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   45004篇
  免费   4086篇
  国内免费   2052篇
电工技术   2602篇
技术理论   2篇
综合类   2547篇
化学工业   7799篇
金属工艺   2678篇
机械仪表   2992篇
建筑科学   3083篇
矿业工程   1327篇
能源动力   1321篇
轻工业   2901篇
水利工程   671篇
石油天然气   2523篇
武器工业   345篇
无线电   5494篇
一般工业技术   6054篇
冶金工业   2504篇
原子能技术   501篇
自动化技术   5798篇
  2024年   260篇
  2023年   910篇
  2022年   1591篇
  2021年   2250篇
  2020年   1639篇
  2019年   1498篇
  2018年   1568篇
  2017年   1595篇
  2016年   1510篇
  2015年   1972篇
  2014年   2307篇
  2013年   2753篇
  2012年   2825篇
  2011年   3206篇
  2010年   2518篇
  2009年   2480篇
  2008年   2489篇
  2007年   2213篇
  2006年   2319篇
  2005年   1858篇
  2004年   1341篇
  2003年   1208篇
  2002年   1134篇
  2001年   994篇
  2000年   956篇
  1999年   1010篇
  1998年   839篇
  1997年   722篇
  1996年   634篇
  1995年   529篇
  1994年   412篇
  1993年   279篇
  1992年   229篇
  1991年   206篇
  1990年   170篇
  1989年   155篇
  1988年   102篇
  1987年   89篇
  1986年   57篇
  1985年   51篇
  1984年   37篇
  1983年   37篇
  1982年   30篇
  1981年   23篇
  1980年   27篇
  1979年   17篇
  1978年   15篇
  1976年   18篇
  1975年   10篇
  1973年   13篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
计算机应用现状及发展趋势   总被引:1,自引:0,他引:1  
人类步入信息时代以后,计算机和人类的关系也显得日益密切.人们的生活、生产以及科学研究都离不开计算机.在这个计算机飞速发展的年代,我们应该了解计算机应用的现状以及它的发展趋势.  相似文献   
52.
Bonding is an essential step to form microchannels or microchambers in lab-on-a-chip applications. In this paper, we present a novel plastic thermal bonding technique to seal and form large area microchambers (planar characteristic width and length on the order of 1 mm and characteristic thickness on the order of 10–100 μm) without collapse by introducing a holed pressure equalizing plate (HPEP) that includes holes of the same size and shape as the microchambers. To demonstrate the proposed technique, two types of large area microchambers [(1) 20 × 10 mm and 40 μm thick and (2) 12 × 2.5 mm and 120 μm thick] with microchannels were designed and replicated on plastic substrates by means of hot embossing and injection molding processes with prepared two nickel mold inserts. The replicated large area microchambers as well as the microchannels in the plastic lab-on-a-chip were successfully sealed (i.e., no leakage) and formed without any collapse by the proposed thermal bonding technique with the help of the HPEP.  相似文献   
53.
本文首先简单的介绍了总线的发展,从而引出一种新型的串行点对点交换结构RapidIO.DSP在高性能处理系统中的重要性毋庸置疑,但是目前的很多DSP并没有RapidlO接口.本文提出了利用FPGA,将DSP的总线桥接到一个RapidIO IP上,从而实现了DSP与RapidIO网络的互联.  相似文献   
54.
The nature of many sensor applications as well as continuously changing sensor data often imposes real-time requirements on wireless sensor network protocols. Due to numerous design constraints, such as limited bandwidth, memory and energy of sensor platforms, and packet collisions that can potentially lead to an unbounded number of retransmissions, timeliness techniques designed for real-time systems and real-time databases cannot be applied directly to wireless sensor networks. Our objective is to design a protocol for sensor applications that require periodic collection of raw data reports from the entire network in a timely manner. We formulate the problem as a graph coloring problem. We then present TIGRA (Timely Sensor Data Collection using Distributed Graph Coloring) — a distributed heuristic for graph coloring that takes into account application semantics and special characteristics of sensor networks. TIGRA ensures that no interference occurs and spatial channel reuse is maximized by assigning a specific time slot for each node. Although the end-to-end delay incurred by sensor data collection largely depends on a specific topology, platform, and application, TIGRA provides a transmission schedule that guarantees a deterministic delay on sensor data collection.  相似文献   
55.
