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   224968篇
  免费   18638篇
  国内免费   6205篇
电工技术   14538篇
技术理论   22篇
综合类   13827篇
化学工业   35376篇
金属工艺   12414篇
机械仪表   14017篇
建筑科学   16434篇
矿业工程   6666篇
能源动力   6751篇
轻工业   15675篇
水利工程   3975篇
石油天然气   12567篇
武器工业   1670篇
无线电   27251篇
一般工业技术   27301篇
冶金工业   10164篇
原子能技术   2632篇
自动化技术   28531篇
  2025年   926篇
  2024年   5729篇
  2023年   5242篇
  2022年   7916篇
  2021年   10456篇
  2020年   8729篇
  2019年   7087篇
  2018年   7089篇
  2017年   7788篇
  2016年   7125篇
  2015年   9166篇
  2014年   11250篇
  2013年   13103篇
  2012年   14137篇
  2011年   14916篇
  2010年   12692篇
  2009年   12075篇
  2008年   11583篇
  2007年   10637篇
  2006年   10839篇
  2005年   9236篇
  2004年   6142篇
  2003年   5299篇
  2002年   4783篇
  2001年   4292篇
  2000年   4236篇
  1999年   4918篇
  1998年   4071篇
  1997年   3462篇
  1996年   3204篇
  1995年   2627篇
  1994年   2112篇
  1993年   1538篇
  1992年   1274篇
  1991年   931篇
  1990年   696篇
  1989年   584篇
  1988年   450篇
  1987年   310篇
  1986年   238篇
  1985年   166篇
  1984年   143篇
  1983年   110篇
  1982年   114篇
  1981年   77篇
  1980年   78篇
  1979年   35篇
  1978年   31篇
  1977年   31篇
  1976年   29篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
AZO powders were sensitized through chemisorption method by octa-iso-pentyloxy phthalocyanine lead and characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results showed that after sensitization process AZO photo physical properties improved greatly in visible regions. Photocatalytic degradation of methylene blue was studied under visible irradiation in aqueous solution and the pseudo first order model was used to obtain kinetic information of the photocatalytic degradation. The results indicated that photocatalytic activities of PbPc(iso-PeO)8-AZO were better than of AZO powders.  相似文献   
103.
阮青锋  邱志惠  黄丽萍  宋林  杨杨 《功能材料》2016,(4):4139-4142,4146
以CuSO_4·5H_2O为原料,KOH为添加剂,酒石酸为还原剂,在水热条件下通过调整相关的实验参数,制备了一系列不同形态的Cu_2O微-纳米晶体及三维十字形枝晶。采用XRD、SEM等手段对不同形态的Cu_2O晶体进行了表征,探讨了不同因素变化对Cu_2O晶体形态的影响。分析认为,晶体生长过程控制了晶体的具体形貌和大小,Cu_2O晶体显露的单形晶面随晶体生长条件的变化而不同。在低温、弱碱性、高浓度溶液中有利于形成八面体形态的Cu_2O晶体,而菱形十二面体单形晶面在高温、强碱性、低浓度溶液中形成的晶体中显露的面积有所增大。  相似文献   
104.
TiO_2 nanostructures with strong interfacial adhesion and diverse morphologies have been in-situ grown on Ti foil substrate through a multiple-step method based on conventional plasma electrolytic oxidation(PEO) technology, hydrothermal reaction and ion exchange process. The PEO process is critical to the formation of TiO_2 seeding layer for the nucleation of Na_2Ti_3O_7 and H_2Ti_3O_7 mediates that are strongly attached to the Ti foil. An ion exchange reaction can finally lead to the formation of H_2Ti_3O_7 nanostructures with diverse morphologies and the calcination process can turn the H_2Ti_3O_7 nanostructures into TiO_2 nanostructures with enhanced crystallinity. The morphology of the TiO_2 nanostructures including nanoparticles(NP), nanowhiskers(NWK), nanowires(NW) and nanosheets(NS) can be easily tailored by controlling the NaOH concentration and reaction time during hydrothermal process. The morphology, composition and optical properties of TiO_2 photocatalysts were analyzed using scanning electron microscope(SEM), X-ray diffraction(XRD), photoluminescence(PL) spectroscopy and UV–vis absorption spectrum. Photocatalytic tests indicate that the TiO_2 nanosheets calcined at 500?C show good crystallization and the best capability of decomposing organic pollutants. The decoration of Ag cocatalyst can further improve the photocatalytic performance of the TiO_2 nanosheets as a result of the enhanced charger separation efficiency. Cyclic photocatalytic test using TiO_2 nanostructures grown on Ti foil substrate demonstrates the superior stability in the photodegradation of organic pollutant, suggesting the promising potential of in-situ growth technology for industrial application.  相似文献   
105.
