全文获取类型
收费全文 | 16736篇 |
免费 | 546篇 |
国内免费 | 699篇 |
专业分类
系统科学 | 612篇 |
丛书文集 | 408篇 |
教育与普及 | 571篇 |
理论与方法论 | 104篇 |
现状及发展 | 124篇 |
研究方法 | 75篇 |
综合类 | 16084篇 |
自然研究 | 3篇 |
出版年
2024年 | 81篇 |
2023年 | 192篇 |
2022年 | 293篇 |
2021年 | 290篇 |
2020年 | 161篇 |
2019年 | 78篇 |
2018年 | 129篇 |
2017年 | 162篇 |
2016年 | 148篇 |
2015年 | 300篇 |
2014年 | 487篇 |
2013年 | 456篇 |
2012年 | 541篇 |
2011年 | 564篇 |
2010年 | 598篇 |
2009年 | 622篇 |
2008年 | 757篇 |
2007年 | 856篇 |
2006年 | 648篇 |
2005年 | 609篇 |
2004年 | 472篇 |
2003年 | 401篇 |
2002年 | 458篇 |
2001年 | 499篇 |
2000年 | 527篇 |
1999年 | 892篇 |
1998年 | 862篇 |
1997年 | 872篇 |
1996年 | 766篇 |
1995年 | 697篇 |
1994年 | 679篇 |
1993年 | 522篇 |
1992年 | 488篇 |
1991年 | 446篇 |
1990年 | 388篇 |
1989年 | 359篇 |
1988年 | 286篇 |
1987年 | 207篇 |
1986年 | 107篇 |
1985年 | 38篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1974年 | 2篇 |
1972年 | 4篇 |
1971年 | 2篇 |
1970年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
671.
Well-crystalline CeO2 nanowires were prepared via a surfactant-assisted hydrothermal process. Reaction temperature and reaction time were changed for the determination of
optimal synthesis parameters. The as-obtained products were characterized by X-ray diffraction (XRD), high-resolution transmission
electron microscopy (HRTEM), and field emission scanning electron microscopy (FESEM). The results show that single crystal
CeO2 nanowires with high yield and good uniformity can be obtained hydrothermally at 180°C for 12 h with the aid of 2.0 g surfactant
(polyvinyl pyrrolidone, PVP). The role of PVP was then discussed and a possible growth mechanism was proposed. Moreover, room
temperature photoluminescence (PL) spectra were obtained for these CeO2 nanowires, which are believed to be related to the abundant defects in these nanostructures. 相似文献
672.
汽车制动性能的好坏,直接关系到行车安全,它是汽车安全行驶中的重点项目之一.对其进行及时准确的检测是保证道路交通安全的必要手段.文章针对路试检验汽车制动性能的常见问题进行了探讨. 相似文献
673.
674.
Superhydrophobic silver nanocoatings with feather-like morphology are fabricated on copper substrates by electroless galvanic deposition. The coating exhibit superhydrophobicity with a contact angle of 156.4° and glide angle of 4° without any further surface modification. Scanning electron microscope (SEM), X-ray diffraction (XRD) and contact angle measurements are used to investigate the morphology, crystal structure and superhydrophobicity, respectively, of the coatings. The coatings exhibit high thermal stability; their water contact angle did not change when the coatings were heated to 200°C for 2 h. The mechanism of superhydrophobicity of the silver coating is discussed based on the work of Amirfazli, Wenzel and Cassie. 相似文献
675.
高校图书馆借阅超期的原因与对策 总被引:1,自引:0,他引:1
当前高校图书馆借阅超期较为普遍,通过问卷调查得知读者的借阅超期大多无恶意行为。针对这种情况以及高校图书馆自身的条件和特点,实施"告知服务"可减少借阅超期行为,以此提高图书的利用率。 相似文献
676.
Because the intrinsic characteristics of mobile ad hoc networks(MANETs) cause several vulnerabilities,anonymous routing protocols attract much more attention in secure mobile ad hoc networks for the purposes of security and privacy concerns.Until recently,lots of anonymous routing protocols have been proposed.However,most of them are single path or use one path at a time,and the multipath schemes can not thwart both the passive attacks and active attacks simultaneously.Thus an anonymous multipath routing protocol based on secret sharing is proposed.The protocol provides identity anonymity,location anonymity,data and traffic anonymity by employing cryptograph technology and secret sharing in MANET communication process.Meanwhile,a hash function is introduced to detect active attacks in the data transmission process.The protocol can effectively thwart various passive attacks and reduce the successful probability of active attacks(such as interception and physical destroy attacks).Simulation results show that the proposed scheme provides a reasonably good level of network security and performance. 相似文献
677.
678.
山西作为能源大省,一直是中国对外经济活动的活跃力量.但是,近年来,随着对外合作的加深,也体现出一些制约因素,最主要体现在缺乏精通国际商务的高素质人才.从制约人才引进和培养的角度出发,客观分析造成山西国际商务人才现状的原因,并提出相应的对策. 相似文献
679.
"篮球意识"是指在复杂困难的环境中能随即应变地争取主动并正取的实施自己的行动和策略的一种即兴发挥能力.是在比赛中各种技术动力、战术灵活运用和发挥生理机能和技战术能力的自觉的、能动的、富有创造性的、具有特殊作用的心理活动. 相似文献
680.
ZHANG Ke FENG JianTao SUN QuanMei JIN Lin LI Jing WU XiaoChun HAN Dong 《科学通报(英文版)》2013,58(21):2640-2645
An important and difficult issue is simultaneously identifying the detailed locations of various molecules on the cell surface, as this identification requires a synergistic effect between more than one molecule in a living cell. Au nanoparticles (NPs) with different shapes can be readily recognised under low vacuum scanning electron microscopy (lvSEM). Anisotropic Au nanorods (NRs) possess unique surface plasmon resonance (SPR) properties, which can be further utilised for two photon luminescence (TPL) and other optical imaging techniques. In this paper, Au NRs and Au nanooctahedra (Au NOs) are introduced as biomarkers for ICAM-1 and Integrin β1. Combined with the advantages of lvSEM, this multiple-labelling method is a new method for studying the interactions between specific, functional molecules. 相似文献