Han B  Karim MN 《Scanning》2008,30(2):213-220
The cytotoxicity of fullerene C60 particles on two mammalian cell lines, i.e. the Chinese hamster ovary (CHO) cells and the Madin-Darby canine kidney (MDCK) cells, has been investigated. Although innate fullerene particles have a very low solubility in deionized (DI) water, these particles can be dissolved in the tetrahydrofuran (THF) solvent at a great value. Further, the dissolved fullerene particles in the THF solvent could be extracted into a DI water solution at a significantly increased solubility. The formation of fullerene particle aggregates is believed to be the cause of the increased solubility. Results presented here show that once the concentration of the fullerene aggregates reaches a certain level, the cells start to die. The lethal dosage LD50, which is defined as the lowest fullerene concentration that results in a 50% cell death within 24 h, has been determined. Furthermore, the percentage of cell mortality increased with increasing fullerene concentration and incubation time yielding a negative effect on cell viability. These results, illustrated by atomic force microscopy (AFM), dynamic light scattering (DLS) and other microscopic techniques, will help to better understand the side effects of fullerene particles in mammalian cells.  相似文献   
56.
文章针对CSE620R分切机退卷张力控制系统过去使用过渡膜调校方法的不足,从理论上对各个需要调校的参数进行理论计算和曲线校对,并将计算结果对控制板进行设定和曲线校对.这既提高了调校精度又达到稳定生产的目的.避免了浪费大量的薄膜和能耗.  相似文献   
57.
在肾脏移植过程中,经常存在一个病人的亲属愿意将自己的一个肾脏捐赠给此病人,但是他们的肾脏匹配不够好,只能放弃的情况,这明显是一种资源的浪费.一个可行的方案就是肾脏交换系统.在这篇论文中,我们提出了两种解决方法,分别代表了解决此问题的两个解决方向.给一些相应的组织,如美国的OPTN,一定的改进建议,并对其他国家建立类似的组织起到一定的指导作用.  相似文献   
58.
Despite the outstanding power conversion efficiency (PCE) of perovskite solar cells (PSCs) achieved over the years, unsatisfactory stability and lead toxicity remain obstacles that limit their competitiveness and large-scale practical deployment. In this study, in situ polymerizing internal encapsulation (IPIE) is developed as a holistic approach to overcome these challenges. The uniform polymer internal package layer constructed by thermally triggered cross-linkable monomers not only solidifies the ionic perovskite crystalline by strong electron-withdrawing/donating chemical sites, but also acts as a water penetration and ion migration barrier to prolong shelf life under harsh environments. The optimized MAPbI3 and FAPbI3 devices with IPIE treatment yield impressive efficiencies of 22.29% and 24.12%, respectively, accompanied by remarkably enhanced environmental and mechanical stabilities. In addition, toxic water-soluble lead leakage is minimized by the synergetic effect of the physical encapsulation wall and chemical chelation conferred by the IPIE. Hence, this strategy provides a feasible route for preparing efficient, stable, and eco-friendly PSCs.  相似文献   
59.
Ferromagnetic materials with a strong spin-orbit coupling (SOC) have attracted much attention in recent years because of their exotic properties and potential applications in energy-efficient spintronics. However, such materials are scarce in nature. Here, a proximity-induced paramagnetic to ferromagnetic transition for the heavy transition metal oxide CaRuO3 in (001)-(LaMnO3/CaRuO3) superlattices is reported. Anomalous Hall effect is observed in the temperature range up to 180 K. Maximal anomalous Hall conductivity and anomalous Hall angle are as large as ∼15 Ω−1 cm−1 and ∼0.93%, respectively, by one to two orders of magnitude larger than those of the typical 3d ferromagnetic oxides such as La0.67Sr0.33MnO3. Density functional theory calculations indicate the existence of avoid band crossings in the electronic band structure of the ferromagnetic CRO layer, which enhances Berry curvature thus strong anomalous Hall effects. Further evidences from polarized neutron reflectometry show that the CaRuO3 layers are in a fully ferromagnetic state (∼0.8 μB/Ru), in sharp contrast to the proximity-induced canted antiferromagnetic state in 5d oxides SrIrO3 and CaIrO3 (∼0.1 μB/Ir). More than that, the magnetic anisotropy of the (001)-(LaMnO3/CaRuO3) superlattices is eightfold symmetric, showing potential applications in the technology of multistate data storage.  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