全文获取类型
收费全文 | 6655篇 |
免费 | 1025篇 |
国内免费 | 945篇 |
专业分类
化学 | 2588篇 |
晶体学 | 42篇 |
力学 | 898篇 |
综合类 | 69篇 |
数学 | 378篇 |
物理学 | 2836篇 |
无线电 | 1814篇 |
出版年
2024年 | 14篇 |
2023年 | 99篇 |
2022年 | 220篇 |
2021年 | 221篇 |
2020年 | 226篇 |
2019年 | 207篇 |
2018年 | 254篇 |
2017年 | 274篇 |
2016年 | 332篇 |
2015年 | 327篇 |
2014年 | 428篇 |
2013年 | 568篇 |
2012年 | 449篇 |
2011年 | 512篇 |
2010年 | 412篇 |
2009年 | 406篇 |
2008年 | 419篇 |
2007年 | 396篇 |
2006年 | 374篇 |
2005年 | 339篇 |
2004年 | 291篇 |
2003年 | 249篇 |
2002年 | 239篇 |
2001年 | 184篇 |
2000年 | 172篇 |
1999年 | 167篇 |
1998年 | 153篇 |
1997年 | 112篇 |
1996年 | 99篇 |
1995年 | 95篇 |
1994年 | 82篇 |
1993年 | 58篇 |
1992年 | 43篇 |
1991年 | 37篇 |
1990年 | 19篇 |
1989年 | 26篇 |
1988年 | 19篇 |
1987年 | 17篇 |
1986年 | 7篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 2篇 |
1982年 | 17篇 |
1981年 | 9篇 |
1980年 | 2篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有8625条查询结果,搜索用时 15 毫秒
1.
2.
A zinc coordination polymer derived from pyridine-2,6-dicarboxylate (PDC), {[Zn2(PDC)2]}n, was successfully prepared via conventional, sonication and microwave-irradiation methods. The composition and characteristics of the obtained coordination polymers (CPs) were investigated by elemental analysis, TGA/DTA, X-ray diffraction and spectroscopic techniques. The so obtained CPs were heat-treated in the air at 600 °C for 2 h to produce ZnO of nanosized particles (NPs). It is of interest to note that the synthesis approach of the precursor greatly affects both the nanoparticle size and the structure of the resulting ZnO NPs. Moreover, the smallest particle size was associated with the sample derived from the ultrasonically prepared precursor. TEM analysis revealed that all samples have sphere-like morphologies. Structural analysis of the prepared ZnO samples was conducted and compared using Rietveld analysis of their PXRD patterns. Optical band gap calculations based on analysis of the UV–vis spectra of ZnO samples using Tauc's power law were achieved. The highest band gap of 3.63 eV was observed for ZnO sample obtained from the ultrasonically prepared precursor. Furthermore, the photocatalytic activity of ZnO NPs for the removal of Eosin Y color was monitored. The highest removal efficiency was recorded for ZnO originated from the ultrasonically synthesized precursor. Enhancement of removal efficiency that reached 98% was attained in only a period of 8 min. Its recycling test showed that it can be reused without structural changes over four cycling experiments. 相似文献
3.
4.
5.
本文概述了离子注入过程中污染产生的原因和防止污染的措施,特别强调了对微粒污染和金属污染的防护以满足ULSI加工对离子注入的要求。 相似文献
6.
7.
A new unified electroweak model is proposed in this paper. In this unified electroweak model, Higgsmechanism is not used, so no Higgs particle exists in the model. In order to keep the masses of intermediate gaugebosons non-zero, two sets of gauge fields will be introduced. In order to introduce symmetry breaking and to help tointroduce the masses of all fields, a vacuum potential is needed. Except for those terms concerning Higgs particle, thefundamental dynamical properties of this model are similar to those of the standard model. And in a proper limit, thismodel will approximately return to the standard model. The purpose of this paper is not to say that the Higgs particledoes not exist in Nature, it is only to prove that, without a Higgs particle, we can also set up a unified electroweak modelwhich is consistent with present experiments. 相似文献
8.
飞秒激光烧蚀研究进展 总被引:10,自引:3,他引:7
介绍飞秒激光烧蚀材料的机理论模型,阐述飞秒激光烧蚀的特性,揭示飞秒激光烧蚀的广泛应用前景。 相似文献
9.
束晕-混沌的复杂性理论与控制方法及其应用前景 总被引:18,自引:0,他引:18
本文系统论述涉及强流加速器等强流离子束装置中产生的束晕-混沌的复杂性理论与控制方法及其应用前景。强流离子束在核材料生产与增殖、洁净核能、放射性废物嬗变、放射性药物生产、重离子聚变、高能物理、核科学与工程、国防与民用工业和医疗等许多方面都有极其重要的应用潜力和诱人的发展前景。尤其是,近年来强流加速器驱动的放射性洁净核能系统是国内外关注的热门课题,因为它比常规核电更安全、更干净、更便宜。但是,强流离子束形成的束晕-混沌的复杂性现象已引起了国内外广泛关注,需要加以抑制、控制和消除这类现象,解决这一难题已经成为强流离子束应用中的关键问题之一。目前不仅必须深入研究这类束晕-混沌的复杂特性及其产生的物理机制,而且需要研究如何实现对束晕-混沌的有效控制,并寻求和发展其新理论、新方法和新技术。这就向强流离子束物理和非线性-复杂性科学及其技术提出了一系列极富挑战性的新课题。本文结合国内外的研究概况,根据我们多年来的研究成果,特别是我们首创性地提出了一些束晕-混沌的有效控制方法,它们包括:非线性反馈控制法,小波反馈控制法,变结构控制法,延迟反馈控制法,参数自适应控制法等,进行重点的介绍。对上述课题当前的主要进展及相关问题进行系统的总结和比较全面综述的评论。最后,指出该领域今后的研究方向,以推动这个崭新领域的深入研究和应用发展。 相似文献
10.
The transport of monodisperse as well as polydisperse colloid suspensions in a two-dimensional, water saturated fracture with spatially variable and anisotropic aperture is investigated with a particle tracking model. Both neutrally buoyant and dense colloid suspensions are considered. Although flow and transport in fractured subsurface formations have been studied extensively by numerous investigators, the transport of dense, polydisperse colloid suspensions in a fracture with spatially variable and anisotropic aperture has not been previously explored. Simulated snapshots and breakthrough curves of ensemble averages of several realizations of a log-normally distributed aperture field show that polydisperse colloids exhibit greater spreading than monodisperse colloids, and dense colloids show greater retardation than neutrally buoyant colloids. Moreover, it is demonstrated that aperture anisotropy oriented along the flow direction substantially increases colloid spreading; whereas, aperture anisotropy oriented transverse to the flow direction retards colloid movement. 相似文献