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   21444篇
  免费   1032篇
  国内免费   151篇
电工技术   378篇
综合类   30篇
化学工业   4597篇
金属工艺   686篇
机械仪表   702篇
建筑科学   407篇
矿业工程   49篇
能源动力   1457篇
轻工业   1273篇
水利工程   169篇
石油天然气   111篇
武器工业   1篇
无线电   2630篇
一般工业技术   4921篇
冶金工业   1901篇
原子能技术   206篇
自动化技术   3109篇
  2024年   77篇
  2023年   445篇
  2022年   892篇
  2021年   1216篇
  2020年   996篇
  2019年   993篇
  2018年   1286篇
  2017年   1037篇
  2016年   996篇
  2015年   658篇
  2014年   921篇
  2013年   1724篇
  2012年   980篇
  2011年   1200篇
  2010年   967篇
  2009年   925篇
  2008年   836篇
  2007年   687篇
  2006年   570篇
  2005年   427篇
  2004年   333篇
  2003年   292篇
  2002年   238篇
  2001年   214篇
  2000年   216篇
  1999年   213篇
  1998年   396篇
  1997年   317篇
  1996年   274篇
  1995年   228篇
  1994年   224篇
  1993年   180篇
  1992年   128篇
  1991年   149篇
  1990年   131篇
  1989年   117篇
  1988年   107篇
  1987年   107篇
  1986年   96篇
  1985年   111篇
  1984年   89篇
  1983年   88篇
  1982年   74篇
  1981年   81篇
  1980年   65篇
  1979年   46篇
  1978年   42篇
  1977年   43篇
  1976年   63篇
  1975年   26篇
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
51.
The current research work presents a facile and cost–effective co-precipitation method to prepare doped (Co & Fe) CuO and undoped CuO nanostructures without usage of any type of surfactant or capping agents. The structural analysis reveals monoclinic crystal structure of synthesized pure CuO and doped-CuO nanostructures. The effect of different morphologies on the performance of supercapacitors has been found in CV (cyclic voltammetry) and GCD (galvanic charge discharge) investigations. The specific capacitances have been obtained 156 (±5) Fg?1, 168(±5) Fg?1 and 186 (±5) Fg?1 for CuO, Co-doped CuO and Fe-doped CuO electrodes, respectively at scan rate of 5 mVs?1, while it is found to be 114 (±5) Fg?1, 136 (±5) Fg?1 and 170 (±5) Fg?1 for CuO, Co–CuO and Fe–CuO, respectively at 0.5 Ag-1 as calculated from the GCD. The super capacitive performance of the Fe–CuO nanorods is mainly attributed to the synergism that evolves between CuO and Fe metal ion. The Fe-doped CuO with its nanorods like morphology provides superior specific capacitance value and excellent cyclic stability among all studied nanostructured electrodes. Consequently, it motivates to the use of Fe-doped CuO nanostructures as electrode material in the next generation energy storage devices.  相似文献   
52.
A flower‐shaped ultra‐wideband fractal antenna is presented. It comprises a fourth iterative flower‐shaped radiator, asymmetrical stub‐loaded feeding line, and coplanar quarter elliptical ground planes. A wide operating band of 12.12 GHz (4.58‐16.7 GHz) for S 11 ≤ ? 10 dB is achieved along with an overall antenna footprint of 15.7 × 11.4 mm2. In addition, other desirable characteristics, that is, omnidirectional radiation patterns, peak gain upto 5 dB, and fidelity factor more than 75% are achieved. A good agreement exists between the simulation and measured results. The obtained results illustrate that this antenna has wide operating range and compact dimensions than available structures.  相似文献   
53.
The Journal of Supercomputing - In the last decade, cloud computing has brought enormous changes to people’s lives. Cloud computing gives a client-driven computational model. In this case,...  相似文献   
54.
Metallurgical and Materials Transactions B - The effect of the surface tension–viscosity dissipation driving liquid Ti flow into a B4C packed bed was analyzed at 1941 K and 2573 K. The model...  相似文献   
55.
Context and objective: The aim of this study was to develop, characterize and evaluate a mucoadhesive caplet resulting from a polymeric blend (polymeric caplet) for intravaginal anti-HIV-1 delivery.

Materials and methods: Poly(lactic-co-glycolic) acid, ethylcellulose, poly(vinylalcohol), polyacrylic acid and modified polyamide 6, 10 polymers were blended and compressed to a caplet-shaped device, with and without two model drugs 3′-azido-3′-deoxythymidine (AZT) and polystyrene sulfonate (PSS). Thermal analysis, infrared spectroscopy and microscopic analysis were carried out on the caplets employing temperature-modulated DSC (TMDSC), Fourier transform infra-red (FTIR) spectrometer and scanning electron microscope, respectively. In vitro and in vivo drug release analyses as well as the histopathological toxicity studies were carried out on the drug-loaded caplets. Furthermore, molecular mechanics (MM) simulations were carried out on the drug-loaded caplets to corroborate the experimental findings.

Results and discussion: There was a big deviation between the Tg of the polymeric caplet from the Tg's of the constituent polymers indicating a strong interaction between constituent polymers. FTIR spectroscopy confirmed the presence of specific ionic and non-ionic interactions within the caplet. A controlled near zero-order drug release was obtained for AZT (20 d) and PSS (28 d). In vivo results, i.e. the drug concentration in plasma ranged between 0.012–0.332?mg/mL and 0.009–0.256?mg/mL for AZT and PSS over 1–28 d.

Conclusion: The obtained results, which were corroborated by MM simulations, attested that the developed system has the potential for effective delivery of anti-HIV-agents.  相似文献   
56.
Ghosh  Puja  Bhowmick  Brinda 《SILICON》2020,12(5):1137-1144

This paper addresses reliability issues associated with temperature of Ferroelectric Dopant Segregated Schottky Barrier Tunnel Field Effect Transistor (Fe DS-SBTFET). The simulated results are compared with Dopant Segregated Schottky Barrier TFET (DS-SBTFET). This is achieved by varying the operating temperature from 300 to 500 K. DC parameters such as ION/IOFF ratio, drain current characteristics and subthreshold swing (SS) for a range of temperature have been highlighted. Moreover, the influence of temperature on various RF figure of merits such as gate capacitance (CGG), intrinsic delay, cutoff frequency (fT) etc. have been investigated. The device linearity has been analyzed by considering the effect of temperature variation on linearity parameters like gm2, gm3, 1-dB compression point, VIP2, VIP3 and IIP3. The device characteristics get upgraded by the increase in cut-off frequency and reduction in intrinsic delay at elevated temperature.

  相似文献   
57.
Neural Computing and Applications - We propose “Deep Autoencoders for Feature Learning in Recommender Systems,” a novel discriminative model based on the incorporation of features from...  相似文献   
58.
Neural Computing and Applications - The identification of water stress is a major challenge for timely and effective irrigation to ensure global food security and sustainable agriculture. Several...  相似文献   
59.
Semiconductors - In the present paper, analytical modeling of surface potential and drain current for hetero-dielectric double gate tunnel FET (HDG-TFET) has been done. The two dimensional (2D)...  相似文献   
60.
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