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   2562篇
  免费   369篇
  国内免费   199篇
化学   1356篇
晶体学   25篇
力学   146篇
综合类   13篇
数学   190篇
物理学   752篇
无线电   648篇
  2024年   11篇
  2023年   51篇
  2022年   84篇
  2021年   117篇
  2020年   86篇
  2019年   78篇
  2018年   92篇
  2017年   88篇
  2016年   111篇
  2015年   141篇
  2014年   159篇
  2013年   185篇
  2012年   230篇
  2011年   228篇
  2010年   145篇
  2009年   152篇
  2008年   156篇
  2007年   147篇
  2006年   124篇
  2005年   102篇
  2004年   54篇
  2003年   54篇
  2002年   54篇
  2001年   47篇
  2000年   52篇
  1999年   54篇
  1998年   48篇
  1997年   37篇
  1996年   43篇
  1995年   25篇
  1994年   27篇
  1993年   19篇
  1992年   9篇
  1991年   20篇
  1990年   27篇
  1989年   16篇
  1988年   12篇
  1987年   13篇
  1986年   9篇
  1985年   2篇
  1981年   2篇
  1976年   2篇
  1957年   1篇
  1942年   1篇
  1941年   1篇
  1936年   4篇
  1930年   2篇
  1929年   1篇
  1927年   1篇
  1923年   1篇
排序方式: 共有3130条查询结果,搜索用时 0 毫秒
921.
The rank information of samples is widely utilized in nonlinear signal processing algorithms. Recently developed fuzzy transformation theory introduces the concept of fuzzy ranks, which incorporates sample spread (or sample diversity) information into the sample ranking framework. Thus, the fuzzy rank reflects a sample's rank, as well as its similarity to the other sample (namely, joint rank order and spread), and can be utilized to improve the performance of the conventional rank-order-based filters. In this paper, the well-known lower-upper-middle (LUM) filters are generalized utilizing the fuzzy ranks, yielding the class of fuzzy rank LUM (F-LUM) filters. Statistical and deterministic properties of the F-LUM filters are derived, showing that the F-LUM smoothers have similar impulsive noise removal capability to the LUM smoothers, while preserving the image details better. The F-LUM sharpeners are capable of enhancing strong edges while simultaneously preserving small variations. The performance of the F-LUM filters are evaluated for the problems of image impulsive noise removal, sharpening and edge-detection preprocessing. The experimental results show that the F-LUM smoothers can achieve a better tradeoff between noise removal and detail preservation than the LUM smoothers. The F-LUM sharpeners are capable of sharpening the image edges without amplifying the noise or distorting the fine details. The joint smoothing and sharpening operation of the general F-LUM filters also showed superiority in edge detection preprocessing application. In conclusion, the simplicity and versatility of the F-LUM filters and their advantages over the conventional LUM filters are desirable in many practical applications. This also shows that utilizing fuzzy ranks in filter generalization is a promising methodology.  相似文献   
922.
简要论述了黑龙江省6大本地网新建长途局的比要性,介绍了长途局兼做智能网业务接入SSP及信令转接STP功能、长途中继电路物分配原则、网同步实施方法及信令组织的方案和原则等。  相似文献   
923.
The near-threshold highly bound states of all three stable isotopic variants of molecular hydrogen have been studied. Numerous perturbations and unexpected transitions are observed as far as 1cm\sj{-1} just below the second dissociation threshold. This complex structure may arise from a combination of nonadiabatic coupling between B, B', C electronic states, perturbations due to fine and hyperfine interactions, and strong shape resonances. The perturbed near-threshold states and vibrational continuum exhibit finegrained structure, differing greatly between isotopes because of varying nonadiabatic coupling.  相似文献   
924.
925.
实验研究了部分相位共轭的特性,实验表明非完全相位共轭对相位共轭保真度及相位共轭光的能量集中度具有一定的影响,在没有吸收的情况下,根据能量守恒和互逆原理,推导了相位共轭保真度和相位共轭镜的有限尺寸之间的简单关系。  相似文献   
926.
927.
聂江  姜镇林  陈华 《电子技术》2011,38(12):13-14
文章提出了一种基于网格的仪器设备共享模型,能为提供超强的计算能力,将设备对用户透明化,并用一个实验实例来对模型进行论证.在面对更为复杂的实际情况时,对提出的模型进行修正,改进.  相似文献   
928.
A series of α-glucosidase inhibitors with the oleanolic acid core and different cinnamic amide ligands were designed and synthesized. Their preliminary structure-activity relationships were analyzed. In general, the compounds with 3,28-disubstituted oleanolic acid exhibited stronger activity than those 28-monosubstituted analogues, and variation of cinnamic amide substitution significantly affected α-glucosidase inhibition activities. Most of the compounds showed potent inhibitory activity against α-glucosidase with much greater efficacy than a typical α-glucosidase inhibitor, acarbose.  相似文献   
929.
A low-energy hydrogen bombardment method, without using any chemical additives, has been designed for fine tuning both physical and chemical properties of molecular thin films through selectively cleaving C-H bonds and keeping other bonds intact. In the hydrogen bombardment process, carbon radicals are generated during collisions between C-H bonds and hydrogen molecules carrying ~10 eV kinetic energy. These carbon radicals induce cross-linking of neighboring molecular chains. In this work, we focus on the effect of hydrogen bombardment on dotriacontane (C(32)H(66)) thin films as growing on native SiO(2) surfaces. After the hydrogen bombardment, XPS results indirectly explain that cross-linking has occurred among C(32)H(66) molecules, where the major chemical elements have been preserved even though the bombarded thin film is washed by organic solution such as hexane. AFM results show the height of the perpendicular phase in the thin film decreases due to the bombardment. Intriguingly, Young's modulus of the bombarded thin films can be increased up to ~6.5 GPa, about five times of elasticity of the virgin films. The surface roughness of the thin films can be kept as smooth as the virgin film surface after thorough bombardment. Therefore, the hydrogen bombardment method shows a great potential in the modification of morphological, mechanical, and tribological properties of organic thin films for a broad range of applications, especially in an aggressive environment.  相似文献   
930.
A new wireless sensing method for the detection of uranium in water samples has been reported in this paper. The method is based on a sandwich-type detection strategy. Salophen, a tetradentate ligand of uranyl ion, was immobilized on the surface of the polyurethane-protected magnetoelastic sensor as receptor for the capture of uranyl ion. The phosphorylated polyvinyl alcohol coated magnetic Fe3O4 nanoparticles were used as signal-amplifying tags of uranyl ion. In a procedure of determining uranium, firstly uranyl ion in sample solution was captured on the sensor surface. Then the captured uranyl bound the nanoparticle through its coordination with the phosphate group. The amount of uranium was detected through the measure of the resonance frequency shift caused by the enhanced mass loading on the sensor surface. A linear range was found to be 0.2–20.0 μg/L under optimal conditions with a detection limit of 0.11 μg/L. The method has been applied to determine uranium in environmental water samples with the relative standard deviations of 2.1–3.6 % and the recoveries of 98.0–101.5 %. The present technique is one of the most suitable techniques for assay of uranium at trace level in environmental water samples collected from different sources.  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