年   67篇
  2000年   64篇
  1999年   55篇
  1998年   25篇
  1997年   17篇
  1996年   21篇
  1995年   16篇
  1994年   15篇
  1993年   9篇
  1992年   11篇
  1991年   5篇
  1990年   7篇
  1989年   4篇
  1988年   5篇
  1987年   2篇
  1986年   1篇
  1985年   3篇
  1984年   1篇
  1982年   2篇
  1979年   1篇
  1971年   1篇
排序方式: 共有3793条查询结果,搜索用时 15 毫秒
1.
Employing an organic dye salt of trans-4-[p-[N-methyl-N-(hydroxymethyl)amino]styryl]-N-methylphridinium tetra\-phenylborate (ASPT) as the active layer, 8-hydrocyquinoline aluminium (Alq3) as the electron transporting layer and N,N’-diphenyl-N,N’-bis(3-methylphenyl)-[1,1’-biphenyl]-4,4’-diamine (TPD) as the hole transporting layer, respectively, we fabricate a multi-layered organic light-emitting diode and observe the colour tunable electroluminescence (EL). The dependence of the EL spectra on the applied voltage is investigated in detail, and the recombination mechanism is discussed by considering the variation of the hole-electron recombination region.  相似文献   
2.
乔善宝 《光谱实验室》2005,22(4):737-739
盐酸异丙肾上腺素在伯瑞坦-罗比森缓冲溶液(pH=6.80)介质中有很强的荧光。其最大激发波长和发射波长为287nm和622nm。荧光强度与纯盐酸异丙肾上腺素浓度在0.1—2.3mg/L范围内呈线性关系。回归方程F=351.91C(mg/L) 139.02,r=0.9995,检出限为0.0087mg/L。测定注射用针剂中盐酸异丙肾上腺素的含量,方法简单,快捷,灵敏度高,结果令人满意。  相似文献   
3.
介绍了利用连通器及水密封原理实现气体状态改变的简单实验装置. 根据测得的气体压缩过程的压强曲线及简单的理论分析,得出利用该装置能实现准静态绝热过程的结论;同时,对实验装置的潜在应用进行了探讨,利用初步的实验数据计算的各热学量与对应的理论值均符合很好.  相似文献   
4.
采用微波消解-等离子体发射光谱法同时测定果汁中K、P含量,优化了实验所需的各种条件。与国家标准方法湿法消解-分光光度法的测定结果作了实验比较,结果表明本实验方法更简单、高效,节省了样品的前处理时间,减小了最终结果的误差。该法灵敏度高、线性范围宽、加标回收率高,结果令人满意。  相似文献   
5.
热敏电阻温度计的设计与制作   总被引:2,自引:0,他引:2  
本文介绍了设计性实验“热敏电阻的设计与制作”的实施情况。说明了只要选题合适、要求恰当,设计性实验不仅可行,而且对物理实验训练的总结提高十分有效。  相似文献   
6.
Zong W  Liu R  Sun F  Teng Y  Fang X  Chai J 《Journal of fluorescence》2011,21(3):1249-1254
To identify and eliminate the inner filter effects (IFEs), prepositive and side cells containing absorbents are fixed beside the fluorescer contained cell. In this way, excitation and emission lights can be quenched by primary and secondary outer filter effects respectively, depending on absorbent concentration and cell length. Herein the quenching of emission fluorescence caused by IFEs can be equally reduced by outer filter effects (OFEs) and the interference of IFEs was eliminated. This approach was experimentally used for identifying the interaction mode and mechanism between BSA and nanoAg. Results showed that the quenching of BSA fluorescence and synchronous fluorescence mainly attributes to IFEs, instead of static/dynamic fluorescent quenching. In view of the above, the elimination of the interference of IFEs by the design of OFEs plays an important part in the precise application of fluorescence detector.  相似文献   
7.
Three-dimensional (3D) laser carving is a new, very flexible process and is very useful for machining the hard and/or brittle materials such as ceramics, carbide and hardened steel with high precision, excellent productivity and surface quality. In this paper, the effects of laser processing parameters on single-layer carving depth and surface quality are analyzed by laser carving on an Al2O3 ceramic with different processing parameters. The mechanisms of laser carving are also studied. A mathematical model of the relationship between the laser processing parameters and the laser carving depth is established, which is useful in obtaining the best machining parameters with the shortest time. Finally, a 3D pattern is successfully carved using the optimum parameters.  相似文献   
8.
This paper reports the photoluminescence (PL) properties of nanocrystalline CaZrO3:Tm phosphor synthesized by the polymerizable complex method based on the Pechini-type reaction. Nanosized phosphors with paving stone morphology were prepared at a relatively low temperature about 800 °C with the particle size being about 30 nm. The transmission electron microscope (TEM) images showed that further heat treatment at higher temperature could increase the particle size to 50 nm, but its morphology remained unchanged. The luminescence spectra indicated that the blue emission of CaZrO3:Tm could be produced by four kinds of excitation energies, i.e. the charge transfer (CTS) between Tm3+-O2−, band-band absorption of host, the absorption defects in the host and the 3H6-1D2 transition. The luminescent mechanism of CaZrO3:Tm was deduced tentatively based on the luminescence spectra.  相似文献   
9.
Using the Lie Symmetry under infinitesimal transformations in which the time is not variable, the nonNoether conserved quantity of nonholonomic system having variable mass and unilateral constraints is studied. The differential equations of motion of the system are given. The determining equations of Lie symmetrical transformations of the system under infinitesimal transformations are constructed. The Hojman‘s conservation theorem of the system is established. Finally, we give an example to illustrate the application of the result.  相似文献   
10.
Phase structures of immiscible polypropylene (PP)/polystyrene (PS) blends with different volume proportions, PP90/PS10, PP80/PS20, PP70/PS30, PP60/PS40, PP50/PS50, PP40/PS60, PP30/PS70, PP20/PS80, PP10/PS90, were observed by means of scanning electronic microscopy (SEM). The zero shear viscosities of the blends were determined according to a modified Carreau model by fitting the curves of static shear rate sweeps of blends tested at 190°C in a Stress Tech Fluids Rheometer. The results showed that the compositional dependence of zero shear viscosity of PP/PS deviated greatly from linear or log‐linear additivity. When PS was dispersed in a PP continuous phase, the blends showed negative deviation, while for blends with PP dispersed in a PS matrix, positive deviation was generated. When different theoretical equations of Nielsen, Utracki, Taylor, Frankel‐Acrivos (FA), Choi‐Schowalter (CS), and Han‐King (HK) were used to fit the experimental data of zero shear viscosities of blends, none of them was suitable for PP/PS blends. These experimental phenomena may result from the complex phase structures of the blends and their response to shear conditions, which are discussed in detail and compared with the experimental analysis.  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