Jiang  Lei  Ding  Yang  Xue  Xialin  Zhou  Sensen  Li  Cheng  Zhang  Xiaoke  Jiang  Xiqun 《Nano Research》2018,11(11):6062-6073
Nano Research - Developing multifunctional nanoparticles to support new therapy models is a promising and challenging task to address the current dilemma on antitumor treatment. Herein, we...  相似文献   
106.
BACKGROUND AND PURPOSE: Mood disorders are common after stroke and may impede physical, functional, and cognitive recovery, making early identification and treatment of potential importance. We aimed to compare the accuracy of the General Health Questionnaire (GHQ-30) and the Hospital Anxiety and Depression (HAD) Scale in detecting psychiatric morbidity after stroke and to determine the most suitable cutoff points for different purposes. METHODS: One hundred five hospital-referred stroke patients completed both the GHQ-30 and HAD Scale 6 months after onset before a blinded psychiatric assessment in which the Schedule for Affective Disorders and Schizophrenia with some supplementary questions was used to determine a DSM-IV (Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition) diagnosis. Measures were compared in terms of sensitivity, specificity, and receiver operating characteristic curves. RESULTS: No significant differences were found between the GHQ-30 and the HAD Scale in identifying those patients with any DSM-IV diagnosis (P=0.95), grouped depression (P=0.56), or anxiety (P=0.25) disorders. The previously recommended cutoff points for identifying "cases" for the GHQ (4/5) and for the HAD Scale (8/9 and 11/12) were found to be suboptimal in this population. CONCLUSIONS: The GHQ-30 and HAD scale exhibited similar levels of sensitivity and specificity. Data are presented, taking into account the "cost" of false-positives and negatives, to allow a choice of cutoff points suitable for differing situations.  相似文献   
107.
The non-fragile dynamic output feedback H controller design problem is investigated. The controller to be designed is assumed to be with additive gain variations. A two-step procedure is proposed to develop sufficient conditions for the non-fragile H controller design by employing the structured vertex separator. A comparison between the proposed and the existing controller design methods is provided, and a numerical example is carried out to support the theoretical findings.  相似文献   
108.
109.
In order to improve decision-making efficiency about emergency event, this paper proposes a novel concept, i.e., Agile-Delphi Method, which is an integration of agile decision and Delphi Method implicating that the decision-makers instantly deliver, respond, treat, and utilize information via Delphi process while conducting group decision-making about emergency event. The paper details the mechanism of group decision-making about emergency event based on network technology and Agile-Delphi Method. Finally, the paper conducts an empiric analysis taking the “111 event”, i.e., the liquid ammonia spill event happened on November 1, 2006 in a phosphorus chemical company in China, as an example.  相似文献   
110.
The twisted cube is an important variant of the most popular hypercube network for parallel processing. In this paper, we consider the problem of embedding multi-dimensional meshes into twisted cubes in a systematic way. We present a recursive method for embedding a family of disjoint multi-dimensional meshes into a twisted cube with dilation 1 and expansion 1. We also prove that a single multi-dimensional mesh can be embedded into a twisted cube with dilation 2 and expansion 1. Our work extends some previously known results.  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